Fluidized Bed Combustion Boiler Technology For Cogeneration

Transcription

1 Technical Study Report on B I O M A S S F I R E D Fluidized Bed Combustion Boiler Technology For Cogeneration

2 II About the Technical Study Report Cleaner Production (CP) and Energy Efficiency (EE) are established and powerful strategies helping enterprises throughout the world to reduce costs, generate profits by reducing waste and mitigate climate change. Integration of CP and EE provides synergies that broaden the scope of their individual application and give more effective results both environmental and economic. Implementing CP-EE projects in industries also requires efficient and environment-friendly technology interventions. Co-generation through fluidized bed combustion (FBC) boiler using biomass (such as rice husk, straw etc.) is one such proven technology which could help in mitigation of green house gases emissions. UNEP-DTIE's Energy Branch is planning to develop a series of technical study reports covering various specific technologies that can be adopted by the industries all over the world as a part of their CP-EE initiatives. This is first such technical study report that documents the various techno-economical and managerial aspects of biomass-based FBC technology for practical use by the industries in the regions where large amounts of biomass are available. The study report provides an overview of FBC technology, co-generation system and practical aspects of implementing such a system in an industry. A detailed case study provides insights to the technical specifications of the various equipments, systems and cost economics. It also provides list of technology providers and suppliers worldwide. All in all, this technical report is a comprehensive and complete documentation for implementation of biomass based FBC boiler for co-generation. The technical study report is targeted to the decision makers, technical personnel in the industry, academia, consultants as well as government agencies. Specifically, it is very useful for the technical managers in the industries who would like to implement biomass based co-generation systems in their facilities.

3 III Contents About the Technical Report...ii Contents...iii List of Tables...v List of Figures...vi Abbreviations and Acronyms Used...vii 1.0 Introduction Cleaner Production & Energy Efficiency Biomass as a Fuel Biomass Energy Conversion Technologies FBC Boiler & Cogeneration Systems FBC Boilers Cogeneration (Combined Heat & Power) Biomass-based FBC and Co-generation Technology Overview of the Technology Areas of Application Issues in Implementation of Biomass-based Cogeneration Systems Environmental Benefits of Biomass based cogeneration Systems Social Benefits of Biomass based cogeneration Systems Implementing Biomass Cogeneration Technology Raw material, Energy Resource requirement Infrastructure Requirement Supporting Technologies Waste Disposal Human Resources Demand Equipment Suppliers Case Study Introduction...49

4 IV 5.2 Manufacturing Process Baseline Energy Scenario Implementation of Rice Husk based Cogeneration System Further Suggestions Power Generation using bio-mass in FBC Boiler Power Generation through Biomass Gasifier...59 Annex 1 Block Diagram of Kraft Paper...61 Annex 2: Block Diagram of White Duplux Board...62 Annex 3: Technical Specification of Key Equipment/Components...64

5 V List of Tables Table 1 Global Biomass-fuel based Electricity Generation Capacity, Table 2 Crop Residue from 4 Major Crops in EJ (1987)...11 Table 3 : Global Bagasse Residues...12 Table 4 Comparison of Different Types of Biomass Conversion Technologies 16 Table 5: Heat to Power ratios and other parameters of cogeneration systems 31 Table 6 : Typical heat to Power ratio for Certain Energy intensive Industries 32 Table 7 : Fuels and their typical calorific values...43 Table 8 : External Infrastructure Requirements...43 Table 9 : Area requirements for different components of a typical cogeneration system...44 Table 10 : Supporting Technologies for Cogeneration Systems 44 Table 11 : Waste Generated in Cogeneration Plant...46 Table 12 : Suppliers for Steam Turbine and FBC Boiler...47 Table 13 : Specifications of the DG sets installed for captive power generative 50 Table 14 : (A) Preliminary & Preoperative Expenses...53 Table 15: (B) Cost Involved for procuring Land & Site Development 53 Table 16 (C): Cost of Civil Works Required...53 Table 17 : (D) Cost of Plant & Machinery Required...54 Table 18: (E.)Repair & Maintenance Cost for Building, Plant & Machinery 54 Table 19: (F) Additional Manpower required for Co-generation project 54 Table 20 : Summary of Costs (From A to E)...55 Table 21: Cost Analysis Before and After Implementation of Cogeneration Scheme...55 Table 22 : Greenhouse Gases Emissions Reduction due to Cogeneration

6 VI List of Figures Figure 1: Electricity Generation by Source...10 Figure 2 Regional Distribution of various Sources of Biomass & its use in EJ / annum...11 Figure 3 Global Agricultural Residues, Figure 4 : Principles of Fluidization...19 Figure 5 A View of AFBC Boiler...20 Figure 6 : A Detailed View of Different Components of AFBC Boiler 21 Figure 7 : A CFBC Boiler...23 Figure 8 : Energy Balance of a Typical Thermal Power Plant in India 26 Figure 9: Configurations of different types of turbine systems27 Figure 10: Different Configurations of Back Pressure Turbine28 Figure 11: Configuration of Extraction cum condensing turbine 28 Figure 12 : Elements of a Biomass Based Cogeneration System using FBC Boiler...31 Figure 13: Chipping Machine for Cajurina branches & coconut fronds at Varam Power, India...36 Figure 14 : Collection & Baling Machine for sugarcane trash at GMR technologies, India...36 Figure 15 : Example on estimation of fuel requirement for co-generation 42 Figure 16 Annual Production Trend...49 Figure 17 : Electrical Power requirements trends- Baseline values 51 Figure 18: Steam requirements trends- Baseline values...51 Figure 19: Electrical Power Requirements after Installing the Cogeneration System...52 Figure 20: Steam Requirements after Installing the Cogeneration System 52 Figure 21 : Schematics of the Cogeneration System...53 Figure 22 : Various Biomasses based power plants and their numbers in India 59 Figure 23 : Biomass Gassifier in Operation...59

7 VII Abbreviations and Acronyms Used BBCS CHP CP CPEE DG sets EJ ESP FBC GWh H.T. KVA KWth KWe MNRE MW 0C Biomass based Cogeneration System Combined Heat & Power Cleaner Production Cleaner Production Energy Efficiency Diesel Generator Set Exa-Jourles (IEJ = 1 x 1018 Joules) Electro static Precipitators Fluidized Bed Combustion Giga Watt hour High Tension Kilo Volt Ampere Kilo Watts Thermal Kilo Watts electrical Ministry of New & Renewable Energy, India Mega Watt Degree Centigrade

8 8 1.0 Introduction 1.1 Cleaner Production & Energy Efficiency For decades UNEP has been championing the concepts and practices of Cleaner Production (CP) and Energy Efficiency (EE) in a systematic manner. Recognizing the immense benefits that can be realized by the end-users, UNEP has recently developed guidelines for integration of CP and EE. The idea of this integrated approach is to incorporate the energy management principles into the resource efficiency approach that lies at the heart of CP. These guidelines have been presented in a form of a manual popularly known as the CP-EE Manual. This guidance manual is primarily used by facility personnel for conducting in-house assessments as well as by external consultants. While managers gain insights into the role they can play in instigating and supporting an ongoing, cost-effective process for continual improvement leading to both economic and environmental advantages, CP professionals and consultants (who may not necessarily be energy specialists) find such guidance on incorporating energy issues into their CP assessments at industrial or other facilities immensely valuable. The integrated methodology is derived from the basic principles of the Deming s Cycle of Plan Do Check Act popularly acronymed as PDCA Cycle. Moreover, it addresses eight different categories for identifying the options for resource conservation: 1. Good housekeeping 2. Process Optimization 3. Operation Practices/management 4. Raw Material Substitutions 5. New technology 6. New product design 7. Onsite recycle and reuse 8. Recovery of useful by products As seen from the list above, New Technology is one of the most important categories amongst the CP-EE options. For this, rapid technological advancements in the current times require the professionals to remain updated about the new technologies that are continuously evolving in response to the various environmental challenges. Global warming and Climate change is one of the most pressing and burning issues that needs urgent global action at all levels. The key to address this problem is by mitigation of carbon dioxide and other greenhouse gases produced by combustion of various fuels (both fossil and non fossil). Various new technological solutions are being tried and tested around the world to address this serious problem for the humankind. This study report highlights the use of one such proven technology viz. Biomass based Fluidized Bed Combustion Boilers for Combined Heat and Power Applications which could possibly help in addressing the issue of global warming and climate change.

9 9 1.2 Biomass as a Fuel 1 Biomass, the oldest form of renewable energy, has been used for thousands of years. However, with the emergence of fossil fuels, its relative share of use has declined over past years. Currently some 13% of the world s primary energy supply is from biomass, though there are strong regional differences. Developed countries source around 3% of their energy from biomass while, in Africa it ranges between 70-90%. With adverse environmental effects on the environment such as climate change coming to the forefront, people everywhere are rediscovering the advantages of biomass. Potential benefits of biomass: Reducing carbon emissions if managed (produced, transported, used) in a sustainable manner Enhancing energy security by diversifying energy sources & utilizing local resources Reduced problem of biomass waste management Possible additional revenues for the agricultural and forestry sectors Until the industrial revolution, humankind relied almost exclusively on biomass for their energy needs. Most of the biomass is burnt to provide heat for cooking or warmth. Some is used for small industrial applications (For instance, Charcoal is used in steelmaking in countries like Brazil, which have no major coal reserves). A small percentage of biomass is also used to generate electricity. Total biomass consumption at the beginning of the twenty-first century was 55 exa- Joules or 55EJ 2 out of total global energy consumption of around 400EJ. Estimates of the total quantities of biomass available vary widely but could represent up to 100EJ of energy. Biomass energy accounts for around 14% of total primary energy consumption. This bold figure hides a major disparity between the developed and the developing world. Estimates of the amount of energy that can be supplied from biomass too vary widely, but according to some estimates, by 2050 it could provide as much as 50% of global primary energy supply. Generating electricity from biomass is perhaps one very attractive and easy option to make use of this valuable resource. It uses exactly the same technology that has become common in the power generation industry - furnaces to burn coal, boilers to raise steam from the heat produced and steam turbines to turn the steam into electricity. Table 1 represents the electricity generation capacity of the world using biomass as fuel. Table 1 Global Biomass-fuel based Electricity Generation Capacity, 2004 Region Approx. Installed Capacity (MW) Europe 8000 US 7000 ASEAN region 2000 Australia 300 Indonesia 300 Philippines 20 Thailand Biomass, Issue Brief Energy and Climate Change, World Business Council for Sustainable Development 2 1EJ = 1x1018 Joules

10 10 In 2000, biomass was the largest renewable energy source for electricity generation - other than hydro - generating around 1% of the world s electricity or 167 TWh. However, its share is and will remain small in comparison to fossil-based sources (see Figure 1). Figure 1: Electricity Generation by Source Biomass as a Carbon Neutral Fuel Use of biomass as a fuel is considered to be carbon neutral because plants and trees remove carbon dioxide (CO 2) from the atmosphere and store it while they grow. Burning biomass in homes, industrial processes, energy generation, or for transport activities returns this sequestered CO 2 to the atmosphere. At the same time, new plant or tree growth keeps the atmosphere s carbon cycle in balance by recapturing CO 2. This net-zero or carbon neutral cycle can be repeated indefinitely, as long as biomass is regrown in the next management cycle and harvested for use. The sustainable management of the biomass source is thus critical to ensuring that the carbon cycle is not interrupted. In contrast to biomass, fossil fuels such as gas, oil and coal are not regarded as carbon neutral because they release CO 2 which has been stored for millions of years, and do not have any storage or sequestration capacity Sources of Biomass as fuel3 There are a variety of biomass residues available around the world. The most important of these are crop residues but there are significant quantities of forestry residues and livestock residues as well, which can also be used for energy production. Most of the world's crops generate biomass residues that can be used for energy production. Wheat, barley and oats all produce copious amounts of straw, which have traditionally been burned (approx. 1-2 Billion T of crop residues may be burned annually). Rice produces both straw in the fields and rice husks at the processing plant which can be conveniently and easily converted into energy. (Recent legislation has made straw burning illegal in some parts of the world. Since the straw must still be removed from fields, such legislation could make it cost effective to convert these residues into energy. ) When Maize is harvested significant quantities of biomass remain in the field. Much of this needs to be returned to the soil but when the harvested maize is stripped from its cob the latter remains, more biomass which can easily be converted into energy on-site. 3 Business Insights, The Future of Global Biomass Power Generation: The technology, economics and impact of biomass power generation By Paul Breeze, 2004

11 11 Sugar cane harvesting leaves harvest 'trash' in the fields while processing produces fibrous bagasse. The latter is a valuable source of energy. Harvesting and processing of coconuts produces quantities of shell and fibre that can be utilized. Peanuts leave shells, which is a great source of biomass energy. Figure 2 Regional Distribution of various Sources of Biomass & its use in EJ / annum Figure 3 Global Agricultural Residues, 1987 Putting figures on the quantities of each of these crops is rather difficult. One estimate is shown in Table 2 where the total residue from the four major crops listed is equivalent to 32EJ. Another estimate puts the total of crop residues at 65EJ7 while yet another, from 1993, suggested that utilizing only 25% of the waste from the world's main agricultural crops could generate 38EJ. Table 2 Crop Residue from 4 Major Crops in EJ (1987) REGION MAIZE STRAW WHEAT STRAW RICE STRAW BAGASSE TOTAL Africa US & Canada Latin America Asia Europe Oceania Total

12 12 Varying Estimates A major problem when estimating the quantity of residues that might be used for energy production is to determine how much of each is required for other purposes. At least, part of many crop residues must be returned to the soil to maintain soil quality. Similarly, livestock residues need to be returned to pastures as manure. Taking this into account, a recent exercise carried out by US Department of Agriculture concluded that crop residues alone could provide electricity equivalent to 5% of US consumption in Though local factors make direct comparisons with other regions difficult, a similar contribution might be expected in other parts of the developed world. Given the high per capita electricity use in the US, developing countries might expect to be able to find a greater proportion of their electricity in this way. The figures in Table 2 also suggest that Asia produces the largest quantities of agricultural residues and there is potential across all the continents. However, mere availability of the residue does not guarantee its use. From the perspective of electricity generation, the cost of collection of the residue becomes the key factor in determining its viability. Wheat straw can be baled, making collection more efficient. Several European projects have demonstrated that power plants based on straw can become cost effective when the straw cannot be burned in the fields where it is cut. Another aspect to consider is the seasonal nature of the harvest, which necessitates the plants to either have a large storage facility or alternative sources of fuel. Fuels such as rice husks and maize cobs are produced during processing of these crops. This takes place after harvesting of the crop, so the waste is already concentrated at a point and is an easily exploitable source of energy - particularly if it can be utilized on site to provide heat and power. Sugar cane bagasse is another valuable source of fuel and one that can be exploited easily because it, too, is generated during the processing of the cane. Table 3 provides a breakdown of global bagasse potential from the World Energy Council. Table 3 : Global Bagasse Residues REGION QUNATITY OF BAGASSE (,000 MT) Africa North America South America Asia Europe 502 Middle east 914 Oceania Total The bagasse figures in Table 3 represent only part of the biomass generated during sugar cane farming. The 'trash' which is left in the fields represents about 55% of the total, and this is often burned. With efficient collection methods, this could provide a further rich source of energy, provided minimum required amount is returned to the soil to maintain fertility. Sugar processing plants have traditionally burned this fuel, generally inefficiently, to generate process heat which is all used on-site. Modern combined heat and power plants can produce more energy than is required by the plant itself. According to one estimate, the amount of surplus electricity that sugar processing plants could generate and export to their local grids could, by 2025, account for 15%- 20% of the total demand in the developing countries.

13 13 Biomass Availability in India and Potential for Co-generation Biomass is the traditional fuel in India, used for cooking, and even today, most households, in rural India, use it as cooking fuel. This biomass, mostly consists of agricultural farm residues (e.g. paddy straw, sugar cane trash etc), agro-industrial residues (e.g. paddy husk, coffee husk etc), forests & social forests residues and energy plantations, which (i.e. energy plantation) is just picking up. The following Table, provides the different types of biomass, that are presently being used in India Biomass varieties presently used in India for Co-generation Agro and farm Biomass Agro-Industrial Biomass Forest Residues & plantations Babul Stems Coffee Husk Fire Wood Chilly stalks Bagasse Forest residues Coconut husk De oiled bran Julie Flora Coconut Pith Ground nut husk Other woody biomass chips Corn cobs Cotton Stalk Maize Stems Mango residues Mustard Stalk Palm leaf Prosopis Rai Stems Sugar Cane Trash Tamarind husk Til stems Casurina branches & fruit Ground nut shells Rice Husk Saw dust Indian Ministry of New and Renewable Energy s Annual Report for indicates surplus agro & forest residues of 60 Million MT available for power generation. Further, the report also projected an availability of 40 million MT of woody biomass annually, from energy plantation, on 4 million hectares of wasteland. Considering plant load factor of 70%, the estimated potential for power generation in India alone is 13,000 MW from various biomass based sources. 1.3 Biomass Energy Conversion Technologies There are a number of ways for converting biomass into electricity. The simplest approach is to burn the biomass in a furnace, exploiting the heat generated to produce steam in a boiler, which is then used to drive a steam turbine. This approach, often called direct firing, is the most widespread means of deriving heat and electricity from biomass today. It is also generally rather inefficient, though new technologies will be able to improve efficiency significantly. A simple, direct-fired biomass power plant can either produce electricity alone or it can operate as a combined heat and power unit, producing both electricity and heat. This latter is common in the textile, food processing, chemical and paper industries where the heat is used in the processing plant. The electricity generated is used by the plant

14 14 too, with any surplus exported to the grid. Simplicity is the key feature of direct firing type of application. A more advanced approach is biomass gasification. This employs a partial combustion process to convert biomass into a combustible gas. The gas has a lower energy content than natural gas. Nevertheless, it can be used in the same way as natural gas. In particular it can provide fuel for gas turbines and fuel cells. Biomass gasification is still in the development stage but it promises high efficiency and may offer the best option for future biomass-based generation. An intermediate option for exploiting biomass is to mix it with coal and burn it in a coal fired power station. In the short term this may offer the cheapest and most efficient means of exploiting biomass. Finally there are number of specialized methods of turning biomass wastes into energy. These include digesters, which can convert dairy farm waste into a useful fuel gas, and power stations that utilize chicken farm litter, which they burn to generate electricity. In terms of conversion technologies, following technologies are commonly used: 1. Pile Combustion 2. Stoker Combustion 3. Suspension Combustion 4. Fluidized Bed Combustion Pile Combustion The simplest form of direct firing involves a pile burner. This type of burner has a furnace, which contains a fixed grate inside a combustion chamber. Wood is fed (piled) onto the grate where it is burned in air, which passes up through the grate (called under-fire air). The grate of a pile burner is within what is known as the primary combustion chamber where the bulk of the combustion process takes place. Combustion at this stage is normally incomplete - there may be significant quantities of both unburned carbon and combustible carbon monoxide remaining - so further air (called overfire air) is introduced into a secondary combustion chamber above the first - where combustion is completed. The boiler for raising steam is positioned above this second combustion chamber so that it can absorb the heat generated during combustion. The heat warms, and eventually boils water in the boiler tubes, providing steam to drive a steam turbine. From the steam turbine the steam is condensed and then returned to the boiler so that it can be cycled through the system again. (In a combined heat and power system, steam will be taken from the steam turbine outlet to provide heat energy first.) Wood fuel is normally introduced from above the grate, though sometimes there is a more complicated arrangement, which feeds fuel from under the grate. The pile burner is capable of handling wet and dirty fuels but it is extremely inefficient. Boiler efficiencies are typically 50%-60%. There is no means to remove the ash from a pile burner except by shutting down the furnace. Thus the power plant cannot be operated continuously. Pile burners are also considered difficult to control and they are slow to respond to changes in energy input. This means that electricity output cannot easily be changed in response to changes in demand. Power generation in a pile-burner based power station will usually involve a single pass steam turbine generator operating at a relatively low steam temperature and pressure. This adds to the relatively low efficiency of the power plant, which can operate, with an overall efficiency as low as 20%.

15 Stoker Combustion The pile burner represents the traditional method of burning wood. However, its basic operation can be improved by introducing a moving grate or stoker. This allows continuous removal of ash so that the plant can be operated continuously. Fuel can also be spread more thinly on the grate, encouraging more efficient combustion. The first US stoker grate for wood combustion was introduced by the Detroit Stoker Co. in the 1940s. In this type of furnace, combustion air still enters below the grate of a stoker burner. This flow of air into the combustion chamber helps cool the grate. The air flow and consequent grate temperature determines the maximum operating temperature of the combustor. This, in turn, determines the maximum moisture content allowable in the wood fuel if combustion is to proceed spontaneously. There are refinements of the basic stoker grate such as inclined grates and water-cooled grates, both of which can help improve overall performance and make the operation less sensitive to fuel moisture. Nevertheless stoker combustors are still relatively inefficient, with boiler efficiencies of 65%-75% and overall efficiencies of 20%-25% Suspension Combustion Most modern coal-fired power stations burn pulverized coal, which is blown into the combustion chamber of a power plant through a specially designed burner. The burner mixes air with the powdered coal, which then burns in a flame in the body of the combustion chamber. This is suspension combustion and in this type of plant there is no grate. Finely ground wood, rice husk, bagasse, or sawdust can be burned in a similar way. Suspension firing requires a special furnace. The size and moisture content of the biomass (wood) must also be carefully controlled. Moisture content should be below 15% and the biomass particle size has to be less than 15mm. Suspension firing results in boiler efficiency of up to 80% and allows a smaller sized furnace for a given heat output. However it also requires extensive biomass drying and processing facilities to ensure that the fuel is of the right consistency. It also demands special furnace burners. A small number of plants designed to burn biomass in this way have been built. The technology is also of great interest as the basis for the co-firing of wood or other biomass with coal in pulverized coal plants Fluidized Bed Combustion Aside from suspension firing of wood, the most efficient method of directly burning biomass is in a fluidized bed combustor (FBC). This is also the most versatile since the system can cope with a wide range of fuels and a range of moisture contents. The basis for a FBC system is a bed of an inert mineral such as sand or limestone through which air is blown from below. The air is pumped through the bed in sufficient volume and at a high enough pressure to entrain the small particles of the bed material so that they behave much like a fluid. The combustion chamber of a fluidized bed plant is shaped so that above a certain height the air velocity drops below that necessary to entrain the particles. This helps retain the bulk of the entrained bed material towards the bottom of the chamber. Once the bed becomes hot, combustible material introduced into it will burn, generating heat as in a more conventional furnace. The proportion of combustible material such as biomass within the bed is normally only around 5%. There are different designs of FBC system which involve variations around this principle. The most common for biomass combustion is the circulating fluidized bed which incorporates a

16 16 cyclone filter to separate solid material from the hot flue gases which leave the exhaust of the furnace. The solids from the filter are re-circulated into the bed, hence the name. The fluidized bed has two distinct advantages for biomass combustion: First, it is the ability to burn a variety of different fuels without affecting performance. Second is the ability to introduce chemical reactants into the fluidized bed to remove possible pollutants. In FBC plants burning coal, for example, limestone can be added to capture sulphur and prevent its release to the atmosphere as sulphur dioxide. Biomass tends to contain less sulphur than coal so this strategy may not be necessary in a biomass plant. A fluidized bed boiler can burn wood with up to 55% moisture. One specialized application is in plants designed to burn chicken litter, the refuse from the intensive farming of poultry. Power stations have been built that are devoted specifically to this fuel source and these plants use FBCs. Of the four different types of combustion technologies discussed above, the FBC technology is best suited for a range of small and medium scale operation for combined heat and power. With technological advancements the FBC boilers give efficiency of as high as 80-82% and can be used for a wide variety of fuels Comparison of Different Types of Biomass Conversion Technologies Table 4 below compiles a quick Comparison of Different Types of Biomass Conversion Technologies commonly used worldwide. Table 4 Comparison of Different Types of Biomass Conversion Technologies Parameter Pile Combustion Stoker Combustion Suspension Combustion Grate Fixed / Stationary Grate Fixed or moving grate No grate or moving grate Fuel Size Uniform size of the fuel Uneven fuel size can be Preferable for high % in the range of range 60 used of fins in the fuel to 75 mm is desired & % fines should not be more than 20% Combustion Bed temperature Moisture Difficult to maintain good combustion due to : Air fuel mixing is not proper Bed height is in stationary condition resulting in clinker formation Difficult to avoid air channeling Due to intermittent ash removal system it is difficult to maintain good combustion The combustion is better & an improved version of pile combustion. Since most of the fuel is burnt in suspension the heavier size mass falls on the grate. If the system has a moving grate the ash is removed on a continuous basis & therefore the chances of clinker formation are less. It is similar to stoker combustion, but since the fuel sizes is small & even the combustion efficiency is improved as maximum amount of fuel is combusted during suspension. Fluidized Bed Combustion No grate Uniform size fuel in the range of 1 to 10 mm. Best combustion takes place in comparison with the other types since the fuel particles are in fluidized state & there is adequate mixing of fuel & air ºC ºC ºC ºC High moisture leads to bed choking & difficult combustion conditions Combustion condition not very much disturbed with 4-5 % increase in moisture Same as Stoker Combustion It can handle fuels with high moisture condition up to 45-50% but high moisture in the fuels is not desirable, & adequate precautions are to be taken up in the design stage itself.

17 17 Parameter Pile Combustion Stoker Combustion Suspension Combustion Draft Natural Draft / Forced Forced Draft / Balance Balance draft Conditions Draft/ Balance Draft draft Maintenance Not much maintenance Frequent problems Variation in fines in problems due to moving grate fuel leads to delayed combustion thereby affecting the boiler tubes Fluidized Bed Combustion Balance draft Erosion of boiler tubes embedded in the bed is quite often

18 FBC Boiler & Cogeneration Systems 2.1 FBC Boilers Introduction to FBC Boilers The traditional grate fuel firing systems have several limitations and hence are technoeconomically unviable to meet the challenges of the future. FBC has emerged as a viable alternative as it has significant advantages over conventional firing system. FBC offers multiple benefits, such as: compact boiler design, flexibility with fuel used, higher combustion efficiency and reduced emissions of noxious pollutants such as SO x and NO x. The fuels burnt in these boilers include coal, washery rejects, rice husk, bagasse and other agricultural wastes. The fluidized bed boilers have a wide capacity range- 0.5 T/hr to over 100 T/hr Mechanism of Fluidized Bed Combustion When an evenly distributed air or gas is passed upward through a finely divided bed of solid particles such as sand supported on a fine mesh, the particles remain undisturbed at low velocities. As the air velocity is gradually increased, a stage is reached when the individual particles are suspended in the air stream and the bed is called fluidized. With further increase in air velocity, there is bubble formation, vigorous turbulence, rapid mixing and formation of dense defined bed surface. The bed of solid particles exhibits the properties of a boiling liquid and assumes the appearance of a fluid bubbling fluidized bed. At higher velocities, bubbles disappear, and particles are blown out of the bed. Therefore, some amounts of particles have to be re-circulated to maintain a stable system and is called as circulating fluidized bed". This principle of fluidization is illustrated in Figure 4. Fluidization depends largely on the particle size and the air velocity. The mean solids velocity increases at a slower rate than does the gas velocity. The difference between the mean solid velocity and mean gas velocity is called as slip velocity. Maximum slip velocity between the solids and the gas is desirable for good heat transfer and intimate contact. If sand particles in fluidized state are heated to the ignition temperatures of fuel (rice husk, coal or bagasse), and fuel is injected continuously into the bed, the fuel will burn rapidly and the bed attains a uniform temperature. The fluidized bed combustion (FBC) takes place at about 840 C to 950 C. Since this temperature is much below the ash fusion temperature, melting of ash and associated problems are avoided. The lower combustion temperature is achieved because of high coefficient of heat transfer due to rapid mixing in the fluidized bed and effective extraction of heat from the bed through in-bed heat transfer tubes and walls of the bed. The gas velocity is maintained between minimum fluidization velocity and particle entrainment velocity. This ensures a stable operation of the bed and avoids particle entrainment in the gas stream. 4 Energy Efficiency in Thermal Utilities, A Guide Book for Energy Managers and Auditors, Bureau of Energy Efficiency, Ministry of Power, Government of India, 2005

19 19 Fixing, Bubbling & Fast Fluidized Beds: As the velocity of a gas flowing through a bed of particles increases, a value is reaches when the bed fluidizes and bubbles form as in a boiling liquid. At higher velocities the bubbles disappear; and the solids are rapidly blown out of the bed and must be recycled to maintain a stable system. Figure 4 : Principles of Fluidization Any combustion process requires three T s - that is Time, Temperature and Turbulence. In FBC, turbulence is promoted by fluidization. Improved mixing generates evenly distributed heat at lower temperature. Residence time is many times higher than conventional grate firing. Thus an FBC system releases heat more efficiently at lower temperatures. Since limestone can also be used as particle bed (in case the fuel with sulphur content is used), control of SOx and NOx emissions in the combustion chamber is achieved without any additional control equipment. This is one of the major advantages over conventional boilers Types of Fluidized Bed Combustion Boilers There are three basic types of fluidized bed combustion boilers: 1. Atmospheric Fluidized Bed Combustion System (AFBC) 2. Atmospheric circulating (fast) Fluidized Bed Combustion system (CFBC) 3. Pressurized Fluidized Bed Combustion System (PFBC).

20 AFBC / Bubbling Bed AFBC is one of the most important types of FBC boilers as it can be used for variety of fuels - such as agricultural residues like rice husk or bagasse and even low quality coal. This type of boiler find use in industries where there is a possibility of having a combined heat and power generation application. In AFBC boilers the fuel is sized depending on the type of fuel (in case of coal, the coal is crushed to a size of 1 10 mm depending on the grade of coal) and the type of fuel feeding system and is fed into the combustion chamber. The atmospheric air, which acts as both the fluidization air and combustion air, is delivered at a pressure and flows through the bed after being preheated by the exhaust flue gases. The velocity of fluidizing air is in the range of 1.2 to 3.7 m /sec. The rate at which air is blown through the bed determines the amount of fuel that can be reacted. Almost all AFBC/ bubbling bed boilers use in-bed evaporator tubes in the bed of limestone, sand and fuel for extracting the heat from the bed to maintain the bed temperature. The bed depth is usually 0.9 m to 1.5 m deep and the pressure drop averages about 1 inch of water per inch of bed depth. Very little material leaves the bubbling bed only about 2 to 4 kg of solids is recycled per ton of fuel burned. Typical fluidized bed combustors of this type are shown in Figures 5 and 6. Figure 5 A View of AFBC Boiler The combustion gases pass over the super heater sections of the boiler, flow past the economizer, the dust collectors and the air pre-heaters before being exhausted to atmosphere. The main special feature of atmospheric fluidized bed combustion is the constraint imposed by the relatively narrow temperature range within which the bed must be operated. With coal, there is risk of clinker formation in the bed if the temperature exceeds 950 C and loss of combustion efficiency if the temperature falls below 800 C. For efficient sulphur retention, the temperature should be in the range of 800 C to 850 C. General Arrangements of AFBC Boiler AFBC boilers comprise of following systems: Fuel feeding system Air distributor

21 21 Bed & In-bed heat transfer surface Ash handling system. Many of these are common to all types of FBC boilers. Figure 6 : A Detailed View of Different Components of AFBC Boiler a) Fuel Feeding System For feeding fuel and adsorbents like limestone or dolomite, usually two methods are followed: under bed pneumatic feeding and over-bed feeding. Under Bed Pneumatic Feeding If the fuel is coal, it is crushed to 1 6 mm size and pneumatically transported from feed hopper to the combustor through a feed pipe piercing the distributor. Based on the capacity of the boiler, the number of feed points is increased, as it is necessary to distribute the fuel into the bed uniformly. Over-Bed Feeding The crushed coal, 6 10 mm size is conveyed from coal bunker to a spreader by a screw conveyor. The spreader distributes the coal over the surface of the bed uniformly. This type of fuel feeding system accepts over size fuel also and eliminates transport lines, when compared to under-bed feeding system. Now a days for rise husk and other agricultural residues Over bed feeding system is quite prominent and economical. Some of the boilers are so designed that they have both types of feeding systems. b) Air Distributor The purpose of the distributor is to introduce the fluidizing air evenly through the bed cross section thereby keeping the solid particles in constant motion, and preventing the formation of de-fluidization zones within the bed. The distributor, which forms the furnace floor, is

22 22 normally constructed from metal plate with a number of perforations in a definite geometric pattern. The perforations may be located in simple nozzles or nozzles with bubble caps, which serve to prevent solid particles from flowing back into the space below the distributor. The distributor plate is protected from high temperature of the furnace by: Refractory Lining A Static Layer of the Bed Material or Water Cooled Tubes. c) Bed & In-Bed Heat Transfer Surface: Bed The bed material can be sand, ash, crushed refractory or limestone, with an average size of about 1 mm. Depending on the bed height these are of two types: shallow bed and deep bed. At the same fluidizing velocity, the two ends fluidize differently, thus affecting the heat transfer to an immersed heat transfer surfaces. A shallow bed offers a lower bed resistance and hence a lower pressure drop and lower fan power consumption. In the case of deep bed, the pressure drop is more and this increases the effective gas velocity and also the fan power. In-Bed Heat Transfer Surface In a fluidized in-bed heat transfer process, it is necessary to transfer heat between the bed material and an immersed surface, which could be that of a tube bundle, or a coil. The heat exchanger orientation can be horizontal, vertical or inclined. From a pressure drop point of view, a horizontal bundle in a shallow bed is more attractive than a vertical bundle in a deep bed. Also, the heat transfer in the bed depends on number of parameters like (i) bed pressure (ii) bed temperature (iii) superficial gas velocity (iv) particle size (v) Heat exchanger design and (vi) gas distributor plate design. d) Ash Handling System i) Bottom Ash Removal In the FBC boilers, the bottom ash constitutes roughly % of the total ash, the rest being the fly ash. The bed ash is removed by continuous over flow to maintain bed height and also by intermittent flow from the bottom to remove over size particles, avoid accumulation and consequent defluidization. While firing high ash coal such as washery rejects, the bed ash overflow drain quantity is considerable so special care has to be taken. ii) Fly Ash Removal The amount of fly ash to be handled in FBC boiler is relatively very high, compared to conventional boilers. This is due to elutriation of particles at high velocities. Fly ash carried away by the flue gas is removed in number of stages; firstly in convection section, then from the bottom of air pre-heater/economizer and finally a major portion is removed in dust collectors. The types of dust collectors used are cyclone, bag filters, electrostatic precipitators (ESP s) or some combination of all of these. To increase the combustion efficiency, recycling of fly ash is practiced in some units Circulating Fluidized Bed Combustion (CFBC) Circulating Fluidized Bed Combustion (CFBC) technology has evolved from conventional bubbling bed combustion as a means to overcome some of the drawbacks associated with conventional bubbling bed combustion (see Figure 7).

23 23 Figure 7 : A CFBC Boiler CFBC technology utilizes the fluidized bed principle in which crushed (6 12 mm size) fuel and limestone are injected into the furnace or combustor. The particles are suspended in a stream of upwardly flowing air (60-70% of the total air), which enters the bottom of the furnace through air distribution nozzles. The fluidizing velocity in circulating beds ranges from 3.7 to 9 m/sec. The balance of combustion air is admitted above the bottom of the furnace as secondary air. The combustion takes place at C, and the fine particles (<450 microns) are elutriated out of the furnace with flue gas velocity of 4 6 m/s. The particles are then collected by the solids separators and circulated back into the furnace. Solid recycle is about 50 to 100 kg per kg of fuel burnt. There are no steam generation tubes immersed in the bed. The circulating bed is designed to move a lot more solids out of the furnace area and to achieve most of the heat transfer outside the combustion zone convection section, water walls, and at the exit of the riser. Some circulating bed units even have external heat exchanges. The particles circulation provides efficient heat transfer to the furnace walls and longer residence time for carbon and limestone utilization. The controlling parameters in the CFB combustion process are temperature, residence time and turbulence. For large units, the taller furnace characteristics of CFBC boiler offers better space utilization, greater fuel particle and adsorbent residence time for efficient combustion and SO 2 capture, and easier application of staged combustion techniques for NOx control than AFBC generators.

24 24 CFBC boilers are said to achieve better calcium to sulphur utilization 1.5 to 1 vs. 3.2 to 1 for the AFBC boilers, although the furnace temperatures are almost the same. CFBC requires huge mechanical cyclones to capture and recycle the large amount of bed material, which requires a tall boiler. A CFBC could be good choice if the following conditions are met. Capacity of boiler is large to medium Sulphur emission and NOx control is important The boiler is required to fire low-grade fuel or fuel with highly fluctuating fuel quality. Major performance features of the CFBC system are as follows: It has a high processing capacity because of the high gas velocity through the system. The temperature of about 870 C is reasonably constant throughout the process because of the high turbulence and circulation of solids. The low combustion temperature also results in minimal NOx formation. Sulphur present in the fuel is retained in the circulating solids in the form of calcium sulphate and removed in solid form. The use of limestone or dolomite adsorbents allows a higher sulfur retention rate, and limestone requirements have been demonstrated to be substantially less than with bubbling bed combustor. The combustion air is supplied at 1.5 to 2 psig (pounds per square inch gauge) rather than 3 5 psig as required by bubbling bed combustors. It has high combustion efficiency. It has a better turndown ratio than bubbling bed systems. Erosion of the heat transfer surface in the combustion chamber is reduced, since the surface is parallel to the flow. In a bubbling bed system, the surface generally is perpendicular to the flow. CFBC boilers are generally claimed to be more economical than AFBC boilers for industrial application requiring more than T/hr of steam, therefore this type of boilers is beyond the scope of the document Pressurized Fluid Bed Combustion Boiler Pressurized Fluidized Bed Combustion (PFBC) is a variation of FBC technology that is meant for large-scale coal burning applications. In PFBC, the bed vessel is operated at pressure up to 16 ata ( 16 kg/cm2). The off-gas from the FBC drives the gas turbine. The steam turbine is driven by steam raised in tubes immersed in the fluidized bed. The condensate from the steam turbine is pre-heated using waste heat from gas turbine exhaust and is then taken as feed water for steam generation. The PFBC system can be used for cogeneration or combined cycle power generation. By combining the gas and steam turbines in this way, electricity is generated more efficiently than in conventional system. The overall conversion efficiency is higher by 5% to 8%. PFBC Boiler is beyond the scope of this document Advantages of FBC Boilers 1. High Efficiency: FBC boilers can burn fuel with a combustion efficiency of over 95% irrespective of ash content. FBC boilers can operate with overall efficiency of 84% (±2%). 2. Reduction in Boiler Size: High heat transfer rate over a small heat transfer area immersed in the bed results in overall size reduction for the boiler.

25 25 3. Fuel Flexibility: FBC boilers can be operated efficiently with a variety of fuels. Even fuels like flotation slimes, washer rejects, agro waste can be burnt efficiently. These can be fed either independently or in combination with coal into the same furnace. 4. Ability to Burn Low Grade Fuel: FBC boilers would give the rated output even with an inferior quality fuel. The boilers can fire coals with ash content as high as 62% and having calorific value as low as 2,500 kcal/kg. Even carbon content of only 1% by weight can sustain the fluidized bed combustion. 5. Ability to Burn Fines: Coal containing fines below 6 mm can be burnt efficiently in FBC boiler, which is very difficult to achieve in conventional firing system. 6. Pollution Control: SO 2 formation can be greatly minimized by addition of limestone or dolomite for high sulphur coals (3% limestone is required for every 1% sulphur in the coal feed). Low combustion temperature eliminates NOx formation. 7. Low Corrosion and Erosion: The corrosion and erosion effects are less due to lower combustion temperature, softness of ash and low particle velocity (around 1 m/sec). 8. Easier Ash Removal No Clinker Formation: Since the temperature of the furnace is in the range of C in FBC boilers, even coal of low ash fusion temperature can be burnt without clinker formation. Ash removal is easier as the ash flows like liquid from the combustion chamber. Hence less manpower is required for ash handling. 9. Less Excess Air Higher CO 2 in Flue Gas: The CO 2 in the flue gases will be of the order of 14 15% at full load. Hence, the FBC boiler can operate at low excess air - only 20-25%. 10. Simple Operation, Quick Start-Up: High turbulence of the bed facilitates quick start up and shut down. Full automation of start up and operation using reliable equipment is possible. 11. Fast Response to Load Fluctuations: Inherent high thermal storage characteristics can easily absorb fluctuation in fuel feed rates. Response to changing load is comparable to that of oil fired boilers. 12. No Slagging in the Furnace No Soot Blowing: In FBC boilers, volatilization of alkali components in ash does not take place and the ash is non sticky. This means that there is no slagging or soot blowing. 13. Provisions of Automatic Coal and Ash Handling System: Automatic systems for coal and ash handling can be incorporated, making the plant easy to operate comparable to oil or gas fired installations. 14. Provision of Automatic Ignition System: Control systems using micro-processors and automatic ignition equipment give excellent control with minimum supervision. 15. High Reliability: The absence of moving parts in the combustion zone results in a high degree of reliability and low maintenance costs. 16. Reduced Maintenance: Routine overhauls are infrequent and high efficiency is maintained for long periods. 17. Quick Responses to Changing Demand: FBC can respond to changing heat demands more easily than stoker fired systems. This makes it very suitable for applications such as thermal fluid heaters, which require rapid responses. 18. High Efficiency of Power Generation: By operating the fluidized bed at elevated pressures, it can be used to generate hot pressurized gases to power a gas turbine. This can be combined with a conventional steam turbine to improve the efficiency of electricity generation resulting in a potential fuel savings of at least 4%.

26 Cogeneration (Combined Heat & Power) Cogeneration or Combined Heat and Power (CHP) is defined as the sequential generation of two different forms of useful energy - typically mechanical energy and thermal energy - from a single primary energy source. Mechanical energy may be used to drive an alternator for producing electricity, or rotating equipment such as motor, compressor, pump or fan for delivering various services. Thermal energy can be used either for direct process applications or for indirectly producing steam, hot water, hot air for dryer or chilled water for process cooling. Cogeneration provides a wide range of technologies for application in various domains of economic activities. The overall efficiency of energy use in cogeneration mode can be up to 85 per cent - and even above in some cases. Along with the saving of fossil fuels, cogeneration also helps reducing the emissions of greenhouse gases (particularly CO 2 emission) Need for Cogeneration Thermal power plants are a major source of electricity worldwide. The conventional method of power generation and supply to the customer is wasteful in the sense that only about a third of the primary energy fed into the power plant is actually made available to the user in the form of electricity (Figure 8). Figure 8 : Energy Balance of a Typical Thermal Power Plant in India The major source of loss in the conversion process is the heat rejected to the surrounding water or air due to the inherent constraints of the different thermodynamic cycles employed in power generation. Also further losses of around 10 15% are associated with the transmission and

27 27 distribution of electricity in the electrical grid. In cogeneration, the production of electricity being on-site, the burden on the utility network is reduced and the transmission line losses eliminated. Cogeneration therefore makes sense from both macro and micro perspectives. At the macro level, it allows a part of the financial burden of the national power utility to be shared by the private sector; in addition, indigenous energy sources are conserved. At the micro level, the overall energy bill of the users can be reduced, particularly when there is a simultaneous need for both power and heat at the site, and a rational energy tariff can be practiced in the country Steam Turbines Steam turbines are the most commonly employed prime movers for cogeneration applications. In the steam turbine, the incoming high pressure steam is expanded to a lower pressure level, converting the thermal energy of high pressure steam to kinetic energy through nozzles and then to mechanical power through rotating blades. The different types of steam turbine include extraction cum condensing type and back pressure steam turbines. Steam Steam Fuel Turbine Fuel Turbine Boiler Condenser Boiler Process Process Cooling Water (i) Back-Pressure Turbine (ii) Extraction -Condensing Turbine Figure 9: Configurations of different types of turbine systems Back Pressure Turbine In this type of turbines, steam enters the turbine chamber at high pressure and expands to low or medium pressure. Enthalpy difference is used for generating power/work. Depending on the pressure (or temperature) levels at which process steam is required, backpressure steam turbines can have different configurations as shown in Figure 10. In extraction and double extraction backpressure turbines, some amount of steam is extracted from the turbine after being expanded to a certain pressure level. The extracted steam meets the heat demands at pressure levels higher than the exhaust pressure of the steam turbine. The efficiency of a backpressure steam turbine cogeneration system is the highest. In cases where 100 per cent backpressure exhaust steam is used, the only inefficiencies are gear drive and electric generator losses, and the inefficiency of steam generation. Therefore, with an efficient boiler, the overall thermal efficiency of the system could reach as much as 90 per cent.

28 28 High Pressure Steam Extracted Steam Exhaust Steam (I) Simple Back Pressure (II) Extaction Back Pressure (III) Double Extraction Back Pressure Figure 10: Different Configurations of Back Pressure Turbine Extraction Condensing Turbine In this type, steam entering at high / medium pressure is extracted at an intermediate pressure in the turbine for process use while the remaining steam continues to expand and condenses in a surface condenser and work is done till it reaches the condensing pressure (vacuum). In extraction-cum-condensing steam turbine as shown in figure 11, high pressure steam enters the turbine and passes out from the turbine chamber in stages. In the process of twostage extraction cum condensing turbine MP steam and LP steam pass out to meet the process needs. Balance quantity condenses in the surface condenser. The energy difference is used for generating power. This configuration meets the heat-power requirement of the process. Steam Generator Steam Turbine G Q H Feed Water Pump Condenser Figure 11: Configuration of Extraction cum condensing turbine The extraction condensing turbines have higher power to heat ratio in comparison with back pressure turbines. Although condensing systems need more auxiliary equipment such as the condenser and cooling towers, better matching of electrical power and heat demand can be obtained where electricity demand is much higher than the steam demand and the load patterns are highly fluctuating. The overall thermal efficiency of an extraction condensing turbine cogeneration system is lower than that of back pressure turbine system, basically because the exhaust heat cannot be utilized (it is normally lost in the cooling water circuit). However, extraction condensing cogeneration systems have higher electricity generation efficiencies.

29 Factors Influencing Cogeneration Choice The selection and operating scheme of a cogeneration system is very much site-specific and depends on several factors, as described below: Base Electrical Load Matching In this configuration, the cogeneration plant is sized to meet the minimum electricity demand of the site based on the historical demand curve. The rest of the needed power is purchased from the utility grid. The thermal energy requirement of the site could be met by the cogeneration system alone or by additional boilers. If the thermal energy generated with the base electrical load exceeds the plant s demand and if the situation permits, excess thermal energy can be exported to neighboring customers Base Thermal Load Matching Here, the cogeneration system is sized to supply the minimum thermal energy requirement of the site. Stand-by boilers or burners are operated during periods when the demand for heat is higher. The prime mover installed operates at full load at all times. If the electricity demand of the site exceeds that which can be provided by the prime mover, then the remaining amount can be purchased from the grid. Likewise, if local laws permit, the excess electricity can be sold to the power utility Electrical Load Matching In this operating scheme, the facility is totally independent of the power utility grid. All the power requirements of the site, including the reserves needed during scheduled and unscheduled maintenance, are to be taken into account while sizing the system. This is also referred to as a stand-alone system. If the thermal energy demand of the site is higher than that generated by the cogeneration system, auxiliary boilers are used. On the other hand, when the thermal energy demand is low, some thermal energy is wasted. If there is a possibility, excess thermal energy can be exported to neighboring facilities Thermal Load Matching The cogeneration system is designed to meet the thermal energy requirement of the site at any time. The prime movers are operated following the thermal demand. During the period when the electricity demand exceeds the generation capacity, the deficit can be compensated by power purchased from the grid. Similarly, if the local legislation permits, electricity produced in excess at any time may be sold to the utility.

30 Biomass-based FBC and Co-generation Technology This technical study report is on the use of rice husk as a fuel in an FBC boiler to generate medium to high pressure steam and using this steam to generate electricity by a steam turbine and also use part of the steam in the manufacturing process in the industry. In the preceding sections different types of FBC boilers, steam turbines and their configurations have been discussed in detail to develop a thorough understanding of the equipments used in the process. The contexts in the other sections are with reference to this specific technology only. Although numerous configurations are possible, but for small and medium scale of operations the following four are the main configurations i) Steam generation using FBC boiler and no electricity generation ii) Steam generation using FBC boiler and electricity generation using Backpressure type of turbine iii) Steam generation using FBC boiler and electricity generation using Extraction cum condensing type of turbine iv) Steam generation using FBC boiler and electricity generation using condensing type of turbine with no steam used in process The fourth case is rarely used by the industries and is more applicable to the thermal power plants which use biomass as a fuel and FBC boilers for steam generation. The configurations of system and the design of the boiler and the turbine are wholly dependent on the site specific requirements and a detailed feasibility analysis needs to be conducted to determine the correct configuration and the design parameters. Beside this, the choice is also governed by other factors like, economic feasibility, fuel availability, electricity availability, etc. For example if the cost and availability of the grid electricity supply is satisfactory, industries rarely go for co-generation systems and just settle for steam generation by a FBC boiler (Case i). The most important parameters which helps us to determine the choice of technology implementation between Case ii and iii are, the steam quantity and steam pressure requirements in the process house. Beside this a choice has to be made as per section Overview of the Technology The overall working of the technology with major process steps and equipments with inputs and outputs is depicted in Figure 12. The process steps may vary from site to site depending on the nature and quality of Biomass, the type of system and the local environmental regulations.

31 31 Biomass from Field Baling of Biomass at Site Storage of Biomass at Site Sizing of Biomass if required Raw Water Condensate to Boiler Water Treatment Plant (DM) Water Fuel Mixing of Biomass if required Condenser TURBINE Low Pressure Steam High Pressure Steam G F B C BOILER Flue Gases ESP Bottom Ash Fly Ash Medium Pressure Steam to Process Electricity Clean Flue Gases to Chimney Figure 12 : Elements of a Biomass Based Cogeneration System using FBC Boiler 3.2 Areas of Application The cogeneration technology can be adopted in various industrial sectors such as textile, pulp and paper, brewery, food processing etc.). The first and basic requirement for implementation of cogeneration system is that the industry must require both steam and electrical power in its operations. The ratio of the heat value of the steam required to the electricity required is known as heat to power ratio and is one of the most important factor which helps to decide the type and configuration of the cogeneration systems to be installed. Heat to Power Ratio is defined as the ratio of thermal energy to electricity required by the energy consuming facility. It can be expressed in different units such as Btu/kWh, kcal/kwh, lb./hr/kw, etc. The heat-to-power ratio of a facility should match with the characteristics of the cogeneration system to be installed. Basic heat-to-power ratios of the different cogeneration systems are shown in Table 5 along with other technical parameters. The steam turbine cogeneration system can offer a large range of heat-to- power ratios. Table 5: Heat to Power ratios and other parameters of cogeneration systems Cogeneration System Back-pressure steam turbine Extraction- Condensing Turbine Heat-to-power ratio (kwth / kwe) Power output (as per cent of fuel input) Overall efficiency (per cent) Cogeneration is likely to be most attractive under the following circumstances: The demand for both steam and power is balanced i.e. consistent with the range of steam: power output ratios that can be obtained from a suitable cogeneration plant.

32 32 A single plant or group of plants has sufficient demand for steam and power to permit economies of scale to be achieved. Peaks and troughs in demand can be managed or, in the case of electricity, adequate backup supplies can be obtained from the utility company. The ratio of heat to power required by a site may vary during different times of the day and seasons of the year. Importing power from the grid can make up a shortfall in electrical output from the cogeneration unit and firing standby boilers can satisfy additional heat demand. Many large cogeneration units utilize supplementary or boost firing of the exhaust gases in order to modify the Heat to Power Ratio of the system to match site loads. The proportions of heat and power needed (heat: power ratio) vary from site to site, so the type of plant must be selected carefully and appropriate operating schemes must be established to match demands as closely as possible. The plant may therefore be set up to supply part or all of the site heat and electricity loads, or an excess of either may be exported if a suitable customer is available. The following Table 6 shows typical heat: power ratios for certain energy intensive industries: Table 6 : Typical heat to Power ratio for Certain Energy intensive Industries Industry Minimum Maximum Average Breweries Pharmaceuticals Fertilizers Food Paper Issues in Implementation of Biomass-based Cogeneration Systems The key issues in implementation of a biomass based cogeneration systems (BBCS) are broadly classified as: technical and economical, environmental and social issues and are discussed in the following sections Technical Issues and Barriers Biomass based cogeneration is faced with some technical barriers, which not only have a direct impact on day-to-day operations, but also on overall viability of the project. These issues are sometimes stand-alone issues and some are more complex and interrelated. In the following sections, these issues and problems have been discussed in detail. It may be noted that, some of the issues/problems are interconnected and complement each other and thus add to the complexities in the overall scenario. However, for reasons of clarity, these problems have been presented as stand - alone issues Technology Sourcing for Bio- Mass Power Generation In a typical thermal power station, the basic fuel is prepared to the specific size, according to the technical requirements of the boiler furnace in order to ensure efficient combustion. In such cases, the boiler furnaces are specifically designed to suit the characteristics and parameters of the fuel (say, coal or gas) on which the system is proposed to run. The availability of this specific fuel is ensured by the user well in advance through techno-legal agreements with fuel suppliers, for guaranteed supply of the fuel in the specified quality and quantity.

33 33 Ironically, in case of biomass projects, no such agreements exist as biomass fuel market is unorganized and rural based. The supply position of any particular type of fuel is never assured, and the biomass based projects are forced to fend for themselves in the best way they can against the whims, fancies and the vagaries of the biomass supply chain. Making the right technology choice for biomass-based FBC boiler therefore is a key element for the success of such projects Viable Availability of Biomass Fuel There have been innumerable instances, where the supplier have taken undue advantage of demand supply gap and wrested very high prices from reluctant but helpless biomass based cogeneration projects. Even assuming that the biomass based cogeneration project is lucky enough to strike a cordial deal with the suppliers, more critical issue of the wide variation in the sizes of the biomass as it is received, poses another bottleneck. This calls for an additional process of appropriate sizing of the bio mass. If it were the case of a particular biomass, the situation would perhaps have been comparatively simple. But considering the wide variation and seasonality in the availability of the bio mass, and their basic characteristics, (size, shape, texture, moisture content, volatile matter, Calorific Values, etc.) make effective preparation of biomass to suit the boiler technical requirements, a very complex exercise. It is but natural that the efficiencies of the boilers would be low as compared to a boiler operating with a single fuel, for which the basic operating parameters can be set once & for all, needing only periodic adjustments. This is very difficult with multi-fuels scenario with frequently changing mix. Apparently, this seems to be one of the reasons, for several biomass based cogeneration projects, to have opted for higher heating surface area, compared to the well established fossil fuel based power plants (of equivalent rating). Following is a summary of various factors related to the availability of biomass, which can greatly affect the viability of the cogeneration projects; A) Types of biomass used in biomass based cogeneration projects In any country there could be several varieties of biomass which are in use, depending upon the geographic regions, geo-climatic conditions, agricultural practices, growing patterns, season and their commercial availability. Considering wide variety of biomass being used, with different moisture content, volatiles, unknown chemical composition and external impurities like mud, clay, sand etc. It is easy to appreciate the technical difficulties of collecting, preparing and combusting them in an efficient manner. B) Availability of Biomass: It is a well known fact that, biomass availability is highly influenced by crop patterns of a region, climate, weather and seasons, added to these factors is the diffused availability of biomass, which makes the collection and transport logistics a difficult and costly task. These factors impose constrains on the total quantity of biomass that can be made economically available at the project site. C) Fuel Collection & Logistics: When biomass power generation was conceived in the mid 1990 s in India and entrepreneurs came up with project proposals with rice husk as biomass, the early biomass plants did not face any problems in collecting their main biomass fuel (i.e., rice husk), since rice husk was available in plenty at rice mills. In fact, the rice millers were more than happy to give away the rice husk at very nominal rates (some times free of cost) since that would solve their disposal problem. The plants only had to engage transporters to bring in the rice husk from rice mills.

34 34 However, with installation of more and more biomass based cogeneration plants, the situation changed, to an extent that, today, biomass based cogeneration plants are looking for any agro or forest residue (woody biomass) that could be burned in their boilers. Accordingly, the spectrum of biomass fuels broadened from one or two main fuels to 5 to 10 different types of biomass being used in a single cogeneration plant. This has led to several technical and financial problems for these plants: More number of biomass types necessitated different types of collection and handling equipment. Since most of these biomass fuels, such as Cajurina branches, cotton stalks, husks of different pulses, sugar cane trash, spent coffee waste, coconut fronts & shells, jute waste, marind husk, red chilly waste etc., were new to these plants, there were no readily available equipment/machines to suit the new requirements. Hence, all biomass cogeneration plants were forced to spend a sizable amount of money in sourcing such equipment from domestic / international vendors or developing these machines indigenously. There are also cases of in-house design & development to manufacture collection equipment resulting additional capital investment and operating cost. Many of the agro residues need to be collected manually, baled and transported to cogeneration plants. Since this is a highly labor intensive activity and biomass is available in distributed quantities, some small and some large, the fuel contractors would only be interested to supply biomass that is available in large quantities at a single location. Thus biomass available in smaller lots would be ignored. The transport of biomass from rice mills / other places of availability is effected by transport contractors. Sometimes, transport contractors also become fuel supply contractors. Depending on type, biomass is transported in lorries/trucks, tractor trolleys, bullock carts etc., The major problem is, the high bulk density of biomass fuels, which results in lower tonnage per vehicle, spillage due to light weight when transported in open trucks, and thus higher transportation cost. The transportation cost (including loading and unloading cost) constitutes a significant portion of the landed cost of the biomass. For example, rice husk in India costs around INR800 (US $ 20) to INR1,000 (US $ 25) per ton at the rice mill, whereas transportation costs are an additional INR300 (US $8) to INR400 (US $10) per ton. For biomass fuels which have to be collected directly from the fields (such as sugar cane trash, coconut fronds, forest residues etc), and which do not have a centralized collection point, the cost of logistics (collection, loading, transport and unloading) further increases Fuel Pricing The biomass fuel, presently an unregulated commodity and available in the open market, makes its price very dynamic and varies extensively from region to region. The price is influenced by several factors; such as: supply-demand gap (fierce competition among entrepreneurs), seasonality, distance to be transported, quantities available in single lots etc. Depending on the price, the cost of fuel constitutes a major portion in total generation cost. The cost of fuel ranges between 50 to 70% of electricity generation cost, in case only electricity is produced Fuel Storage Handling and Preparation A) Problems in biomass storage It is observed that many of the cogeneration plants have no sheltered storage space wherein different types of (degradable) biomass could be safely stored, protected from the vagaries of the weather. The propensity of biomass fuel to decay/decompose with

35 35 time, when exposed in open yards, puts a limit on the fuel inventory that a biomass based cogeneration plant can have (to take care of availability). This also means that these plants have to put a sustained effort to procure biomass for their plant, on a regular basis, as they cannot store large amounts of biomass. It would be beneficial to build sheltered storage yards, where loss of biomass due to decay can be reduced. Storage sheds need to be built with bay arrangements and necessary tools for stacking and reclaiming. B) Need for Multiple Preparation & Handling Equipment Biomass power projects, can no longer afford the luxury of depending on a single fuel, for sustained operations. It has become quite normal that, multi biomass fuel is the way to go. This has imposed, the necessity to introduce various types of fuel preparation options, to suit the various fuels, in the way and sizes, they have to be fed to the boiler. This makes it very difficult for any single unit to invest in many different kinds of fuel preparation equipment. More so, there is a dearth of such equipment, and most of those in use, have been indigenously developed, by individual plants. In India, some of the plants have designed and developed equipment for fuel preparation on their own (with a little help from others and not necessarily very efficient), which range from basic cutters and chippers to bailing, drying, and feeding systems. Some of the equipments are listed below: Sizing equipment (Chopping) for woody biomass Saw cutter and wood chipper for woody biomass like Juliflora etc, Chippers for making palm bunches into fibrous material for ease in firing Chippers for making coconut fronds, into smaller pieces & powder Rotary shredding machinery for bushy biomass like Jute Stick, Cotton stalk, Casurina branches etc. De Oiled Bran Crusher Shredders Screening Briquette making (yet to be tried out) Sieving machines for coir pith Dryers for moisture removal by air drying, Drying - natural (solar) drying Conveying equipment (Belt, drag chain, bucket, pneumatic) Other problems associated with storage and handling of biomass include: Many biomass are collected directly from fields, which adds complications of external impurities like mud, sand and unknown chemical compositions. It has been observed that typically the moisture content ranges between 25% to 38%. While sun drying is a simpler option, it has its own constraints, e.g. Large floor area requirement where the bio mass can be spread to provide maximum exposed surface area. There is unfortunate situation that when there is bright sun there is no bio mass and the reverse.

36 36 Technical Study Report: Biomass Fired FBC Boiler for Cogeneration Enormous labor requirement for handling and transporting, stacking, etc., which pushes up the cost of the fuel beyond the capacity of the unit. Most of the biomasses have a typical and peculiar characteristic that only about the top 2 inches thick material dries up but the inner mass do not get dried.this calls for periodic restacking/disturbing of the heaps of the bio mass, calling for extra labor and other costs. Figure 13: Chipping Machine for Cajurina branches & coconut fronds at Varam Power, India Figure 14 : Collection & Baling Machine for sugarcane trash at GMR technologies, India While some of the units use the waste gases for this preliminary drying, they had faced the problem of huge capital investment for the appropriate equipment. Since the cogeneration plants are using variety of biomass fuels, separate conveying and handling systems are required for each (or group of similar) biomass fuels. For example, separate conveyers have to be used for rice husk & woody biomass (juliflora chips) as they have to be fed at different locations/ways. Another example is

37 37 screw feeders used for conveying rice husk cannot be used for sugar cane trash as the trash would roll around and jam the screw. Further, to meet the demand several fuels (of similar nature) such as rice husk, pulse husks are mixed and fed to the boiler. All these factors contribute additional capital and operation and maintenance (labour, energy etc.) costs for industries Issues in Use of Supplementary Fuels The poor quality of biomass in terms of high moisture content, low calorific value and low bulk density, often results in low heat generation in the boiler, which can not sustain power generation at the rated capacity. This problem gets further aggravated during the rainy season. Also, unavailability of sufficient biomass, due to seasonal constraints, necessitates cofiring of fossil fuels such as coal, to maintain the required steam parameters and/or power generation. While use of coal as a supplementary fuel is allowed, care should be taken with regards to the quality of the coal, and it should be of a low quality or it would result in high bed temperature and subsequently choking of the bed due to ash fusion Other Technical Problems in BPP Operations A) High heat rate of Biomass based FBC boilers Compared to coal based power plants, biomass based cogeneration plants operate with higher heat rate (low efficiency) due to poor fuel quality (high moisture and low GCV), lack of optimization of boiler parameters and the turbine parameters (such as optimization of excess air and steam parameters). It is natural, that the efficiencies of these boilers would be low in comparison with boilers operating with a single fuel, for which the basic operating parameter can be set once for all, needing only periodic adjustments. This is very difficult with multi-fuels, with frequently changing mix. This is one of the reasons for high heat rate or low boiler and system efficiency. To circumvent this problem the cogeneration plants opted for higher heating surface area in the FBC boiler, compared to the well established fossil fuel based power plants (of equivalent rating), giving them operational flexibility. Another rationale for opting for higher heat transfer area is fouling of heat transfer area due to unavoidable dust loading in the boiler furnace (due to inherent biomass properties). The overall heat transfer coefficient, especially in closely packed convective zone, would deteriorate gradually with time and spare heat transfer area in these situations, would help maintain required heat transfer. On the down side, the additional heat transfer provided, would impose part loading on the boiler, when the tubes are relatively clean. To sum up, the much talked about low efficiency (with a wide variation) of power generation cycle in the biomass based cogeneration systems is on account of the following factors: Problems in technology adequacy Varying multi fuel mixes and improper sizing Technology is not yet fully matured & optimized (for smooth & efficient operations) B) Others Some of the troublesome operational problems being faced by biomass based cogeneration plants are highlighted below: Uneven spreading of biomass fuel on boiler grate is leading to secondary combustion at super heater zone, resulting in over heating of super heater tubes and also

38 38 fluctuations in steam pressure. Due to troublesome flow characteristics of biomass in bunkers, some plants feed the biomass directly from the top of the boiler with conveyors, leading to uneven distribution. Also, since the bunkers (which serve as reserve capacity to smoothen the variations in flow from the conveying system), are bypassed, furnace loading and combustion are not uniform, resulting in fluctuating steam parameters and generator output. Corrosive constituents in biomass badly effect boiler internals, especially the superheater tubes. Chloride content in some biomass (8-9% for cotton stalks) combined with sodium and potassium at high temperatures can cause much damage. Frequent erosion of super-heater & economizer coils also results due to high silica content in the biomass. High extraneous matter in biomass (sand and mud) causes boiler tube fouling and also requires fluidized bed to be drained more frequently with resultant heat loss. Carbon and dust coating of boiler tubes resulting in lowering of steam temperatures, especially during soot blowing. Pesticides used during cropping add to tube failure frequencies - especially the content of potassium. Corrosion of heating surfaces (coils) is a big issue. Such is the uncertainty of their well being that, many plants are compelled to stock at least one bundle, as spare, at all times. There are instances where the super heater coil bundle was replaced at least once a year Financial Issues / Barriers The first and the foremost barrier in implementation of the biomass based cogeneration plant is the capital investment. The capital investment cannot be ascertained off-hand as it depends on various configurations of the boiler and the steam turbine system, and these two equipments are strictly site specific. It would be grave mistake to follow a same type of approach and design for two process houses even though they are of similar nature. As a rule of thumb the capital cost for Indian condition is approximately US 300,000 per MW. This includes the FBC boiler, turbine, and all other accessories. This capital cost is somewhat high for the small and medium enterprises to invest, more so in the absence of government subsidies or an encouraging mechanisms. The second biggest financial risk in implementation of the biomass based cogeneration plants is the uncertainty in the prices of the biomass. The cost of the biomass is highly variable and depends on the market demand. Therefore there is always a degree of uncertainty with regards to the profitability of the project. This is more so in the absence of government interference in the biomass pricing as compared to the regular fossil fuel pricing. It sometimes so happen that in order to make the complete project viable the industry chooses a configuration so as to export the surplus electricity or steam generated (most of the times it is the export of electricity rather than steam) to another industry close by or to the local electricity service company through the grid. In such a case there is always a power tariff agreement between the supplier and the receiver with regards to the minimum quantity of electricity supplied and the cost at which the electricity is supplied. In lieu of increased biomass prices the supplier is not able to increase the tariff of the electricity exported, whereas it has to necessarily keep on supplying the minimum quantity of electricity as agreed upon during the time of contract. This makes the project financially unviable.

39 Environmental Benefits of Biomass based cogeneration Systems The benefits of biomass use as a source of fuel in cogeneration systems, besides energy security & independence of the industries, include several environmental benefits, mainly in terms of GHG reduction. Biomass Power generation, is considered to be CO 2 neutral, since only the amount of carbon fixed during the growth of a crop/tree, is emitted during its combustion. Biomass is traditionally used as cooking fuel in households in many countries, especially in rural areas, which is the cause of indoor air pollution and health impacts, such as asthma, bronchitis, respiratory infections etc. on women & children, leading to morbidity & mortality. Governments in various countries provide clean fuels such as LPG & kerosene, at subsidized prices, to reduce & disengage firewood/ biomass as a cooking fuel. Hence power generation through biomass, is a good alternative, not only in the use of surplus agro & woody residues but also because, it brings in efficiency. The surplus biomass is burnt in the fields, by farmers, to get rid of it and at the same time to retain some nutrients in the fields. This open burning in the fields, have environmental & health impacts which can be alleviated due to efficient utilization and burning process in the FBC boilers. Open burning and cooking cause a high level of particulate matter problems, which are addressed effectively, with electrostatic precipitators (ESP) in cogeneration plants. It reduces the transmission losses which otherwise would have incurred when the electricity is supplied to an industry. This in turn leads to less fuel usage to produce electricity by an equivalent amount. 3.5 Social Benefits of Biomass based cogeneration Systems Biomass power generation undoubtedly leads to several social benefits as below: Biomass power plants monetize the heat value of biomass, which brings in additional income to various players in the biomass supply chain (farmers, traders, agro processing industries such rice mills etc). It creates additional employment in collection and transportation of biomass, as well as additional employment in power generation. It brings additional economic and income generation activity into rural areas especially for women - thereby contributing to local & regional development. It would diversify the rural economy, which generally rely entirely on food crops, by introducing energy plantations. This is all the more important, since most energy plantations are grown on so called wasteland which have, no/minimal access to irrigation. This is a significant aspect in water stressed areas. In countries like India the employment generation, in fuel collection and logistics, have excellent gender mix in favor of women, which, is lacking in many employment generation schemes of the government and in other sectors such as infrastructure building (roads, highways etc.). It brings additional skills to rural areas and can raise the income levels of farmers and laborers, which in turn improves the standard of living. The creation of employment opportunities in rural areas would reduce the government spending on employment generation and at the same time would bring in additional tax revenues to the government.

40 40 It would reduce the equivalent fossil fuel import bill of the government & thereby improve the balance of payment position. Biomass based cogeneration projects have given impetus to technology development, by encouraging use of different agro and woody biomass in plants. It would also give impetus to technology development at the farm level, by introducing farm level machinery, to facilitate collection and baling. The success of biomass power plants using combustion route, has led to increased efforts in power generation through other routes, like gasification.

41 Implementing Biomass Cogeneration Technology After understanding the basics of the FBC based biomass cogeneration technology, it is important to know the various practical requirements in order to effectively implement and ensure smooth and trouble free operation of the technology. Of course, these requirements can not be elaborated to the last detail - as a lot depends on many site specific factors. Broadly, the various requirements of the technology implementation can be divided into the following: Raw material and energy resources requirement Waste & its disposal Infrastructure requirement including land Supporting technologies Human Resource Requirement Technology suppliers 4.1 Raw material, Energy Resource requirement FBC boilers can be used to burn many grades and types of solid fuels like rise husk, bagasse, etc. In fact, depending on the available fuel, the boiler suppliers design and supply the boiler. In case of rice husk, with a calorific value in the range of 3,000-3,100 kcal/kg, and boiler efficiency of 80%, 0.25 tons of fuel (rice husk) is required to produce 1 ton of saturated steam at a pressure of 26 kg/cm 2. But the amount of rice husk consumption would be increased if the steam is in superheated condition. For cogeneration plant with a capacity of electricity generation of 1 MW and above, the degree of superheat is in the range of 220 to 290 ºC. It means the temperature of steam is in the range of 390ºC to 460ºC. The amount of fuel required is totally dependent on the quantity and pressure of steam required and the degree of superheat at that pressure. This in turn is dependent on the on-site requirements. Therefore, the primary data required to estimate the total fuel required is - the pressure at which steam needs to be generated and the degree of superheated steam required - the quantity of steam required - the amount of electricity needs to be generated. The quantity of fuel required can be worked out by back calculation after having determined the steam requirements in the process house and electricity to be generated and the steam to the condenser. Thereafter an energy balance could be performed. Let us consider a case as in Figure 15:

42 42 Steam (saturated) = x tons/hr Temperature = 450 o C Pressure = 26 kg/cm 2 TURBINE Electricity Output = y (known) Steam (to process) = z tons/hr (known) Temperature = 250 o C Pressure = 10 kg/cm 2 Steam (to condenser) Pressure = 0.10 kg/cm 2 Figure 15 : Example on estimation of fuel requirement for co-generation Making a Material & Energy Balance a) Input Enthalpy of steam (kcal/hr) = [Quantity of steam input to turbine (x)] X [Enthalpy of steam at 26 kg/cm 2 & 450ºC temperature (from steam table)] b) Output i) Electrical Energy = [Electricity produced in watts (y) X 860] / [Efficiency of Turbo generator & Steam Turbine i. e. 81%] = [y x 860] / [0.81] kcal/hr ii) Enthalpy of steam to process (kcal/hr) = [Quantity of steam (z)] X [Enthalpy of steam at 10 kg/cm 2 & 250ºC temperature (from steam table)] iii) Enthalpy of steam to condensate = (x-z) X enthalpy of steam at 0.1 kg/cm 2 i.e. vacuum Since; Energy Input = Energy Output, the only variable unknown is x i.e. quantity of steam required which can be calculated using: a) = b(i) + b(ii) + b(iii) The quantity of fuel can be determined as: Fuel quantity (kg/hr) = [Enthalpy of steam at inlet to turbine] / [Boiler efficiency X GCV of fuel] It can be observed from the above calculations than the quantity of fuel used is totally dependent on the electricity to be generated and the steam requirement in the process house. However it must be noted that the steam demand in the process house and the electricity requirements are never constant in an industry. Therefore the actual fuel requirement can be estimated only over a period of time after the system is in place. It is a general practice to maintain at least 7 days inventory of the fuel required. Another aspect to keep in mind while estimating the fuel requirement is the peak load period. If the system is designed to operate optimally at the time of peak loads then, it is going to perform at low efficiency during the average or low load period. In order to remove this anomaly the FBC boilers are generally designed to handle different type of fuels

43 43 and there is also a provision of co-firing using solid fossil fuel like coal (of a very low quality); since even a low quality coal do have higher energy contents than the rice husk. Therefore in order to meet the peak load demands either the rice husk is mixed with coal or there is a separate coal feeding system from which coal is fed and combusted in the boiler in parallel to the rice husk. Table 7 lists the various fuels and there calorific value which can be used in a FBC boiler for steam generation. Table 7 : Fuels and their typical calorific values No. Fuel Calorific Value (Kcal/Kg) Moisture Content ( % ) Ash (%) 1 Rice Husk Bagasse Straw Nuts and Shells Wood In addition to the fuel in the boiler, another very important input into the co-generation system is the electricity required by the various equipments in the cogeneration system. These include: boiler feed water pumps, air supply fans, (induced & force drafts) compressed air, ESP, water treatment plant, ash handling system, cooling towers for condenser etc. The total electricity consumed by these auxiliaries is named as auxiliary power consumption. Primarily all the auxiliary power consumed is drawn from the electricity product by the turbo generator there the turbine. As a rule of thumb, the auxiliary power consumption is in the range of 12-15% of the total power generated. This however varies with the type of turbine system configuration and the fuel mix used for the boiler. Therefore when estimating the power requirements of the industry an addition sum amounting least 15% may be added on to the average demand. 4.2 Infrastructure Requirement Infrastructure requirement for a biomass based cogeneration plants can be broadly divided into two categories (i) External Infrastructure i.e. outside the industry premises (ii) Internal Infrastructure i.e. within the industry premises. External infrastructure: Although the industry which is setting up a cogeneration system does not have control one the conditions outside, but still during conducting detailed feasibility analysis external factors should be taken into consideration. Table 9 lists the important parameters to look out for. Table 8 : External Infrastructure Requirements No Parameters Remarks 1 Road connecting 2 Close to bio mass market Wide metalled roads to cater to the need of fuel transports in large quantities by truck all through the year To ensure perennial supply of bio-mass 3 Water availability Either ground water or municipal supply. 4 Ash disposal Facilities for ash disposal in landfill or road construction material etc. 5 Electrical Grid To upload the excess power generated to the grid.

44 44 Internal Infrastructure: One of the most important infrastructure requirements in case of implementation of the biomass fired co-generation system is the availability of land area. Large space is required to set up the boiler house, the turbine house, the electrical distribution system etc. The land/area required for each of the component would be different and would depend on the configuration and size of the cogeneration system. In absence of space availability it would be not possible to set up the described technology. The following table lists the area and other infrastructure requirements to be analysed before starting the project. The data in the table 10 is for a typical cogeneration plant generating 3-5 MW of electricity and high pressure steam generation of about 25 tons/hr. Table 9 : Area requirements for different components of a typical cogeneration system No. Equipment Approx. Area & Other Requirements Comments 1 Boiler house 5000 sq. ft Industrial type shed with a height of a plant 50 ft. 2 Biomass storage and Open space/ shed of about Depends on the climate of the region handling 10,000 sq ft to maintain 7 days inventory of fuel 3 Water treatment 1000 sq. ft plant 4 Turbine house 7000 sq ft The turbine house is a permanent concrete structure with typically two floors. The same structure houses the electricity load monitoring & distribution panel. 5 Electrical load monitoring & distribution panels 6 Water storage tank 20,000 m 3 of water storage tank, preferably overhead 7 Laboratory, store & maintenance workshop 1000 sq ft 4.3 Supporting Technologies In implementation of new technologies it is imminent that some additional and supporting technologies are required along with the new technology implemented. Although in implementation of a biomass fired boiler and cogeneration system the additional technologies are part of the system and generally the supplier of the system do install and commission all the other technologies as a package rather than just the boiler, or the turbine. Nevertheless it is important for the industries to know about the additional technologies as it helps them identify the new work areas they have to handle & maintain at a later stage. The additional technologies required for a cogeneration plan are listed in table 11. Table 10 : Supporting Technologies for Cogeneration Systems No. Equipments/Technologies Remarks 1 Water treatment plant The input TDS should be less than 10 mg/l for high pressure boiler 2 Fuel preparation & handling system Needed in case of multi fuel use 3 ESP/Bag filters/multi cycle Choice depends on the norms of the country 4 Ash handling system Depends on volume of ash to be handled & disposal pattern. 5 Fuel drying system Dependent on the type of fuel to be used 6 Cooling Towers Size and choice depends on the climatic condition of the area

45 45 The capacity & design of these additional technologies will depend on the size of the boiler & the co-generation system Water Treatment Plant: Typically the water treatment plant consists of a Reverse Osmosis plant followed by an ion exchange plant. For a high pressure boiler, typically the TDS of the water being fed into the boiler should be less than 10 mg/l. These two technologies do have limited environmental impact. The rejects from the RO plant and the waste water generated from the ion exchange plant is neutralized in a tank and can be used for sundry purposes like floor washing, gardening etc Fuel Preparation & Handling: Generally the biomass like straw etc. is just picked up from the agricultural field and brought to the industry. These types of fuels need to be sized so as to be used in the boiler. Therefore there is a need for a shredding machine which would size the fuel to be used. In many cases the fuel brought to the industry is in form of bales. These bales are de-baled by a de-baling machine before it could be fed to the FBC boiler. Further since the industry maintains an inventory of about 7 days the fuel is stored over a large area. To collect this spread over fuel and bring it to the fuel feeding system requires either manual work by workers or loaders and pushers operated by their drivers. Although there is no direct and major environmental pressure associated with these technologies but the use of the various equipment increase the auxiliary power consumption Suspended Particulate Matter (SPM) Control: In any case of a solid fuel fired FBC boiler the control of particulate matter is a necessity. The amount of fly ash depends on the type of the fuel used. In case of bagasse the amount of fly ash is quite less where as for rice husk it is more. Therefore the choice of SPM control technology is also dependent on the nature of fuel being used. But since FBC boilers are designed to combust multiple fuels the most prominent technology for particulate control is Electrostatic Precipitators (ESP) or bag filters. The capital cost of ESP is more than the bag filter, although its operation cost is less than that of a bag filter. These technologies themselves do not have any negative environmental impacts. The choice is also governed by the local laws and regulation with respect to the limits of the SPM in the flue gases Ash Handling System: Ash is generated as bottom ash from the boiler furnace and is also collected as fly ash from the ESP or any pollution control device. The ash handling system depends on what is the end use of the ash generated. In case the ash is to be used for cement manufacture or bricks making or as a subgrade material in road construction etc. The ash is handled in dry form. It is pneumatically conveyed through pipes by help of compressed air, but this is a very costly type of system and is used only in case of large amount of ash to be handled. For a small cogeneration plant of 3-5 MW capacity this type of system is not economically feasible. In such plants the ash is handled manually using loaders, excavators and trucks or tractors/ trolley. The loaders load the ash to the trucks and trolleys which are then transported to the desired site. Another method to handle ash is to form slurry by mixing with water and this slurry is then pumped to the ash dyke (a huge pit). In the ash dyke the water is drained and the wet ash is deposited. The drained water can be recycled back for slurry preparation Fuel Drying System: Some of the biomass fuel like bagasse, have high inherent moisture content. Therefore these types of fuel need to be dried before being fed into the boiler. High moisture in the fuel could lead to problems in the fluidization of the fuel. The high moisture will also increase the stickiness and would cause deposition on the boiler tubes; it would also lead to formation of black smoke from the chimney and choking of the bed. A very common method of fuel drying is by spreading it over a large area and sun drying it. But in some cases where the quantity of fuel to be dried is large, special fuel drying system is installed, where in the fuel is dried by the waste heat from the flue gases. In such system addition environmental pollution control system to control the particulate matter are generally installed.

46 Cooling Towers: Cooling towers are part of the boiler-turbine system. The type and the size of the cooling tower is dependent on the climatic condition of the region where it is installed. The cooling tower by itself does not have any negative environmental impact. The amount of water evaporated in the cooling tower is about 5-7 % of the total cooling water used in the circuit. 4.2 Waste Disposal Both solid and liquid wastes are generated from different areas of a cogeneration plant. Although the wastes generated are not hazardous, but need good practices to mange them so that they may not result in any additional environmental impacts. The major wastes generated from the cogeneration system are listed in table 8. Table 11 : Waste Generated in Cogeneration Plant No. Waste Area Frequency of Generation 1 Used lube oil Turbo generator, turbine etc. Once in 6 months 2 Cooling water Turbine being cooling etc. Continuous 3 Reverse Osmosis (RO) Reject Water Water Treatment Plant Continuous and DM plant wash water 4 Ash Boiler bottom ash from boiler furnace, fly ash from ESP or bag filter Continuous The most significant waste that is produced is the ash. The quantity of ash varies according to the fuel mix used. In case only rice husk is used as a fuel, the total quantity of ash generated from the process is about 28-30% of the rice husk used by weight considering that the rice husk has a moisture content of about 10% only. If we analyse the composition of fuels like rice husk and bagasses as in Table 7, we observe that the quantity of ash content in the fuel is only 19.4% and 7.03% respectively. However, when these fuels are burned in a boiler there is some unburnt carbon particles. This unburned carbon comes out mixed with ash. The quantity of unburnts in FBC boilers is dependent on many factors, the most prominent one being the mode of firing & type of distribution system to spread the fuel inside the boiler furnace. The quantity of ash generated in case of use of bagasse as a fuel is in the range of 10-12% of the total fuel used. Therefore in comparison to the rice husk it is a better fuel in terms of quality of solid waste generated. The ash generated from the ESP and the boiler is collected and is disposed off in landfills. However, there are certain more ways of effectively using the fly ash generated namely Use as sub-grade material in road construction. Used for making fly ash bricks Partial use in cement manufacturing The other wastes like spent lube oil, cooling water, R.O. rejects water are not of much environmental consequence as their quantities are quite low in comparison. The lube oil is recycled back to the company which provides it. The cooling water is in a closed circuit and the losses in the circuit are only evaporation losses through the cooling towers. The rejects from the R.O. plant/dm Plant are neutralized and used in gardening and other purposes like floor washing etc. 4.5 Human Resources Demand A trouble free operation of implemented technology is very much dependent on the way it is handled and operated. Therefore the role of both trained and untrained manpower at

47 47 supervisory level and operations level are of utmost importance. In most of the cases and especially in case of biomass fired cogeneration plant it is very difficult to assign the number of people which would be optimum for the purpose of plant operation and maintenance, since the manpower requirement is more or less a function of the size of the plant. However, for a plant size of 3-5 MW about personnel s are required. This includes managers, supervisors and operators. 4.6 Equipment Suppliers The main equipments in case of a biomass based cogeneration plant are : Atmospheric Bubbling Fluidized Bed Combustion Boiler and a Extraction cum condensing Steam Turbine. The FBC technology for the use of rice husk as a fuel is quite matured in India. There are more than 200 cogeneration plants using the FBC boilers in operation in the country. Table 12 lists the various suppliers of steam turbine and the biomass fired FBC boilers. All the other auxiliary equipments like cooling tower, water treatment plants, ESP, ash handling plant etc are supplied by the boiler manufacture as a part of the package. Table 12 : Suppliers for Steam Turbine and FBC Boiler Disclaimer : The addresses provided in the table above are only representative and in no way it is implied that the product are being endorsed by DTIE, UNEP Components Supplier Country Address Phone Fax Supplied Steam Turbine Triveni Engineering & Industries Ltd India 12A,Peenya Industrial Area, Bangalore, Karnataka India Steam Turbine Turbo Engineers India 2/C/1, Picnic Garden 3Rd Lane, Kolkata, WB, India Steam Turbine UES India A-302,2nd floor, Vikashpuri, New Delhi, India Steam Turbine Citation USA Haggerty Road/Suite Corporation 420,NoviMichigan USA Steam Turbine Skinner Power USA 8214 Edinboro Road, Erie, Systems LLC Pennsylvania USA Steam Turbine Canton Drop USA 4575 Southway St. SW, Forge Canton, OHIO USA Steam Turbine eturbines Inc. USA 3030 Greens Road, Houston TX USA Steam Turbine National USA 800 King Avenue, Columbus, Electric Coil Ohio USA Steam Turbine Solar Thermal USA 2736 N. Palmer, Milwaukee, & Biomass Wiscosin USA Power Plant Steam Turbine Turbosteam USA 161 Industrial Blvd., Turners Falls, Massachusetts USA Steam Turbine HPG Limited Canada 2240 Speers Rd, Oakville,Ont Canada L6L 2X8 Steam Turbine CITIC Heavy China 206 Jianshe Road Luoyang City Machinery Henan China Company Ltd. Steam Turbine Steam Turbine HI Efficiency Turbomachinery PVT. LTD Mitsubishi Heavy industries, Ltd. India Japan # B-143A/1,3rd Cross, 1st Peenya Industrial Estate, Bangalore Karnataka India Environmental Systems Division,2-5-1, Marunouchi,Chiyoda-ku,100 Tokyo, Japan /

48 48 Components Supplied Steam Turbine Steam Turbine Steam Turbine FBC BOILER (Biomass Fired) FBC BOILER (Biomass Fired) FBC BOILER (Biomass Fired) FBC BOILER (Biomass Fired) FBC BOILER (Biomass Fired) FBC BOILER (Biomass Fired) Supplier Country Address Phone Fax Peter Brotherhood Ltd Solar International Energy Ltd. Spilling Energie Systeme Gmbh Thermax Limited Babcock & Wilcox Wartsila Biomass Power Indtex Boilers Pvt Ltd. Fluidcon Boilers Equipments Pvt. Ltd. A.V.U. Engineers Pvt. Ltd. UK Werrinton Parkway, Peterborough, UK,PE4 5 HG Germany Margarethenstraβe 25, Frechen B. Koln, Nrw Germany Germany Werftstrasse 5, Hamburg, Germany India 9, Community Centre, Basant Lok, Near Priya Cinema, New Delhi USA 20 S. Van Buren Avenue Barberton, OH, U.S.A Finland Wärtsilä Corporation John Stenbergin ranta 2 FI Helsinki / P.O. Box 196 FI Finland India Mr. B. K. Gupta 204, Amber Tower, B/H, Akash Cinema, Badlapur, New Delhi India India India 208, Vikas Surya Arcade, Plot No. 8, Sector 11, Dwarka, New Delhi , India Survey No. 53, Bahadurpally Village, Qutubullapur (M), Ranga Reddy, Hyderabad, Andhra Pradesh , India / / / / / FBC BOILER (Biomass Fired) Mega Retro Thermal Equipments India 192, Banjara Hills, Raod No. 3, Plot No. 4, Hyderabad, Andhra Pradesh , India

49 Case Study This case study is an illustration of how a biomass (rice husk) fired cogeneration technology using an FBC boiler is implemented and operated in a techno-economically feasible manner in a small/medium scale pulp and paper industry in India. The project feasibility studies were conducted in the year and the project was commissioned in Most of the data in the case are taken from the project, however to simplify the case for easy understanding, some of the values/data has been modified. 5.1 Introduction Bindlas Duplex Limited (BDL) an ISO company belongs to the Bindal Group, which has three companies viz. Neeraj Paper Marketing Limited, Bindlas Duplex Limited and Tehri Pulp & Paper Limited. The annual group turnover is about 1,000 million rupees (23.8 Million US $). The project was initiated in the year 1991 with the installation of a high quality Kraft paper manufacturing unit, with an installed capacity of 5,000 TPA, which was later enhanced to 6,600 TPA. In the year 1997, the company initiated another project for manufacturing duplex board with an installed capacity of 13,200 TPA. Later, in year 2000, the duplex board unit was modernized to produce coated duplex board. Presently, the industry has two production lines: Unit 1 for Kraft paper and Unit 2 for duplex board. The management of BDL is highly committed towards growth. The unit has shown growth since its inception and in the year achieved 100 % capacity utilization. The management in year had a planning for capacity addition and production of Kraft Paper & Coated Duplex Board to increase gradually over the next few years. The Figure 16 below gives the projects annual production trend. 5.2 Manufacturing Process Figure 16 Annual Production Trend In the industry/factory Kraft Paper-manufacturing line is referred to as Unit # 1 and the Duplex Board manufacturing line is referred to as Unit # 2. The present capacity of the Units # 1 & 2 are 6,600 & 13,200 tons per annum (TPA) respectively Kraft Paper Manufacturing Process The raw material used for Kraft paper manufacturing is a mix of agriculture residue (60%) such as bagasse, wheat straw, etc. & waste paper (40%). A rotating spherical

50 50 digester is used for cooking agro based raw material along with caustic. After cooking, the pulp is passed through mechanical devices such as refiners, and the ratio of agro based pulp & waste paper pulp is maintained as the per requirement. Again this stock is passed out through the refiners. In the blending chest, the chemicals & colors are added as per requirement, after which the pulp is fed to machine chest & to subsequent machine sections. The Unit #1 is installed with a four dryer machine with Machine Glazed (MG) & 16 dryer s cylinder for producing Kraft paper. Steam supply to digester for cooking and dryers is provided by help of boilers installed in the utilities section of the industry. The process flow diagram is illustrated in Annexure Duplex Board Manufacturing process The raw material used for Duplex board manufacturing is entirely waste paper. In Unit # 2, the Duplex board (coated) manufactured is prepared in four layers. The 1st layer is white, the 2nd layer is for protection purposes, the 3rd layer is the filler and the 4th layer is the back layer. For the 1st & 2nd layers, de-inking & bleaching is carried out for improving whiteness. Steam supply to the process is supplied by the boilers installed in the utility section. The process flow diagram is illustrated in Annexure Baseline Energy Scenario The present electrical load of the plant is MW and the steam requirement is around 10 TPH. The management has already initiated measures for modernization, which would increase the production as well as quality. After the modernization i.e., by the end of financial year , the production is expected to increase to 8250 TPA of Kraft paper & TPA of Duplex board. Simultaneously the power & steam requirement are also expected to raise to 2.38 MW & TPH respectively Electrical Energy The industry had its own captive power generation through the Diesel generating sets because of the fact that the utility power company namely Uttar Pradesh State Electricity Board (UPSEB) power supply has been erratic and unreliable, the management of BDL was compelled to discontinue use of UPSEB power and install its own captive power generation plant. This consists of a battery of DG sets, with a combined aggregate capacity of 5.7 MVA. The ratings of the four DG sets are presented in the table 13: Table 13 : Specifications of the DG sets installed for captive power generative No. Make Rating KVA Fuel Used 1 Plistic (Marine) 2500 Furnace Oil 2 Kirloskar 750 HSD 3 Skoda 1450 Light Distillate Oil 4 Kirloskar 1000 HSD Under normal circumstances, the 2500 KVA DG set (Plistic make) and 750 KVA DG Set (Kirloskar make) are put online while the other two remain as standby. At times, however, the 1000 KVA DG set (Kirloskar make) is also put into service, for short duration. The Skoda make generator is hardly used and is just kept for emergency purposes. The annual fuel oil consumption by the DG sets during the year is kilo litre furnace oil (FO) and high speed diesel (HSD). The overall annual fuel oil bill (energy) for power generation through DG sets is around 68.6 million rupees (1.6 Million US $). The average specific generation (kwh / litre) for each of the DG sets is 3.2 kw/litre for Plistic 2500 KVA DG set and 3.5 kw for Kirloskar 750 KVA and 1000 KVA DG sets. The existing and projected electrical power requirements of the industry is depicted in figure 17

51 Power Requirement Trend- baseline values in MW (With Existing Setup) Year Figure 17 : Electrical Power requirements trends- Baseline values Thermal Energy - Steam Towards meeting plant process steam requirements, two boilers (Industrial Boilers Ltd - IBL make & Thermax make) have been installed. The IBL & Thermax boilers cater to the steam demand of Unit # 1 and Unit # 2 respectively. Fuel used in IBL and Thermax boilers is low grade coal. The rated capacity of both the boilers is 10 tons per hour (TPH) and saturated steam is generated at a pressure of kg/ cm 2 (g). As the maximum steam pressure requirement by the process is 4 kg/cm 2 (g), the boiler steam pressure is regulated through pressure reducing valves and subsequently distributed in the industry. The total annual fuel consumption in by the boilers was tons amounting to Rs 32.4 million (US $0.7 million). The existing and projected steam requirements of the industry is depicted in figure 18 Steam (T/hr) Steam Requirement Trend- baseline l (With Existing Setup) Year Figure 18: Steam requirements trends- Baseline values 5.4 Implementation of Rice Husk based Cogeneration System After analysis of the various system configurations it was concluded that an extraction cum condensing turbine type of system would be the best option for implementation. The steam to this turbine would be supplied from a new Fluidized bed combustion boiler in place of the two existing boilers. In this scheme, steam is generated in a high-pressure boiler at a high pressure & is expanded through a extraction cum condensing turbine. A part of steam (60%- 65%) is extracted to meet the process requirement and the rest is condensed. The

52 52 advantage with this scheme is that the entire process steam & power requirement of the unit would be met through the project. Since the installation of a new FBC boiler and steam turbine system would require additional electrical power and steam requirements, the projected steam and electrical demands were revised and the system was designed for revised demands. Further, the start of the project was taken to be in the year as it takes at least 6-9 months to erect and commission the system. Till the time the new system comes up the old system continued to be in operation. The revised electrical power and steam demands are depicted in figure 19 and 20. kwh & MW Requirement (After Co-generation) Year kwh (Millions) MW Figure 19: Electrical Power Requirements after Installing the Cogeneration System kwh (Millions) MW Steam Requirement (After Co-generation) TPH Year Figure 20: Steam Requirements after Installing the Cogeneration System Details about the suggested scheme Considering the steam & power requirement of the plant, it is suggested that the plant may install a co-generation system with the following configuration. Type: Alternator rating: Steam turbine rating: Extraction-cum-condensing turbine 5 MVA 4 MW FBC Boiler: 30 TPH(64 kg/cm2 and 4850C) The schematic diagram of the suggested system along with the envisaged steam & power generation potential is given in figure 21.

53 53 64 kg/cm2 (a), C, 21.2 T/hr BASE YEAR Turbine 2.7 MW To condenser 7.5 MT/ hr 0.1 kg/cm 2 To process MT/ hr 5 kg/cm 2 (a) & C To de-aerator 1.25 MT/ hr 5 kg/cm 2 (a) Figure 21 : Schematics of the Cogeneration System The technical specifications of the various equipments and accessories are enclosed in Annexure Investment details (investment break up of cogeneration project) A total investment of Rs million (US $ 2.46 million) was made for implementation of this project. The break up of investment for the different heads is detailed in Table The cost economics of the scheme has been worked out keeping the base line year as Table 14 : (A) Preliminary & Preoperative Expenses No. Particulars Amount (Rs.-Million) Amount (US $) 1 Processing legal & professional Fees , Final Run Expenses 0.1 2, Miscellaneous Expenses 0.1 2, TOTAL , Table 15: (B) Cost Involved for procuring Land & Site Development No. Particulars Amount (Rs-Millions) Amount (US $) 1 Cost of Land Rs.0.8 millions 95, Cost of Site Development Rs millions 32, Total Cost Rs millions 127, ADDITIONAL LAND REQUIRED FOR INSTALLATION OF POWER PLANT: 1.3 HECTARE Table 16 (C): Cost of Civil Works Required No. Particulars Proposed Area Type of Construction 1 Shed for Turbine & D.M.Plant 7000 sq. ft. A.C. Sheet roofing over steel column (@Rs.400/- Amount Amount (Mil Rs.) (US $) ,333.33

54 54 sq.ft) 2 Shed for high pressure Boiler 5000 sq. ft. A.C. Sheet roofing over steel column with tubular steel braces , Over head tank of 40 T capacity RCC , Lab/Store/Godown shed for fuel storage Electrification & other miscellaneous expenses (@ 10% of civil works) , ,047.6 TOTAL ,523.8 Table 17 : (D) Cost of Plant & Machinery Required Reference Amount (Mil. Rs.) Amount (US $) Turbine (Capacity 4 MW) , Air compressor for Turbine , Cooling Towers for Turbine , High Pressure Boilers (30TPH) , Boilers chimneys structure Insulation, Refractory & , fuel handling system & others miscellaneous accessories R.O. Plant , Pressure Reducing Station , Safety valves & others valves , Steam pipe line & pump , Crane , Electrical cable, panel, motors , Transformer , Sub Total ,864, Trade Tax 4.00% , Sub Total ,939, Freight 10% , Total ,132, Table 18: (E.)Repair & Maintenance Cost for Building, Plant & Machinery Year Cost (Million Rupees) Amount (US $) , , , Table 19: (F) Additional Manpower required for Co-generation project No. Designation Number 1 Maintenance Engineer 1 2 Shift Supervisor 3

55 55 3 Turbine Supervisor 3 4 Boiler Supervisor 3 5 Skilled Workers 9 6 Semiskilled workers 15 Total 34 Nos. Annual Salary bill for the above personnel is Rs.1.75 million (US $ 208,333.33) Table 20 : Summary of Costs (From A to E) No. Particulars Amount (Mil. Rs.) Amount (US $) A Preliminary & Preoperative Expenses , B Cost Involved for procuring Land & Site Development , C Cost of Civil Works Required , D Cost of Proposed Plant & Machinery Required ,132, E Repair & Maintenance Cost for Building, Plant & Machinery , Contingencies , TOTAL ,460, The industry paid an advance of 10 % for initiating the project and 60 % of the payment was made after receipt of the machinery & accessories at the industry premises. After the successful erection and commissioning of the equipment the unit paid 20% of the total cost and the balance 10 % was made after the warranty period of equipment (Year-2005). The order was placed in July 2003 and erection and commissioning of the boiler and turbine was completed by the end of March Cost benefit of the scheme The cost benefit analysis of the scheme was worked out on actual basis taking all the cost. The complete analysis is depicted in Table 21 Table 21: Cost Analysis Before and After Implementation of Cogeneration Scheme ITEM DETAILS ANNUAL PAPER THOUSAND PRODUCTION TONS COST OF STEAM Quantity of (with existing set up) Steam T/hr Quantity of 77, , , , , Steam T/yr Quantity of Coal T/hr Quantity of Coal 14, , , , , T/yr Rate of Coal Rs/T 2, , , , , TOTAL ANNUAL COST OF STEAM (Mil. Rs.)

56 56 ITEM DETAILS TOTAL ANNUAL COST OF STEAM (US $) COST OF Units of 1, , , , , ELECTRICITY PRODUCED (with existing setup) electricity produced kw/hr from DG set 1 Quantity of FO(litre/hr) Quantity of FO( 3, , , , , KL/yr) Rate of FO 13, , , , , (Rs/KL) Annual Cost (Mil. Rs.) Units of electricity produced in kw/hr from DG set 2 Quantity of LDO(litre/hr) Quantity of 1, , , , , LDO(KL/yr) Rate of 19, , , , , LDO(Rs/KL) Annual Cost (Mil. Rs.) Annual Maintenance Cost of DG sets(mil. Rs.) Total Annual MW electricity produced TOTAL ANNUAL COST OF ELECTRICITY (Mil. Rs.) TOTAL ANNUAL COST OF ELECTRICITY TOTAL COST OF STEAM AND ELECTRICITY (US $) Mil. Rs./year Million US $ TOTAL COST OF STEAM AND ELECTRICITY IN CASE OF COGENERATION Quantity of Steam(T/hr) Quantity of Rice husk (T/hr) Quantity of Rice husk (T/yr) Rate of Rice Husk (Rs/T) Total Cost of Rice Husk (Mil. Rs.) , , , , , , , ,

57 57 ITEM DETAILS Total Annual MW electricity produced Additional annual Cost of manpower (Mil. Rs.) TOTAL ANNUAL COST OF STEAM AND ELECTRICITY (Mil. Rs.) (Million US $) PROFITS DUE TO (Mil. Rs.) SAVINGS IN FUEL COSTS Million US $ It can be clearly seen from table 21 that the total investment of 2.46 Million US $ would be recovered in just 18 months after the cogeneration plant comes into operation. However in reality, due to various other miscellaneous expenditures like price variations, disposal cost of ash generated etc. the total cost was recovered after 24 months. In addition to the tremendous cost benefits, the adoption of co-generation could substantially reduce the energy related GHG emissions by the industry as the furnace oil, LDO/HSD & coal used for steam & power generation could be avoided. The direct GHG reduction possible for the unit for the year will be 47,322 Tons (The GHG emission for Diesel: 2.68 Tons/KL, Furnace Oil: 3Tonnes/KL; Coal 1.53 T/T). This will increase further in the following years due to expected increase in production. An illustration is depicted in Table 22. Table 22 : Greenhouse Gases Emissions Reduction due to Cogeneration Fuel Quantity GHG emission in ton BEFORE COGENERATION Coal (T) 191, Furnace Oil (FO) (KL) 4, LDO (KL) 1, TOTAL GHG 47, AFTER COGENERATION Rice Husk 55,968.0 ZERO

58 Further Suggestions The technology described in the earlier sections would fit into the system and process only if certain specific criteria s are met and this varies from place to place. Therefore detailed project feasibility should be undertaken on the guidelines of the case study in section 5 and then one should go for implementation. While conducting a detailed feasibility study latest prices should be obtained from various suppliers. Generally it is a practice to involve the local technology supplier in undertaking such a detailed feasibility study. There could be places where the technology would have to be adapted to be used according to local conditions. Description of such adaptations is beyond the scope of the document. The technology as described in the earlier sections is for the industries with both steam and electrical power requirements. However the biomass like rice husk, wood chips etc can be also used for generating electrical power only. Especially, in areas where electric power is not available through the grid supply (e.g. in remote villages and inaccessible areas) biomass based technologies are put to use to generate power. Few of the technologies which have been successfully demonstrated for rural electrification/application are as follows: Power generation through direct burning of bio-mass in fluidized bed boiler. Power generation through bio-mass gasifier. 6.1 Power Generation using bio-mass in FBC Boiler This is exactly the same technology as described in earlier sections. The only difference is that in place of an extraction cum condensing turbine, the system has a condensing turbine only. All the other equipments remain the same. However the sizes of condensers and cooling towers may slightly increase. Sometimes, it so happens that the power generated from such power plants are also supplied to the grid (existing network of electrical power distribution cables). Grid connected bio-mass power projects, based on direct combustion, have started to pick up in most of the countries. Compared to the conventional power plants, the biomass operated power plants have higher heat rate or low efficiency because of high moisture content in fuel and low gross calorific value. This affects the operating parameters of boilers & turbine. Normally coal based power plants operate at a heat rate of kcal/kwh whereas rice husk fired power generation system the heat rate is in the vicinity of 4500 kcal/kwh. In India there are several power plants which are in operation using various kinds of biomass. Figure 22 5 depicts the number of biomass based power plants and the various fuels used. 5 Based on survey done by National Productivity Council for An evaluation study on impact of MNRE incentive for biomass power generation /cogeneration program.nov 2006, by A. K. Asthana and team.

59 59 Figure 22 : Various Biomasses based power plants and their numbers in India 6.2 Power Generation through Biomass Gasifier Biomass fuels available for gasification include charcoal, wood, wood waste agriculture residues such as coconut shells, rice husks, maize cobs, cereal straws etc. The biomass fuels differ greatly in their chemical, physical properties; they make different demands on the method of gasification and require different gasification technology. The range of different gasifier design includes updraft, downdraft, fluidized bed etc. (Figure 23). All systems show relative advantages and disadvantages with respect to type of fuel. The followings fuel properties have direct bearing on performance of gasifier. Energy content Moisture content Volatile matter Ash content & ash composition Reactivity Size Bulk density Charring properties Figure 23 : Biomass Gassifier in Operation

60 60 Before choosing a gasifier for any individual fuel, it is important to ensure that the fuel meets the requirements of the gasifier. Practical tests are needed if the fuel has not previously been successfully gasified. For smooth operation of internal combustion engine for power generation the gas as a fuel requires a fairly clean gas. The gas to be dust and tar free and during the process it is cooled down. The biomass gas used for power generation must be virtually tar and dust free in order to minimize engine wear, and should be as cool as possible in order to maximize the engine's gas intake and power out put. Biomass gasification for power generation is the befit technology to meet the power requirement for rural electrification. For small power generating units say (50 kw kw) the overall efficiency level varies from 12-18%, whereas for circulating fluidized bed gasifiers can be used for higher capacity say 4-4 MW - 10 MW with an efficiency of 23-28%. The capital investment for bio-mass gasifier power generation system varies from US$ /kwh.

61 61 Annex 1 Block Diagram of Kraft Paper WASTE PAPER PULPER PULPER KIT DECKER AGRO R.M DIGESTER BLOW TANK TDR/SDR CHEST POTCHER CHEST TDR M/C CHEST CENTRI CLEANER SCREEN HEAD BOX WIRE PRESS DRYER M.G DRYER PAPER ROLL

62 62 Annex 2: Block Diagram of White Duplux Board T/L PULPER PULPER PIT PULPER P/L PULPER PIT CHEST 01 H.D H.D 3F SCREEN F.N. SCREEN SLOTTED DECKER Jhonson.Screen Jhonson. SCREEN SLOTTED DECKER REFINING M/C CHEST HEAD BOX DDR M/C CHEST HEAD BOX B/L PULPER PULPER PIT CHEST SMALL PULPER H.D TURBO TURBO JOHNSON SCREEN PRIMARY CC PIT SLOTTED SCREEN SLOTTED SCREEN DECKER SECONDARY CC PIT TERTIARY CC PIT

63 63 CHEST SDR TDR CONICAL M/C CHEST M/C CHEST HEAD BOX HEAD BOX CALANDER MOULD PRE COATING PRESS SECTION CALANDER PRE DRYERS TOP COATING M.G POST DRYER DRYER SIZE PRESS BACK COATING DRYER CALENDAR PAPER ROLL DRYER

64 64 Annex 3: Technical Specification of Key Equipment/Components A. BOILERS (MCR) Steam flow at super heater outlet Steam pressure at super heater outlet Steam temp. at super heater outlet 30,000 kg/hr 65 kg/cm2 (g) 485+/-5 Deg.C. Super heater turndown % Feed water temp. Entering Deaerator 55 Deg.C. Feed water temp. Leaving Deaerator Peak load 105 Deg.C. 5% of MCR (for half an hour per shift) Boiler turndown 1:3 Deaeration steam requirement Approx Kg/hr at 4.0 kg/cm2g & 230 Deg.C. Pr. Control station inlet. B. BOILER ACCESSORIES GENERAL Type of combustion system Type of Boiler Type of feeding system Type of water circulation Type of support/installation No. of Boilers FBC Bi-drum Overbed firing Natural Bottom supported/indoor One FLUIDISED BED AND INBED TUBES Total number of beds Two Expanded bed height mm (approx) Distributor plate section - Top plate thickness 12 mm - Plate material specification IS 2062 Nozzles - Material of construction Alloy C1 Inbed tubes - Tube size mm x mm Dia 50.8 x 6.35 Thk. - Tube material specification BS 3059 Part 1 Gr. 320 seasmless - Inbed headers - Material specification SA 106 Gr. B - Header dia mm OD

65 65 Type of fluidized bed wall cons. Combustor Refractory Material Upto 1500 mm above ADP Above 1500 mm top of ADP Outer Layer Refractory Brick lined (by customer) IS 8 (50% Alumuina) IS 8 (40% Alumina insulation bricks (IS 2042 Gr.II) FUEL FEEDING SYSTEM FUEL FEEDERS (Rice Husk) * Type of feeders Screw Feeder * No. of feeders Four (Total) * From drive arrangement CGD/ECV FUEL FEEDERS (Bagasse) * Type of feeders Rotary feeder * No. of feeders Two (Total) * From drive arrangement Constant speed motor ECONOMISER Location Tube size mm Arrangement and type Tube material specification Headers size Headers material specification Casing material Tube protection Between Boiler Bank and Air preheater Dia 38.1 x 3.66 Thk Horizontal in line tubes, counter flow BS 3059 Part 1 Gr. 320 ERW Dia mm SA 106 Gr. B IS 2062./4 mm thick Dummy tubes at inlet anti-chanelling baffles AIR HEATER Arrangement and type Staggered tubes Tube size Dia 63.5 x 2.34 Thk Tube material Specification BS 6323 ERW Flow medium - Inside tube GAS - Outside tube AIR Casing material specification 4 mm Thi IS 2062 Erosion protection Extended tube length of 150 mm at the inlet Ducting Air ducting thickness Flue gas ducting thickness Plate material specification 3.15 mm Thk 4.00 mm Thk IS 2062 Gr. A

66 66 DRAUGHT EQUIPMENT SPECIFICATION Item reference FD FAN ID FAN Design Volume, m3/min Design head, mmwg Medium Air Flue gas Temperature Deg.C BOILER FEED PUMPS Design flow Pressure head Feed water temperature Quantity Connected load 38 m3/hr 840 mtc 105 Deg. C 2 nos (one working one standby) 160 KW (Approx.) DEAERATOR AND DEAERATOR WATER STORAGE TANK Design code As per IS 2825/ASME Sec. VIII Design Pressure & Temp 1.5 kscg. 150 Deg C. Source of deaerator steam Turbine bleed Design capacity 36 m 3/ hr Capacity of deaeraeted water tank 10 m3 Condensate temp. at deaerator inlet 55 Deg. C Steam required at deaerator inlet (Approx.) 3 4 kg/cm2g and 240 Deg. C. Material of construction of shell IS 2062 Nozzle/Stubs IS 1239 C Class Flanges IS 2062 Spray Nozzles SS 304 Trays SS 304 C. RECOMMENDED FEEDWATER AND BOILER WATER QUALITY Feed water Hardness, max ppm Nil PH at 25 Deg.C Oxygen, max ppm Total iron max. ppm 0.01 Total copper max. ppm 0.01 Silica, Max ppm 0.02 TDS max ppm 0.1 Conductivity at 25 Deg.C measured max. us/cm after cation exch. In H+ from and after CO2 removal 0.2 Hydrazine residual ppm

67 67 D. ULTIMATE ANALYSIS OF RECOMMENDED FUELS (% BY WT) Composition Rice Husk Bagasse Carbon Hydrogen Nitrogen Sulphur Moisture Ash Oxygen GCV Kcal/Kg E. TURBINE PARAMETERS Type : Multistage, extraction cum condensing Horizontal, Impulse type. Inlet steam conditions : 63 kg/cm2g, Deg. C. Extraction pressure Inlet steam flow Extraction flow Exhaust flow to condenser Power developed Gearbox out speed Alternator Voltage : 4 kg/cm2g : 26 tph : 23 tph : 6 tph : 4000 KW : 1500 rpm : 4000 rpm : 11 KV Cooling water inlet : 32 Deg. C. Cooling water outlet temp. : 40 Deg. C F. ALTERNATOR PARAMETERS Rating Type Generation Voltage Frequency Speed Cooling : 4000 kw, 5000 kva : Brushless Excitation Volts : 50 Hz : 1500 rpm : CACW G. CONDENSER PARAMETERS Tube material : Admiralty Brass Cleanliness factor : 0.85 Cooling water inlet temp. Cooling water outlet temp. Cooling Water Flow : 32 Deg. C : 40 Deg. C : 556 Cu.m/hr The steam turbine with speed reduction gearing shall comprise of the following equipment.

68 68 1. One Number Horizontal spindle, two bearing, multistage, impulse type, extraction cum condensing steam turbine, capable of generating electrical power at generator terminals. 2. One Number Set of hardened and ground speed reducing gears, capable of transmitting continuously the power generated by above turbine. The gear output speed will be 1500 RPM. 3. One Number High speed coupling (non-lubricated, flexible type) between the turbine and gearbox and low speed coupling (non-lubricated, flexible type) between gearbox and alternator. The A.C. Generator and its control switchgear will be consisting of the following: 1. One Number KVA, 4000 kw, Volts, 50 Hz, 0.8 p.f.1500 RPM, revolving field, double pedestal horizontal alternator. 2. The alternator will be complete with excitation, automatic voltage regulator and is of brush less excitation type. H. HT PANEL 1. One Number H.T. Panel, sheet metal clad, cubicle type for controlling the generator output. The panel shall be totally enclosed, self-supporting, floor mounting type for indoor installation. It shall be complete with following equipment: 2. Vacuum circuit breaker of suitable rating.