Biogas Refining for Production of Bio-Methane and its Bottling for Automotive Applications and Holistic Development Virendra K. Vijay 1 1. Centre for Rural Development and Technology, Indian Institute of Technology Delhi, Hauz Khas, New Delhi- 110 016, India Abstract: A study was carried out for development of biogas upgradation and bottling system for production of bio-methane to substitute fossil fuels used in automobile and transport applications in Indian scenario. Upgraded biogas had been used in automobile vehicle after its purification (removing CO 2, H 2 S and vapour present in it). A biogas upgradation system had been designed and developed at Indian Institute of Technology Delhi based on physical absorption of CO 2 in water at elevated pressure. Developed packed bed scrubbing column is able to remove more than 95 percent CO 2 from raw biogas ( around 60 % methane and 40 % carbon dioxideavalable in raw biogas ) when pressurized raw biogas was fed into it and pressurized water is sprayed from top in counter-current action. Biogas purification depends on gas and water flow rates and pressure in the scrubbing coloumn. These parameters have been optimised for getting CO 2 free biogas. The upgraded biogas was compressed up to 20 MPa pressure using a three stage compressor after moisture removal and filled in special high pressure steel cylinders (as used in CNG filling). The upgraded biogas was filled in CNG cylinders and tested in a vehicle. The paper deals with design and development of biogas purification and bottling system and its techno- economic feasibility. Keywords: Biogas upgradation, scrubbing coloumn, bottling, Engines 1. INTRODUCTION More than 65 percent population in India lives in rural areas. It has more than 300 million cattle population ( about 20% of the world's total). An estimate indicates that India has a potential of generating 6.38 x 10 10 m 3 of biogas from 980 million tones of cattle dung produced annually. The heat value of this gas amounts to 1.3 x 10 12 MJ. In addition, 350 million tons of compost would also be produced [1]. Generally this dung is directly burned as fuel for cooking without harnessing its full potential as biogas and rich manure following after methanation. If other available organic wastes such as sewage, municipal solid waste, industrial effluent, distilleries etc. are also be taken as feedstock for gas production, the total biogas potential would increase further. Different categories of urban municipal and industrial organic wastes and their estimated quantity available in India are shown in Table 1 [2]. This clearly shows wide scope of biogas as an alternative source of energy in India. More than 3.9 million biogas plants have been built in India so far which are being used to meet house hold requirements. In view of present scarcity and increasing import bill on petroleum demand, and environmental pollution, India has also started bio-fuels program in the country for its energy security and sustainable development in long pace of time. Like biodiesel and ethanol, upgraded biogas can be a promising fuel for internal combustion engines. Table 1. Organic wastes and their estimated availability in India Type of waste available Estimated quantity Municipal solid waste 30 million tons/year Municipal liquid waste 12000 million litres/day* Distillery (243 units) 8057 kilolitres/day Press mud 9 million tons/year Food and fruit processing 4.5 million tons/year wastes Willow dust 30000 tons/year Dairy industry waste 50-60 million litres/day Paper and pulp industry 1600 m 3 /day waste (300 mills) Tannery (2000 units) 52500 m 3 waste water /day *212 class I and II cities Source: Ministry of Non-conventional Energy Sources Report, Renewable energy in India and business opportunities, MNES, Govt. of India, New Delhi, 2001. Biogas comprises of 60-65% methane, 35-40 % carbon dioxide, 0.5-1.0 % hydrogen sulfide and traces of water vapour. It is almost 20% lighter than 623
air and has ignition temperature of 650-750 ºC. Its calorific value is 20 M J (4713 kcal) per cubic meter. Biogas, like Liquefied Petroleum Gas (LPG) cannot be converted to liquid state under normal pressure and temperature. Critical temperature for liquefaction of methane is - 82.1 o C at 4.71 MPa pressure. In such situations, removing carbon dioxide and compressing it into cylinders makes it easily usable for transport applications, three wheelers, cars, pick up vans etc and also for stationary engines for various applications at remote locations. Since CNG technology has already been into use and therefore, bio-methane (upgraded biogas) which is nearly same as CNG, can be used for all applications for which CNG is being used. The upgraded biogas (without CO 2 ) has its calorific value as 34 MJ/m 3 against 20 MJ/m 3 of raw biogas. Upgraded biogas can be successfully used as substitute of CNG in internal combustion engines. 2. POTENTIAL OF UPGRADATION AND BOTTLING OF BIOGAS IN RURAL AREAS India s biogas programme is one of the largest in the world, next only to China. So far, biogas has mostly been used as fuel for cooking and running stationary engines. In the absence of proper storage facility, lack of mobility and flexibility of operation, the biogas potential has not yet been fully utilized. There is great potential scope for utilization of biogas where large capacity biogas plants can be installed or are already in operation e.g. dairy farms, institutional biogas plants in Goshalas (common cattle sheds), or community biogas plants in a village or a cluster of villages, sewage treatment plants, food processing industries, distilleries etc. These plants can produce required quantity of biogas to be upgraded and compressed in economic manner. Biogas after enrichment and compression can be stored in steel cylinders at high pressure, thus have mobility and flexibility of biogas use for multi-dimensional operations i.e. operating water pumps for irrigation, producing motive power for rural industries or using as vehicle fuel for transportation. This will provide cash inflow and direct monetary benefits to biogas plant owners. Goshalas ( Common cattle shed) are generally having 300-500 old & sick cows run on charity basis and most of them are not in good financial position. Installation of large capacity biogas plant, enrichment and compression system will enable them to utilize their own resources i.e. cattle dung to produce biogas; enrich, compress and stored in cylinders and earn money by selling these cylinders to probable users. Digested slurry of biogas plant is enriched compost and its sale also adds income to Goshala. Dairy farms can also boost their profit in similar manner by installing biogas production, enrichment and compression system. The enrichment and compression system based on community biogas plant in a village or a cluster of villages will encourage rural entrepreneurship, which will help in sustainable rural development. 3. METHODS OF METHANE UPGRADATION IN BIOGAS There are different techniques through which carbon dioxide from biogas can be removed to enhance methane content in it. Some of widely used techniques viz. water scrubbing, membrane separation, gas liquid absorption membrane, cryogenic separation can be used under varying conditions. The water scrubbing of CO 2 by absorption process is purely physical. Usually the biogas is pressurized and fed to the bottom of a packed column where water is fed on the top and so the absorption process operates counter-currently. The water which exits the column with absorbed carbon dioxide can be regenerated and re-circulated back to the absorption column. Stripping with air is not recommended when high levels of hydrogen sulphide are handled since the water will soon be contaminated with elementary sulphur which causes operational problems [3, 4]. Pressure Swing Adsorption, or PSA, is a method for the separation of carbon dioxide from methane by adsorption/ desorption of carbon dioxide on zeolite or activated carbon at different pressure levels. The upgrading system consists of four adsorber vessels filled with adsorption material. The gas leaving the top of the adsorber vessel contains >97% methane. [5, 6, 7]. Gas-liquid absorption using membranes is a separation technique which was developed for biogas upgrading only recently. The essential element is a micro porous hydrophobic membrane separating the gaseous from the liquid phase. The molecules from the gas stream, flowing in one direction, which are able to diffuse through the membrane will be absorbed on the other side by the liquid flowing in counter current. The absorption membranes work at approx. atmospheric pressure (1 bar) which allows low-cost construction. The removal of gaseous components is very efficient. At a temperature of 25 to 35 C the H 2 S concentration in the raw gas of 2 % is reduced to less than 250 ppm. [8]. The cryogenic method of enrichment involves the separation of the gas 624
mixtures by fractional condensations and distillations at low temperatures. Condensation is the change of phase of gas to liquid. Gas removal by condensation can be accomplished by cooling or by compression or by a combination of both. Usually, only water vapour is removed by condensation. High cost involved makes it impractical for biogas applications. The process has the advantage that it allows recovery of pure component in the form of liquid, which can be transported conveniently. Capital cost and utility requirements are high [9]. A variety of processes are available for enrichment i.e. removing CO 2, H 2 S and water vapour. Most of these processes have been developed for use in the natural gas, petroleum and petrochemical industries. As a consequence, some of them may not be suited for biogas applications unless high flow rates are involved. One of the simple and cheap method involves is the use of pressurized water as an absorbent liquid for removal of CO 2. Due to simplicity, it suits rural applications. In this method, the biogas is pressurized and fed to the bottom of a scrubber column where water is sprayed from the top. In counter-currently operated absorption process, the carbon dioxide present in the biogas is absorbed in down going water and methane goes up and collected in a vessel. 4. WATER ABSORPTION SYSTEM DEVELOPED FOR BIOGAS UPGRADATION4 Biogas upgradation and bottling technology has been designed and developed at Indian Institute of Technology Delhi based on physical absorption. A packed bed upgradation column was designed and developed for biogas purification with 3500 mm packed bed height was designed for absorption of CO 2 at operating pressure of 1.0 MPa of biogas inlet. Ceramic Resching rings were used as packing material. The details of experimental setup of biogas Upgradation and compression is shown in Figure 1. The details of various components involved in the system are described below: Figure 1. Experimental Setup of Biogas Upgradation and Compression Unit Figure 1. Experimental Setup of Biogas Upgradation and Compression Unit 625
4.1 Biogas Enrichment Unit The unit comprise of a scrubber, a water supply system, a gas supply system, a low capacity compressor, a pressure vessel, pipe fittings and various accessories. 4.1.1 Biogas upgradation column The diameter of the scrubber and packed bed height were taken as 150 mm and 3500 mm respectively to process 200 m 3 biogas per day. The scrubber consists of a packed bed absorption column and a supporting frame as described in following sub-sections: (I) Top section It has provision for water inlet pipe, water spraying system, gas outlet pipe and a safety valve. Water spraying system was connected with water inlet pipe to provide fine atomized spray of pressurized water inside the absorption column. A safety valve is provided at the upper portion to release the excess pressure as it is a pressurized column. (II) Middle section In this section Resching rings have been filled as packing material. Two sieves are fitted at the top and bottom of the section to hold the packing height of column. A view glass, to see the water level inside the column and a dry type pressure gauge, to check column pressure; are also mounted at the upper portion of the middle section. (III) Bottom section This section has provision for inlet gas feeding pipe and a view glass at upper side. Lower side has been transformed into truncated cone shape with 50 mm diameter outlet opening. It is fitted with a ball valve to control the outlet water flow. Outlet water is stored in a water collection tank. All the three sections are joined together with flanges, bolts and nuts. 4.1.2 Supporting frame Supporting frame comprises of three legs, which is fabricated from MS angle size 55 x 55 x 5 mm. The legs are grouted firmly in ground with cement, sand and stone gravel mixture and fitted with the absorption column in the middle. A staircase, made of MS angle and flats, has also been attached with the absorption column to climb up to the top of the column to check water level and column pressure. 4.1.3 Water supply system Screw pump is used to pump water from water storage tank into the scrubber. Screw pump is selected to provide pressurize water at low discharge. 25 mm diameter Galvanized Iron (GI) pipe fitting have been used for water supply. The water flow rate is controlled through a flow regulating valve. A rotameter and a dry type pressure gauge are mounted to measure the water flow rate and pressure of water respectively. 4.1.4 Gas supply system. The gas supply system consists of a biogas plant, a single stage compressor, a pressure vessel, pipe fittings and accessories. 4.1.5 Biogas plant Raw biogas is fed to the scrubber from a cattle dung based floating drum type biogas plant. The raw gas is supplied from the biogas plant, through 25 mm diameter rigid PVC pipeline to a single stage compressor, after removing water condensed in pipeline using a water remover. 4.1.6 Single stage compressor A single stage compressor having 1.1 kw power rating and 10.0 m 3 /h suction capacity is utilized for initial compression of raw biogas up to 1.0 MPa pressure before sending it to the scrubber. 4.1.7 Pressure vessel To ensure steady supply of compressed raw biogas to the scrubber, it is first stored in a pressure vessel. It is made from MS sheet and has storage capacity of 1.0 m 3. 4.1.8 Pipe fittings and accessories 12.5 mm diameter G I pipe line is used to supply gas from compressor to the pressure vessel and then to the scrubber. Between the pressure vessel and the scrubber, a rotameter and a dry type pressure gauge are installed to measure the rate of discharge and pressure of the raw biogas respectively. The gas flow rate is controlled through a valve provided near inlet point of the scrubber. 4.2 Upgraded Biogas Compression Unit It comprises of a three stage compressor for compression of upgraded biogas up to 20 MPa pressure, a set of filters for removal of water vapour, storage cylinders for storing highly pressurized biogas and pipe fittings. 4.2.1 Three stage high pressure compressor A low suction capacity and high pressure developing compressor is utilized in the present investigation. A three stage compressor is used for bottling. It can compress gas up to 34.5 MPa pressure. 4.2.2 Ultra filters A set of three filters (Pre filter, Micro filter and Sub Micro filter) are employed in the G I pipeline connected with storage pressure vessel (containing upgraded biogas) and three stage compressor. They are designed to remove almost all water vapour from the upgraded biogas. 4.2.3 Storage cylinders 626
High pressure steel cylinders (available in the market for CNG storage) are used for final storage of upgraded and compressed biogas. These cylinders are shorter in length and larger in diameter than most gas cylinders and had been specifically built for high pressure gas storage. 4.2.4 Pipe fittings and accessories 12.5 mm diameter G I pipeline is employed to deliver upgraded biogas from the scrubber to the storage vessel (0.5 m 3 capacity). From vessel, it is sent to the three stage compressor via ultra filters and rotameter through 12.5 mm diameter G I pipe line. From compressor, compressed & upgraded biogas is finally filled in a cylinder. A pressure gauge is mounted in the pipeline near cylinder to check the gas pressure inside the cylinder and provision is made to release the back pressure from the pipeline after cylinder filling. 5. RESULTS AND DISCUSSION 5.1 Performance of Water Upgradation System on Removal of CO 2 from Biogas Percentage absorption of carbon dioxide in water was determined in terms of variation in inlet gas flow rates and inlet gas pressures. The scrubber was designed for 95 % CO 2 absorption from raw biogas in pressurized water for 2.5 m 3 /h inlet gas flow rate at 1.0 MPa gas pressure. Accordingly, the variation in inlet gas flow rates from 1.0-3.0 m 3 /h were studied at 1.0 MPa gas pressure. The values of CO 2 absorption observed were 87.66, 99.00, 83.96, 73.82 and 53.77 % at 1.0, 1.5, 2.0, 2.5 and 3.0 m 3 /h gas flow rates respectively. It was found that the percentage CO 2 absorption from raw biogas has initially increased when gas flow rate vary from 1.0 to 1.5 m 3 /h and afterwards it decreased continuously. The highest CO 2 absorption (99 %) was observed at 1.5 m 3 /h gas flow rate at 1.0 MPa inlet gas pressure. The best performance of the scrubber was found at 1.5 m 3 /h gas flow for maximum CO 2 absorption at 1.8 m 3 /h wash water flow rate. The scrubber works perfectly well around 1.8 m 3 /h wash water flow rate, above this flow rate, flooding starts. The effect of gas pressure on percentage CO 2 absorption was also determined for all gas flow rates for pressure variation from 0.6 to 1.0 MPa. The percentage CO 2 absorption ranged between 38.34 to 66.03 % at 0.6 MPa pressure and 53.77 to 99.00 % at 1.0 MPa pressure. Again the highest percentage CO 2 absorption is observed for 1.5 m 3 /h gas flow rate for all pressure variation i.e. from 0.6 to 1.0 MPa. It has also been found that, the percentage absorption of carbon dioxide is increased with increase in gas pressure for all gas flow rates. The highest absorption (99 %) was observed at 1.0 MPa gas pressure. This is in agreement with Wellinger & Lindberg [7], who reported that 1.0 MPa pressure for inlet gas can give more than 90 % CH 4 enrichment in biogas. 5.2 Stationary Engine/Automobile Vehicle Testing on Upgraded and Bottled Biogas The upgraded biogas is compressed into CNG cylinders using a three stage compressor up to a recommended pressure of 200 bar. This enriched biogas filled cylinder can be used as substitute of CNG. The upgraded biogas was tested in stationary diesel engine converted into spark ignition (SI) mode. The maximum brake power developed by the engine was 2.03 kw on raw biogas, while 3.25 kw on upgraded biogas, showing a 1.6 times increase in power over raw biogas. Lower specific gas consumption and an improvement in brake thermal efficiency were noted when upgraded biogas was used instead of raw biogas in engine operation. Thus, upgraded biogas gave better performance than raw biogas in SI engine. Experiments were conducted on the use of upgraded biogas in an automotive car having three cylinders, four strokes, 800 cc, 39.5 bhp at 5500 rpm). Upgraded biogas contained 85 % methane. The results of automotive car testing on compressed & upgraded biogas were encouraging. After minor adjustments in air fuel ratio settings, the vehicle started smoothly and showed similar performance as CNG. Plate 1. Automotive Car tested on upgraded biogas compressed in CNG cylinder 627
6. CONCLUSIONS (I) There is large potential of biogas generation in India to make it an alternate fuel for vehicle. Biogas produced in large size biogas plants should be upgraded before bottling for storage and mobile purpose, as upgraded biogas has more calorific value and better fuel quality. Out of several methods of biogas enrichment, water scrubbing is found to be a simple, low-cost and suitable method for enrichment of biogas in rural areas. (II) The developed biogas scrubber is able to remove 99 % v/v of carbon dioxide present in raw biogas. (III) To make biogas suitable for automobile application, the upgraded biogas was compressed up to 20.0 MPa after moisture removal and filled in special high pressure seamless steel cylinders (as used in CNG filling). Stationary engine and automotive vehicle performance on upgraded biogas showed its performance comparable to CNG fuel and had lesser amount of pollutants coming out from the exhaust. Overall, the study concludes that biogas upgradation and compression system is a profitable venture for rural areas as an industry. It is recommended that rural entrepreneurship should be developed based on this system for the effective utilization of biomass for production of biogas energy in decentralized manner and holistic rural development. 7. Wellinger A and Lindeberg A. Biogas upgrading and utilization. 1999. Available online http://www.novaenergie.ch./iea-bioenergy-task37/ documente/biogas.pdf. 8. Glaub J C and Digz L F. Biogas purification processes. Biogas and alcohol fuels production. Vol. II. Biocycle J. of waste recycling.emmous the J P Press Inc., 1981. 9. Donald L and Wise C. Analysis of systems for purification of fuel gas. Fuel gas production from biomass. Vol 2. CRC press INC. Boca Raton, Florida, 1981. 7. REFERENCES 1.Mittal K.M. Biogas systems: Principles and Applications. New Age International (P) Limited, New Delhi, 1996. 2. Kishore V. V. N. and Srinivas S. N. (2003) Biofuels of India. Journal of Scientific & Industrial Research, Vol. 62, 106-123, Jan.-Feb. 3. Bhattacharya T. K., Mishra T. N. and Singh B. Techniques for removal of carbon dioxide and hydrogen sulfide from biogas. XXIV annual convention of ISAE, Akola, 1988. 4. Kapdi S S, Vijay V K, Rajesh S K and Prasad R. Biogas scrubbing, compression and storage: perspective and prospectus in Indian context. Renewable Energy, 30, 1195-2002, 2005. 5. Hagen M and Polman E. Adding gas from biomass to the gas grid. Final report submitted to Danish Gas Agency, 2001. 6. Shannon R. Biogas conference proceedings. 2000. Available online http://www.rosneath.com.all/ipc6/ch08/shannon2/ 628