State of the Art for Waste Incineration Plants

Transcription

1 State of the Art for Waste Incineration Plants

2

3 State of the Art for Waste Incineration Plants Vienna, November 2002

4 Authors: Josef Stubenvoll (TBU) Siegmund Böhmer (UBA) Ilona Szednyj (UBA) Coordination of the joint study: Gabriele Zehetner Note: The studie is also retrievable from the internet ( Impressum: Published by: Federal Ministry of Agriculture and Forestry, Environment and Water Management, Devision VI/3, Stubenbastei 5, 1010 Wien Printed by: Druckerei Berger, 3850 Horn, Austria Printed on Recyclingpaper Copyright: Federal Ministry of Agriculture and Forestry, Environment and Water Management All rights reserved ISBN X Cover photo: Bernhard Gröger (UBA), AVN, WAV, AVE RV Lenzing Reproduction is permissible if the source is quoted In case of having no use for this publication please return it for reuse resp. recovery to the Federal Ministry of Agriculture and Forestry, Environment and Water Management

5 1 State of the Art / Waste Incineration Content CONTENT CONTENT...2 SUMMARY INTRODUCTION Aims and Objectives The connection to the IPPC-Directive FIRING TECHNOLOGIES Delivery and pretreatment of waste Firing system and waste heat boiler Grate firing systems Rotary kiln Fluidised bed combustion Degassing and/or gasification of wastes TECHNOLOGIES FOR FLUE GAS CLEANING Separation of dust and non-volatile heavy metals Electrostatic precipitator Fabric filters Fine wet scrubbing HCl, HF, SO 2 and Hg removal Dry and semi-dry processes Wet flue gas cleaning NO x removal Primary Measures Secondary measures Reduction of organic emissions and PCDD/F Primary measures Secondary measures Simultaneous removal of acid gases, NO x and dioxins Moving bed adsorber with activated carbon Fluidised bed systems Avaibility and use in Austria WASTE WATER TREATMENT Gravity separation Neutralisation...43

6 State of the Art / Waste Incineration Content Increase of ph Reduction of ph Precipitation Flocculation Flotation Filtration Ion exchanger Activated coke filter DISPOSAL AND TECHNOLOGIES FOR WASTE TREATMENT Landfilling in big bags Solidification Separation of metals Washing processes Thermal treatment UTILISATION OF ENERGY Corrosion CROSS-MEDIA ASPECTS DESCRIPTIONS OF PLANTS Domestic waste incineration Waste incineration plant Flötzersteig Waste incineration plant Spittelau Waste incineration plant Wels Incineration of hazardous wastes Rotary kilns of the Plant Simmeringer Haide Waste incineration plant Arnoldstein Incineration of clinical waste Clinical waste incineration plant Baden Incineration of sewage sludge Fluidised bed reactors of the Plant Simmeringer Haide Incineration of treated waste fractions Combined waste incineration AVE - Reststoffverwertung (AVE-RVL) Lenzing Pyrolisis of wastes Gasification...109

7 1 State of the Art / Waste Incineration Content 8.9 Planned plants and plants under construction Waste incineration plant Zistersdorf Plant Simmeringer Haide: Fluidised bed reactor Waste incineration plant Dürnrohr Waste incineration plant Arnoldstein Thermal residue utilisation plant Niklasdorf ESTIMATION OF COSTS Discharge and storage Firing system and boiler Water-steam cycle Flue gas treatment Dry flue gas cleaning Absorption and adsorption plants for separation of HCl, HF and SO NO x reduction Posttreatment plants Cost estimations for whole plants Costs of fluidised bed combustion STATE OF THE ART Location of the waste incineration plant Emissions into the air Monitoring Emissions of air pollutants Emissions into the water Monitoring Emissions of water pollutants Accumulation of waste Utilisation of energy General State of the art NATIONAL AND EUROPEAN LEGISLATION Emissions to air National regulations Emissions to air from Austrian waste incineration plants Emissions to water National regulations European Community Solid waste from waste incineration Legal regulations for solid waste from waste incineration...178

8 State of the Art / Waste Incineration Content Waste and solid residues from Austrian waste incineration plants Monitoring Monitoring of operating parameters Monitoring of emissions to air national regulation Monitoring of emissions to air waste incineration plants Monitoring of emissions to water waste incineration plants Monitoring of waste from waste incineration and solid residues GLOSSARY AND ABBREVIATIONS REFERENCES Internet adresses...189

9 6 State of the Art / Waste Incineration Summary SUMMARY The aim of this study is to describe the state of the art for waste incineration plants with respect to the IPPC-Directive. The study deals with the complete process of waste incineration starting from the delivery of waste and ending with the treatment of solid residues from the incineration process. The following technologies are depicted in detail: - waste storage and pre-treatment, - introduction of waste into the combustion chamber, - applied firing technologies, - systems for energy utilisation, - applied technologies for flue gas cleaning, - treatment of waste water, - treatment and disposal of waste from combustion. Cost estimations splitted into investment costs, operating costs (including enumeration of relevant items) and maintenance costs are presented both for single technologies mentioned above and for whole waste incineration plants. This study should form the basis of the Austrian contribution to the exchange of information between Member States and the industries concerned on best available techniques (BAT) for waste incineration plants. This exchange of information is made in accordance with Article 16 paragraph 2 of European Council Directive 96/61/EC from 24 th September 1996 on Integrated Pollution Prevention and Control (IPPC-Directive). Presently about 190 plants for thermal treatment of waste with an overall capacity of about 2.7 Mio. t yr -1 are operated in Austria. In 135 of them only waste which is produced within the company is combusted. The operators of the other plants also accept waste fractions from other parties, however, some have contracts with certain partner companies. At present hazardous waste is incinerated in 14 plants with an overall capacity of about 233,000 tons per year, whereas the major part can be allocated to the Plant Simmeringer Haide of Fernwärme Wien GmbH. In addition to existing plants there is a number of plants under construction or planned. The sum of planned combustion capacity is estimated to be in the range of 1.4 to 1.7 Mio. t yr-1. In the study the following waste incineration plants are described in detail:! MVA Flötzersteig, MVA Spittelau Domestic waste incineration plants with grate firing! MVA Wels Grate firing for combustion of domestic and industrial waste! Rotary kilns of the Plant Simmeringer Haide Incineration of hazardous wastes! Fluidised bed reactors in Arnoldstein (ABRG Arnoldstein) Incineration of hazardous wastes! Pyrolysis plants in Baden Incineration of hospital wastes! Fluidised bed reactors of the Plant Simmeringer Haide Incineration of sewage sludge

10 State of the Art / Waste Incineration Summary 7! Fluidised bed reactor in Lenzing (AVE-RVL Lenzing) Combined waste incineration (e.g. treated household waste, sewage sludge)! Planned and already permitted waste incineration plants Dürnrohr, Arnoldstein, Zistersdorf, Niklasdorf, fourth fluidised bed reactor of the Plant Simmeringer Haide. Waste acceptance, treatment and introduction into the combustion chamber At grate firing plants for the combustion of household waste delivered waste is dumped into so-called acceptance bunkers and fed into the combustion chamber after mixing using bridge cranes without any further pretreatment. As to the processing of bulky refuse at most plants shears are provided in the vicinity of the bunker. Fresh air needed for combustion is sucked off from the waste bunker. Thus a slight vacuum is produced so that odour and dust emissions through the dumping devices to the ambient air are minimized. The maximum storage time is limited to a few days. Hazardous wastes are combusted in rotary kilns (and to a lower extent in fluidised bed reactors). After delivery hazardous wastes are visually examined whereby the accordance with accompanying documents is verified. Afterwards chemical and physical parameters are determined according to ÖNORM S2110 (1991). On the basis of analysis results single waste fractions are evaluated, stored in intermediate bunkers, mixed according to existing recipes and supplied to the combustion process. Also in this case combustion air is sucked off from the bunkers. In fluidised bed reactors usually a mixture of several waste fractions are combusted together. The waste fractions are visually examined before acceptance, randomly controlled, pulverized and mixed before combustion. Storage takes place in tanks or daily bunkers depending on the state of aggregation. Exhaust air from waste treatment and storage is either dedusted with fabric filters or introduced into the firing as combustion air. The fluidised bed boilers for exclusive combustion of sewage sludge are located directly to the main waste water treatment plant (WWTP) of Vienna. Thin sludge is supplied via pipelines and dewatered by means of centrifuges. Waste water from dewatering is pumped back to the WWTP and the remaining thick sludge is combusted. Pyrolysis for thermal treatment of hospital waste is performed discontinuously. Wastes are heated by means of gas burners until the distillation temperature is reached. At all described plants fuel oil, natural gas or coal can be introduced for starting up or shutting down as well as for satisfying the required minimum temperature for hazardous and non hazardous wastes using auxiliary burners. Use of energy With the exception of the small hospital waste incineration plants energy of flue gases is used at all waste incineration plants described in this study. The present spectrum of energy use can be described as follows: Pure electricity production (e.g. Wels), pure heat production (e.g. MVA Flötzersteig), Co-generation (CHP: Combined heat and power) (e.g. Plant Simmeringer Haide) and CHP with increased steam parameters (500 C, 80 bar: e.g. AVE- RVL Lenzing). If the energy of the flue gas is fully converted into heat a theoretical overall efficiency up to 80 % can be achieved. As to pure electricity production the overall efficiency (= net electrical efficiency) applying normal steam parameters will only be about 20 %. In case of increased

11 8 State of the Art / Waste Incineration Summary steam parameters and pure power generation an overall efficiency (= net electrical efficiency) up to 30 % can be achieved. At the waste incineration plant Dürnrohr that is presently under construction steam shall be fed into the steam cylce of the neighbouring coal power plant immediately before the intermediate superheater. With this concept the electric net efficiency shall be increased to 35 %. Technologies for flue gas cleaning At Austrian waste incineration plants dry and wet processes are combined for separation of the air pollutants dust, non-volatile and volatile (e.g. Hg) heavy metals, SO x, NO x, HCl, HF and organic compounds (dioxins and furans) (see Table 1). These processes can be implemented independent from the used firing system. Table 1: Combination of flue gas cleaning processes in existing waste incineration plants in Austria - electrostatic precipitator, - two-stage wet scrubber with precipitation, - wet removal of fine dust and - catalytic plant (low-dust circuit) - fabric filter with dosage of lime and activated coke, - two-stage wet scrubbing with gypsum scrubber and - downstream catalytic plant (low-dust circuit) - electrostatic precipitator, - two-stage wet scrubbing with precipitation, - activated coke adsorber (cross current) - downstream catalytic plant (low-dust circuit) - electrostatic precipitator, - two-stage wet scrubber, - wet removal of fine dust and - catalytic plant (low-dust circuit) - electrostatic precipitator, - two-stage wet scrubbing with NaOH scrubber, - fabric filter with dosage of lime and activated coke and - downstream catalytic plant (low-dust circuit) - electrostatic precipitator, - two-stage wet scrubber with precipitation, - wet removal of fine dust and - activated coke adsorber (counter current) Emission levels that can be achieved using these combinations of processes are presented in the following table (as half hourly mean values): Table 2: Emissions to air from Austrian waste incineration plants (as half hourly mean values in mg Nm -3 ; dioxin emissions are given in ng Nm -3 ; standardised at 11% O 2, dry gas, 273 K and kpa) Pollutant Type of measurement Range of emissions [mg Nm -3 ] Dust continuously < SO 2 continuously HCl continuously < HF continuously or discontinuously < CO continuously NO x continuously < 150

12 State of the Art / Waste Incineration Summary 9 Pollutant Type of measurement Range of emissions [mg Nm -3 ] Pb discontinuously < Cr discontinuously < Zn discontinuously Σ Pb + Cr + Zn 1 discontinuously < < As discontinuously < < Co discontinuously < Ni discontinuously < Σ As + Co + Ni 1 discontinuously < Cd discontinuously Hg continuously or discontinuously Σ As, Pb, Sb, Cr, Cu, Co, Mn, Ni, discontinuously V, Sn 1 Σ HC NH 3 continuously or discontinuously continuously or discontinuously PCDD/F (ng Nm -3 ) discontinuously Heavy metals have to be measured as single substance or as a sum depending on the permit. Waste water treatment Waste water from the first (acid) scrubber, the SO 2 scrubber and from the ash and slag treatment are cleaned in the waste water treatment plant. As the case may be this cleaning can be performed together for all partial flows. In Austria a multistage cleaning of waste water has become generally accepted. The first cleaning step, the heavy metal precipitation, usually comprises the processes precipitation, flocculation, sedimentation, neutralisation and sludge dewatering. The second cleaning step usually consists of a gravel filter, an activated coke filter and an ion exchanger. Applying the multistage cleaning of waste water emission limit values prescribed in the ordinance pertaining to the limitation of waste water emissions from the cleaning of combustion gas (Federal Legal Gazette 886/1995) can usually be easily attained (Table 3). Chemicals necessary for waste water treatment are stored and treated in chemical stations. Sludges accumulated during the particular processes are usually collected in sludge tanks and mostly dewatered to a water content of about 50 % by means of chamber filter presses. The occurring filter cake has to be disposed of as hazardous waste.

13 10 State of the Art / Waste Incineration Summary Table 3: Volumes and parameters of treated waste water from Austrian waste incineration plants after waste water treatment in the year 2000 [REIL, 2001; KROBATH, 2001; WACHTER, 2001; WERNER 2002] Cleaned waste water Temperature Electric conductivity Parameter Emission [mg l -1 ] ,657 [l t -1 waste] < [ C] [ms] Fish toxicity 2 ph [-] Undissolved compounds 10 < 30 Settleable solids < 0.3 < 10 Filterable substances 7 20 Residue on evaporation 1.4 g l -1 Salt content 35 [g l -1 ] Al 0.12 As < < 0.05 Ba 0.19 Ca < 5 [g l -1 ] Cd < < 0.05 Co < 0,05 Chlorides 7 < 20 [g l -1 ] Cyanides < < 0.1 Cr < 0.05 < 0.1 Cr (VI) < 0,05 Cu < 0.05 < 0.3 Fluorides < < 10 Hg < < 0.01 Mn < 0,05 NH 4 N Nitrate (NO 3 ) Nitrite (NO 2 ) 0.07 < 8 Ni < 0.05 < 0.5 P < 0.05 Pb < 0.01 < 0.1 Sn 0.06 Sulphate (SO 4 ) 325 8,000 Sulphides < 0.01 < 0.1 Sulphites < 1.0 < 8 Zn < 0.05 < 0.5 AOX / EOX 1.02 / 0.01 < 0.1 BTXE < COD < 75 Total Hydrocarbon 0.05 < 3

14 State of the Art / Waste Incineration Summary 11 Parameter Emission [mg l -1 ] Phenol < 0.01 < 0.1 TOC Tensides < 0,02 Volatile chlorinated hydro carbons < 0.1 Saponifiable fats and oils < 4 Sb 0.05 < 0.1 Tl < V 0.01 < 0.05 Chlorine (free) < 0.05 Chlorine total < 0.05 Non volatile lipophilic components < 20 Treatment of accumulated solid waste fractions By incineration wastes are reduced to one third of the original weight and to one tenth of the original volume. Fly ash, slag, ferrous scrap, filter cake from the waste water cleaning, gypsum and loaded activated coke primarily remain as wastes. These wastes are to a great extent classified as hazardous wastes and are treated and disposed of in Austria as follows:! Fly ash and the mixture slag/gypsum from the domestic waste incineration plants Spittelau and Flötzersteig are solidified and subsequently landfilled. Slags and fly ashes from the Plant Simmeringer Haide are landfilled too.! Slag from the waste incineration plant Wels is washed with water and landfilled. Fly ash from the waste incineration plant Wels is treated by a wet-chemical process and landfilled. Gypsum from this plant is also landfilled.! Bed ash and coarse ash from the fluidised bed reactor in Lenzing (AVE-RVL) are exempted and disposed of at landfills for residual waste. Ash from pre-dedusting devices, eco- and fabric filter ash and neutralisation sludge are exported as hazardous waste and disposed of underground.! Filter cake from waste water treatment is heavily charged with Hg. In general it is filled in so called big bags and disposed of underground. In addition to Hg also the concentrations of Zn and Cd as well as the residue on evaporation exceed the limit values for landfills for residual waste and mass waste landfills prescribed in the Austrian ordinance for landfills.! Separated metallic scrap is either delivered to a scrap dealer or returned to the steel industry.! In Wels, Arnoldstein and at the Plant Simmeringer Haide loaded activated coke is combusted together with waste. In addition to theses current practices various attempts (e.g. thermal treatment) were performed in order to utilize wastes from waste incineration plants or at least lower the hazardous potential. In most cases these attempts were terminated as on the one hand legal and economic conditions didn t justify the treatment and on the other hand technical problems complicated the permanent realization.

15 12 State of the Art / Waste Incineration Summary Costs The costs of a waste incineration plant basically depend on following factors:! Plant design! Size! Local infrastructure! Specific boundary conditions for waste disposal! Possibility for energy utilisation The main components are:! Repayment of investment! Maintenance and re-investment costs! Personnel costs! Other fix costs such as administration and insurance! Operating costs proportional to throughput such as chemical supply and waste disposal! Revenues from energy production proportional to throughput Basically it has to be considered that the thermal output is the important parameter for the investment and operating costs and not the mass throughput. The thermal output determines the size of the boiler and primarily the flue gas volume and therefore the size of the flue gas cleaning devices. Based on certain assumptions and on market prices of the last 5 years specific costs for following parts of a waste incineration plant have been estimated (in per ton combusted waste):! Discharge and storage! Firing system and boilers (various systems)! Water-steam cycle (various options)! Flue gas cleaning system (various processes) Additionally specific costs also based on certain boundary conditions for whole plants have been estimated as a function of plant size, type of energy utilisation and installed flue gas cleaning system. Estimated costs are between 91 and 148 per ton combusted waste depending on the plant. Cost calculation revealed that plants size has a great influence on overall costs. The maximum cost difference between identical plants of different size is about 37 per ton combusted waste. On the other hand different systems of energy utilisation result in cost differences of maximum 9 per ton, whereas different systems of flue gas cleaning cause cost differences of maximum 13 per t. If grate firing and fluidised bed combustion systems (equipped with the same system of energy utilisation and flue gas cleaning) are compared some general statements can be given:

16 State of the Art / Waste Incineration Summary 13 In Austria fluidised bed plants are exclusively charged with crushed or grinded wastes, whereas grate firings are operated with untreated waste. On the basis of certain assumptions and a capacity of 70,000 t yr -1 treated waste (Fluidised bed) respectively 100,000 t yr -1 untreated waste (grate firing) approximately the same specific treatment costs can be calculated based on the rated thermal input. Based on the mass throughput incineration costs of fluidised bed combustion systems are noticeably higher than those of a grate firing systems. In case of large plants with a throughput of 200,000 t yr -1 treated waste (for fluidised bed combustion) resp. 300,000 t yr -1 untreated waste (for grate firing) specific costs related to the rated thermal input will be more favourable if fluidised bed combustion is applied. It can be expected that in future even bigger units of fluidised bed firings can be built. That means that the fluidised bed technology represents a cost-efficient alternative for wastes with high calorific value. However, if waste has first to be separated into low and high calorific fractions and subsequently crushed and grinded, separation and subsequent combustion in a fluidised bed reactor will be uneconomic in comparison to a grate firing system.

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18 14 State of the Art / Waste Incineration Introduction 1 INTRODUCTION 1.1 Aims and Objectives The aim of this study is to describe the state of the art of waste incineration plants with respect to the European Council Directive 96/61/EC on Integrated Pollution Prevention and Control (IPPC-Directive). The main emphasis lies in the depiction of existing waste incineration plants in Austria. This includes a description of the type of the plants, demand of raw-materials and energy, type of incinerated waste fractions and installed systems for flue gas and waste water treatment (together with emission levels). Also, solid waste which accumulate from waste incineration are characterised with respect to volume and physical and chemical parameters. Applied techniques for treatment and disposal of accumulated waste are presented. Different systems of energy utilisation solely production of electricity, solely production of heat or co-generation of heat and power and how they influence cost efficiency of a waste incineration plant are discussed in detail. Cost estimations splitted into investment costs, operating costs (including enumeration of relevant items) and maintenance costs are presented both for single technologies (especially for flue gas cleaning systems which are installed at Austrian waste incineration plants) and for whole waste incineration plants. This study also deals with so-called Cross Media Effects, i.e. the transfer of pollutants between air, water and soil. The complex theme of Co-Incineration of waste is not dealt with in this study. 1.2 The connection to the IPPC-Directive In accordance with Article 16 paragraph 2 of European Council Directive 96/61/EC from 24 th September 1996 on Integrated Pollution Prevention and Control IPPC, the Commission organises the exchange of information between Member States and the industries concerned on best available techniques, associated monitoring and developments in them. The elaboration of the BAT documents for the categories of installation referred to in appendix I of the IPPC-Directive is carried out in Technical Working Groups which are set up by the European Commission in agreement with the Information Exchange Forum. The work of the Technical Working Groups is supported by the European Integrated Pollution Prevention and Control Bureau specially set up at the IPTS (Institute for Prospective Technological Studies) in Seville for this purpose. As defined in Article 2, Clause 11 of the IPPC-Directive, the term "Best Available Techniques" refers to the most effective and advanced stage in the development of activities and their methods of operation which indicate the practical suitability of particular techniques for providing in principle the basis for emission limit values designed to prevent and, where this is not possible, generally to reduce emissions and impacts on the environment as a whole. The term "techniques" includes both the technology used and the way in which the installation is designed, built, maintained, operated and decommissioned. "Available" techniques refers to those developed on a scale which allows implementation in the relevant industrial sector, under economically and technically viable conditions, taking into consideration cost and benefit analyses.

19 State of the Art / Waste Incineration Introduction 15 "Best" means most effective in achieving a high general level of protection of the environment as a whole. The following points should be given special attention when establishing Best Available Techniques in accordance with Annex IV of the Directive on "Integrated Pollution Prevention and Control": The use of low waste technology The use of less hazardous substances The promotion of the recovery and recycling of material and, where appropriate waste, produced and used in individual processes. Comparable processes, facilities and methods of operation which have been tried successfully on an industrial scale. Advances in technology and scientific knowledge. Type, impacts and volume of emissions involved. Date of commencement of operation of existing or new installations The length of time required for the introduction of a better available technology Type and consumption of raw materials (including water) used in individual processes and their energy efficiency. The necessity to prevent or at least reduce to a minimum the dangers and the overall impact of emissions on the environment. The necessity to prevent accidents and minimise their impact on the environment. The information publicised by international organisations or as set out in article 16 paragraph 2 by the Commission.

20 16 State of the Art / Waste Incineration Firing Technologies 2 FIRING TECHNOLOGIES As an introduction a general survey about the installations for handling and pre-treatment of waste is given. Afterwards descriptions of following firing technologies are presented: Grate firing Rotary kiln Fluidised bed combustion Degassing and/or gasification of wastes Particular descriptions of firing technologies include system-specific aspects of delivery, discharge, storage and conditioning of wastes for combustion. 2.1 Delivery and pretreatment of waste Waste can be delivered to the waste incineration plant either by truck or train. There it is dumped into bunkers, where it is stored before combustion or pretreatment. As far grate firing systems and rotary kilns are concerned no equipment for waste pretreatment or waste size reduction is required. Using these technologies waste from the bunker can directly be fed into the firing chamber. In case of fluidised bed combustion only crushed or grinded waste can be used. A direct feed as practiced at grate firing systems and rotary kilns can only be managed if specific operations (e.g. slowly rotating double screw) are provided. Therefore devices for waste conditioning (e.g. pulverizer, screens, magnetic separator) and another bunker for the intermediate storage of treated wastes are arranged after the first bunker. In Austria pyrolysis plants (degassing/gasification plants) are small plants which are charged discontinuously with waste either in unpacked form, in barrels or in bags. 2.2 Firing system and waste heat boiler During combustion of solid fuels including wastes four phases can be distinguished: Drying Degassing Gasification Complete burnout of gases and solids As to classic processes drying, degassing, gasification and burnout take place in the combustion and afterburning chamber. Processes described above happen slowly on the grate and in the rotary kiln and can be controlled by the combustion air supply. On the contrary, at fluidised bed reactors velocity of the combustion process cannot be controlled by this means because every single phase happens spontaneously. Main components of combustion gases are predominantly determined by the composition of incinerated wastes. Depending on the firing system composition of combustion gas varies according to the excess air and primary measures (e.g. temperature, residence time of combustion gases depending on the temperature). With firing specific measures, emissions of following pollutants can be reduced: Nitrogen oxides (NO x ), carbon monoxide (CO), hydro-

21 State of the Art / Waste Incineration Firing Technologies 17 carbons (C x H y ) and dust. Using fluidised bed combustion sulphur dioxide can be chemically bound into the combustion bed ash under certain conditions. At all waste incineration plants in Austria combustion heat introduced by wastes is totally transformed in waste heat boilers. Differences between particular processes occur concerning the height of radiation losses and other supplied energies (e.g. air preheating, auxiliary firing equipment). Therefore the overall efficiency of waste incineration plants (ratio from utilizable produced energy to totally applied (from waste, fuels and external sources) energy) mainly depends on the design parameters of the boiler but less on the kind of firing system. Quantity of solid wastes from waste incineration plants mainly depends on the composition of used wastes and the quality of burnout. Added chemicals such as limestone (fluidised bed combustion) or lime hydrate (into the waste gas stream before dust removal) only have small effects on total quantity of solid wastes from combustion Grate firing systems Presently in Austria three domestic waste incineration plants (Flötzersteig, Spittelau and Wels) are equipped with a grate firing system. This system should also be installed in the planned waste incineration plants Wels - Line 2, KRV Arnoldstein and Dürnrohr. Delivery, discharge and storage systems In municipal regions waste is directly delivered to the waste incineration plant by refuse collection vehicles and dumped into bunkers. In rural regions waste incineration plants are either planned or under construction. Delivery of waste should take place primarily by train. Planned transport systems for such plants include the use of modern refuse collection vehicles, which are equipped with containers. These containers are directly filled at the vehicle and subsequently transferred to the train. At the waste incineration plant, the containers are automatically emptied into the bunker. The logistic system also comprises external reload stations. Waste dumped into the bunker is stored 5 days at maximum. A considerable part of the combustion air is sucked off directly from the bunker in order to reduce odour nuisances to a minimum. This leads to a slight underpressure in the bunker so that ambient air is sucked into the bunker. Basically waste is not pretreated before combustion on the grate. In order to treat bulky refuse, at most plants shears are provided in the vicinity of the bunker. Waste is mixed in the bunker by using a bunker crane. Firing system and boiler Using a crane mixed waste is delivered from the bunker into the waste chute, which is located before the firing chamber. The waste pillar in the waste chute forms the airside sealing between the firing chamber and the bunker. If there is not enough waste in the chute, the waste chute will be closed by a pusher or a shutter. Actually waste is fed onto the grate by allocators that are arranged at the lower end of the chute and can be formed as pestles or as travelling grate. The velocity of the pestles or of the travelling grate is regulated according to the provided output. In Austrian waste incineration plants only pestles are used as allocators.

22 18 State of the Art / Waste Incineration Firing Technologies On the grate waste is moved further, stocked and contacted with primary air. Different grate velocities and air flow rates in various zones can be adjusted. In Austria following grate systems are used: Bar grates: In case of bigger grates more channels are arranged along the width. Stationary and moveable rows of bars alternate over the length. The moveable rows of bars are fixed to so-called grate slides. Forward feed grate: The movable row of bars pushes the waste forward. Applying different velocities in various zones the height of the waste bed can be controlled. Reciprocating grate: The movable row of bars pushes the waste, that directly lies on the grate, back. Waste in the upper regions of the waste bed is turned over by the slope of the grate. Combined forward and backward moving grate: Each second movable row of bars runs countercurrent to the row between. A movable row pushes the waste forward, the next pulls back and creates place for the waste pushed forward. Roller grates: In Austria no roller grate is presently operating or planned. At all times new surfaces for combustion are uncovered by stocking. Therefore velocity of solids burnout can be regulated by stoking and addition of primary combustion air. Secondary air injection into the combustion chamber at the side results in complete mixing of gases ignited by the primary combustion air and therefore complete burnout of combustion gases. At modern plants the coaction between allocator, grate movement, primary and secondary air supply and if needed by flue gas recirculation (for flue gas cooling, e.g. used at AVE - RVL Lenzing) is regulated by the controller of the firing performance depending on the firing parameters and the boiler output. Natural gas or heating oil is used for starting up and shutting down. Normally operation of auxiliary burners is not necessary for a continuous operation. Slag is used for heating the combustion air and thereby cooled. At the end of the grate slag is conveyed into the deslagger. Most of the deslaggers are built as wet deslagging systems. The chute is immersed in the water of the deslagger thereby establishing an air seal between the combustion chamber and the deslagging unit. In the slag bath the slag is cooled again. Pestles, dragline scrapers or plate conveyors are removing the slag from the deslagger. During this process the slag is simultaneously dewatered. Several plants (Flötzersteig, Wels) are equipped with a slag washing unit. There water is passed through the deslagger countercurrently to the slag, withdrawn from the deslagger being almost free from solids and further used for cleaning of flue gases. By this step the amount of soluble components remaining in the slag is minimized to a great extent. The delivered slag is classified by a coarse sieve and a magnetic separator. Firing system and boiler form a procedural unit. The combustion grate with the subsequent wet deslagger is integrated in a ceramically lined combustion chamber that is cooled by the tubes of the evaporator. A residence time of flue gases of two seconds at least at a temperature > 850 C is reached in the combustion chamber after the last combustion air supply. Subsequently flue gases pass a void zone of the boiler until they are cooled to a temperatur of about 650 C. This zone is followed by heating surfaces such as evaporators, superheaters and feedwater preheaters. Produced steam is expanded in a steam turbine. Depending on requirements low pressure steam can be withdrawn for a district heating system or for the use in an industrial plant. If

23 State of the Art / Waste Incineration Firing Technologies 19 there is no demand for heat, only electricity is produced. In this case the overall efficiency of a waste incineration plant is about 20 %. An overall efficiency of more than 80 % can be achieved with combined heat and power generation Rotary kiln In Austria a central waste incineration plant having two independent lines of rotary kilns (Plant Simmeringer Haide of Fernwärme Wien GesmbH) is in operation. Additionally to them there exist some small industrial waste incineration plants. Delivery, discharge and storage systems Delivery, discharge and storage systems of solid waste are basically similar to those of grate firings. In addition to solid wastes liquid and waste with high viscosity can be combusted in rotary kilns. In this case sedimentation facilites but also tanks and pump facilities are installed for treatment and interim storage. Firing system and boiler Mixed solid wastes are delivered from the bunker into the waste chute which is located in front of the firing using a crane. In most cases a sluice is integrated into the chute where waste can directly be fed into the rotary kiln. Highly viscous and liquid wastes can be inserted through the front wall of the rotary kiln. As a result of the slope and the rotation of the rotary kiln, wastes are transported and circulated, which leads to intensive contact with primary air, that flows through the rotary kiln. In contrast to grate firings rotary kilns are closed systems. Therefore also liquid and highly viscous materials can be inserted. Melted slag can be recirculated and/or discharged. Velocity of combustion cannot be regulated by zones as it is feasible at grate firing systems. Exhaust gases coming out of the rotary kiln are treated in an afterburning chamber. In order to assure high temperatures necessary for complete destruction of organic compounds ( C depending on the waste) afterburning chambers are equipped with burners that automatically start when the temperature falls below the given value. At the end of the rotary kiln slag arises either sintered or melted. By dropping into the water of the deslagging unit, granulated slag is formed. When the slag is sintered then this part of the plant is similar to that of a grate firing system. Rotary kilns and afterburning chambers are in most cases constructed as adiabatic, ceramically lined combustion chambers. After the combustion chamber flue gases pass a void zone until a temperatur range of about 700 C is reached. Subsequently heating bundles such as evaporators, superheaters and feedwater preheaters are arranged. Waste heat boiler and energy supply system is comparable to that of grate firing systems.

24 20 State of the Art / Waste Incineration Firing Technologies Fluidised bed combustion Fluidised combustion plants are in operation at three sites in Austria. They are exclusively used for waste incineration. Stationary fluidised bed reactors are installed at the Plant Simmeringer Haide and in the waste incineration plant Arnoldstein. A circulating fluidised bed reactor was erected by AVE - RVL Lenzing. In Austria fluidised bed reactors are used for the combustion of not utilizable plastic wastes, separately collected packaging wastes, fractions from waste separation plants, rejects from waste paper utilisation, separately collected wastes from trade and industry and for sewage sludge. In several industrial fluidised bed combustion plants wastes are co-combusted. In contrast to grate firings and rotary kilns the maximum grain size of wastes using fluidised bed combustion is limited so that usually treatment plants have to be installed. Wastes from the bunker or the storage depot are either classified by a sieve or directly put into the pulverizer. The fine fraction is classified by a magnetic separator and afterwards stored in a bunker. In Europe fluidised bed technology is playing a minor role in contrast to Japan. Above all two reasons are decisive: A fluidised bed combustion needs a good dosing of the waste which above all hardly can be realized using uncrushed or ungrinded municipal waste. The Japanese waste collection system is harmonized with combustion in fluidised bed reactors while the grain size is limited from the start. Without additional measures the major fraction of the non-combustible part of waste at fluidised bed combustion plants arises as fly ash that has to be landfilled at great expense. A precondition for the cost-effective use of fluidised bed reactors is the preseparation of dust with a separation efficiency of about 80 to 90 % at temperatures above 400 C so that the pollution burden of coarse and bed ash is lowered. In Austria fly ash and bed ash from waste incineration plants are hazardous wastes according to the waste classification ordinance (BGBl Nr. II 227/1997). Those wastes can be exempted (i.e. they are taken out of the scope of hazardous wastes) if it is proved that the hazardous properties don t apply (waste classification ordinance). A mixture of fabric filter ash and boiler ash doesn t meet the conditions for exempting in any case. Landfilling of hazardous wastes is noticeably more expensive than landfilling of non hazardous wastes because higher storage costs for underground depository arise. In Austria there are no underground depositories available. Compared with conventional grate firing systems and rotary kilns, fluidised bed combustion offers several advantages such as a smaller size at the same thermal output, a greater output of particular lines and a greater range of the calorific value of waste for combustion. Delivery, discharge, pretreatment and storage systems Systems for delivery, discharge and storage of solid wastes are basically similar to those of grate firings. Firing system and boiler Stationary fluidised bed combustion systems can be used for a rated thermal input up to 100 MW, for higher rated thermal inputs and in practice from 50 MW upwards circulating fluidised bed reactors are in use. Stationary fluidised bed reactors are equipped with a sand-

25 State of the Art / Waste Incineration Firing Technologies 21 bed that is held in abeyance by primary air introduced through nozzles. Using circulating systems sand is carried out of the combustion chamber by the flue gases and led to a cyclone. In the dip pipe of the cyclone flue gases with fine ash escape. Sand and coarse ash are separated in the cyclone and returned into the lower zone of the combustion chamber. Introduced wastes are mixed into the hot sandbed and combust spontaneously. Therefore a regulation of the combustion velocity by the air supply is not feasible. High demands that in general only can be achieved with crushed and grinded waste are made on the uniformity of the introduction system and the quality of mixing. Pulverized waste from the bunker is fed into the firing by dosing stations. Small ash particles enter the flue gas as fly ash. Heavy parts sink to the bottom of the bed and can be carried out in dry form together with bed material. Metallic parts accumulate dry, cooled and like sand blasted together with granular bed material and thus can be separated easily. Depending on the design combustion chambers of fluidised bed combustion plants can be constructed cooled or lined. The large amount of sand in the combustion chamber levels the temperature of the combustion chamber and supports a good mixing of wastes, additives and combustion gases. SO 2 can efficiently be bound by addition of lime or limestone so that under certain conditions a downstream desulphurisation step can be avoided. However the salt load is increased by addition of lime or limestone. Therefore a wet scrubbing for SO 2 separation after fluidised bed combustion may be reasonable because of economic reasons considering landfill properties of the produced wastes. The waste heat boiler and the waste gas treatment plant are similar to those of grate firings Circulating fluidised bed with upstream crushing and grinding AVE - RVL Lenzing operates a circulating fluidised bed reactor with upstream pulverization, that will be shortly described in the following text. The firing system mainly consists of: Uncooled combustion chamber with slightly conical shape at the bottom and cylindrical form at the top Cyclone Afterburning chamber Recirculation system for bed material with fluidised bed cooler Delivered wastes such as packaging materials, rejects, light fraction and waste wood are declared by the deliverer and randomly tested by the operator, crushed and grinded and interimly stored in two daily bunkers that are situated directly near the boiler. Feeding of waste into the pulverizer, distribution in the daily bunker and discharge from the daily bunker is carried out in view of good homogenization. Sewage sludge is directly dumped into two charging hoppers with discharge floor and interimly stored in a silo. Sewage sludge is usually stabilized and combusted a few hours after delivery. In all cases transport from the pretreatment site to the boiler house is established periodically with a pipe belt conveyor. Grinded wastes such as plastics, rejects, sieve overflow and waste wood can be fed from the charging hopper into the firing zone using 3 pneumatic conveyors. For sewage sludge, a separate conveyor line with a plug screw as feeder is available.

26 22 State of the Art / Waste Incineration Firing Technologies For oil and natural gas, burners and oil lances are provided. Coal can be fed with a separate dosing plant. Exhaust gas from the neighbouring viscose rayon production containing H 2 S (hydrogen sulphide) and CS 2 (carbon disulphide) is used as combustion air. Exhaust gas from waste treatment and storage is dedusted with fabric filters and discharged into the atmosphere. Combustion air is injected into the combustion chamber through the valve tray, two secondary air levels and several process-related places such as pneumatical conveyors and fluidising plates in the ash circle. Dosing of particular wastes, co-fired fuels and combustion air is regulated by a firing performance control system. The demand for air and fuel is calculated online. The most important parameters such as calorific value and demand on combustion air are calculated automatically from process data and adapted to the combusted wastes. Wastes are mixed homogeneously into the lower part of the combustion chamber and transported through the firing chamber with combustion air. In order to preseparate SO 2 limestone is continuously added to the fluidised bed reactor of AVE - Reststoffverwertung Lenzing. This is a necessary procedure, because the exhaust air of the viscose rayon production that is used as combustion air contains high amounts of sulphureous compounds. Bed material is separated from the flue gas by a cyclone and fed into the syphon and fluidised bed cooler. A regulated quantity of bed material is passed over the fluidised bed cooler in order to extract heat from bed material either for steam production and superheating of steam or temperature regulation of the combustion chamber. Flue gases leaving the cyclone are fully combusted in the afterburning chamber at sufficient temperature and residence time. Flue gases leaving the afterburning chamber are passing two vertical void zones with heating surfaces for evaporation, a horizontal zone with hanging heating surfaces for evaporation and superheating, a cyclone battery system and a preheater for feedwater Stationary fluidised bed combustion Stationary fluidised bed reactors for the combustion of sewage sludge and certain waste fractions are in operation at the Plant Simmeringer Haide. At the site Arnoldstein hazardous wastes are also combusted in such a combustion system. A stationary fluidised bed reactor consists of a bricked adiabatic combustion chamber with a valve tray, a stationary fluidised bed and an afterburning chamber. At the Plant Simmeringer Haide crushed and grinded wastes are delivered, interimly stored in receiver bunkers and fed into the fluidised bed by dosing conveyors. In Arnoldstein wastes also can be pulverized on site if necessary. Sewage sludges are pressed into the firing with high consistency pumps. Oil is directly combusted or mixed with wastes. In the lower part of the combustion chamber wastes are mixed homogeneously into the bed material and distributed in the fludized bed. In order to preseparate SO 2 it is possible to add limestone. Exhaust air from waste storage can be used as combustion air. Slightly contaminated exhaust air from waste treatment is dedusted in fabric filters. In Arnoldstein highly contaminated exhaust air, that doesn t pass the combustion, is purified with a continuously working countercurrent adsorber, that is filled with bark and activated coke. The charged adsorber material is subsequently combusted in the fluidised bed reactor.