Kymijärvi - Lahden Lämpövoima Oy Finland

Transcription

1 THE ANALYSIS REPORT OF PLANT NO. 19 Cofiring of biomass - evaluation of fuel procurement and handling in selected existing plants and exchange of information (COFIRING) - Part 2 Kymijärvi - Lahden Lämpövoima Oy Finland Evaluated by Timo Järvinen, VTT Energy

2 1. General information Lahden Lämpövoima Oy is owned by the Lahti Energia Oy, which is a municipal company. The aim of the company is to provide heat and electricity (CHP plant) for Lahti area. It can also be used as a peak reserve power station for electricity. Originally the power station was burning heavy fuel oil and it was brought into commercial operation in The boiler was converted also coal-fired When the natural gas net work was extended to the Lahti it was realised gas turbine (49 MW e, when the outside temperature is -25 C) and recovery boiler plant next to the existing power station and supplement gas burners in main boiler in The plant has an electric capacity of 185 MW e in a back pressure operation and district heat capacity of 250 MW th. The net efficiency of the power station can reach 85 %. The Kymijärvi power plant represents the common power plant concept, i.e. the pulverized coal-fired steam boiler producing high-pressure steam for the steam turbine. These power plants are rather large and the steam cycles in the plants are quite efficient. Steam boiler 350 MW (coal/oil/gas-fired): Benson type, once trough tower, steam values: 125 kg/s, 540 o C/170 bar, 540 o C/40/42 bar. The operating hours of the boiler are total to about 7000 h/a. In the summer, when the heat demand is low the boiler is shut down. In the spring and autumn, the boiler is operating in low capacity, with natural gas as a sole fuel. Increasing fuel costs, environmental demands and increasing energy consumption pushed the company further to look for new solutions to energy production. It was considered different solutions, like BFB retrofit, separate front FB burner and gasifier. The last one was selected because of the modern technology and emission control. The support of EU THERMIE programme for the new technology helped the selection. The aim of the Lahden Lämpövoima Oy`s Kymijärvi Power Plant gasification project is to demonstrate on a commercial scale the direct gasification of wet bio fuel and the use of hot, raw and very low calorific gas immediately in the existing coal-fired boiler. The gasifier replaces 15 % of the fossil fuels and reduces SO 2, NO x and CO 2 emissions. The effect of the atmospheric CFB-gasifier is MW th and the fuels are different types solid biofuels and recycled fuel (REF) from source separated waste. The gasifier was delivered by Foster Wheeler Energia Oy. Figure 1 presents schematically the process. 2

3 CFB BIOMASS GASIFIER MWth LAHDEN LÄMPÖVOIMA KYMIJÄRVI POWER PLANT KYMIJÄRVI, FINLAND Figure 1. Lahden Lämpövoima Oy biofuel gasifier connected to pulverised coal-fired boiler. The company employes a staff of approx. 68 persons. The maintenance operations bind 31 person of the total number. 2. Process description Fuels will be transported to the power plant in trucks. There is one receiving hall for REF and one receiving station for in coming bio fuels. The REF hall is equipped with a receiving pit having a lamella feeder to control the flow of fuel to a crusher. Coarse bio fuel from the wood refining industry is also fed through the REF system. The trucks tip the REF and coarse material on the floor of the hall or directly into the pit. The REF and coarse bio fuel will be crushed in the slowly rotating crusher. The underground conveyor from the first receiving bunker transports REF and bio fuels from the crusher. The other receiving bunker is for the fine material, like saw dust and milled peat. These fuels are taken to the site by trucks equipped with chain unloading system. The truck can drive through the receiving tunnel. The discharging takes place on a flat chain conveyor, which drops the fuels on the screen. Accepted fraction falls down onto the 3

4 chain conveyor at the bottom of bunker. Over sized particles are moved back to the REF hall for pre-crushing. The underground conveyor lifts the fuels to belt conveyor provided with magnetic separator. The belt feeds a disc screen. The overflow falls down into the final crusher, while the accepted fuel fraction and crushed material will be transported by a chain conveyor into the intermediate storage. The fuel storage silo is used also for homogenisation of fuel mixture before the feed of the gasifier. The storage will be unloaded by the screw reclaimer. The fuel handling layout is in figure 2 and grosssection in figure 3. FUEL HANDLING LAY OUT Intermediate Storage Screening Station Screw Reclaimer Bio fuel Reception Chain Conveyor to gasifier Electrification and Automation REF Reception Figure 2. The fuel handling layout. FUEL HANDLING GROSS-SECTION Stacking Conveyor Chain Conveyor Magnetic Separation Screening Final Shredding Screw Reclaimer Belt Conveyor Figure 3. The fuel handling gross-section and intermediate storage. 4

5 The fuel will be taken into two feeding silos on the both side of gasifier. The feeding bins are equipped with screw dischargers and they dose the fuel through the two block feeders into the gasifier. The bed material and limestone will be added into the fuel flow in feeding silos. 3. Fuels and fuel procurement The boiler uses about 5760 TJ/a (180,000 ton/a) coal and about 1440 TJ natural gas. The boiler is not equipped with a sulphur removal system. However, the coal utilized contains only % sulphur. In the beginning the gasifier fuel consisted of mainly bio fuels like bark, wood chips, saw dust and uncontaminated wood waste. When the system to collect combustible, source separated classified waste material was started in 1997 on the Lahti area also this REF fuel was used. The REF originates both from househould and industry. The quantity of REF has been lower than gasification capacity, but it is expected the amount and quality to increase in the future. Besides the above-mentioned fuels, railway sleepers (chipped on site) and shredded tires have been utilised. The following table presents fuels used in the gasifier in 1998 and in first half of the year Year Fuel TJ GWh Wood residues REF Railway sleepers 14 0 Shredded tires Total The recovered fuel (REF) in 1999 includes typical REF fuel: 281 TJ, plastic 169 TJ and paper unsuitable for the recycling 68 TJ. The fuel consumption was totally 810 TJ (225 GWh, t) in 1998 and consequently about 1224 TJ (340 GWh, t) in At the moment there are 50 different fuel suppliers and approx. 100 different fuel types. The fuel supplier is presupposed to follow the REF quality spesifications of the Päijät-Hämeen Jätehuolto Oy. 5

6 The REF consists of: % (wt) Plastic 5-15 Paper Cardboard Wood The moisture content of fuels are typically: % for the saw dust and wood residues, % for the dry wood residues from refining and % for the REF. The energy density of fuels varies GJ/m 3 ( MWh/m 3 ) The high moisture content of wood fuel may cause problems. The plastic in the REF improves the heat value. Chlorine control is important. According emission measurements the HCL content of flue gas increased approx. 5 mg/mj, when gasifier was in operation (REF fuel and tires). 4. Fuel handling and feeding system 4.1 Fuel receiving, handling and conveyors There is separate receiving places for REF and coarse materials. Totally the number of truckloads in a month is approx The delivery of fuels takes place in two shifts (16 h/d) and on Saturdays in one shift (8h/d). The fuel company takes care of the receiving stations operations. The system employs one worker. REF can easily blockade the disc screen. It will be daily cleaned. Chain conveyors were chosen because of closed construction (dust control). They are thermally isolated and heated by electrical resistance wires. The bottom of conveyor is covered by stainless steel plate. The chain and scrapers are made from normal carbon steel. Under the sliding chain is a teflon covered guideway. The line is designed also for the peat fuel. The all chutes and conveyor crossing places are made from stainless plate and equipped with heating system. Ferrous material separation takes place on a short belt conveyor just before screening. The particle classifying is made by the disc screen. The rotation velocity of disc axis is progressive to the end of screen because of large variety of materials. The screen is installed at a small inclination. 6

7 The two stage crushing is absolute necessary. The pre-crushing takes place in a low speed crusher (n x 10 rpm) and the final crusher has a rotor, which rotates at a middle speed (n x 100 rpm) and has a screen plate at the bottom of the crushing chamber. The teeth of both crushers are reinforced by hard-welding. The teeth have to re-weld and grind 1-2 times in a driving season. 4.2 Storage and gasifier feed The gasification plant has one storage. The volume of the intermediate storage is m 3. The form of the storage silo is rectangular. The bottom is concrete and walls and roof are steel construction. The fuels will be taken into storage by stacking chain conveyor. The idea is to divide the fuel flow even according to the silo length on the pile in the storage. This has not succeeded well, because the light material will be taken by scrapers into the end of storage. The system will be repaired at this summer. The discharge of intermediate storage takes place with one screw reclaimer. The screw blade and housing plate of central pipe are made from stainless steel. The screw reclaimer moves linear on the bottom of storage. The revolution time of screw will be controlled. The screw unloader is able to transport designed fuel quantity into the boiler hoppers. The main problem is to get even discharge because of material density changes in the pile. The REF material makes flexible layers in the pile and materials will be compressed on a different manner. The starting torque also increases considerably according to the height of a pile. So far there has been sufficiently motor effect and screw construction has been strong enough for the maximum tensions. There are two feeding silos (a 10 m 3 ) on the both side of gasifier. These hoppers have down opening inclination angle. The fuel discharge occurs by adjustable screw feeders. The material will dosed into the casification chamber trough two block feeders per line. The blades of block feeders will welded and grind after every driving season. The long fibres and particles in fuels can cause problems in feeding. The fuel handling system was supplied by Roxon Oy. 4.3 Gasification The CFB gasifier consists of the inside refractory-lined steel vessel, where fuel is gasified in a hot fluidised gas-solid particle suspension. Bio fuels and REF will be converted to combustible gas at atmospheric pressure at the temperature of about 850 7

8 o C. The hot gas flowing through the uniflow cyclone will be cooled down in the air preheater before feeding to the main boiler. Simultaneously, the gasification air will be heated up (Fig. 4). Fluidised bed material like sand and limestone are needed in the gasifier process; consumption of the bed materials is approx kg/h. CFB GASIFIER REACTOR UNIFLOW CYCLONE 850 C GASIFICATION AIR FAN BIOFUEL FEED 900 C RETURN LEG AIR PREHEATER HOT LOW CALORIFIC GAS ( C) BOTTOM ASH COOLING SCREW Figure 4. CFB gasifier From the process point of view, the major difference compared to the gasifier supplied in mid 80 is that fuel will not be dried in this application, but the moisture content of fuel can be up to 60 %. From the mechanical and equipment point of view some changes compared to the standard atmospheric biomass gasifiers have been made. This due to the special nature of some of the fuel components to be used in the gasifier. For example fuels like REF, some wood wastes and shredded tires contain many kind of solid impurities (nails, screws, metal wires, concrete). Therefore the air distribution grid and the bottom ash extraction system have been designed in a different way compared to the standard design. The hot gas is led directly from gasifier through the air preheater into two burners locating below the coal burners in the main boiler. The gas burns in the boiler and it replaces part of coal used in boiler. When the fuel is wet, the heat value of the gas is very low. Typically, when the fuel moisture is about 50 % the calorific value is only 8

9 approx. 2,2 MJ/kg. The design of the product gas burners is unique and heavily based on both the pilot scale combustion tests and CFD modelling work. The stability of the main boiler steam cycle has been excellent. The large opening that were made for the low Btu gas burners have not caused any disturbance in the water/steam circulation system. Furthermore, as regards of product gas burners, the product gas combustion has been stable even though the moisture content of solid fuel has been mostly high and the heat value of the gas very low. The stability of the main boiler coal burners has been normal despite placing burners very close to the lowest level coal burners. The coal burners are provided with flue gas circulation and staged combustion to reduce NO x -emissions.the changes in the emissions were rather and stayed under the limits determined for the boiler. The dust content in the flue gas after the ESP decreased appr mg/m 3 n. Perhaps the most positive phenomenon has been the decrease in the NO x emission. According to the measurements the NO x content of the main boiler decreased typically app. 10 mg/mj, which means the decrease of 5 to 10 % from the base level. Furthermore, because of the extremely low sulphur content of solid biofuels, the main boiler SO x emission decreased app mg/mj. Instead of that, because of the very low chlorine content (0.01 %) of the main boiler coal, the HCl content of flue gas increased app. 5 mg/mj when the gasifier was in operation. The reason for this was the use of REF fuel and shredded tires in the gasifier. Both of these fuels are known to contain chlorine. As regards the CO emission of the main boiler, no changes could be seen. The emissions of dangerous compounds, like dioxins, furans, PAH, benzenes and phenols did not change. Gasifier bottom ash will transported and disposed in a local dumping site. 5. Control and cleaning The control system is delivered by Neles Automation (Damatic). The driving takes place by keeping one feeding silo always full and the other one controls feed i.e. the surface level fluctuates. The silos are provided with weight measurement. The storage screw reclaimer adjusts the fuel feed. The surface level sensors of feeding bins only stops the unloading of storage. The discharging of the full feeding silo functions better than the adjusting bin. The sampling of fuel takes place in two different places. There is a hatch on the bottom of chain conveyor, which can be opened automatically. The sample will be taken into a sack. This sample is taken for the pricing of fuels. An other sampling place is the belt in the storage house. During the sampling the belt will be stopped. This sample is taken for the gasifier driving control and authorities. 9

10 The whole feeding line is equipped with fire water and sprinkler system. Every chute is provided with sparkle detecting system which can launch the sprinkler system for a short moment. The gasifier feeding systems inside of the boiler house can be steamed. The dust control have also be seen very important. There have been two fires needed fire brigade extinguishing. Self ignition of wooden fuel material is sometimes occurred. Too fine material is not aloud to take to the power plant (wood grinding dust). 6. Investment and maintenance costs The total investment was 71 million FIM (12 million EUR). The cost saving comes from the substitution of import fossil fuels with bio and waste fuels. The estimated payback time is approx. 10 years. The fuel handling investment outside of boiler house was about 15 million FIM (2,5 million EUR). Totally handling, feeding and control system costs were approx. 27 million FIM (4,6 million EUR). Operational and maintenance costs are approx. 3,15 million FIM/a (0,5 million EUR/a). The maintenance costs for fuel handling are about EUR/a and for the gasifier about EUR/a. The significant costs cause also the bed material approx EUR/a. Also the quality control of fuels makes EUR/a. 7. Remarks The operating experiences of the first operation periods has been good. Only a few problems occurred at the gasification plant and the availability of the plant has been high since the beginning of operation. Most of problems are related to the fuel processing and feeding. The best receiving and feeding system would be based on three lines: untreated source separated municipal waste (fuel fraction)/wood fuel/ref or plastic. It is estimated the additional cost of such a system would be around 5 million FIM (< 1 million EUR). The system like that would extend also the fuel base of the gasifier. As the gasifier and the overall cocombustion concept has been proven to work technically very well, the system will be in commercial use as long as the general surrounding conditions are favourable. In practise, the future of gasifier and the coalfired boiler of Lahden Lämpövoima Oy depends strongly on the development of fuel, electricity and heat prices, taxes of fuels as well as the environmental standards. 10