Objective To demonstrate the pressurised fluidised bed gasification and combustion stages of the British Coal Topping Cycle, on a 12 t/d pilot plant. The Topping Cycle Power Generation System uses a non-agglomerating, air blown, pressurised, spouted bed gasifier to produce a low calorific value gas. This gas would be burnt in a high temperature (1250 deg. C) gas turbine forming part of a combined cycle power generating system using a circulating fluidised bed combustor.It is expected that the Topping Cycle efficiency will be in excess of 45% compared with 38% for a pf fired power station fitted with flue gas desulphurisation. Per unit of electricity produced it will also reduce the emissions of CO2 by 20%, SO2 by 95% and NOx by up to 60%.L%Two periods of extended operation have been completed on the gasifier. The gasifier has operated for a total of 530 hours under gasification conditions at pressure between 2 and 12, and 150h at 12 bar pressure. Tests have been conducted both with and without limestone addition. Operational availability was poor during both runs due to equipment failures.As a component of the British Coal Topping Cycle the pressurised gasifier must achieve a number of performance targets. These targets are; a coal conversion efficiency of 70 to 80-% (dry ash free basis), a minimum gas calorific value of 3.6MJ/m3 (wet, nett) and a sulphur retention efficiency of 90%.Performance data from the plant indicates that the first two criteria (coal conversion efficiency and gas calorifc value) have been achieved. Sulphur retention efficiencies are lower (64%) than the desired target due to the high steam levels required to control the plant and the resultant low overall bed temperatures.The problems aredue to the size of the reactor. In a large scale plant the heat of combustion will be distributed over a large area, particle mobility and hence heat transfer will also be improved. Therefore, in larger scale plant, there is every indication that sulphur retention efficiencies of the order 90% should be achievable.The combustion of char residues from the gasifier has been demonstrated successfully in a laboratory scale combustor. Evaluation of the combustion characteristics in a CFBC unit was also planned. However, due to plant problems the work was not achieved. The combustion of a metallurgical coke was demonstrated. Thermographic analyses have shown that the coke is less reactive than char fines. Successful combustion of char/fines in a CFBC should be achievable.An existing pressurised fluidised bed combustor at the British coal Corporation, Coal Research Establishment has been extensively modified to enable it to operate as a pressurised, spouted bed, air blown gasifier. This is being used to investigate, on a 12 t/d scale, the gasification characteristics of the process.These characteristics have been thoroughly explored, at the same scale, at atmospheric pressure.The process involves the fluidisation of a bed of char and ash by an air and steam mixture. The fluidising gas mixture is introduced as a jet at the bottom of an inverted conical shaped base to a vertical cylindrical reactor. The jet promotes rapid recirculation within the bed and so enables caking coals to be processed without agglomeration problems. Coal can be fed either under or over bed from lock hoppers and provision has been made for limestone to be injected either under bed or in bed. Both coal and limestone are independently controlled and metered to enable changesin the Ca:S ratio and sulphur retention to be achieved. The gasifier will be operated at temperatures of up to 1000 deg. C and pressures of up to 20 bar.The project includes investigations into the combustion characteristics of the residual char captured by the cyclones and the material removed from the bed, this being a demonstration of the second stage of the Topping Cycle - combustion. Programme(s) ENG-ENDEMO C - Programme (EEC) of demonstration projects and industrial pilot projects (EEC) in the energy field, 1985-1989 Topic(s) 6.1 - GASIFICATION Call for proposal Data not available Funding Scheme DEM - Demonstration contracts Coordinator BRITISH COAL CORPORATION (RESEARCH ESTABLISHMENT EU contribution No data Address COAL RESEARCH ESTABLISHMENT STOKE ORCHARD, CHELTENHAM GL52 4RZ Gloucester United Kingdom See on map Total cost No data
