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CONTROL OF NITROGEN OXIDES IN PRESSURISED FLUIDISED BED SYSTEMS.

Objective

THE MAIN REQUIREMENT OF THE WORK IS TO PROVIDE INFORMATION ON THE EFFECT OF DESIGN AND OPERATING MODE ON THE EMISSION OF NOX FROM PFBC, FOR USE BY MANUFACTURERS AND POWER GENERATION COMPANIES. A SECUNDARY REQUIREMENT IS TO PROVIDE INFORMATION ON THE EFFECTS WHICH THE MEASURES TAKEN TO REDUCE EMISSION OF NOX WILL HAVE ON OTHER ASPECTS OF PERFORMANCE, PARTICULARLY COMBUSTION EFFICIENCY AND SULPHUR RETENTION.

THE INFORMATION OBTAINED WILL BE USED BY POWER GENERATION COMPANIES AND THEIR BOILER SUPPLIERS IN DESIGNING PFBC PLANTS TO COMPLY WITH THE REQUIRED EMISSION STANDARD FOR NITROGEN OXIDES.
The effects of a wide range of operating parameters on nitrogen oxide emissions have been assessed. The level of excess air has been shown to be the dominant parameter although fluidisation conditions may also be important. There is some indication of an effect of bed temperature. The effectiveness of staged combustion for reduction of nitrogen oxide emissions was determined and it was found that staging at the bed surface gave the best results since some 65% reduction in nitrogen oxide levels could be achieved without adverse effects on the off gas temperature or combuster performance. Studies of the use of ammonia injection for nitrogen oxide control were undertaken and the indications are that reductions can be achieved with very low (1-2 ppm) levels of ammonia slip. The implications for a commercial plant are that nitrogen oxide levels should be inherently low for full load conventional operation but will be higher for a part load. While staged combustion may be an effective means of nitrogen oxide control for full load conditions, it may not be acceptable at part load. In this respect ammonia injection may be a better technique for nitrogen oxide control. The engineering practicalities and economic impact of both techniques need to be evaluated. It is also recommended that predictive techniques are developed to aid the design of full scale plant.
PRESSURIZED FLUIDIZED BED COMBUSTION (PFBC) IS A NEW COAL BURNING SYSTEM WHICH GIVES IMPROVED POWER GENERATION EFFICIENCY THROUGH THE USE OF A COMBINATION OF A GAS TURBINE AND A STEAM TURBINE. THUS THERE IS A REDUCTION IN ALL EMISSIONS PER UNIT OF ELECTRICITY PRODUCED. IN ADDITION, PFBC, EVEN IN ITS CONVENTIONAL FORM, PRODUCES A RELATIVELY LOW LEVEL OF NOX EMISSION PER UNIT OF COAL FIRED, AND THERE IS CONSIDERED TO BE POTENTIAL FOR A FURTHER REDUCTION IN EMISSIONS BY MODIFYING THE DESIGN AND OPERATING PROCEDURES.

THE PROJECT HAS TWO MAIN OBJECTIVES :

1) TO ASSESS THE EFFECT OF PROCESS AND OPERATIONAL VARIABLES ON NOX EMISSIONS FROM A PRESSURIZED FLUIDIZED BED COMBUSTOR (PFBC) IN CONVENTIONAL OPERATING MODE.

2) TO INVESTIGATE THE ABILITY TO REDUCE THE EMISSION OF NOX BY MAKING MODIFICATIONS TO THE DESIGN AND THE OPERATING MODE.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

British Coal plc
Address
Hobart House Grosvenor Place
SW1X 7AE London
United Kingdom

Participants (2)

Bergbau-Forschung GmbH
Germany
Address
Franz-fischer-weg 61
45307 Essen
Central Electricity Research Laboratory
United Kingdom