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DEVELOPMENT AND DEMONSTRATION OF IMPROVED AIR DISTRIBUTORS FOR BED BOILERS TO BURN UNTREATED AND POWER STATION TYPE COALS

Objetivo

THE PRINCIPAL AIM OF THIS RESEARCH PROPOSAL IS TO DEVELOP AIR DISTRIBUTORS FOR FLUIDIZED BEDS WHICH WOULD FACILITATE THE USE OF UNCLEANED COALS IN BOILERS AND FURNACES OF LESS THAN 40 MW THERMAL OUTPUT.
A SECONDARY OBJECTIVE IS TO INVESTIGATE THE BEHAVIOUR OF FLUIDIZED BED FIRED EQUIPMENT WITH EITHER RELATIVELYHIGH ASH COALS OR COALS WITH A HIGH INHERENT SHALE CONTENT, TO ENABLE BED CLEANING SYSTEM DESIGNS TO BE DEVELOPED WHICH ARE EFFECTIVE FOR THESE TYPES OF COAL.
The Coal Research Establishment has carried out a programme to develop improved distributor systems for high ash coals, in conjunction with boiler manufacturers. 2 concepts have been identified for further development after a review of high ash distributors. They are: a directed standpipe air distributor with internal air classifier of screw conveyor, and a spare air distributor with bed solids extraction and screening via air slides, a screw conveyor, and a rotary screen classifier. Supporting studies have also been carried out. Hot testwork on a 0.5 square metre rig has shown that a directed standpipe air distributor with a single air classifier removes oversized ash particles entering at rates between 3.3% and 8.7% of the coal feed rate. Cold model studies of a full scale screw conveyor have shown that screws with either variable pitch or tapered flights remove solids along their length uniformly. Hoppers that feed the screw require baffles to give a suitable delivery over the entire hopper cross-section. A correlation between oversize ash accumulation rate and ash input rate has been developed which confirms that British coals with ash content above 18% will give oversize ash accumulation rates exceeding 3% and therefore require high ash types of distributor for their use in a fluidised bed combustor.

A prototype directed standpipe air distributor system with either a screw conveyor, or an air classifier for bed maintenance has been designed. A prototype sparge pipe distributor system has also been designed. Cold tests and 2 weekly periods of hot testwork have been undertaken. These tests suggest that the system is suitable for extended commercial operation. The air slides handled hot bed solids containing up to 30% oversize ash satisfactorily. The complete bed cleaning system could maintain an oversize ash concentration in the bed below 15% when the oversize ash input rate was up to 7% of the coal feed rate.
WHEN THIS WORK IS COMPLETED, IT IS EXPECTED THAT BRITISH COAL AND AT LEAST TWO MAJOR BOILER SUPPLIERS WILL HAVE SYSTEMS TO OFFER WHICH CAN BE USED WITH LESS PREPARED FUELS. THE DESIGNS DEVELOPED MAY ATTRACT ROYALTIES SINCE THEY WILL OFTEN BE MORE APPROPRIATE FOR BOILER SALES ABROAD - PARTICULARLY IN DEVELOPING COUNTRIES - WHERE COAL PREPARATION TENDS NOT TO BE PRACTISED.
THE RESULTING SYSTEMS WILL HAVE TO BE SATISFACTORY IN EVERY DAY COMMERCIAL USE WITH UNTREATED OR PART-TREATED DEFINED COALS WITH ASH CONTENTS OF UP TO 17%

Tema(s)

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Convocatoria de propuestas

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Régimen de financiación

CSC - Cost-sharing contracts

Coordinador

British Coal plc
Aportación de la UE
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Dirección
Hobart House Grosvenor Place
SW1X 7AE London
Reino Unido

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Participantes (2)