THE AIM OF THIS PROJECT IS TO DEVELOP A CARBONACEOUS MATERIAL PRODUCED FROM WITHIN THE DIRECT LIQUEFACTION PROCESS AS A FILTRATION AID.
An analytical assessment of 9 different coke materials, nominated as being suitable for use as filter aids in coal liquefaction, has been completed. All coke products in the size range 55-125 um bridge a 200 um screen, but the initial breakthrough losses are higher with precoats that contain considerable quantities of fine particles. All coke products, at various sizes, give satisfactorily low cake resistivities which are within the range offered by commercial suppliers of diatomaceous earth precoats. The severity of the handling that these precoats can withstand is limited, with the most robust of those tested being petroleum cyclone fines.
None of the precoats tested eliminates blinding of metal screens, but all reduce the rate of blinding. For example, the use of petroleum cyclone fines as a precoat halved the frequency with which screen cleaning was required.
THE SEPARATION OF INERT SOLIDS ASSOCIATED WITH THE COAL FEED IS AN ESSENTIAL OPERATION WITHIN ALL DIRECT COAL LIQUEFACTION PROCESSES.WHILE HOT PRESSURISED FILTRATION IS AN EFFICIENT METHOD OF SEPARATION THERE WOULD BE TECHNICAL AND ECONOMIC ADVANTAGES IN SUBSTITUTING PROCESS DERIVED CARBONACEOUS FILTER PRECOATS FOR THE MINERAL PRECOATS CURRENTLY USED.THIS COLLABORATIVE PROJECT INVOLVING SEPARATE CONTRACTS WITH BRITISH COAL AND BERGBAU-FORSCHUNG GMBH. WILL TRY TO DEVELOP PRECOATS FOR THE BRITISH AND GERMAN VERSIONS OF THE DIRECT LIQUEFACTION PROCESS.
BRITISH COAL WILL SCREEN IN THE LABORATORY A TOTAL OF 13 CANDIDATE PRECOATS AGAINST TEN EVALUATION CRITERIA.THEY WILL SELECT,IN CONJUNCTION WITH BERGBAU-FORSCHUNG THREE MATERIALS FOR FURTHER DEVELOPMENT.THESE WILL LIKELY INCLUDE A PETROLEUM DERIVED COKE,A COAL EXTRACT DERIVED COKE AND A CARBONISED MATERIAL,EACH HAVING LOW SPECIFIC CAKE RESISTIVITY,GOOD MEDIA BRIDGING AND GOOD MEDIA PROTECTION POTENTIAL.
BRITISH COAL WILL FURTHER EVALUATE THE THREE SELECTED COKES IN A PROPRIETARY VERTICAL LEAF FILTER.THE FILTER SCREENS WILL BE REGULARLY EXAMINED TO ASSESS THE EFFECTIVENESS OF THE PRECOATS.
BERGBAU-FORSCHUNG WILL SELECT THEIR OWN PRECOAT FROM FIVE DIFFERENT SIZE FRACTIONS OF CARBONISED COAL HAVING TESTED THESE FOR COKE RESISTIVITY,FLOW RATE AND EFFECT OF PURIFICATION.THE CHOSEN FRACTION WILL BE USED FOR A HUNDRED CYCLE TEST IN A CANDLE FILTER UNIT.RESULTS WILL BE COMPARED TO PERFORMANCE WITHOUT FILTER AID, PERFORMANCE WITH CARBONISED FILTER CAKE AND TO BRITISH COAL FINDINGS.
STATE OF ADVANCEMENT:
THE FIRST PROGRESS IS EXPECTED IN FEBRUARY 1988.