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PROCESS & ECONOMIC IMPROVEMENTS IN COAL LIQUEFACTION - LSE PILOT PLANT PROJECT [PHASE 4 C]

Ziel

The overall project aim is to design, construct and operate a pilot plant for the evaluation of British Coal's Liquid Solvent Extraction Process for the production of transport fuels from coal. This entry refers to part of the Operating Phase of the project. The specific aims of the current programme are to :
- Improve process efficiency, economics and reliability by carrying out testwork on specific unit operations within the overall process.
- Carry out an extended process demonstration run.
- Prepare a preliminary design for a larger scale Process Demonstration Plant from which a detailed design could be prepared in due course.
Early mechanical problems have now been resolved, in many cases by improvements to the original manufacturer's equipment made either at the suggestion of the project or directly by project engineers. Filtration has been demonstrated to be an effective and practicable means of removing unreacted coal and other solids from liquefaction process streams.
Basic yield patterns have been obtained for operation of the process at a range of conditions. It has been shown that an all-distillate liquid product slate can be obtained at yields in excess of 60% of the dry ash-free coal fed to the process. This figure is based on the use of Point of Ayr bituminous coal, which is not an ideal liquefaction feedstock since it gives an unreacted residue of 16% on daf coal. With other coals it would be possible to improve the extraction by 5-10% and hence to increase distillate product yields into the range 65-70% daf.
Product upgrading routes to produce gasoline and diesel fuel have been confirmed and it has been shown that fuels meeting all current and anticipated future specifications can be produced.
Process economics have been evaluated on the basis of a costing for a commercial scale plant prepared by an external contractor. A wide range of assumptions is involved, but it is estimated that, in Europe, the process would be commercially viable at a crude oil price in the range UKL 35-40/bbl for a stand-alone plant into which coal was the only energy input. A separate study has identified many opportunities for partial integration of a liquefaction plant with an existing oil refinery and in these circumstances the necessary crude oil price would be in the range UKL30-35/bbl.
British Coal is developing a two-stage coal liquefaction process. Coal is dissolved in a process derived solvent, insolubles (including mineral matter) are filtered out and the resulting coal solution is hydrocracked and then fractionated to yield products and recycle solvent.
The objectives of the Project are to:
- Demonstrate the process under continuous full recycle operation, determine operational flexibilities and establish the operating envelope.
- Identify and solve effluent disposal problems.
- Produce tonnage quantities of light to medium oils for testing.
The plant design allows for variations in certain key parameters to allow the investigation and proving of the technical and technological feasibility of the process. In the process, coal is dried, pulverised and slurried with a hydrogen donor solvent (a mixture of aromatic hydrocarbons) produced within the process, pressurized to 24 bar and preheated to 410 deg. C. The slurry is fed to a digester, where 90% of the coaldissolves, cooled to 300 deg. C and depressurized to 2 bar to remove light liquids and gases. Undissolved coal and mineral matter is filtered out, and the filter cake is washed with solvent and vacuum dried. The coal solution is pressurized to 210 bar, heated to 420-440 deg. C and hydrocracked in two reactors arranged in series with hydrogen injection facilities to cool the reactants. Liquids leaving the hydrocracker are fractionated to give three main liquid products, in the ranges :
- C5 - 250 deg. C (light distillate)
- 250 deg. C - 450 deg. C (basis for recycle solvent)
- pitch (nominally + 450 deg. C)
The pitch may be fed to a delayed coker, to provide an analogue of one configuration of a commercial plant, producing coke and additional solvent, light distillate and gases.
The total project is expected to take approximately 13 years to complete, terminating in 1996, at an overall cost of UKL 44 million. The UK Department of Trade and Industry, Ruhrkohle AG, Esso Engineering(Europe) Ltd and Amoco Chemical (UK) Ltd are participating in the project. Participation by other organisations could be accommodated.

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BRITISH COAL CORPORATION (RESEARCH ESTABLISHMENT
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Coal research establishment stoke orchard, cheltenham
GL52 4RZ Gloucester
Vereinigtes Königreich

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