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Content archived on 2019-03-15

THE EVAPORATION OF VISCOSE PROCESS LIQUORS BY LOW ENERGY MEANS

Objective



THE RESEARCH STUDY AIMS AT ACHIEVING AN ALTERNATIVE MEANS OF EVAPORATING WATER FROM VISCOSE PROCESS LIQUORS (USED FOR VISCOSE FIBRE PRODUCTION), IN ORDER TO CONSIDERABLY REDUCE THE ENERGY REQUIREMENT OF THE OPERATION. IN ORDER TO ACHIEVE THIS, COURTAULDS DEVELOPED A HEAT EXCHANGER CONSISTING OF THIN WALLED PLASTIC TUBES. THE LIQUOR IS EVAPORATED UNDER VACUUM FROM A FALLING FILM ON THE OUTSIDE OF THE TUBES. THIS VAPOUR IS THEN BROUGHT INSIDE THE TUBES VIA DEMISTERS, SCRUBBERS AND A COMPRESSOR (MECHANICAL VAPOUR RECOMPRESSION), WHERE IT CONDENSES AND SUPPLIES THE CONDENSATION HEAT FOR THE EVAPORATION OF THE LIQUOR FILM OUTSIDE THE TUBES. IN 1980 IT WAS CALCULATED THAT IF THIS WORK WAS TO BE SUCCESSFUL AND THE RESULTING TECHNOLOGY SHOULD BE APPLIED TO 50 % OF THE VISCOSE PRODUCTION IN THE EEC (APART FROM COURTAULDS) THE ENERGY SAVING WOULD BE AROUND 0.5 X 10EXP5 TOE/YEAR.

LABORATORY INVESTIGATIONS HAVE BEEN UNDERTAKEN TO DETERMINE THE PHYSICAL PROPERTIES OF THE VISCOSE LIQUORS INVOLVED, AND DATA ON VISCOSITIES, SPECIFIC GRAVITIES, BOILING POINT ELEVATIONS, THERMAL CONDUCTIVITIES AND SPECIFIC HEATS HAVE BEEN GATHERED. AN EXAMINATION OF THE PROPERTIES OF PLASTIC HEAT EXCHANGER TUBES HAS BEEN EXECUTED, WITH PARTICULAR EMPHASIS ON SHORT AND LONG TERM MECHANICAL STABILITY, RESISTANCE TO FOULING AND WETTABILITY.

A BENCH SCALE MECHANICAL VAPOUR RECOMPRESSION EVAPORATOR HAS BEEN CONSTRUCTED; HEAT TRANSFER COEFFICIENTS OF 800-1000 W/M2 DEGREE K ACROSS THE TUBE BUNDLE HAVE BEEN OBTAINED WITH THE VISCOSE LIQUORS.

A RESEARCH PLANT TO EVAPORATE 100 - 150 KG/HR WATER HAS BEEN DESIGNED AND CONSTRUCTED. THE DETAILED MECHANICAL DESIGN HAS PRODUCED A NUMBER OF INTERESTING ENGINEERING CHALLENGES, PARTICULARLY WITH REGARD TO THE COMPRESSOR, THE CONCRETE VACUUM VESSEL WITH ITS CORROSION RESISTANT LINING AND THE POLYETHYLENE TUBE BUNDLE (1344 TUBES WITH WALL THICKNESS IN THE RANGE 0.13 - 0.20 MM AND A DIAMETER OF ABOUT 17 MM). HEAT TRANSFER COEFFICIENTS OF UP TO 550 W/M2K WERE MEASURED ON THIS RESEARCH PLANT. RELATIVELY LOW COMPRESSION RATIOS UP TO 1.4 WERE USED SO THAT A HIGH THERMODYNAMIC EFFICIENCY WAS ACHIEVED LEADING TO A LOW SPECIFIC ENERGY CONSUMPTION. AN OPTIMUM DESIGN FOR A 5O T/HR COMMERCIAL UNIT HAS BEEN CALCULATED TO GIVE A PAYBACK PERIOD OF AROUND 1.2 YEARS. THIS IS VERY ATTRACTIVE AND COURTAULDS INTENDS TO CONSTRUCT A DEMONSTRATION PLANT.

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Coordinator

Courtaulds Ltd
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Address
345 Foleshill Road
CV6 5AE Coventry
United Kingdom

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