HEAT EXCHANGE METHOD AND APPARATUS

Abstract: There is disclosed a method and apparatus for exchanging heat between a first fluid and a second fluid immiscible with said first fluid comprising the step of presenting one of said fluids in finely divided form for direct contact with the others. One fluid may be a molten metal which is sprayed or bubbled through the other.

Description: This invention concerns a method of heat exchange, particularly, though by no means exclusively, adapted for use in effluent treatment, and apparatus for effecting same. Clearly for the transfer of a given quantity of heat in unit time the area of the heat exchange surface and the temperature differential may vary inversely. The present invention is based upon an appreciation of the possibility of providing a heat exchange surface resistant to fouling and greatly larger than normally attainable with conventional heat exchange technology. According to one aspect of the present invention there is provided a method of exchanging heat between a first fluid and a second fluid immiscible with said first fluid comprising the step of presenting one of said fluids in finely divided form for direct contact with the other. The one fluid be comprised by molten metal. The molten metal may be sprayed into, bubbled through or otherwise mixed with the other, or the other may be sprayed into bubbled through or otherwise mixed with the metal. There has long been concern about water use and effluent disposal in the textile finishing industry. This arises from the costs of each item and increasingly stringent discharge conditions such that many plants already have to undertake a degree of effluent treatment.The treated effluent is not always suitable for reuse even after expensive tertiary chemical treatment, and its discharge is usually accompanied by significant heat loss. At present, for a typical finishing works, water costs between £5,000 and £39,000 per year, depending on source; effluent disposal costs between £23,000 and £3l,000 per year, and the heat in the effluent is equivalent to about £70,000 per year in fuel oil costs. Therefore the total cost of water and its disposal lies between £98,000 and £l40,000 per year. For the finishing sector in the United Kingdom as a whole this becomes about £20 million per year. Effluent treatment by distillation using a mechanical vapour recompression system does not seem to have been practised presumably on account of the need for low temperature differentials and consequently inconveniently large heat exchange surfaces in order to attain acceptably low process costs. Fouling of the heat exchange surfaces would be another problem. It is believed that the heat exchange method proposed by the present invention will provide a solution to this problem enabling cost effective effluent treatment enabling repeated use of process water in the textile finishing and other industries. The invention will be further apparent from the following description with reference to the single figure of the accompanying drawing which shows, by way of example only, and in diagrammatic form one form of effluent treatment plant utilising the heat exchange method proposed by the invention. Referring now to the drawing, it will be seen that the plant comprises an evaporator vessel l0 and condenser ll. Effluent to be treated enters the plant through line l2 and is heated by heat exchange with the outflowing treated effluent in line l3 by passage through a heat exchanger l4 of conventional kind and by a preheater l4a. The heated effluent enters the evaporater l0 and is vapourised by direct contact heat exchange with molten metal which is sprayed into the evaporater l0 in the form of fine droplets presenting a large surface area from a spray-head l5. A preferred metal is Wood's metal, an alloy of bismuth, cadmium, tin and lead which is relatively inert and liquid at temperatures above 7l°C. The metal sinks through the effluent and collects the bottom of the evaporater l0 leaving contaminants floating thereon for harvesting by a mechanical scraper arrangement generally indicated at l6. The vapour generated in the evaporater l0 is compressed by vapour compressor l7 and passed through line l8 to the condenser ll. The cooled but still liquid metal flows by gravity through line l9 into the base of condenser ll, there to be reheated by heat exchange with the compressed vapour which is bubbled therethrough from a diffuser head 20. The condensed vapour forming water of high purity is led away through line l3 via heat exchanger l4. Uncondensed vapour or flash steam is collected in line 2l from the top of condenser ll condensed in the inflowing effluent and returned to the evaporater l0 by means of a flash steam recovery unit 22 such as a sparge pipe. Molten metal is pumped by pump 23 from the condenser ll through line 24 to the spray-head l5. The effluent might be chemically treated if necessary to prevent the metal from being dissolved. It will be appreciated that it is not intended to limit the invention to the above example only, many variations, such as might readily occur to one skilled in the art, being possible, without departing from the scope thereof. Other metal alloys may be used such as Cerrotru alloy which whilst having a higher melting point does not include highly toxic heavy metals. The compressor drive is advantageously a gas engine with heat recovery from coolant to the effluent preheater. Stirrers and or baffles may be provided in the evaporator and condenser to increase contact times between the two fluids.

Claims: 1. A method of exchanging heat between a first fluid and a second fluid immiscible with said first fluid comprising the step of presenting one of said fluids in finely divided form for direct contact with the other. 2. A method according to claim l wherein said one of said fluids is sprayed into the other. 3. A method according to claim l wherein said one of said fluids is bubbled through the other. 4. A method according to any preceding claim wherein one of said fluids is molten metal. 5. A method according to claim 4 wherein said metal is Wood's metal. 6. A method according to claim 4 wherein said metal is Cerrotru alloy. 7. Apparatus for exchanging heat between a first fluid and a second fluid immiscible with said first fluid comprising means for presenting one of said fluids in finely divided form for direct contact with the other. 8. Apparatus according to claim 7 wherein said means comprises a head for spraying said one of said fluids into a vessel containing the other. 9. Apparatus according to claim 7 wherein said means comprises a diffuser head for bubbling said one of said fluids into a vessel containing the other. l0. Apparatus according to any one of claims 7-9 wherein said one of said fluids is molten metal. 11. Apparatus according to claim l0 wherein said metal is Wood's metal. 12. Apparatus according to claim l0 wherein said metal is Cerrotru alloy. 13. Apparatus according to claim 7 for the treatment of effluent comprising an evaporator and a condensor, means for introducing the effluent to be treated into the evaporator, a head for spraying molten metal through the effluent in the evaporator to effect evaporation thereof, means for transferring the cooled but still molten metal from the evaporator to the condensor, means for compressing vapour from the evaporator and diffusing it through molten metal in the condenser to cause condensation thereof and reheating of the metal, and means for pumping metal from the condenser to the spray head in the evaporator.

Inventors: REED, COLIN MICHAEL
Applicants: SHIRLEY INSTITUTE
Application year: 1986
Main classification: F28C3
IPC codes: F28C3, F22B1, D06B23, C02F1