Low temp. evapn. by heat pump - incorporating heat transfer from condenser to evaporator by compressor with expansion valve maintaining pressure difference

摘要

A plant for evapn. at low temp., partic. for concentrating solns. which are sensitive to temp. e.g. pharmaceutical and food prods., comprises two heat exchangers and a heat pump. The first exchanger is for the evapn. of the soln. being processed. The second is for the condensn. of the vapour sepd. from the soln. The heat pump consists of a compressor and an expansion valve. The compressor takes in a heat transfer fluid which has passed through the condenser and forces it through the evaporator. The expansion valve maintains a fixed pressure difference over the circuit returning the heat transfer fluid from the evaporator to the condenser. The heat transfer fluid is any refrigerating fluid, e.g. ammonia or dichlorfluormethane. The plant consumes less energy than existing plants in which the condenser water is sub-cooled by a refrigerating machine or in which the vapour is recompressed by a jet system. Only electrical energy is required so that expenditure on installating a boiler is avoided. The cost of energy is low, 50-100 kWh. per tonne of water evaporated, four to ten times lower than that of a conventional evaporator operating at the same temp.