A New Vapor Absorption Heat Transformer With Improved Performances

Among the different systems currently adopted for the recuperation of waste heat, absorption plants are considered to be the most competitive because they ensure important savings in primary energy. Although sizeable quantites of waste heat may be extracted from different thermal processes, they may not always possess the necessary temperature level for the industrial utilization. Under these conditions, we can use the vapor absorption heat transformers (VAHT) for producing heat at elevated temperatures by uprading the heat available from a lower temperature sensibile heat source. Convetional one-stage VAHT cannot produce temperatures above a certain value. To obtain high heat delivery temperatures, Wilkinson proposed a two-stage VAHT. The paper presents another similar two-stage plant which may be used to produce very high temperatures of heat flux delivered by the absorber. Our VAHT with water-lithium bromide operates at three pressure levels. Heat is rejected at the low-pressure condenser to the ambient. Heat is supplied at the low-pressure generator and the mediupressure evaporator. Heat released by the medium-pressure absorber is received at the high-pressure evaporator. The useful heat is delivered at the high-pressure absorber. The paper presents the calculation procedure with an original theoretical approach. We proposed some evaluation criteria of these VAHT: the heat pumping index, the heat recovery capacity, the coefficient of performance and the exergetic efficiency. A comparative study of different VAHT types shows that the proposed system ensures even better performances, than the similar plant invented by Wilkinson.