ABSORPH

Development of High-Temperature Resorption Heat Pumps with Natural Refrigerants for Industrial Applications

In many industrial plants a large amount of waste heat between 40 to 50ºC is available due to various industrial operations. An interesting solution for many of these plants in which there is a heat demand at temperatures up 90-140ºC, is to increase the thermal level of this waste heat using a heat pump for further use.

Currently, most industrial heat pumps supply heat between 50 and 90 ° C. This temperature limit is restricted by the thermodynamic behavior of the working fluids and the limitations of commercially available components, such as the temperature and pressure in the compressor discharge.

A very interesting option are resorption heat pumps using a zeotropic mixture (refrigerant/ absorbent) and a solution circuit between a desorber and resorber, instead of the conventional evaporator and condenser. As the evaporation in de desorber of the zeotropic mixture is not complete, besides the vapor stream is generated a residual solution stream that returns to the resorber in the circuit solution. The main advantage of the resorption cycles involves the best performance due to pressure reduction of the cycle high pressure compared to the case using pure refrigerant, and the improvement of the cycle efficiency due to lower internal and external temperature gradients at the desorber and resorber (Lorentz cycle). Moreover, heat production may be varied by changing the concentration of the circulating solution between the desorber and resorbedor. Of special interest is the case where the resorption heat pump incorporates a compressor able to perform a "wet" compression of the biphasic vapor stream and desorber solution, because in this way the resulting heat pump has the same number and type of components as a conventional compression, that is, two heat exchangers (desorber and resorber), a "wet" compressor and an expansion device.

The main objective of this project is to contribute to the development of resorption/absorption and resorption/compression heat pumps for the recovery of industrial waste heat between 40 and 60ºC and to upgrade its temperature between 90 and 140ºC, and also the simultaneous production of cold and heat using similar temperature lifts (between 50 and 80°C) and natural refrigerants such as CO2 and NH3. For both refrigerants will be identified new absorbents and determined the thermophysical properties of refrigerant / absorbent pairs to be able to evaluate the performance of the resorption cycles and study the resorption and desorption processes.

This project will be the basis for the development of resorption heat pumps with CO2 identifying the absorbents and designing the main components as well as obtaining experimental information based on NH3 equipment to determine the feasibility of this type of heat pumps in high temperature industrial applications.