AbSorbEnt - Development of a new generation of sorbents and optimisation of the absorption heat pump cycle

In absorption heat pumps, a so-called "thermal compressor" is used to overcome the pressure difference between evaporation and condensation pressure, in which a "thermal power process" takes place. In this, the refrigerant (e. g. water) is present absorbed in a liquid solution (e. g. aqueous lithium bromide solution) while overcoming the pressure difference. As a result, absorption heat pumps require negligible electrical power to operate a solution pump and allow very large temperature lifts between the heat source and sink. The "thermal compressor" is thereby largely "driven" with exergy in the form of heat far above the useful temperature. As a result, absorption heat pumps enable the utilization of "low-grade" energy such as waste heat from industrial processes and, due to high thermal efficiencies, are essential to increase the overall energy efficiency of thermal plants and processes. However, especially at high drive temperatures, the use of lithium bromide can lead to performance reductions and operating problems, as well as irreparable plant damage due to crystallization and corrosion including the associated formation of inert gases. For this reason, absorption heat pumps are usually used only rarely, or with high maintenance costs, in high-temperature applications (sink temperatures above 100 °C). In the course of this project, possible alternative absorbents based on ionic liquids and deep eutectic solvents to replace lithium bromide are developed, analyzed and evaluated with respect to their sorption and material properties. Based on the results, the most promising absorbent will be selected. In addition, a high-temperature absorption heat pump functional model, for operation with the alternative absorbent, will be developed using simulation. To determine the operating characteristics of the functional model, it will be integrated into a test rig and experimentally measured (drive temperatures up to about 200 °C and sink temperatures of at least 100 °C). Based on the obtained data, the applied methods, the potential of the newly developed absorbent as well as the high-temperature absorption heat pump will be evaluated by ecological and economic analyses. Finally, the improvements compared to H2O/LiBr absorption heat pumps will be quantified.