Waste Heat Driven Thermochemical Heat Transformation based on a Salt Hydrate

Kurzfassung

In the course of efforts to reduce primary energy consumption in chemical process industries, recovery of low enthalpy energy sources such as low temperature waste heat has come into the focus of interest. However, there is no heat pump commercially available yet that offers an output temperature of more than 140 °C, which is a minimum temperature required for many industrial applications. In this regard, thermochemical heat transformation based on gas-solid reactions can be used to generate a high temperature heat pump-like effect. The reversible reaction of strontium bromide with water vapor is proposed in this work for thermochemical heat transformation: SrBr2(s) + H2O(g) ⇌ SrBr2 x H2O(s) + ΔRH. Driven by 90 °C waste heat, this chemical reaction offers the possibility to “lift” process heat flows to a higher temperature level in the range of 180 °C to 230 °C. By variation of the partial pressure of water vapor, the equilibrium temperatures of the both the hydration and dehydration reaction can be controlled. Consequently, it is possible to conduct the exothermic reaction at a higher temperature than the endothermic reaction. Process heat which is stored in the form of chemical potential during the dehydration reaction can afterwards be recovered at a higher temperature during the hydration reaction. In the proposed process, water vapor supply is covered by low temperature waste heat. The resulting thermal upgrade of process heat allows to cut down on additional heating and thus leads to a reduced consumption of primary energy resources. The oral contribution will outline the thermodynamic principle of thermally driven heat transformation and its main difference to conventional heat pumps. In addition, the potential of the reactant couple SrBr2/H2O will be discussed based on experimental results from a lab-scale reactor setup.