Chemical heat pump is promising alternatives in waste heat recovery applications. The present paper focuses on the technical and economic feasibility analysis of the Isopropanol-Acetone-Hydrogen Chemical Heat Pump (IAH-CHP) system. A small scale prototype of the IAH-CHP was established. Coefficient of performance (COP), exergy efficiency and entransy efficiency analysis were adopted to evaluate the performance of the IAH-CHP prototype. The stable operation is given with the waste heat temperature of 90℃ and the high-level output temperature of 160℃. The COP, exergy efficiency and entransy efficiency of the system are up to 24.3%, 42.3% and 29.1%, respectively. Moreover, based on the detailed experimental results of the lab-scale apparatus, a 100 kWth model was built to evaluate economic feasibility of the IAH-CHP. The exergy cost and the thermo economic cost based on the structural theory, as well as the payback period were evaluated. The results indicate that the exergy destruction and investment cost of the distillation column is the highest, and the payback period is 5.6 year for the case of the optimal performance. The unit exergy cost of the final exergetic product is 6.56 W/W. The results proved that the IAH-CHP system is efficient in recovering the low-level waste heat.
Conclusions
In this work, we investigated the technical and economic feasibility of the IAH-CHP system. First, a small lab-scale prototype was established. Its performances at the low-level heat source with the temperature of 363 K were evaluated experimentally in terms of the COP, the exergy efficiency and the entransy efficiency. The results of this study and those in literature were also compared. Based on experimental data, a rigorous mathematic model was established to simulate the 100 kWth IAH-CHP system. The economic feasibility of the IAH-CHP system was analyzed in terms of the payback period and the thermo economic costs. The following major conclusions can be drawn.
(1) The optimal thermal performances of the system were obtained when the waste heat temperature of 90℃ and the high-level output temperature of 160℃ were generated. The results showed that the conversion and selectivity of acetone in the exothermic reactor were 34.08% and 100%, respectively and the COP, the exergy efficiency and the entransy efficiency were 24.3%, 42.3% and 29.1%, respectively, at the same condition. In comparison to other studies in literature, the energy performances of our present prototype were technical feasible considering the energy efficiency and cycling durability.
(2) The results of thermo-economic analysis display that the total investment cost of a 100 kWth IAH-CHP system is about 59,674$, and the investment cost of the distillation column is the biggest in the system. The payback period is 5.6 year in the case of the optimal performance. The unit exergy cost and thermo economic cost of the system's final product are 6.56 W/W and 9.94×10-5 $/kJ, respectively. The results prove that the IAH-CHP system is efficient in the viewpoint of economic feasibility.
A 50 kWth pilot-scale plant of the IAH-CHP system is under constructed in our lab. We hope that these works will promote the applications of this type of chemical heat pumps.
The results have been published on Energy 139 (2017) 1030-1039.
Fig.1. The schematic of experimental setup for the IAH-CHP system.
