A resorption cogeneration cycle for power and refrigeration

Abstract

Heat-driven energy system attracts ever increasing attentions to improve the efficiency of overall energy utilisation by recovering the heat energy such as solar thermal energy, wasted heat from industry and geothermal energy. Adsorption technology is recognised as one of the promising solutions to convert low-grade heat to refrigeration or be used as heat pump. Based on the working principle of this technology, it can promisingly be developed into combined refrigeration and power generation system by integrating an expander in to the system. However, due to the limited research efforts on the system investigation, refrigeration generation by adsorption technology is still immature. The investigation on the working conditions of the system, the selection of proper expansion machine for power generation part of the cogeneration and overall system evaluation are important to be conducted. This study aims to explore the feasibility of integration the adsorption technology with expansion machine for refrigeration and power generation. The proposed cogeneration combines resorption system, which has potentially twice of the cooling capacity compared with conventional adsorption system, integrated with expansion machine to continuously produce refrigeration and power. The design and optimisation methods of the proposed system were studied in order to select the proper resorption working pairs under different heat source conditions. Furthermore, the system performance with and without the optimisation methods were evaluated by the first and second law analysis. Results indicated attractive performance and MnCl2-SrCl2 was stood out as the optimal resorption working pair for the purpose of high refrigeration generation under low grade heat source, when ammonia is the working fluid in the system.Scroll expander was selected as the expander to be explored in this study because of its highest average isentropic efficiency, low cost, low vibration noise, high availability and easy modification from compressor to expander for our special application demand. A lab scale scroll expander test rig was designed, constructed and tested to obtain the performance such as isentropic efficiency and electrical efficiency of a selected scroll machine under various working conditions. An assessment of a case study of the resorption cogeneration system was conducted to evaluate the variation of the power and refrigeration performance with the time. Results indicated that a resorption cogeneration with 25.2 kg MnCl2 and 18.9 kg SrCl2 could potentially produce 1 kW power and 2.5 kW cooling capacity when the cycle time is around 25 minutes.