Energy and exergy analysis of a two-stage cascade refrigeration system

Abstract

A noble integration of a cascade refrigeration system with a two-stage compression chiller is proposed. The compression and the absorption systems have a cascade inter-cooler/evaporator, and the compression system has two compressors working in series. The compressors can be either reciprocating or screw type. This system runs by a driving unit which can be a micro-turbine or a solid oxide fuel cell. The system components are modeled and analyzed through the energy and exergy approaches. The performance parameters of the systems and the second law efficiency are calculated in different operating conditions. The results show that the maximum irreversibilities happen in the generator and the first-stage compressor, and the total destruction is higher when a micro-gas turbine is used as the prime mover. It appears that by using reciprocating compressors, energy and exergy are consumed up to 260% and 188% more efficiently in the proposed system compared to a traditional single-stage compression refrigeration system. The two latter parameters would be 53.7% and 29.2% in case of using screw compressors.

Practical application: So much of our lives rely on refrigeration, from the food that we eat to the transportation and processing of vital resources. Industrial refrigeration systems such as gas compression, oil and gas processing, petrochemicals, power generation, carbon capture and food processing and storage are dependent on low-temperature refrigeration systems. Multi-stage refrigeration cycle is a conventional approach to provide low temperature for industrial processes. The proposed cascade system can reduce the energy consumption of a two-stage refrigeration system, using the waste heat from an industrial process. The first and second law analysis of the proposed system approves the upgrade in energy and exergy efficiencies of this system.