Performance testing of CO2-NH3 cascade freezer for seafood processing

Abstract

Most of India’s seafood sector relies on ammonia refrigerant for fish processing. However, due to safety concerns these natural refrigerants are being replaced by synthetic refrigerants in some regions. Carbon dioxide is becoming an alternative refrigerant for deep-freezing applications. For high ambient temperature climate, ammonia cannot be excluded, but low-charge ammonia which is confined to the condenser side can be used in a CO2-NH3 cascade refrigeration system. There is a lack of experimental studies in the fish processing sector, therefore in this study, a 350 kW CO2-NH3 cascade freezer installed in a fish processing factory in Kochi, India is investigated. The NH3 circuit condenses CO2 at -10 °C in gravity flooded plate heat exchanger and the throttled -42 °C CO2 is pumped to five flooded evaporators at a feed rate of 2.5. Higher COP was achieved for -40 °C and below evaporating temperature compared to the previously installed two-stage ammonia refrigeration systems.