Investigation on heat recovery strategies from low temperature food processing plants: Energy analysis and system comparison

Industrial food processing plants often have significant thermal requirements at both low and high temperatures. These plants can produce a variety of products including frozen, chilled and grilled/steamed foodstuff, creating thermal demands at several temperature levels. Rapid freezing of the foodstuff at temperatures below -40 °C is required to preserve a high-quality product while steaming/grilling of foodstuff require heat above 100 °C. Heat recovery from the low-temperature refrigeration system provides an interesting opportunity to reduce the overall energy consumption of the plant. This paper presents different strategies to achieve heat recovery from a CO2/NH3 cascade refrigeration system. The low stage of the cascade features pump-circulated CO2 circuits at -40 °C and -5 °C evaporation levels, while the high temperature stage consists of an ammonia circuit. For this investigation, a case is defined based on requirements for temperature level and heat quantity from the industry. Subsequently, different strategies for the integration and control of the energy systems are examined. Finally, the strategies are compared with selected key parameters and the results are presented.