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.