Studies on a Solar Assisted, CO2 Based Trigeneration System for Milk Processing: Performance Comparison between Throttle Valve and Ejector Expansion Valve

Abstract

19 doi: 10.18178/jocet.2019.7.2.504  Abstract—In this study, a transcritical CO2 based solar assisted trigeneration system for a dairy farm is analyzed. Performance comparison is made between an ejector based system (C1) and a conventional throttle valve based system (C2). A mathematical model of the system operating under steady state conditions is developed in Engineering Equation Solver (EES). The results are presented based on the consideration that the evaporator load for chilling of milk exactly matches with heating load in the process heat exchanger for pasteurization of milk. A parabolic trough collector is assumed to be used to heat the working fluid and an auxiliary heater is used to supplement the solar heat. The operating parameters are adjusted in such a manner that net power produced is always positive. The effects of turbine inlet temperature, ambient temperature, turbine inlet pressure and process heat exchanger pressure on overall COP, cooling COP and power cycle efficiency are analyzed. It is observed that compressor power input required in C1 configuration is about 45% lower than that required in C2 configuration. Increase in turbine inlet temperature marginally affects the power cycle efficiency for both the configurations. Cooling COP reduces significantly with increase in ambient temperature for both the configurations. This study provides a basis for the feasibility of trigeneration systems in dairy application where simultaneous heating and cooling are required in addition to small amount of electricity for parasitic loads such as lights, fans etc.