Thermodynamic analysis on the effect of supercritical CO2 ejector in cogeneration cycle for dairy application

Dairy plants are energy-intensive due to the combined loads of milk pasteurization (heating), chilling (cooling), and the demand for various supplementary equipment, making the cogeneration cycle suitable. Solar based cogeneration cycle with CO2 as a working fluid is eco-friendly and has a small real estate footprint. Ejectors are passive devices providing compression by energy exchange between coflowing fluid streams with the potential to reduce overall energy consumption. A new CO2 cogeneration circuit that better utilizes thermal energy is first proposed. Thereafter, further improvements are made by adding a supercritical CO2 (s-CO2) ejector. A comprehensive thermodynamic analysis of both cogeneration systems is carried out. Substantial real gas effects and thermodynamic property variations of CO2 render the system intractable for analytical solutions requiring numerical iterative solutions, where the algorithms use REFPROP 9.0 coupled with MATLAB 2019a. The per-formance maps of the proposed cycles due to variations in gas cooler pressure, ejector primary pressure, ejector secondary pressure, turbine inlet temperature, turbine inlet pressure and turbine discharge pressure are elabo-rated. The system operating parameters are constrained to produce a net positive power output. The new cogeneration circuit adds a recuperator in the power cycle for dairy applications improving the circuit perfor-mance. However, exergy losses due to throttling and recuperation prevailed in the system, impeding further COP improvement. The implementation of an s-CO2 ejector reduces throttling and recuperation exergy losses, consequently improving the system COP by a maximum of 35%. Additionally, the milk handling capacity of the ejector based system increases by 20%.