Comparative Exergy Analysis and Environmental Impact of a Dairy Plant Integrated with a Transcritical Heat Pump System: A Feasibility of Throttle Valve, Expander, and an Ejector as Expansion Devices.

The present investigation aims to reuse the heat rejected in the condenser unit of an NH3-based dairy plant to preheat the groundwater used for pasteurization of milk. A detailed thermodynamic analysis (both energetic and exergetic) of the refrigeration unit of an existing dairy plant and the boiler unit used for pasteurization is carried out in the current work. The chemical exergy of the air–water vapour mixture and the standard Indian coal is considered while analysing the evaporative condenser and the boiler unit. Cascading of the existing system with a transcritical vapour compression cycle is proposed to effectively use the heat rejected by the combined system to preheat the boiler feed water. A comparative study for different modifications, such as the inclusion of an expander and an ejector in place of the throttle valve in the top cycle of the proposed cascade system, is carried out. Additionally, the cascade systems are being analysed for two different refrigerants, i.e., CO2 and N2O. The study demonstrates that the cascade system with an expander employing N2O as the refrigerant gives the maximum benefit in terms of saving of $16.5 to $21.5 per day, 1.5 to 2% reduction in total CO2 emission, and a 2.5% reduction in total exergy destruction, as compared to the existing NH3 system. [ABSTRACT FROM AUTHOR]