Exploitation of Low-Grade Heat In Site Utility Systems

The site utility system provides the heating, cooling load along with power production for the processes on the total site. Low-grade heat is available in large amount across the process industry from temperatures of 30^oC to 250^oC as gases (e.g. flue gas) and/or liquids (e.g. cooling water). Various technologies are available for generating, distributing, utilizing and disposing of low grade energy. Low grade heat can be recovered by integration of heat pumps, Organic Rankine cycle, energy recovery from gas turbine exhaust, absorption refrigeration, and boiler feed water heating etc with the total site. It is not straightforward to identify the most appropriate technology along with the optimal design option to be implemented.

In this work the integration of heat pump, absorption refrigeration, absorption heat pump, organic Rankine cycle (ORC) and boiler feed water (BFW) heating to the total site has been studied with the help of a case study. HYSYS models have been developed to estimate the coefficient of performance (COP) of the low grade heat upgrade technologies. Linear correlations are generated to estimate the capital cost of the various design options. It has been shown that the integration of heat pump and absorption heat pump with the total site is not economically viable. However, integration of absorption refrigeration, ORC and BFW heating has shown to reduce the total annual cost for the site utility system.

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