Heat pump integration for total site waste heat recovery

Abstract

Total Site Heat Integration (TSHI) promotes energy recovery between processes to enhance overall energy efficiency of an industrial complex. Various industrial waste heat utilisation technologies have been studied to improve the energy efficiency of energy system. Vapour compression as an open loop heat pump system has good potential to be used to upgrade the waste heat to useful heat in Total Site systems. Vapour compression systems upgrade low grade waste heat by supplying a low quantity of high pressure steam (thermocompressor) or mechanical work (mechanical-compressor) to generate higher pressure steam, as is common with evaporation systems. The vapour compression system recovers the latent heat content of the industrial waste heat, which reduces cooling demand, decreasing the demand for high quality steam and reducing boiler load. This paper introduces an effective Total Site targeting methodology to integrate open cycle heat pump systems, i.e. vapour compression technologies, into an integrated industrial energy system for enhancing overall site energy efficiency. Industrial waste heat and high quality steam demand are able to be reduced simultaneously though this integration. The energy reduction and cost-benefit of thermo-compressor and mechanical-compressor installations are compared through a literature case study. The case study showed a deficit of heat at the MPS and a surplus of heat the LPS, which was identified as a candidate for compression according to the appropriate placement principle for heat pumps. For the case study, a four-stage mechanical vapour compression system and two-stage thermal vapour compression system resulted in an energy cost reductions of 343,859 USD/y and 168,829 USD/y.