Optimization of the utilization of different industrial waste heat streams via high temperature heat pumps
The utilization of industrial waste heat for process or district heat supply is key for a sustainable energy supply. The potential of industrial waste heat is high, and the temperature levels are beneficial to achieve high Coefficient Of Performances (COP). However, those waste heat streams are mostly sensible and not latent. To use their full potential of usable heat, those heat fluxes have to be cooled down to ambient temperature levels within the heat pump. This paper shows a new methodology for reference COP evaluation to assess the full potential of usable sensible waste heat sources cooling it down to ambient temperature level, because neither the Carnot or the Lorenz or the Adler/Zotter/Längauer cycle are suitable for this. In order to achieve highest heat output at the maximum of sensible waste heat streams utilization, two new reference cycles and COP assessments are introduced. The LZ reference cycle must be used for sensible waste heat utilization supplying sensible heat sinks (e.g. hot pressurized water) and the CZ for sensible waste heat utilization supplying latent heat sinks (e.g. steam). For a heat pump supplying steam at 150 °C from a sensible heat source at 90 °C, different reference COPs lead to significantly different performance indicators (COP_Carnot = 4.7, COP_Lorenz = 4.3, COP_AZL = 5.6). However, when sensible waste heat is to be fully utilized, the entire available heat flow must be cooled down to near ambient temperature. In this case, cooling the source from 90 °C to 0 °C instead of 60 °C allows approximately three times more waste heat to be recovered, but limits the achievable efficiency to a maximum COP of about 4.4 based on the CZ efficiency using the full waste heat potential. The effects of different theoretical heat pump cycles on possible COPs and their potential for industrial hightemperature heat pump applications are described in detail.