Hot water storage for increased electricity production with organic Rankine cycle from intermittent residual heat sources in the steel industry

摘要

In energy intensive industries, organic Rankine cycles (ORC) can significantly increase energy efficiency and reduce carbon emissions by converting low- and medium-temperature residual heat to electricity. However, fluctuations in residual heat availability can negatively affect the operation of an ORC unit. By integrating intermediate thermal energy storage (TES) these fluctuations can be mitigated and part-load operation of the ORC unit can be avoided. In this paper, a solution for utilizing residual heat from flue gases fluctuating in both temperature and volume flow rate by means of an ORC is assessed. A TES system in the form of a pressurized hot water storage is modelled with the purpose of providing a steady thermal power and temperature to the ORC system. It is shown that thermal power variations are effectively attenuated by the thermal capacity of the water inside the TES system and thermal power to the ORC can be controlled by varying the mass flow rate to the ORC. Furthermore, a financial analysis including the main techno-economic parameters is presented, giving useful insights about the key factors influencing the feasibility of combined TES-ORC investment.