Utilisation of waste heat from the power plant by use of the ORC aided with bleed steam and extra source of heat

Abstract

Utilization of waste heat recovered from the exhaust gases of the power generation unit by means of ORC (organic Rankine cycles) installation is considered. The waste heat is available in the form of a stream of hot water having temperature of 90 °C in the amount of 200 MWt. To increase evaporation temperature of ORC working fluid the heat of steam from the extraction points from the low-pressure part of steam turbine is used. Subsequently additional heat from compressor cooling of the carbon dioxide capture and storage installation is also considered as a way to provide extra heat to the ORC. Thermodynamic analysis of the supercritical plant with and without incorporation of ORC was accomplished using a commercial code Aspen Plus. For ORC considered were four working fluids such as n-pentane, ethanol, R236ea and R245fa. Determined were major parameter describing the operational features of the hybrid power plant such as the change of the unit power, efficiency and increase of electricity production of the hybrid installation consisting of the reference plant and the ORC. The highest thermal efficiency of the ORC is obtained in the case ethanol as working fluid, whereas the highest amount of electricity is produced in the case of R236ea.