Waste heat harvesting from continuous blowdown for power generation via organic Rankine cycle network: Case study of a coal-fired power plant

Abstract

This paper proposed a method of waste heat harvesting from 1.3 kg/s continuous blowdown at 354.67 °C from a 300 MW coal-fired power plant for generating electrical power by organic Rankine cycle (ORC) networks in series and parallel connections. The suitable ORC working fluid that gave highest cycle efficiency at various ranges of ORC evaporating temperatures was determined from R114, R236ea, R236fa, and R245fa by Figure of Merit (FOM) approach, and R245fa was selected. In this paper, a new method to get highest single ORC capacity related to the blowdown mass flow rate and its temperature with a correlation among these parameters was also presented. From the correlation, the ORC networks in series and parallel connections with the ORC capacities to recover the waste heat for generating electricity were selected. The ORC networks of 200/5 kW in series and 110/110 kW in parallel connections were selected and the units gave second law efficiencies of 28.50 and 30.58 % compared with 27.80 % of the single 200 kW ORC. The economic analysis revealed that the 110/110 kW network with parallel connection showed lowest, levelized cost of electricity which was 0.038 USD/kWh compared with 0.040 and 0.043 USD/kWh for single 200 kW ORC and 200/5 kW ORC in series connection, respectively.

Keywords

• Organic Rankine cycle network
• Power generation
• Electricity unit cost
• Waste heat recovery
• Boiler blowdown