Development of a 200-kW Organic Rankine Cycle Power System for Low-Grade Waste Heat Recovery

Abstract

In this study, we designed a new plate-type heat exchanger system for the previous shell-and-tube evaporator with the same heat rate and additional turbine safety measure. The new evaporator system consists of two plate heat exchangers; one for preheating and the other for subsequent evaporation and superheating. The separate design reduces the liquid level of the evaporator and lowers the risk of liquid inflow into the turbine. For an additional driving stability, a co-current flow configuration was used for the preheater so that a subcooled liquid is introduced to the evaporator instead of a liquid-vapor mixture. A detailed design of the plate heat exchangers was carried out using a commercial software. The new heat exchangers are 75% smaller in volume and 83% smaller in weight. The designed heat exchangers were manufactured and installed in the previous ORC system. The performance was evaluated using an electric heater and a cooling tower as a heat source and heat sink. For the test, the working fluid pump was operated at the design point turbine inlet pressure of 2.13 MPa. Meanwhile, the condensation conditions were not matched to the design point due to the weather effect. Under the analysis condition, the new evaporator system showed an evaporator heat rate of 1662 kW, which is 91% of the design value with a pressure loss of 46 kPa. We calculated a pressure loss of 62.8 kPa for the design point using an equation for simple friction loss. The results showed that our new evaporator system successfully replaced the previous one without big performance losses.