An organic Rankine cycle for two different heat sources: steam and hot water

Abstract

Direct use of a steam heat source for the organic Rankine cycle system is one of the key challenges in various plant industries where low-grade steam is available and is becoming difficult as the parent system has a strong variability. In addition, changing the type of the heat source fluid among steam, hot water, thermal oil and others from the parent plant could increase the operation time of the heat recovery system, which increases system economics and makes it more attractive. Although a variety of ORC systems have been developed mainly using single heat source as hot water heat source or a heat transfer loop. An ORC system with the direct use of a steam heat source has been rarely reported, and a system using two different heat sources have not been reported yet. Here we evaluate the performance characteristics of an ORC system using two different heat source fluids: steam and hot water. The target ORC system was originally developed for the hot water heat source and has a simple cycle configuration with R245fa as working fluid, and is composed of typical four components as: a two-stage radial turbine and a coupled generator, plate-type heat exchangers with a refrigerant tank, and a multi-stage centrifugal pump. The nominal net power output at the design point is 187.9 kW with the turbine expansion ratio of 9.5. The heat exchanger analysis showed that the steam heat source can be applied to this system. The isothermal heat exchange and high heat transfer coefficient at the two-phase region of the steam showed a large overdesign for the current application. We tested the ORC system using a steam generated from an incineration plant. The temperature and pressure of the steam were 143.5℃ and 302 kPa. We showed that the ORC system originally developed for the hot water heat source could be used for the steam heat source without any major system changes.