Organic Rankine cycle thermal architecture – From concept to demonstration

Waste heat to power conversion is expected to play a key role in reducing CO2 emissions in the mid-to-large scale internal combustion engines. The realisation of cost-effective deployment of Organic Rankine Cycles (ORC) is shown to be hindered by several key factors, including, disconnect between parameters considered in simulation studies to those demonstrated experimentally, utilisation of low-grade ORC practice for high-grade applications, challenges in integrating multiple heat recovery sources etc. To address such challenges, a programme of ‘concept-to-demonstration’ is in progress at the University of Brighton, with the presented focus here being on the thermal architecture.This paper describes some of the important features of a new experimental ORC test-rig that may contribute towards increased overall conversion efficiencies. These features include, firstly, a variable heat source setup, allowing the potential to replicate a wide range of realistic gaseous sources. Secondly, the direct utilisation of the High-Temperature (HT) exhaust gases, which is expected to lower the specific evaporator exergy cost by 22%. Thirdly, deployment of HT water blends, this is estimated to increase the potential of overall conversion efficiency by 2.4 times. Fourthly, a flexible thermal platform, offering multiple and efficient heat utilisation, with a holistic approach to NOx reduction, downsizing and exhaust heat recovery. Finally, advanced process conditions (e.g. 29.3 bar, 270.9 °C), which corresponds to the near-optimal region, and offers the possibility of a 12.5% conversion rate of heat recovered to expansion power. The potential benefits are quantified using a combination of published literature, procurement findings, simulation results (Aspen HYSYS) and preliminary experimental measurements (NI LabVIEW). The paper concludes with the rational for the next intended research effort, i.e. high-pressure ratio and two-phase expansion machines