CHEMICAL ENGINEERING TRANSACTIONS VOL. 57, 2017 A publication of The Italian Association of Chemical Engineering Online at www.aidic.it/cet Guest Editors: Sauro Pierucci, Jiří Jaromír Klemeš, Laura Piazza, Serafim Bakalis Copyright © 2017, AIDIC Servizi S.r.l. ISBN 978-88-95608- 48-8; ISSN 2283-9216 Model-based Analysis of Novel Heat Engines for Low- Temperature Heat Conversion Torben Knoke a , Eugeny Y. Kenig* a , Alexander Kronberg b , Maxim Glushenkov b a Paderborn University, Chair of Fluid Process Engineering, Pohlweg 55, 33098 Paderborn, Germany b Encontech B.V., P.O. Box 217, 7500 AE Enschede, The Netherlands eugeny.kenig@upb.de To overcome the lack of economic technologies for conversion of low-grade heat into power, Dutch company Encontech B.V. has recently suggested a novel-type external combustion engine. This Encontech Engine utilizing dense working fluids promises effective energy conversion and large power density at low specific cost. In the study presented in this paper, a simplified thermodynamic model has been developed and applied to identify optimal working conditions and suitable working fluids for the Encontech Engine. Although the utilization of dense working fluids promises several advantages over gas-phase heat engines (e.g., Stirling engine), efficient regeneration is a difficult task. For this reason, approaches to combine the benefits of dense working fluids with enhanced regeneration have been investigated. 1. Introduction A recent study by Forman et. al. (2016) has shown that around 73 % of the globally converted energy is lost during the transition into the final energy service. Roughly two-thirds of these losses is waste heat. Pinch analysis methods have found wide application in industries and contributed to remarkable improvements in process efficiency by smart linkage between heat sources and sinks within individual processes, plants or entire production sites (Semkov et. al., 2014). However, large portions of energy still remain unutilized. Approximately 42 % of the global industrial waste heat arises at temperatures below 100 °C (Forman et. al., 2016), for which only minor demand exists in many industrial production processes. If utilized at all, low- temperature heat is used for heating of facilities, heat upgrading (heat pumps) or production of cold (absorption refrigerators). Conversion of low-grade waste heat into power is usually not considered due to lacking economic conversion technologies. Organic Rankine Cycles (ORC) constitute the most proven and industrially applied technology to convert low-temperature heat into power. They are considered to be the most efficient and economic technology in temperature ranges of 200-400 °C (De Pascale and Bianchi, 2011), but they have high specific costs of 2,000-4,000 €/kW at lower temperatures (Heberle and Brüggemann, 2015). The Kalina cycle, a variation of the classical ORC utilizing water-ammonia mixtures, is a promising alternative for very low temperature sources. However, studies indicate that the promised benefits of Kalina cycles appear over-estimated, while this process is much more complex and maintenance-demanding than classical ORC processes (Goswami et. al., 2010) Alternative technologies, such as piezo-electric (Hendricks and Choate, 2006) or thermo-electric conversion concepts (Snyder, 2009), are still in the early stages of development and highly cost-intensive. Encontech BV, a spin-off company of Twente University, has recently suggested a novel-type externally heated engine (Glushenkov and Kronberg, 2012). This device, combining the advantages of the technically interesting but mainly forgotten concepts of the ‘thermocompressor’ (Bush, 1939) and the ‘tidal regenerator engine’ (Hagen et. al., 1976) with additional features (e.g., a self-driven displacer, a hydraulic load and application of several dense working fluids), promises high power density and energy efficiency at low specific cost. The Encontech Engine is hence particularly attractive for conversion of low-temperature heat into power (Kronberg et. al., 2016). DOI: 10.3303/CET1757084 Please cite this article as: Knoke T., Kenig E.Y., Kronberg A., Glushenkov M., 2017, Model-based analysis of novel heat engines for low- temperature heat conversion, Chemical Engineering Transactions, 57, 499-504 DOI: 10.3303/CET1757084 499