Recoverability of the waste heat of a biogas fulled combined heat and power (CHP) engine by using simple and regenerative organic rankine cycle (ORC) designs, energy and exergy analysis

Renewable energy sources are an important alternative to rapidly consuming fossil fuels. There are many renewable energy sources such as solar, wind, hydrogen, biogas. Biogas, one of the most important renewable energy sources, is often used as fuel in combined heat and power engines (CHP) and is converted to electricity. However, the efficiency of these engines is very low, and a large part of the energy that enters with the combustion of biogas is thrown into the atmosphere through exhaust gas and jacket cooling water. In this thesis study, the recovery of waste heat to power of a combined heat and power (CHP) engine located in a biogas production plant in Belgium region has been studied. In the scope of the study, organic Rankine cycles (ORC) using R245fa as working fluid with and without regenerator are designed for high temperature exhaust gas waste heat. These two designs are optimized parametrically for both subcritical and supercritical operating conditions. The ORC designs using R245fa as working fluid with and without regenerator for recovery of waste heat of low temperature jacket cooling water (CS) is then parametrically optimized in subcritical operating conditions. For system parameters where the best performance is obtained, exergy-based analysis of ORC cycles designed for recovery of exhaust gas and CS waste heat is performed. In addition to determining the best operating conditions of the ORC cycles using R245fa, the effects of the regenerator on the ORC were also investigated. During the study, EBSILON® Professional (EBSILON) software developed by Steag GmbH was used for the design and parametric optimization of the ORC systems.