Biomass gasification coupled to an EFGT-ORC combined system to maximize the electrical energy generation: A case applied to the olive oil industry

Abstract

This research presents the modelling and simulation of an innovative small-scale power system composed of a downdraft gasifier, an externally fired gas turbine (EFGT) and an Organic Rankine Cycle (ORC) as a bottoming unit for increasing the electrical energy generation. Olive tree pruning (217 kg/h) was the biomass used, producing more than 200 kWe and an electrical efficiency of 20.7%. The producer gas achieved suitable mole composition (H2: 14.8%, CO: 19.5%, CH4: 2.2%, CO2: 9.3%, H2O: 12.0% and N2: 41.5%), lower calorific value (4.53 MJ/kg) and gasification efficiency (89%). The hot producer gas was burnt directly at atmospheric pressure in an EFGT, producing 150 kWe and exhaust gases at 290 °C. Five ORC working fluids were studied to maximize the electricity generation: isopentane, benzene, cyclohexane, R113, R245fa. Isopentane was the most suitable fluid, reaching 57.1 kWe and 20.45% of ORC thermal efficiency. On the other hand, despite R113 gave minor electricity production (49.1 kWe), this allowed to generate thermal power for CHP applications.