Solar-assisted micro gas turbine with humid air or steam-injected option

In the present work a low environmental impact, innovative, hybrid plant for the field of distributed energy is presented. The plant is obtained from the integration of a 30 kW micro gas turbine with a solar field and a bottoming ORC system. The plant is supplied with hydrogen fuel and is provided with steam injection to mitigate NO x formation. Furthermore, the cogeneration arrangement of the plant allows for flexibility in the choice between the production of electrical and thermal energy. A thermodynamic analysis of the plant was conducted and various organic fluids for the bottom ORC plant are tested. The feasibility of a single-stage Radial-Inflow Turbine (RIT) as expander for the ORC cycle is verified for various working fluids, with a two-step approach: a preliminary screening is carried out based on kinematic considerations; subsequently, a proper turbine preliminary design is developed for most interesting working fluids. Moreover, the combustion process resulting from the introduction of hydrogen fuel is studied by means of 3D CFD calculations and the effectiveness of the steam injection is verified. Finally, the off-design performance of the plant is investigated by means of a thermodynamic analysis. Results show that the novel plant achieves significant improvements in terms of power output and efficiency and fuel saving is achieved over several months thanks to the solar field and the ORC plant. The ORC working fluid is found to play a crucial role over plant performance and particularly over the feasibility of a single stage RIT, making working fluids with larger molecular weight preferable. Finally, CFD calculations proved the steam injection to be effective for NOx production reduction.