Experimental and Numerical Analysis of Steam-Oxygen Fluidized Gasifier Feeding a Combined SOFC/ORC Power Plant

The aim of this work is to experimentally and numerically analyze the performance of a combined power plant, composed by a steam oxygen fluidized bed biomass gasifier fed by woods, a Solid Oxide Fuel Cell (SOFC) and an Organic Rankine Cycle (ORC). The gasifier model is developed and validated by means of experimental activities carried out with a bench scale gasifier in our lab. Different compounds (Benzene, Toluene, Naphthalene, Phenols) were chosen to analyze the tar evolution in the gaseous stream during the gasification process. Hot gas cleaning (based on catalytic ceramic filter candles inserted in the freeboard of the gasifier - UNIQUE concept) is adopted to remove tar and particulate at high temperature from the fuel gas stream. The numerical analysis is carried out by means of the software Aspen Plus®. In particular, the SOFC and the gasifier are modelled using proper developed Fortran subroutines interfaced to the basic software. The adopted SOFC model was already validated by the authors in previous works. Finally, a realistic ORC is modelled. Different moisture contents in the range of 10–30 % (i.e. in a deviation of 10% around the usual wood moisture content of 20%) are investigated in the simulations, as also the degree of purity of the oxygen used in the power plant (between 25 and 95%, rest N₂). The power requirement for the production of pure oxygen for this kind of gasification technology leads to a reduction of the electrical efficiency of the whole power plant. For this reason a sensitivity analysis was conducted to find the optimal operation conditions in order to maximise the syngas content in the produced gas (H₂, CO) maintaining a high overall electrical efficiency.