Integrated 5 kW_e + 5 kW_t PEM-FC Generator From Bioethanol: A Demonstrative Project

A power unit constituted by a reformer, a H₂ purification section and a fuel cell is being installed c/o the Dept. of Physical Chemistry and Electrochemistry of Universita` degli Studi di Milano, on the basis of a collaboration with Helbio S.A. (Hydrogen and Energy Production Systems, supplier) and the support of some sponsors (Linea Energia S.p.A., Parco Tecnologico Padano and Provincia di Lodi). The system is suitable to obtain 5 kW_electric (a.c.) + 5 kW_thermal (hot water at 70°C) as peak output. H₂ is produced by steam reforming (SR) of second generation bioethanol, obtainable by different non-food competitive biomass. The assessment of the effect of biomass nature and of the consequent different impurities left in the produced bioethanol is part of the experimentation, together with the evaluation of the impact of bioethanol production cost on the final energy cost. Furthermore, the effect of different ethanol/steam ratios will be taken into account to lighten as much as possible the energy demanding ethanol dehydration process. The former point focuses on catalyst life, imposing careful ethanol characterisation and proper catalyst formulation, whereas the latter is connected with the overall energetic efficiency and economic sustainability. Indeed, the reforming process requires co-feeding of water, opening the way to the research of different, cheaper, ethanol purification strategies, leading to lower ethanol concentration with respect to the azeotrope. The reformate is purified from CO down to a concentration below 20 ppm, suitable to feed the proton exchange membrane fuel cells (PEMFC) stack integrated in the fuel processor. This result is achieved by feeding it to two water gas shift reactors, connected in series and operating at high and low temperature, respectively. The expected CO concentration in the outcoming gas is ca. 1 vol% and the final CO removal to meet the specifications is accomplished by selective methanation. The purified H₂ is fed to a 5 kW_e PEMFC stack, which should have an expected overall efficiency around 80% (including thermal output). The main goal of the present project is to check system performance under widely different operating conditions and load, to verify the effectiveness of the proposed technology and to suggest adequate improvements. Different operating conditions are under evaluation as for ethanol origin, purity, concentration, temperature and space velocity of every reaction step, so to obtain the best compromise between H₂ yield, power output and operating costs.