Biomass-fuelled PEM FuelCell systems for small andmedium-sized enterprises

Detta är en avhandling från Stockholm : KTH Royal Institute of Technology

Sammanfattning: Biomass-fuelled proton exchange membrane fuel cells (PEMFCs) offer asolution for replacing fossil fuel for hydrogen production. Through using thebiomass-derived hydrogen as fuel, PEMFCs may become an efficient andsustainable energy system for small and medium-sized enterprises. The aim ofthis thesis is to evaluate the performance and potential applications of biomassfuelledPEMFC systems which are designed to convert biomass to electricity andheat. Biomass-fuelled PEMFC systems are simulated by Aspen plus based ondata collected from experiments and literature.The impact of the quality of the hydrogen-rich gas, anode stoichiometry, CH4content in the biogas and CH4 conversion rate on the performance of the PEMFCis investigated. Also, pinch technology is used to optimize the heat exchangernetwork to improve the power generation and thermal efficiency.For liquid and solid biomass, anaerobic digestion (AD) and gasification (GF),respectively, are relatively viable and developed conversion technologies. ForAD-PEMFC, a steam reformer is also needed to convert biogas to hydrogen-richgas. For 100 kWe generation, the GF-PEMFC system yields a good technicalperformance with 20 % electrical efficiency and 57 % thermal efficiency,whereas the AD-PEMFC system only has 9 % electrical efficiency and 13 %thermal efficiency. This low efficiency is due to the low efficiency of theanaerobic digester (AD) and the high internal heat consumption of the AD andthe steam reformer (SR). For the environmental aspects, the GF-PEMFC systemhas a high CO2 emissions offset factor and the AD-PEMFC system has anefficient land-use.The applications of the biomass-fuelled PEMFC systems are investigated on adairy farm and an olive oil plant. For the dairy farm, manure is used as feedstockto generate biogas through anaerobic digestion. A PEMFC qualified for 40 %electrical efficiency may generate 360 MWh electricity and 680 MWh heat peryear to make a dairy farm with 300 milked cows self-sufficient in a sustainableway. A PEMFC-CHP system designed for an olive oil plant generating annual 50000 m3 solid olive mill waste (SOMW) and 9 000 m3 olive mill waste water(OMW) is simulated based on experimental data from the Biogas2PEM-FCproject1. After the optimization of the heat exchanger network, the PEMFC-CHP system can generate 194 kW electricity which corresponds to 62 % of the totalelectricity demand of the olive oil plant.The economic performance of the PEMFC and biogas-fuelled PEMFC areassessed roughly including capital, operation & maintenance (O&M) costs of thebiogas plant and the PEMFC-CHP, the cost of heat and electricity, and the valueof the digestate as fertilizer.