PROBIO – Conversion of Biomass into Electrical Energy
Sustainable produced Biomass is considered to be a CO2-neutral energy carrier. A technically feasible and efficient process option for the conversion of biomass into electrical energy is the thermochemical gasification and the subsequent electrochemical oxidation of the product gas in fuel cells.
The PROBIO Project is dedicated to the computer aided design of a stationary fuel cell power plant based on biomass, along with the investigation and characterization of novel processes which might have the potential to increase the overall efficiency of the power plant.
The computer aided design is based on a library of unit models, which comprised many different processes enabling multiple design possibilities of the conversion process from biomass to electrical energy (see Fig. 1). This library was used to implement a superstructure describing the process design problem [1-3]. In order to reduce the high computational effort, the PSE group has very recently developed a new algorithm especially tailored for the solution of Mixed Integer Nonlinear Program (MINLP) problems for energy systems design .
Furthermore, new process units, applicable within the regarded fuel cell power plant, are being developed by the PSE group. These activities comprise the description, characterization and design of novel reactors for the conditioning of carbon monoxide containing hydrogen rich fuel gas for the utilization in subsequent fuel cell units. Here, the Cyclic Water Gas Shift Reactor (CWGSR) constitutes a tubular reactor, filled with a fixed bed of iron oxide particles, which is operated at 600 to 800°C . The iron oxide particles are periodically reduced by the purified effluent stream of the biomass gasification reactor, and thereafter oxidized by steam . The hydrogen gas produced during the oxidation phase is free of carbon monoxide and can thus be used to feed low temperature PEM fuel cells . The Electrochemical Water Gas Shift Reactor (EWGSR) likewise supplies hydrogen gas free of any contaminations, produced by hydrogen separation and generation from reformate gas at 110 to 150°C. This reactor employs an electrochemical membrane reactor setup and electrical energy to drive the process . Additionally, a concept for deep CO removal from reformate gas (so-called ECPrOx = Electrochemical Preferential Oxidation) as an alternative to the conventional preferential oxidation (PrOx) was also developed as a electrochemical membrane reactor process . The main advantage of ECPrOx, in comparison to PrOx, is that non-selectively oxidized hydrogen is converted into electrical energy instead of being burned. The ECPrOx studies carried out within the PSE group aim at the mechanistic understanding of the system's complex nonlinear behavior, which exhibits spatially distributed oscillations [10-12].