Investigating hot gas cleaning of woody biomass derived bio-syngas for SOFC operation

Abstract

In the current transition to new and durable methods of generating energy, biomass is becoming a primary source of energy. Solid Oxide Fuel Cells, when integrated in a combined heat and power system, can yield high efficiencies in the conversion from biomass to thermal and electrical energy. One of the challenges that this process faces is the damaging effects of the contaminants that are formed in the gasification of biomass fuels. These damage effects include the clogging up of lines, de-activation of the catalysts and a decreased carbon conversion. Among these contaminants, tars, particulate matter, HCl and H2S are the most prominent and can cause severe damage on downstream equipment, interfere with electrochemical reactions and pressure drops, which all negatively affect the SOFC performance. This study focuses on the effectiveness of a re-designed high-temperature gas cleaning unit on removing these contaminants. Under the FlexiFuel-SOFC project, which aims to develop a highly efficient fuel flexible biomass CHP system, an integrated system consisting of a gasifier, gas cleaning unit and a SOFC has been built in the laboratories of BIOS Bioenergiesysteme. HCl, H2S and tar contents in the syngas were analyzed at different points in the process. The operating temperatures are monitored to see if the design parameters are achieved. It is critical for each reactor/component to reach the design temperature, as this can greatly influence the gasification process, the effectiveness of catalysts and fuel cell bio- syngas to electrical energy conversion. The temperature evaluation shows a normal heating up of the gasifier and reactors during the test runs. The design temperature parameters were achieved. The tar content analysis shows the most abundant tar compounds were naphthalene, toluene and phenol. The total tar content in the syngas was measured on two test days and was found to be 3.64 and 3.37 g/nM3 before gas cleaning and 0.11 and 0.41 g/Nm3 after gas cleaning, which comes down to a 97% and 88% resp. reduction in total tar content.