Conversion of CO2 during the DFB biomass gasification process
Anna Magdalena Mauerhofer, Stefan Müller, Alexander Bartik, Florian Benedikt, Josef Fuchs, Martin Hammerschmid, Hermann Hofbauer
Abstract
Abstract In many industrial processes, the climate-damaging gas CO 2 is produced as undesired by-product. The dual fluidized bed biomass gasification technology offers the opportunity to tackle this problem by using the produced CO 2 within the process as gasification agent. Therefore, a 100 kW th pilot plant at TU Wien was used to investigate the use of CO 2 as gasification agent by converting softwood as fuel and olivine as bed material into high-valuable product gas. A parameter variation was conducted, where the typically used gasification agent steam was substituted stepwise by CO 2 . Thereby, the amount of CO and CO 2 increased and the content of H 2 decreased in the product gas. These trends resulted in a declining H 2 /CO ratio and a decreasing lower heating value when CO 2 was increased as gasification agent. In contrast to these declining trends, the carbon utilization efficiency showed an increasing course. As second part of this work, a temperature variation from 740 to 840 °C was conducted to investigate the change of the main product gas components. With increasing temperature, CO and H 2 increased and CO 2 decreased. To determine the degree of conversion of CO 2 in the DFB reactor system, two approaches were selected: (1) a carbon balance and (2) a hydrogen balance. This way, it was found out that a certain amount of CO 2 was indeed converted at the investigated process conditions. Furthermore, under certain assumptions, the reverse water-gas shift reaction was identified to be the predominant reaction during CO 2 gasification.