(70c) Allothermal Gasification of Lignite and Biomass with Integrated Syngas Cleaning and CO2 Removal

Due to increasing dependence on natural gas imports the generation of substitute natural gas (SNG) from coal and biomass is again becoming a frequently discussed topic within the European Union. For the generation of SNG different processes are available. After the thermochemical conversion in the gasifier follows a gas cleaning and conditioning step to remove particles, undesirable gaseous compounds and sulphur components from the raw syngas. Subsequently the syngas enters the methanation unit where the syngas is drawn through a catalyst bed for the methanation. Before the final injection into the gas grid the SNG is dried and conditioned to meet the technical requirements.

Within the European research project CO2freeSNG2.0 funded by the Research Fund for Coal and Steel (RFCS) the research efforts concerning allothermal steam gasification and methanation of the chair of energy process engineering, Friedrich-Alexander-University Erlangen-Nuremberg, are intensified. In addition to the formerly proposed hot gas cleaning a gas scrubbing unit based on the Benfield process is integrated in the process chain to provide the removal of heavy tars, sulphur components and surplus CO₂before the methanation process step. By implementing said gas scrubbing unit the integrated removal of undesirable components within the raw syngas with less thermodynamic losses can be accomplished.

The comparison between the carbonate scrubbing and cold scrubbing processes like methanol scrubbing in prior simulations showed that for small and medium-scale plants the Benfield process can reach higher coal-to-SNG efficiencies. Based on these simulations the complete process chain is demonstrated on two levels within the research project CO2freeSNG2.0. The bench scale process line is based on an allothermal lab scale gasifier (5 kW) and the pre-pilot process chain on the 100 kW EVT Heatpipe-Reformer (HPR). Prior tests with the lab scale gasifier and methanation reactor proofed the possibility of a tar tolerant methanation allowing a temperature peak at the inlet of the methanation reactor to reform light tar components and make them available for methanation. Within the current research project both process lines include a hot potassium carbonate scrubbing gas cleaning unit. The focus of research is set on the raw syngas cleaning evaluated on the basis of removal efficiency of CO₂, sulphur components as well as heavy tars.

The commissioned bench scale process line for the production of SNG from biomass or coal introduced and the results of the 5 kW gasifier and scrubber will be presented proving the feasibility of the proposed syngas cleaning process with integrated removal of surplus CO₂. In addition the influence of different process parameters of the gasification process on gas composition, tar and sulfur loading is investigated.