Advanced substitute natural gas from coal with internal sequestration of CO₂ (CO₂freeSNG2.0) : final report

The project addressed a simplified integrated SNG process chain for small- to mid-scale lignite based SNG plants with integrated sequestration of CO2. The experimental proof was accomplished at two integrated SNG process chains at FAU laboratory. Within the 1st part of the project, thermodynamic analyses revealed lignite-to-SNG efficiencies of up to 45.6 %. The bottom-up economic analysis resulted in SNG costs of ~6 ct/kWh. Each process step has been investigated experimentally. The carbonate scrubbing did not affect the thiophene concentration in the raw syngas (~10 ppm) whereas H2S was reduced by 90 %. Thiophene caused a specific catalyst consumption in the range of 0.6 - 1.7 gcatalyst/mmolC4H4S. Increasing gasification temperatures by 25 K and the doubling of the steam surplus reduced tar species by 25 % and 65 % respectively. In the 2nd part of the project, the integrated SNG process chains in bench-scale and pre-pilot scale (i.e. 100 kW fuel input) have been erected at FAU laboratory for combined operation with real lignite-derived syngas. Several experimental campaigns with the integrated bench-scale SNG process chain proved stable operation (up to 32 h) and high removal efficiencies for H2S and heavy tars. CO2 removal of the scrubbing processes did not meet the simulated levels most likely due to wall effects in the bench scale absorption columns. However, the experiments indicated no negative effect of the tar content on the scrubber performance. Experiments with 100 kW Heatpipe Reformer and pre-pilot scrubber confirmed the bench scale findings.