Production of a fuel gas by fluidised bed coal gasification compatible with CO₂ capture

A continuously fed, laboratory scale spouted bed gasifier has been used to study oxy-fuel gasification of German lignite. In this paper, the influence of different gasification agents and bed temperature on the process performance, during tests at atmospheric and elevated pressure are studied. Two gasification agents have been used, CO₂ (with different CO₂/C ratios) and mixtures of CO₂/steam. The results show that despite the relatively slow CO₂-char reaction, good gasification performance could be achieved with German lignite by adjusting the operating conditions at atmospheric pressure: complete carbon conversion, high energy conversion and a medium heating value fuel gas (8–10 MJ m⁻³). The CO₂/C ratio was found to have a large effect on the gasification performance. Increasing the ratio increased the carbon conversion, but the CO₂ conversion decreased. At 950 °C, maximum carbon conversion was already achieved with pure CO₂, therefore using steam at this temperature could not increase the conversion, but did increase the H₂/CO ratio in the fuel gas. At 850 °C, replacing 25% of CO₂ with steam increased the carbon conversion to the level achieved at 950 °C without steam. Replacing more than 25% of CO₂ with steam increased the H₂/CO ratio further. Therefore, with the addition of steam, the operating temperature could be reduced from 950 °C to 850 °C while maintaining the gasification performance. The changes of gasification performance with steam addition at pressures up to 10 bar_a followed the same trends achieved at atmospheric pressure.