Hydrogen rich syngas production from oxy-steam gasification of a lignite coal – A design and optimization study

This study describes an experimental and computational fluid dynamics (CFD) effort towards optimizing: hydrogen rich syngas production and cold gas efficiencies during the thermochemical conversion of a lignite coal using oxygen and steam as gasifying agents. A bubbling bed gasifier was systematically designed, constructed and commissioned to achieve these objectives. The bed temperature was maintained at 1023 K during the gasification testing of the highly reactive lignite coal. The hydrogen levels in the syngas were examined as a function of oxygen, coal and steam flow rates. A maximum hydrogen concentration of 50% (dry-basis) was achieved at low oxygen to carbon ratios and the cold gas efficiencies were in the range 80–90%. The observed experimental trends in syngas compositions and cold gas efficiencies were reasonably well represented by the CFD simulations and compared favorably with data obtained from a transport reactor integrated gasification system. Simulations predicted that the major product gases at the reactor outlet were close to their equilibrium levels. The decrease in hydrogen concentrations in the syngas at high oxygen and steam flow rates resulted from changes in the oxidation reaction rates, hydrodynamics and steam levels. The levels of steam were attaining saturation conditions. - Highlights: • Measurements from and CFD simulations of a bubbling bed gasifier are reported. • Syngas compositions at different oxygen, coal and steam flow rates were examined. • H₂ concentration peaked at 50% (dry-basis) at low oxygen to carbon ratios. • Cold gas efficiencies were in the range 80–90%. • The major product gases at the reactor outlet were close to equilibrium levels.