Steam-Oxygen Gasification of Potassium-Loaded Lignite: Proof of Concept of Type IV Gasification

An advanced type of gasification at atmospheric pressure, which is termed type IV gasification, has been proposed with potential performance to achieve a stand-alone cold gas efficiency over 95% lower heating value (LHV). This work aimed to prove the concept of type IV gasification of lignite. Continuous conversion of a Victorian lignite was simulated experimentally in a sequence of pyrolysis of potassium (K)-loaded lignite, vapor-phase steam-oxygen reforming of volatiles, and simultaneous steam reforming over the K-loaded char and its steam gasification. Systematic investigation of the effects of key operating variables on the process performance has reached their combination that realized steady-state carbon conversion of ∼100% together with tar concentration in the syngas of <30 mg Nm^-3 dry. A suite of variables, K loading to the lignite of 3.3 wt % dry lignite, steam/carbon molar ratio of <0.8, oxygen/carbon molar ratio of <0.24, temperature for the pyrolysis of 600 °C, and char bed temperature for steam gasification/reforming of 750 °C, satisfied the requirement for type IV gasification.