Effect of pyrolysis temperature on burning reactivity of lignite char

Elbistan lignite is low-quality Turkish lignite with high ratio of volatile matter/fixed carbon contents that causes very high thermal reactivity. Partly elimination of volatiles from lignite was performed by pyrolysis at different temperatures to study effects of volatile matter removal on thermal reactivity. Hence, it was subjected to pyrolysis in both a horizontal tube furnace and a thermal analyzer at temperatures between 300-700 ^oC. Then, the semi-chars were burned in a thermal analyzer up to 900°C to compare the effects of pyrolysis temperature on char burning reactivity. Seven different criteria were considered to compare the thermal reactivity of the pyrolytic semi-chars during nonisothermal burning process. It was concluded that the extent of volatile matter removal (especially in oxygen content) provides enrichment in carbon content, and accordingly reduction in reactivity. The severity of pyrolysis step determines the thermal history of char which affects the reactivity in sequential processes. Increasing final temperature in pyrolysis step reduced the burning reactivity of the forming char. Ignition temperature shifted to higher temperatures owing to reducing reactivity, and complete burning of the char occurred at elevated temperatures and took longer times. This successively affected many reactivity-related parameters such as burn-out levels, maximum burning rate and its temperature, conversion levels, heat flow rates, etc.