A comparative study of the pyrolysis and combustion characteristics of sodium-rich Zhundong coal in slow and rapid processes

Coal with high content of alkali metal has limited use in the combustion process. The slow and rapid pyrolysis and combustion characteristics of sodium-rich Zhundong coal were investigated using a thermal gravimetric analyzer and one-dimensional drop-tube furnace. The results show that the process was complete when the final temperature exceeds 900°C in slow pyrolysis, while in rapid pyrolysis it lasts for short residence time in the whole furnace. The weight loss ratio in rapid pyrolysis was significantly higher than that in slow pyrolysis, and shows different trends at different reaction temperatures. There is an extremum value of weight loss ratio obtained at 800°C in rapid pyrolysis, which is accompanied by the maximum value for the diameter of pores and the minimum value for specific surface area. Most alkali elements are released from the solid product, and the amounts of released alkali elements in combustion are higher than that in pyrolysis process. The apparent activation energy in the two pyrolysis processes and release of alkali in combustion were evaluated using different models, which demonstrates that the alkali release trend in combustion is easier than that of pyrolysis.