Effect of primary air and coal properties on the formation of fine mode particles during low NO_x gasification-combustion of coal in a self-sustaining furnace

Gasification-combustion technology can reduce NO_x while the formation characteristics of fine mode PM is unclear. This research studied the impact of the excess air coefficient (α_g) of the gasifier and the properties of coal on the formation and evolution of fine mode PM. The experiment was conducted on a self-sustaining furnace consisting of a gasifier where pyrolysis/gasification occurs and a combustion chamber where burnout of gasification gas and char occurs. The results showed that fine mode PM and NO_x can be synergistically reduced by optimizing α_g during gasification-combustion. A low or high α_g can lead to a high furnace temperature in the gasifier or combustion chamber, respectively. Elimination of high temperature is crucial to reduce element vaporization which promotes the formation of fine mode PM. Additionally, an optimized combination of furnace temperature and reducing atmosphere in the gasifier can decrease NO_x. The optimal α_g was 0.32 for bituminous coal (BC). Fine mode PM generated from gasification-combustion of BC, lean coal (LC), and semi-char (SC) mainly consists of Ca, Si, Fe, and S. The vaporization of element from LC and BC primarily occurs during char combustion in the combustion chamber, while the vaporization of element from SC occurs almost equally in the gasifier and combustion chamber.