Computational modeling of furnace sorbent injection for SO2 removal from coal-fired utility boilers

Furnace sorbent injection (FSI) is used to remove SO2 formed during coal combustion by injecting sorbent into the high temperature zone of a furnace above the fireball. FSI is cost effective for older coal-fired boilers, especially when space or capital budgets are limited. To optimize the design and performance of FSI, an SO2/sorbent modeling scheme that simultaneously considers calcination (or dehydration), sintering, and sulfation has been developed and implemented. It is coupled with a three-dimensional combustion model based on computational fluid dynamics to determine the most desirable locations for sorbent injection and to optimize the amount of sorbent needed to achieve a targeted SO2 removal efficiency. A sensitivity analysis was conducted to determine the effect of flue gas temperature, particle diameter, and SO2 concentration on the extent of sulfation. This SO2/sorbent sub-model was applied to a 126-MW front-wall fired boiler firing eastern bituminous coal. The SO2 removal efficiencies predicted by the model agreed well with those measured in the field. The modeling results indicated that sorbent injected directly into the furnace through boosted over-fired air ports is more effective at removing SO2, due to longer residence time and better mixing, relative to ports higher in the furnace with poor mixing. This modeling approach is optimized for full-furnace application to facilitate the design process.