Predicting Acid Gases Removal by Advanced Chemistry Modeling of Dry Sorbent Injection

摘要

EPA’s recently issued Mercury and Air Toxic Standards (MATS) rule aims at removing mercury, SO2, SO3 and HCl from flue gas of combustion boilers. Dry Sorbent Injection (DSI) technology is usually installed before or after air preheater to remove these acid gases with sodium or calcium based sorbent. Without chemical kinetics modeling, the DSI injection strategy and its performance cannot be predicted well, particularly when multiple acid gas species competitively and simultaneously react with sorbent particles. In this paper, an advanced chemistry sub-model is discussed, which includes trona calcination, sintering, and simultaneous reactions with HCl and SO2. Both chemical reactivities (i.e. kinetics and equilibria) and species diffusion (i.e. mass transfer) are considered in the model. By coupling the sub-model with the computational fluid dynamics (CFD) model, the sorbent usage and the extent of removal of each acid gas species can be predicted. The impact of parameters related with sorbent properties and operating conditions on HCl and SO2 removal is investigated through sensitivity analysis. The competitive reaction of HCl and SO2 with sorbent can be well predicted. The sub-model is validated against tests conducted in a combustion testing facility. Predicted HCl and SO2 removals by the coupled model have reasonable agreement with the measured results for both before and after air preheater injection. It is a useful tool and can be directly applied to other units for predicting acid gas removal.