A model for dry sodium bicarbonate duct injection flue gas desulfurization

A mathematical model is developed for simulation of dry sodium bicarbonate (NaHCO 3) duct injection for the removal of sulfur dioxide (SO 2) in flue gases across a fabric filter (baghouse). The model employs parallel reaction kinetics and assumes that the sodium bicarbonate injection process can be separated into two stages. The first stage is a transport duct section where NaHCO 3 particles are injected into the sulfur dioxide laden gas stream. The second stage is the fabric filter section where sodium sorbents are collected and behave as a variable depth fixed bed reactor. The process simulation for the efficiency of desulfurization in flue gas is performed and evaluated for a variety of operating conditions such as system temperature, particle size, residence time, normalized stoichiometric ratio, concentration of sulfur dioxide and decomposition time. It is found that the removal of SO 2 within the duct section is small and negligible for most practical conditions, with a contribution normally less than 5% of total SO 2 removal. The major removal of SO 2 occurs across the filter cake, which accumulates the sorbent particles on the fabric filter. These particles are periodically disposed as the filter is cleaned. The major factors for the process are temperature, particle size and SO 2 gas concentration for all operating conditions. At low temperatures, the removal of SO 2 increases as temperature increases, but the removal decreases at higher temperatures due to the impact of the thermal decomposition reaction of NaHCO 3 on SO 2 removal. It was found that the temperature for the highest removal of SO 2 is within the range of 127–150 °C and the removal efficiency also depends on particle size.