Simultaneous adsorption of SO 2 NO x from flue gases in a riser configuration

Simultaneous adsorption of SO 2 –NO x is a new, promising process in treating industrial flue gases in a short‐contact‐time dilute phase riser with Na/γ‐Al 2 O 3 sorbent particles of 50–100 μm diameter at 370–430 K. A major part of the sorbent is recycled for maximum utilization of the sorbent capacity before regeneration. A steady‐state model for the riser adsorber is developed by combining independently determined rate equations with a 1‐D, two‐phase hydrodynamic model of the riser. The simulation was validated with the operating data from a pilot‐scale installation of 4.2 Nm 3 /s flue‐gas capacity and solid fluxes between 1 and 3 kg·m −2 ·s −1 . The riser operates in an extremely dilute phase with a solid volume fraction below 7.0 × 10 −4 and a slip velocity that is constant for almost the entire riser length, indicating fully developed flow. The experimental observation that an increase in the SO 2 –NO ratio in the feed gas leads to a higher NO removal efficiency is explained as resulting from an increased concentration of the adsorbed SO 2 . The SO 2 removal efficiency, however, may drop if free adsorption sites are not sufficiently available. Recycling of the sorbent has only a marginal effect on the NO removal, but helps to maximize the SO 2 adsorption. For the first time, the simultaneous removal of SO 2 above 95% and of NO x above 80% is reported using a dry, regenerable sorbent in a riser reactor.