Experimental study on the spray characteristics in the spray drying absorber

Abstract

A pilot-scale spray drying absorber (SDA) system was set up to evaluate the effect of spray characteristics on flue gas desulfurization efficiency. Varying spray injection conditions and inlet gas conditions, SO2 concentrations were measured using a combustion gas analyzer. As a reagent, a slaked lime (Ca(OH)(2)) slurry was treated with flue gas containing SO2. The influence of each parameter is determined by the compromise between the droplet absorption capability and SO2 gas supply to the region of the droplet cloud. When the SO2 molecules are sufficiently supplied to the wet droplet surface, the variation of the total droplet surface area plays a dominant role in the desulfurization process. The conditions of low inlet gas temperature and low slurry feed rate are included in this case. However, when the droplets of sprayed slurries are too small or evaporation proceeds too fast, the SO2 molecules cannot be sufficiently transferred to the droplet surface. The excess calcium sorbents in the droplets dry out before they react with the hot gas. Consequently, the desulfurization efficiency as well as the utilization efficiency of Ca decreases for the smaller droplets. This trend appears to be dominant in conditions of high gas temperature and large slurry feed rate with the small Sauter mean diameter (SMD) of spray droplets. From the experimental results, we proposed two empirical models for the desulfurization efficiency and operating conditions.