Effect of spray characteristics of slurry on the flue gas desulfurization efficiency 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 the flue gas desulfurization efficiency. The size distribution and the Sauter Mean Diameters of slurry droplets were measured in advance using optical size measurement system, Malvern 2600. The desulfurization yield of the drying chamber by size was measured for conditions of inlet gas and spray injection. As a reagent, 10% limestone slurry of $Ca(OH)_2$ was treated with flue gas containing $SO_2$, and the combustion gas analyzer and gas detectors were attached to measure the $SO_2$ concentration. With a flow rate of 144 N㎥3/h and a temperature range from 200 to 300˚, the experiments were performed for the Stoichiometric Ratio (SR) of 1.0 to 3.0 and droplet mean diameter of 6.5 to 34.3 micrometer. In case of smaller spray droplets, the desulfurization efficiency was improved due to the increase of total droplet surface area, while the reduction in evaporation time reduced the contact time between the droplets and flue gas. In some typical region of droplet diameter, this negative effect, reduction of contact time, became dominant and the desulfurization yield decreases in spite of the expansion in absorption area. In addition, with the spray condition of high number density, the $SO_2$ molecules being transferred to the droplet region by diffusion are not sufficient to maximize the desulfurization capability of each droplet. These results revealed that there exists the optimal size of spray droplets for a given state, which is determined by the compromise between the total surface area of slurry droplets and the evaporation time of droplets. The measurements also indicated that the inlet temperature of flue gas changes the optimal injection condition by varying the driving force for evaporation. In the meantime, the numerical simulations were performed to evaluate the effect of each operating parameter using the commercial computational fluid dynamic...