When an SDA unit that was showing signs of improper droplet evaporation, CFD modeling was used to predict spray and deposition patterns in an SDA reactor in order to develop a solution to improve droplet evaporation.

Background

Spray Dryer Absorbers (SDAs) are designed to remove acid gases, mainly sulfur dioxide (SO2), from flue gas streams. Atomizers are used to inject droplets of lime slurry into the SDA reaction chamber, which then evaporate and react with the sulfur dioxide in the flue gas to form calcium sulfate, a solid powder that is typically captured in a fabric filter (or baghouse). Proper evaporation of the injected slurry is critical to the performance of SDA units. When the droplets do not evaporate, the system can have decreased removal performance, exhibit deposition on the walls, and cause droplet carryover into the outlet ductwork, which can then create issues with fabric filter operation.

Work Performed

A Computational Fluid Dynamic (CFD) model of the SDA reactor was used to simulate the gas and droplet flow patterns, droplet evaporation, and wall wetting due to droplet deposition. The model was validated using temperature and moisture content field data, as well as by the comparison of the predicted wall wetting to field photographs of deposition. The model predictions were incredibly accurate and provided a unique insight into the spray patterns within the reactor. Using this information, modifications to the reactor swirl vanes and outlet hood design were made to improve evaporation and mitigate wall wetting.

Results

The new reactor modifications were implemented in the field. The client has happily reported improved SDA removal performance, the elimination of deposits on the walls, no fabric filter bag wetting, and reduced operating pressure loss—all of which result in reduced SDA operating costs.