Each of the three boilers at the power plants were identical and rated at 51 MW while burning wood. The SDA vessel for each unit was 31 feet in diameter and the atomizer’s opening in the well was 21 inches.
A detailed CFD study was performed to understand the interaction of spray droplet with flue gas inside SDAs. Based on the CFD study, eight (8) twin-fluid spray lances were selected to create the spray pattern. In order to achieve the maximum interaction between the droplets and the fluegas, the lances were designed to mimic the spray pattern of a rotary atomizer. The droplet size and spray angle of dual fluid lances were also carefully selected to ensure complete evaporation. One of the major advantages of dual fluid sprays over a rotary atomizer sprays is that the spray angle from the dual fluid nozzle can be manipulated while the spray from rotary atomizer is always horizontal and almost perpendicular to gas flow direction. Also the droplet size from dual fluid spray nozzles can be changed very easily by modulating compressed air. Thus, a dual fluid spray nozzle provided much more freedom in designing good spray pattern that matched the process requirement from boiler startup to shutdown.
The system was designed in such a way that no modifications were made to SDA vessel. The dual fluid spray nozzles were designed as 1:1 replacement of the rotary atomizer. The pump and control system were added to control the liquid flowrate of dual fluid spray lances.
Since each station has two SDAs, a duplex skid was designed to pump and control water and slurry to each SDA. Each control skid has three pumps in which two are running and the third one is a common backup. The slurry skid also has three pumps to inject lime slurry. This skid is also designed for a fifty percent redundancy.