'Dominion's Approach to Optimizing Spray Dry Absorbers by Replacing Rotary Atomizers with Dual Fluid Spray Nozzles'

摘要

Liquid sprays play an integral part in SDA's by generating high liquid surface area and enhancing gas-liquid interaction for gas cooling and SO2 removal. Traditionally, rotary atomizers have been the preferred choice for producing sprays in a Spray Dry Absorber (SDA). However, there are certain limitations to rotary atomizers that may cause issues during operation. One way to overcome these limitations is by using an air atomized spray injection system. Dominion AltaVista, Hopewell and Southampton stations were all converted from coal to Biomass facilities and as a result of this change, the boiler rating to change from 63 MW to 51 MW. After this conversion, hopper wetting became an issue. The resolution was to replace their rotary atomizers with an alternate spray technology utilizing air atomized spray nozzles. Initially, a detailed study was conducted to evaluate the feasibility of this project and determine the impact of a spray nozzle on the SDA vessel and process stream, which are both designed to work with a rotary atomizer. A CFD study was then completed to determine the type of nozzle, total number and orientation of lances, and appropriate droplet size required for evaporation within the SDA prior to reaching the hopper. The newly installed spray lance system using air atomized nozzles has been running successfully at all three plants without any modifications to the SDA vessel. This retrofit provided a more reliable SDA system for the plant while eliminating hopper wetting issues and atomizer maintenance. A successful atomizer retrofit relies heavily upon the performance of the nozzle. The initial tests and installation of the nozzles at both Dynegy Havana and Baldwin stations, reinforced this theory. Nozzle technology can solve the perennial challenge of SDA reliability and energy usage. A significant reduction in maintenance time and compressed air power consumption were achieved for the SDA operations at both Dynegy plants. The SDA ash product produced after retrofitting the new nozzle technology at Dynegy was dryer than what was achieved using the original nozzle technology, even with the reduction of compressor air power consumption. It should be noted that this power consumption was also lower than the original operating point. These results were the basis of our design in retrofitting and upgrading the rotary atomizer at Dominion.