Falling fuel prices recently led one of Emerson's customers to upgrade their bark boiler from heavy fuel oil to natural gas as an auxiliary fuel. The switch was expected to cut long-term fuel costs, but it also brought with it increased CO emissions regulations, which the customer needed help addressing. The customer asked Emerson, which had installed the boiler control system, to find a solution.
An array of nozzles that inject high velocity air on the side walls of the boiler had been installed in an interlaced pattern. Emerson’s combustion tests revealed that the overfire air system was creating turbulence that upset the bark fuel in the boiler. This turbulence was creating vortices that were stirring up fuel and ash into suspension firing. These particles were accumulating in the ash hoppers in the back pass of the flue gas system and emitting high CO levels as they burned in a reduced atmosphere.
Using the air flow control system, Emerson altered the flow pattern of the overfire air nozzles to create a broader, more efficient airstream matrix inside the boiler. The individual air nozzles were automated and specific damper position curves were built into the control system to optimize the process throughout the entire load range of the boiler. Not only did CO emissions from the unit fall by 60 percent as a result, but the customer was also able to continue saving on fuel costs by using natural gas without worrying about environmental infractions.
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