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Wet Flue Gas Desulfurization Scrubbers (pH/ORP)

Wet Flue Gas


Coal fired power plants will use a flue gas desulfurization (FGD) scrubber to remove the SO2 before release up the stack. The scrubbing process is pH dependent. In this paper we will explore some of the challenges in this type of pH measurement.

pH Measurement Challenges
FGD scrubbers have multiple variables that can effect their efficiency.
These include:

  • flue gas flow rate
  • changing coal supplies
  • coal sulfur content
  • coal moisture
  • chloride content
  • fly ash content
The pH of the slurry in the absorber is one of the main control parameters of the scrubber. It is typically kept in a range of 5.7 to 6.8 pH. If the slurry drops below 5 pH then the scrubber will not effi ciently remove SO2 from the flue gas. If the pH gets above 7.5pH then CaCO3 / CaCO4 scale can begin to plug nozzles, mist eliminators, and other hardware. In addition to build-up problems, maintaining high pH increases reagent chemical usage resulting in additional wear on pumps and valves plus increased chemical cost.