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Wet Gas FCC Scrubber (pH/ORP)

Wet Gas FCC Scrubber


A byproduct of the FCCU process is flue gas. The flue gas contains many impurities. The main acidic component is sulfur dioxide (SO2). When released into the environment SO2 creates acid rain; thus the gas must be treated before reaching the atmosphere. The most common method is through a wet gas scrubber.

pH Measurement Challenges
pH is one of the main measurements in the wet gas scrubber. The flue gas flow rate and changing crude oil feedstock can vary the concentrations of SO2. A setpoint of 6.0 to 6.5 pH helps balance the corrosive effects of sulfuric acid with the high cost of NaOH reagent. pH is best measured in the recirculation piping to the misting nozzles. The challenges of the scrubber pH measurement are as follows:
  • High temperature
  • Corrosive high sulfide environment
  • Abrasive particulates (catalyst fines)
pH is also measured downstream of the scrubber in the oxidation towers. The measurements are crucial to waste treatment however reduced temperatures and solids make these measurements less demanding on the pH sensor.