We installed a new knockout drum with a better mist eliminator (Figure 1) to replace a drum that was giving us problems. The new drum, like its predecessor, is at the inlet of two thermal oxidizer (TOX) systems. "Flow is controlled by a pressure transmitter downstream of the mist eliminator," notes the production foreman. Operations had project engineering install two redundant transmitters in the old drum. However, the impulse tubing for both transmitters plugged so often that the TOX systems downstream tripped on low pressure every few weeks. Those systems run at 2 psig at the inlet with the trips set at 0.5 psig.
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