2 replies to this topic

[Winston Smith]

I am working (as a student placement engineer) with a two stage process scrubbing plant with an activated carbon bed for solvent recovery and an environmental scrubber to remove the remaining pollutants.

NH3 is scrubbed with H2SO4 in the 1st stage and acid fumes are scrubbed with casutic soda (NaOH<10%) in the 2nd stage. The scrubbers are all chemical, random packed beds in vertical, compact construction with a chevron type demister. The packing consists of PP pall rings.

The scrubber unit has been operating at lower efficiency than desired for quite some time and has been neglected in general as resources are stretched. My efforts to improve the efficiency have begun with taking some basic pressure and flow readings across the all the stages.

I have noticed in the 1st stage that the pumping pressure from the sump tank is 1.4bar (above the desired range of 0.8-1.2), yet the flow meter in the pump suction pipe to the gas scrubber is below the desired flow of 2m3/h at only 1.5m3/h. Am I right to conclude that the strainers attacted to the pumps are badly clogged and that the spray nozzles are too?
At the same time there is an excessive flow rate in the pump suction pipe to the jet fan (measured at 3.15m3/h, desired at 2m3/h) but the differential pressure in the scrubber is only 90Pa when it should be 400Pa. Am I right to conclude that the insufficient liquid flow rate is causing the packing to dry up, resulting in channelling of both the scrubbing liquid and the exhaust gas? Is it likely that the packing or demister is heavily contaminated in some parts or that particulates in the sump tank are blocking the spray nozzles.

I have a mountain of questions on this unit but I fear this post is already excessively long. If anyone can provide me with any general or specific advice on achieving good results I would be very grateful.

Thank you for your time (and patience),

Winston

[Steve McGahey]

I am working (as a student placement engineer) with a two stage process scrubbing plant with an activated carbon bed for solvent recovery and an environmental scrubber to remove the remaining pollutants.

NH3 is scrubbed with H2SO4 in the 1st stage and acid fumes are scrubbed with casutic soda (NaOH<10%) in the 2nd stage. The scrubbers are all chemical, random packed beds in vertical, compact construction with a chevron type demister. The packing consists of PP pall rings.

The scrubber unit has been operating at lower efficiency than desired for quite some time and has been neglected in general as resources are stretched. My efforts to improve the efficiency have begun with taking some basic pressure and flow readings across the all the stages.

I have noticed in the 1st stage that the pumping pressure from the sump tank is 1.4bar (above the desired range of 0.8-1.2), yet the flow meter in the pump suction pipe to the gas scrubber is below the desired flow of 2m3/h at only 1.5m3/h. Am I right to conclude that the strainers attacted to the pumps are badly clogged and that the spray nozzles are too?
At the same time there is an excessive flow rate in the pump suction pipe to the jet fan (measured at 3.15m3/h, desired at 2m3/h) but the differential pressure in the scrubber is only 90Pa when it should be 400Pa. Am I right to conclude that the insufficient liquid flow rate is causing the packing to dry up, resulting in channelling of both the scrubbing liquid and the exhaust gas? Is it likely that the packing or demister is heavily contaminated in some parts or that particulates in the sump tank are blocking the spray nozzles.

I have a mountain of questions on this unit but I fear this post is already excessively long. If anyone can provide me with any general or specific advice on achieving good results I would be very grateful.

Thank you for your time (and patience),

Winston

Your analysis sounds reasonable to me (with my limited operational experiences).

There are reams of things out there on troubleshooting process equipment and typical processing problems...., have you considered locating any of those?

[Winston Smith]

Thanks,

Yeah I have researched the most common causes/solutions of scrubber inefficiencies but I'm unsure as to how to go about implementing them and getting the maintenance guys involved because they're very busy. It's reassuring to know that there's probably not much more to it than proper cleaning and using the correct flow rates though!