Scruber Controls

[vds002]

Hi All,
I was wondering if anyone here has any experience controlling a scrubber. In our scrubber vapor at 175C is scrubbed with liquid at 27C. I am controlling the level inside the scrubber by manipulating the liquid in. Is this sufficient or do i need second degree of freedom by controlling the differential pressure across the scrubber by putting a butterfly valve at the top of scrubber and manipulate it based on the differential pressure inside the scrubber.

http://files.engineering.com/getfil...f-b635-2915be3289bb&file=Scruber_Question.JPG

 

[duncan8943]

I am a little confused. Is there a recirculation pump that isn't shown? Are you batching out the liquid in the sump based on pH or a lab analysis? I have done scrubbers a couple of different ways depending on the process. If you aren't using a recirculation pump and are varying the liquid flow into the scrubber, then does your flow range always ensure that your packing is wetted? You don't typically try to control differential pressure across a scrubber. Does your scrubber pressure swing based on the downstream process?

 

[vds002]

Sorry for not being clear. I am not recirculating. Its batch draw. There is no packing. My Vapor comes in via sparger. I have the level transmitter that maintains level inside the scrubber but controlling the liquid coming in from side.

This is not exactly a scrubber. My process vapor coming in is quenched by the liquid and effluent vapor from the top is send to distillation for purification.

 

[duncan8943]

Does the vapor or scrubbing liquid flow swing? Does the discharge temperature stay constant? Since this is a quench/scrubbing column, how are you removing heat from the column?

 

[dcasto]

your outlet stream will have a variable temperature if you control the level with the cooler stream at top. If you need the outlet temperature to be fixed, then you will control the cooler liquid stream in oder to maintain the outlet stream temeperture. Then you will need a valve the allows liuid to flow out based on a level transmitter.

 

[duncan8943]

I'm guessing that you are batching based on caustic/scrubbing liquid conservation. In this case, a recirculation loop with a cooler to remove heat would work well. Depending on the make-up amount, you could leave the level control as is or re-route the level addition to the sump. More details of the process would be needed to give a better solution.