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Is Air Blower Needed For Tank Vent Scrubber?

tank vent scrubber caustic scrubber vent back pressure

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#1 WilliamN

WilliamN

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Posted 21 July 2014 - 10:32 AM

Dear peers,

I am working on a tank venting scrubber design. The tank has MAWP 2.5 psig with PSV of set pressure 2 psig. A dedicated vent line will be used for the scrubber. The vent flow can be estimated using API 2000 breathing out method. The contaminant HCL concentration can be estimated using vapor pressure at ambient temperature. We can size the scrubber based on this basic information. I have not done the sizing yet, but started  wondering if the back pressure is too high for the tank. For example, do we need air blower to pull the vent  from the tank to scrubber? I know this should be a low cost project, but the need for air blower will make it too expensive for the scale of the this project. Here I want to check out experiences from peers if the air blower is needed for the tank vent scrubber design.

Thanks.



#2 Art Montemayor

Art Montemayor

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Posted 21 July 2014 - 12:33 PM

The answer to your basic query is: NO, you do not need a blower to “pull” HCL vapors from your storage tank to your vent scrubber.  HOWEVER, since you don’t tell us all of the facts and characteristics of your HCL storage systems or furnish us with at least a flow diagram, I feel compelled to state them here and with attached documents in order to make sure that we are all on the “same page” and that what we are discussing will reflect a safe and controllable operation for you.

 

I believe we all should know that what you are storing and handling is not hydrogen chloride (HCL).  You are obviously storing and handling an aqueous SOLUTION of HCL GAS that fumes when exposed to air.  The HCL gas is always dissociating itself from the solution.  Fumes are emitted from HCℓ bulk storage tanks during storage and during off-loadings.  Fumes are also always escaping during the offloading procedure and these are more serious to handle.

 

You don’t tell us the concentration(s) you are handling or the loading / unloading method you are using.  Are you blanketing your storage tank with an inert gas – such as nitrogen?

Your tank has a very conservative MAWP – which a good sign for this type of hazardous storage.  Are you maintaining a positive vapor pressure on top of the stored solution?  If so, what is that storage pressure?  I have to ask this question even though I believe that you have an open vent to the vent scrubber which in turn is vented to the atmosphere.  I believe we need to have all the basic details of the installation in order to answer your query in an intelligent and correct manner.

 

If you refer to the attached documents you will note that Solvay doesn't show any blower being required for applying the necessary and regulated vent scrubber.  The pressure in the storage tank vapor space should normally be that amount needed to overcome the pressure drop in the vent piping and the vent scrubber.  Therefore, if you are liberal in these sizings, you should only have a minimal amount of backpressure.  How you are going to come up with the sizing of the maximum amount of HCL being vented at any one time is something I am very interested and curious to see.  I would appreciate it if you submit your calculations even if they are preliminary or “rough”.     Attached File  HCL Storage & Handling Information.pdf   177.07KB   44 downloads   Attached File  Solvay HCL Storage Tank Guidelines.pdf   49.17KB   49 downloads






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