[b]CO2 SCRUBBER USING KMnO4[/b] 1

[gladkenn]

I am currently designing a tank for the bubbling of CO2 gas(7-10 psig)on a potassium permanganate liquid. CO2 gas come the beer fermentation. Can anybody tell me the necessary parameters in order for my CO2 scrubber tank to work? The tank is 1.20m in diameter and 2m in height. A bubbler is installed at the bottom 232 holes at 10mm diameter per hole (Is 10mm diameter enough for scrubbing?). Also I need to know how much would be the volume(or height from the bottom of tank) of KMnO4 to be able to really scrub the odors from CO2 gas. Please tell also the headspace that I should provide.

Thank you.

 

[Montemayor]

gladkenn:

What you are proposing is the old-time method of oxidizing and removing the pernicious odor of fermentation CO2. I have done this many times in purifying and liquefying CO2 industrially. Allow me to detail out the answers to what you asking and give some pointers at the same time:

1) You haven’t given the most important data of all: the CO2 flowrate; so what I can tell you is that the superficial velocity through the permanganate scrubber should be 15 – 20 ft/min at approximately 5 psig;

2) The method you are hinting of using (a CO2 sparger at the bottom of the permanganate solution) is not going to work for long; what you are describing is not what has proven to be the workable and practical method of doing the operation. The technique used successfully is to employ perforated plates within the vertical vessel (always with clean-out hand holes on the shell at each plate). These plates are all submerged in the solution (as opposed to the pump-around version of scrubbing – which is more efficient, but requires a pump, piping and controls) and they act as sequential spargers. The reason for not allowing a sole sparger at the bottom of the vessel is that the bottom soon gets ladened and covered with solid sludge from the oxidized product. You must leave a liberal volume at the bottom of the vessel to collect this sludge product. Depending on the capacity, I would allow for at least 18 – 24” of dead sump space at the bottom of each vessel pass.

3) Another detail item is that the vessels are normally piped up to function in at least 2 stages. In other words, two vessels are used in a unit; one vessel is in operation while the other is on stand-by service and they are switched manually when one gets exhausted or plugged. The method of staging each vessel is that each vessel is separated by a mid-height located solid steel plate that effectively converts each vessel into two chambers. The top of the bottom chamber is piped out and up into the bottom of the top chamber through an “inverted” goose-neck pipe configuration. This gives you two passes of gas through solution in each vessel.

4) Use Cast Iron or plastic Saunders diaphragm valves to separate the vessels and the solution. These valves are field-proven to give the best results in this taxing service.

5) Liquid solution level indicators are a challenge and all I can tell you here is that you have a constant problem with the sludge formed. I have never found a level gauge to work to my satisfaction.

6) Again, since you haven’t given any flowrates or capacity, we can’t furnish dimensions on the vapor disengagement space at the top of each pass. You also fail to state if you are going to water scrub the CO2 immediately afterwards, and I don’t know the importance of removing any permanganate solution from the product overhead. However, I always sent my purified CO2 to a reciprocating compressor, so I always allowed liberal vapor disengagement volume at the top and subsequent water scrubbing downstream, before the compressor. Use the Souders-Brown relationship for the vapor disengagement space.

7) I would not worry too much about the diameter of the holes to give you good scrubbing as I would about the holes getting plugged with sludge material. The sludge is what will neutralize the operation if you don’t take it into consideration and design around its prescence.

I hope the information helps you out in this application.


Art Montemayor
Spring, TX