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RE: [PSUBS-MAILIST] CO2 Scubber Design Guidelines



Cliff, Check this out:

 

http://people.oregonstate.edu/~atwaterj/zeolite.htm

 

 

 

 


From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of Cliff Redus
Sent: Monday, February 08, 2010 2:00 PM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] CO2 Scubber Design Guidelines

 

Greg

 

A molecular sieve separates the CO2 gas stream from the O2 and N2 gas stream by forcing the air mixture through an engineered media ( zeolite ) that is sized to allow the larger O2 (3.5 angstroms) and Nitrogen (3.6 angstroms) molecules to pass and blocks the smaller CO2 molecules (3.3 angstroms) from passing.  So now that you have a slip stream of pure CO2 you have to do something with this like compress the CO2 and purge the gas out of the hull for figure out something else to do with this concentrated CO2 stream.   I personally think it is to complicated for a psub and breaks the KISS rule. It is a better fit for a large nuclear boat.

 

Cliff



Cliff Redus
Redus Engineering
USA Office: 830-663-6445
USA mobile: 830-931-1280
cliffordredus@sbcglobal.com

 

 


From: Greg Cottrell <greg@precisionplastics.com>
To: personal_submersibles@psubs.org
Sent: Mon, February 8, 2010 12:10:21 PM
Subject: RE: [PSUBS-MAILIST] CO2 Scubber Design Guidelines

Hi Cliff,

 

What do you think about using molecular sieve for CO2 removal?

 

Greg C

 


From: owner- personal_submersibles@psubs.org [mailto:owner- personal_submersibles@psubs.org ] On Behalf Of Cliff Redus
Sent: Monday, February 08, 2010 10:48 AM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] CO2 Scubber Design Guidelines

 

The easiest way to build a CO2 scrubber is to buy some SodaSorb HP (4/8 mesh) and use 2.2 lbs of this absorbent for every 8 hours per person in the boat. You pack enough of this absorbent for your normal dive into canister or any container with a fan and your good to go. If you follow ABS rules, you carry some reserve absorbent to give you an additional 72 hours of bottom time.  For ABS rules this this means for say and 8 hour dive time plus the 72 hours reserve, you would need about 22 lbs of Sodasorb HP.  As a check, the Deepwork 2000 carries 24 lbs of this absorbent.

 

The 2.2 lbs for 8 hours comes from  http://www.sodasorb.com/English/downloads/Sodasorb_Manual.pdf, page 16 in which is says "In a properly packed and well designed canister... for 8-hour capacity... a canister should hold approximately 1 kilogram of (2.2 pounds) of SodaSorb absorbent".

 

On my boat, I picked a canister size to meet my normal mission time and then played around with different fan motors until I found a fan size that would circulate the cabin air through the canister without pulling so much current that it would drain my emergency battery bank before I reached the 72 hours limit.

 

While this worked fine, I wondered about what a "properly packed and well designed canister" meant.  I recently came across an excellent technical report that goes into a lot more detail on this subject.  It is titled "Design Guidelines for Carbon Dioxide Scrubbers", (May 1983, revised July 1985) by M.L. Nuckols, A. Purer and G.A. Deason of the Naval Systems Center , Panama city Florida .  http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA160181&Location=U2&doc=GetTRDoc.pdf

 

This goes into the impact of design variables such as temperature, pressure, canister length and diameter, relative humidity, CO2 concentration, flow rate through the canister and particle size.  The experimental work sited in the paper is for SodaSorb.  While this report was written for designing re-breather canisters operating at elevated pressures that a diver would see, it does handle the limiting condition of 1 atm that we would see in a 1-atm. psub.

 

So if you need a little "light" reading while your doing your business in the morning, you might want to have a read.  Now if we could just get someone to drop this into an excel spreadsheet, we would be in business.

 

 

 Cliff