Carbon Dioxide (CO2) Solubility in Water

[JasonMoore]

Greetings,

While using a packed scrubbing bed, is there a chart, reference table or simple equation that I can use to determine the water flow and pressure required to remove a known quantity of CO2 from a gaseous stream?

Is there any need to worry about the water picking up some of the trace amounts of CH4?

I know other liquids could work more efficiently, but I have a liberal supply of water and want to avoid chemical usage at all costs.

The gas is 93% CO2 and 7% CH4 @ 350 cfm.

Thanks a ton.

 

[DeltaCascade]

Water quality used will be key due to formation of carbonic acid:
CO2 + H2O <==> H2CO3
If you neutralize the acid, it will increase the carbonate loading achievable.
Stripping towers to remove CO2 from water (after an acid cation ion exchange bed in water demineralization plans) are likely more common. Maybe Perry's Handbook has something?
Isnt PSA or other process more standard for this?

 

[zdas04]

JasonMoore,
Do a Google search on "Henry's Law" to get an idea of the amount of gaseous CO2 that can be disolved in water. Be careful with the constant because it is stated at atmospheric pressure, ambient temperature, and pure solute.

Adjustments for pressure are pretty consistent from one reference to the next, but the adjustments for temperature vary widely--you have to end up picking one and going with it. The adjustments for non-pure solutes are really ugly. It gets especially difficult if the solute is contaminated with NaCl.

Once you have determined how much CO2 can be absorbed at your conditions (the number is really amazingly small for most conditions), then you need to understand the CO2 reactions with water. It is very complex. The reaction that DeltaCascade quoted will happen at certain values for pH. At other values of pH the reaction results in a BiCarbonate radical (which creates a base). Prediciting which reaction will happen in a given stream is the topic of hundreds of NACE papers since CO2 is a major driver for several types of corrosion (which are also pH dependent).

Luckily, the ability of CH4 to disolve in water is very weak (but not zero). Generally what happens is small amounts of CH4 are disolved, then at some inconvenient time the CH4 evolves out of the water due to a pressure or temperature change. The quantites are small enough not to be a major factor in the chemical reactions you are trying to accomplish, but big enough to gas-lock a pump or pipe.

Using water to try to get rid of CO2 is a really risky undertaking that will create a significant corrosion risk, require amazing amounts of pump energy, and be pretty ineffective. Have fun with this.



David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

The harder I work, the luckier I seem

 

[m777182]

The rate of adsorption of CO2 in water is governed by a diffusion of gaseous CO2. The maximun attainable concentration is given by Henry's low.
The adsorption with chemical reaction would be much more efficient.It seems like a problem of optimization of alkali costs against size of equipment and energy consumption.
m777182

 

[25362]

Besides the above factors (diffusion, Henry's Law solubilities, pH of water) one must consider that the efficiency of gas scrubbers is governed by factors such as the surface of contact, the volumetric gas/liquid ratio, contact time, temperature, pressure, and type of absorber (parallel or counterflow) for example, a bubbler, a spray chamber, a packed, baffled or trayed vessel, a venturi, etc., and their respective loadings.

Chapter 14, in Perry Ed VI, may be useful reading on this respect.

 

[sbush]

I have a chart that was produced by the German company that manufactures Norpac, polypropylene packing material. I can send a copy through the link below.

S. Bush

http://www.water-eg.com