CO2 Removal 1

[mmilbury]

I am working on a system that is to remove CO2 from Natural Gas. The composition is as follows:

(Mole %)
O2: 8.154
Nitrogen: 29.401
Carbon Dioxide: 29.596
Carbon Monoxide: 0

Methane 30.3
Ethane 0.882
Propane 0.187
IsoButane 0.091
n-Butane 0.105
IsoPentane 0.109
n-Pentane 0.141
Hexanes + 1.035

How can I determine how much NaOH I will need to remove CO2 from this gas at a rate of 250,000 SCFD?

Any help is greatly appreciated.

----
An optimist sees the cup half full
A pessimist sees it half empty
An engineer sees it twice as large as it needs to be.

 

[nosaMgiarC]

mmilbury,

Removal of CO2 from natural gas usinf NaOH is only possible if you were to convert the CO2 to it's acidic form by for example bubbling it through water to form carbonic acid. This seems like a strange way of doing it when there are already a number of other more sucessful methods available ie. amine scrubbing or through the use of membranes.

On your specific question. You need 2 mol of NaOH per mol of C02. For your rates specified you would need ~7 tonnes of NaOH per day. However you would generate lots of waste sodium carbonate and if this is in a water stream it's a bugger to recover, and how would you dispose of it?

Realise I've rambled a bit so hope some of this helps.

Craig

 

[mmilbury]

Thanks a ton. Thats exactly what I was looking for. We are trying to see if how much NaOH we are going to consume a day and 7tonnes is quite a bit. Not exactly cost effective since, in the long term, there are cheaper things out there.

----
An optimist sees the cup half full
A pessimist sees it half empty
An engineer sees it twice as large as it needs to be.

 

[zdas04]

MMilbury,
You've got tougher problems than how much base to use to neutralize carbonic acid. 29% N2, 8% O2, and 30% CO2 is a tough a mix of gases as I've seen (if you had any H2S I'd expect the piping to disolve before your eyes). The technology to get rid of each of those products is big and expensive. Any way to not inject the air that is adding the N2 and O2 (e.g., can you inject CO2 instead of air, then you only have one nasty problem instead of 3)?

David

 

[Fausto]

Hi,

Theoretically, you don't need that much NaOH to remove the
CO2 from your gaseous stream. It happens that the actual
NaOH+CO2 reaction is:

NaOH (aq.) + CO2 --> NaHCO3

So, sodium bicarbonate (a.k.a as "baking soda&quot will form
thus removing your CO2 at a 1:1 mole basis. Therefore, only
3.7 tonnes/day of NaOH would be necessary (at a 100%
reaction yield). Only in *excess* of NaOH the reaction

NaHCO3 + NaOH (aq.) --> Na2C03 + H2O

would take place.

Yet the effluent disposal problem would persist.

Hope I'm not mistaken...

---Fausto

 

[MortenA]

But remember that co2 solutability in water is relatively low. You would therefor need a very big contactor compared to a similar capacity amine contactor.

Best regards

Morten

 

[jcaiken]

Don't forget the potassium carbonate based Benfield type of processes when doing your process evaluation.

Removing the CO2 will still leave a gas with only 40% methane and 40% nitrogen with a heating value about half that of typical natural gas. Will N2 removal be the next stage? Would a process to remove the 30% methane be more efficient?

I'd suggest that you use it as fuel as is for local power greneration.

This is an unusual mix of gases but the O2/N2 ratio doesn't match with air injection.

 

[pkv61]

PSA SYSTEM USING MOLECULAR SIEVES IS THE BEST OPTION FOR REMOVAL OF CO2 FROM NATURAL GAS WITHOUT WORRYING ABOUT WASTE FORMATION

 

[zdas04]

PKV61, Why are you shouting? We're listening.

PSA can be effective, but the regeneration-gas quantity is pretty large at low pressures and that can be both an economic and environmental concern. Also a mole-sieve designed for CO2 won't touch the N2 and O2. A 3 media bed gets pretty large and expensive.

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

 

[dcasto]

Walk away from the gas. The amount of energy it is going to take will almost exceed what is available. unless this gas is at 1000 psi to begin with, you'll have to have a compressor burning propane or diesel.

 

[jsummerfield]

zdas04
David, your posts are normally outstanding. Please do not make the silly utterances without explaining what it is that you are going on about. A newby will not understand your point without some additional detail.

PKV61, David is pointing out that since the early days of news groups, the web forums regard ALL CAPS as shouting.

There appears to be a lot of O2 in that gas too.

Regards,

John Summerfield, PE

John

 

[rjmag]

I am making this reply in hopes of generating a less costlier(as compared to AMINE Treating) way of reducing CO2 in a natural gas well stream. This web source came up indirectly in a GOOGLE search of CO2 removal with caustic. The idea of using caustic was mentioned to me by someone who said he had used it on low flow marginal well however I have not found anything available or discussed that is used commercially.

If someone has any suggestions let me know. The following describes the problem i face which is trying to determine a low cost CO2 reduction process based on the parameter noted and less costlier than the high capital and high operating cost Amine Treating system.

I need to reduce the CO2 level from about 2.8% to 2% for the total concentration of 3 gas wells before the gas will be accepted by the pipeline. While the past production history of these wells illustrate very marginal rates ~ 40 to 50 mcfd total, there is room for improvement and such circumstances as fluid loading, holes in tubing and perforation covered over indicate such improvement can be made. If these problems are fixed I feel that rates of 100 - 300 mcfd may be attainable with ~ .25 to 5 bcf reserves.

The main economic obstacle that I am facing in restoring production on these wells is the potential cost of a standard CO2 reduction sytem (AMINE TREATING UNIT, initial quotes of $75,000 not counting installation)and its high operating cost drain.

I would like to get the wells online without mitigating the production problems noted above and then later tackle them after generating some income. There is no way that this project will move forward if an Amine unit is my only choice to get my gas to meet pipeline specs.

It would be interesting to be able to create the chemical processes, equilibriums and equipment designs that would go on with the reaction of caustic and CO2 in some type of system that would lower CO2 in natural gas streams of marginal production rates noted as opposed to using the standard Amine treatment.

The reality however is that if reaction of CO2 with the NaOH is 1:1(I have read in other forums that if CO2 is gas phase, it may be 1:1), then .8% removal of CO2 from a 50 mcfd rate would still yield a volume of 400 cu ft of CO2 which is just over a mole(400/379ft3 per mole). This would correspond to the need for ~ 50 #/day of NaOH and disposal. for 200 mcfd, ~ 200 #/day NaOH.

At this point I wa tying to find prices for blk Naoh and I am having trouble but if it is under $1/lbs and if disposal of NaHCO3(Sodium Bicarbonate could be near what salt water is then it would definitely cost less than Amine Treatment.

any feedback or commets on the above analysis would be appreciated

 

[CANDO123]

have you considered a prism membrane?

i too have a project to remove co2 from marginal wells