CO2 Recovery in a Packed Tower Scrubber

You say you are "working" on a study?

Sounds more like homework. Of one sort or another.

We don't do other people's homework.

Interesting idea but why use caustic soda? I would have thought the use of lime would be a little less hazardous and could be done in a dry state. Regeneration would be the same. Need to check out uses for calcium chloride but no worse than salt solution.

Carbon dioxide is very soluble in water especially under pressure and cold. It is just seltzer - if some pressure was used the solubility would increase - just like making seltzer/soda water bubbling it through a pressurised tank/column - this could be used to water the plants or just heated to generate CO2 again. Pressurising the packed tower could help but there might be too much agitation. It would be interesting to see how much CO2 you could get out of the flue gasses which would be very high in nitrogen. A long skinny tube might be the answer just like making sodium hypochlorite, the water head creates the pressure at the point of injection - the bottom. Let me know if it works this is theory.

I wonder if the problem entry is a homework assignment to help you understand chemistry and engineering, or if you have a serious inquiry. On the chance you are serious, I will point you in the right direction.

There are several variations of industrial processes for removing CO2 from a gas stream such as flue gas and recovering the CO2 as relatively pure CO2. Most use an organic amine solution in water as the working fluid and not NaOH. The reason is that it is too difficult, costly, hazardous, and energy intensive to regenerate the NaOH using the scheme you mentioned. If you are wanting a "green" process for recovering CO2, the process you mention is not the way to go for a lot of reasons. Industrial recovery of HCl from NaCl is accomplished using the "Kelchlor" (spelling might be off) process. Look it up.

In one more energy efficient commercial scheme, CO2 is scrubbed from the flue gas using a chilled (or at lease cool) aqueous organic amine solution. The CO2 loaded solution is then heated to release the CO2 in a second tower. In the scrubber, lean solution gravity flows counter current to the flue gas. The lean solution must be cooled before it enters the top of the scrubber. As the solution flows down the tower, it absorbs CO2. The amount is temperature dependent (cooler is better). There are several variations of this process which are offered by the orginic amine vendors who want to sell the technology and the amine.

In the stripper, loaded solution enters the top of the stripper and gravity flows counter current to the CO2 gas stream. The bottom of the stripper is heated to release the CO2 from the loaded solution. Efficient heat transfer between the loaded and lean solutions is the key to making this process economically viable. Use Google or Wikepedia to search for CO2 recovery processes if you are interested in the flowsheet.

Hope this helps.

I wish to recover CO2 from fermentation of sugar and use purified CO2 for food industy. CO2 absorption and later desortion process is interesting. Can you tell me how much of methyl amine is found in the CO2 gas after desorption tower. Can it meet the standards of ISBT to be used in food industry.

Wish to hear from you.

Vainateya

Hazman + HarrelW

Both thanks for your positive reactions.

The problem is the temperature of the flue gasses, in the flow downwards of the scrubber liquid,
it will be heated up from the hot gas, so what you absorbed in the cool liquid zone on top will be
escape from the warm liquid zone in lower part of the scrubber.

In vegetable greenhouses the amount of CO2 required during daylight is approx 200 kg/h for
6 to 8 hours and the average area is 2 HA (5 acres), so a need of storage capacity of 1600 kg dissolved CO2 gas is required.

I accept both your concerns and doubts and going back to the drawing board to start over again with a more users friendly and safer process.

Thanks a lot

Thanks to all of you gentlemen. I work with a company that manufacture packed tower scrubbers for a number of uses but mainly large scale biological odour control. With the current world wide attention being given to carbon sequestration and reduction of 'global warming' agents I have been wondering for a while if our technology could somehow be adapted to meet this challenge. I have followed this string with considerable interest as it now gives me some new ideas that I can research and perhaps develop into another "string in our bow".

I thank you all for your ideas.

Pete.

Cool the hot flue gas by cross exchange with the recovery tower bottoms. In that way the heat needed to release the CO2 is recovered waste heat and does not cost anything except the return on capital, and the scrubber flue gas feed is cooled. Also if the flue gas has too much CO2 then use a slip stream sized to match the CO2 requirements.

CO2 storage will be the same issue regardless of the flue gas scrubbing scheme you choose. You can compress it, use a large ballone, leave it in the solution, or maybe something else, but you still have to deliver what is needed when it is needed.

A little innovative thinking will lead you to a workable solution.

Good luck.

Peter,

I understand your concern with regard to the hot flue gases. Is there some way you could cool the flue gases before adsorption, perhaps with a longer flue pipe that can radiate to the outside air, or perhaps passing it through a regenerative heater jacket? Perhaps you may be able to recover heat from the hot flue gas that can be used elsewhere in your process while helping to cool it for more efficient adsorption. This way your costs are lowered, thus making the CO2 adsorption process more affordable.

Pete.

If heating a greenhouse why are you wasting the energy by putting it up the stack, Pass the flue gases through a heat exchanger and, after filtering, use this air to heat the greenhouse. To maximise the solution of carbon dioxide you need to cool as far as possible -a chiller in the circuit would be best. Otherwise mix the cooled gas with air and put it into the greenhouse you should get the CO2 and the heat. Problem could be the excess of nitrogen.

Maybe a large gas or oil fired refrigerator could be what is needed. Make the CO2 at the input end and dissolve the CO2 out at the chilled end. ? could this provide the heat required?

Hazman

On this very moment the greenhouse growers firing the heating boilers also on sunny day times in summer times, even they don't need the heat but only for generating and dosing the CO2 included the not wanted N2 and latent heat inside.
The flue gasses are cooled down as far as possible by economizers, all produced heat are used to heat water which is stored in big vertical insulated storage tank and is used (extracted from the storagetank) when the heating is needed.
In principle there is not a lot of waste energy during the winter time but in summer when the maximum CO2 is required, there is .

To get rid from the extra N2 (and heat also) inside, is to get out the CO2 from the flue gas during the nighttime, when heating is necessarily, and recover only pure CO2 during daytime from the dissolver liquid.

Another process is available that can scrub CO2 from other gases and disolve it into water. It then be pulled back out of the water with an inverse process for when you need it.

see www.mittonvalve.com under valve R&D.

Hi all, our company is working with a new product.

It can absorb only the Co2 from the flue gas(it can be tuned for different or multiple gases), the Co2 can then be compressed and stored for use at a later date. The product itself is a nanofibre and this can be easily regenerated in situ and cycled mulriple times much like a psa system.

I have also been working with a company recently dealing with PCM (phase change materials) which absorb and release heat in a certain tempreture range so regulating the heat in buildings. This could be adapted to work in green houses. If you want anymore info on either please let me know.

What is the operating temperature and pressure of the system? If it is greater than 413K the operating parameters change as it affects the equilibrium more rapidly. Assuming 1atm pressure, 298K, 1000Nm3 of CO2 would translate to 40816.326 moles of CO2. which means No. of moles of Na2CO3 is also 40816.326 assuming the system is 100% efficient. However since this is never the case, previous studies show operating efficiency of about 75%. One would need amount of HCl=twice the no of moles of CO2=81632.652 moles of HCl. if u use 1M solution, u would require 81632.652 L of HCl, 0.5M 163265L HCl etc. yogendra.kanitkar@gmail.com