Compressing captured CO2
Compressing captured CO2
(OP)
I am in the very early stages of designing a system to capture and compress CO2. I have made many assumptions like: complete combustion (of my system), 90% capture ability, MEA is my "capture" solvent, 100% of captured CO2 is stripped and available for compression, compression is 1 stage. This allowed me to come up with "ideal" sizing of compressors depending on my process conditions.
I have been asked to evaluate multi-stage compression with inter-coolers as well as compression versus refrigeration & pumping. I'm really struggling to find a starting point for that request. While I have a chemical engineering degree, I went directly into industry and haven't maintained my thermo and mass transfer.
Could you point me in the right direction? If I know the volume I need to compress, it's initial temperature and pressure, and the pressure I need it compressed to, how do i figure out how many stages I need, and how hot it gets between stages?
I would also like some information regarding how to actually compare energy requirements of pumping CO2 to the pressure I need versus compressing it. I have a small stream (in terms of both volume and concentration), in which pumping may actually be reasonable. I don't know where to start to evaluate it.
Thank you. If i'm missing any pertinent information for your help, please let me know. I may have it and accidentally left it out.
I have been asked to evaluate multi-stage compression with inter-coolers as well as compression versus refrigeration & pumping. I'm really struggling to find a starting point for that request. While I have a chemical engineering degree, I went directly into industry and haven't maintained my thermo and mass transfer.
Could you point me in the right direction? If I know the volume I need to compress, it's initial temperature and pressure, and the pressure I need it compressed to, how do i figure out how many stages I need, and how hot it gets between stages?
I would also like some information regarding how to actually compare energy requirements of pumping CO2 to the pressure I need versus compressing it. I have a small stream (in terms of both volume and concentration), in which pumping may actually be reasonable. I don't know where to start to evaluate it.
Thank you. If i'm missing any pertinent information for your help, please let me know. I may have it and accidentally left it out.
Maggie (ChE 2002 from RHIT)
Specialty Chemical Manufacturing, Electric Utility, Medical Device Manufacturing, Plastic Packaging Manufacturing, CO2 Capture Research





RE: Compressing captured CO2
Some points that came to mind reading your post:
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist
RE: Compressing captured CO2
Thanks for your reply. I'm stripping diesel engine exhaust, and my flowrate varies from 0.25MMSCFD to 0.66MMSCFD depending on the type and size of engine. Coming out of the stripper, depending on the technology, puts me in the range of 1atm-5atm (i'm also evaluating multiple capture technologies. i just started with the MEA). I have various levels of useful pressurized CO2: 1600psi for storage, 2200psi for pipelines, and 3500+ for industrial uses.
I wasn't super clear about my flowrates. I'm sure that I will need a centrifugal compressor. I have multiple potential process operations, and each one would require a different sized compressor. I have 4 different/separate process scenarios I'm trying to evaluate.
I have been asked to size both a 3-stage and 6-stage centrifugal compressor, and if i'm being completely honest I don't know where to start. I'm reading through my Perry's Handbook, and surfing Google. I'm looking for a refresher on what I should be doing so I can remember some fundamentals I've long since lost.
I spent most of my time since graduation in manufacturing and electric utilities as a project/process engineer. I'm now in a research role and struggling a little trying to get up to speed quickly and be a contributor.
Greatly appreciate your response, thank you.
Maggie (ChE 2002 from RHIT)
Specialty Chemical Manufacturing, Electric Utility, Medical Device Manufacturing, Plastic Packaging Manufacturing, CO2 Capture Research
RE: Compressing captured CO2
You do need in this case that the compressor casing is capable to withstand quite some high pressure (up to 200 bar) of course lower in case of solution with a pump. It is also important to have max possible efficiency at 1st impeller. Peripheral speed can be quite high only with open type impellers. Also attention is to be paid to the dryer where is it located...
Alternative is to use between bearing design centrifugal compressors...also possible.
"If you want to acquire a knowledge or skill, read a book and practice the skill".
RE: Compressing captured CO2
Our two centrifugal compressors were as follows: The low pressure machine was 6 stages and the high pressure machine was 5 stages. They were driven off of two pinions on a single gearbox with a motor driver. This was a very bad set-up for many reasons. The two pinion gearbox was a very bad idea. The compressors were designed for refrigeration service and were not well designed for a process that generates as much heat of compression as C02. We had coupling and alignment problems because of the high temperatures.
I would recommend that you contact some compressor manufacturers and get their recommendations. We had trouble with our York system but they may have better technology than they had when our system was built in the 1970’s. And, I think they have quite a bit of experience with CO2 compression and liquefaction. I don’t know of any other manufacturers with specific expertise in CO2.
Johnny Pellin
RE: Compressing captured CO2
For instance, if i have 1MMSCFD of 95% pure CO2 at 1atm and 100F, and I want to compress it to 150atm, how hot will it get (T2 if you will), and how many stages will i need to get from 1atm to 150atm? How do I determine the heat from each stage of compression? For example, if I compress from 1atm & 100F to 5atm, how much heat will be created? Then, if I cool that back down to say 100F and then compress from 5atm to 50atm, how much heat will I have?
I think I'm missing some fundamentals of isobaric and isothermal operations within the compressor (as a whole).
Could someone help me understand elementary compressor equations?
Maggie (ChE 2002 from RHIT)
Specialty Chemical Manufacturing, Electric Utility, Medical Device Manufacturing, Plastic Packaging Manufacturing, CO2 Capture Research
RE: Compressing captured CO2
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist
RE: Compressing captured CO2
Thank you!
Maggie (ChE 2002 from RHIT)
Specialty Chemical Manufacturing, Electric Utility, Medical Device Manufacturing, Plastic Packaging Manufacturing, CO2 Capture Research
RE: Compressing captured CO2
You need to be aware of a few issues when trying this scheme.
1) CO2 at 95% has a markedly different phase diagram than the pure CO2 diagrams you will find. There is no sharp line between gas and liquid, but more of a 2 phase zone which no one really understands. Hence to go from gas to liquid you need to basically keep it above 35C as you rise in pressure and then keep it above 80-85 barg and no colder than -30C to keep it liquid to stay out of this zone.
Each stage will probably have a compression ratio of 2 or less, but 5 or 6 stages is usually about as far as you can go in any one unit and may need intercooling.
Heat output is not so easy as you are changing many things, including state, but I'm sure there is a lot out there to explain this and provide some worked examples.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Compressing captured CO2
As part of a pressure maintenance program for a retrograde condensate field, my predecessor designed a set of compressors that would take ehaust gas from the intergal engine. Then compress to 2000 psig. The material and enetgy balance work. In practice, the compressor was corroded to the ground in 6 months.
Installing a CO2 sytem to extract just the CO2 is not without the same issues. Corrosion
Next, to get to 1700 psig from the system, itll be a 5 stage recip. 3500 psig is a 6th stage or a 5 stage with a punp. The proble will come when the gas is going through the critical point. My moto, a compressor or a pump doesnt care about the fluid, but just dont change phases in the middle of the process.
Water will be your enemy and your friend. Deal with dehydration. Its an issue the same as phase change
Any more than that, you need to hire a PE to get it right