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What is Largest Practical Limit? 1
- Thread starter ppeng01
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Let's assume that you're talking about an air compressor going from about 14.73 psia and 60F (so the suction acfm is basically SCFM) to 100 psig. That is less than 8 compression ratios so it is probably a 2 stage recip or single flooded screw. In either case it is around 330 hp. That is what is called a small industrial air compressor. Yeah, they come a bit larger than that. The practical limit is at least 20 times larger.
If you told us what you were trying to do, you might get some help selecting equipment.
David
If you told us what you were trying to do, you might get some help selecting equipment.
David
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- #3
I may not have been clear about the flowrate. The flowrate should be 2,000,000 acfm @ 14.7 psia, 130 deg F, and at a density of 0.06 lbs/ft^3. This is just a thought problem, but I am curious about the feasibility of compressing fluegas from a power boiler from 15 psia to 100 psig.
The flow rate is around 2.5 MMSCF/day (the elevated temp reduces the SCF number about 12%) and you are not going to a very high pressure.
Most of the time I get asked to look at this sort of problem, the target discharge is 1,000 to 10,000 psig and the hp requirements go way up. Your application is 250 hp (with the lower mass flow rate)--to go to 1,000 psig the hp goes to 1100 hp in three stages, and at 10,000 it is around 2,800 hp in 5 stages.
Compressing flue gas is done every day. Your boiler doesn't sound particularly large (I don't have a feeling for the BTU rating of the boiler based on flue gas flow rate) and this is a pretty easy application.
David
Most of the time I get asked to look at this sort of problem, the target discharge is 1,000 to 10,000 psig and the hp requirements go way up. Your application is 250 hp (with the lower mass flow rate)--to go to 1,000 psig the hp goes to 1100 hp in three stages, and at 10,000 it is around 2,800 hp in 5 stages.
Compressing flue gas is done every day. Your boiler doesn't sound particularly large (I don't have a feeling for the BTU rating of the boiler based on flue gas flow rate) and this is a pretty easy application.
David
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- #5
Am I slipping a decimal point somewhere?
2E6 acfm * 60 min/hr * 24 hr/day * 88% = 2.5e9 scf/day
= 2500 mscf/day
Theoretical Hp if one stage is approximately
144/33,000*(1.4/(1.4-1))(14.7 psia)*(2e6 acfm)*((115/15)^((1.4-1)/1.4) - 1)
= 354,500 Hp
It looks like we're off by a factor of 10^3.
2E6 acfm * 60 min/hr * 24 hr/day * 88% = 2.5e9 scf/day
= 2500 mscf/day
Theoretical Hp if one stage is approximately
144/33,000*(1.4/(1.4-1))(14.7 psia)*(2e6 acfm)*((115/15)^((1.4-1)/1.4) - 1)
= 354,500 Hp
It looks like we're off by a factor of 10^3.
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1
- #6
guys its 2.88 BCFD!!!! that is about 6 times larger than GE has listed under it's axial compressors.
My speculation is; you will only need to get the flue gas pressure to 30 to 50 psig inorder to remove the CO2.
My speculation is; you will only need to get the flue gas pressure to 30 to 50 psig inorder to remove the CO2.
- Thread starter
- #7
Thank you! The 33,000 is the conversion from ft-lbf/min to Horsepower and the equation I posted is for acfm. I am talking about 7.5 million pounds per hour of gas or 2.5 billion scf/day.
Thank you for the reference to axial compressors. I knew I would have to use multiple compressors, if it was realistic at all. If my pressure was lower, say the 30 psig you mention, would that allow me to use fewer centrifugal compressors, or some other type?
Thank you for the reference to axial compressors. I knew I would have to use multiple compressors, if it was realistic at all. If my pressure was lower, say the 30 psig you mention, would that allow me to use fewer centrifugal compressors, or some other type?
As the great Emily Latella said "Never Mind". It really is amazing how attached you can get to a wrong bit of arithmetic. The OP was right about the magnitude of the hp, I get 360,000 hp.
As to how high you need to get the pressure, that depends on what you are going to do with the stuff. If you're just going to separate out the CO2 from the water and Nitrogen compounds then you can do it at a pretty low pressure, but what then? Putting pure CO2 into the atmosphere has the same "carbon tax" risks as just letting the mixture go up the stack (to say nothing of the emissions from the compressor drivers). CO2 sequestration projects generally require pretty hig pressures (the one I worked on late last year was at 1,200 psig and that is the lowest I've seen). If you are going to try to get to food grade CO2 the market is pretty saturated.
David
As to how high you need to get the pressure, that depends on what you are going to do with the stuff. If you're just going to separate out the CO2 from the water and Nitrogen compounds then you can do it at a pretty low pressure, but what then? Putting pure CO2 into the atmosphere has the same "carbon tax" risks as just letting the mixture go up the stack (to say nothing of the emissions from the compressor drivers). CO2 sequestration projects generally require pretty hig pressures (the one I worked on late last year was at 1,200 psig and that is the lowest I've seen). If you are going to try to get to food grade CO2 the market is pretty saturated.
David
if you go to and then to publications and then to papers 2008, you will find two papers discussing CO2 capture from stacks.
I also ran simulations and what you find out is you will have amine circulation rates in 50,000 gallons/minute with 20 to 25% of the power plants electricity and low pressure steam being used in recovering the CO2. Then you will expend another 5% to 15% of the power plants output compressing the CO2 to pressure wher it can be sequestered. These papers will also verify the cost to remove. The recovery plant will have a capital of about 25% of the original power plant, then with the loss of 35% of the plants capacity, you'll have to make the power plant 50% larger than you need. The net is the capital cost will nearly double and the energy output price will nearly double.
I also ran simulations and what you find out is you will have amine circulation rates in 50,000 gallons/minute with 20 to 25% of the power plants electricity and low pressure steam being used in recovering the CO2. Then you will expend another 5% to 15% of the power plants output compressing the CO2 to pressure wher it can be sequestered. These papers will also verify the cost to remove. The recovery plant will have a capital of about 25% of the original power plant, then with the loss of 35% of the plants capacity, you'll have to make the power plant 50% larger than you need. The net is the capital cost will nearly double and the energy output price will nearly double.
I got similar numbers. The only way I can see sequestration working is if you need the CO2 for an enhanced recovery project. Then the compression capital and operating costs go to the EOR/ECBM project and the economics get much better. Without that, the "carbon tax" would really have to be huge to offset.
David
David
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