Help for CO2 pipe 1

[Daniele1979]

Hello,
first of all I'm sorry for my english, but I hope you will help me
I would have need help to project a CO2 piping. The pipe will be 50 km, at the end of pipe I need 80 bar, and the gas capacity is 47 ton/hour.
Thank you

 

[Montemayor]

Daniele:

What do you mean by "project a CO₂ piping"? Do you mean that you want forum members to calculate the diameter and specify the alloy and type of pipe, valves, and fittings as well as defining how to install the pipeline? If so, I'm afraid it won't happen.

You should tell us your scope of work: is this a real, industrial project or an academic exercise or problem? How is it you are working on such a project and you don't know enough about it to give us the necessary basic data? For example: you tell us the end pressure you want, but you fail to tell us the starting pressure. What is the difference in levels between the start and finish - or is the P/L level? What is the temperature of the CO₂ fluid and what is its state. Is it gaseous, liquid, or supercritical? It seems to be liquid (even though you say it is gas), but you should verify that.

I'll await your reply.

 

[Daniele1979]

Ok, I'm sorry, the question was incomplete.
The state of CO2 is supercritical, the initial pressure is approximately 110 bar. At the moment I do not know the difference in levels, but it would be enough to know some formulas in order to calculate the geometric characteristics of the line.
I hope of to have been preciser and that you can help me.
Thanks

 

[BigInch]

Compressibility and density are nolinear with pressure and temperature, thus its difficult to predict CO2 flow. There's no easy equation I know.

You're going to need to get the basic elevation profile. Its critical information.

There are a few kinds of tons. How many Kg does your ton have?

Is it pure CO2, or is it associated with some natural gas, N2, O2, H2S, H2 or water content?


What is the high and low design temperatures along the route?

Going the Big Inch!

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[insult2injury]

The behavior of CO2 follows the generallized compressibility chart extremely well.

 

[BigInch]

Yes. Highly nonlinear. Agreed?


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[Montemayor]

Daniele:

You still don’t furnish answers to my questions. The flowing temperature is a key parameter now that you reveal that we’re talking about supercritical CO₂ – and not a gas as first stated. The viscosity is in the range of 0.02 - 0.1 cP, where conventional water-like liquids have viscosities of approximately 0.5 - 1.0 cP and gases approximately 0.01 cP, respectively. Since you don’t state the temperature, you don’t fix the viscosity values.

Contrary to what Insult2 states, the behavior of supercritical CO₂ does not “follows the generalized compressibility chart extremely well”. In fact, we don’t even know what to call the fluid – a liquid, a gas, or a “mush”.

The advantage to transporting the fluid as a supercritical one is the resultant low pressure drop due to the low viscosity exhibited. If you are a professional engineer you should easily be able to apply the Darcy Weisbach equation to generate the size of pipe required to yield your 30 bargs of pressure drop.

For the physical properties (especially the viscosity) on the fluid go to:

http://webbook.nist.gov/cgi/fluid.c...nit=kJ/mol&WUnit=m/s&VisUnit=uPa*s&STUnit=N/m

Happy calculating.

 

[BigInch]

Montemayor,

I didn't know you could use D-W for dense CO2. Any special limitations? C value? Short segments?

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[Daniele1979]

Ok thank you
I'm an engineer but it's the first time I must project a supercritical gas pipeline. Anyway I will try to continue using your suggestions

 

[Montemayor]

BigIncher:

The Darcy-Weisbach relationship (also simply called the Darcy equation) is valid, according to the GPSA Engineering Databook, for both laminar and turbulent flow of any liquid, and may be used for gases with certain restrictions. This equation can be rationally derived by dimensional analysis, with the exception that the corresponding friction factor must be determined empirically. Therefore, knowing that we are dealing with a fluid (even though we don’t know what to call it – a gas or a liquid?) that is pretty close to the constraints imposed on the equation, such as constant fluid density, we are free to take license and employ it – as long as we stay within the confines of the equation’s basic constraints. Those basically are the limitations.

I don’t know what is meant by a “C” value. Are you referring to the Hazen-Williams equation (which is not even close to Darcy in applicability)?

And yes, I would divide the line length into convenient and reasonable segments – to ensure we stay within the equations constraint on density variance. Please note that the reason I go to the NIST is to make a strong point: note the relatively stable values of the density and viscosity at an isothermal condition of 25 ^oC (77 ^oF): Density varies by 7% and viscosity by 14%. With this kind of relative stability, I don’t have any ill feelings in using the Darcy-Weisbach. But perhaps others do. I’d like to hear about it because I’ve used the Darcy on supercritical CO₂ in the past and always got results as good as if it had been water.

 

[BigInch]

Did I say "C"?

Right, I guess there would be no reason D-W wouldn't work, as long as the state is tracked accurately. My apprehensions should have been more directed towards doing a simple one flow, one state analysis and from what I've seen reported from Midwest Regional Carbon Sequestation Partnership/2005-6 Battelle, where, if state was allowed to vary significantly, I could see where it would be difficult to analyze propery by hand.

Maybe that has more to do with the apparently typical CO2 pipeline mixture not being 100% pure, or the necessity for transitions through 0 to 10 bar in pipelines from time to time.

With the special characteristics of CO2
accounted for, design methods for natural gas pipelines generally apply also to CO2 pipelines. Compressibility and density of CO2 undergo significant non-linear variation in the normal pipeline
operating conditions (within normal pipeline pressure and temperature ranges). Design of CO2 pipelines
therefore requires the use of computer codes that allow point-by-point estimation of fluid properties using
an equation of state (Farris, 1983). Property correlations may need to be validated with bubble point
experiments to ensure accuracy (King, 1982a, 1982b). Also, impurities impact compressibility of CO2 and
result in reduced flows through the pipeline. Table 4.2 shows the effect of some impurities on CO2 pipeline capacity. It is therefore important to also consider the impurities present in the gas stream and
their likely impact on the flow characteristics. The impurities present in the CO2 stream depend on its
source as well as the capture and purification methods used.

1 In a blowdown test with a 9.9 mile (16 km) section of 16” pipe (40.6 cm), with initial CO2 pressure and
temperature of 1500 psi (10.3 MPa) and 40 °F (4.4 °C), respectively, the fluid parameters dropped to the liquid
vapor envelope (560 psi and 40 °F or 3.5 MPa and 4.4°C) in 2.5 minutes. After that the rate of pressure drop
decreased dramatically and required 10 hours to depressurize the systemto 100 psi (0.63 MPa) while the
temperature dropped to -52 °F (- 47 °C).

It goes on to mention some other pipeline concerns

Temperature changes are accompanied by changes in the pipeline pressure and similarly, pressure swings
cause the temperature to change. Therefore, it is necessary to use thermal relief valves to protect segments
of pipe that can become isolated by valve closures.A leakage causing rapid pressure drop in the pipeline
can cause the temperature to drop to -50 oF (- 45 oC). In order to avoid damage to pipeline components
from such low temperatures, the system design must include measures to avoid rapid pressure reduction.
The blowdown valves need to be carefully sized to limit the rate of release such that the pressure
reduction does not cause excessive cooling (Recht, 1986).

For the ease of coordinating the operation of the compressor and the pipeline, some surge storage capacity
is also required to control pressure transients during flow changes (similar to water hammer in liquid
pipelines). During start-up and shutdown operations, fail safe valves divert the flow to the surge storage
tanks; however, due to the high flowrate and high pressure involved, it is not possible to provide enough
storage for uninterrupted operation during prolonged outages. Consequently, the pipeline and compressor
systems require high reliability to avoid release of CO2 into the atmosphere or interference with the
operations of the CO2 source (such as a power plant).

Measures are also required to avoid over-pressurization of the pipeline. A “linepack” occurs when the
upstreamcompressor continues to operate even when a downstreamvalve is closed. Eventually the
compressor shuts down when the discharge pressure rises sufficiently. Such accumulation of CO2 in a
section of the pipeline, which can be several miles long, is undesirable because CO2 cannot be vented or
disposed off without some risk to the personnel, equipment or nearby populations. A CO2 accumulation
monitoring systemalong the pipeline is therefore essential.

Booster Pumps
Longer pipelines or hilly terrain are likely to necessitate booster pumps to compensate for the pressure
loss. These pumps are likely to be centrifugal pumps designed generally in accordance with the
requirements of API 610. The material combinations specified in API 610, column 6 have been used for
CO2 applications. However, due to the differences between CO2 and the fluids pumped in the petroleum
industry, it may be desirable to use low temperature resistant materials for pump casings, and selflubricating
materials such as molded graphite with metal fill for station portions of wearing parts due to
the low lubricity of CO2. Low lubricity of CO2 would also necessitate the use of double or triple
mechanical seals with a lubricating buffer fluid or dry gas seals. Use of sleeve or tilting pad bearing
arrangements has proven to be successful in CO2 service (Eyen, 1986).

Valves. Valves are typically used for control functions around compressor and metering stations
and at the injection sites. Additionally, block valves are used to isolate sections of pipe in the
event of a leak or for maintenance. Block valves are spaced at 10-20 mi (16-32 km) depending on
the location of the pipe. Block valves are more frequent near critical locations such as river
crossings and urban areas.
Valves meant for CO2 service need to be designed to minimize water traps following hydro
testing, in order to minimize corrosion from carbonic acid. Packing materials need to be corrosion
resistant and able to withstand extreme low temperatures encountered during blowdown events.

You have a lot of experience with this, so I'm very interested in any thoughts you want to share on those points.

Going the Big Inch!

http://virtualpipeline.spaces.msn.com

 

[zdas04]

BigInch,
This is not an area where I have much experience, but the last paragraph caught my eye--the fear of carbonic acid is rampant whenever CO2 is in the same pipe as water. I've seen tons of chemically inert piping used because of this fear. I've taken thousands of pH readings on lines at natural-gas gathering-system pressures and temperatures and rarely have they been acidic. Most often the reaction is toward carbonates instead of towards acids. I don't know if this is true when dealing with supercritical CO2 pressures and temperatures, but the fear of carbonic acid is so deeply rooted that I've made it my mission to warn people that the fear may be ungrounded.

In a LOT of study I can't find a mechinisim that will predict if a aqueus mixture of CO2 will drive toward acid or base, but it seems that the total energy is slightly lower with a small shift toward basic (7.2-7.4 pH) so that direction seems to be the most common.

I didn't mean to hijack this discusison, but my mission, you know.

David

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.

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[BigInch]

David, Its not a private discussion and you're more than welcome. Good thought. Usually when rabid fear is involved, its founded on more myth than truth. It would be interesting to find out where that monster originated.

Going the Big Inch!

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[Montemayor]

BigIncher:

Thank you for amplifying the meaning and depth of this thread to further help others that may feel restricted or hindered when confronted with supercritical or mixed phases. Most - if not all - of the subject matter we are discussing was not taught in university (at least not to me) and I suspect that most other engineers feel like I did 40 years ago when I had to realize that not all fluids were 100% pure or single phase, just like in my text books. Certainly, my profs never discussed the subject. Today it may be different, but I suspect that public and engineering pressure has forced engineering curriculums to finally put the correct stress on mixed phase flow and phase phenomena. Basics are the stuff that define and lead to a problem's solution. And supercritical fluids are not a boogey man. Here, allow me to apologize if it sounds that I'm on a soap box. I've always felt a sense of fear on the part of young engineers when discussing such seemingly arcane subjects - I know I did. The part of engineering that I always try to impart on young engineers is that we in the profession never stop learning once we leave the Ivy Walls of universities. And we never should; there is more to engineering than is found in the text books. That's the main reason why we join Eng-Tips and participate in these Forums.

Dealing with supercritical fluids is now catching on while 40 years ago it was not even discussed (just like sex). I was one of the lucky ones who got thrown into the supercritical pond in my first job. I didn't realize it until a year later, but every cylinder of CO₂ that we filled in my plants was a product of supercritical flow. A lot of engineers today don't realize it either, but it's all around us.

The point I want to make and share is the same one you expound: it ain't that hard nor difficult. If you can define the parameters and the properties, you've practically got it licked. We have the tools; it's a matter of know how and when to apply them. In my experience, you've hit the nail on the head when you bring up the question of gas purity or composition identification. That is probably 75-90% of any problem of this nature. We "believe" Daniele is dealing with 100% CO₂; she may not be. And that, I believe, is also part of the problems discussed in the Battele paper you've quoted.

You will note that the Battele discussion revolves a lot on the academic side with regard to considering and recommending methods of design and operation. When you relieve a supercritical fluid or a saturated liquid due to thermal expansion you can't be thinking about "the blowdown valves need to be carefully sized to limit the rate of release such that the pressure reduction does not cause excessive cooling". Hell, you've got to keep the damn pressure below the MAWP of the pipe and nothing else matters for the moment. That's why you must design with the knowledge and foresight that you may have to work with very low temperatures resulting from free, adiabatic expansion of a compressed liquid or supercritical fluid.

Additionally, the employment of "surge storage capacity" is said to be required. I can't imagine how this is going to be applied - nor why. I can't imagine what the so-called "sugre storage tanks" would look like or what they would do. If a bladder-type tank is being considered, it isn't defined. I doubt if the author gave it any further thought. Containment (100%) is the answer to a supercritical fluid. That's what keeps it as such. Any over-pressure has to be relieved.

The discussion about the water contamination and the corrosion hazard is, as David has noted, just so much paranoia about a subject that hasn't been looked at in detail. The water is in solution with a huge amount of CO₂; it's not the other way around - as we're accustomed to seeing in in a bottle of Coca-Cola.

The good news in all of this is that the application of supercritical fluids isn't nuclear science. Coffee makers are using it every day in selective extraction methods. And you never hear much about it unless you go into Google and look for it. We still have a lot to learn - but then that's our business.

 

[BigInch]

Thanks. I do appreciate the view from your perspective. I've always been passively interested in CO2 pipelines, never having had a chance to work with one.

I've noticed the same difference going from university to flatlands. At U[ß], everything was given and working out the problem was hard. Since then it has always seemed to be the reverse. I too was wondering about the practicalities of retaining surge volumes. While technically possible, the cost/benefit would be rather high. Seems someone was thinking low pressure liquid systems, when that one slipped out.

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