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Velocity and pressure drop for MEG line

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Velocity and pressure drop for MEG line

processengineer1998

(Chemical)

(OP)

Hi all
I am looking for some criteria for velocity and pressure drop/100m for MEG in order to perform line sizing for MEG line and pipeline.
I know general criteria for liquids such as what mentioned in TOTAL or others standards, but winteresting thing for me is special criteria for MEG.
Please let me know if there is such criteria.
Thanks

RE: Velocity and pressure drop for MEG line

georgeverghese

(Chemical)

Am not aware of any other requirements for MEG-water solutions. Obviously, the pressure drop calc would be done at the lowest operating temp when viscosity would be high.

RE: Velocity and pressure drop for MEG line

LittleInch

(Petroleum)

As a general guide, long distance pipelines usually end up with around 2 to 3 m/sec as the most economic velocity, shorter systems sometimes a bit faster.
Each system needs design on its own for your particular requirements, end pressures etc.
E.g. if you're injecting MEG at the end into a high pressure system, the pipe size might need to be bigger to reduce the friction element of the overall pressure.
Do the options, find the best / most economic design for your system.

RE: Velocity and pressure drop for MEG line

processengineer1998

(Chemical)

(OP)

Dear Georgeverghese, dear LittleInch
Thanks for your response, actually I have done my sizing, just wanted to make sure that there is no special consideration for MEG.
Another question which I need to work on is about the turndown ratio for an MEG pipeline. Is there any manual or standard which elaborates the correct method to specify the right turndown ratio?
Thanks in advance
P.s. There is a pump upstream of the pipeline.

RE: Velocity and pressure drop for MEG line

LittleInch

(Petroleum)

Often you're better off batching it if you can but if not you might need some different pumps below about a 1:3 turndown.
BTW, there is no such thing as the right pipe size or right turndown, it's simply the best compromise for your particular situation and drivers.

RE: Velocity and pressure drop for MEG line

georgeverghese

(Chemical)

Obviously at low flows, the destination pressure will approach pump discharge pressure, since frictional dp will be much less. So the injection fitting has to deal with pressure ranging up to supply pump discharge pressure.

RE: Velocity and pressure drop for MEG line

processengineer1998

(Chemical)

(OP)

Thanks a lot, all friends.

RE: Velocity and pressure drop for MEG line

processengineer1998

(Chemical)

(OP)

Is there any concern with a velocity of 0.5 to 0.6 m/s?

RE: Velocity and pressure drop for MEG line

EmmanuelTop

(Chemical)

I'd say yes. Just make sure you are always in the turbulent flow regime and keep MEG at reasonably high temperatures to avoid flow problems at increased viscosity. There is a threshold value above which the pump will not be able to deliver the required flow, unless the entire system is designed for a cold start.

RE: Velocity and pressure drop for MEG line

processengineer1998

(Chemical)

(OP)

Thanks a lot for your great post. Actually, in our study, we selected a 6-inch pipe rather than 4 inches in order to use the existing pump and to prevent new pump installation and because there is a good static head available in the piping system (around 3 bar static head against 8 bar friction loss). Temperature at the piping inlet is around 60C and hysys predicts a temperature decrease to 31C along the pipeline in the worst case. MEG is 70%wt and viscosity is around 5.8 cp @31C. Also, Reynolds would be 17000 under these conditions. However, it seems that we should be careful in defining the turndown ratio for the pipeline. Therefore according to your chart, there would not be any problem. What is your idea? Would you please let me know the reference of your diagram? Thanks in advance.

RE: Velocity and pressure drop for MEG line

EmmanuelTop

(Chemical)

I don't know what economics and design criteria you used to prove that a 3km 6" pipeline is a cheaper and better option than a 4" pipeline and a shipper pump. With Reynolds 17,000 you are actually in the transition zone, not in a fully developed turbulent flow regime - and you are there for the design (max flow case). Something's wrong there. Viscosity chart is taken from MEGlobal.

RE: Velocity and pressure drop for MEG line

processengineer1998

(Chemical)

(OP)

Dear Dejan, Thanks a lot for your great posts. To be honest, I have not compared two options (3 km, 6-inch pipe against 3km, 4-inch pipe plus pump and associated control valve), but the main reason is that we prefer to not touch the existing package and just take a branch from the tie-in point. Actually, I am still a little bit worried about the Reynolds number. For 6-inch pipe depending on the temperature, Reynolds would be between 17000 up to 38000. For 4-inch pipes under the best conditions, Reynolds would be 58000. For both cases, we are not in the fully developed regime. The velocity for 4-inch is 1.33m/s and for 6-inch is 0.60m/s. Maximum flowrate is 40m3/hr and it is a normal flowrate because we are going to use the package as much as possible in a predetermined time. However, in the case of the selection of a 6-inch pipe, we should select a high turndown ratio (e.g. 80%). Your and other people's advice is highly appreciated.

RE: Velocity and pressure drop for MEG line

EmmanuelTop

(Chemical)

Ask yourself how robust, flexible, and reliable your current design is. Does it allow Operations to move a bit left, right, up and down, is it sensitive to flowrate, soil temperatures, inlet conditions, etc.? You don't seem yourself convinced that the design you propose (or the client proposes) is good enough or not, or whether there are better (less costly or more costly) options. You need to sit with your team and go through what you have developed so far and see what you can do about it. Because it looks like there are quite a few things that could be done. If the company you work for is an engineering design company, it has to be able to demonstrate why a particular design option has been selected and developed. This, on many occasions, involves cost-benefit analysis, as well as sensitivity analysis and analysis of exposures to various construction and operational risks. That should be your strongest argument in convincing the client why it is better to choose option A versus option B, even if they strongly prefer option B. Failing to do so will always make your standpoint weak, and the client can always insist on a more complicated, expensive, less efficient, or even completely wrong solution, because the engineering design team failed to properly evaluate all options, sensitivities, and risks, and present full argumentation for the final selection to the client.

RE: Velocity and pressure drop for MEG line

processengineer1998

(Chemical)

(OP)

Dear Dejan, Thanks a lot for your post, You are completely right. A report considering all economic, operational, and construction aspects will be prepared. But first of all, I need to be sure that my design is technically acceptable to be considered an option. I mean if the 6-inch case is acceptable then I can compare it with the 4-inch case in cost, operation, and other points of view. Best regards.

RE: Velocity and pressure drop for MEG line

georgeverghese

(Chemical)

For piping and fitting losses in non-turbulent flow, use the Darby 3-K method to work out fitting pressure losses. If you don't have the correlations for this method, you can still use the Crane method, but use the friction factor for fully developed turbulent flow for fitting losses, even though your actual flowing friction factor is much lower.

RE: Velocity and pressure drop for MEG line

processengineer1998

(Chemical)

(OP)

Dear Dejan, We are currently working on using both 4" and 6" sizes in our pipeline, I mean some part of the piping would be 4 inches and another part is 6 inches. With this strategy, we omit new pump installation and on the other hand using 6-inch pipe would be economically feasible rather than pump installation case. Let me know if you or other friends have any idea.

RE: Velocity and pressure drop for MEG line

georgeverghese

(Chemical)

You haven't said what the application for this MEG is: note that an aqueous MEG solution can drop out any dissolved salts if the operating temp for this supply line is low, and that can reduce the effective line ID and increase pipe roughness also, so a healthy margin on dp may be required to account for salt deposition. Else an MEG reclaimer/ion exchange unit may be required in the regen circuit to keep TDS low.

RE: Velocity and pressure drop for MEG line

LittleInch

(Petroleum)

I think for pipe fully developed turbulent flow is normally once you go past Re of 4000. Fully developed flow into the open end of a pipe occurs within 40 D. That line on the chart is misleading for pipe flow. The flow at 4 and 6 inches is fully turbulent IMHO. If 6 inches is cheaper then it's ok. Have you considered OPEX as well?

RE: Velocity and pressure drop for MEG line

processengineer1998

(Chemical)

(OP)

Dear georgeverghese, The supply line transfers MEG plus salt, the return pipeline from the reclaimer transfers MEG containing a small amount of salt. We have calculated pressure drop for the supply pipeline at the lowest temperature, it means worst case design. For the return pipeline, MEG temperature at inlet is high enough.
Dear Littleinch, Actually CAPEX for 6 inches is more than 4 inches plus pump. So, we are going to use option A (1000m 4" pipe and 1500m, 6" pipe without pump) instead of option B (2500m, 4-inch pipe plus pump). Absolutely pump OPEX would impact on overall cost estimation and we should consider it.

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