3 replies to this topic

[NKonyashkin]

Hi to all! 

 

Colleagues! I have problem with calculation of critical gas velocity to avoid liquid accumulation in wet gas pipelines. We had to purge some of our wet gas pipelines for 5 times in a week due to liquid (water, condensate) blockage in low places of pipeline vertical profile. Can you help me with determination of gas velocity we need to sweep out liquid and have stable flow without such problems?

As I know from my calculations our pipelines have stratified flow regime (it also confirmed by GAP calculations).

 

Data:

 

Gas rate = 1116000 Nm3/day

Z-factor = 0.68

Gas rate at linear conditions = 9000 m3/day

Liquid rate = 263 tonnes/day

Liquid density = 0.762 tonnes/m3

Average pipeline pressure = 8.9 MPa

Average pipeline temperature = 22 C (It varies from 33 (at the beggining of pipeline) to 11 C (at the end))

Inner diameter = 179 mm

 

Can you help me with it?

 

Best regards,

Konyashkin Nikita,

Junior Process Engineer

Oil, Gas and Condensate Production Department

CJSC ROSPAN International

[paulhorth]

Nikita,

I cannot give you a clear answer to this problem. The problem of liquid hold-up in a two-phase pipeline depends on a number of factors including the topography, the length, the inlet and outlet pressure and the flow regime. To study the problem you need to use a steady-state pipeline flow program such as PIPESIM or PIPEFLO, and then follow this with a transient flow program such as OLGA.

In a typical wet gas pipeline (with a lower liquid content than your example), the liquid holdup stays about the same as flow is reduced until a certain flowrate is reached, when the liquid content starts to rise sharply. See my attached curve as an example. The pipeline should be operated at flowrate higher than this point. However, the actual value of this recommended minimum flow will be different for each case, and you have to find it with the computer modelling.

 

There is also the problem of receiving the liquid at the outlet, in a slug catcher. If the liquid content in the pipeline has been allowed to get too high, this vessel can be completely filled and the downstream system can be flooded with liquid.

 

Paul

Attached Files

•  pipeline holdup vs flow.pptx   70.14KB   103 downloads

[NKonyashkin]

Paul, 

Unfortunately, I haven't pipeline vertical profile. 

Paul, what program did you use for this curve? OLGA? Can you share example of this case?

Edited by NKonyashkin, 11 June 2014 - 12:44 AM.

[paulhorth]

Nikita,

I unfortunately cannot share any more data on this case as this information is now out of my hands, and anyway it is the property of the client for that project. The curve was made from runs in OLGA, as part of a study for both steady state and  transient hydraulic modelling of the two phase pipeline. However, the curve could have been constructed using a simpler steady-state modelling program such as Pipesim or Pipeflo, which will tell you the liquid holdup for a given steady-state flow.

I attached this curve as it is typical for many two phase pipelines and illustrates the typical liquid holdup vs flowrate characteristic.

 

The vertical profile (topography) of your pipeline is important for studying the flow patterns and liquid content. At least, you should establish the change in height from the inlet to the outlet.  If you can then run one of the simple programs, it is easy for you to add in some rises and falls in the pipeline route, just to see what difference it makes. Run each of  your profiles with a range of flowrates and plot a set of graphs like the one I showed.

 

Paul