2 replies to this topic

[CheAmine]

Hello,

 

We are currently facing high velocity in a 15 km  30 " Sales gas pipeline. The sales gas is produced from an NGL recovery unit and is transferred via pipeline for domestic use. The high velocity is usually experienced while running the unit in 110 % capacity and on NGL rejection mode. This leads to more slippage of Ethane and Propane with sales gas and hence increasing the sales gas flow rate. The attached file summarizes the findings of the calculations I have done.

 

The company standards limits the (density x velocity^2) factor to be less or equal to 15000 kg.m.s^-2 and based on the actual density you can find the maximum allowable velocity. I believe Shell Standard limits the (density X velocity^2) factor  to be less or equal than 20000 kg.m.s^-2 and the gas velocity to be between 10 m/s and 20 m/s.

 

Note that we are operating on rejection mode for approximately 1 month a year only depending the downstream requirements. Recovery mode calculations shows that we are at the limit in terms of velocity and (density x velocity^2) factor 

 

Kindly let me know your views regarding this issue and whether the above is still considered acceptable with regards to other standards and what are the modifications (I.e. pipeline supports) that can be implemented to withstand this velocities.

 

 

Thank you in advance for your help.

 

Amine

Attached Files

•  Pipeline velocity.xlsx   9.21KB   40 downloads

[amad]

Amine,

 

General comment:

- first of all, you should refer to company standard for determining the criteria for gas pipeline sizing (velocity). if no reference, you can refer to the code/standard (API 14E, Norsok, GPSA, or other relevant code).

- Make sure the design of your plant (flow, pressure, temperature). For the worst case line sizing is max flow, low pressure, and high temperature.

- Higher/more flow will also impact to higher pressure drop and higher velocity. If your velocity (or momentum) > criteria, please check again your calculation. If your calculation (and data) is OK, of course, change the size can be considered.

- you can also do the simulation using relevant software to check your problem

 

hope this help.

 

amad

[CheAmine]

Amad,

I think it was missed during the design phase to design this pipeline for 110 % capacity eventhough all the safeguarding equipment and other process equipment are designed to handle 110 % capacity.

In the current situation we are not in favor to re-design the 15 km pipeline but we would rather deal with this issue (maybe reducing the capacity to 100 % during C2 rejection mode).

I will do a simulation check to confirm my findings.

Thanks for your input.

CheAmine