MortenA
Chemical
- Aug 20, 2001
- 2,998
Blow down of long pipeline seems to be a source of endless speculations 
This is from a current job:
- High pressure (150 barg) sub sea pipeline, medium size: 14", medium length: 24 km, buried to 1 meter (sand) not insulated but with a little coating
- Natural gas (sales quality)
- Blow down shall aim to ensure pipe wall temp>-10ºC
I use pipeline studio for this - it works fine and i fell confident that its not just "black box" but that i understand hydraulics and thermodynamic sufficiently to spot "abnormalities" e.g. from bad input data or wrong assumptions.
I have however the following problem: PS uses two different equations for calculating gas/wall heat transfer resistance one for very low velocity and one for the rest. This causes two problems:
1. A sudden change in the development of the temperature when the pipeline is "empty"
2. Low temperatures in the upstream segments
1. i think i can explain and does not cause a change of the conclusion
2. This is a bigger problem. PS seems to find expansion similar to isentropic combined with very low heat transfer and this leed to extreemly low temperature <-110ºC even if the rest has temperatures >-10ºC.
Does anybody have references that deals with this issue or good arguments why the PS results must be in error?
The model assumes heat transfer to the surrounds to be a single heat transfer resistance coefficient based on pipe size, burial depth, soil conductivity as described in an ASEE paper from the '50 that are used many places also e.g. in HYSYS. But i could also model the soil as a "insulation layer" and include "heat storage" in the soil during blow down.
Best regards
Morten
This is from a current job:
- High pressure (150 barg) sub sea pipeline, medium size: 14", medium length: 24 km, buried to 1 meter (sand) not insulated but with a little coating
- Natural gas (sales quality)
- Blow down shall aim to ensure pipe wall temp>-10ºC
I use pipeline studio for this - it works fine and i fell confident that its not just "black box" but that i understand hydraulics and thermodynamic sufficiently to spot "abnormalities" e.g. from bad input data or wrong assumptions.
I have however the following problem: PS uses two different equations for calculating gas/wall heat transfer resistance one for very low velocity and one for the rest. This causes two problems:
1. A sudden change in the development of the temperature when the pipeline is "empty"
2. Low temperatures in the upstream segments
1. i think i can explain and does not cause a change of the conclusion
2. This is a bigger problem. PS seems to find expansion similar to isentropic combined with very low heat transfer and this leed to extreemly low temperature <-110ºC even if the rest has temperatures >-10ºC.
Does anybody have references that deals with this issue or good arguments why the PS results must be in error?
The model assumes heat transfer to the surrounds to be a single heat transfer resistance coefficient based on pipe size, burial depth, soil conductivity as described in an ASEE paper from the '50 that are used many places also e.g. in HYSYS. But i could also model the soil as a "insulation layer" and include "heat storage" in the soil during blow down.
Best regards
Morten
