3 replies to this topic

[yakubu]

I want to estimate the purging volume using inert gas.

- Pipeline volume = 44000 litres
- Desired injection pressure = 10 barg

Question
- what is my required nitrogen gas, if the commercial available nitrogen gas bottles are 50 litres @ 170 bar
- A pressure regulator would be installed to regulate the pressure from 170 barg to 10bar, what would be the expectd volume due to change in pressure and density.

[Zauberberg]

Try this spreadsheet, I think it gives reasonably good estimates for pressure purges.
It depends what is the target LEL - that drives the quantity of Nitrogen required for purging.

Best regards,

Attached Files

•  Nitrogen Purge D.Crowl.xls   73KB   298 downloads

[yakubu]

Is surge pressure relevant in instantaneous valve closure in a gas pipeline, since it’s a compressible fluid? The pipeline is a straight pipeline of about 4km with isolation valves at both ends, my concern is if the valve closes at 8 sacs will that create a pressure increase. The line operates at 10 bar , 600NB pipe diameter and flow rate of 90 000NM3/hr. @ 50oC

[kkala]

Water hammer in gas lines (especially low pressure) is usually insignificant, since gases are compressible fluids. But transient analysis is performed through software for long natural gas pipelines. Despite low density, moving gases have some kinetic energy and momentum, which can create some pressure increase (surge) on a sudden valve closure.
A four km NG (natural gas) line is neither short nor long; a way to check potential water hammer on sudden valve closure at its end would be useful. Attached NGhammer.xls is an attempt to specify this surge, extending the elementary liquid water hammer theory found in Perry. Results show insignificant pressure rise (surge), about 0.32 Bar under the specific conditions.
Assumptions and calculations of this estimate are made for first time. Any comments to improve the estimated result would be appreciated.

Attached Files

•  NGhammer.xls   25.5KB   120 downloads

Edited by kkala, 09 October 2011 - 02:27 PM.