10 replies to this topic

[sv10491]

hi everyone
I need to pressurise a gas pipeline from atmospheric pressure to the desired pressure.
i need to find the time it will take to pressurise the pipeline to the desired pressure.
so any kind of equation to be used to find a relation between pressure and time and then integrate the expression.
its a gas pipeline.density will change with time.
only inlet.no outlet of flow.
please reply back asap!
thnx
regards

[breizh]

http://www.cheresour...ressurize-time/


It might helps
Breizh

[ankur2061]

sv10491,

The reference provided by Breizh is considering a steady-state model for pressure rise and considering isothermal conditions for a 100% gas phase. From a practical operations view-point this should suffice. But if you are intent on calculating the pressure rise as an unsteady-state or transient pressure-rise phenomena from a theoretical view-point, it would be difficult using a simple equation and just integrating it. The following effects need to be considered when doing such transient pressure-rise effect:

1. Instantaneous gas density changes due to instantaneous pressure rise
2. Effect of instantaneous heat transfer between the pipeline and the surroundings
3. Effect of liquid aerosols (entrained ultrafine liquid droplets) in the gas

Normally these calculations are done using a process / pipeline simulator such as HYSYS / OLGA which can do thousands of iterations using complex equations considering both pressure change and thermal effects.

Hope this helps.

Regards,
Ankur.

[sv10491]

Breizh,
thanks so much for the help but i need the time for an unsteady state.
thanks anyways

[sv10491]

Ankur,
First of all thanks so much for the help.
yes my query is for an unsteady state or transient pressure rise phenomena.
cn HYSYS/OLGA help in pressurisation of line as well.
and is there no way to work out the question theoretically.
like any relation or equation to be used?

[ankur2061]

sv10491,

In HYSYS there is a dynamic depresssurization utility. Instead of modeling it as a depressurization to atmosphere, you can build it up as a pressurization operation from a higher pressure source (container) to a lower pressure destination (another fixed-volume container). I do not have any practical reference for doing such a pressurization operation using the HYSYS dynamic depressurization utility, but I believe it is possible to do so.

Pipeline simulators OLGA / TGNET (from Pipeline Studio) can do a better job in defining time to pressurise the pipeline using the option of start-up operations in transient analysis.

Regards,
Ankur.

[sv10491]

Ankur,
Thsnx so much for ur advice.
i will get in touch with my people and try using HYSYS as a pressurization operation.
Will have a look into OLGA/TGNET
thanx
Regards

[sv10491]

Ankur,
Taking it as a reversible adiabatic process and then solving it to find a relation between pressure and temeperature?
ny way u know other than hysys

[PaoloPemi]

an approximate solution can be obtained by defining the pipeline as a series of piping elements then integrating with n steps at constant properties, which is what many simulators do,
as Ankur said gas properties and flow distribution pressures are not linear which makes difficult to define an analytic solution, instead a simple integration with n steps can provide a decent approximation if you are prepared to accept the limits of this method,
an example of the limits is that you do not take in account many effects of propagation of waves, i.e. energy losses as a pressure wave propagates in a pipeline, internal reflections caused by the geometry of the pipeline, and the vibrations, these analysis would require a more complex model.
I have used Excel and the pipeline model available in Prode Properties (see prode.com) with this simplified approach to model pipeline's depressurization and pressurization,
the approximated results obtained with this method are comparable with those produced by common simulators.
More accurate models are available (i.e. solutions of partial differential equations based on suitable numerical methods as characteristics or finite elements) but I have not compared the results.

[sv10491]

Hi paolopemi,
Thanx for the advice..i looked up prode.com but i couldnt find the pipeline model over there.if u could send me a link or anything which could be helpful.

[PaoloPemi]

as said I use Prode Properties which is a library that links with Excel, Matlab and other Windows software.
To simulate (steady-state solution) a segment of pipeline in Excel you have a macro PIPE (one of the methods included in the library) which solves single phase and multiphase flow operations with heat added (or subtracted),
then you can assembly a Excel page to create a model of the pipeline and integrate over the time,
that of course requires some work, the alternative being a ready to use simulator as suggested by Ankur and others