28 replies to this topic

[kkala]

Post No 25 by ankur2061 appears also in http://www.cheresour...ow-temperature/ '> http://www.cheresour...ow-temperature/ . I believe its proper place is there, so a general reply should be there.
The query here is whether duration of depressurization affects the minimum flow temperature. Answer has been given, based on some logic (not contradicting post 25). The quantity for depressurization is only 0.11 m3 (4 ft3), resulting piping diameter is certainly small, but of course one is free to try a sophisticated option, even though material cost saving is not expected to be high. Looking at Dynamic Depressuring Results.xls (I could not open it before), lower temperatures are developed in the 15 min blow down (low rate), contrary to post 14 (and post 21, if heat gain is considered). Probably rechecking is needed?

[kp-tasc]

Hi Fallah,

Below is the required information. Please note that BDV was existing and client wanted to know the minimum temperatures experienced for two different blow down times, 15 mins and 15sec. The 15 sec time is actual time for which orifice was sized by an engineering services company. I do not know the logic for this short time.

Propacket,

 

You getting lower temperature in 15 min case because your final pressure will be very less than your 15 sec case.  - Thanks Ketan

[zorro21072107]

In case of depressurization of pipeline containing Natural gas, it takes long time typically in hours. However, time can be reduced by having a higher size valve (Correct me if I am wrong). Can any body tell me how the valve size is fixed in case of pipeline depressurization?. This is a general question. Please dont ask me tons of data 

[serra]

for compressible fluids consider that properties as density assume
different values as pressures (in different segments) change,
you can adopt a simple (iterative) method

1) assume an (average) discharging flow (initial amount of fluid - final amount of fluid) / time, you can calculate the qty of fluid in each segment at initial (and final) consitions as volume of segment * fluid desnity, final qty depending from specified (final) pressure,
2) adopt (for example) 10 time steps, at each time step calculate pressure profile (i.e. pressure on each segment) fluid properties and flow discharged (use common equations to estimate pressure drops on piping and valves)
3) once completed the serie  verify that discharged flow equals initial amount of fluid - (specified) final amount of fluid,

if not correct CV (different valve), time etc. ad recalculate depressuring cycle.

I solve these problems in Excel with the Pipe() macro available in Prode but
you should get similar values with any simulator.