1 reply to this topic

[abelletti]

Hi Guys,

I am attempting to determine if the cryogenic portion of the deepcut natural gas facilty I am working on can be blended with another source (Sales gas compressor blowdown) to avoid a cryogenic flare KO drum and stack. All PSV's in this section are fire case and are not sources of cryogenic relief.

I have been using the dynamic depressuring utility in HYSYS in steady state mode and was wondering how reliable this utility is for determining the blowdown temperatures and flowrates. When using it for blowdown of the confined volume within my sales gas compressor unit at settle out conditions I achieved temperatures at the lower end of low temperature carbon steel which raised some concern since it was starting around 80 C.

I used the fisher calculation method, a valve opening of 100%, and selected calculate Cv based on a final blowdown pressure of 100 psig in 15 mins.

Any help or guidance would be greatly appreciated.

[ankur2061]

abelletti,

When performing blowdown calculations, it is normal practice to check the minimum temperature that can be achieved at the minimum ambient temperature. For exampple, if a compressor loop is depressurized after settle-out conditions with minimum ambient temperature, this will give you the most conservative minimum temperature for material selection.

Another aspect while doing depressurization calcualtions in the HYSYS dynamic depressurizing utility is to consider the minimum back pressure at the blowdown valve outlet.

The combination of minimum ambient temperature and the minimum back pressure will provide you the lowest temperature that your blowdown / flare line can see and the material selection, CS, LTCS or SS should be based on this.

Hope this helps.

Regards,
Ankur.