4 replies to this topic

[T.Sik]

Hi,

I am currently a trainee at an engineering consulting company and was asked to read the API RP 521 and extract from it the peak level, final pressure and final temeprature. The company has the 4th edition of API 521 so I am not sure if me not finding these issues is due to the outdated API or my stupidity. I have to find those three issues for a fire case and for normal shutdown. I knoe that for the fire case the pressure should be reduced to 50% of set pressure within ~15 minutes; I also know the Grote equation but the equation has two unkowns for me, the peak flow and the final pressure (I assumed the blowdown time to be 15 minutes). For normal shutdown, I am assuming that the vessel needs to be depressurized to atmospheric pressure or a value slightly above it. Please advice on how to obtain information on the peak flow, final pressure and final temperature for the depressurization of both the fire case and the normal shutdown. Thanks in advance.

T.I.

[fallah]

Hi,

I am currently a trainee at an engineering consulting company and was asked to read the API RP 521 and extract from it the peak level, final pressure and final temeprature. The company has the 4th edition of API 521 so I am not sure if me not finding these issues is due to the outdated API or my stupidity. I have to find those three issues for a fire case and for normal shutdown. I knoe that for the fire case the pressure should be reduced to 50% of set pressure within ~15 minutes; I also know the Grote equation but the equation has two unkowns for me, the peak flow and the final pressure (I assumed the blowdown time to be 15 minutes). For normal shutdown, I am assuming that the vessel needs to be depressurized to atmospheric pressure or a value slightly above it. Please advice on how to obtain information on the peak flow, final pressure and final temperature for the depressurization of both the fire case and the normal shutdown. Thanks in advance.

T.I.

You can use Grote equation/HYSYS to obtain peak initial flowrate and compare the results.

You now should use API 521 FIFTH ED. as a base.

[T.Sik]

You can use Grote equation/HYSYS to obtain peak initial flowrate and compare the results.

You now should use API 521 FIFTH ED. as a base

The assigned task was to read the standard and find out what the final pressure and temperature are (how to obtain them). I found that for the emergency blowdown (i.e. during fire), it can go as low as 6.9 barg (not lower). To obtain the temeprature, it's not safe to use the ideal gas law, is it?

T.I.

[fallah]

To obtain the temeprature, it's not safe to use the ideal gas law, is it?

Temperature of which point? BDV outlet? Upstream vessel?

Vessel is gas filled? Vessel is full/partially liquid filled?

Better to use relevant software such as PRO II.Attached is a typical output of PRO II ran for depressurizing in fire case and shown temperature variation during pressure reduction.

Attached Files

•  Fire_case.pdf   18.71KB   151 downloads

[T.Sik]

Temperature of which point? BDV outlet? Upstream vessel?

Vessel is gas filled? Vessel is full/partially liquid filled?

Better to use relevant software such as PRO II.Attached is a typical output of PRO II ran for depressurizing in fire case and shown temperature variation during pressure reduction.

It's the temperature at the end of the depressurizing process so I guess it is the temperature of the vessel at the end. He did not specify whether it is gas or liquid filled. But I just recently found "Depressuring___A_Practical_Guide.doc" in another topic (I think posted by Mr. Art). Since I have HYSYS (version 2006) on my computer, I will check it out and see what develops from there. Anyways, thank you fallah for your prompt reply and help.

T.I.