4 replies to this topic

[ali.jabbaran]

Dear friends
I'm Dealing with a Gas Pressure Reduction Station Project for a Power Plant Project(GTGs).
There are some PSV's with Discharge to Safe location route.
My question is about the vent stack height result of API-521 standard.
In one Case our data are as bellows:
Discharge of PSV to Atm.(as per P&ID) : 4"
Relief load = 11600 Sm3/hr ~ 7871kg/hr
Ro(Methane at 25C and 0barg)=0.68(Disch. To Atm.)
V(at discharge of stack) = (7871*2/3600)/0.68*(pi/4*(4*0.0254)^2)=793.6 m/s >444 (m/s)[Sound velocity in methane at 15C and 0barg]-------> we have Chocke flow
Re=ro*V*d/mo = 0.68*444*0.1016/0.000011= 2788463 > 15400*(roj/ro∞)=8845
so we have jet domminant flow

There are 3 points in API-521-2008:
1- as Per equation 23 of API
y= the height at which typical hydrocarbon relief streams are diluted to their lower flammable limit=12m

2-As per Figure-4 with considering of 10m/s for air velocity
X=(u∞/ uj)=10/444=0.0225
Y=85=y/0.1016*Sqrt(roj/ro∞) y=85*0.1016*0.758=6.55 m and 13 m for still air

3- bellow item in API:

7.3.4 Vent stacks
7.3.4.1 Sizing
Where the atmospheric vent handles combustible vapours, the outlet from the vent should be elevated
approximately 3 m (10 ft) above any adjacent equipment, building, chimney or other structure


Now I'm Confused, Which height Should be considered for vent stack.
Do I need a precise Calculation of dispersion, for example a PHAST Analysys?
Is 13 m height reasonable ?
I couldn't find a GPR Station with such a vent height for their stack.

Thanks alot

[demank]

Dear friends
I'm Dealing with a Gas Pressure Reduction Station Project for a Power Plant Project(GTGs).
There are some PSV's with Discharge to Safe location route.
My question is about the vent stack height result of API-521 standard.
In one Case our data are as bellows:
Discharge of PSV to Atm.(as per P&ID) : 4"
Relief load = 11600 Sm3/hr ~ 7871kg/hr
Ro(Methane at 25C and 0barg)=0.68(Disch. To Atm.)
V(at discharge of stack) = (7871*2/3600)/0.68*(pi/4*(4*0.0254)^2)=793.6 m/s >444 (m/s)[Sound velocity in methane at 15C and 0barg]-------> we have Chocke flow
Re=ro*V*d/mo = 0.68*444*0.1016/0.000011= 2788463 > 15400*(roj/ro∞)=8845
so we have jet domminant flow

There are 3 points in API-521-2008:
1- as Per equation 23 of API
y= the height at which typical hydrocarbon relief streams are diluted to their lower flammable limit=12m

2-As per Figure-4 with considering of 10m/s for air velocity
X=(u∞/ uj)=10/444=0.0225
Y=85=y/0.1016*Sqrt(roj/ro∞) y=85*0.1016*0.758=6.55 m and 13 m for still air

3- bellow item in API:

7.3.4 Vent stacks
7.3.4.1 Sizing
Where the atmospheric vent handles combustible vapours, the outlet from the vent should be elevated
approximately 3 m (10 ft) above any adjacent equipment, building, chimney or other structure


Now I'm Confused, Which height Should be considered for vent stack.
Do I need a precise Calculation of dispersion, for example a PHAST Analysys?
Is 13 m height reasonable ?
I couldn't find a GPR Station with such a vent height for their stack.

Thanks alot

The vent stack is form one PSV or from vent header (from multiple PSVs)?
I think 13 m height is reasonable, based on dispersion and radiation criteria on API 521.

[ali.jabbaran]

Dear friends
I'm Dealing with a Gas Pressure Reduction Station Project for a Power Plant Project(GTGs).
There are some PSV's with Discharge to Safe location route.
My question is about the vent stack height result of API-521 standard.
In one Case our data are as bellows:
Discharge of PSV to Atm.(as per P&ID) : 4"
Relief load = 11600 Sm3/hr ~ 7871kg/hr
Ro(Methane at 25C and 0barg)=0.68(Disch. To Atm.)
V(at discharge of stack) = (7871*2/3600)/0.68*(pi/4*(4*0.0254)^2)=793.6 m/s >444 (m/s)[Sound velocity in methane at 15C and 0barg]-------> we have Chocke flow
Re=ro*V*d/mo = 0.68*444*0.1016/0.000011= 2788463 > 15400*(roj/ro∞)=8845
so we have jet domminant flow

There are 3 points in API-521-2008:
1- as Per equation 23 of API
y= the height at which typical hydrocarbon relief streams are diluted to their lower flammable limit=12m

2-As per Figure-4 with considering of 10m/s for air velocity
X=(u∞/ uj)=10/444=0.0225
Y=85=y/0.1016*Sqrt(roj/ro∞) y=85*0.1016*0.758=6.55 m and 13 m for still air

3- bellow item in API:

7.3.4 Vent stacks
7.3.4.1 Sizing
Where the atmospheric vent handles combustible vapours, the outlet from the vent should be elevated
approximately 3 m (10 ft) above any adjacent equipment, building, chimney or other structure


Now I'm Confused, Which height Should be considered for vent stack.
Do I need a precise Calculation of dispersion, for example a PHAST Analysys?
Is 13 m height reasonable ?
I couldn't find a GPR Station with such a vent height for their stack.

Thanks alot

The vent stack is form one PSV or from vent header (from multiple PSVs)?
I think 13 m height is reasonable, based on dispersion and radiation criteria on API 521.

Thanks for your reply.
It's from vent header(Multiple PSV)
I've seen lots of GPR station around different cities in my country, but I havn't seen such a high stack there.

[demank]

Yes, your feeling may be right. 13 m for 7800/hr seem to high. If 35000 kg/hr the height stack may up to 13 m.

You already re-calculate the height based on the criteria of radiation and dispersion?

[ali.jabbaran]

Hi Dear friend;
Sorry for delay.
No. I've never done disperssion calculation.
Could you please reccomend me some useful references(Book-paper or softwares) for this calculation.
Thanx.