8 replies to this topic

[powerox6]

Hello all,

 

I'm sizing a blowdown valve in Hysys by using the Hysys Blowdown utility. I understand that the blowdown initial conditions should be at PZAHH (high pressure trip) and normal operating temperature. I'm curious does anyone know why it is standard practice to set the initial conditions like this? I'm looking through API521 and I'm not sure where it states that the blowdown initial conditions are set.

 

Thanks in advance.

[fallah]

 

I'm sizing a blowdown valve in Hysys by using the Hysys Blowdown utility. I understand that the blowdown initial conditions should be at PZAHH (high pressure trip) and normal operating temperature. I'm curious does anyone know why it is standard practice to set the initial conditions like this? I'm looking through API521 and I'm not sure where it states that the blowdown initial conditions are set.

 

 

Hi,

 

The blowdown valve initial conditions are provided in engineering practices of the reputable oil and gas companies...or process design criteria of the relevant project...

[breizh]

Hi,

Can you clarify the issue please? The initial conditions are the pressure P0 and temperature T0 at the source. Let say a vessel or a pipe.

my 2 cents

Breizh 

[powerox6]

Hi,
Can you clarify the issue please? The initial conditions are the pressure P0 and temperature T0 at the source. Let say a vessel or a pipe.
my 2 cents
Breizh

[powerox6]

Hi,

In the blowdown option in Hysys, it’s required to specify the blowdown initial conditions. My understanding is that I should size the valve according to the worst case scenario, i.e. high pressure in order for Hysys to calculate the peak mass flow rate. From this I have two questions:

- Is my assumption correct in taking the high high pressure trip value (100barg) as the blowdown initial condition?

- Assuming this is correct, where does this statement (taking high pressure trip value as initial condition) come from i.e. which API Standard etc.

Thanks

[breizh]

Hi,

I don't think you will find a standard, should be based on your engineering judgement.

My view 

Breizh 

[fallah]

In the blowdown option in Hysys, it’s required to specify the blowdown initial conditions. My understanding is that I should size the valve according to the worst case scenario, i.e. high pressure in order for Hysys to calculate the peak mass flow rate. From this I have two questions:

- Is my assumption correct in taking the high high pressure trip value (100barg) as the blowdown initial condition?

- Assuming this is correct, where does this statement (taking high pressure trip value as initial condition) come from i.e. which API Standard etc.

 

 

Hi,

 

It should be as relevant project's "Process/Safety Design Criteria" dictates...but normally the high or high high pressure value could be applied...

[shvet1]

Assuming may be correct or not depending on what worst conditions are. Highest pressure gives max volumetric flux but some other case is able to give max mass flux as gas density will differ.

 

You should consider worst credible scenarios for all elements of flare system. One criterion (pressure in your case) is not enough to ensure that depressuring will be ok. For flare header it may by max volumetric flowrate, sound pressure, or Mach number. For flare it may be max mass flowrate and max mol weight. And so on.

 

A designer should understand how overpressure protection actually works and how to provide a reasonable operation range of that. No magic, just a lot of calculations.

Edited by shvet1, 24 July 2023 - 12:41 AM.

[powerox6]

Hello everyone. Thanks for all your prompt replies.