3 replies to this topic

[JoeWong]

Hi all,

Hot gas is discharged into flare system during fire case. In some event, we experience the gas is at elevated temperature (> 350 degC) before PSV is opened. As JT effect is not significant, the PSV downstream temperature still high (~350 degC).

i) Do we design flare system for 350 degC ? Where shall we stop this design temperature ? At flare KO drum inlet ?

ii) If not, what will be the justification?

iii) Any rule of thumb and practices indicate maximum flare design temperature ?




regards,

JoeWong

[tonywen]

Hi all,

Hot gas is discharged into flare system during fire case. In some event, we experience the gas is at elevated temperature (> 350 degC) before PSV is opened. As JT effect is not significant, the PSV downstream temperature still high (~350 degC).

i) Do we design flare system for 350 degC ? Where shall we stop this design temperature ? At flare KO drum inlet ?

ii) If not, what will be the justification?

iii) Any rule of thumb and practices indicate maximum flare design temperature ?




regards,

JoeWong

Hello Joewong,

At so high tempreture, if there isn't any chemical reation like decompostion, and these fluid equations stand up all the same, you can use it. So whether we can use FLARENET to simulate your cases in high tempreture, depends on the nature of substances and also the limit conditions of the mehod equations. I don't have any data about these equations, sorry that I can't answer directly your question.

best regards,

Tony

[gvdlans]

When you have a major fire in your plant you have other things to worry about than the point that you may have exceeded the flare line design temperature... Flare line should be capable to keep the flare gases contained, which I am sure will be the case at a temperature of 350°C and pressures of a few bars maximum.

After the fire incident you may have to replace part of the flare line, supports etc. but again, you will have to replace part of your plant anyway.

[JoeWong]

When you have a major fire in your plant you have other things to worry about than the point ..."

I do agree with you with above statement. After fire, there are many parts needs to be assessed, replaced, modified, etc.

Flare line should be capable to keep the flare gases contained, which I am sure will be the case at a temperature of 350°C and pressures of a few bars maximum.

I would think the flare line is to evacuate the flare gases as quick as possible...

Infact my main concerns is more on the thermal shock induced stress due to hot gas relieving to flare piping in case i set the design temperature too low. However, high design temperature may results many difficulties in designing the flare piping....

In my mind, in case of upstream vessel temperature exceeded 350 degC, the vessel material (normally CS, if SS even worst) yield strength will drop drastically, vessel may have failed prior to PSV discharge hot gas to flare header. Secondly the hot gas discharge to flare header may take some time to heat the flare header. By the time the flare piping temperature reach 300 degC (no basis), upstream fluid may have exceeded 350 degC.

Based on above arguments, i am just think if i can set the flare piping at 300 degC.

regards,

JoeWong