2 replies to this topic

[B-2 Spirit]

Folks,

 

 

I am designing a flare system for a Gas Plant.

 

Description: The Liquid seal has not been considered due to potential of ice formation during cold (sub zero) releases (isochoric blowdown). The absence of liquid seal means that there is danger of subatmospheric pressure followed by air intake into the flare system. Given that there are some condensing loads (steam) into the flare system, the chances of pulling air are quite high. Well, we do have reliable purges but the capacity of the nitrogen system is only good for normal operation. The emergency purge flow rate is very high. So, I have taken the following approach:

 

Design pressure of the system is upgraded to 10 barg to take care of internal deflagration.

 

Question:

(1) As per the Mechanical Team on the project the structures and supports needs to be checked for adequacy to handle the shockwaves that occur as a result of internal deflagration. Do you have experience of how this check can be performed and what financial implication it can have on the design of structures and supports?

(2) Emergency Purge with Nitrogen: This systen is activated on sensing low pressure (close to vacuum) in the system (which means that air is already present in the system) so we need to purge the system with a high flow of nitrogen within the accpetbale time limit.

(a) The condensing steam case produced a very high purge gas flow rate to purge the whole flare system within 30 mins. of time.

( I understand that 30 mins, is acceptable time limit when air will be present in the system. But, its not given in any of the standards. Any suggetions?

 

well, we are still in FEED and looking for the most safe and optimum solution. Any suggestions are welcome.

 

thanks and regards,

 

[Profe]

Hi B-2 Spirit

Why not use a seal of alcohol, water with antifreeze, diesel or use heating to prevent liquid seal freezing?
Or molecular seal?
Good luck
Fausto

Edited by Profe, 09 May 2014 - 11:34 AM.

[Bobby Strain]

A water seal doesn't alleviate the hazard you describe. After a big blow, the water is all gone. Flare system vendors have some sensors and valves to dump copius quantities of gas into the system. You can use natural gas. In all my nearly 50 years of plant operation and design I have never encountered the concern that you express.

 

Bobby