Pop Tanks and PSV connection on Oil Treaters 1

[Shooze]

Hi,

I am looking for some opinion and directions on what is required on relief system for oil treaters.

I am trying to figure out if I need to install a pop tank off the oil treater PSV or can I tie the PSV on the treater into our flare system.

I have both low pressure and high pressure flare at the site.

The oil treater operates at 30psi, there are a few control shutdowns (LSHH & PSHH) on the treater to control the inlet control valves before we would every pop the PSV. Essentially is the is a high level or high pressure the control closes and we bypass the treater to the oil settling tank (slop tanks) until an operator heads to site and addresses the issue. In the event there is a LEL or FIRE the plant shutdown and equipment is isolated and blown down.

The questions is:

In event that PSV does lift (highly unlikely) on the treater can I tie the PSV into flare or do I have to tie it to a pop tank vented to atmosphere?

Thanks,

Shooze

 

[don1980]

This decision hinges on two key considerations.

First, is it feasible to route this PSV to the flare - is the flare backpressure low enough to to allow this PSV to be routed to the flare without overpressuring the treater? The backpressure must be low enough to allow the PSv to open and flow at the required rate.

Second, how much liquid will be released from this PSV - does the flare drum have enough available volume to safely contain this liquid release? Flare systems can tolerate incidental volumes of liquid, but they're generally not designed to contain high-volume liquid releases.

If it's feasible and safe, then route it to the flare. Otherwise, utilize a pop tank.

 

[Shooze]

Hi Don1980,

Thanks for your reply.

I have checked both the capacity of the flare KO drum, I have a large KO drum with lots of volume capacity. Flare backpressure is also good and velocities in the flare header are good. I do not anticipate any large volume of liquids carrying over to the flare system if this PSV lift. We have proper shutdown and control & bypass valves to isolate the treater if the PSV lifts. The oil side of the battery operates at a pretty low pressure.

Everything check out good.

I will be constructing this battery in Alberta, Canada. There seems to be some opinion that an oil treater PSV cannot be tied into flare rather it must be tied into a pop tank vented to atmosphere. I can't find anything in the code and AER Directives that states that. I beleive this design add more risk for a release to the environment. Obvisously, the pop tank would have to be design correctly with the proper in/out flow and venting capacities to not over pressure the pop tank.

Any thoughts?

Thanks,

Shooze

 

[don1980]

This question is far too detailed to be addressed in ASME code, so there's no constraint there. It's possible that this decision is constrained by local Albertan regulation (e.g. air-quality, flammable vapor release). I don't know of any such regulation but I can't say for sure. However if there is such a regulatory constraint, i think it would be one that pushes/requires routing to a flare and not the other way around. It seems inconceivable to me that such a regulation would require the use of an atmospheric tank.

 

[Shooze]

Thanks Don1980 for your reply, it is much appreciated!

 

[SNORGY]

I am inclined to take the treater PSV to the pop tank, unless you expect a lot of treater off-gas; the "deader" the oil, the more the pop tank makes sense to me. You probably don't want a lot of liquids going to flare if you can avoid it, plus it's easier to get the inventory back into the front end from a pop tank than from the knockout in the event the PSV lifts - something the local Regulations will probably force you to do within an operating shift anyway. If you do go to flare, I suggest HP flare - leave LP flare for tank off-gas, VRU etc. Another potential issue you might have with the treater PSV going to flare is that it *could* (depending) force you into a smokeless flare.