3 replies to this topic

[icingrock]

I am assigned to design the offgas overpressure protection system for the plant offgas system. There are several questions along the way and please read them one by one.

Please check the attached drawing for better understanding of the case. The overpressure protection device is in parallel with two valve ( with same actuator). Normally, offgas goes to incinerator. If there is problem with incinerator or if pressure on suction side of blower is > 20mbar, the valve will switch to stack automattically. The overpressure protection device is designed to give additional protection again the condition in which the valve can not be switched to stack for some reason.

The pipe is plastic lined with Fiber reinforcement.

1: how to set Pressure at which overpressure protection device can be activated to ensure pressure on suction side of blower does not exceed certain value, say, 50mbarg (blower is VFD controlled by pressure on suction side). The plant process parameters showed that there is really no linear correlation between pressure on suction side of blow and discharge side where the overpressure protection device is located.

2: Basically, there are two approaches to the design. One way is to use pressure relief valve as used in tank overpressure protection.But as indicated above, the set pressure of relief valve is not easy to define at a fixed value, and once the relief valve is activated, it should be taken offline to recalibrate, which is not possible because it requires shutdown. The other, as preferred by plant people, is to use liquid seal vessel with some liquid inside to use hydraulic seal leg of certain height to protection against overpressure.


That's basically the background for my assignment. Please give comments and I will along the way provide more information which maybe valuable to find final solution.

Attached Files

•  PFD for offgas system.xls   19KB   44 downloads

[Erwin APRIANDI]

Hi icingrock,

My first question to you is why you want to put the overpressure protection system in at the discharge of the blower and not on the blower suction side if you wanted to protect the suction side.

Please clarify this matter, I have made some suggestion for the suction line protection, feel free to comment on it

Attached Files

•  PFD for offgas system-suggest1.xls   20.5KB   30 downloads

Edited by erwin.apriandi, 25 February 2011 - 03:44 AM.

[icingrock]

Thanks for enlightening me.
Your answer seems obvious now for me, although I never though about it deeply since the task is assigned to me and they want to have the piping as I have described.

But that brings to me another question(although not a technical one): sometimes I found myself in a situation where my thinking was focusing on one way. Maybe I step back for a second and I can enlighten myself.

So it's a problem of accumulated experiences(means you are more enlightened as time goes by or I just need to think more openly. Actually I found other engineers also have similar problems although I don't know to how much degree.

So any open discussion or personal experiences sharing on how to think effective a chemical/mechanical engineer working in a chemical plant ??

Looking forward to your comments and experiences from other engineers in this forum.

Edited by icingrock, 19 March 2011 - 09:31 AM.

[Erwin APRIANDI]

Dear icingrock,

Just to remind, that there are lots of way to solved any problem
and in engineering there's no such things as the only solution

It is mostly the most efficient and effective way of problem solving
in simple words, cheapest, simplest and safest solution

So you can expect to have more than one solution, for any problems

Edited by erwin.apriandi, 20 March 2011 - 10:23 PM.