5 replies to this topic

[aka007]

In our Vacuum Unit we have 2 Identical Trains, Train -1 constructed in 1984 and 2 constructed in 1989.

Our Vacuum system is Wet Vacuum with 2 Pre- Condensers in parallel and 3 Stage Ejector system, each having 3 no. of Vacuum Ejectors, with Condenser, with the cooling medium being Sea Water and the Sea Water entry is to the Pre-Condensers and it's return going to the other 3 Stage condensers simultaneously and also provided with a By-Pass to increase the flow to those condensers if and when required.

 

Actually in the middle of May 2023, we experienced sudden break in vacuum in only Train - 1 and this phenomenon was continuing on & off, with this phenomenon occurring every 7-10 days and would resolve by switching the Ejectors and /or hammering the Pre- Condensers leg lines, till our Scheduled Biennial Turnaround in October 2023.

 

And after Start-up of the unit on October 31, 2023, till December 30/31 2023 for about a couple of months the unit was running very smoothly, before the vacuum issue started cropping up again and this time the frequency of the drop/break in Vacuum was about 10-15 days, continuing upto March 2024. But, our Operation personnel thought this is due to the Pre-condensers leg line getting blocked due to Metal rust & corrosion and instructed to externally Hammer those leg lines twice in every shift from February upto Middle of March 2024., and by that that issue also resolved. 

 

And for a period of more than 6 months upto 2024 October first week, we did not face any issue except little increase in Vacuum twice or thrice when sea water flow was getting dropped, or more lighter in feed from Tankfarm. Also, as compared to the other Train, we were having 2 ejectors more online i.e.., 6 Ejectors with 2 each in all the 3 stages.

But again we faced sudden break in Vacuum itself on October 5th at around 04:00 hrs., even with unit running on extremely low Throughput. So, I kindly request you to help with this issue.

 

Note:- As per my observation, I have noticed 2 separate phenomenon happening with none being related to each other or happening together even once.

1. Pre-Condensers leg line temperatures getting low

2. 3rd Stage Condenser outlet temperature getting high which in turn increases the pressure of the non-condensible from the Hotwell increasing the back-pressure of the system irrespective of burning in our Heater or flaring it.

[breizh]

Hi,

Can it be ice built up in the steam ejector?

Breizh 

Attached Files

•  IceBuildup steam ejector.pdf   138.81KB   7 downloads

[PingPong]

Hi aka007,

 

As you already noticed it is very difficult to troubleshoot a problem even if one is in the plant, having access to all design data (heat and material balances, equipment datasheets, PFD, P&ID, linesizes, instrument data) and actual operating data from DCS, so for outsiders like us without such info it would be a wild guess what is actually wrong.

 

Obviously your company will not allow you to provide all that info, but DCS screen prints of the vacuum column and vacuum system would be very helpful for our understanding.

 

 

In the mean time let's start simple:

 

What is the vertical distance between the liquid level in the hotwell and the bottom of the Pre-Condensor and the bottom of each of the subsequent condensors ?

 

What is the absolute pressure and temperature of the vapour at the Pre-Condensor outlet (first ejector inlet) when the unit works properly ?

Does the vacuum column use stripping steam ?

 

Your operators seem to think that plugging of the Pre-Condensor legs due to rust or dirt might be the cause.

That sounds unlikely unless there is a horizontal part in those legs. Is there ?

What is the diameter of those legs ?

Was a lot of dirt and rust found in the Hotwell during the Scheduled Biennial Turnaround in October 2023 ?

 

You say: "1. Pre-Condensers leg line temperatures getting low"

What temperature do you mean by "low" ?

What is the temperature of the sea water during winter and during summer ?

 

In general: when troubleshooting always keep an open mind and don't get obsessed by focussing on one particular item that everybody thinks must be the cause. The fact that the problem is still not solved after one year may indicate that the real cause is something else than everybody thinks.

Edited by PingPong, 10 October 2024 - 05:56 AM.

[aka007]

Pre-Condensers leg line temperatures getting low"

What temperature do you mean by "low" ?

 

Ans:- I mean the Pre-Condenser liquid outlet line to Hotwell, it's temperature is getting low Sir

[PingPong]

And we still don't know what that "low" temperature reading is.

 

If you can't answer the few simple questions that I asked then you will never figure out what is really going on.

[aka007]

And we still don't know what that "low" temperature reading is.

 

If you can't answer the few simple questions that I asked then you will never figure out what is really going on.

Sir, I meant it's dropping to around current Ambient temperature ranges prevailing here, like right now it's 86F here.