9 replies to this topic

[rizwangoheer]

Good day all Experts,

 

We are facing problem of sudden drop in lean amine flow to amine contactor which caused amine circulation and amine booster pump trips due to low low discharge flow at one of our Gas Treatment facilities. Based on data analysis we found that lean amine flow control valve on amine circulation pump discharge line to amine contactor was opened but the flow started to drop suddenly which caused the amine circulation pump on low low discharge flow. This incident was repeated 3 times in last 6 months which is causing production loss.

 

During this incident it was observed that amine circulation pump discharge pressure increased at the same time when lean amine flow dropped to low low which tripped the pump. Here it is worth to mention these pumps are provided with min flow recycle valve which was originally provided with a logic to open at low flow condition to save pump from tripping. But later on a new logic was created to open this min flow recycle valve on high discharge pressure of pump. So during the trip incident when the pump discharge pressure increased then min recycle valve opened up to 70~  but even then pump tripped due to low low flow conditions. Actually new logic was change in original design to control the high discharge pressure of pump and vibration on lean amine flow line to Amine Contactor. So now the pump min recycle flow is working low flow & high discharge pressure based on high selector.

 

During plant data analysis before the trip incidents we found that when pump discharge pressure increased, min recycle valve opened up to ~70% and then we observed high pressure drop across lean amine cooler on suction side of the pump. We also observed that lean amine flow control valve on pump discharge line to amine contactor was open 50~% but pump discharge pressure started to open and then pressure increased further. lean amine flow control valve opening reached upto 100% but pressure increased maximum and then it open the min flow recycle valve 70%. But still pump tripped on low low flow.

 

Based on plant data analysis we found that all process parameters including feed gas pressure, amine absorber, flash drum and Stripper levels, Amine Absorber and stripper DP was normal. Also we check the amine quality it was good. Then we concluded that low low at pump discharge was occurred due to high DP across the lean amine cooler which was created due to opening of pump min recycle valve.

 

But still we can not clearly pin point the true cause for the pump trip due to low low flow conditions. I need your expert opinion regarding the stated problem.  I have also attached herewith the Unit PFD with detail system description.

[rizwangoheer]

Dear Expert,

 

I hope there are many experts who have good experience in amine systems and specifically in amine booster and circulation pump operation. Any body can help me to comment on topic which I shared yesterday.

 

regards,

[Bobby Strain]

You should note that you have not provided a PFD.

 

Bobby

[rychurek]

If pump discharge flow decreased and discharge pressure increased at the same time, it's mean that there is some restriction in discharge line for sure. Did you check discharge control valve ?

[rizwangoheer]

Dear rychurek,

 

 

Many thanks for your comment. In discharge line of pump there is only flow control valve with manual isolation valve which all are in open position. We also confirm the actual opening of control valve through read back signal which shows that control valve is working fine. Other than this there is no other restriction in 24 inch line which is going to amine contactor.

 

 

[rizwangoheer]

Dear Bobby strain,

 

Sorry I missed PFD I will upload the same.

 

thanks

[rychurek]

If flow control valve is performing well. Than you have to check your instrumentation. Higher dp across heat exchanger could be caused of higher than normal flow caused by opened minimum flow line.

[Bobby Strain]

Your pump would be the only one without a discharge check valve. Look again. Is it really a 24 inch line?

 

Bobby

Edited by Bobby Strain, 06 December 2017 - 05:35 PM.

[aanita]

There might be a NRV discharge of Pump which may lead to improper functioning. If the situation happens occationally, check the pump design flow. You should upload the PFD by now.

[Art Montemayor]

PFDs are not meant to depict control valves or any instrumentation.

 

What is needed here for clarity and accurate description of what is installed and operating is an as-built P&ID.