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Avoiding Gas Condensate In Process

process simulation gas condensate gas plant fuel gas scrubber

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#1 Ganesh Dhage

Ganesh Dhage

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Posted 17 January 2017 - 10:02 AM

Dear Friends,

 

I am currently stuck with a project that we are doing for a portion of Gas Processing Plant and would need your help.

Attached is a BFD for the particular part of the plant which we are evaluating. 

 

Problem Description:

Whenever there is a malfunction in the Gas Chiller (Propane system failure, Low Propane Level in the chiller etc.), the plant observes a lot of Gas condensate in the Fuel Gas Scrubber, GR-V-003A and the level keeps on increasing. They have to drain this condensate in an open pit which is hazardous and not allowable as per the HSE regulations.

 

In order to resolve this issue, the project proposes to use an existing Slug Catcher, GR-V-002 to separate any Gas Condensate coming through Stream 340A (which then can be routed through an existing line from GR-V-002 to the Closed Drain System).

 

The gas coming at the inlet of LTS (V-0640) has about 20% (by wt) liquid, however all the liquid gets separated in the LTS (V-0640). Even if there is any liquid carryover, this liquid should get separated at MP Fuel Gas KO drum (V-0653).

 

Still the Plant observes Gas Condensate in the Fuel Gas Scrubber (This may be due to Malfunction in Chiller or there may be a different reason which I might not be aware of).

 

I am trying to simulate the malfunction scenario (using HYSYS) but somehow, I am unable to see any condensate in Fuel Gas Scrubber.  I did the Carryover calculations for the Vessels as well but even that didn't help. Could you please help me understand what other possibilities are there that might lead to Gas Condensate in the Fuel Gas Scrubber.

 

I am sure I might be missing on something (due to lack of sufficient experience).

 

What might be other reasons that would contribute to the incoming of Gas Condensate in Fuel Gas Scrubber? 

Does this problem needs to be thought in a different way?

Is a Dynamic simulation really necessary to understand the problem?

 

 

I hope that I was able to describe the problem though I may not have provided all the details. In case if any further information is required, I would be more than happy to provide.

 

Any help would be really appreciated. Thanks a lot in advance.

 

Regards,

Ganesh

Attached Files



#2 pavanayi

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Posted 17 January 2017 - 12:25 PM

Ganesh,

Could you help us understand your system a bit better? 

1. Are there level transmitters on the two vessels upstream? (Low Temp Separator, MP Fuel Gas k/o drum)? What is the trend?

2. When the gas chiller malfunctions, I presume it is triggering a trip?

3. What is the fail mode of control valve upstream of fuel gas k/o drum?

4. What is the fail mode of the fuel gas k/o drum drain line? (You have not shown this line in the diagram).

5. Is this a new plant?

6. Have you observed the trend of the temperature and pressure u/s and d/s of the control valve located u/s of the k/o drum when a trip is activated?

 

My first guess for the reason for liquid to appear in the fuel gas scrubber is that after the pressure reduction step, the gas is getting cooled to a point where the flow is 2 phase, and that the k/o drum is not doing its duty of removing the liquid. It may be that the k/o drum liquid drain is not opening enough, or the control valve has the wrong failure mode, or the control valve in the field is closing on failure when it should open (even though P&ID may show fail open).

 

Could you add all these details to the sketch?  


Edited by pavanayi, 17 January 2017 - 12:38 PM.


#3 Bobby Strain

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Posted 17 January 2017 - 05:55 PM

If the MP separator has some type of demister, it may be damaged. Check the K (Souders & Brown) of both the MP separator and the fuel gas scrubber.



#4 colt16

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Posted 18 January 2017 - 12:24 AM

Could there be a leak in Gas Cooler No. 1?

The Gas from the Dust Filter is higher pressure and when leaking it encounters the really low temperature of 4.5C and spews out a lot of Gas Condensate.






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