12 replies to this topic

[Mohsin3689]

Hello Engineers, wondering whether you can help.

 

I have a 3 stage Export Compression system, with TEG dehydration between 2nd/3rd Stage

 

Each stage has a suction scrubber. The 2nd Stage has both suction and discharge scrubber, before the wet gas enters the TEG contactor.

 

The 2nd Stage Discharge Scrubber Condensate is routed/recycled back to the 2nd Stage Suction Scrubber. Why is this? I have a feeling that it is to do with recovering as much gas as possible, but then why is it not routed to the upstream HP separator unit?

 

Awaiting your response

 

Regards,

Mohsin

[Mohsin3689]

OK, I had a think and here are my thoughts:

 

1. By recycling to suction scrubber, you recover additional gas.

2. By recycling to suction scrubber, you avoid pressure loss by reducing it to separator pressure (much less than suction scrubber pressure)

3. By recycling to suction scrubber, you avoid temperature loss forming hydrates and freezing temperatures that will form by the JT effect.

 

Is this correct?

[Bobby Strain]

It is probably decided by your designer who copied his previous project.

 

Bobby

[himant]

1. Can you please tell where the condensate from 2nd suction scrubber is routed ?

2. Can you provide a rough sketch showing pressure and temperature? I am little confused by your description.. is it like this : 1st stage scrubber-> 1st stage compressor->2nd stage suction-> 2nd stage compression->2nd stage discharge scrubber-> TEG->3rd stage suiction scrubber->.......? Is this correct?

3. What is the feed composition?

4. Is this condensate mainly water or liquid HC?

[Art Montemayor]

Kindly furnish a flow diagram of your compressor.

Show all streams, temperatures, and pressures.

Give the stream composition of the 1st stage inlet - even if rough estimate.

Is your compressor a reciprocating or centrifugal model?

 

 

 

[Mohsin3689]

Please see the following link for the Overall PFD

 

http://i.imgur.com/8lzSmfT.jpg

 

As you can see, the export compression is located at the top left (2 train system).

 

The compressor is a centrifugal model.

 

Stream Composition to 1st Stage Suction Scrubber:

 

Pressure: 10.1bara

Temp: 60C

Flow: 59189 kg/hr

 

Component % Nitrogen 0.35 CO2 2.2242 C1 72.3437 C2 9.2064 C3 5.9577 IC4 1.0697 NC4 3.3874 IC5 1.2146 NC5 1.4955 C6 0.7407 C7 0.3146 C8 0.1153 C9 0.033 C10 0.0103 C11 0.0031 C12 0.0011 C13 0.0004 C14 0.0001 C15 0.0001 H20 1.5321

 

1st Stage: 10.1bara > 22.8bara

2nd Stage: 21.8bara > 69bara

[Mohsin3689]

Sorry the formatting for the composition didnt come out right. Let me know if you require further information.

 

Thanks.

[Mohsin3689]

The 1st stage aftercooler reduces the temperature to 50C

The 2nd stage aftercooler no1 reduces the temperature to 50C and no2 reduces to 24C

[himant]

Hi

 

Thanks for sharing the information.

 

That's a tough one! I am just guessing here... lets see what experts have to say!

 

I guess 24 deg C after H-1160 A is your requirement for TEG Unit. Now the extra condensate formed in V-1159A due to further lowering of temperature needs to be recovered by directly routing to V-0151 or by routing to V-1157 A (same as in current process)

 

Condensate formed is around 11000 kg/h. If we flash it to 22.8 pressure, vapor fraction shall be 0.3 (30 % vapor) but if we flash to 10.1, vapor fraction shall be 0.4 (40% vapor)

 

Now, routing back to V-0151 will not make sense because if vapor load is recycled back, it will lead to more compressor load and loss of heavier hydrocarbons. However, routing it back to V-1157 A will also increase load but to some lower extent. 

 

However, one benefit I could envisage by going through this scheme is that it will actually maximize condensate recovery and it shall lower down the temperature of 2nd stage suction temperature which may ultimately lead to lower power consumption.

 

It's just guessing and I am eagerly waiting for the experts comments...

 

Regards

Himant

[Mohsin3689]

Thank you for your input Himant. Let us see what anyone else says.

 

Regards,

Mohsin

[PingPong]

The 2nd Stage Discharge Scrubber Condensate is routed/recycled back to the 2nd Stage Suction Scrubber. Why is this? I have a feeling that it is to do with recovering as much gas as possible, but then why is it not routed to the upstream HP separator unit?

What exactly do you mean by upstream HP separator unit ?

Is that shown on the PFD ? If so, which equipment numbers ? What operating P & T ?

[Mohsin3689]

By upstream separators, I am referring to V-0151 and V-0154, operating at 55C and 11bara. It is the separators that receives the fluids from the fields, and then the gas is routed to the compression export system. 

 

Regards,

Mohsin

[Bhavinkumar]

I am also thinking in the same train with hemant ...... I can guess it would be done trade of between the 1st stage /2nd stage power consumption. By recycleing condensate also changes the MW in the feed of both the options 1) 1st stage suction 2) Inlet seperator(V-0151). Lower the MW higher the power consumption in centrifugal machine. So, flashing at V-0151, results in more lighter and decreses the MW and gas load to the compressor .....hence more power. While flashing at 1st Stage leads to lower flowrate of gases due to flashing against hight pressure as compare to V-0151. And also keep MW higher relatively....hence less power relatively. Ofcourse, recovery of gases from the condensate and loosing minimum energy is also important factor as stated by Himant earlier.

 

This is just guess ......and my opinioin.......