12 replies to this topic

[nazari.at]

Our details are as below:
Gas handled: natural gas for gas turbine unit of oil refinery

Flow rate: 12500 Nm3/h

Suction pressure: from 180 to 400 psi variable (the pressure in the pipeline in cold weather situation drops down to even 180 and depend on the weather and temperature it changes to different values up to 400)!
Discharge pressure: shall be 400 psi (we need a constant discharge pressure in the pipeline)
Hazardous area classification: non-hazardous

So there is some questions to answer :
1- What is your suggestion to have a constant pressure in pipeline?
2- If you suggest we use a compressor, which type of compressor is suitable for this application?
3- What is your idea about variable suction pressure? How can the compressor manage this different suction pressures? please explain.

Your prompt reply would be highly appreciated.
Thanks in advance.

[ankur2061]

nazari,

 

Pointwise reply to your queries:

 

1. Use of a compressor is obvious for constant pipeline pressure

2. For the flow rate mentioned a centrifugal compressor would be the most suitable.

3. The variation of suction pressure has to be in limits. A variation from 180 psig to 400 psig in suction pressure would be too much to handle even with a variable speed drive or suction throttling.  

 

There are some questions which you need to answer:

 

1. Why is there so much variation in the pipeline inlet pressure? Temperature variation cannot be the sole reason for such variation in pressure. 

 

2. Is your capacity also varying which could be the reason for the wide inlet pressure variations?

 

3. Any requirement for your pipeline inlet pressure has to be based on the destination pressure required at the end or termination of the pipeline, the pipeline size and the capacity (maximum or rated) of the pipeline. It cannot be based on some arbitrary number. You need to clarify the destination pressure, the capacity and the pipeline size for arriving at the required pipeline inlet pressure.

 

Hope this helps.

 

Regards,

Ankur.

Edited by ankur2061, 07 January 2014 - 03:04 AM.

[S.AHMAD]

Hi

Alternatively design the gas turbine that be able to consume fuel gas at lower pressure and install pressure control valve at the battery limit. We normally refer to as pressure let down station.

Edited by S.AHMAD, 07 January 2014 - 04:10 AM.

[nazari.at]

Dear ankur,

Many thanks for your reply. About your questions:

1- You are absolutely right. Temperature variation is just one reason, the other is gas demand from another places like home demands.

2- I don't have any information about the relation of flowrate and pressure also, but the variation of the capacity is being checked in parallel. and I will tell you immidiately after completing our survey about the capacity.

3- The size of the pipe will be measured later but we need 400 psi pressure with 12500Nm3/h flowrate in our site. A general diagram of the site is attached .

http://rioupload.com/qn3rhxhmf9ek

Attached Files

•  oil and gas refinery.jpg   48.86KB   3 downloads

[nazari.at]

Dear Ahmad,

Thanks for you reply. Pressure control valve is a good idea, but do we have any pressure control valve that just decrease the pressure?or it decreases the flowrate too? can u explain in this regard i mean the operation of pressure control valve and relation between flow and pressure.

thanks

[sanchit_11]

Dear Nazari,

 

It seems you are talking about fuel gas supply line to gas turbine. If i am wrong please correct me.

 

From the thumbnail you have provided it has been noticed that main header supply pressure is 1000 psi (max) to 400 psi (min).

But, in your query you mentioned that pressure is varying from 400 psi (max) to 180 psi (min). Please clarify that is there any pressure control valve installed between main supply header and gas turbine supply line for reduction of pressure?

 

What is change in temperature between cold weather and normal weather?

 

From my experience fuel gas supply to gas turbine is taken from high pressure dehydrated gas header available in plant. This dehydrated gas is normally available at 1000 psi and used for fuel gas at 400 psi after pressure reduction using downstream pressure control valve. Thus if dehydrated gas supply is not of good quality i.e. it have high HC Dew point and Water Dew Point then formation of hydrate occur downstream of pressure control valve, resulting in decrease in downstream pressure and flow rate.

 

regards

Sanchit

[nazari.at]

 

Dear ankur,

 

Many thanks for your reply.  About your questions:

1. You are absolutely right. Temperature variation is just one reason, the other is gas demand from another places like home demands.
2. I don't have any information about the relation of flowrate and pressure also, but the variation of the capacity is being checked in parallel. and I will tell you immidiately after completing our survey about the capacity.
3. The size of the pipe will be measured later but we need 400 psi pressure with 12500Nm3/h flowrate in our site. A general diagram of the site is attached .

Attached Files

•  oil and gas refinery.jpg   48.86KB   3 downloads

[nazari.at]

Dear Ahmad,

 

Thanks for you reply. Pressure control valve is a good idea, but do we have any pressure control valve that just decrease the pressure?or it decreases the flowrate too? can u explain in this regard i mean the operation of pressure control valve and relation between flow and pressure.

thanks

[nazari.at]

Hello Gerardo,

 

With many thanks for your reply. It is variable because of the weather and also gas demand from the other pipelines which are connected to the main pipeline.

1. What is your idea about screw compressor?
2. Is using a reciprocating compressor possible or common for projects like this case?  Before I heard some thing from an engineer that using reciprocating compressor for a booster compressor is not common, then what's your idea?

[nazari.at]

Sanchit:

 

With many thanks for your reply. You are absolutely right. About your question When we have max pressure (1000psi) in the main pipeline our pressure is good(400psi), but when we have 400 psi in the main pipeline our pipeline pressure becomes 180psi.

 

I dont have any information about out of our site(refinery) but in our site we dont have any control valves.

We have +45 to _15 degrees variance in temperature.

 

Actually the most important problem for us is finding suitable type of compressor.

[sanchit_11]

Dear Nazari,

 

I hereby like to advise you that before going for any compressor you shall find out why there is pressure drop of 600 psi (=1000 - 400) between main line and your site.

 

There can be pressure drop due to only 2 reasons:

 

Case-1: Distance between main pipeline and your site is too large resulting in pressure drop of 600 psi

Case-2: There is some control valve installed upstream of your site for flow & pressure control.

 

If Case-1 is valid then you don't have any option other than to go for installation of compressor.

If Case-2 is valid then control valve sizing shall be checked along with hydrate formation scenario at low operating temperature of +45 to -15 deg C.

 

regards

Sanchit