8 replies to this topic

[camad]

Let says that gas outlet pressure for my LP separator is 6 bar (fixed) and it going to gas compressor. The inlet pressure for gas compressor decrease as flowrate decrease. I show you some example :-

 

For inlet pressure for gas compressor 4.7 bar, the flowrate is 23mmscfd but for inlet pressure for gas compressor 3.3 bar, the flowrate is 18mmscfd.

 

Why this happened? Can anyone explain to me please. Thank you.

 

*These are further information that might be useful

-current supplied to operate the motor of gas compressor is decreased

-anti-surge control valve for gas compressor is increased

-more percentage of gas leaving from LP separator going to HP flare

[shan]

To maintain the same actual volumetric flow.

[camad]

To maintain the same actual volumetric flow.

Could you explain further please mr shan?

[latexman]

A P&ID of this process would help us help you.

[shan]

You have a positive displacement compressor (I guess), which compresses the identical actual volume of gas at the suction conditions for each stroke.  The same actual volume of gas at higher pressure is larger than that at lower pressure when the gas is converted to the standard conditions. 

[camad]

You have a positive displacement compressor (I guess), which compresses the identical actual volume of gas at the suction conditions for each stroke.  The same actual volume of gas at higher pressure is larger than that at lower pressure when the gas is converted to the standard conditions. 

 

A P&ID of this process would help us help you.

Data for pressure drop

 

from left : data at jun 2013, jun 2014, and jun 2015

 

V1030 Outlet Pressure (bar)

6.017

6.002

5.99

V1030 Outlet Flowrate (mmscfd)

23.358

21.521

20.894

K2430 Inlet Flowrate (mmscfd)

23.772

21.978

17.535

K2430 Inlet Pressure (bar)

4.739

4.011

3.543

K2430 Inlet Temperature (degree celcius)

62.036

61.629

61.266

K2430 Outlet Pressure (bar)

23.982

22.795

23.537

K2430 Current to Operate the Motor(A)

221.692

217.391

197.045

V1030 Outlet Flowrate (MMCF/D)

15.766

17.107

15.362

 

https://cdn.fbsbx.co...e=55B7A2B8&dl=1

 

https://cdn.fbsbx.co...e=55B7C792&dl=1

 

I hereby attached some link to my PFD and graph, hopefully u guys cab help me. Thank you.

[camad]

You have a positive displacement compressor (I guess), which compresses the identical actual volume of gas at the suction conditions for each stroke. The same actual volume of gas at higher pressure is larger than that at lower pressure when the gas is converted to the standard conditions.

FYI, I am using dynamic compressor which is centrifugal compressor. Why does the compressor maintain the inlet volumetric flowrate? Is it to maintain the efficiency of compressor or any good reason? Thank you for your reply sir.

[shan]

6 bar is the LP Separator operating pressure (inside vessel pressure not "outlet pressure"), which is controlled by a PCV.  The pressure at downstream of PCV is controlled by the compressor.  The same actual volumetric flow rate is because of the same RPM of the compressor.  The higher differential pressure of compressor is, the lower compressor flow rate per the compressor performance curve. 

[camad]

6 bar is the LP Separator operating pressure (inside vessel pressure not "outlet pressure"), which is controlled by a PCV. The pressure at downstream of PCV is controlled by the compressor. The same actual volumetric flow rate is because of the same RPM of the compressor. The higher differential pressure of compressor is, the lower compressor flow rate per the compressor performance curve.

Mr shan.. May I know what is the equation that I should use to calculate the actual volume?? FYI, im using dynamic compressor with constant rpm and straight through impeller.. How does this effect the actual volumetric flowrate? If I was not mistaken, suction pressure increase as flowrate increase buat discharge pressure increase as flowrate decrease.. Am I right?? Could you elaborate it?? Thanks sir

Edited by camad, 03 August 2015 - 12:14 AM.