7 replies to this topic

[hafiz akhtar]

Steam flow rate 400 000 lb/hr
Steam pressure 42 bara

Compressor inlet pressure 190 psig
Compressor outlet pressure 500 psig
gas flow rate 405 MMSCFD
Compressor inlet temperature 140 F
Compressor outlet temperature 270 F

Polytropic Efficiency ?

I have calculated the efficiency on HYSYS but cannot include the steam data. This compressor consuming 40% more steam than others. Therefore we have to check based on steam consumption.Please provide the supporting calculations and info.

Haorchard

Edited by hafiz akhtar, 28 December 2012 - 11:58 PM.

[hafiz akhtar]

No one reply yet. Can any one give an idea about this compressor issue. I could not understand why this compressor is consuming more steam than others compressors at the same inlet and outlet pressures and flow rates.

Haorchard

Edited by hafiz akhtar, 31 December 2012 - 11:26 AM.

[Anjaney Shukla]

Have u observed any difference in gland leakages from turbine.

This can be the reason for low power consumption for the same inlet flow and properties

[Art Montemayor]

hafiz akhtar:

In case you have not noticed, your topic has absolutely nothing to do with Process Heat Transfer even though you have failed to state that you are operating a steam-driven turbine that is the prime driver for a gas compressor. Am I correct?

Your steam consumption has little to do with process heat transfer and more to do with the Rankine Cycle. This has to do with basic thermodynamic conversion of energy into useful work and is defined in all basic Thermodynamic textbooks. Because of this, this topic does not belong in this Forum and is being transferred to the Industrial Professional Forum.

Please be specific in what it is that you are trying to calculate. Is it the thermodynamic value of the polytropic exponent on the gas compression cycle? (which has nothing to do with the Rankine cycle or the steam consumption taking place in the steam turbine)

It would be so much simpler and direct if you supplied a detailed sketch carefully outlining your operation and indicating the pressures, temperatures, & flow rates there. Perhaps that is why you are not receiving any attention to this topic.

[hafiz akhtar]

Thanks for reply. I have mentioned in the title that Compressors are steam turbine driven. Anyhow I was asking only the reasons or supporting calculations for high steam consumption than other three parallel steam turbine driven compressors. Inlet and outlet conditions for compressor is mentioned and steam turbine data is included. I shall show these parameters on Sketch as per your advice. I shall see the response in Industrial Professional Forum.

[sheiko]

Hafiz,

1/ Compressor:
You already have all the data to calculate the polytropic efficiency, except the k-value or specific heat ratio (but you can consider 1.4 as a good approximation). Just look for the definitions in a book or in your courses or in this forum archives.

2/ Steam turbine:
You can also calculate an efficiency for the steam turbine. Again, you can search through the archives of the forum (search button), you will find a lot about how to calculate this efficiency.

Once you have calculated both efficiencies and compared them to their design values, you would be abble to know if the higher steam consumption is due to a MECHANICAL problem in the compressor or in the turbine.

A PROCESS problem could be that the Fuel Gas being compressed is becoming heavier (higher molecular weight). In this case the turbine will run slowlier. But the speed control valve will open to increase the steam rate, thus re-increasing the speed to maintain the set point.

Edited by sheiko, 05 January 2013 - 10:05 AM.

[hafiz akhtar]

Thanks sir let me calculate

[Anjaney Shukla]

Are inlet and outlet steam flow are same.

normally there are some gland leakages from valves. So please do a material balance across the turbine. I think there will more gland leakage in one turbine compared to others.