Natural Gas Compressors 2

[SelenaHolmes]

Hello,

I need help on the following subject. I need knowledge on natural gas compressors. For ex., the natural gas is supplied at 15 barg, 15 celcius and compressed to 40 barg 150 celcius. Then it's cooled to 40 celcius befor entering combustion chamber of a gas turbine. I also know that the pressure of natural gas before entering combustion chamber is 18 barg. I would like to ask you what could be the reasons of this pressure drop and what caused this pressure drop? (i.e. is there a pressure reducing valve) Besides I would like to know the reason of cooling the natural gas?
I am sure this kind of configuration is similar in most of power plants. So, if anyone has knowledge, I would be glad.
Thanks!

 

[jsummerfield]

Clarify the basis of this pressure temperature knowledge. What is the nature of your application?

I assume that you are talking about a gas turbine driven compressor turning a gas compressor. I doubt that your pressure/temperature generalizations are necessarily correct for all manufacturers. Gas may be processed at transported by compression at very high pressures in the oil and gas fields. Gas may also be processed at one bar. Does your application pertain to a domestic gas compressor in a low-pressure distribution system?

John

 

[pmover]

generally stating...

compressors are classified as either positive displacement (reciprocating, rotary, etc.) or dynamic type (centrifugal). critical process parameters for compressors are flow, gas composition, inlet/outlet pressures & temperatures.
upon compression of natural gas, the process may require the gas to be cooled by air coolers (typically) to protect the piping (corrosion issue). once cooled, the higher-pressure gas may be used as a source of fuel for the driver (i.e. gas turbine, internal combustion engine, etc.). the justification for using the higher-pressure gas for fuel source is that the engine requires the higher pressure (more so than compressor inlet pressure) to get the gas into the engine and/or material costs (i.e. larger diameter pipe for lower pressure gas). the pressure drop is a result of passing the gas through a pressure reduction valve (station). of course, the natural gas should possess a quality suitable for the engine.

i hopes this helps.
good luck!
-pmover

 

[sailoday28]

What is the mechanism for the cooling from 150 to 40C? Also, is there any mass transfer such as water injection?
Then perhaps your question of the pressure drop can be answered.
The temperatures by them selves (for an adiabatic process) do not indicate the pressure drop is due to a control valve.

 

[quadtracker]

Compressed gas from the final discharge of the compressor is normally cooled down to 30 or 40c for better handling and control through various processes,conrol valves, regulators and other downstream lines and equipment. In the case of fuel gas supply for the gas turbine there is a fuel gas regulator to reduce fuel gas pressure to a safe operable level given by the turbine manufacturer. Sometimes the fuel gas supply from the compressor discharge may be reduced a couple of times through a pressure control valve to be used to supply other plant equipment fuel gas requirements. The gas turbine will then get its supply from the plant fuel system and the reduce the pressure further through the fuel gas regulator located usually near the gas turbine.

 

[butlen]

The gas regulator (control valve) is probably causing the pressure drop at the inlet to the turbine.

The compressor discharge pressure is higher than the actual gas pressure utilized at the turbine inlet because the control valve needs a differential pressure to control flow.

I have looked at similar situations and asked the same question "why do I compress from 15 bar to 40 bar, then back down to near 18 bar". There may be a good answer for this, but it is possible that the plant is overcompressing the gas for no good reason.

 

[wedoplus]

Hi,

For ur quetion, in Gas turbines system we often use an axial compressor,Because it gives high amount of mass flow rate which is needed for the combution procees to have the required fuel to air ratio. after the compression the gas temperature increases so we have to cool it down with an intercooler and then we can use another compressor to compress it again. which is called compression with intercooling.

I hope u seeked what ur looking for.
Byeeeeee