6 replies to this topic

[B-2 Spirit]

Hello members,

I am currently doing an oil and gas study in which we have considered use of gas turbine for power generation.
Can you please tell me the typical superheat and inlet temperature requirement of the Gas Turbines.
As for the pressure we have taken 35 barg.

thanks and regards,
Alok

[Flame]

Dear Alok,

Gas Turbines (GTGs) are fired by fuel and the hot gases expand in the turbine to deliver power. The exit flue gases are then sent to an HRSG in the case of cogeneration mode of operation. Whereas, steam is used to deliver power in the steam turbines.

The refinery / oil & gas unit steam & power requirements are defined in a separate design basis, detailing out different modes of heat & power generation, as and when required. How did you arrive at the steam pressure of 35 barg?, have you considered steam production from any process unit from the plant, that may be generating steam at high pressure?

Degree of superheat is also an economic choice. Less superheat can lead to water condensation in the low pressure areas of the turbines whereas unnecessary high superheat increases fuel consumption in the boilers. It is advised to check out with ST vendors for the correct amount of superheat.

Regards,

[B-2 Spirit]

Flame,
I think you are confusing steam and fuel gas.
My question is about generally acceptable degree of superheat required for FG for use in GT and inlet temperature. It is note related with steam/fuel balance.

[Art Montemayor]

B-2:

What is happening is that you may think that Flame is confused, but in reality you have caused the confusion.

Please refer to the attached Excel Workbook. You have failed to fully explain and detail out what you are referring to. Consequently, Flame – as anyone else – has assumed that you are referring to a Waste Heat Recovery Unit that is sometimes installed on the Gas Turbine exhaust gas to generate steam (Rankine Cycle) and subsequently more power from the same fuel gas input – and thereby raising the energy recovery efficiency of the Gas Turbine. The obvious reason he/she has assumed this is because you make mention of the term “superheated”. This term is commonly attached to steam fed to steam turbines.

Your fuel gas fed to the Gas Turbine is “superheated” because it exists at a temperature well above its saturation temperature at the pressure it finds itself at. It normally is never described as “superheated” when describing it – although technically it is. This is always done for other conventional gases – such as air. The air we breathe everyday is also technically “superheated”; however, it is never described as that. So much for technicalities.

What I believe you are trying to describe is a regenerative cycle. Is that correct? If not, then please sketch out the specific Gas Turbine Cycle you are proposing – just the same as I have done on Excel. It is the least basic data you can supply in order to correctly address your query and try to help you out.

Without giving us any basic data, you ask: “Can you please tell me the typical superheat and inlet temperature requirement of the Gas Turbines?” And the best guess I can furnish is that the temperatures are normally “ambient”. If you furnish a detailed sketch and description of your GT cycle, then we all can give you specific responses.

Await your response.

Attached Files

•  Gas Turbine Cycles.xlsx   12.35KB   112 downloads

[aransari85]

Hi B2-Spirit,

As per your description gas turbine is for power generation purpose, also you have mentioned 35bar fuel gas pressure. This reminds me one of gas turbine i previously came in touch which was for gas boosting station(GT linked with compressor). It also had near about same conditions, Fuel gas was coming at about 40bar and about 75-80 deg C temperature, that fuel gas is coming from FG header at 11bar and then compressed to 40bar in reciprocating compressor and then it had electric heater downstream to compressor before it goes to gas turbine. Important think to mention is it has low low temperature trip at GT inlet. I understand the importance of superheat is avoid condensing small drops of fuel gas in cold weather condition which may lead to problem in gas turbine.
I hope this may help you...

Abdul

[B-2 Spirit]

Thanks all for your valuable inputs, especially Art Montemayor and Abdul, for your suggestions.
Art you have invested a lot of time to my query. thanks for that.
It may be my fault, the reason for this confusion is my limited knowledge and your vast knowledge on the subject. I was only interested in fuel gas inlet degree of superheat required for a GTG.
Well, I have contacted the vendors like GE and Solar, and as per our Rotary Equipment experts, the degree of superheat requirement has increased, earlier typical values were 20-25 °C, which has now gone up to superheat of 30 °C.
When we use a Gas Engine the degree of superheat required is low. It howver depends on the gas composition also.

The inlet gas temperature to the turbine is also important and typical upper limit is 90 deg C.

I am sorry to confuse Flame.

regards,
B-2 Spirit

[andybud]

For starters, the term superheat is used widely in the oil and gas Industry for the North Sea in the UK Sector to describe an inlet gas temperature at the GT above the Hydrocarbon dew point (HCDP) and water dew point (WDP) temperatures. ASME recommends 45 F to 54F (25 to 30 C) of superheat be used for combustion turbine gaseous fuel. Take this as a rule of thumb to be safe.

 

However, vendors such as GE have their own guidelines and give formulas specific to their products. Look at GE document "GEI 41040G - Specification for Fuel Gases for Combustion in Heavy-Duty Gas Turbines" for further information.

 

So, Arts suggestion that fuel gas "normally is never described as “superheated” when describing it", is incorrect.