There are many types of gas turbine: all comprise a compressor, combustor and expansion turbine. The main split is Aero-derivative engines and Heavy-duty engines, aero-derivatives are jet engines modified for power generation rather than thrust. The pressure of 30 bar that you mention is not unusual in heavy duty turbines, at this pressure the air that is compressed is heated to about 250 - 300 C. It is not practical to compress isothermally (i.e. at 25 C).

The hot compressed air is then heated by combustion, or external heat input, before expanding through the turbine. To balance the energy of compression the combustor outlet temperature must exceed 550 C: modern units exceed 1300 C. The higher this temperature is the higher the efficiency.

There are many good texts that explain turbines further, but in simple terms if you expanded 30 Bar air at 25 C to atmospheric pressure, the outlet gas would be at about -150 C.

Hope that this helps you.

Thank you for your detailed explanation, Dr. Jack! It helps clarify a lot of the principles behind gas turbines.

Regarding the idea I had: I’m considering using oxygen at 25°C and 30 bar, which comes from a chemical process, is it possible to direct it to combustion chamber what is its effects

Typical Thermal Input for Gas Turbines

The thermal input for a gas turbine can vary significantly based on the size, application, and design of the turbine. Typical ranges are as follows:

• Small industrial gas turbines: 1–10 MW of thermal input
• Medium-sized turbines: 10–50 MW of thermal input
• Large power generation turbines: 100–400 MW or more of thermal input

For precise information, you'd need to specify the type and model of the gas turbine (e.g., aeroderivative or heavy-duty turbines) and its application (e.g., power generation, aviation, or mechanical drive).

Purpose of Raising Air Pressure and Temperature Before the Combustion Chamber

Raising the air's pressure and temperature before entering the combustion chamber serves several purposes:

Handling Air at 25°C and 30 bar Before Entering the Turbine

If the air entering the turbine is at 25°C and 30 bar, it is suboptimal because:

• Turbines are designed to handle hot, high-pressure gases for efficient energy conversion.
• A significant temperature difference between the air entering the turbine and the combustion chamber exhaust can cause thermal stress and reduce efficiency.

To handle this:

Laith Mustafa If you have oxygen at 30 bar, it seems that the best approach would be to combust it with high pressure fuel in a small combustion chamber, then expand the hot gas through a turbine. This is not a conventional gas turbine approach and would need a purpose designed turbine based on the normal gas turbine's turbine stage.

Oxygen is of little benefit in conventional gas turbines because they work at very high excess air levels, so the oxygen would be "diluted".

Oxy-fuel combustors are used in steel-making, but are rare, as oxygen is usually expensive. Simply expanding the oxygen through an expander would generate a good cooling duty.

The inlet temperature and pressure to the turbine depends on the type of turbine and compressor.

Increasing temperature and pressure increases efficiency.