PURPOSE: To provide a natural gas turbine system in which the size of the rotary machine used is minimized, which is capable of enhancing energy efficiency thermally when mechanical and mechanical-thermal energies are generated simultaneously, and is beneficial for environment protection.

CONSTITUTION: A natural gas turbine system comprises at least one combustion chamber 1, an expansion turbine 2, an air compressor driven by the expansion turbine 2, and means for coupling the expansion turbine 2 to at least one external receiver 4 of mechanical energy. The natural gas turbine system further includes means for injecting water to constitute a thermal ballast in the combustion chamber, the quantity of compressed air used remaining close to the quantity of oxidizing air required for stoichiometric combustion.