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Combustors

 Combustors

  • All gas turbine combustors perform the same function: they increase the temperature of the high-pressure gas.
  • The gas turbine combustor uses very little of its air (10%) in the combustion process. The rest of the air is used for cooling and mixing.
  • New combustors are also circulating steam for cooling purposes. The air from the compressor must be diffused before it enters the combustor.
  • The velocity of the air leaving the compressor is about 400–600 ft/sec (122–183 m/sec) and the velocity in the combustor must be maintained below 50 ft/sec (15.2 m/sec).
  • Even at these low velocities, care must be taken to avoid the flame to be carried on downstream.
  • The the combustor is a direct-fired air heater in which fuel is burned almost stoichiometrically with one-third or less of the compressor discharge air.
  • Combustion products are then mixed with the remaining air to arrive at a suitable turbine inlet
  • temperature. Despite the many design differences in combustors, all gas turbine combustion chambers have three features: (1) a recirculation zone, (2) a burning zone (with a recirculation zone, which extends to the dilution region), and (3) a dilution zone, as seen in Figure 1-23. The air entering a combustor is divided so that the flow is distributed between three major regions: (1) Primary Zone, (2) Dilution Zone, and (3) Annular space between the liner and casing.
  • The combustion in a combustor takes place in the Primary Zone.
  •  Combustion of natural gas is a chemical reaction that occurs between carbon, or hydrogen, and oxygen. Heat is given off as the reaction takes place.
  • The products of combustion are carbon dioxide and water. The reaction is Stoichiometric, which means that
  • the proportions of the reactants are such that there are exactly enough oxidizer molecules to bring about a complete reaction to stable molecular forms in the products.

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