The present invention relates to a combustor of a gas turbine and, more particularly, to a combustor of a gasturbine which can effectively withstand the vibration and thermal distortion generated during the combustion.
It is a current measure for preventing the pollution of air attributable particularly to lower nitrogen oxide (NOx) content to effect a spray of water, steam or the like into the combustors of gas turbines. This spray lowers the temperature of the combustion gas to effectively suppress the production of NOx in the combustor. On the other hand, however, the lowered temperature of the combustion gas considerably hinders the combustion of the fuel in the combustor. More specifically, the pulsation of the combustion is enhanced due to the lowered combustibility, resulting in a cyclically repeated application of load. This repetitional load is concentrated to the thermally weak portions of the combustor to cause a break down due to a stress concentration.
Generally, in the gas turbines for industrial purposes, compressed air produced by an air compressor is introduced into a combustor where the compressed air is mixed with the fuel and the mixture is burnt to form a combustion gas. This combustion gas is introduced to drive the turbine which in turn drives a load connected thereto. The combustor is mainly constituted by a liner forming a combustion chamber, a transition piece connected to the liner, an outer casing surrounding the liner and the transition piece and a fuel nozzle attached to the outer casing.
The fuel atomized into a liner from the fuel nozzle is burnt under the presence of the air which has been compressed by the air compressor and introduced into the liner through the jacket defined between the outer casing and the combined body of the liner and the transition piece and then through the combustion air port formed in the wall of the liner. The combustion gas produced as the result of the combustion then flows through the liner and introduced into the gas turbine after a rectification performed by the transition piece.
The transition piece is partially cooled by the compression air which flows toward the liner defining the combustion chamber. However, the transition piece has some portions which are in locations relatively inaccessible to the cooling air flow and, hence, the cooling is rather difficult. More specifically, this portion is the radially outer part of the gas outlet of the transition piece closest to the gas turbine. In consequence, this portion of the transition piece is heated excessively and broken due to the stress concentration.
The liner and the transition piece are supported for free thermal expansion and shrinkage. In other words, they are supported rather loosely. Therefore, the vibration caused by the pulsating combustion is transmitted from the liner to the transition piece to generate a vibration of a considerably large amplitude in the transition piece, particularly at the gas outlet side of the latter.