Patent Application
20120036859
This invention relates generally to gas turbine combustion technology and, more specifically, to a transition piece construction that promotes uniform cooling of hot gases flowing through the transition piece to the turbine.
It is well known that air-polluting emissions are typically produced in gas turbines burning conventional hydrocarbon fuels. Those emissions are usually oxides of nitrogen, carbon monoxide and unburned hydrocarbons. It is also well known that oxidation of molecular nitrogen is dependent upon the temperature of the hot gases produced by the turbine combustor that flow through a transition piece to the first stage nozzle. The residence time for the reactants at these high temperatures is also a factor in the production of the undesirable emissions.
Various concepts have been proposed and utilized to maintain the reaction zone temperatures below the level at which thermal NOx is formed, or by reducing the residence time at high temperatures such that there is insufficient time for the NOx formation reaction to go forward, or both. One method of reducing the temperature of the reactants in the combustor is to provide a lean mixture of fuel and air prior to combustion. Thus, dilution air is oftentimes provided within the combustion liner to absorb heat and reduce the temperature rise to a level where thermal NOx is not formed. However, in many cases, and even with lean premixed fuel and air, the temperatures are sufficient to produce undesirable emissions.
Dilution air has previously been provided in the transition piece between the combustor and the first stage nozzle. For example, in one prior art construction, dilution holes have been provided at both ends of the transition piece. However, undesirable emissions remain a problem, and it would be desirable, therefore to provide a transition piece design which promotes more effective and uniform cooling of combustion gases flowing between the turbine combustor and the turbine first stage.
In accordance with an exemplary but nonlimiting embodiment, a gas turbine transition piece adapted to carry combustion gases in a hot gas path extending between a gas turbine combustion chamber and a first stage of the gas turbine, comprises a hollow duct having a forward end adapted for connection to a combustor liner and an aft end adapted for connection to a first stage nozzle; one or more dilution air holes proximate the forward end and substantially equally spaced from one another, each of the one or more dilution holes fitted with a hollow sleeve penetrating into the hot gas path within the hollow duct, the hollow sleeve adapted to supply cooling air into the hot gas path.
In another nonlimiting aspect, a gas turbine transition piece adapted to carry combustion gases in a hot gas path extending between a gas turbine combustion chamber and a first stage of the gas turbine comprises a hollow duct having a substantially cylindrical forward end adapted for connection to a combustor liner and an aft end adapted for connection to a first stage nozzle; one or more dilution air holes proximate the forward end and substantially diametrically opposed to one another, the dilution holes each fitted with a substantially cylindrical hollow sleeve penetrating into the hot gas path within the hollow duct, the substantially cylindrical hollow sleeve having a tapered edge at an outlet end thereof.
In still another nonlimiting aspect, the invention provides a method of promoting temperature uniformity in a gas turbine transition piece extending between a gas turbine combustion chamber and a first stage of the gas turbine, the transition piece comprising a hollow duct having a forward end adapted for connection to a combustor liner and an aft end adapted for connection to a first stage nozzle, the method comprising providing one or more cooling air dilution holes in the transition piece; and inserting a sleeve in each of the one or more cooling air dilution holes, each sleeve penetrating into an interior space of the hollow duct, thereby, in use, enabling cooling air to more uniformly mix with hot gases within the hollow duct to provide enhanced temperature uniformity in the transition piece.
With reference now to
In an exemplary but nonlimiting embodiment of this invention, the gas turbine transition piece 14 is in the form of a hollow duct having a forward end 18 adapted for connection to the combustor liner and an aft end 20 adapted for connection to the first stage nozzle. The manner in which the transition piece 14 is connected at its opposite ends is well understood and needs no further discussion here. In accordance with an exemplary but nonlimiting embodiment, one or more dilution air holes 22, 24 (see
With particular reference to
In the exemplary but nonlimiting embodiment, each of the hollow dilution sleeves 26 may be about 3 inches long, with a length-to-diameter ratio of between about 1.5 and 2.0. The tapered edge 34 may extend inwardly in the direction of flow at an angle of less than twenty (20) degrees (e.g., twelve (12) degrees) relative to the turbine rotor axis. The plural axially-spaced turbulator rings 38 may have a substantially square or triangular cross section with a height (i.e., the extent of radial projection into the dilution sleeve 26) of about 0.075 inch (or between about five and ten percent of the interior radius of the sleeve 26), and they are axially spaced by between about five and six times the height of the turbulator (e.g., about 0.425 inch) along the length of the sleeve.
It will be appreciated that variations in the sleeve construction (including dimensions) and specified location of the sleeves 26 on the transition piece 14 are within the scope of the invention. For example, the sleeves 26 may be oval-shaped, teardrop-shaped, airfoil shaped (with trailing edges on the downstream side) or other suitable shapes that do not create undue stress or hot points. In addition, the one or more of dilution holes 22, 24 could be moved from the 12 o'clock and 6 o'clock positions shown in
It will also be appreciated that the invention is applicable in both new and retrofit situations. In the case of a retrofit, where in a nonlimiting example, the transition piece may normally have three smaller dilution holes indicated at locations A, B and C in
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
