Patent Application
20110041507
The present invention relates to apparatus and methods for minimizing or eliminating dilution air leakage paths in a gas turbine combustor and, more particularly, the invention relates to apparatus and methods for managing dilution air leakage to achieve lower emission levels.
As is well known, significant products of combustion in gas turbine emissions are oxides of nitrogen, i.e., NO and NO2 collectively called NOx, carbon monoxide CO, and unburned hydrocarbons as well as other particulates. Various systems have been proposed and utilized for reducing emissions. For example, water or steam injection into the burning zone of the gas turbine combustor, catalytic clean-up of NOx and CO from the gas turbine exhaust and dry low NOx combustors have been used in the past. Compressor discharge dilution air introduced into the liner sleeve of the combustor and transition piece has also been utilized to reduce emissions.
It would be desirable to substantially reduce or eliminate leaks so that air flow in more non-critical areas is conserved and made more consistent from can to can. Additionally, it would be desirable to substantially reduce or eliminate leaks so that air flow can be increased in usable areas in a more dispersed and even mixing through the mixing holes.
In an exemplary embodiment, a combustion liner assembly for a gas turbine combustor includes a plurality of fuel nozzles disposed circumferentially about a central axis of the combustor, and a venturi section disposed downstream of the fuel nozzles and connected to a head end of the liner assembly. The venturi section defines an annular throat area downstream of the fuel nozzles. A liner sleeve is connected to and commences at a downstream end of the venturi section. At least a portion of the venturi section serves as a liner upstream of the liner sleeve.
In another exemplary embodiment, a method of reducing air flow losses between a venturi section and a liner sleeve of a combustion liner assembly in a gas turbine includes the steps of utilizing at least a portion of the venturi section as a liner upstream of the liner sleeve; and providing an annular weld at a joint between the venturi section and the liner sleeve and at a joint between the venturi section and a head end of the combustion liner assembly.
In still another exemplary embodiment, a combustion liner assembly for a gas turbine combustor includes a venturi section connected to a head end of the liner assembly via an annular weld, where the venturi section defines an annular throat area within the liner assembly; and a liner sleeve connected to and commencing at a downstream end of the venturi section, where the liner sleeve is connected to the downstream end of the venturi section via an annular weld. At least a portion of the venturi section serves as a liner upstream of the liner sleeve.
Referring now to the drawings, particularly to
It has been discovered that variations in the leakage paths of the dilution air supplied to the combustor have a significant effect on emissions and that these variations are a result of parts tolerances and assembly of the parts. For example, a primary leakage path of concern is between the liner sleeve 14 and the outer sleeve 28 of the venturi 18 in the area of the rivets 44. It will be seen that the compressor discharge air supplied to the annular plenum 46 from externally of the combustion liner via apertures 24 may leak past the riveted connection. Variations in leakage flow past the riveted joint, however, have been discovered with respect to various identical combustors, and consequently, emissions will vary. Those emissions resulting from leakage path flows heretofore have not been identified or controlled.
There is an additional leakage path for the dilution air flowing from plenum 46 into the space between the inner and outer venturi sleeves 26 and 28, respectively, via apertures 50 in the outer venturi sleeve 28. This additional leakage path passes between the flanges 38 and 40 of the inner and outer liners 34 and 36 respectively of venturi 18. While these flanges 38 and 40 in the past engaged each another and were riveted to the liner sleeve 14, a variable gap between the flanges and from combustion liner to identical combustion liner appeared, resulting in variable emissions from ostensibly identical combustors.
A further leakage gap appears between the liner sleeve 14 and the overlapped flanges 38 and 40 of venturi 18. These gaps have been demonstrated to vary between identically constructed combustors and hence result in leakage flows causing variable emissions. Also, it is important that the venturi throat area 32 must be maintained within pre-determined limits, notwithstanding the removability of the venturi from the liner sleeve for maintenance and service. It is also important that the throat area be maintained upon original manufacture of the venturi and liner sleeve and throughout the various service procedures performed on the combustor during its life.
Yet another alternative embodiment is shown in
The described embodiments substantially reduce or eliminate air flow losses between the venturi wall and the liner wall. Elimination of air flow losses will allow more consistent air flow to be utilized in the fuel air mixture in the head end combustion zone rather than leaking air flow into direct stream. The simple constructions as described use similar parts and technology as is found in current designs. The embodiments are easy to manufacture and will produce a more repeatable air flow from can to can and will in turn help to create better fuel air mixture patterns than the current design while also lowering combustion emissions. The design substantially reduces or eliminates air flow leaks in areas between the venturi and the liner wall so that the air flow can be used in areas in a more dispersed and even mixing through the mixing holes than with the current design. The components can be used as control points to adjust air flow such that additional air flow by virtue of the reduced air flow losses can be utilized to lower emissions as well as lower variation from can to can.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
