Power plants – Combustion products used as motive fluid – Combustion products generator
Reexamination Certificate
1998-12-15
2001-03-20
Kim, Ted (Department: 3746)
Power plants
Combustion products used as motive fluid
Combustion products generator
C060S746000
Reexamination Certificate
active
06202420
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to gas turbines. More specifically, the present invention relates to a pre-mixing combustion chamber for a gas turbine. The present invention also relates to annular combustion chambers equipped with a plurality of pre-mixing combustion chambers.
BACKGROUND OF THE INVENTION
Pre-mixing combustion chambers are low-pollutant gas turbine combustion chambers. Gas turbines can be utilized both stationary mechanisms such as generator drives in power plants, as well as in aircraft engines. Maximum limits for nitrogen oxide emission of stationary gas turbines have been set in numerous industrialized countries. Since corresponding recommendations also exist for aircraft engines, great significance is accorded to the reduction of nitrogen oxide formation in the combustion chambers in the framework of reducing pollutant emissions. Rich/lean combustion ratios wherein the combustion ensues with a first, rich stage and a second, lean stage with air excess is currently utilized for reducing nitrogen oxide in aircraft engines.
Compared thereto, even greater reductions can be achieved with the pre-mixed lean combustion applied in stationary gas turbines. Since the nitrogen oxide formation increases with, among other things, the highest temperature, methods have been developed to lower the highest flame temperature. A distinction is thereby made between wet and dry methods. In the previously predominantly employed, wet methods, water or water vapor are introduced into the combustion zone separately or pre-mixed with the fuel. It is thereby disadvantageous that processed water is required, the consumption thereof also being high. Over and above this, the system efficiency drops given the wet methods.
Due to these disadvantages, dry methods wherein the excess air coefficient in the combustion zone is increased as far as possible and air and fuel are entirely or partially pre-mixed are increasingly desired. In order to meet the legal regulations and recommendations, air and fuel must be mixed as uniformly as possible preceding the combustion chamber. The peak temperatures in the flame can be reduced in this way by itself. To this end, pre-mixing combustion chambers have been developed wherein a specific length of the pre-mixing chamber or a minimum dwell time in the pre-mixing chamber is needed in order to achieve a high degree of homogeneity. However, there is thereby the risk that the fuel/air mixture will ignite in the pre-mixing chamber. Since the blending process is not completed in this case, high temperatures that lead to increased nitrogen oxide formation arise locally as a consequence of inhomogeneities. Further, there is the risk of a flashback from the combustion zone into the pre-mixing chamber. In order to avoid this, paddle grids or the like are attached at the end of the pre-mixing chamber given traditional pre-mixing chambers in order to accelerate the mixture and produce a twist. When a flashback nonetheless occurs, this leads to damage or destruction of combustion chamber parts such as, for example, the paddle grid.
In a known combustion chamber arrangement according to German Letters Patent 43 18 405, a reduction of the nitrogen oxide formation is enabled with pre-mixed lean combustion without risk of self-ignition in a pre-mixing path in that the fuel is injected into a pre-mixing chamber fashioned essentially straight that tangentially discharges into an essentially rotationally-symmetrically fashioned combustion chamber, as a result whereof a creation of twist is achieved when the mixture flows in. Since the twisting is not generated with additional component parts such as paddle grids, the risk of parts damage given a potentially occurring flashback is eliminated. An adequate combustion stability is assured with a supporting pilot combustion that ensues in a separate combustion zone. The hot gasses from the pilot zone are mixed into the lean main zone, whereby the stabilizing effect is highly dependent on the existing flow field and can be subject to greater fluctuations in different operating conditions. Moreover, the flow from the main combustion zone into the after-combustion zone is deflected by 90°, which leads to an increased pressure loss.
Therefore, there is a need for a pre-mixing combustion chamber of the species initially described wherein the stabilizing effect of the pilot combustion is improved.
SUMMARY OF THE INVENTION
The inventive solution is characterized in that the main combustion zone in the combustion chamber proceeds or, respectively, is arranged essentially coaxially or, respectively, parallel to the after-combustion zone. i.e. the flow path is essentially straight and proceeds without significant deflection, and the pilot stage is arranged at that end of the combustion chamber remote from the after-combustion zone.
The advantage of this pre-mixing chamber is comprised therein that the flow within the combustion chamber from the main combustion zone to the after-combustion zone is not deflected by 90° and the pressure loss connected therewith is eliminated. Due to the pilot stage arranged directly at the combustion chamber, this has a direct connection to the main combustion or, respectively, recirculation zone, as a result whereof the stabilizing effect of the pilot combustion is noticeably improved. The inventive pre-mixing combustion chamber can be utilized both in stationary gas turbines as well as in aircraft engines.
In a preferred embodiment of the invention, the region of the combustion chamber forming the main combustion zone expands conically in flow direction, which proceeds from the main combustion zone in the direction toward the after-combustion zone. The recirculation zone and, thus, the flame stability can be controlled by the aperture angle of the cone. Whereas an additional pre-evaporation region derives given smaller aperture angles, the stability of the combustion is promoted given larger aperture angles.
The pilot stage is preferably arranged at the end of the combustion chamber with smaller radius at the end face and proceeds coaxially thereto.
It can be expedient that the pilot stage comprises a pilot combustion chamber arranged between the pilot injection device and the combustion chamber.
In an embodiment, the present invention comprises a pre-mixing combustion chamber assembly for a gas turbine. The pre-mixing combustion chamber assembly comprises a first main stage housing comprising an inlet end and a discharge end and further defining a first pre-mixing chamber disposed therebetween. the discharge end of the first main stage housing is connected to a combustion chamber. The combustion chamber comprises a pilot end and an outlet end. The combustion chamber defines a main combustion zone. The outlet end of the combustion chamber is connected to a housing section which defines an after-combustion zone. The combustion chamber and housing section being disposed coaxially with respect to each other. The main combustion zone is disposed longitudinally between the pilot end of the combustion chamber and the after-combustion zone. The discharge end of the first main stage housing provides communication between the first pre-mixing chamber and the main combustion zone. The pilot end of the combustion chamber is connected to a pilot stage comprising a pilot injection mechanism.
In an embodiment, the first pre-mixing chamber is a rectangular channel.
In an embodiment, the combustion chamber has a longitudinal axis and the first pre-mixing chamber is a rectangular channel having a height extending perpendicular to the longitudinal axis of the combustion chamber and a width extending tangentially to the combustion chamber. The width being greater than the height.
In an embodiment, the combustion chamber is conically shaped with a longitudinal axis and a maximum eccentricity. The discharge end of the first pre-mixing chamber is disposed along the maximum eccentricity of the combustion chamber.
In an embodiment, the present invention further comprises a second main stage housing com
Ripplinger Thomas
Zarzalis Nikoloas
Kim Ted
MTU Motoren-und Turbinen-Union Munchen GmbH
Schiff & Hardin & Waite
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