Power plants – Combustion products used as motive fluid – Combustion products generator
Reexamination Certificate
1999-06-21
2001-02-20
Kim, Ted (Department: 3746)
Power plants
Combustion products used as motive fluid
Combustion products generator
C060S748000, C431S009000, C431S284000, C239S400000
Reexamination Certificate
active
06189320
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a burner for fluidic fuels, in particular for use in a gas-turbine plant.
A burner for fluidic fuels, which is used in particular in a gas-turbine plant, has been disclosed by German Published, Non-Prosecuted Patent Application DE 42 12 810 A1. It is apparent from that publication that air is fed through an annular air-feed-duct system and fuel is fed through a further annular-duct system to the combustion. In that case, fuel is injected from the fuel duct into the air duct, either directly or from swirl blades constructed as hollow blades.
The intention is thus to achieve, inter alia, a homogeneous mixing of fuel and air as far as possible in order to achieve combustion having a low concentration of nitrous oxides. It is an essential requirement for combustion, in particular for combustion in the gas-turbine plant of a power station, to achieve as low a production of nitrous oxides as possible, for reasons of environmental protection and corresponding statutory guidelines for pollutant emissions. The formation of nitrous oxides increases exponentially with the flame temperature of the combustion. If there is inhomogeneous mixing of fuel and air, a certain distribution of the flame temperatures in the combustion region results. In accordance with that exponential connection between nitrous-oxide formation and flame temperature, the quantity of nitrous oxides being formed is substantially determined by the maximum temperatures of such a distribution. Accordingly, the combustion of a homogeneous fuel/air mixture, at the same average flame temperature, achieves a lower nitrous-oxide discharge than the combustion of an inhomogenous mixture. In the case of the burner structure of the publication cited, spatially effective mixing of air and fuel is achieved.
European Patent Application 0 561 591 A2 discloses a rotation cascade for generating a turbulent flow for use in a burner, in particular in a premix burner of a gas turbine. The rotation cascade serves to generate two concentric, contra-rotating flows so that, during partial-load operation of the gas-turbine plant, a reduced fuel quantity is burned in an inner flow in an air quantity reduced by splitting up into two flows and thus stable combustion can also be maintained during partial-load operation. Furthermore, the rotation cascade generates backflow zones which directly adjoin the rotation cascade and constitute combustion zones for stable combustion.
European Patent Application 0 619 134 A1 discloses a mixing chamber for mixing substances, e.g. in chemistry and in the production of foodstuffs or pharmaceuticals. The substances to be mixed are subjected to vorticity in separate ducts by a vortex generator and then brought together. The vortex generator is formed by deflecting elements constructed as elongated half pyramids.
A method and a device for the combustion of a free-flowing fuel, in particular in the burner of a gas turbine, are described in German Published, Non-Prosecuted Patent Application DE 44 15 916 A1. A turbulence-generating configuration is inserted in the air duct of the burner, so that combustion air is subjected to vorticity. Fuel is admitted to the vortical combustion air, so that an especially effective intermixing of fuel and combustion air is obtained. The vorticity is achieved by a number of obtuse flow obstacles, in particular by rods or discs. German Published, Non-Prosecuted Patent Application DE 41 23 161 A1 discloses a vortex element designated as a static mixer. It has a multiplicity of deflecting elements, which are small relative to the diameter of a pipe line or a flow duct in which it can be inserted and are inclined relative to the axis of the flow duct or the pipe line. The inclination of the deflecting elements, which are lined up in rows, is in the same direction within a row and in opposite directions from row to row. Such a vortex element covers a single cohesive area, e.g. a circular or rectangular cross section. It serves to subject a flow of a medium through the pipe line or the flow duct to vorticity, as a result of which effective intermixing with a substance fed into the medium can be achieved. Comparable, large vortex elements are also described in European Patent 0 634 207 B1 and in International Publication No. WO 95/26226 A1. The main field of application of such vortex elements is the nitrous-oxide reduction of flue gas by the admixing of ammonia in flow ducts having a cross-sectional area of typically a few square meters.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a burner for fluidic fuels, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which permits effective mixing of combustion air and fuel while at the same time other parameters of the combustion are only slightly affected.
With the foregoing and other objects in view there is provided, in accordance with the invention, a burner for fluidic fuels, in particular for use in a gas-turbine plant, comprising an air duct for feeding combustion air; a fuel duct for feeding fuel; an inlet for conducting fuel from the fuel duct into the air duct; and a vortex element upstream of the inlet for generating high turbulence in the combustion air, the vortex element including a first boundary ring having an axis of symmetry, a second boundary ring larger than the first boundary ring, the second boundary ring having a center on the axis of symmetry, a connecting area defined or spread out by the boundary rings, and a multiplicity of flat deflecting elements disposed along circles lying on the connecting area, each of the deflecting elements having a respective center lying on the axis of symmetry and each of the deflecting elements inclined relative to a normal to the connecting area.
A burner having such a vortex element has an especially small pressure lose caused by the vortex element. In addition, the vortex element is suitable for use in an annular flow duct. At least two and preferably three circles are provided.
The advantages of such a vortex element are obtained in particular when used for subjecting combustion air to vorticity in a burner, in accordance with the explanations given herein.
In accordance with another feature of the invention, the pressure loss produced by the vortex element is less than 2%.
An essential advantage of the invention lies in the fact that especially effective mixing of combustion air and fuel can be achieved by the turbulent flow of the combustion air, while at the same time a pressure loss caused by the vortex element is slight. Improved spatial homogeneity of the mixture is achieved by the mixing of fuel and combustion air in the turbulent flow. In addition, the variation in the mixture ratio with time has been determined in extensive tests for the first time. Locally occurring variations in the mixture ratio with time, as well as the spatial inhomogeneity, lead to a distribution of the flame temperature having the adverse effects on the nitrous-oxide emission which are explained above. The results of the tests showed that the fuel/air mixture produced exhibits a slight variation in ratio with time. Thus mixing of fuel and air which is largely homogeneous spatially and with time and thus reduced nitrous-oxide production are achieved. The pressure loss, which at the same time is only slight, leaves the efficiency of the burner virtually unaffected. This constitutes a considerable improvement over previously used vortex elements which were constructed as obtuse flow obstacles. Such flow obstacles result in a considerable pressure loss, so that improved mixing of fuel and combustion air had to be paid for with a markedly reduced efficiency of the burner.
In order to avoid flame stabilization at the vortex element, the fuel is admitted on the downstream side of the vortex element. Thus only combustion air flows through the vortex element, and the risk of combustion in the region of the vortex element, which could damage
Ganzmann Ingo
Hoffmann Stefan
Poeschl Gerwig
Greenberg Laurence A.
Kim Ted
Lerner Herbert L.
Siemens Aktiengesellschaft
Stemer Werner H.
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