Power plants – Combustion products used as motive fluid – Combined with regulation of power output feature
Reexamination Certificate
1998-03-20
2001-02-27
Thorpe, Timothy S. (Department: 3746)
Power plants
Combustion products used as motive fluid
Combined with regulation of power output feature
Reexamination Certificate
active
06192669
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a combustion chamber having an interior space to which burners are operatively connected.
2. Discussion of Background
Combustion chambers of modern gas-turbines are preferably designed as annular combustion chambers. They are arranged axially in the direction of flow between compressor and turbine, care being taken to ensure that the hot gases formed there are directed optimally in terms of flow and combustion between the two fluid-flow machines, normally between compressor and turbine. This regularly leads to such annular combustion chambers having a relatively long axial extent if, in particular, the combustion stipulations or minimum requirements are to be met. The combustion aspects have a not insignificant effect on the absolute axial length of such combustion chambers. The length of a main annular combustion chamber is regularly decisive for the design of the entire gas-turbine; thus, for example, whether more than two bearings then have to be provided for the rotor support, or whether the gas-turbine has to be of twin-shaft design. This initial situation is accentuated when the gas-turbine is operated with sequential firing; the axial lengths of the two combustion chambers of annular design are then decisive for the feasibility and largely also for the market acceptance of such a machine. For the abovementioned reasons, the gas-turbines with annular combustion chambers which have been disclosed by the prior art have, without exception, a considerable length, as a result of which the further step towards a qualitative leap concerning the compactness of these plants remains blocked.
In addition, it should be pointed out that elongated combustion chambers tend to initiate pulsations within the combustion-space section, these pulsations then having an adverse effect on the operation of the burners, in particular if these premix burners work with an integrated premix section and have a backflow zone as a flame retention baffle.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention, is to provide a combustion chamber of the type mentioned at the beginning, is to propose measures which are able to remove at least the disadvantages listed above.
An essential advantage of the present invention may be seen in the fact that the combustion chamber, while maintaining superior combustion with regard to the efficiency and the minimization of the pollutant emissions, has an extremely compact axial length such that this same combustion chamber, in combination with the fluid-flow machines of a gas-turbine, no longer has any important effect on the rotor length.
A further essential advantage of the present invention may be seen in the fact that this combustion chamber is of basically very simple construction. Its design in terms of combustion and flow permits optimum fluidic operation upon admission of the hot gases to the downstream turbine.
As viewed geometrically, this combustion chamber is essentially of toroidal configuration, certain deviations from an ideal torus form being permissible. Such a combustion chamber can be arranged without problem between any two fluid-flow machines. Furthermore, the combustion chamber according to the present invention is just the right combustion chamber for installing as a retrofit unit in existing gas turbines, for example in place of a silo combustion chamber.
In addition, this combustion chamber, in particular in the case of premix combustion, develops its full potential with regard to maximizing the efficiency and minimizing the pollutant emissions.
Owing to the fact that the combustion process inside this combustion chamber takes place entirely in a compact toroidal space, several fluidic advantages, which up to now could only be achieved by the implementation of costly and complicated measures, can be achieved at the same time. These advantages can be listed as follows, in which case the following explanations do not claim to be definitive:
The removal of pulsations, which, in particular in the case of premix combustion, adversely affect the flame front and the backflow zone, which is in interdependent relationship with the flame front.
The distribution and injection of the fuel or fuels is of very simple configuration. The burners, to the greatest possible extent, react insensitively to non-uniformity in the fuel injection, whether caused by pressure differences or by delays in the responsiveness during load variations.
Leakage during the introduction of the combustion air or non-uniform injection of the fuel has no effect on or only a slight effect on the so-called pattern factors at the turbine inlet. Therefore a robust hot-gas flow, which is unaltered by external factors or interference, is formed inside the annular toroidal interior space in the shape of a swirl flow.
A congenial swirled hot-gas flow for admission to the downstream turbine is fluidically formed inside this annular toroidal interior space by virtue of the fact that the hot gases flow directly to the turbine without further flow deflections. The forming centrifugal-force zone of this vortex then results in considerable evening out of the gas-temperature distribution in the peripheral direction in such a way that hot gases are then admitted to the blading of the turbine over the entire periphery and they have a uniform pressure profile and temperature profile. The torus form of the combustion chamber combined with the centrifugal-force zone reduces the convective heat transfer to a minimum on account of the gas centrifuge effect and the flow against a concave wall. In addition, the smallest possible surface is achieved for a predetermined combustion-chamber volume.
There is great interdependence between the individual burners distributed over the periphery of the annular toroidal interior space. At the same time, the operating characteristic, during a shut-down of individual burners, does not behave intermittently with regard to the hot gases delivered to the turbine. Accordingly, such a combustion chamber, without giving up the advantages of the hot-gas flow forming in the annular toroidal interior space, can be run up from part-load operation to full load without problem or, conversely, can be reduced in load in a controlled manner. The cross ignition is therefore decisively improved. Ignition over cold burners is possible. The burner graduation in the peripheral direction is therefore also possible in the case of a single-row burner arrangement. The simple operating concept also leads to low pollutant emissions (NOx, CO, UHC) at part load.
If the combustion chamber is operated with premix burners, for example according to one of the proposals according to EP-B1-0 321 809 (EV) or EP-A2-0 704 657 (AEV), which form an integral part of this description, the swirl flow from the individual burners, by appropriate disposition of the same in the peripheral direction of the annular toroidal interior space, can easily be transformed into a uniform vortex flow inside the interior space, in the course of which a stable core, which fulfills the function of a bodiless flame retention baffle, forms in the center of this interior space. There is therefore a causal relationship between the stability of this vortex core and the fact that it has uniform tightness in the region of its annular axis.
Such an annular toroidal combustion chamber is also suitable for being used in a sequentially fired gas-turbine group, preferably as a high-pressure combustion chamber, but not only as such. Thus, it may also be readily used as a self-igniting combustion chamber within sequential combustion by a system of vortex generators being provided in place of the premix burners proposed here, which vortex generators, in a manner analogous to a burner-operated combustion chamber, form a vortex core for stabilizing the flame front against flashback.
However, the premix burners proposed here are not an indispensable condition for the operation of the annular toroidal combustion chamber. Thanks to its des
Keller Jakob
Suter Roger
Asea Brown Boveri AG
Gartenberg Ehud
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Thorpe Timothy S.
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