Power plants – Combustion products used as motive fluid – Plural combustion products generators in ring coaxial with...
Reexamination Certificate
1999-07-09
2001-04-24
Freay, Charles G. (Department: 3746)
Power plants
Combustion products used as motive fluid
Plural combustion products generators in ring coaxial with...
C060S039300
Reexamination Certificate
active
06220015
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to gas-turbine engine combustion systems, and in particular to combustion systems in which combustion chambers are interconnected by crossfire tubes for ignition purposes.
2. Description of the Related Art
In a typical industrial gas-turbine engine, a number of combustion chambers (hereinafter referred to as combustors) are arranged in parallel around the engine to receive the pressurized air flow from the compressor stage as oxidant for gaseous or liquid fuel which is burnt therein. For example, there may be six to eight combustors equiangularly spaced around the engine's centerline at a given radial distance therefrom. To avoid the need for igniters in every combustor to initiate combustion on start-up, it has become common practice to interconnect the combustors with tubes, called crossfire tubes, which are adapted to pass a flame from an ignited combustor to another combustor. A problem that has been experienced with this type of arrangement is that of the crossfire tubes or the combustors becoming damaged by the flow of hot gases during normal running after start-up. One way of reducing this problem is disclosed and claimed in our European Patent No. 0 503 018. In this arrangement, air is introduced into the crossfire tube in such a manner as to be constrained to flow over the inner surface of the crossfire tube adjacent to its connection with the combustor, thereby cooling the crossfire tube without adversely affecting the cross-lighting performance, and so extending its working life.
Although this arrangement has proved to be a significant improvement over earlier crossfire tube designs, it has been found in practice that there remains a possibility of overheating of the combustor wall adjacent to the position where the crossfire tube enters it.
U.S. Pat. No. 5,001,896 discloses a crossfire tube assembly for interconnecting combustors, in which a double-walled crossfire tube is used, the outer wall being perforated to admit cooling air into the space between the walls, and the inner wall also being provided with apertures to bleed some air into the gas flow within the crossfire tube. The outer wall fits into an annular flange projecting through the combustor wall and inwardly into the combustor, while the inner wall of the crossfire tube projects beyond its outer wall into the flange. Although this arrangement improves cooling of the tube, there is still a problem with localized heating of the inwardly directed flange, as well as the combustor wall surrounding it, and the inner wall of the interconnecting tube where it projects into the flange. In extreme conditions, this localized heating might cause failure of these components, resulting in fragments of metal being propelled into the turbine, possibly in turn causing its failure. While the risks of such a major failure are very low, the likelihood of early failure of the combustor through overheating around the flange is considerably higher.
The present invention seeks to avoid these problems and therefore to improve life expectancy of the combustion system.
SUMMARY OF THE INVENTION
According to the invention there is provided a gas-turbine engine combustion system in which adjacent combustors are connected by a crossfire tube assembly adapted to pass an ignition flame from an ignited combustor to another combustor, wherein each crossfire tube assembly comprises inlet means for introducing air to film-cool an inner ignition flame-facing surface of the crossfire tube assembly, characterized by cooling means surrounding the crossfire tube assembly at its connection to a combustor and adapted to film-cool an outer surface of the crossfire tube assembly, thereby creating film cooling over both inner and outer surfaces of the crossfire tube assembly.
Also according to the invention there is provided a gas-turbine engine combustion system comprising:
a plurality of combustors,
a crossfire tube assembly for passing an ignition flame between adjacent combustors, each crossfire tube assembly including an end-tube for passing the ignition flame into and out of a combustor, the end-tube having an inner surface and an outer surface, and
means for feeding coolant air into the crossfire tube assembly so as to film-cool the inner surface of the end-tube.
The invention is characterized in that the end-tube is connected to the combustor through a sleeve which extends from a wall of the combustor to surround and overlap the end-tube over a part of its length adjacent the combustor, thereby to define an annular gap between the outer surface of the end-tube and an inner surface of the sleeve, the sleeve having inlet means for introducing coolant air into the annular gap so as to film-cool both the outer surface of the end-tube adjacent the combustor wall and the inner surface of the sleeve.
Preferably, the sleeve is provided with a plurality of apertures therearound, adjacent to a point at which the sleeve is connected to the end-tube, so that air is admitted to film-cool the outer surface of the end-tube.
Preferably, each end-tube is arranged so that it does not extend beyond the sleeve into the interior of the combustor. More preferably, the overlap between the sleeve and the end-tube does not extend over the entire lengthwise extent of the sleeve, whereby there is a gap between an internal surface of the combustor wall and the end-tube. It has been found that good performance is obtained if the lengthwise extending gap as measured between the end-tube and an inner surface of the combustor wall is approximately twice the annular gap between the inner surface of the sleeve and the outer surface of the end-tube.
The sleeve is also preferably arranged not to project into the combustor, whereby cooling air exits from the sleeve over an inner surface of the combustor wall surrounding the sleeve.
The crossfire tube assembly preferably comprises an arrangement of the type disclosed in European Patent No. 0 503 018, in which a complete crossfire tube arrangement extending between first and second combustors comprises a central crossfire tube portion and first and second end-tubes extending from the first and second combustors respectively, a first end of the central crossfire tube portion being welded into the first end-tube and a second end of the central crossfire tube portion being a push-fit into the second end-tube, cooling air being directed into an annular gap formed between an outer surface of the central crossfire tube portion and an inner surface of each end-tube to film-cool the ends of the central crossfire tube portion and the inner surfaces of the end-tubes.
The present invention also includes a gas turbine incorporating the above combustion system.
REFERENCES:
patent: 2722803 (1955-11-01), Travers
patent: 3001366 (1961-09-01), Shutts
patent: 3811274 (1974-05-01), Calderon
patent: 3991560 (1976-11-01), DeCorso et al.
patent: 4249372 (1981-02-01), White
patent: 5001896 (1991-03-01), Hilt et al.
patent: 5265413 (1993-11-01), Cannon et al.
patent: 5361577 (1994-11-01), Cromer
patent: 5402635 (1995-04-01), Smith et al.
patent: 5896742 (1999-04-01), Black et al.
patent: 0 503 018 B1 (1995-12-01), None
Alstom Gas Turbines Ltd.
Evora Robert Z.
Freay Charles G.
Kirschstein et al.
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