Power plants – Combustion products used as motive fluid – Combustion products generator
Reexamination Certificate
1999-06-25
2001-09-25
Freay, Charles G. (Department: 3746)
Power plants
Combustion products used as motive fluid
Combustion products generator
Reexamination Certificate
active
06293105
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of gas turbines. It refers to a gas turbine with a plurality of individual burners which are connected to a fuel distribution system and are supplied with fuel from a common fuel feed via the fuel distribution system, there being provided, within the fuel distribution system, means by which the fuel mass flows to the individual burners can be varied in order to improve the operating perimeters of the gas turbine.
Such a gas turbine is known, for example, from the publications U.S. Pat. No. 5,024,055 or U.S. Pat. No. 5,319,931 or U.S. Pat. No. 5,373,692.
2. Discussion of Background
High-powered gas turbines, such as are used in combined cycle power stations, are often operated with a plurality of burners. Examples of gas turbines of this kind are found in the publications initially mentioned. Gas turbines of this type which are used commercially have been sold by Asea Brown Boveri AG, for example under the type designations GT
13
E
2
, GT
24
or GT
26
. A block diagram of such a gas turbine is illustrated in FIG.
1
. The gas turbine
10
includes a compressor
12
and a turbine
14
, which are conventionally arranged on a common shaft
13
. Between the compressor
12
and turbine
14
is provided a combustion chamber
18
, in which a plurality of (in the example, six) burners B
1
, . . . , B
6
generate hot combustion gases as a result of the combustion of a liquid or gaseous fuel. The burners B
1
, . . . , B
6
may be equipped, for example, with extractable burner lances which introduce the fuel and, if appropriate, combustion air for injection into the burner. The various burners B
1
, . , B
6
of the gas turbine
10
are supplied with fuel from a fuel source (not shown) via a fuel distribution system
21
. The fuel is fed to the fuel distribution system
21
via a central fuel feed
28
and one or more fuel regulating valves
20
. Individual branch lines
23
extend from the common distribution line
22
to the burners B
1
, . . . , B
6
. The combustion air necessary for the combustion of the fuel is sucked in by the compressor
12
via an air feed
11
, compressed and subsequently fed, via a compressed-air duct
16
, into a plenum chamber
19
, from where it passes through corresponding orifices into the burners B
1
, . . . B
6
or fuel lances. The hot combustion gases from the combustion chamber
18
pass, via a hot-gas duct
17
, into the turbine
14
, where they perform work in one or more stages and are subsequently available, at an exhaust-gas outlet
15
of the turbine
14
, for further use (for example, for generating steam in a waste-heat boiler).
In order, then, to ensure that the (leanly operated) burners deviating downward from the average value remain well above the extinguishing limit LG, and so that the machine can be operated reliably and stably, the average value M to be set via the fuel regulating valve
20
must be selected well above the lean extinguishing limit LG. Fuel-enriched burners (B
3
, B
4
, B
5
) therefore run in addition to lean burners (B
1
, B
2
, B
6
). In an extreme situation, the fuel-enriched burners must even assist combustion in the lean burners (external pilot control). The result of this, ultimately, is that the emission average value M to be set in this way deviates markedly from the minimum obtainable (individual burner evidence in the individual burner test). Under some circumstances, therefore, in the case of a multiburner configuration, a considerably worsened lean extinguishing limit can be obtained, as compared with the individual burner. The same also applies to the temperature profile. The actual aim, specifically also to achieve a homogeneous emission and temperature profile, particularly in the case of annular combustion chambers, by means of homogeneous combustion, has hitherto, in practice, been achieved only approximately on account of manufacturing tolerances, design accuracy and the like. This may, indeed, be sufficient for a reliable (rough) setting of the gas turbine, however, the existing potential of gas turbines with multiple burner arrangements is certainly not fully utilized in this way.
U.S. Pat. No. 5,024,055 describes a gas turbine with a multiple burner arrangement, in which the unburned hydrocarbons (UHCs) of the individual burners are detected at the turbine outlet by means of sensors arranged in a distributed manner. The measured values are used for adjusting the fuel/air ratio for each individual burner to its optimum value via individual regulating valves in the fuel feed lines (branch lines) to the burners. Regulation of the air feed also takes place in addition. Although this regulation makes it possible for essentially optimum combustion ratios to be achieved permanently in the individual burners, this regulation, with its multiplicity of sensors and, in particular regulating valves (two regulating valves for each two-stage burner), is not only extremely complicated, but also susceptible to faults.
U.S. Pat. No. 5,319,931 proposes a method for trimming the fuel/air ratio of the individual burners in a gas turbine with a two-stage multiple burner arrangement and with an inhomogeneous air feed, in which a trimming unit, which contain s an adjustable valve, is arranged in each of the fuel feed lines (branch lines) to the burners. In order to compensate the unequal operating parameters of the burners, which occur as a result of an unequal air feed, the fuel feed to the individual burners is retrimhed manually or automatically by means of the trimming device in accordance with specific measurement values (for combustion chamber pressure, temperature and fuel mass flow). Trimming, in this case, relates to an unequal air feed, but not to an unequal fuel feed. Furthermore, in this case too, a multiplicity of valves equipped with moveable parts and susceptible to faults are used. In addition, during operation in the automatic mode, various diaphragms also have to be arranged in the trimming units, in order to ensure reliable and accurate regulation.
Finally, U.S. Pat. No. 5,373,692 discloses a trimming system for minimizing the NOx emissions of a gas turbine with a multiple burner arrangement, in which two parallel-connected regulating valves are arranged in each case in the fuel feed lines (branch lines) to the individual burners, said regulating valves being actuated by central control in accordance with the measurement values from an NOx sensor. The main valve of the parallel connection serves, in this case, for the basic setting, whilst the secondary valve is provided for trimming. In this case, too, due to the two valves for each burner, there is a considerable outlay in terms of apparatus and increased susceptibility to faults.
SUMMARY OF THE INVENTION
The object of the invention, therefore, is to provide a gas turbine with a multiple burner arrangement, in which the different fuel mass flows of the individual burners, caused by inequalities in the fuel distribution system, are compensated by simple and effective means which are easy to install, even at a later date, and which are safe from faults.
The object is achieved, in a gas turbine of the type initially mentioned, in that a fixed throttle member, determining the fuel mass flow to at least one of the burners is arranged in the fuel distribution system upstream of the at least one burner, and in that the reduction in cross section of the throttle member is selected in such a way that existing inequalities in the fuel distribution system as regards the fuel mass flows to the individual burners are reduced. The invention, at the same time, is based on the knowledge that, on the one hand, it is usually simpler to adapt and homogenise the fuel mass flow and that, on the other hand, in most machines (gas turbines), an approximately even air feed to the individual burners is ensured, so that, in most cases, irrespective of the air feed, a significant improvement can be achieved solely by evening the fuel feed. The essence of the invention is, in those bu
Claesson Ola
Hellat Jaan
Kessler Werner
Reiss Frank
Strittmatter Wilfried
Asea Brown Boveri AG
Burns Doane Swecker & Mathis L.L.P.
Freay Charles G.
Rodriguez William
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