Power plants – Combustion products used as motive fluid – Combined with regulation of power output feature
Reexamination Certificate
1999-06-11
2001-07-24
Freay, Charles G. (Department: 3746)
Power plants
Combustion products used as motive fluid
Combined with regulation of power output feature
Reexamination Certificate
active
06263663
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of gas turbines and more particularly to combustion chambers associated with such turbines.
BACKGROUND OF THE INVENTION
One of the problems at the root of the present invention concerns the pollution generated by the operation of these turbines. More precisely, nitrogen oxides (NOx) and carbon monoxide (CO) emissions must be reduced because they are the most harmful to the environment.
Furthermore, rather stringent standards are in force or will come into force in most industrialized countries.
Nitrogen oxides (NOx) are mainly thermal nitrogen oxides that form at high temperature, i.e. above 1700 K in gas-turbine combustion chambers where the fumes have residence times generally ranging between 2 and 10 milliseconds.
Carbon monoxide (CO) forms at a lower temperature (<1600 K) by incomplete combustion of the fuel.
The optimum temperature range for reduced NOx and CO emissions is thus between about 1650 K and 1750 K.
FIG. 1
illustrates, by means of (CO and NOx) curves, the respective carbon monoxide and nitrogen oxides emissions as a function of the temperature T (in K) under the operating conditions of a gas-turbine combustion chamber.
NOx and CO emissions are thus directly linked with the air-fuel mixture strength in the combustion chamber, i.e. the ratio of the flow of air to the flow of fuel. Given that the air-fuel ratio of the mixture must be imposed if one wants to operate within a certain temperature range, such as that mentioned above, the adiabatic flame temperature of the mixture will approximately vary proportionally to the mixture strength.
Conventionally, as it is well-known, the flow of fuel is the only parameter allowing to control the operating conditions of the turbine. For a given flow of fuel, the flow of air is therefore perfectly set to a value depending only on the characteristics of the machine and in particular on the cross-sections of flow in the furnace. The mixture strength is thereafter totally determined.
However, the mixture strength range allowing to respect the temperature range defined above does not always correspond to the mixture strength imposed by the characteristic curve of the machine.
Several concepts can be envisaged to solve this problem.
One of them consists in carrying out a combustion in several stages, ignited successively. This known solution is illustrated by
FIG. 2
that shows a combustion chamber having a pilot stage followed by two other stages having each an air inlet and an inlet for a fuel such as natural gas for example. Combustion then has to be performed in each stage successively and according to the total power required. The pilot combustion is carried out whatever the speed. This solution theoretically allows to obtain acceptable mixture strengths in the ignited stages, for each engine speed, if a sufficient number of stages is available. The major drawback is that it requires a complex fuel delivery circuit, hence reliability, control and cost problems.
Another concept allowing to obtain combustion chambers operating in a determined temperature range consists in equipping it with a series of shutters, clappers or other shutoff means allowing to control the flow of air in the furnace. Of course, control and actuation of such elements is complex and delicate to implement. This equipment is furthermore costly.
SUMMARY OF THE INVENTION
The present invention thus aims to propose a reliable and simple solution to the problem of mixture strength control in a gas-turbine combustion chamber.
The object of this control is to be able to carry out combustion in an optimum temperature range notably as regards carbon monoxide and nitrogen oxides emissions.
The present invention thus allows automatic combustion air flow control. A mechanical control system is advantageously achieved by means of a very limited number of mechanical parts.
The object of the invention is a gas-turbine combustion chamber comprising at least a zone referred to as pilot injection zone into which at least a first pilot fuel injection means and an associated first oxidizer injection means open; a main combustion zone into which at least a second main fuel injection means and an associated second oxidizer injection means open, all of it being maintained under a pressure P
1
inside an enclosure.
According to the invention, said combustion chamber further comprises a mechanical means for controlling the second flow of oxidizer, which reacts to the pressure difference between the inside (P
1
) and the atmospheric pressure (Po) outside the enclosure, said pressure difference being directly linked with the engine speed.
More precisely, said control means comprises at least a shutoff element that seals more or less the second air inlets in the combustion chamber, several tie rods between the shutoff elements and a support element, a compression element, a bellows joint placed around the compression element delimiting, with the support element, the volume at the atmospheric pressure (Po) in relation to the enclosure under pressure (P
1
).
Particularly, the first fuel injection means and the first oxidizer injection means are placed substantially close to the longitudinal axis (XX′) of the combustion chamber.
According to a specific layout of the invention, the second main fuel injection means and the second oxidizer injection means are situated on a circumference, downstream from the pilot combustion zone in relation to the direction of propagation of the flame.
Furthermore, the combustion chamber according to the invention comprises a third oxidizer injection means opening into the combustion chamber downstream from the second oxidizer injection means in relation to the direction of propagation of the flame.
Moreover, the means for controlling the second flow of oxidizer allows to control the flow of the third air injection means (bypass function).
The compression element can comprise a pile of washers or springs.
According to an embodiment of the invention, the chamber comprises three zones in which the second main fuel injection means (
7
) and the main oxidizer injection means (
8
) are grouped together, each zone lying 120° apart.
REFERENCES:
patent: 3691761 (1972-09-01), Jackson
patent: 3765171 (1973-10-01), Hagen
patent: 3869246 (1975-03-01), Hamond, Jr.
patent: 4296599 (1981-10-01), Adamson
patent: 5069029 (1991-12-01), Kuroda et al.
patent: 5159807 (1992-11-01), Forestier
patent: 281961 (1988-09-01), None
patent: 2270448 (1975-12-01), None
Grienche Guy
Laborde Patrice
Le Gal Jean-Herve
Martin Gerard
Schott Gérard
Antonelli, Terry & Kraus, LLP
Freay Charles G.
Gartenberg Ehud
Institut Francais du Pe'trole
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