Power plants – Combustion products used as motive fluid – Process
Reexamination Certificate
2001-03-12
2002-12-10
Freay, Charles G. (Department: 3746)
Power plants
Combustion products used as motive fluid
Process
C060S039281
Reexamination Certificate
active
06490867
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method of operating a burner that is supplied with a quantity of a fuel by a fuel supply line. The fuel quantity is set by the degree of opening of a control element as a function of a selected output of the burner. The invention also relates to a corresponding burner configuration.
Various control systems for gas turbine burners are described in the book “Die Gasturbine (The gas turbine)” by J. Kruschik, Springer-Verlag, Vienna 1960, Second Edition, Pages 354 ff. Depending on the field of employment of the gas turbine, quite different configurations for the control systems exist. A common feature of the control systems is that a fuel supply to the burner is controlled, in each case, in accordance with a preselected output of the gas turbine. The control takes place, for example, as a function of rotational speed by a handling of a control element in a fuel supply line with a centrifugal force pendulum. In the example shown in Fig. 359 on Page 356 of Kruschik, the fuel quantity supplied to the burner is controlled as a function of the air pressure generated by the compressor of the gas turbine. In a further example shown in Fig. 361 on Page 358 of Kruschik, the fuel quantity to be burnt is controlled by a supply/return nozzle. Starting on Page 365 of Kruschik, a control system for the fuel supply to an aircraft turbine is described as particularly demanding because, in this case, it is necessary to deal with large temperature and pressure fluctuations in the external air.
In “Dubbel, Taschenbuch für den Maschinenbau (Machinery Handbook)”, published by W. Baltz and K. H. Kütner, Springer-Verlag, 1990, 17
th
Edition, Section X15 6.4, it is stated that control elements for setting a mass flow of a medium cause a pressure drop as a function of the density and the velocity of the medium. From VDI/VDE Guideline 2173, the k
V
value (characteristic value of the valve) determined experimentally for each configuration characterizes the through-flow of incompressible media as a volume flow of water (density &rgr;
0
) at temperatures between 5 and 30° C. and a pressure drop &Dgr;p
V0
of 0.98 bar. Arbitrary pressure drops &Dgr;p
V
and other densities &rgr; provide the volume flow:
V
.
v
=
k
v
Δ
p
v
p
0
/
(
Δ
p
vo
p
)
.
The way in which the k
V
value depends on the setting parameter is the valve characteristic. For the completely open valve, k
V
is referred to the maximum value k
VS
. The value:
k
vs
=
V
.
0
Δ
p
vo
p
/
(
Δ
p
v
p
0
)
,
with the maximum through-flow {dot over (V)}
0
, is provided by the valve manufacturer, for example.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method of operating a burner and burner configuration that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and that provides a method of operating a burner with a supply of fuel based on a preselected output and a corresponding burner configuration.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a method of operating a burner, including the steps of supplying a burner with a quantity of a fuel through a fuel supply line, setting the fuel quantity by a degree of opening of a control element as a function of a selected output of the burner, determining a calorific value of the fuel, and calculating and directly setting the degree of opening using the output and the calorific value of the fuel.
The invention is based on the knowledge that a conventionally employed, iterative control of the fuel quantity supplied as a function of the preselected output is too sluggish relative to suddenly modified operational boundary conditions. In such an iterative control system, the degree of opening is controlled in steps for setting the preselected power. In other control systems, the required output is, for example, converted directly into a setting parameter that fixes the degree of opening by a mechanical system which, as a rule, is very complex. In such systems, there is generally very limited variability with respect to the reaction to modified boundary conditions because any conversion from the preselected power into the degree of opening takes place only by a preset, fixed mechanism.
In accordance with another mode of the invention, the burner of the invention can be a burner for a gas turbine, in particular, a stationary gas turbine, and also, for example, suitable for an internal combustion engine of a vehicle. Fuel for the burner can, for example, be: mineral oil, natural gas, diesel, gasoline, or kerosene.
For the invention, on the other hand, the degree of opening is first calculated based on the output and, then, is set directly. The invention provides the advantage of removing the need to carry out an iterative control. Consequently, there is a significantly faster system reaction. The system, therefore, reacts more rapidly to, for example, external perturbations such as a pump switching operation. An additional advantage is that it is possible to deal in a better and more variable manner with the current operating conditions because the degree of opening is calculated in a manner matched to the respective operating conditions. For example, modifications to the temperature, density, or type of fuel or a variable pressure at the location of the burner can be employed in a simple manner for regulating the fuel quantity to be supplied. Compared with control systems having a direct, mechanical conversion from the preselected output to the degree of opening, the invention provides a substantially increased flexibility with respect to modified boundary conditions.
The calorific value of the fuel is preferably determined and employed in the calculation of the degree of opening. It is preferable for a mixture of at least two materials to be used as the fuel. The calorific value of the fuel is employed in the determination of the fuel quantity required because the calorific value also determines an effective output from the combustion system. Such a determination of the calorific value is of particular advantage when a fuel mixture is used, possibly even with a composition that varies with time. An oil/water mixture is preferably used as the fuel, the energy consumption for any evaporation of the water being determined during the combustion and being employed in the calculation of the degree of opening. Such an oil/water emulsion or dispersion is used to reduce emissions of oxides of nitrogen. The average combustion temperature is reduced by the admixture of water. Part of the energy of the fuel is consumed by the evaporation of the water and does not, therefore, contribute to the desired output.
It is preferable for the density of the fuel to be determined and employed in the calculation of the degree of opening. The density of the fuel contributes to the determination of the mass flow of the fuel through the fuel supply line. The determination of the density of the fuel is of advantage, particularly when a fuel mixture is used.
A pressure loss in the fuel supply line is preferably determined and employed in the calculation of the degree of opening. Such a pressure loss contributes to the determination of the mass flow of the fuel through the fuel supply line so that the pressure loss is taken into account, in an advantageous manner, in the calculation of the degree of opening.
The burner preferably opens into a combustion chamber in which a combustion chamber pressure is present, the combustion chamber pressure being measured and employed in the calculation of the degree of opening.
The pressure in the combustion chamber has an effect on the quantity of fuel entering the combustion chamber. Particularly in the case of a gas turbine, the pressure in its combustion chamber is substantially higher than the ambient pressure because combustion air from a compressor is
Braun Gilbert
Deuker Eberhard
Freay Charles G.
Greenberg Laurence A.
Mayback Gregory L.
Siemens Aktiengesellschaft
Stemer Werner H.
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