Combustion – Process of combustion or burner operation – Controlling or proportioning feed
Reexamination Certificate
2000-07-31
2002-03-26
Clarke, Sara (Department: 3743)
Combustion
Process of combustion or burner operation
Controlling or proportioning feed
C431S075000
Reexamination Certificate
active
06361310
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention lies in the field of combustion plants. The invention relates to a method of operating a combustion plant. It also relates to an apparatus for carrying out the method.
For the combustion of a fossil fuel in a combustion space, efforts are focused on constantly improving the combustion process. A suitable firing control is normally provided to achieve an especially good combustion process with as low an emission of pollutants as possible, in particular, CO and NOx, with an especially high efficiency and, at the same time, with a low volumetric flow of flue gas. In such a firing control, the concentration of at least one reaction product produced in the combustion process is usually determined.
During the combustion of fossil fuel or garbage, fluctuations in the calorific value of the fuel or of the fuel mixture may occur, particularly when the fuel has different origins or the garbage has a heterogeneous composition. These fluctuations adversely effect the pollutant emission. The disadvantages also exist during the industrial combustion of residues, during which solid and liquid, as well as gaseous, fuels are usually burned at the same time. If the temperature distribution and the concentration profile of reaction products arising in the combustion process are known, an improvement in the firing control, and, thus, an improvement in the combustion process with regard to low pollutant emissions, can be achieved.
German Utility Model 197 10 206.9 having the title Method and apparatus for analyzing the combustion and monitoring the flame in a combustion space, describes a method in which the temperature distribution and the concentration distribution of a reaction product (produced in the combustion process) in a flame are determined with an optical system. With such a method, the changes in the concentration distribution of the reaction product to be tested can also be determined locally in the combustion space, particularly in a flame. However, only global effects of the combustion process enter the firing control. Thus, efficiency in the case of locally determined distributions is only limited.
In addition, German Utility Model DE 80 17 259.4 41 discloses a firing plant for the controlled combustion of solid fossil fuels. In the firing plant, a plurality of radiation sensors is assigned to the flame region of each individual burner of the firing plant. Control of the individual burners is made possible with reference to the radiation intensity determined for each individual burner. A disadvantage of the plant is that the radiation intensity of an individual flame is determined by a plurality of radiation sensors respectively recording a line of the flame. To record a section of the flame, the radiation sensors are pivotably disposed. Such a configuration is especially time-intensive and complicated. In particular, for a heterogeneous temperature distribution, which normally characterizes the combustion process of a combustion plant configured as a garbage incineration plant, the resulting different local densities of combustion gases are not taken into account in the firing control. Therefore, the influence of the firing control with regard to an especially low pollutant emission is slight.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method and apparatus for operating a combustion plant that overcomes the hereinafore-mentioned disadvantages of the heretofore-known methods and devices of this general type and that sets the combustion process for an especially low pollutant discharge simply and quickly.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a method of operating a combustion plant having a number of burners, the composition of the fuel mixture of each burner being controlled by at least one setpoint determined with reference to dynamic characteristic quantities characterizing the combustion process. In the method, the setpoint for each individual burner is determined as a function of or independence on its contribution to the total proportion of a reaction product produced in the combustion process, in which case, the contribution of each burner to the reaction product is determined for each burner with reference to the dynamic characteristic quantities and static characteristic quantities characterizing the combustion plant.
The invention is based on the idea that global measured values are not sufficient for an especially simple and quick setting of an especially low pollutant discharge. On the contrary, the individual contribution of each burner should be determined and taken into account in the firing control. The determination of the contribution of an individual burner to the concentration quantity of a reaction product produced in the combustion process, in particular, at the outlet of the combustion space, enables the effect of each individual burner with regard to the total contribution to the pollutant emission to be taken into account. Thus, the combustion behavior of an individual burner and its effect on the combustion process can be optimized.
In accordance with another mode of the invention, the determining step is performed by determining the contribution of each burner to the reaction product using spatial resolution.
The local progress of at least one reaction product to be tested, e.g., of a combustion radical or a flue-gas quantity CO or NOx inside the combustion space, up to the outlet of the combustion space is advantageously calculated for each individual burner. The contribution of the burner or of each burner to the reaction product is expediently determined in a spatially resolved manner. In dependence on the contribution of the relevant burner to the concentration quantity of the reaction product, at least one setpoint for the composition of the fuel mixture of this burner is determined. By tracing the respective contribution to the total proportion of the reaction product to be tested in the combustion space, the entire combustion is homogenized and improved by optimizing the individual burners.
In accordance with a further mode of the invention, at least one of the dynamic and static characteristic quantities is processed with a combustion model of the combustion process.
In an especially advantageous manner, the combustion model simulates the combustion process. The combustion model describes the combustion process with reference to the chemical reaction kinetics with suitable differential formulations. The transport processes are described, for example, with reference to the diffusion, the mass flow, and/or the heat flow. The chemical reactions in the combustion space or in the flame, e.g., the oxidation, are described with reference to elementary reactions taking place during the combustion. The physical couplings between the transport processes or material flows of the individual burners and between components of the combustion space, e.g., heat flow between the burner and the wall of the combustion space, are taken into account in the combustion model by the exchanged heat flow, the convection, and/or the radiation.
In accordance with an added mode of the invention, the processing step is performed by simulating chemical reaction kinetics with the combustion model of the combustion process.
In an expedient development, at least some of the characteristic quantities, in particular the dynamic characteristic quantities, are determined with the aid of measurements. For example, the concentration of the reaction product is reconstructed in a computer-tomographic manner from an emission spectrum recorded in the combustion process. In addition, at least some of the characteristic quantities are advantageously output from a memory as filed characteristic quantities. The individual phases of the combustion process can be simulated with these filed characteristic quantities, in which case, by changes in individual characteristic quantities, e.g., the addition of oxygen for O
2
enrichment, th
Fastnacht Felix
Merklein Thomas
Clarke Sara
Greenberg Laurence A.
Lerner Herbert L.
Siemens Aktiengesellschaft
Stemer Werner H.
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