EP2920515B1 - Cfd simulation of a combustion chamber with a plurality of burners with separate consideration of the fuel and air components originating from each burner - Google Patents

Description

The invention relates to a method for improving the combustion in a furnace, in particular a power plant or an industrial plant, wherein a plurality of burners are arranged in a burner layer and wherein at least a portion of the burner, a fuel and / or air mass flow can be adjusted. It may alternatively be arranged in the combustion chamber, even a single burner. There may also be multiple fuel and air inlets in a burner layer or in other geometry, e.g. vertical or spiral. A local distribution of a parameter characterizing the combustion quality is determined by measurement in an overlying ignition / burnout region. Based on the local distribution, at least one area is identified with an unfavorable parameter with regard to the quality of the combustion.

The invention further relates to the use, i. the use of such a method of improving combustion in a fossil, i. fossil-fueled, thermal power plant or in an industrial plant.

Finally, the invention relates to a device for carrying out such a method.

From the publication of the U.S. Patent Application 2011 / 0056416A1 For example, a method and a system for improving the combustion in a furnace of a thermal power plant are known. Also, there are several burners arranged in a burner layer, and it can be set at the burners a fuel and / or air mass flow. It is proposed to record above the burners or afterburner several operating conditions such as temperature and CO concentration values in a common area level. If combustion anomalies are detected, they should be able to be fluidly traced back to the originating burner based on a mathematical model and then optimize combustion by altering the fuel and / or air mass flow. The local distribution of the CO concentration values as a measure of the quality of combustion can be checked at the outlet opening of the combustion chamber, which faces the burners downstream (see FIG. 4A to 4D ).

Fire chambers are known in the art, e.g. Firebreaks in a fossil thermal power plant, in a rotary kiln or in any other thermal plant having a plurality of burners, e.g. eight, ten, 16 or 20. The firebox typically has a rectangular or square cross section or the shape of a pipe.

The dimensions, such as the edge length of such a firebox can be in the range of 5 to 25m or even 5 to 50m. The height of such a combustion chamber can even be in the range of 10 to 100 m, measured from the horizontal burner level, in which the burners are arranged circumferentially around the combustion chamber. Also known are fire chambers with other, for example overlying burner areas in which more burners are arranged as a kind of fire ring, so to speak. Also known are fire chambers with a further, overlying burner level, in which more burners are arranged, so to speak, as another fire ring. It is also known that the each burner air and the fossil fuel, such as coal dust from lignite and / or hard coal, or natural gas, slightly offset from the geometric center blow (see FIG. 3 ). As a result, a combustion-technically more favorable turbulence and mixing of the air / fuel mixture is achieved. Typically, the injection of the air / fuel mixture is additionally carried out at a small angle "down" in the range of 10 ° to 20 °, measured from the horizontal plane. This leaves even more time for the mixing of the air / fuel mixture. The fuel and the air is usually preheated injected into the furnace, wherein the fuel temperature is preferably in a range of 150 ° C - 200 ° C and the air temperature around 300 ° C.

The whole, not yet ignited air / fuel mixture is e.g. In coal dust-fired power plants to the furnace center thermally torn up. In this pyrolysis area, which lies above the firing layer or burner layer, the entire not yet ignited air / fuel mixture is decomposed into its volatile combustible fractions by endothermic reactions. At the same time, the water still bound in the fuel evaporates. With the further rise of the pyrolyzing mixture at the same time as the temperature continues to rise, finally the entire mixture ignites spontaneously from a temperature of about 600 °. Above a temperature of 750 ° C, the mixture even burns explosively. Finally, in an overlying area extending into a burnout area, coke, i. E. quasi-pure carbon, if there is enough oxygen left. This oxygen may e.g. be added in the form of air via additional fans in this Ausbrandebene to avoid the emission of unburned and carbon monoxide.

It is also known to analyze the ignition region or the burn-out region, or the entire ignition / burnout region, to find areas with too much oxygen or regions with too much fuel, typically represented by the so-called air / fuel ratio. A ratio of 1 means that there is sufficient air and consequently also oxygen in order to completely and thus optimally burn the fuel fraction present there. Combustion unfavorable areas are consequently areas with an air / fuel ratio of greater than 1, such as 1.2, which would correspond to a so-called "lean" air / fuel mixture. Analog would correspond to an air / fuel ratio of less than 1, such as 0.8, a "rich" air / fuel mixture. Consequently, there is too little air for combustion. The local temperature distribution is another important factor, which mainly determines the speed of the combustion process. Are also known rotary kilns, which have a furnace. Such an O-fen is used for continuous processes in process engineering. It has a rotary tube which is slightly inclined in the longitudinal direction, so that feed material introduced from an inlet side is transported longitudinally along the circulating furnace tube to an outlet side. From the outlet side, the ignition of the fuel is achieved with burners, and set a suitable temperature profile in the oven via the burner. The heat is thus supplied from within the furnace, wherein the feedstock is in direct contact with the resulting flue gas. In at least part of the burners, the fuel and / or air mass flow can be adjusted to improve the quality of the combustion. In addition to the fuel and air quantities and their mixing especially the final temperature for the quality of the finished goods is an important parameter.

The rotary kiln has proven its worth from the stone and earth industry, the basic materials industry and the chemical and disposal sectors. The products used for the thermal treatment of the rotary kiln are various bulk materials such as cement clinker, lime, dolomite, magnesite, chamotte, titanium dioxide, barium sulfate, strontium and barium carbonate, kaolin, iron ore, quartz sand, petroleum coke, gypsum and many more ,

Furthermore, measuring devices are known from the prior art by means of which a local distribution of the air / fuel ratio in the ignition / burnout region can be determined by measurement. In other words, these measuring devices allow a preferably horizontal section through the combustion chamber in the ignition / burnout area. This cut or cut area can also be referred to as a measurement plane or measurement plane layer. Consequently, a two-dimensional distribution of the prevailing air / fuel ratio can be determined for the combustion-relevant area in the ignition / burnout area. Technically, this may e.g. accomplished by a horizontally movable lambda probe, by means of which measurements are made at a plurality of measuring points in the ignition / burnout.

Furthermore, measuring devices are known from the prior art, such as eg laser grids or pyrometers, by means of which a local distribution of the temperature in the ignition / burnout region can be determined by measurement. The temperature is another parameter characterizing the combustion quality. It mainly determines how fast the air / fuel mixture explodes more or less. The temperature develops with the available fuel and the air. The temperature should not be too high (typically below about 1400 ° C), otherwise the ash "soft" and the boiler is dirty. In addition, environmentally harmful, so-called "thermal" NO _x is disadvantageously formed.

Furthermore, laser grids are known from the prior art as measuring devices by means of which a local distribution of the CO, NO _x , O ₂ , CO ₂ fractions or concentration values in the flue gas can be measured. The respective share value is another parameter characterizing the combustion quality. The measurement typically takes place where the combustion is virtually complete and where only slight absorption is present, ie in the ignition / burnout region and in particular in the burnout region.

The aforementioned measuring devices may also be combined with each other, e.g. for reasons of plausibility of the acquired measured values and / or for reasons of increasing the measuring accuracy.

Preferably, an optical measuring method is used, e.g. a camera-based measuring method.

From the German patent application DE 197 10 206 A1 For example, a method and apparatus for combustion analysis and flame monitoring in a combustion chamber is known. In order to be able to detect both the temperature distribution and the concentration distribution of reaction products and flame parameters particularly quickly, an image of a flame is taken and a spatial distribution of a parameter characterizing the combustion process is determined from spatially resolved intensities of the image for at least one predeterminable spectral range. An optical system of the device comprises a lens for detecting the flame and three downstream beam splitters. The bundle beams detected by the lens are divided by the beam splitters into a total of four spectral ranges and are each fed to a CCD image sensor.

From the European patent application EP 1091175 A2 is a method and a corresponding device for determining the excess air in a combustion process known by the rates of formation of the reaction products formed CN and CO are determined. Subsequently, the ratio of the determined formation rates is formed as a quantity representing the excess air in the sense of an air / fuel ratio. At least four special cameras are provided for detecting the radiation intensities.

On the basis of the metrologically determined local distribution of the air / fuel ratio in the ignition / burnout area, areas with a combustion-technically unfavorable air / fuel ratio can be determined, such as, for example, of areas with ratios greater than 1.2 or less than 0.8.

In order to improve the combustion in the identified areas, it is known to vary the mass air flow or fuel, e.g. the fan speed of one of the fans is increased or decreased or by the injected fuel quantity is increased or decreased at a burner.

Problem is that due to the turbulence and the large number of burners can not be determined which of the burner is "responsible" for the unfavorable combustion significantly. Therefore, successively, the air or fuel mass flow is only changed at one of the burners, to then check whether the combustion has improved in the considered area. However, it may take up to 15 minutes for the effects of the change in air or fuel mass flow throughout the combustion chamber to settle stationary in the combustion process. The time required is therefore enormously high.

Typically, the combustion process is also not very stable. Here, for example, different fuel qualities cause the entire combustion process to change and in turn change to a stationary level. Also, the frequent failure of one or more burners, such as Due to service work or technical failure, this leads to a changed combustion process and consequently to different areas with a combustion-technically unfavorable air / fuel ratio.

In the textbook " Simulation of Power Plants and Thermal Installations "by Bernd Epple et al., Springer Verlag, Vienna, 2009 , various methods of a combustion chamber simulation are known, such as based on a so-called CFD simulation model (CFD Computational Fluid Dynamics) for numerical fluid mechanics. Based on this model, a flow pyrolysis and combustion simulation of a combustion chamber is possible. The application of a finite-volume method is described for the approximate solution of the dynamic fluid-mechanical model equations. Depending on the modeling effort and computer power, the temperature prevailing there, the pressure, the flow velocity and direction of the combustion gases and their chemical composition such as oxygen content, proportion of pyrolyzed fuel and proportion of already burned fuel can be specified for each volume element in the modeled combustion chamber.

Starting from the aforementioned prior art, it is an object of the invention to provide a method which allows improved combustion in a furnace.

It is a further object of the invention to provide a method which allows a rapid correction of the respective fuel and / or air mass flow in order to improve the combustion in the combustion chamber again.

It is a further object of the invention to provide suitable applications of the method according to the invention.

Finally, it is an object of the invention to specify a device corresponding to the method.

The object of the invention is achieved with the features of the independent claims. Advantageous method variants, a suitable use as well as advantageous embodiments of the corresponding device are specified in the dependent claims.

According to the invention, a part of the combustion chamber which is essential for a flow, pyrolysis and combustion simulation is imaged in a numerical simulation model, divided into a multiplicity of volume elements. In the numerical simulation of each volume element, the source of the fuel and air fractions originating from the respective burners is taken into account continuously and separately. One of the metrologically determined local distribution is determined in the simulation model spatially appropriate distribution of the fuel and air fractions. At least one burner is determined for the respective identified area of the relevant fuel and air fractions in order to improve combustion by correcting the respective fuel and / or air mass flow.

As a result, based on the numerical flow pyrolysis and combustion simulation for each metrologically identified area, which has an unfavorable in terms of combustion quality characteristic, advantageously determined for the unfavorable combustion burner determined. By correcting the associated air and / or fuel mass flow can then at least iteratively the local Combustion can be improved. For example, if the measured air / fuel ratio in the identified area, for example, at 0.75, ie there is too little air for optimal combustion, the air mass flow of the determined relevant responsible burner can be increased, such as by 5%. In this case, the air mass flow can be corrected the more, the greater the measured air / fuel ratio is away from the optimal ratio 1.0. In the reverse case, ie in the event that the measured air / fuel ratio in the identified area is eg 1.25, ie there is too much air for optimal combustion, the mass air flow of the determined authoritative burner can be reduced, such as at 10%.

Alternatively or additionally, the fuel mass flow can also be increased or decreased. From a technical point of view, it is in most cases advantageous to correct the air mass flow by changing the fan speed or suitable adjustable fan flaps. The fuel mass flow remains unchanged. If the respective burner has a fuel injection device for the fuel mass flow and at least one associated, separate fan for the air mass flow, then it is advantageous to change only the air mass flow of the fan.

The core idea of the invention is that in the numerical flow pyrolysis and combustion simulation for each "simulated" volume element, the respective burner-related origin of the injected fuel and the injected air are carried and transferred to the next adjacent volume elements during the simulation. Thus, a volume element, such as e.g. with the dimensions 10cm x 10cm x 10cm, a fuel content of 5% of burner 1, 80% of burner 2.10% of burner 4, etc. and have an air content of 60% from the burner 3, 30% of burner 6 etc. , By means of the numerical flow pyrolysis and combustion simulation, for this volume element on the basis of the aforementioned origin-related components as well as further existing boundary conditions, such as e.g. Air temperature, fuel temperature, flow rates and pressures, pyrolysis and combustion are calculated stepwise. The result of a calculation for this volume element may e.g. that the total existing fuel is already pyrolyzed to 95% and burned to 20%, and at a temperature of 693 ° C at an oxygen content of 17.3% and at a current flow vector of Vx = 1m / s, Vy = - 0.2m / s, Vz = 0.1m / s.

In other words, the fuel and air fractions originating from respective burners are continuously and separately taken into account.

Using the numerical flow pyrolysis and combustion simulation, at least the origins of the fuels and airs can be qualitatively determined for each volume element. However, this is completely sufficient to be able to specifically correct the combustion in the metrologically recorded areas with insufficient air / fuel ratio.

According to a variant of the method, a substance is admixed to the fuel and / or the air for a respective burner.

The substance may e.g. be introduced at the input side of the respective burner, as e.g. in powder or in the form of granules. It can be input side, e.g. be introduced by means of a screw conveyor or blown there. Alternatively, the substance may also be at the exit side of the burner, i. be introduced into the air outlet of a fan of the respective burner or in the outlet of a fuel injector of the respective burner. It can also be blown there in powder form or in the form of granules or introduced by means of a screw conveyor. The substance can also be sprayed there in liquid form. In other words, the substance is introduced into the fuel and / or air mass flow of the respective burner. Alternatively or additionally, the substance can be injected in the gaseous state into the outlet of a fuel injector of the respective burner.

The substance leaves an (optically significant) trace of light during combustion in the furnace, whereby the local and temporal propagation of the substance is detected by means of an optical measuring system that is spectrally matched to the trace of light. In other words, the propagation of the substance in the furnace is detected temporally and / or spatially by the optical measuring system. An actual propagation of the fuel originating from the respective burner and the air originating from the respective burner in the numerical simulation model, which accompanies the actual propagation of the substance, is assumed as a boundary condition. By adapting the numerical simulation model to the actual propagation, the sought-after areas with the insufficient air / fuel ratio can be more reliably determined.

For this purpose, the data recorded by the optical measuring system of the individual traces of light for the respective fuel and / or air mass flows can be converted separately into spatial distributions and their propagation speed, divided into a multiplicity of volume elements. The calculated traces of light of various fuel and / or air mass flows can then be stored in a tracer model. Depending on the modeling effort and computer performance, as far as metrologically possible, for each volume element in the modeled combustion chamber, the prevailing there Flow rate and direction of the combustion gases and how allocation to the fuel and / or air mass flows with respect to the various fuel and / or air inlets can be specified.

Preferably, the substance is added not only to the fuel and / or the air for a single burner but for a plurality of burners. This can e.g. cyclic for a selection from all burners, e.g. every other or every third burner, or for all burners, e.g. turn. By temporally successive admixture, the local and temporal propagation of the luminous substance in the furnace can be detected by means of the optical measuring system, i. be tracked. Since the timings of the admixture of the substance for the respective burners are known, the different sources of fuel and / or air can be assigned to the respective burners. The conformity of the numerical simulation model with the actual flow conditions in the combustion chamber is thereby further advantageously increased. As a result, the sought-after areas with the insufficient air / fuel ratio can be determined even more reliably and even more targeted corrections can be made to the fuel mass flow and / or air mass flow of the at least one authoritative burner for optimizing the combustion.

Other metrologically detected quantities, e.g. the temperature distribution, the distribution of the air / fuel ratio in the furnace and the mass flows are additionally deposited at the burners in the light track model. It is also possible for a plurality of spectrally different luminous substances to be mixed simultaneously with the fuel and / or the air of different burners, so that the substances leave different optically significant traces of light during combustion in the combustion chamber, such as, for example, red, blue or green. The local and temporal propagation of the substances can then be detected by means of an optical measuring system that is spectrally matched to the tracer tracks. For this purpose, the optical measuring system can be used e.g. have a series of spectral filters which are tuned to the dominant emitted spectral line of the respective substance.

As is known from chemistry, discoloration of a flame can be achieved with some substances. For example, lithium causes a red discoloration, sodium a yellow, barium a green and copper chloride a blue discoloration. In each case one or more spectral lines are generated in the spectrum. Preferably, substances are used which radiate with thermal excitation in the green or blue with high intensity, since they can then be separated and distinguished from the intense thermal radiation in the red and infrared spectral range with optical filters.

Under certain circumstances, the characteristics characterizing the combustion quality can not be measured in all areas of the combustion chamber and the tracer analysis can not be evaluated for all areas. Therefore, alternatively or additionally, with a combustion calculation and / or with a flow model, it is also possible to calculate the parameters for the combustion quality for areas which could not be detected metrologically and / or for which no tracer analysis could be carried out. With such a luminous trace model or such an expanded CFD simulation model, at least one burner can be determined for the respective identified region in order to improve combustion by correcting the respective fuel and / or air mass flow.

According to a variant of the method, the at least one authoritative burner is repeatedly and preferably cyclically determined and the respective fuel and / or air mass flow is corrected automatically. As a result, a largely optimal combustion in the furnace can be accomplished automatically without human intervention.

According to a further variant of the method, the firebox, the geometrical arrangement and orientation of the burners in the firebox, their currently predefined velocity injection vector, their current actual value for the fuel and air mass flow and / or the current predetermined temperature of the respective fuel and air mass flow in the numerical simulation model displayed. As a result, the simulated conditions in the firebox due to the large number of predetermined or measurable boundary conditions at least qualitatively agree with the actually prevailing real conditions in the firebox.

According to an advantageous variant of the method, the flow, pyrolysis and combustion simulation model is a Computational Fluid Dynamics Simulation Model (CFD), which simulates the dynamic flow, pyrolysis and combustion processes in the combustion chamber through fluid mechanical model equations such as Navier-Stokes, Euler or potential equations describes. The use of such models has long been known and mature in fluid mechanics, such as in the engine area in aircraft or gas turbines in the power plant area. Due to the computing power available today, accurate and fast modeling and simulation are possible.

In particular, a finite-volume method is used for the approximate solution of the Navier-Stokes, Euler or potential equations of the computational fluid dynamics simulation model. Such a method is also widespread and recognized.

According to a further variant of the method, the parameter characterizing the quality of the combustion is an air / fuel ratio. Of course, it may alternatively be the reciprocal, ie be a fuel / air ratio. Alternatively or additionally, the parameter may be a temperature which is detected by means of a pyrometer, a laser grating or by means of a horizontally movable temperature sensor. The parameter may alternatively or additionally be the CO, NO _x , O ₂ or CO ₂ content or concentration value of the flue gas present in the ignition / burnout region. From these respective proportions or concentration values, it is finally possible to derive a value that represents the fuel / air ratio or air / fuel ratio. If, for example, the local distribution of oxygen, ie of O ₂ , is uneven, NO _{x is} formed in areas with too much air, while CO is formed in areas with too little air due to incomplete combustion there. Here, CO and NO _{x are} quasi opponents whose opposing behavior in the proportion or concentration values can be used advantageously in order to derive as a further parameter for the quality of combustion a value representing the fuel / air ratio.

According to a preferred variant of the method, a camera-supported method is used for the metrological determination of the local distribution of the air / fuel ratio in the ignition / burnout region. In particular, the rates of formation of the chemical reaction products CN (cyanide) and CO (carbon monoxide) formed during combustion are determined, the ratio of the determined formation rates being formed as a variable representing the air / fuel ratio. CN is even more present in the combustion process, the more excess air is present during combustion. In contrast to this, the more CO is present, the more lack of air there is in combustion.

The chemical reaction products are gaseous radicals that typically occur during a high-temperature process of more than 1000 ° C in the combustion of hydrocarbons. Instead of CN and CO, another suitable pairing for the representation of the air / fuel ratio can be used, such as from the amount of C ₂ -, CH, CHOH, CHO, NH, OH or O ₂ - Radical.

The acquisition rates can be determined, for example, by means of special cameras, to which an optical cut-off filter with a predefinable pass-wave range for a characteristic transmission filter Spectral line of the respective reaction product upstream. As a result, a particularly high selectivity is possible with regard to the emission of a chemical reaction product. Typically, such a notch filter has a passband range in the range of about 5 to 20 nm. Thus, for example, the specific frequency band of one of the spectral lines for CO (carbon monoxide) in the range of 445 to 455 nm and for the reaction product CN (for cyanide) in the range of 415 to 425 nm. The barrier filters can also be an IR filter, that is an infrared filter, upstream, to filter out a large part of the incoming heat radiation. Both filters can also be integrated in a single blocking filter. The two formation rates, such as preferably for CO and CN, are formed from the difference of a respective band radiation value and a respective thermal radiation value, the latter preferably by means of ratio pyrometry.

The method described above can be advantageously applied to improve combustion in a fossil thermal power plant or in a rotary kiln

According to a further variant of the method, a common camera-aided method is used for the metrological determination of the local distribution of the air / fuel ratio in the ignition / burnout region and for the optical detection of the light path emitted during the propagation of the substance. Such a camera-based method is for example from the European patent application EP 1091175 A2 known. Preferably, in this case, copper chloride is used in combination with the measurement system disclosed therein to obtain the spatial association with the fuel and / or air outlets. On the temporal behavior of the tracer traces of copper chloride in the combustion chamber, the flow rate can also be estimated.

It can be used instead of in the European patent application EP 1091 175 A2 described camera system can be used on a laser measuring grid. This measuring grid can thus be used both for the metrological determination of the local distribution of the air / fuel ratio in the ignition / burnout area and for detecting the light path and / or absorption track emitted during the propagation of the substance likewise in the ignition / burnout area.

Finally, the object of the invention is achieved by a device corresponding to the method.

The device according to the invention comprises means for detecting an actual value of at least the current fuel and / or air mass flow of a respective burner. she includes means for outputting a setpoint to an actuator for the fuel and / or air mass flow of a respective burner. Furthermore, it has measuring means for determining a local distribution in the ignition / burnout region of a parameter characterizing the combustion quality, in particular of the air / fuel ratio. Finally, the device comprises computer-aided means for simulating reacting flows in a combustion chamber by means of a numerical flow, pyrolysis and combustion simulation model for determining a spatially corresponding distribution of the fuel and air fractions spatially corresponding in the simulation model for identification of at least one local distribution Area with an unfavorable in terms of combustion quality characteristic, in particular with a combustion technically unfavorable air / fuel ratio, for determining the relevant at least one burner with respect to the simulated fuel and air fractions and for outputting a corrected setpoint for the fuel and / or air mass flow to the actuator a respective burner.

The actual value of the actual fuel mass flow may be e.g. indirectly derived from the speed of a burner upstream coal mill or directly from a gas meter with natural gas as fuel. The air mass flow may e.g. derived from the fan speed of a fan as a separate part of a burner based on the technical characteristics of the fan. The temperature values for the fuel mass flow and air mass flow may e.g. be detected by a temperature sensor. The respective setpoint may be a numerical value, such as a percentage ranging from 0% to 100%. A percentage of 0 may e.g. a set fuel mass flow of 0, i. in this case, the fuel supply of a burner is switched off. 100%, however, correspond to a maximum possible flow rate of the burner or the fuel injection device.

As a computer-aided means is preferably a computer, such as an industrial PC in question, can be run on the multiple programs. The simulation of reacting flows in the combustion chamber by means of the numerical flow, pyrolysis and combustion simulation model, the determination of one of the metrologically determined local distribution in the simulation model spatially corresponding distribution of fuel and air fractions, the identification of at least one local area with a combustion technically unfavorable air / Fuel ratio, the determination of the relevant at least one burner with respect to the simulated fuel and air fractions and the output of a corrected setpoint for the fuel and / or air mass flow to the actuator of a particular burner is preferably carried out in the form of executable software programs and stored in the form of model data be executed or processed by a microprocessor of the computer-aided means.

According to an alternative embodiment, the device has the means for detecting an actual value of at least the current fuel and / or air mass flow of a respective burner. It has the means for outputting a desired value to an adjusting device for the fuel and / or air mass flow of a respective burner. It also has means for individually controlling an admixer for admixing a substance in the fuel and / or in the air of a respective burner, wherein the substance leaves a trail of light during combustion in the furnace.

The respective admixer is preferably electrically actuatable via the means. The admixer may e.g. be a screw conveyor. It can e.g. a druc Kluftgestützte blowing device, via which the substance can be injected via an electrically controllable compressed air valve.

The device furthermore has a camera-supported measuring system for determining a local distribution of a quality characterizing the combustion quality in the ignition / burnout region and for the optical detection of a spectrally significant and spatially and temporally propagating tracer trace. Furthermore, the device has computer-aided means. They are provided for simulating reacting flows in a combustion chamber by means of a numerical flow, pyrolysis and combustion simulation model and for taking over the actual propagation of the fuel originating from the respective burner and the air originating from the respective burner on the basis of the detected propagation of the tracer track as boundary condition in the numerical simulation model. The computer-aided means are further provided for determining one of the metrologically determined

local distribution in the simulation model spatially appropriate distribution of fuel and air fractions. The computer-aided means are also provided for the identification of at least one local area with an unfavorable with regard to the combustion quality parameter. The computer-aided means are further provided for determining the relevant at least one burner with regard to the simulated fuel and air fractions. Finally, the computer-aided means are provided for outputting a corrected setpoint value for the fuel and / or air mass flow to the adjusting device of a respective burner.

According to one embodiment, the computer-aided means are adapted to repeatedly, preferably cyclically, determine the at least one authoritative burner and automatically output a corrected setpoint value for the fuel and / or air mass flow to the adjusting device of a respective burner. The determination of the at least one authoritative burner can e.g. be carried out by the fact that the determined by means of the simulation model fuel and air fractions are examined by the respective burners in the volume elements in the ignition / burnout area to maximum share values out. This is preferably done only with the volume elements which correspond to the local distribution of unfavorable air / fuel ratios.

According to another embodiment, in the numerical flow, pyrolysis and combustion model, on the basis of which the reacting flows in a firebox are simulated by the computerized means, the firebox, the geometrical arrangement and orientation of the burners in the firebox, their currently given velocity injection vector respective current predetermined value for the fuel and air mass flow and / or the current predetermined temperature of the respective fuel and air mass flow shown.

In another embodiment, the flow, pyrolysis and combustion simulation model is a computational fluid dynamics simulation model. Such a model is intended for the description of dynamic flow, pyrolysis and combustion processes in the combustion chamber through fluid-mechanical model equations such as Navier-Stokes, Euler or potential equations.

According to another embodiment, the use of a finite-volume method for approximating the Navier-Stokes, Euler or potential equations of the computational fluid dynamics simulation model is provided.

In another embodiment, the measuring means for the metrological determination of the local distribution of the air / fuel ratio in the ignition / burnout region is realized as a camera-supported measuring system in which the formation rates of the chemical reaction products formed during combustion, such as CN and CO, can be determined. The ratio of the determined formation rates can represent the air / fuel ratio. Alternatively, the measuring means may also comprise the movable lambda probe described above.

According to another embodiment, the respective burner is a concentrically constructed round burner. The respective burner may also include a fuel injector as well as an underlying and / or overlying fan.

The object of the invention is further achieved by a device corresponding to the method according to the invention.

FIG 1

ein Beispiel für einen Feuerraum eines Kraftwerks mit acht Brennern in einer Brennschicht,

FIG 2

eine beispielhafte Ausführungsform der Brenner im Feuerraum mit jeweils einer Brennstoffeinblasvorrichtung und jeweils zwei zugeordneten Lüftern,

FIG 3

eine Aufsicht auf die Brenner gemäß FIG 2 mit sieben von den acht Brennern im Betrieb,

FIG 4

ein Beispiel für eine messtechnisch ermittelte örtliche Verteilung eines in einem Zünd-/Ausbrandbereich gemäß FIG 1 herrschenden Luft-/Brennstoffverhältnisses mit vier Gebieten mit verbrennungstechnisch ungünstigem Luft-/Brennstoffverhältnis,

FIG 5

eine der örtlichen Verteilung gemäß FIG 4 örtlich entsprechende Verteilung der von den Brennern stammenden Brennstoff- und Luftanteile auf Basis eines numerischen Strömungs-, Pyrolyse- und Verbrennungs-Simulationsmodells gemäß der Erfindung, und

FIG 6

ein Beispiel für Vorrichtung zur Durchführung des erfindungsgemäßen Verfahrens zur Korrektur des Brennstoff- und/oder Luftmassenstroms der jeweiligen Brenner in einem Feuerraum.

The invention and advantageous embodiments of the invention will be described in more detail below with reference to the following figures. Show it

FIG. 1

an example of a combustion chamber of a power plant with eight burners in a firing layer,

FIG. 2

an exemplary embodiment of the burner in the furnace, each with a Brennstoffeinblasvorrichtung and two associated fans,

FIG. 3

a top view of the burner according to FIG. 2 with seven of the eight burners in operation,

FIG. 4

an example of a metrologically determined local distribution of one in a firing / burnout area according to FIG. 1 prevailing air / fuel ratio with four areas with combustion technically unfavorable air / fuel ratio,

FIG. 5

one of the local distribution according to FIG. 4 locally corresponding distribution of the fuel and air fractions originating from the burners on the basis of a numerical flow, pyrolysis and combustion simulation model according to the invention, and

FIG. 6

an example of apparatus for performing the method according to the invention for correcting the fuel and / or air mass flow of the respective burner in a furnace.

FIG. 1 shows an example of a combustion chamber 1 of a power plant with eight burners 2 in a firing layer E. The furnace 1 has a rectangular cross-section. By way of example, eight burners 2 are arranged in a common horizontal focal plane BE, in which air and fuel are blown through the burners 2. With P is an overlying pyrolysis B and ZA with a firing / burnout üherender Designated area. With Z itself an ignition area and A denotes a burn-out area. The boundaries between the respective areas are flowing and serve in this representation only for better understanding. Finally, reference numbers 5 designate measuring cameras which are arranged in a measuring plane M for the metrological detection of the ignition / burnout region ZA and, as it were, look into the combustion chamber 1. The measuring cameras 5 are part of a camera-supported measuring system, which is provided for the metrological detection of a local distribution of the prevailing in the ignition / burnout ZA air / fuel ratio. X, y, z are the axes of a Cartesian coordinate system. The focal plane BE and the measuring plane M are thus in an xy plane. Each perpendicular to it is the z-axis.

FIG. 2 shows an exemplary embodiment of the burner 2 in the combustion chamber 1, each with a Brennstoffeinblasvorrichtung 3 and each with two associated fans 4. It is in each case a fan 4 directly above and another fan 4 arranged directly below the associated Brennstoffeinblaseinrichtung 3. Of the fans 4, only the quadrangular air inlet window and of the fuel injection direction 3 only a round, concentric opening in the combustion chamber 1 can be seen. The Brennstoffeinblaseinrichtung 3 is also shown symbolized by a flame, even if in this firing layer E still no open combustion takes place. This takes place only in the ignition / burnout area.

FIG. 3 shows a plan view of the burner according to FIG. 2 with seven of the eight burners 2 ₁ -2 ₈ in operation. In this illustration, it can be seen that air and fuel are injected slightly offset from the geometric center in order to achieve a targeted turbulence and mixing of the air / fuel mixture. With ṁ _{B 1} -ṁ _{B 8} , the fuel mass flow injected by the respective burner 2 ₁ -2 ₈ and with ṁ _{L 1} -θ _{L 8} the air mass flow injected by the respective burner 2 ₁ -2 ₈ is designated. These physical quantities are time-dependent quantities with the unit kilogram per second (kg / s), symbolized by the point above the physical designation of the mass m. With v ₁ -v ₈ , the respective velocity injection vector is designated for both the air and the fuel. The velocity injection vector v ₁ -v ₈ itself has three Cartesian scalar velocity values v _x , v _y , v _z , not further shown, which are based on the FIG. 1 based coordinate system x, y, z are related. For the sake of simplicity, a common fuel temperature T _B was entered for the injected fuel and a common air temperature T _L for the air. Of course, for each fan 4 and each fuel injector 3 of the respective burner 2 ₁ -2 _8, the current temperature and separate Geschwindigkeitseinblasvektoren are specified or detected for the air from the respective fan 4 and for the fuel from the respective fuel injector 3.

In the example of FIG. 3 is still the burner 2 ₄ shown in phantom. This symbolizes that the shown burner 2 _{4 is} not in operation. Reasons for this may be a technical failure, revision work or a partial load operation.

FIG. 4 shows an example of a metrologically determined local distribution V _R one in an ignition / burnout ZA according to FIG. 1 prevailing air / fuel ratio with four areas G1-G4 with combustion technically unfavorable air / fuel ratio. The shown two-dimensional representation in the xy plane shows areas G1-G4 with a combustion-technically unfavorable air / fuel ratio. Thus, the hatched areas G1, G2 show an air / fuel ratio of less than 0.8. In the direction of the interior of the area, the air / fuel ratio in the sense of contour lines decreases still further, for example in the area center to a value of 0.6. Analogously, the unshaded areas G3, G4 show an air / fuel ratio of more than 1.2. In the direction of the interior, the air / fuel ratio in the sense of contour lines increases even further, for example in the area center to a value of 1.4.

FIG. 5 shows one of the local distribution V _R according to FIG. 4 locally corresponding distribution V _S of the burner originated fuel and air components A _B1 -A _B8 , A _L1 -A _L8 based on a numerical flow, pyrolysis and combustion simulation model according to the invention.

The in the FIG. 5 shown regions G1-G4, which extend in the grid of a volume element dV of the simulation model, correspond approximately to the areas G1-G4 in FIG. 4 with the extreme values for the air / fuel ratio there. These now identified, combustion technically unfavorable areas G1-G4 will now be examined with regard to their fuel and air shares A _B1 -A _B8 , A _L1 -A _L8 . More specifically, the respective volume elements dV associated with the identified areas G1-G4 are examined. Since, according to the invention, in the numerical simulation of each volume element dV the origin of the fuel and air components A _B1 -A _B8 , A _L1 -A _L8 originating from the respective burners were taken into account continuously and already separately, G1 can now be determined for each area. G4 the relevant burner 2 are determined. This is typically the burner 2, whose fuel or air content A _B1 -A _B8 , A _L1 -A _L8 in comparison to the fuel and air portions A _B1 -A _B8 , A _L1 -A _{L8 of} the other burner 2 is maximum. For example, for the area G1 in FIG. 5 which according to FIG. 4 has an air / fuel ratio of 0.6, so is too "fat", 60% of the fuel exclusively from one Burner 2 originate and 30% of the air comes mainly from another burner 2. In the present case, it is then particularly suitable to reduce the fuel mass flow of the burner 2 with the 60% share in order to improve the combustion there. It can also be used for example for this area G1 in FIG. 5 For example, 50% of the air come from just one burner 2 and distribute the fuel components approximately evenly on all burners 2. In this case, it is particularly suitable to increase the air mass flow in this authoritative burner 2 with the 30% air content in order to improve the combustion there. Preferably, in a plurality of identified areas G1-G4, the areas G1-G4 are successively corrected for the air and fuel mass flow.

FIG. 6 shows an example of an apparatus 10 for carrying out the method according to the invention for correcting the fuel and / or air mass flow m _{B 1} -M _{B 8,} M _{L 1} - M _{L 8} of the respective burners 2 ₁ -2 ₈ in a combustion chamber 1. By reference numeral 11 denotes means for detecting an actual value IW, with 12 means for outputting a setpoint SW, with 13 measuring means and with 14 computer-aided means, such as a computer. The detected actual values IW are current air mass flow values ṁ _{L 1} -θ _{L 8} , fuel mass flow values ṁ _{B 1} -θ _{B 8} and temperature measured values T _B , T _L received, for example via a power plant control system. The measuring means 13 are realized in the present example by a camera-based measuring system with four cameras 5. On the output side, this system provides a local distribution V _{R of} the measured air / fuel ratio λ in the ignition / burnout region ZA, eg as a two-dimensional data field λ _xy corresponding to the xy plane of the measurement plane M. The computer-aided means 14 exemplarily have a data model numerical simulation model CFD for the flow, pyrolysis and combustion simulation of the combustion chamber 1 on. On the output side, the numerical simulation model CFD outputs the fuel and air components A _B1 -A _B8 , A _L1 -A _L8 that can be assigned to the respective burners 2. Furthermore, the computerized means 14 comprise an identification block ID to identify corresponding areas G1-G4 from the local distribution V _{R of} the air / fuel ratio _values λ _xy provided by the measuring system 13. A comparison block CMP of the computer-aided means 14 now compares fuel and air portions A _B1 -A _B8 , A _L1 -A _L8 in volume elements dV locally corresponding to the identified areas G1-G4 with each other for maximum and minimum proportion values around the relevant burner 2 or determine the relevant Brennstoffeinblasvorrichtung 3 or the relevant fan 4. Based on this, a modified desired value .DELTA.SW is output to the means 12 for outputting a desired value SW, such as again via the power plant control system, to the combustion by correcting the respective fuel and / or air mass flow ṁ _B , ṁ _L improve. After a predetermined waiting time, such as 10 minutes, a check is made as to whether the output of the changed setpoint SW has led to an improvement of the combustion. This can be done iteratively until an optimum for the combustion has been found. Subsequently, the next identified area G1-G4 can be iteratively optimized in the same way. It is also possible to determine only a single area G1-G4 with a maximum combustion / combustion-maximum unfavorable air / fuel ratio λ, and then optimize this area G1-G4. After the iterative optimization, the identification of a new area G1-G4 takes place with the maximum combustion / air ratio λ.

The inventive method and the corresponding device 10 is particularly advantageous for cases in which one or more burners 2 have failed or deliberately not operated in the partial load range. Here, by targeted control of the air / fuel mass flow of the other burner 2, in turn, optimal combustion can be accomplished.

LIST OF REFERENCE NUMBERS

1

Firebox, combustion chamber, combustion chamber

2, 2 ₁ -2 ₈

burner

3

Brennstoffeinblasvorrichtung

4

Fan

5

Measuring camera, video camera

10

Apparatus for carrying out the method

11

Means for acquiring an actual value

12

Means for outputting a setpoint

13

measuring Equipment

14

computerized means, computer

A

burnout

A _B , A _B1 -A _B8

fuel portion

A _L , A _L1 -A _L8

air content

BE

burner level

CFD

numerical simulation model

CMP

comparison block

dV

voxel

e

burning layer

F

flame

G1-G4

combustion-technically unfavorable areas

ID

identification block

IW

actual value

λ

Air / fuel ratio

λ _xy

Air / fuel ratio in the xy plane

M

measuring plane

ṁ _B , ṁ _{B 1} -m _{B 8}

Fuel mass flow

ṁ _L , ṁ _{L 1} -m _{L 8}

Air mass flow

P

pyrolysis

SW

setpoint

ΔSW

corrected setpoint

T ₁ -T ₈

flame temperature

T _B

fuel temperature

T _L

air temperature

V

Combustion chamber volume

v, v ₁ -v ₈

Geschwindigkeitseinblasvektor

V _R

metrologically determined local distribution

V _S

local distribution in the simulation model

x, y, z

reference coordinates

Z

ignition

ZA

Ignition / burnout

Claims (14)

1. Method for improving the combustion in a combustion chamber (1), in particular of a power plant, wherein a plurality of burners (2) are arranged in a burner layer (E) or in another geometry and wherein a fuel and/or air mass flow (ṁ_B, ṁ_L ) may be adjusted in at least some of the burners (2), wherein a local distribution (V_R) of a characteristic (λ, T) characterizing the combustion quality is ascertained by metrological means in an overlying ignition/combustion region (ZA) and wherein at least one area (G1-G4) with an inexpedient characteristic (λ, T) in respect of the combustion quality is identified on the basis of the local distribution (V_R),
   characterized

   - in that part of the combustion chamber (1) essential for a flow, pyrolysis and combustion simulation is mapped to a numerical simulation model (CDF), subdivided into a multiplicity of volume elements (dV),

   - in that the origin of the fuel and air portions (A_B, A_L) originating from the respective burners (2) are also considered continuously and separately in the numerical simulation of each volume element (dV),

   - in that a distribution (V_S) of the fuel and air portions (A_B, A_L) locally corresponding to the local distribution (V_R) in the simulation model (CFD) ascertained by metrological means is ascertained, and

   - in that the at least one burner (2) which is decisive in respect of the ascertained fuel and air portions (A_B, A_L) is ascertained for the respectively identified area (G1-G4) in order to improve the combustion by correcting the respective fuel and/or air mass flow (ṁ_B, ṁ_L ).
2. Method according to Claim 1, wherein a substance is added to the fuel and/or the air for a respective burner (2), wherein the substance leaves a luminous trace during the combustion in the combustion chamber (1), wherein the local and temporal propagation of the substance is captured by means of an optical measuring system matched spectrally to the luminous trace and wherein an actual propagation of the fuel originating from the respective burner (2) and of the air originating from the respective burner (2) accompanying the actual propagation of the substance are included as boundary conditions in the numerical simulation model (CDF) .
3. Method according to Claim 2, wherein the method steps according to Claim 2 are applied, in particular repeatedly, at each individual burner (2).
4. Method according to one of the preceding claims, wherein the at least one decisive burner (2) is ascertained repeatedly, preferably cyclically, and wherein the respective fuel and/or air mass flow (ṁ_B, ṁ_L ) is corrected in an automated manner.
5. Method according to one of the preceding claims, wherein the combustion chamber (1), the geometric arrangement and alignment of the burners (2) in the combustion chamber (1), their current predetermined blowing-in velocity vector (v), their respective currently predetermined value for the fuel and air mass flow (ṁ_B, ṁ_L ) and/or the current predetermined temperature (T_B, T_L) of the respective fuel and air mass flow (ṁ_B, ṁ_L ) is mapped in the numerical simulation model (CFD) .
6. Method according to one of the preceding claims, wherein the flow, pyrolysis and combustion simulation model is a computational fluid dynamics simulation model (CFD), which describes the dynamic flow, pyrolysis and combustion processes in the combustion chamber (1) by fluid mechanical model equations such as the Navier-Stokes equation, the Euler equation or potential equations.
7. Method according to Claim 6, wherein a finite volume method is used for the approximate solution of the Navier-Stokes equation, Euler equation or potential equations of the computational fluid dynamics simulation model (CDF).
8. Method according to one of the preceding claims, wherein the characteristic (A, T) characterizing the combustion quality and ascertained by metrological means is an air/fuel ratio (λ), a temperature (T) and/or the CO, NO_x, O₂ or CO₂ content in the flue gas present in the ignition/combustion region (ZA).
9. Method according to Claim 8, wherein a camera-assisted method is used for the metrological ascertainment of the local distribution of the air/fuel ratio (λ) in the ignition/combustion region (ZA), with the formation rates of the chemical reaction products CN and CO formed during the combustion being ascertained in said camera-assisted method, wherein the ratio of the ascertained formation rates is formed as a variable representing the air/fuel ratio (A).
10. Method according to one of the preceding Claims 2 to 8, wherein a common camera-assisted method is used for the metrological ascertainment of the local distribution of the air/fuel ratio (λ) in the ignition/combustion region (ZA) and for the optical capture of the luminous trace emitted during the propagation of the substance.
11. Use of the method according to one of the preceding claims for improving the combustion in a fossil-fuel-based thermal power plant or in an industrial installation.
12. Apparatus for carrying out the method according to one of Claims 1 to 10, wherein, to this end, the apparatus comprises

    - means (11) for capturing an actual value (IW) of at least the current fuel and/or air mass flow (ṁ_B, ṁ_L ) of a respective burner (2),

    - means (12) for outputting an intended value (SW) to an actuator for the fuel and/or air mass flow (ṁ_B , ṁ_L ) of a respective burner (2),

    - measuring means (13) for ascertaining a local distribution (V_R), present in the ignition/combustion region (ZA), of a characteristic (λ, T) characterizing the combustion quality and

    - computer-assisted means (14)

    - for simulating reacting flows in a combustion chamber (1) by means of a numerical flow, pyrolysis and combustion simulation model (CFD),

    - for ascertaining a distribution (V_S) of the fuel and air portions (A_B, A_L) locally corresponding to the local distribution (V_R) in the simulation model (CFD) ascertained by metrological means,

    - for identifying at least one area (G1-G4) therein which has an inexpedient characteristic (̇λ, T) in respect of the combustion quality,

    - for ascertaining the decisive at least one burner (2) in respect of the simulated fuel and air portions (A_B, A_L) and

    - for outputting the corrected intended value (SW') for the fuel and/or air mass flow (ṁ_B, ṁ_L ) to the actuator of the respective burner (2).
13. Apparatus according to Claim 12 for carrying out the method according to one of Claims 2 to 10, wherein, to this end, the apparatus comprises

    - means for individually actuating a mixer for adding a substance into the fuel and/or into the air of the respective burner (2), wherein the substance leaves a luminous trace during the combustion in the combustion chamber (1),

    - a camera-assisted measuring system (13) for ascertaining a local distribution (V_R), present in the ignition/combustion region (ZA), of a characteristic (λ, T) characterizing the combustion quality and for optically capturing a spectrally significant luminous trace propagating both spatially and temporally and

    - the computer-assisted means (14) for simulating reacting flows in a combustion chamber (1) by means of a numerical flow, pyrolysis and combustion simulation model (CFD) and for adopting the actual propagation of the fuel originating from the respective burner (2) and of the air originating from the respective burner (2) as a boundary condition in the numerical simulation model (CDF) on the basis of the captured propagation of the luminous trace.
14. Apparatus according to Claim 12 or 13, wherein the respective burner (2) comprises a fuel injection apparatus (3) and an underlying or overlying fan (4).

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