EP0897086A2 - Method for determining the average radiation of a burner bed in an incinerating plant and for the control of the combustion process - Google Patents

Abstract

The radiation measuring method uses an IR camera (22), or a thermography camera, for viewing the flat region of the combustion bed (24), with the measurement limited to a defined wavelength range in which the effect of the combustion gases above the combustion bed is a minimum and analysis of successive images for each partial area of this region, for determining the corresponding temperature.

Description

The invention relates to a method for determining the average radiation and that associated with this radiation Average temperature of a flat area Burning bed using infrared camera or thermography camera in incinerators and control of the incineration process at least in the observed area this incinerator.

Known methods of this type result from DE 39 04 272 C2 and DE 42 20 149 A1. In practice there are difficulties hired to carry out these procedures which consist in that the radiation or temperature values determined not always the exact temperature values of the Correspond to the combustion bed because they are influenced by radiation values located between the infrared camera and the burning bed Flames, exhaust gases and soot particles are affected. The consequence of which is that on the basis of such controlled variables carried out regulations of the combustion processes frequently do not meet the desired requirements.

The object of the invention is a method of the above specified type so that the interference by Flame radiation, radiation of those present in the exhaust gases Gases and solid-state radiation of soot particles and the like. Largely be excluded.

This task is based on a process of the beginning explained type solved according to the invention in that the Measurement is limited to a waveband that the Corresponds to the minimum of the disturbing gases above the combustion bed, that the area to be recorded is in an area grid is divided with several sub-areas that in one Period in which in the area to be recorded the burning bed as still and the radiation or temperature of the burning bed can be assumed to be almost constant multiple images taken in time be that by comparing the images of a period of time the sub-areas with each other with a radiation of static radiation media from the partial areas with a Radiation from moving radiation media can be distinguished and that to calculate the average radiation or the average temperature of the surface area only the radiation or temperature of the partial areas of the radiation of stationary radiation media are taken into account.

The invention thus makes two fundamental considerations Use, the one basic idea of which is through Spectral analysis the radiation intensity at least the most most common gases, the minimum to determine this radiation intensity of the gases and the used measuring device in the form of infrared cameras or To tune thermographic cameras to this waveband, in order to eliminate most of the disruptive gas radiation. The second basic idea is that the between Combustion bed and measuring device existing radiation, e.g. of solid particles, in particular of soot or individual gas components, thereby eliminating that you have several images of one divided into an area grid Area in short time intervals and thereby those partial areas of the area grid for the averaging is eliminated, the strong fluctuations are subject. One is thinking about it assumed that the burning bed is almost immobile, while the radiating solid particles or gases of a strong one Are subject to movement if you have enough small ones Time intervals as a basis for assessment. So that as Burning bed that can be viewed at rest is also subject to short Intervals of a few tenths of a second are not strong Temperature fluctuations, so that when conspicuous occurs Temperature fluctuations can be assumed that between Burning bed and measuring device interference radiation occur. So if you have those pictures for rating the Radiation is excreted by the radiation of moving particles or gases are affected, you get one largely unaffected average value for the radiation of a Area to which a certain temperature value corresponds, which is the control variable for influencing the Various parameters can serve the combustion process influence. It can all known so far Parameters are affected, of which below essential parameters in a non-exhaustive list can be specified. Such parameters can be: the total amount of air supplied to the combustion process, the Amount of primary air, the air volume distribution in the primary air, the oxygen concentration of the primary air, the temperature the primary combustion air, the fuel feed quantity overall or on certain sections of the grate related, the stoking speed of the entire grate, the local stoking speed of the grate etc.

For the implementation of the method according to the invention it is advantageous if using the fuzzy logic from the detected Measured values a controlled variable for controlling individual or all so far in direct or indirect dependence on the combustion temperature controllable processes is formed.

In order to suppress erratic control processes, it is advantageous if in a further embodiment of the invention for determination of the controlled variable is an average of the average radiation or the average temperature from several consecutive periods is formed. Here a time period can be 0.1 to 5 seconds.

As a practical measure to determine the controlled variable the mean of the averages is 5 successive periods of time.

The area to be observed should be at least 1m ² and be divided into an area grid with at least 10 partial areas. For grate furnaces, it has proven to be expedient if the area grid corresponds to the primary air zones of the grate area that is active for the combustion.

The method according to the invention is also particularly suitable advantageous for checking the proper Operation of a grate. For this, at strongly from Average value of a period of time deviating radiation values or temperature values of individual partial areas Radiation or temperature values of the corresponding sub-areas observed over several periods and the corresponding Images of the partial areas with regard to deviations with one another compared. So if a certain sub area over always an average of several times has a significantly different value, for example has a much too high temperature, this can be due to a mechanical defect and a related one indicate poorly distributed air supply. If in contrast an area the temperature is constantly too low, so this is due to constipation and therefore much too low Indicate primary air supply.

Hindurchblicken" durch diese Schicht wegen fehlender Fenster" eine brauchbare Bildauswertung nicht zuläßt. Solche Zustände sind nur von kurzer Zeitdauer und außerdem können solche Zustände durch Anordnung mehrerer Infrarotkameras, die unter unterschiedlichen Blickwinkeln auf das Brennbett gerichtet sind, vermieden werden.The infrared camera or thermographic camera used is equipped with filters so that it works in a wave range of 3.5 to 4 µm. In this area, the emission strength of the gases that normally occur in a furnace is a minimum. These are the gases CO ₂ , CO and water vapor. The soot, which cannot always be avoided, has a lower value in this wavelength range than in the lower wavelength range, but it does represent a considerable source of interference, which is eliminated with the aid of the procedural measures explained at the beginning. The evaluation device downstream of the camera with a fuzzy control system is set up in such a way that the images or the measurement signals obtained are fuzzified, subjected to an inference process and then defuzzified. The result is a relative quality of the image information that comes very close to the actual state of the surface of the burner bed. A threshold is set in the software, below which an infrared image is defined as no longer usable. The radiation information or temperature information obtained is passed on above this threshold without further evaluation of the image quality. If the image quality is poor, for example for more than two minutes, the image control loops override the camera control loops and then reactivate them. This is to prevent that, due to bad images, regulation takes place which does not correspond to the actual conditions. This can be the case, for example, if excessive soot development, which practically forms a gap-free layer between the separating bed and the infrared camera, occurs

"Look through this layer because of missing Window "does not allow usable image evaluation. Such states are only of short duration and, in addition, such states can be avoided by arranging several infrared cameras which are directed at the combustion bed from different angles.

Figur 1:

Einen Vertikalschnitt durch eine schematisch dargestellte Feuerungsanlage mit Einrichtungen zur Durchführung des erfindungsgemäßen Verfahrens;

Figur 2:

Ein Strahlungsdiagramm verschiedener Gase;

Figuren 3 bis 5:

Schematisch dargestellte Bildfolgen und deren Auswertung; und

Figur 6:

Ein Regelschema für eine Feuerungsanlage.

The invention is explained below in connection with the drawing, for example. The drawing shows:

Figure 1:

A vertical section through a schematically illustrated furnace with devices for performing the method according to the invention;

Figure 2:

A radiation diagram of various gases;

Figures 3 to 5:

Schematically represented image sequences and their evaluation; and

Figure 6:

A control scheme for a furnace.

The furnace shown in Figure 1 includes one Firing grate 1, a loading device 2, a firebox 3 with subsequent throttle cable 4 and a reversing space 5, in which the exhaust gases into a downward gas train 6 are routed, from which they into the usual, a firing system downstream units, especially steam generators and emission control systems.

The furnace grate 1 comprises individual grate levels 7, which in turn formed from individual, adjacent grate bars are. Every second grate level of the designed as a push-back grate Firing grate is marked with a total of 8 Drive connected, which allows the stoking speed adjust. Below the grate 1 are subdivided in both the longitudinal and transverse directions Underwind chambers 9.1 to 9.5 are provided, which are separated supplied with primary air via individual lines 10.1 to 10.5 become. At the end of the grate, the burned out falls Slag via a slag roller 25 into a slag chute 11, in which possibly also the heavier ones, in the lower one Reversing space 12 solid particles separated from the exhaust gas reach.

In the firebox 3 there are several rows of secondary air nozzles 13, 14 and 15 aligned for controlled combustion of flammable gases and those in the air Fuel parts by supplying so-called secondary air to care. These secondary air nozzle rows can be controlled separately, since different conditions are spread over the firebox to rule.

The feed device 2 comprises a feed hopper 16, a feed chute 17, a feed table 18 and one or several side by side, possibly independent of each other controllable feed piston 19, which in the feed chute 17th falling garbage over the loading edge 20 of the feed table 18 in the firebox on the grate 1.

In the ceiling 21, which closes off the upper reversal space 5 an infrared camera 22 is mounted, which has a device 23 is connected, which is used to evaluate the received Images, formation of a controlled variable and output of control commands for the various furnishing systems serves to influence the combustion process. At 23 is thus referred to an evaluation and control device.

The infrared camera 22 is used to determine the on the combustion bed 1 located combustion bed 24 outgoing Radiation or to determine the combustion bed temperature, the is assigned to the combustion bed radiation. This will cause disruptions by the flame 24a or those contained in the exhaust gases gaseous and solid components largely excluded, as explained in more detail below.

The heaped up bed and the burning bed 24 fuel is pre-dried through the downwind zone 9.1 and the radiation in the combustion chamber warmed and ignited. In the area of the underwind zones 9.2 and 9.3 is the main fire zone, while in the area of the downwind zone 9.4 and 9.5 the slag that forms burns out and then got into the slag chute. The one from the burning bed rising gases still contain combustible parts that by supplying secondary air through the rows of secondary air nozzles 13 to 15 are completely burned. The regulation the feed quantity of the fuel, the primary air quantities in the individual underwind zones and their composition regarding the oxygen content will be dependent the burning behavior, which depends on the calorific value of the fuel depends, and subject to large fluctuations in waste is regulated, whereby to record the necessary controlled variable the radiation emanating from the burning bed and the associated temperature is used, which with Help of the infrared camera 22 detected and by the evaluation and Control device 23 evaluated and to the corresponding Actuators is passed on.

Various actuators are shown in schematic form in Figure 1 indicated, with 29 the actuator for Influencing the rust speed, with 30 the adjusting device for influencing the speed of the slag roller, at 31, the control device for influencing the grate speeds regarding different courses, with 32 the Setting device for the switch-on and switch-off frequency or the Speed of the feed piston, at 33 the actuating device for setting the primary air volume, with 34 the control device for adjusting the composition of the Primary air in terms of oxygen content and with 35 die Actuator for setting the temperature of an air preheater are designated for the primary air.

In the following, with reference to FIGS. 1 to 6 the method according to the invention explained in more detail.

In Figure 1, the infrared camera 22 and its orientation on the burning bed is shown. First, according to FIG. 2, it is examined how the radiation behavior of the gases and solid particles encountered in the combustion chamber 3 is developed. According to FIG. 2, it is found that there is a minimum of infrared radiation for the gases CO ₂ , CO and H ₂ O occurring in high concentrations in the wave range between 3.5 and 4 μm due to the drying and combustion reaction of the fuel. Accordingly, the infrared camera is equipped with a wavelength-selective filter that works in the minimum of these interfering gases, ie in the range from 3.5 to 4 µm. It can also be seen from FIG. 2 that the radiation intensity or the emission strength of the solid particles (soot) of the flame 24a in the firing chamber 3 drops from an initially high value, a relatively low value having already been reached from 3.5 μm and then this value remains approximately constant, so that the interference radiation emanating from dust particles or soot cannot be eliminated by appropriate filters.

This is where the main idea behind the present is Invention one in connection with Figures 3 to 5 is explained.

FIG. 3 shows an area monitored by an infrared camera, which is subdivided into 25 partial areas according to an area grid. The dark sub-areas represent those areas that have a significantly higher radiation intensity and thus a higher temperature than the light sub-areas. The reason for this is that the surface of the combustion bed is relatively cool compared to the gas atmosphere above. If one now considers FIG. 4, it is found that other partial areas have this high radiation intensity or temperature. FIG. 4 shows a recording which was taken a few tenths of a second later and thus captures those changes which can occur within this short period of time. If it is found that there is a different radiation or temperature distribution in FIG. 4 than in FIG. 3, these deviations can only result from those radiating media which can change both their temperature and their position within a short time. The combustion bed is definitely not to be counted for this, because within a fraction of a second the combustion bed cannot experience any noticeable change in position or drastic temperature change. Comparing FIGS. 3 and 4, it is found that, in accordance with FIG. 5, which shows an evaluation of this comparison, those partial areas are drawn in dark, which either have a significantly higher radiation and thus when the image is shown in FIG. 3 or in FIG had a higher temperature. The fields remaining bright in FIG. 5 thus correspond to partial areas of the recording of the area to be observed, which remained unchanged even after a certain time interval. From this it can be concluded that radiation recordings or temperature measurements are taken from a medium which is not subject to abrupt changes and can therefore be regarded as the actual radiation from the combustion bed. In practice, for example, to form a controlled variable which is output by the evaluation and control device 23 to the various actuating devices, seven pictures are taken within 3.5 seconds and an average value is formed from this in accordance with the comparison shown in FIGS. 3 to 5. Five such averages are then combined into a controlled variable. In the present example, this means that there is a new controlled variable every 17.5 sec. Of course, the time intervals within which the individual pictures are taken can be adapted to the respective conditions, so that it is also possible to work with much shorter time intervals. In practice, the partial area observed by an infrared camera corresponds to the area that occupies at least two underwind zones up to 15 underwind zones. In practice, the area of an underwind zone area is about 2-4 m ² , this area then being divided according to the actually existing primary air zones observed by the camera and then each of these image segments corresponding to a primary air zone for evaluation in accordance with the explanations in connection with the figures 3 to 5 is divided into approx. 25 subareas. This subdivision and the specified time intervals for two consecutive recordings have proven to be sufficient in connection with a firing system with sliding grate to determine the combustion bed temperature.

The images according to Figures 3 to 5 are over several Time periods saved and compared with each other, but it’s not just about the burning bed temperature to be detected by the light partial areas in FIGS. 3 to 5 is represented, but with this method one can also determine if there are any abnormal changes gives. For example, over a long period always the same areas compared to the average combustion bed temperature too high on the grate area under consideration or too low in temperature, so you can get a glitch close the grate mechanism or the air supply.

The successive ones formed in the evaluation and control device 23 Control variables serve to influence the individual control devices, as shown in a schematic overview is shown in Figure 6. According to this, the control device 23 the adjusting devices for the grate speed 29 influenced up to the temperature in the air preheater 35 that has already been specified above.

Claims (9)

Method for determining the average radiation and the average temperature associated with this radiation of a surface area of a combustion bed by means of an infrared camera or thermography camera in incineration plants and regulating the combustion process at least in the observed area of this incineration plant, characterized in that the measurement is limited to a wave range which is the minimum The disturbing gases above the combustion bed correspond to the fact that the surface area to be recorded is subdivided into an area grid with several partial areas, that in a period in which the combustion bed is immobile in the area area to be recorded and the radiation or temperature of the combustion bed can be assumed to be almost constant are, several temporally successive images are recorded, that by comparing the images of a time period with each other, the partial areas with radiation from quiescent radiation media from A distinction is made between the partial areas with radiation from moving radiation media and that only the radiation or temperature of the partial areas of the radiation from quiescent radiation media are taken into account for calculating the average radiation or the average temperature of the area. Method according to Claim 1, characterized in that a control variable for regulating individual or all processes previously controllable in direct or indirect dependence on the combustion temperature is formed from the measured values by means of the fuzzy logic. Method according to Claim 1 or 2, characterized in that, in order to determine the controlled variable, an average of the average radiation or the average temperature is formed from a plurality of successive time segments. Method according to one of claims 1 to 3, characterized in that a time period is 0.1 to 5 seconds. Method according to Claim 3, characterized in that the mean value of the average values of five successive time segments is formed in order to determine the controlled variable. Method according to one of claims 1 to 5, characterized in that an area to be observed is at least ¹ m ² and is divided into an area grid with at least ten partial areas. A method according to claim 6, characterized in that in the case of grate firing, the area grid corresponds to the primary air zones of the grate area active for combustion. Method according to one of Claims 1 to 7, characterized in that, in the case of radiation values or temperature values of individual partial areas which differ greatly from the average value of a time period, these radiation or temperature values of the corresponding partial areas are observed over several time periods and the corresponding images of the partial areas are compared with one another with regard to deviations . Method according to one of claims 1 to 8, characterized in that the radiation measurement is carried out in a spectral range from 3.5 to 4 µm.

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