EP0716266A1 - Device and process for controlling a grate furnace with moving grate - Google Patents

Abstract

The regulation system uses optical sensors for detecting the light emitted by the combustible material at spaced points along its transport path between a number of stepped grids. The signals provided by the sensors are evaluated for controlling the quantity of combustion air and/or the feed rate of the combustible material. The sensors are positioned at a viewing angle of between 10 and 30 degrees relative to the grids, for detecting the light emission of the ashes supported by the grids.

Description

The invention relates to a method and a device for regulating a grate firing system with movable grate, from which ash is removed or discharged over an end region of the grate, the material on the grate being observed for the presence of embers, if appropriate at several points in the material path, and in Depending on the observation, the air supply and / or the delivery speed of the fuel is regulated.

The grate furnace can be designed to burn solid fuels such as wood, bark, straw or garbage. The grate can be an inclined (but also horizontal) stair grate, feed grate, return grate or the like. At the beginning of the grate, the solid fuel is added and then mechanically transported over it, the "primary air" being supplied to the grate from below. The ash is thrown away at the end of the grate. In the normal case, the firing zone is in the middle of the grate and the grate is dimensioned so that only ash is left at the end of the grate, which is then thrown off the grate into a collecting or conveying device.

If the grate is overloaded, i.e. charged with more fuel than can burn on the grate during the dwell time, then unburned fuel is thrown away as embers with the ashes. A similar situation can occur if the fuel - which is very often the case with biomass - is very wet and the ignition is therefore delayed. In this case too, burning material is thrown into the ashes. A third reason for the discarding of burning fuel is a strong inhomogeneity, which happens very often with waste. In this case, large and compact pieces of fuel do not find enough time on the grate to burn out.

• Dadurch, daß noch brennfähiger Brennstoff in die Asche transportiert wird, geht Brennstoff verloren und es leidet darunter die Wirtschaftlichkeit der Anlage.
• Die dabei produzierte Asche ist mit Kohlenstoff beladen und daher schwierig deponierbar und für eine Reihe von Anwendungsfällen nicht mehr geeignet.
• Meist ergibt sich ein solcher Zustand, wenn die Feuerung mit Maximallast oder mit Überlast betrieben wird. In solch einem Fall wird brennfähiger Brennstoff in die Asche abgeworfen und neuer, meist nasser, Brennstoff nachgeschoben. Dieses hat zur Folge, daß immer mehr nasser Brennstoff in die Feuerung eingebracht wird und dieser erst trocknen muß, d.h. daß ein Teil der erzeugten Wärme für die Trocknung des eingebrachten zu nassen Brennstoffes verwendet wird. Die tatsächliche Leistung der Feuerung sinkt also, was dazu führt, daß die Regelung den Rost mit mehr Brennstoff beschickt. Dieser Vorgang wiederholt sich so lange, bis das Feuer zur Gänze am untersten Rand des Rostes gelegen ist und immer mehr unverbrannter Brennstoff in die Asche geschoben wird, während die Kesselleistung abnimmt bis schließlich das Feuer erlischt.

The disadvantages of such an operation with fuel dumping into the ashes are threefold:

• The fact that combustible fuel is transported into the ashes means that fuel is lost and the efficiency of the system suffers as a result.
• The ash produced in the process is loaded with carbon and is therefore difficult to deposit and is no longer suitable for a number of applications.
• Such a condition usually arises when the furnace is operated at maximum load or with overload. In such a case, combustible fuel is thrown into the ashes and new, usually wet, fuel is added. The consequence of this is that more and more wet fuel is introduced into the furnace and this has to dry first, that is to say that part of the heat generated is used for drying the fuel which is too wet. The actual performance of the furnace therefore drops, which means that the control unit loads the grate with more fuel. This process is repeated until the fire is completely at the bottom of the grate and more and more unburned fuel is pushed into the ashes, while the boiler output decreases until the fire finally goes out.

• a) Die Lichtschranke zeigt nur an, ob die zulässige Höhe des Glutbettes überschritten ist. Die Lichtschranke kann nicht anzeigen, wenn an dieser Stelle sich keine Glut mehr befindet Es sind darum vielfach mehrere Lichtschranken übereinander angeordnet.
• b) Jede Lichtschranke benötigt zwei horizontale Öffnungen in der Brennkammerwand auf einem Niveau, das vielfach von der Brennstoffschüttung überschritten wird. Um diese Öffnung sauber zu halten, ist darum ein großer Spülluftstrom notwendig. Im Normalbetrieb stellt dieser Spülluftstrom kein Problem dar, da diese Luft als Sekundärluft benötigt wird; lediglich der hohe Vordruck ist ein (geringer) Nachteil. Arbeitet die Anlage jedoch im Aussetzbetrieb, dann bedeutet dies, daß auch während jener Zeit, in der normalerweise keine Luft der Anlage zugeführt wird, Luft in die Brennkammer eintritt und darum die Feuerungsleistung nicht unter einen Grenzbetrag reduziert werden kann.

In the case of feed grates on which biomass - for example bark - is burned, it is known to use light barriers for monitoring the ember bed height. In the case of a moving grate, several light barriers are arranged just above the expected height of the ember bed at various locations above the grate. Openings are arranged opposite one another in the wall of the firebox, with a light transmitter in front of one opening and a light receiver on the other, opposite opening. If the light receiver does not receive a signal, this is a sign that the ember bed is too high and the feed or the rust feed must be reduced. This method has two disadvantages:

• a) The light barrier only shows whether the permissible height of the ember bed has been exceeded. The light barrier cannot indicate when there is no more embers at this point. Therefore, multiple light barriers are often arranged one above the other.
• b) Each light barrier needs two horizontal openings in the combustion chamber wall at a level that is often exceeded by the fuel fill. A large purge air flow is therefore necessary to keep this opening clean. In normal operation, this purge air flow is not a problem, since this air is required as secondary air; only the high form is a (minor) disadvantage. However, if the system is operating in intermittent mode, this means that air enters the combustion chamber even during the period when normally no air is supplied to the system and therefore the firing capacity cannot be reduced below a limit.

Large combustion plants use a TV camera to monitor them. The screen of this TV camera is in the control room, and the operating personnel control the system after observing the screen image. The investments for a sufficiently robust image transmission system and the costs for the personnel for operating the system are high and, moreover, cannot be automated. More recently, automatic image evaluation has been used by inferring the local condition of the ember bed from the infrared radiation. The grate feed and the grate's air supply can then be optimally controlled using a computer (DD 292 068 A5). However, this process is exceptionally expensive and therefore cannot be used for small systems in unattended operation.

The method described in the patent specification DD 292068 (Steinmüller) automatically detects evaluation criteria for the combustion progress and is intended to enable automation of the control. To detect the radiation from a combustion on a grate, the radiation emanating essentially from individual combustion grate zones is detected and the regulation of the individual zones is controlled as a function of the detected radiation. By using a thermographic method, it is possible to record the temperature of the ember bed formed on the grate over a large area, that is, to depict a two-dimensional temperature profile in individual grate zones and thus each of the individual Target zones in order to optimize the combustion in the zones and thus to minimize the formation of pollutants (dioxins, nitrogen oxides .....).

This technology is actually used in waste incineration plants today, using infrared-sensitive TV cameras, which then, after appropriate image processing, indicate isotherms for the entire grate surface. With small, automatically controlled grate furnaces for e.g. This method is not used for biomass because it is too expensive, too complicated and also not necessary. Rather, the caregiver is instructed to observe the lower end of the grate at regular intervals through a shop window and then to stop the grate operation. It is clear that this method is costly, firstly, because the staff has to be paid and secondly, depends on the reliability and level of knowledge of the person.

The disadvantages mentioned can, however, be avoided if the discharge or discharge area of the grate is observed from an angle α of 10 ° to 30 °, preferably 16 ° to 20 °, for the occurrence of light emission from the axis. In the present invention, not the ember bed, but only the rust discharge and not by imaging, but only by an integral detection of the radiation in the wavelength range of visible light in the field of view of the sensor (s) is observed. The present invention would give too little information to control the overall combustion on the grate, but it helps to minimize the dumping of combustible matter into the ashes and furthermore makes better use of the grate length, which also reduces pollutant formation.

In a device according to the invention for carrying out the method described above, in a manner known per se, at least one sensor element which is sensitive in the wavelength range of the light emitted by the embers is aligned with the discharge or discharge area of the grate, the signals of the sensor element (s) optionally after passage by an amplifier, to the input of a control element for the grate feed and / or the fuel supply to the grate and / or the air supply to the grate, in particular to its discharge or discharge area, can be placed, and the at least one Sensor element is designed for the reception of light and a shielding of radiation from other rust areas is provided, which results in a viewing angle of the sensor element of 10 ° to 30 °, preferably 16 ° to 20 °, preferably from the wall of an opening in the combustion chamber wall in which the sensor element is arranged, at least with its light receiver, for example a glass rod, or a sleeve is formed which surrounds the light receiver. A particularly favorable embodiment for observing the ash bed is thereby achieved, with which it can be recognized whether the ash bed still has embers visible, whereby disturbing influences from neighboring regions are eliminated due to the shielding.

Advantageously, in addition to the at least one sensor element that is designed to receive light from the removal or discharge area of the grate, at least one further sensor element that is sensitive to the reception of light in the wavelength range of the light emitted by the embers can be provided comes from an area which adjoins the at least one sensor element for observing the discharge or discharge area, towards the feed area and preferably has approximately the same width as the observed discharge or discharge area, and which shields against radiation other than that observed at the disposal or Discharge area adjacent areas is provided and the shield is preferably formed by a sleeve surrounding the light receiver of the sensor element or by the wall of an opening in the combustion chamber wall, in which the further sensor element is arranged at least with its light receiver, for example a glass rod, and wherein the signals of the further sensor element, if necessary after passing through an amplifier, can be placed at the input of a control element for the grate advance and / or the fuel supply to the grate and / or the air supply to the grate, in particular to its discharge or discharge area. This has the advantage that, based on the additional observation, it is possible to determine up to which rust area there is still embers in order to estimate the fuel feed on the grate in this way can. It can also be determined whether the entire material has been burned due to the air supply or whether there is still flammable residual material. A feed that is too large on the grate can also be recognized in good time. The light receiver, for example glass rod, the sensor elements can be connected directly or in a manner known per se to the electronic signal transmitter of the sensor element via a glass fiber bundle, so that the signal transmitter can be arranged away from the light receiver and protected against heat radiation. As mentioned, it is known per se to guide light beams transmitted by sensor elements via optical fiber bundles from the sensor elements to the signal transmitter. This known design is a possibility of observing a burner, the glass fiber bundles opening out in the center of the burner, so that it can be observed directly. In the present case, however, it is a matter of monitoring a bed of embers for visible embers, in which appropriate shielding and also removal of the signal transmitters is essential, owing to the high heat radiation from the embers. In order to prevent the entry of incorrect air in the area of the grate, the sleeve surrounding the light receiver, for example glass rod, can be provided on the outside with at least one, preferably with three disks, which are arranged in the space between the sleeve and the wall surrounding the sleeve.

Finally, the space between the light receiver and the inner wall of the sleeve can be supplied with a cooling medium, preferably air, via a connecting piece, as a result of which safe operation and high durability of the device are achieved even in the case of higher temperatures in the vicinity of the grate.

• Fig. 1 schematisch einen Längsschnitt durch die Brennkammer eines Kessels mit Vorschubrost,
• Fig. 2 ein Detail aus Fig. 1 und
• Fig. 3 einen Längsschnitt durch ein Detail eines Sensors.

The invention is explained below with reference to the drawing, for example. Show it,

• 1 schematically shows a longitudinal section through the combustion chamber of a boiler with a moving grate,
• Fig. 2 shows a detail from Fig. 1 and
• Fig. 3 shows a longitudinal section through a detail of a sensor.

Solid fuel is added to the sloping feed grate according to FIG. 1 and is conveyed to the right by the movement of the grate elements and the inclination of the grate. In the zone labeled 1, the fuel is first dried, in zone 2 gasification and combustion take place and in zone 3 some fuel residues still burn. For the most part, Zone 3 is already covered with ash. The ash 5 is finally discharged from the combustion chamber via the discharge 4. Primary air 7 flows through the grate from below and is allocated to the grate in accordance with the operating conditions prevailing thereon.

The criterion for ash disposal without fuel parts is now not the ember bed height, which can be e.g. is measured at position 80, but the presence of embers at the bottom of the grate.

The invention consists in monitoring the burnout zone 3 of the grate by one or more optical sensors. These optical sensors are sensitive to the light of the embers and give a signal which is proportional to the received light intensity. Depending on the width of the bed, one or more of the sensors 8 are mounted next to one another in such a way that they are watching the discharge area of the grate. These sensors should not receive a light signal in normal operation. In principle, the sensors 8 are sufficient for regulating the system with the aim of not throwing off any burning fuel, and one could basically get by with the sensor (s) 8. However, it has proven to be advantageous to mount one or more sensors 9 in the case of very wide systems, which are directed towards that part of the fuel bed which is located just above the observation area of the sensors 8. In normal operation, this sensor (sensors) 9 should very well receive a light signal which indicates that there is still embers here and that the grate is thus covered with fuel over its entire length. In the case of extreme part-load operation, the sensor 9 will also not be able to see embers.

The operation of the grate is controlled as follows based on the information from sensors 8 and 9:

When the bottom group of sensors 8 sees embers, the rust advance reduced and - if possible - the air supply to the lower grate area also increased. On the one hand, this results in a longer residence time of the fuel on the grate and, on the other hand, a higher air supply for the fuel to burn out. If these two measures do not yet lead to the goal - ie that sensor 8 no longer sees embers - then the fuel feed 6 must be reduced. Most of the time the fuel is so wet that it ignites too late on the grate and therefore there is not enough time for the burnout.

However, if neither the sensor 8 nor the sensor 9 sees glowing during normal operation, the grate advance should be accelerated in order to cover the grate with fuel as completely as possible. The grate is dimensioned for an even fuel occupancy and can only be operated under this condition with a minimal pollutant emission.

A sensor 14 sensitive to light is an electronic component and therefore must not be exposed to a higher temperature. In addition, the level of the signal depends on the operating temperature of the electronic sensor. It is therefore necessary to place the sensor in such a way that on the one hand it can very well receive the light from the combustion chamber and on the other hand it is in a place where it is not affected by the temperature of the combustion chamber. Usually, a temperature of 50 °, at most 70 °, must never be exceeded - not even if there is a malfunction, for example as a result of a power failure, and possible cooling by air is no longer available. This problem is solved in that, by means of a glass rod 10, the radiation emanating from the embers is collected and guided through it to its end located outside the combustion chamber, as shown in FIG. 2. The glass rod 10 is located in a protective sleeve which is shown in more detail in FIG. 3. At its front end surface 31, the glass rod receives the radiation from the embers, the viewing angle α of the glass rod advantageously being restricted between 10 ° and 30 °. The viewing angle is advantageously determined at 16 ° to 20 ° by means of the optical properties. At this point of view, it is possible, on the one hand, to place the rod at a safe distance behind the front face 12 of the To end thermal insulation 13 of the combustion chamber in order to avoid overheating and to keep the pollution as low as possible. On the other hand, a representative part of the surface of the grate can be detected at this angle. If the length of the glass rod is sufficient (for example 200 mm outside the thermal insulation of the combustion chamber), the optical sensor system 14 can be attached at its end. Another possible solution is that a flexible optical fiber cable is connected to the end of the glass rod 10, which leads together with the optical fiber cables from adjacent sensors to a common housing in which the sensor system of all glass rods is housed. This solution has the advantage that the sensitive electronic part can be installed away from all risks from fire and water. The fiber optic cables can be almost any length. The diameter of the glass rod 10 is between 1 and 6 mm, preferably between 2 and 4.5 mm. If the glass rod 10 becomes too thin, the mechanical strength and the amount of light received are insufficient, if it becomes too thick, then it becomes too expensive. The length of the glass rod is advantageously between 200 and 600 mm, since - if it is shorter than 200 mm - the cold end is too far from the hot combustion chamber and a glass rod that is too long is only expensive and has no advantage.

In Fig. 3, a glass rod 10 is shown as an example in its protective sleeve. The glass rod 10 is housed in a sleeve 24 and glued with its rear end 15 to this sleeve with a heat-resistant adhesive. The front end of the glass rod 10 is loosely guided through a bore 16. This loose guidance is necessary in order to allow the thermal expansion to be stress-free. The front end 3 of the glass rod is surmounted by a continuation 17 of the sleeve 24, on the one hand to offer mechanical protection and on the other hand to limit the viewing angle of the glass rod to such an extent that it does not co-detect the refractory lining 12. On the outside of the sleeve 24, one to three disks 18 are attached in order to prevent the penetration of heat radiation into the rear part of the connecting piece as far as possible. The disks 18 have, distributed around the circumference, a number of holes for purging air which is passed through the nozzle 19 and which is partly through the hole 20 emerges in the area between the sleeve and the protective tube 29 - to flow through. The rest of the purge air flows through the bore 21 past the glass rod in the direction of the combustion chamber. The air flow entering through the nozzle 19 is between 0.5 and 2 kg / h.

In the case of a sufficiently long glass rod 10, the optical sensor 14 can be attached directly to the rear end, which can be done according to the known methods of the prior art. Another embodiment variant according to the invention is that a flexible optical fiber cable (one for each glass rod) is led from the rear end of the glass rod 10 to a common housing in which a sensor with the associated electronics is located for each glass rod. The processing of the sensor signal takes place according to the known methods of electronics. Likewise, the signal emitted from the electronics is connected to the control elements for the grate operation using known technology.

Claims (6)

Method for regulating a grate firing system with movable grate, from which ash is discharged or discharged over an end region of the grate, the material on the grate being observed for the presence of embers, if appropriate, at several points in the material path and, depending on the observation, the air supply and / or the conveying speed of the fuel is regulated, characterized in that the discharge or discharge area of the grate is observed with a viewing angle α of 10 ° to 30 °, preferably 16 ° to 20 °, for the occurrence of light emission from the ash. Device for carrying out a method according to claim 1, characterized in that, in a manner known per se, at least one sensor element (8) which is sensitive in the wavelength range of the light emitted by the embers is aligned with the discharge or discharge area of the grate, the signals of the . The sensor elements (8), optionally after passage through an amplifier, can be placed at the input of a control element for the grate feed and / or the fuel supply to the grate and / or the air supply to the grate, in particular to its removal or discharge area, and that the at least one sensor element (8) is designed for the reception of light and a shielding of radiation from other rust areas is provided, which results in a viewing angle of the sensor element of 10 ° to 30 °, preferably 16 ° to 20 °, preferably from the wall of a Breakthrough of the combustion chamber wall (13) in which the sensor element (8), at least with its light receiver he, e.g. a glass rod (10), or a sleeve (24) surrounding the light receiver is formed. Apparatus according to claim 2, characterized in that in addition to the at least one sensor element (8) which is designed to receive light from the removal or discharge area of the grate, at least one further, In the wavelength range of the light emitted by the glow-sensitive sensor element (9) is provided, which is oriented to the reception of light that comes from an area that is connected to the at least one sensor element (8) for the observation of the discharge or Discharge area, adjoins the feed area and preferably has approximately the same width as the observed discharge or discharge area, and that shielding against radiation from areas other than the observed area adjacent to the discharge or discharge area is provided and that the shielding is preferably from a sleeve (24) surrounding the light receiver of the sensor element (9) or from the wall of an opening in the combustion chamber wall is formed, in which the further sensor element (9) is arranged at least with its light receiver, for example a glass rod (10), and that Signals from the further sensor element (9), if necessary after passing through an amplifier the input of a control element for the grate feed and / or the fuel supply to the grate and / or the air supply to the grate, in particular to its discharge or discharge area, can be placed. Device according to claim 2 or 3, characterized in that the light receiver, e.g. Glass rod, the sensor elements (8, 9) directly or in a known manner via a glass fiber bundle with the electronic signal transmitter (14) of the sensor element (8, 9), so that the signal transmitter (14) away from the light receiver, protected against heat radiation , can be arranged. Device according to one of claims 2 to 4, characterized in that the light receiver, e.g. Glass rod (10), surrounding sleeve (24) is provided on the outside with at least one, preferably with three disks (18) which are arranged in the space between the sleeve (24) and the wall surrounding the sleeve (24). Device according to one of claims 2 to 5, characterized in that a cooling medium, preferably air, can be supplied to the space between the light receiver and the inner wall of the sleeve (24) via a connecting piece (19).

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