EP0716266B1 - Device and process for controlling a grate furnace with moving grate - Google Patents

Description

The invention relates to a method and a device for regulating a Grate firing with movable grate, from the ashes over an end area of the Grate is removed or discharged, with the goods located on the grate The presence of embers, if necessary, in several places along the Gutweg is observed and depending on the observation, the air supply and / or the delivery speed of the fuel is regulated.

The grate firing can be used to burn solid fuels such as Wood, bark, straw but also garbage. The grate can be an inclined (but also horizontal) stair grate, moving grate, moving grate or the like be. At the beginning of the grate, the solid fuel is added and then mechanically transported over this, the "primary air" from below the grate is fed. The ash is thrown away at the end of the grate. Normally the burning zone is in the middle of the grate and so is the grate dimensioned that there is only more ash at the end of the grate, which then from Rust is thrown into a collection or conveyor.

If the grate is overloaded, i.e. loaded with more fuel than during the Can burn on the grate, then unburned fuel is considered Embers emitted with ashes. Similar things can happen if the fuel - which is very often the case with biomass - is very wet and for that reason the Ignition is delayed. In this case, too, is still dropped burning material in the ashes. A third cause of dropping from yet burning fuel is a strong inhomogeneity, which is very common with garbage occurs. In this case, large and compact pieces of fuel cannot be found 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, ie 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 loading 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 even during the period in which no air is normally supplied to the system, air enters the combustion chamber and therefore the firing capacity cannot be reduced below a limit.

Large combustion plants use one to monitor TV camera. The screen of this TV camera is in the control room, and that Operating personnel regulate the system after observing the screen image. The Investments for a sufficiently robust image transmission system and the costs for the plant operation personnel are high and also not automatable. Recently, an automatic image evaluation has been used, by inferring the local state of the ember bed from the infrared radiation. The grate feed as well as the Optimally control the grate's air supply (DD 292 068 A5). This procedure is but extraordinarily expensive and therefore for small systems in the unattended Operation not applicable.

The method described in the patent specification DD 292068 (Steinmüller) automatically records evaluation criteria for the combustion progress and is supposed to Enable automation of control. This is used to record the radiation a burn on a grate which is essentially individual Combustion rust zones outgoing radiation detected and depending on the radiation controlled the control of the individual zones. Through commitment A thermographic process makes it possible to measure the temperature of the grate the embers bed formed, i.e. a two-dimensional one To map the temperature profile in individual rust zones and thus each of the individual Targeting zones in order to optimize combustion in the zones and to minimize the formation of pollutants (dioxins, nitrogen oxides .....).

This technology is actually used in waste incineration plants today applied, using infrared-sensitive TV cameras, which then, After appropriate image processing, specify isotherms for the entire grate surface. With small, automatically controlled grate furnaces for e.g. Biomass becomes this Method not used because it is too expensive, too complicated and not necessary is. Rather, the caregiver is instructed to do so on a regular basis To observe the intervals through a shop window and the bottom of the grate then stop the grate operation. It is obvious that this method is first is expensive because the staff must be paid and secondly by the Reliability and the level of knowledge of the person depends. It was already known (Patents Abstracts of Japan, Volume 5, No. 93 (M-74), 17/06/81; & JP - A - 56 - 040 018), the control of the air supply or the conveying speed of the Fuel by observing the emitted bed's light emission in two places of the fuel path. It is evaluated for the control combustion gradient between the two points. The two Places at which the light emission is measured in the known device are not specified in the publication. The disadvantage here is that the Control based on light emission takes place at only two points in the furnace. A result that allows conclusions to be drawn about the actual state of the furnace therefore not available for the regulation of combustion.

However, the disadvantages mentioned can be avoided if the observation of the goods on the grate in the discharge or discharge area of the grate a viewing angle (α) of 10 ° to 30 °, preferably 16 ° to 20 °, on the occurrence of Light emission from the goods in the discharge or removal area is carried out and there the radiation in the wavelength range of the visible Light is detected integrally. In the present invention, the ember bed, but only the rust discharge and not by illustration, but only by one integral detection of radiation in the wavelength range of visible light in the Field of view of the sensor (s) observed. The present invention would admit give little information to regulate the overall combustion on the grate, however, it helps to minimize the dropping of combustibles into the ashes and furthermore to make better use of the grate length, which also reduces pollutant formation.

In a device according to the invention for controlling grate firing with movable grate, from which ash is discharged via an end region of the grate or is carried out, the goods on the grate for the presence of embers possibly observed at several points along the Gutweg and depending on it from the observation of the air supply and / or the conveying speed of the Fuel is regulated, it is provided that in the discharge or discharge area of the grate in a manner known per se at least one in the wavelength range of sensitive sensor element emitted by the embers is aligned, wherein the signals of the sensor element or elements, if necessary after passage through 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 can be laid and that the at least one sensor element is designed to receive light and a viewing angle of the sensor element of 10 ° to 30 °, preferably 16 ° up to 20 °, resulting shielding against radiation from other rust areas is available. This makes a particularly favorable design for observation of the discharge or discharge area of the grate, with which are recognized can whether the material on the grate still has visible embers, due to the shielding disturbing influences from neighboring regions are switched off.

A simple to implement embodiment provides that the shielding of the at least one sensor element against radiation from other rust areas of the wall of an opening in the combustion chamber wall in which the Sensor element, at least with its light receiver, is arranged, is formed. However, the at least one sensor element can also be shielded against Radiation from other areas of rust from one enclosing the light receiver Be formed sleeve.

In addition to the at least one can advantageously receive aligned by light from the discharge or discharge area of the grate Sensor element at least one more, in the wavelength range of the embers emitted light sensitive sensor element can be provided, which on the Receiving light that comes from an area that is adjacent to that of the at least one sensor element for observing the removal or Discharge area, adjoins the feed area and preferably approximately has the same width as the observed discharge or discharge area, and wherein shielding against radiation from other than that observed at the or discharge area adjoining areas is provided and the shield preferably of a sleeve enclosing the light receiver of the sensor element or is formed by the wall of an opening in the combustion chamber wall, in which the further sensor element at least with its light receiver, e.g. one Glass rod, is arranged, and wherein the signals of the further sensor element if necessary after passing through an amplifier, to the input of a Control device for the grate feed and / or the fuel supply to the grate and / or the air supply to the grate, in particular for its removal or Discharge area, can be placed. This has the advantage that due to the additional Observation can determine up to which rust area still embers is available to estimate the fuel load on the grate can. It can also be determined whether the entire good is due to the air supply is burned or whether there is still flammable residual material. Also can be about large feed on the grate can be recognized in time. The Light receiver, e.g. Glass rod, the sensor elements directly or in itself known way over a fiber optic bundle with the electronic signal generator Be connected to the sensor element so that the signal transmitter is removed from Light receiver, protected against heat radiation, can be arranged. How cited, it is known per se, light beams transmitted by sensor elements to be led from the sensor elements to the signal generator via fiber optic bundles. At this known training is a possibility of observing one Burner, the glass fiber bundles opening out in the center of the burner, so that can be observed directly there. In the present case, however, it is about the monitoring of an ember bed for visible embers nests, in which one appropriate shielding and also due to the high heat radiation of the Embers build up a removal of the auto switch is essential. To the intrusion of To prevent incorrect air in the area of the grate, the light receiver, e.g. Glass rod, surrounding sleeve on the outside with at least one, preferably with three Disks may be provided in the space between the sleeve and the sleeve surrounding wall are arranged.

Finally, the space between the light receiver and the Inner wall of the sleeve, a cooling medium, preferably air, over a Connection piece can be supplied, so that even in the case of higher temperatures in the Close to the grate a safe working method and a high durability of the device is achieved.

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.

The sloping feed grate according to FIG. 1 becomes firmer on the left side Fuel is given up and by the movement of the grate elements and the inclination of the grate conveyed to the right. In the zone labeled 1, the fuel first dried, gasification and combustion take place in zone 2 and in the Zone 3 still burns some fuel residues. For the most part, however, is zone 3 already covered with ashes. About the discharge 4, the ash 5 is finally from the Firing chamber discharged. Primary air 7 flows through the grate from below Rust is allocated according to the prevailing operating conditions.

The criterion for ash disposal without fuel parts is now not 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 is the burnout zone 3 of the grate by one or monitor multiple optical sensors. These optical sensors are on that Light embers sensitive and give a signal which is proportional to the received light intensity is. The sensors 8 are depending on the width of the bed one or more are placed side by side so that they just line the drop area watch the rust. These sensors should not give a light signal in normal operation receive. The sensors 8 are in principle for controlling the system with the Aim not to throw off burning fuel, sufficient and you could generally get by with the sensor (s) 8. However, it has proven to be proven to be advantageous - one sensor - or, in the case of very wide systems, several sensors 9 to attach, which are directed to that part of the fuel bed that is currently located above the viewing area of the sensors 8. This sensor (Sensors) 9 should very well receive a light signal during normal operation indicates that there is still embers and that the rust is full Length is covered with fuel. The sensor is also used in extreme part-load operation 9 can't see embers.

Based on the information from sensors 8 and 9, the operation of the Grate controlled as follows:

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

However, in normal operation, neither sensor 8 nor sensor 9 sees glow, then the grate advance should be accelerated to the fullest possible to fill with fuel. The grate is for an even fuel allocation dimensioned and can only be used under this condition with a minimal Pollutant emissions are operated.

A sensor 14 sensitive to light is an electronic component and may therefore not be exposed to a higher temperature. It also hangs The level of the signal depends on the operating temperature of the electronic sensor. It is So it is necessary to place the sensor in such a way that it does on the one hand light On the other hand, it can receive from the combustion chamber in one place located where it is not affected by the temperature of the firebox. Usually a temperature of 50 °, at most 70 °, may not exceeded - not even if there is a malfunction e.g. as a result of a power failure and possible cooling by air is no longer available Available. This problem is solved by using a glass rod 10 the radiation emitted by the embers is intercepted and be on by it end located outside the combustion chamber is guided, as in FIG. 2 shown. The glass rod 10 is in a detail shown in FIG. 3 Protective sleeve. On its front end face 31, the glass rod receives the Radiation from the embers, the viewing angle α of the glass rod favorably is restricted between 10 ° and 30 °. By means of the optical properties the viewing angle is advantageously determined at 16 ° to 20 °. At this point of view, it is on the one hand, the rod at a safe distance behind the front 12 of the Thermal insulation 13 of the combustion chamber to end to overheat avoid and keep the pollution as low as possible. On the other hand, at this angle, a representative part of the surface of the grate can be detected. At sufficient length of the glass rod (e.g. 200 mm outside the heat insulation the combustion chamber), the optical sensor system 14 can be attached at its end become. Another possible solution is that at the end of the glass rod 10 a flexible fiber optic cable is connected, which together with the Fiber optic cables from neighboring sensors lead to a common housing, in which the sensors of all glass rods are housed. This solution has the Advantage that the sensitive electronic part away from all hazards Fire and water can be assembled. 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 is too thin, it is sufficient the mechanical strength and the amount of light received, it becomes too thick, then it becomes too expensive. The length of the glass rod is conveniently between 200 and 600 mm, because - if it is shorter than 200 mm - the cold end is not far from the hot combustion chamber and only a glass rod that is too long is expensive and has no advantage.

In Fig. 3, a glass rod 10 is shown as an example in its protective sleeve. Of the Glass rod 10 is housed in a sleeve 24 and with its rear end 15 with glued to this sleeve with a heat-resistant adhesive. The front end of the Glass rod 10 is loosely guided through a bore 16. This is loose guidance necessary to enable thermal expansion without tension. The front end 3 of the glass rod is surmounted by a continuation 17 of the sleeve 24, on the one hand mechanical protection and on the other hand the viewing angle of the glass rod to the extent that it does not include the refractory lining 12. On the Outside of the sleeve 24 one to three disks 18 are attached to the Penetration of heat radiation into the rear part of the connection piece as far as possible prevent. The disks 18 have a number of holes distributed around the circumference Purge air, which is passed through the nozzle 19 and partially through the bore 20 emerges in the area between the sleeve and the protective tube 29 - flow through to let. The rest of the purge air flows in through the bore 21 past the glass rod Towards the firebox. The air flow entering through the nozzle 19 is between 0.5 and 2 kg / h.

With a sufficiently long glass rod 10, the Optical sensor 14 are attached, which according to the known methods of State of the art can be done. Another according to the invention Design variant is that a flexible from the rear end of the glass rod 10 Optical fiber cable (one for each glass rod) is led to a common housing, in which has a sensor for each glass rod with the associated electronics. The sensor signal is processed according to the known methods of Electronics. Likewise, the signal emitted from the electronics is included known technology connected to the control elements for the grate operation.

Claims (10)

1. A method for regulating a grate firing with a movable grate from which ashes are carried off or removed over an end section of the grate, with the material disposed on the grate being monitored for the presence of glowing fire optionally at several locations of the path of the material, and the air supply and/or the conveying speed of the fuel being regulated depending on the monitoring, characterized in that the monitoring of the material disposed on the grate is performed in the discharge or carrying-off zone of the grate at an angle of view (α) of 10° to 30°, preferably 16° to 20°, for the occurrence of light emissions from the material located in the discharge or carrying-off zone and the radiation is integrally detected there in the wavelength range of visible light.
2. An apparatus for regulating a grate firing with a movable grate from which ashes are carried off or removed over an end section of the grate, with the material disposed on the grate being monitored for the presence of glowing fire optionally at several locations of the path of the material, and the air supply and/or the conveying speed of the fuel being regulated depending on the monitoring, characterized in that at least one sensor element (8) is in orientation with the discharge or carrying-off zone of the grate in a manner known per se, which sensor element is sensitive to the wavelength range of the light emitted by the glowing fire, with the signals of the sensor element(s) (8) being capable of being applied, optionally after passage through an amplifier, to the input of a control member for the grate advancing means and/or the fuel supply to the grate and/or the air supply to the grate, and that at least said one sensor element (8) is arranged for receiving light and a screening means against radiation from other grate areas is provided which results in an angle of view of the sensor element of 10° to 30°, preferably 16° to 20°.
3. An apparatus as claimed in claim 2, characterized in that the signals of the sensor element(s) (8) can be applied to the input of a control member for the air supply to the discharge or carrying-off zone of the grate.
4. An apparatus as claimed in claim 2, characterized in that the screening means of the said at least one sensor element against radiation from other grate areas is formed by the wall of a breakthrough of the firing chamber wall (13) in which the sensor element (8) is arranged, at least with its optical receiver.
5. An apparatus as claimed in claim 2 or 4, characterized in that the optical receiver of the at least one sensor element (8) is a glass rod (10).
6. An apparatus as claimed in claim 2, characterized in that the screening means of the at least one sensor element against radiation from other grate areas is formed by an extension (17) of a sleeve (24) of the optical receiver, which extension encloses the optical receiver.
7. An apparatus as claimed in one of the claims 2 to 6, characterized in that in addition to the at least one sensor element (8) which is oriented for receiving light from the discharge or carrying-off zone of the grate, at least one further sensor element (9) is provided which is sensitive to the wavelength range of the light emitted by the glowing fire and is oriented for receiving light coming from a zone which, toward the delivery zone, is adjacent to the zone monitored by the at least one sensor element (8) for monitoring the discharge and carrying-off zone and preferably comprises approximately the same width as the monitored discharge and carrying-off zone and that there is provided a screening means against radiation from zones different from the monitored zones which are adjacent to the discharge and carrying-off zone and that the screening means is preferably formed by an extension (17) of a sleeve (24) of the optical receiver or by the wall of a breakthrough of the firing chamber wall in which the further sensor element (9) is arranged at least with its optical receiver, e.g. a glass rod (10), and that the signals of the further sensor element (9), optionally after passing through an amplifier, can be applied to the input of a control member for the grate advancing means and/or the fuel supply to the grate and/or the air supply to the grate, in particular to its discharge or carrying-off zone.
8. An apparatus as claimed in one of the claims 2 to 7, characterized in that the optical receiver, e.g. glass rod, of the sensor elements (8, 9) is connected, either directly or in a manner known per se by way of an optical fibre bundle, with the electronic signal transmitter (14) of the sensor element (8, 9), so that the signal transmitter (14) can be arranged remote from the optical receiver, protected against heat radiation.
9. An apparatus as claimed in one of the claims 2 to 8, characterized in that the sleeve (24) enclosing the optical receiver, e.g. glass rod (10), is provided on the outside with at least one, preferably three discs (18) which are arranged in the space between the sleeve (24) and the wall enclosing the sleeve (24).
10. An apparatus as claimed in one of the claims 2 to 9, characterized in that the space between the optical receiver and the inner wall of the sleeve (24) can be supplied with a cooling medium, preferably air, by way of a connecting sleeve (19).

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