SE517399C2 - Procedure for automated combustion with solid fuel - Google Patents

Abstract

The invention relates to a method for automatized combustion of solid fuel in a combustion apparatus which comprises a burner (1) which is connected to a boiler (400) and has a feeding-in opening (63, 62) for fuel and an outlet opening (3) which opens in a combustion chamber (401) inside the boiler which comprises a convection unit (402) and a flue gas pipe (407) for waste flue gases containing CO2 and not combusted O2, the combustion apparatus comprising a device (27) for feeding combustion air into the burner, and a fuel charge feeder (200, 212) for fuel provided to be driven by a motor (211), here called fuel charge feeding motor, the operation of the fuel charge feeding motor (211) being regulated by command from a control unit (300) in dependency on measured values transmitted to the control unit (300) in dependency on measured values transmitted to the control unit (300) and in dependency of the heat power the burner shall generate, and a measuring device (408) arranged for measuring the content of CO2 and or O2 in the flue gases. The invention is characterized by said measuring device (408) transmitting measuring signal to said cotrol unit (300) regarding the contents of the flue gases and that the contenets of the flue gases is regualted by means of the control unit (300) regulated the fuel charge feeding motor with reference to the values measured in the flue gases, maintaining an optimal content of the gas measured by the measuring device (408) in the flue pipe (407). The invention also relates to a combustion apparatus in which the above mentioned procedure is being applied.

Description

25 30 35 517 399 2 P1533 oil burner, is that the quality of the fuel can vary considerably between different deliveries, and sometimes also one and the same delivery. The solid fuel often varies in volume weight, density and size between different consignments, but sometimes also in one and the same consignment. Thus, optimization of the combustion efficiency of solid fuel burners is hindered by a constantly varying volume weight of the fuel. From an efficiency point of view, it is desired that virtually all the oxygen supplied to the combustion chamber is consumed after complete combustion, ie. in the flue gases leaving via a flue gas line. However, if an insufficient amount of oxygen is supplied to the combustion chamber, unburned pyrolysis gases will be produced, which entails an explosion hazard. Thus, in practice, it must always be ensured that a certain amount of unused oxygen remains in the flue gases in order to eliminate the risk of explosion.

In connection with solid fuel burners, it has been shown that supervisory personnel, in order to be on the safe side, often shut down the fuel, so that variation in fuel quality can never cause saturation. Instead, a higher lu fi surplus and thus a lower efficiency is accepted. The reason why this is the case is thus mainly due to the constantly varying volume weight of the solid fuel, in combination with difficulties in being able to optimize the efficiency in a safe manner. The difficulty with the optimization is due, among other things, to the long delay time between combustion and the possibility of being able to ascertain a change in the concentrations in the flue gases, ie. it takes a long time from the time a new fuel starts to burn until the flue gases from this new fuel can be measured and analyzed.

Attempts, which have so far been made to automatically regulate efficiency, have always been based on changing the air supply. When the air supply changes, however, other variables also change which are decisive for how the combustion takes place and thus what residual oxygen content is obtained in the combustion gases. There are many different attempts made in this direction, but for various reasons so far there is no solution to the problem that can be considered satisfactory.

BRIEF DESCRIPTION OF THE INVENTION The object of the invention is to solve the above-mentioned problems, which are achieved by a process of the type indicated in the preamble, characterized in that the dosing motor operates intermittently and delivers the fuel in batches to the burner. is outside a setpoint, the control unit affects the operating time of the dosing motor depending on the value of the measurement signal, so that the operating time is either increased or decreased to control the flue gas content towards the desired setpoint, so that an optimal content of the of the gas measured by the measuring device is maintained in the flue gas line.

Thanks to this total innovation, optimizing the combustion reaction by regulating the amount of fuel as a function of the residual oxygen value in the flue gases, while keeping the supply constant in contrast to conventional optimization technology, you gain many unexpected benefits and can safely ensure that the combustion device works at peak power while the risk of explosion can be eliminated.

According to further aspects of the invention it applies that - the combustion air supply is kept substantially constant while control of the flue gas content is carried out, the lu supply being preferably arranged by means of a motor driven by a motor, the speed of which is kept at a constant level during approximate control of the flue gas content. works intermittently and delivers the fuel in batches to the burner and that, if the measuring signal from the measuring device regarding the content of the flue gases is outside a setpoint, the control unit affects the operating time of the metering motor depending on the value of the measuring signal, so that the operating time is increased or decreased desired setpoint, - a larger change in the operating time of the metering engine is made if the residual oxygen content in the flue gases is below the setpoint than if the residual oxygen content is above the setpoint, - a certain time interval is allowed to pass after a change in operating time of the metering engine. any further control takes place, in order to wait for the necessary time delay in order to ascertain the effect of the last change made, preferably the time interval is between 30 seconds and 5 minutes, more preferably more than 1 minute, whereby preferably the control change of the pulse length of the dosing motor is at least two times greater in the case of a downward adjustment than in the case of an upward adjustment, for maintenance combustion and a maximum power mode, whereby preferably the temperature of the water in a riser line is transmitted to a control unit for automatic selection of the power mode, andthe metered fuel so that it is fed into the burner in an even flow. 10 15 20 25 30 35 517 399 4 P1533 Furthermore, the invention relates to a firing device for automated firing with solid fuel, comprising a burner, which is connected to a boiler and has an inlet opening for fuel in the rear end of the burner outside the boiler, an outlet opening for fully or partially combusted flue gases in the front end of the burner which opens into a combustion chamber inside the boiler, which comprises a convection part and a flue gas line for flue gases containing CO 2 and combusted O 2, , arranged to be driven by a motor, herein referred to as a dosing motor, characterized by a control unit and a meter for conveying the Oz content of exhaust fumes to the control unit, each unit being controlled to adjust the operation of the dosing motor about the measured value of the Og content conveyed to the control unit is outside a setpoint stored in a computer in the control unit at the same time as the lu supply is kept substantially constant so that the Og content in the flue gases is kept within a desired interval.

According to a further preferred embodiment, said meter consists of a lambda probe.

Additional features and aspects of the invention will be apparent from the following description of a preferred embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS In the following description of a preferred embodiment of the invention, reference will be made to the accompanying drawings, of which Fig. 1 illustrates, partly schematically, an automated firing device according to the invention, Fig. 2 shows a preferred movement pattern for a dosing device Fig. 3 shows a power / power mode diagram for a control program suitable for use with the invention, Fig. 4 shows a preferred embodiment for power optimization according to the invention, and, Fig. 5 shows the same as Fig. 4 but under different conditions.

DETAILED DESCRIPTION Fig. 1 shows, by way of example, a firing device, which can advantageously be adapted to work according to the invention. The main parts of the burner device consist of a PIS33 burner unit 100, a dosing unit 200 and a control unit 300. The burner unit 100 is connected to a schematically shown boiler 400, which may be of a conventional type. In the boiler 400 there is a combustion chamber 401, which is adjacent to a convection part 402. To the convection part 402 are connected lines 403 for rising water, and a flue gas line 407 for removing the combustion gases / flue gases. Arranged in the flue gas line 407 is a meter 408 intended to convey the content of residual oxygen in the combustion gases to the control unit 300. Preferably, this meter 408 consists of a lambda probe. In the riser line 403 there is a temperature sensor 404 which transmits the temperature of the riser water to the control unit 300.

The burner assembly 100 includes a solid fuel burner 1, which according to the preferred embodiment shown is circular-cylindrical and is rotatable about a slightly inclined axis of rotation. It has an outer end 24 for mounting the entire burner assembly 100 on a boiler door to the schematically shown boiler 400, so that an opening 3 for combustion gases in the front end of the burner opens into the combustion chamber 401 of the boiler.

The interior of the burner forms a main or primary combustion chamber 13 and a post- or secondary combustion chamber 14.

The other components of the boiler unit 100 consist of a fl shaft 27 for combustion lu fl z, a fan motor 22, in this text also referred to as a second motor, for rotation of the fan 27 (alternatively two or fl era fl spigots can be arranged with associated motors, of which a fan with associated motor for blowing primary combustion hatch fi in the main or primary combustion chamber 13 and another fl coupled to the associated engine for blowing the secondary combustion hatch fi into the primary or secondary combustion chamber 14), a core-free feed screw 40 in a fuel feed tube 18 fourth engine, for rotation of the feed shaft 40, a stirring motor 34, in this text also called first engine, for rotation of the reactor drum 1 about the inclined axis of rotation 2 and the lower part of a downcomer 42 for the fuel. The angle of inclination of the reactor drum 1 towards the horizontal plane, with the front opening 3 of the reactor drum for combustion gas directed obliquely upwards, amounts to 1 5 °.

The rear end wall of the reactor drum 1, as well as the main part of its cylindrical part, is double-walled. The space between the inner 65, 66 and the outer walls has been designated 54. The inner walls 65, 66 are provided with holes 55 both in the cylindrical part and in the rear end portion for initiating the combustion chamber into the main combustion chamber 13. The holes in the inner cylindrical wall 66 are arranged more densely in the rear part of the primary combustion chamber 13 and slightly sparsely distributed in the front part. Furthermore, the space 54 is divided into channels by longitudinal, radially directed, lamella-shaped partitions in the cylindrical part of the reactor drum and in the rear end of the drum there are partitions, which between them form circular sector-shaped channels for combustion hatches fi. The partitions in the rear part and in the cylindrical part merge into each other, so that each circular sector-shaped channel in the end wall communicates with a longitudinal channel in the cylindrical part, but only with one and not with any further such longitudinal channel.

The air flows through these ducts can be regulated by means of valve means not shown, so that the combustion air is initiated preferably or mainly in the lower rear parts of the combustion chamber, which are located under an inner, smaller drum 60 in the rear part of the reactor drum 1, which will be described in more detail below.

The combustion hatch thus begins preferably or mainly in the parts of the main combustion chamber 13 where the fuel accumulates during combustion. As an alternative or complement, as mentioned above, two or fl era fl spouts can be arranged, which drive lu fi to the primary combustion and secondary combustion chambers, respectively. This can be particularly advantageous for burners with high effects, ie. in the order of 1 MW or greater.

The rear inner wall 65 of the drum 1 and in particular the rear part of the cylindrical inner wall 66 of the drum 1 constitute the rust of the burner 1. At the same time, the drum with its inner walls forms a rotatable device for stirring the fuel in the burner. To further ensure agitation of the fuel, carriers 56 are also provided on the inside of the reactor drum 1, which extend all the way back to the end wall 65 and are included in the rotation of the reactor drum 1.

The inner, smaller drum 60 is cylindrical and has a perforated sheath. According to the embodiment, the drum consists of a sheet metal drum with holes in the jacket, but a mesh drum is also conceivable. The holes in the jacket have been designated 61. These are so small - the diameter or largest extent amounts to a maximum of 10 mm, preferably to a maximum of 8 mm - that the fuel particles cannot pass through them to a significant degree. At the front, the drum 60 is completely open. This opening is designated 62. The drum 60 is coaxial with the reactor drum 1 and surrounds a central feed opening 63, which forms the mouth of the feed pipe 18 for the fuel fed by the feed screw 40. The diameter of the drum 60 is slightly larger than the opening 63. In the annular space 64 between the supply opening 63 and the drum 60, the rear end wall 65 of the reactor drum 1 lacks inlet openings for combustion air. The drum 60 is welded to the rear end wall of the reactor drum 1. 10 15 20 25 30 35 517 399 v Pl533 The fuel supply pipe 18 is surrounded by a concentric, tubular drive shaft 19, which at the same time constitutes a blow-in supply pipe. In the cylindrical space 20 between the feed pipe 18 and the drive shaft 19 there are, in the same way as in the cylindrical space 54 between the cylindrical outer and inner walls of the drum, longitudinally directed partitions extending between the tube 18 and the shaft 19, so that longitudinal channels are formed between said walls in the same way as the channels between the walls in the cylindrical portion of the drum 1. Each partition wall in the space 20 is thus connected to one and only one partition wall in the space 54. Thus a system of separated channels is formed, according to the embodiment eight such channels, which extend from the rear end of the pipe 19 all the way to the front end of the main combustion chamber 13, where the channels are closed by an annular end wall 47.

The rear portion of the drum 1, approximately corresponding to half the length of the drum, is surrounded by a double-walled housing 25, which is obliquely cut off at an angle corresponding to the angle of inclination of the drum and terminates with said fl end 24 for mounting the burner assembly on a boiler hatch or boiler wall. The part of the device which in Fig. 1 is to the left of the boiler 24 thus extends into the combustion chamber 401 in the boiler 400, while the parts to the right of the boiler 24 are located outside the boiler.

The combustion hatch is taken in by the fan 27 through a hatch inlet 27A and pushed in via hatch lines 51 via the valve system (not shown) into the hatch inlet pipe / shaft 19 and from its inner 20 further into the channels in the gap 54 and finally through the holes 55 into the combustion chamber 13.

For the drive motor 22, the stirring motor 34 and the feed motor 41 of the motor 27, the drum 1, and the feed screw 1, respectively, there are not shown transmissions, which, however, can in a conventional manner consist of shafts, chains, belts or other conventional elements. The feed screw 40 is arranged to be rotated by the feed motor 41 in a direction opposite to the rotation of the drum 1.

The fuel that falls into the downcomer 42 is immediately fed on by the feed screw 40. If, due to an error, the feed screw 40 does not have time to feed the fuel at the same rate as it falls down through the downpipe 42, a certain amount of fuel will collect in the lower part of the downcomer 42. This is primarily undesirable from a safety point of view. Therefore, in order to limit this possibly accumulated amount of fuel, a level monitor 70 is placed in the downcomer 42, which gives a signal to the control unit 300, if the amount of fuel in the lower part of the downcomer should rise up to the level monitor 70, then P1533 that continued dosing of fuel to the downcomer 42 is interrupted. According to the embodiment, this volume amounts to only 3 liters. In the lower part of the downcomer 42 there is also a temperature monitor 71, which is arranged to give a signal to the control unit 300, if the temperature should exceed a certain set temperature, so that the burner is emergency stopped, which means that the supply of fuel and combustion cap to the burner is stopped. As a further safety measure, a section 72 has been made of non-combustible plastic hose, which is melted if the temperature in the downcomer in said section would still exceed a certain value. Furthermore, as another precaution, the top section 73 of the downcomer is offset laterally so that fuel does not fall on the burner assembly should the plastic section 70 melt.

It will be appreciated that the burner assembly 100 shown may be varied within a wide range.

For example, the rotating drum 1, whether it contains an inner, smaller drum 60 or not, can be arranged completely horizontally. In this case, however, the drum should be made tapered, eg conically tapered, from the rear wall and fi inwards, so that the bottom of the drum has approximately the same angle of inclination as shown in the described embodiments, whereby the fuel will also accumulate on the bottom of the rear part of the drum, where the supply of primary air is concentrated. It is further conceivable that there is no sharp corner in the transition between the rear end wall and the side wall which corresponds to the mantle of the drum, but instead, for example, a bevelled transition. From a certain point of view, however, the most ideal form has a burner which has no corners at all, for example a burner with the main shape of an egg or pear cut off at both ends, where the sharper part is directed forwards towards the outlet opening. Also in this case, the burner is suitably double-walled with the space between the walls divided into channels, or otherwise provided with channels for the combustion furnace from the lu led inlet pipe, which surrounds the central fuel inlet pipe, and further outwards.

According to the preferred embodiment shown, the dosing unit 200 is connected to a storage container 201 for particulate fuel 202, preferably pellets, via an extreme conveyor screw 203, which can be rotated in a conveyor tube 204 obliquely upwards by means of a fifth motor, here referred to as extreme motor 205. the upper end of the transport pipe 203, the transported fuel falls down through a downhole 207 to an intermediate storage 208 for fuel.

An upwardly sloping metering tube 210 has a rear inlet port for fuel from the intermediate feedstock 208. In the metering tube 210 there is a metering screw 212, which is rotatable with variable variable, in particular intermittently rotatable with variable frequency, by means of of a metering motor 211. The metering tube 210 opens at its upper end into the upper feed end of the downcomer 42, where a smoke detector 213 is provided to signal in the presence of smoke in the downcomer 42 to the control unit 300 to stop all motors in the combustion plant. A temperature monitor 217 is provided in the upper part of or over the downcomer 42. If the temperature in the area of the temperature monitor 217 should rise to a certain set value, the temperature monitor 217 (which is not current-dependent) gives command directly to a non-current-dependent valve, so that water is supplied to a sprinkler 214 at the top of the downcomer 42 for water spraying of the superheated area.

The principles of the operation of the firing device shown are based on the control unit 300 being arranged to be able to be set to a number of fixed power modes, according to the embodiment eight power modes. Using a number of fixed power modes greatly facilitates the tuning of the system. By power mode is meant that the burner 1 at each such power position must emit a certain heat power, which in the convection part 402 of the boiler 400 can be used to heat the boiler water. In a non-limiting exemplary embodiment of the invention, the maximum power of the burner is 100 kW, which corresponds to power mode E8, see Fig. 3. Power mode E1 is a maintenance mode, where the burner generates 2 kW. At power modes E2, E3, E4, ..E7. the burner 1, by programming the control unit 300, shall emit 10, 25, 40, 55, 70 and 85 kW respectively. The temperature of the water in a riser line 403 is suitably measured with a resistive thermometer 404, which emits an analog signal with a strength in relation to the temperature. The measurement signal is transmitted via an analogue digital converter 405, Fig. 5, to a main CPU 308 (Computer Processing Unit, ie a microprocessor or so-called PROM) in the control unit 300. The basic principle is that the output of the burner 1 is switched to a higher power mode , e.g. from power mode E6 where the burner emits 70 kW to power mode E7 where the burner emits 85 kW, if the temperature in the riser water line 403 should fall below a certain setpoint, e.g. 80 ° C, with a certain set margin. Correspondingly, it is switched to a lower power position if the temperature in the riser water line 403 should rise above the upper margin of the setpoint. In this way, the output power of the burner can oscillate between certain fixed power modes, which, however, does not mean, as will be seen from the following, that the mode of operation of the combustion plant acquires a jerky character. On the contrary, the switching between the different power modes takes place smoothly, despite the seemingly jumpy nature, which is likely to give a high efficiency and very low emission of unwanted products in the flue gases. How the burner unit 100 and the dosing unit 200 work in cooperation with each other in dependence on the control unit 300 at the different power positions will now be explained, whereby for simplification purposes it is assumed that the residual oxygen content is within an acceptable range. 10 15 20 25 30 35 517 399 10 P1533 Fig. 2 schematically shows the intermittent movement pattern of the burner and the metering screw 212. The fan motor 22 and other motors rotate in connection with steady-state at speeds which are so adapted to each other that it is blown in for - the amount of combustion air per unit of time corresponds to the amount of fuel dosed per unit of time in order to achieve optimal combustion. Combustion hatch is then sucked in through inlet 27A and blown via the line 51 through the openings 55 in the walls 65, 66 of the grate / burner 1. The burner 1 is rotated intermittently for 1 second alternating with stationary for 3 seconds. The metering screw 212 delivers doses intermittently in pulses of 5 seconds each alternating with the metering screw stationary for 40 seconds. The metering screw 212. picks up pellets from the intermediate bearing 208, which are always kept filled by means of the external screw 203 and its motor 205, which starts as soon as the level of fuel in the intermediate storage 208 has fallen below a certain level, which is detected by a position sensor 215 the control unit 300 stops the extemmotom 205.

The pellet doses which fall down through the downcomer 42 end up in the feed pipe 18 and are successively fed forward by the continuously rotating feed screw 40. At the same time as they are fed forward in the pipe 18 by the screw 40 the pellets are also spread out, i.e. the dose which falls down through the downcomer 42 and is distributed by the screw 40 in such a way that the fuel is delivered in the inner basket in a relatively even flow. The spreading effect is made more efficient by the screw 40 having no core. In the basket 60 the pellets are preheated before the fuel leaves the hose / basket 60 through its opening 62 in order to fall as a further leveling i in the drum / basket 60 onto the inclined bottom / voice, which consists of the inner, perforated jacket 6 of the burner / drum 1.

Due to the setting of the fuel metering and the amount of fuel according to the control program, the burner 1 in power mode E2 generates 10 kW shortly after power mode switching according to the example. Should the power not be sufficient, ski fi as, after a time also set in the control program, automatically to the next power mode, E3, (see Fig. 3), to increase the output power. "In power mode E3 -E8, the burner 1 rotates continuously at a certain controlled speed.

The dosing of pellets by means of the dosing screw 211 in the dosing 200 increases and in proportion thereto the amount of fuel eluated by the 27 27 per unit time, so that the burner 1 in each power position emits the intended power. However, the metering screw 212 is still rotated intermittently but in each higher power position with increasingly shorter pauses between the metering pulses. The feed clamp 40 continues in all power steps E3 -E8 to rotate continuously at an unchanged speed to give the desired equalized feed flow of pellets into the burner.

The power escalation procedure continues by shifting step E3 to step E4, then to step E5, etc., each step having a duration set in the program, e.g. 2 min.

This step-by-step escalation of power generated from the burner continues until the set temperature of the water in the riser line 42 is reached, e.g. 80 ° C. If this occurs e.g. in power stage E7, where the output power according to the example is 85 kW, and if the desired accuracy is set in the control unit 300 to be at 2 ° C, the following occurs if the temperature of the water in the riser line 302 rises to 82 ° C: the dosage of pellets with the dispenser 200, as well as the drum 1, the speed is immediately reduced to the values applicable to the nearest lower power mode, in this case for power mode E6, while the fan 27 continues to blow the combustion hatch into the combustion chamber 13 according to the e7 mode program. The fan continues to blow in an excess of combustion air until the excess fuel in the burner has been burned away, so that the remaining amount of fuel in the burner / drum will correspond to the conditions under power mode E6. This post-blow-in period, preferably 1-5 minutes, preferably about 2 minutes, is programmed into the computer of the control unit 300 to eliminate the risk of pyrolysis gases (risk of explosion) being formed, which can thus occur if insufficient amount of oxygen is supplied. Thereafter, the speed of the kt gear is reduced to the normal speed for the E6 position. The burner now continues to operate in power mode E6 according to the set program. This lasts as long as the temperature stays at 80 at 2 ° C. In a normal case, when the changes in ambient temperature, consumption of hot water, etc. are not remarkable, the temperature will eventually drop to 78 ° C. In this case, skiñas immediately, or with some delay to avoid difficult-to-control oscillations in the system, return to power mode E7. In this way, the combustion plant can oscillate in a controlled manner between a couple of power modes.

Because it is thus possible to work at a number of different power modes with delays between the power modes, no major jumps in the function arise. The system can therefore be described as modulating, as it is constantly adapted to the power demand in the property where the heating plant is located.

If the meter 408 in the flue gas line 407 were to convey that the residual oxygen content is not within a setpoint range, for example if the residual oxygen content (for example by measuring the CO 2 content) is too high, this will be signaled to the control unit 300, the processor 308 automatic control according to the invention will take place in order to restore the optimal amount of residual oxygen and thus the optimal efficiency for the combustion. As is well known to those skilled in the art, it is a good approximation to use the knowledge that a burned oxygen molecule leads to about 1 carbon dioxide molecule. Furthermore, the oxygen content in air is normally about 21%. For safety reasons, the device should be controlled so that a maximum of 20 of the 21 parts of oxygen that are added are consumed. Thus, conversely, one can also measure oneself up to said consumption by measuring the carbon dioxide content. According to most known plants today, it is sufficient that the residual oxygen content is about 5%. As shown in Fig. 4, the fuel supply pulse will be increased to compensate for a reduced CO 2 content (increased residual oxygen content) measured by the meter 408. In order to avoid overcompensation, which in the worst case could lead to an explosion hazard, the rise of the feed time upwards in relatively small control steps. Preferably there is an increase in steps of a maximum of 10%, more preferably an increase of about 2-6%, which in the present case means an increase in the operating time of between 0.1 and 0.3 seconds for the feed screw 211. This thus leads to a additional supply of fuel without changing any other variables, so that a constant amount of air is supplied. If there is a certain desired time interval, suitably about 2 minutes, a new transmission of the residual oxygen content takes place via the meter 408, and if the setpoint has not yet been reached, a further equal change in the operating time of the feed screw 211 will take place. It will be appreciated that instead of using percentages which require a continuously calculating function in the processor 308, fixed, smaller step units may be used, for example steps of 0.1 second, to possibly simplify the system under certain circumstances. This control will thus continue until the measuring device 408 signals that the residual oxygen content is within a desired setpoint. Suitably, this setpoint is an interval, which is preferably 4% -9% with respect to the amount of residual acid.

Fig. 5 shows a reverse situation compared to what is shown in Fig. 4. Namely, a situation is shown where a new fuel batch has been added which has a higher calorific value than the previous combustion batch. The result is that a higher amount of oxygen is consumed than in the previous batch, so that a higher CO 2 content is found in the flue gases. As a consequence, the measuring unit 408 (when these flue gases have reached this one) will signal that the CO 2 content is too high, i.e. the residual oxygen content is too low. As such a fault situation entails a potential explosion hazard, the control system should be designed in such a way that a major rule change is implemented in this situation. As shown in Fig. 5, when such a measuring situation is conveyed, the control unit 300 will automatically reduce the operating time of the feed screw 211 by about 15%, i.e. in the present case a reduction of the operating time by about 0.8 seconds. As a result, in most cases the amount of residual oxygen will increase drastically, since a large excess of oxygen is then available. In connection with the next predetermined measurement, after about 2 minutes, it will then usually be possible to establish that the residual oxygen level is above the range for the setpoint, ie. CO 2 is below the interval, so that the automation then slowly compensates up the residual acid value, in accordance with what is shown in Fig. 4, until it has returned to the setpoint again. It will be appreciated that during this adjustment of the residual oxygen content, the automation regarding power modes is suitably locked at one and the same power mode, so that the control unit retains other values at one and the same level.

The invention is not limited to the above shown but can be varied within the following claims. Those skilled in the art will appreciate that the invention can be used in connection with many different types of solid fuel devices, which may differ greatly from the example above, in connection with which the invention has been described. Thus, it is understood that the invention does not depend on specific design details of, for example, the burner, the feed channels for lu fi, etc. Furthermore, it is understood that the invention can also be used in connection with continuously feeding feed devices, although an intermittent feed in most cases is more preferred.

Claims (8)

10 15 20 25 30 35 517 399 IH P1533-101 PATENT CLAIMS A method of automated solid fuel firing in a firing device comprising a burner (1), which is connected to a boiler (400) and has an inlet opening (63, 62) for fuel and an outlet opening (3), which opens into a combustion chamber (401) inside the boiler, which comprises a convection part (402) and a flue gas line (407) for exhaust flue gases containing CO 2 and unburned 02, each combustion device comprising means (27) for supplying combustion fluxes in the burner, a dispenser (200 , 212) for fuel, arranged to be driven by a motor (211), herein referred to as a metering motor, wherein the operation of the metering motor (211) is regulated on command of a control unit (300) depending on measured values transmitted to the control unit (300) and depending on the heating power which the burner is to generate, and wherein a measuring device (408) is arranged for measuring the CO 2 and / or Og content in the flue gases, said measuring device (408) emitting a measuring signal to said control unit (300) regarding the flue gas content, that the flue gas content is regulated by the control unit (300) regulating the dosing engine with respect to measured values in the flue gases and that the combustion air supply is kept substantially constant while the flue gas content is regulated, characterized by the dosing engine (211) operating intermittently and delivering the fuel in batches to the burner (1) and that, if the measuring signal from the measuring device (408) regarding the content of the flue gases is outside a setpoint, the control unit (300) influences the operating time of the metering motor (211) depending on the value of the measuring signal. either increased or decreased to control the flue gas content towards the desired setpoint, so that an optimal content of the gas measured by the measuring device (408) is maintained in the flue gas line (407). 2. A method according to claim 3, characterized in that a larger change of the operating time of the dosing engine is made if the residual oxygen content in the flue gases is below the setpoint than if the residual oxygen content is above the setpoint. 3. A method according to claim 1, characterized in that the air supply is arranged by means of a shaft (27) driven by a motor (22), the speed of which is kept at a constant level during said control of the flue gas content. Method according to claim 2, characterized in that a certain time interval (T) is allowed to pass after a change of the operating time of the dosing motor (211) has taken place, before any further regulation takes place, in order to wait for the necessary time delay in order to ascertain the effect of the last change made, the time interval (T) preferably being between 30 seconds and 5 minutes, more preferably more than 1 minute. 10 15 517 399 IS P1533-101 Method according to claim 4, characterized in that the control change of the pulse length of the dosing motor (211) is at least twice as large in a downward adjustment than in an upward adjustment. Method according to claim 1, characterized in that at least the majority of the motors (34, 22, 211) included in the firing device, preferably a stirring motor (34), a genuine motor (22) and a dosing motor (211), are rotated according to a number of different programs corresponding to an equal number of different power modes, which are distributed between a minimum power mode (E1) for maintenance combustion and a maximum power mode Method according to claim 6, characterized in that the temperature of the water in a riser line (403) is transmitted to a control unit (300) for automatic selection of power mode. Method according to any one of the preceding claims, characterized in that the dispenser (200, 212) dispenses the fuel to a feed device which operates more continuously than the dispenser by means of the dispensing motor (211) and distributes the dispensed fuel so that it is fed into the burner in an evened-out fate.