NO322436B1 - combustion Apparatus - Google Patents

Abstract

Device (3) for burning granulated solid fuel, for example wood pellets, chips and the like, including a combustion chamber (16) an air inlet (24) with a fan (25) to produce air to the combustion chamber (16) and to form a predetermined blowing of air through the combustion chamber (16) before, during and after combustion of the fuel, a dosing unit (12) for feeding fuel to the combustion chamber (16) an ignition device (28) for igniting the fuel, a control and monitoring unit ( 32) for operation of associated or interacting parts arranged in or at the combustion device (3) and also an outlet (26) for heat combustion gases from the combustion of fuel from the combustion chamber (16) to a boiler section (27) in a boiler (6) for transfer of heat to the heating system in the boiler (6), for example through water-cooled surfaces in the boiler (6). The invention is characterized by the fact that the combustion device (3) also includes a movable ash feeder (29) with a drive unit (30) controlled by the control and monitoring unit (32) for automatic discharge from the combustion chamber (16) of ash, unburnt fuel and slag products (31 ), which are formed during the combustion of the fuel.

Description

The present invention relates to a device for burning granulated solid fuel, for example wood pellets, tiles and the like including a combustion chamber, an air inlet with a fan to supply air to the combustion chamber and to form a predetermined blow-through of air through the combustion chamber before, during and after combustion of fuel, a dosing unit for supplying fuel to the combustion chamber, an ignition device for igniting the fuel, a control and monitoring unit for operation of associated or interacting parts arranged in or at the combustion device and also an outlet for hot combustion gases from the combustion of the fuel of the fuel of the combustion chamber to a boiler section in a boiler for the transfer of heat to the heating system in the boiler, for example through water-cooled surfaces in the boiler.

Combustion devices, also referred to below as burners, of the type indicated above are known in various designs, for example in Swedish patent document SE-B4050734, which shows a burner with a rotating combustion chamber for solid granulated fuel, for example in the form of pellets , or through Swedish patent SE-C-63193, which shows a furnace for burning special municipal waste. The latter combustion device also includes a rotating drum which serves as a fuel grate. Accordingly, in such combustion devices, fuel is rotated during a simultaneous combustion thereof. Combustion produces partly combustion gases, partly ash and other waste products. The largest part of ash, approximately 80-90% of all ash, follows the air flow through the burner as fly ash, which falls out from the combustion gases inside the boiler. The desire is for 100% of the ash to fall out on the outside of the burner, which normally happens if the melting point of the ash is above the temperature interval where the burner will work, that is if the melting point of the ash is above a normal operating temperature of approximately 1100°C. When incinerated at temperatures above the melting point of ash, the original powdery and light ash is transformed into pieces of fused materials, so-called sinter.

Furthermore, a publication EP 0915289 is known in which a device for burning granulated solid fuel of a type which is substantially different from the invention is shown.

However, in certain special cases and above all when burning impure fuel with too large a proportion of certain substances with less or with reducing combustion properties, the ash becomes soft and sticks together to form sinter already at lower temperatures than the aforementioned 1100°C. The basic reason or reasons for this are somewhat unclear but may depend on the content of boron and/or other flux-forming substances in the pellets, i.e. substances that lower the normal melting point of the ash particles. Fuel pellets that are to be burned in heating boilers for smaller houses are an inland renewable biofuel, which is harmless to the environment and does not produce any net increase in carbon dioxide to the atmosphere and which is, for example, produced from waste products from buildings and the sawmill industry, for example saws and planing chips. Normally, fuel pellets consist of about 10% water and about 12% pure coal, while mainly the rest of the pellets contain various hydrocarbon components. However, the content of the pellets varies greatly.

The sintering causes an obstruction of the openings necessary for the air flow through the fuel bed, and an accretion of ash, unburnt pellets and sinter slag is formed. The more sinter, the more air must be added, which leads to less efficiency for the burner as the combustion gases are diluted and because the extra added air also acts as a coolant. It should be noted that combustion devices without a rotating combustion chamber very obviously increase the problems mentioned above. The growth of ash, pellets and slag grows relatively quickly, after which a larger pile is formed from this, which can cause the position of the fuel bed to be transferred to a position that is unfavorable for its function, at the same time that the risk of backlash increases dramatically as well, that is to say that the fire seat is lifted up towards and into the fuel supply pipe, which causes sintering to be both technically difficult and also dangerous.

In many boilers there is a container in the form of a box inside the boiler, in which box the ash ends up while the front part of the burner is led into the boiler. The ashes in the box are emptied either manually or by extracting the ashes using a suction device. The ash pan can be relatively large, after which it can be emptied relatively infrequently without causing trouble. Pellet consumption, when burning pellets with an energy content of approximately 4.7 to 5 kWt/kilo is approximately 4 tonnes/year for a normal heating boiler for a small house and with a normal ash content of 0.5 to 1 percent by weight, it will not be need to empty the ash in about 1 month. By "heating boiler for a smaller house" here is meant boilers with burners with an output in the range of approximately 5-20 kW. Pellet burners used today are normally designed for higher output, approximately 30 kW, while they are unnecessarily large to be used in standard heating boilers for smaller houses.

Consequently, it is realized that the obviously prominent problem for pellet burners is sintering inside the burner itself. In a known construction with a fixed combustion chamber, a detachable grate is arranged, which grate constitutes a shelf with through holes and on top of which shelf the pellets fall down through the supply line. The described sintering blocks the opening in the grate, after which it normally has to be taken out for cleaning every week, but periodically this has to be done much more often, which thereby causes worries and irritation for the user. Because of this, it is desired that the burner must function without special tasks for longer periods, for example there must be no need for the grate to be removed/or cleaned more than once per month.

The problem of sintering can probably be reduced with certain additions to the pellet production itself, for example one or more components should be mixed in that act as catalysts or that raise the melting point, but when the willingness of those who produce the pellets to correct the aforementioned problem is low, then instead, one must work around the burner design to eliminate or at least significantly reduce the problems that accompany sintering from the ash.

The purpose of the present invention is to achieve a device for solid granulated fuel, which device eliminates or at least significantly reduces the problems mentioned above due to the growth of ash, unburnt fuel residues and other slag products such as sinter.

In accordance with the invention, the device is characterized by the fact that the combustion device also includes a movable ash supply with a drive unit, controlled by the control and monitoring unit from the automatic output of ash, unburnt fuel and slag products from the combustion chamber, which are formed during the combustion of fuel.

In accordance with further aspects for a device in accordance with the invention, it is possible that: - It is included in a system for central heating of a building, which central heating system, in addition to the aforementioned boiler with associated heating system, includes at least a further fuel supply and at least one fuel generator for an automatic supply of fuel from the fuel supply to the dosing device. - The combustion device, in addition, instead of fuel consumption and fuel supply, has a fuel supply, which is built into the dosing device. - The dosing device includes a fuel feeder for dosing fuel from the dosing device and further into the combustion chamber via a feed pipe. - The feed pipe has the shape of a preferably slightly inclined fall chute, along which pipe the fuel falls freely a specified length which is determined in advance to prevent kickback. -1 safety devices are arranged near the feed pipe, which include a temperature monitor, which alarms if the heat spreads in the pipe and/or one or more slide valves to close the feed pipe. - The fuel feeder includes a feed screw which is rotatably arranged between and near the upper end of the aforementioned feed pipe at the dosing device and either the inlet to the dosing device or to the bottom of a built-in fuel supply. - The blowing fan includes a variable speed controlled motor and is located at the rear of the combustion chamber to blow and circulate air

through the aforementioned air inlet and forward and further out through the outlet of the front part of the combustion chamber. - The combustion chamber includes outer walls, inner limiting walls and a movable inner bottom, which latter is arranged at a certain distance from the outer walls for dividing the subsequent double-walled combustion chamber into a front, a rear and a lower air chamber and two air channels along the sides in the longitudinal direction of the combustion chamber. - One, several or preferably all of the limiting walls have perforations in the form of smaller openings, holes and/or larger openings for blowing air through. - The limiting walls enclose an inner part of the combustion chamber, which inner part, together with the bottom, constitutes a fire place for burning the fuel. - The ignition device is arranged in the rear air chamber by the rear limiting wall. - The ignition device is arranged in the lower air chamber and is arranged in cooperation with the ash feeder. - The ignition device is arranged in the ash feeder, whereby the ignition device follows the forward and backward movement of the ash feeder. - The rear limiting wall has air holes into the ignition device for blowing air from the blowing fan through the ignition device and further into the fire place. - The ignition device includes an ignition coil for electrical heating of the ignition device.

- The ignition coil is fitted as an induction heater.

- The ignition device has a jacket with an air inlet to blow air from the blowing fan. - The ash feeder includes a front part and one or more elongated rods which are connected to and between the front part and the drive unit for the ash feeder. - The front part and the front end of each rod are arranged in the lower air chamber, while the drive unit and the rear end of each rod are arranged in the mantle by itself. - The mantle is arranged outside the heat-insulated combustion chamber at the rear outer wall and with each rod extending through an opening in the aforementioned rear outer wall. - The front part shaped like a box up/down, open at the back, with three sides and a perforated bottom arranged upwards, which bottom at the same time constitutes the movable inner bottom mentioned above, where one side constitutes the front edge from which the bottom and the

other two sides are arranged in a rear facing direction towards the drive unit and where the sides are arranged at a distance from the longitudinally extending outer walls of combustion chambers to form a continuation below the air ducts mentioned above. - That the ash feeder includes two end positions, a front position, the driving position, where the front position closes the lower end of the furnace and a rear position, the ash-evacuating position, where the furnace is open downwards, and between the mentioned end positions, the front part is arranged for to be transmitted using the drive unit via the rods. - The drive unit includes a fixed front stop, two sliding collars, which are movable arranged along each rod as a front and a rear sliding collar, and a spring, which is arranged between the sliding collars, an eccentric and also a fixed rear stop at the rear end of the rod. - The eccentric includes a pivot rod and two connected arms, one of which is longer than the other, and that the two connected arms are pivotally connected to each other by a mutual end portion, that the other end of the shorter connecting arm is connected to the pivot rod while the other end of the long connecting arm is rotatably fixed to the rear sliding collar. - The drive unit has a motor for operating the eccentric using the pivot rod and thereby for the forward and backward movement of the front part.

The solution by constructing an ash feeder that removes the ash, sinter deposits and any other unburnt residual fuel out of the combustion device and into the ash container in the conventional boiler constitutes a very simple construction with few parts. The burner is particularly intended to replace an oil burner in a conventional oil-fired boiler system, i.e. the basic idea is that a pellet burner is placed in a conventional heating boiler instead of the oil burner that is now so commonly used. This results in a burner which is small, easy to operate and very efficient, which, apart from the ash feeder, mainly contains only a locking fan, an ignition device and a dosing device, whereupon the burner is not expensive to manufacture and furthermore, is very reliable. In addition, the risk of backlash is almost completely eliminated.

With reference to the attached figures, the invention will now be described in more detail in what follows where: fig. 1 is a schematic drawing of parts of the combustion device for solid fuel, which is installed in a conventional central heating system in a smaller house, which central heating system also shows the fuel supply, pipes, boiler and pipe. Fig. 2 is a schematic cross-section through parts of a combustion device in accordance with the present invention, which is to be used in a central heating system in accordance with fig. 1. Fig. 3 is a schematic cross-section through parts of the combustion device in accordance with fig. 2, where the necessary air circulation is shown in more detail. Fig. 4a-f shows schematically how slag evacuation is done in the combustion device according to fig. 3.

With reference to fig. 1 shows a schematic drawing of parts of a device 3 for burning solid fuel in the form of granulated materials, for example compressed wood chip pellets or briquettes, tiles or the like with a suitable diameter of approximately 6-12mm, which is installed in a conventional central heating system 1 for heating a building 2 for example a smaller house, which central heating system 1 also shows, in relation to the combustion device 3, an independent fuel supply 4, at least one fuel supplier 5, a conventional heating boiler 6 with a known heating system (not shown), for example, a water-bearing circulation system that is provided with radiators, which system includes water-cooled surfaces in the boiler 6, and a pipe 7 for the gases that are formed.

The fuel feeder includes a motor 8 with a transfer box for operation of a feed screw 10 which is rotatably arranged in a rigid feed pipe for automatic feeding of fuel from the fuel supply 4 through a downpipe 11, preferably in the form of a flexible hose, to a smaller dosing device 12 in the combustion device 3. The fuel feeder 5 can also be provided with several feed screws 10 with an optional length determined from operational and space-dependent reasons. Feeding with a feeding screw 10 is the best alternative according to expertise in relation to safety during operation, but also other types of known fuel feeders can of course be used with the combustion device 3 in accordance with the invention. In the embodiment shown in fig. 2 of the combustion device 3, this can also, or instead of the described fuel feeder 5 with an external fuel supply 4, have a smaller fuel supply 13 which is built into the dosing device 12 itself, which can be filled manually, and then once or twice per week regularly.

The dosing device 12 includes a further fuel feeder 14 with a

drive motor 15 for automatic dosing of fuel from the dosing device 12 and further into a mainly horizontal combustion chamber 16, which is arranged below the aforementioned dosing device 12, through a feed pipe 17. The feed pipe 17, which ends in the upper part of the combustion chamber 16 is preferably in in the form of a somewhat inclined fall chute along which fuel, after feeding the correct amount of fuel with the fuel feeder 14, freely falls a specific and predetermined length to prevent kickback. Additional safety devices are arranged near the feed pipe 17. These include, for example, a thermal fuse 18, which alarms if the heat spreads up the pipe 17 and one or more sliding walls 19 to close the feed pipe 17.1 the embodiment shown in fig. 2, it further includes

fuel feeder 14 a feed screw 20 which is arranged mainly horizontally and rotatably between the vicinity of the upper end part 21 of the aforementioned feed pipe 17 of the dosing device 12 and either the inlet 22 of the downfall pipe 11 of the dosing device 12 or the bottom 23 of the built-in smaller fuel supply 13, if such is arranged.

The combustion device 3 includes, in addition to the aforementioned dosing device 12 and combustion chamber 16, an air inlet 24 with a blowing fan 24 for supplying pipes to the combustion chamber 16 for burning fuel and for transporting out combustion gases and fly ash, which are thereby produced, through an outlet 26 from the combustion chamber 16 further into a boiler section 27 in the heating boiler 6 for transferring combustion heat to the heating system in the heating boiler 6 (not shown), an automatic ignition device 28 for igniting the fuel, a movable ash feeder 29 with a drive unit 30 for raking out slag products, the ashes and unburnt fuel 31 out of the combustion chamber 16 and further into the boiler 6 and a control and monitoring unit 32 for mainly fully automatic operation of the combustion device 3 and certain or all associated or interacting parts arranged in or at the combustion device 3.

The control and monitoring unit 32 constitutes a known microprocessor-based device with sensors that are necessary for the function, for example the thermal fuse 18, not described in more detail here, however, it should be noted that with the help of the aforementioned unit 32 and through the thermostat for the boiler 6, a fully automatic system from the delivery of fuel from the supply 4 to the extraction of slag products 31 to the ash box 61 from the boiler 6, including the ability to use several pre-programmed power steps, for example 9, 12, 18, 23 kW.

The blowing fan 35 which is placed at the rear part 33 of the combustion chamber 16 to blow and to circulate air in through the said air inlet 24 and forward and further out through the outlet 26 at the front upper part 34 of the combustion chamber 16, has a silent , variable speed motor 35 with a built-in thermal switch that switches off in case of overload. The combustion chamber 16 includes partial outer walls 36, which are preferably formed into a substantially box-shaped combustion chamber 16 on the outside, partial inner limiting walls 37 and a movable inner bottom 35, which is arranged at a predetermined distance from the outer walls 36 for separation of the thereby double-walled combustion chamber 16 in a front, rear and lower air chamber 38, 39, 40 and two air channels 41, 42 along the sides of the combustion chamber 16 in the longitudinal direction thereof. In a preferred embodiment, the combustion chamber 16 forms on its outside a square tube with a square cross-section with a width of approximately 160 mm. One, several or preferably all of the limiting walls 37 have perforations in the form of smaller openings and/or larger openings 43 for blowing air through (see Fig. 3). The limiting walls 37, of which several or only one is arranged starting with a downward slope from the inside of and inside the roof 48 of the combustion chamber 16 or from one, several or all of the inside of the outer walls 36, form an internal and in a suitable manner downward funnel-shaped part 44 of the combustion chamber 16, which inner part together with a bottom 45 forms a primary place for burning fuel. The bottom 45 of the fire place 44 constitutes the grate, that is to say the usually lattice-shaped bottom 45 on which the fuel bed 46 rests during combustion and interrupted or continuous flow of air. The outlet 47 of the feed pipe 17 is suitably arranged in the ceiling 48 of the fire place 44, and in the vicinity of one or more of the inner insides of the limiting walls 37, of which one or more of the inner walls 37 have an inclined position which should give an arrangement against the fuel bed 46 for fuel which falls down in a controlled manner from the dosing device 12 above. The upper and wider tunnel end of the furnace 44 is open at the front upper part 34 of the combustion chamber 16, into the boiler section 27 and, consequently, constitutes the said outlet 26 for the combustion gases mentioned above.

The ignition device 28 for the automatic ignition of a predetermined length of fuel that has fallen from the dosing device 12 to the grate 45 (see

fig. 4e) which is called ignition assembly 49 below and which is arranged in the rear air chamber 39 at the rear limiting wall 37a. After ignition, the ignition composition 49 forms the aforementioned fuel bed 46 as mentioned above. The rear limiting wall 37a has air holes 57 into the ignition device 28 for blowing air from the blowing fan 25, through the ignition device 28 and further into the fire place 44. Preferably, the air holes 57 are oval to allow an optimal air flow. In the embodiment shown in the figures, the ignition device 28 includes an ignition coil 50 of any known type, for example including a so-called cantal wire for electrically heating the ignition device 28 to a temperature of about 800°C, where the cantal wire has a temperature of about 1100°C. The ignition coil may also be provided as an induction heater (not shown).

The ash feeder 29 includes a front part 51, also called a rake below, and one or more elongated rods 52 which are connected at and between the front part 51 and the drive unit 30 for feeding the ash. The rake 51 and the front end of each rod 52 are arranged in the lower air chamber 40, while the drive unit 30 and the rear end of each rod 52 are arranged in an enclosure 53 for themselves, suitably arranged outside the heat-insulated combustion chamber 16 at the rear outer wall 36a and with each rod 52 extending through a hole 60 in the same 36a. The front part 51 has the shape of a box with three sides 54, 55, 56, turned upside down, which box is open at the back, and a perforated bottom which is arranged and which bottom also forms the grate 45 as mentioned above. A side 54 constitutes a front edge which is mainly vertical and from which the bottom 45 and the other two sides 55, 56 extend backwards and towards the drive unit 30. The sides 55, 56 in the longitudinal direction are arranged with mainly the same distance from the outer walls 36 of the combustion chamber 16 in the longitudinal direction as the inner limiting walls 37 in the longitudinal direction form an extension down from the said air ducts mentioned above. The ash feeder 29 includes two end positions, a front position, the operative position 58, whereby the rake 51 closes the lower end of the fire place 44, see fig. 4a, and a rear position, the ash-evacuating position, where the fire place 44 is almost completely open downwards, see fig. 4c, between which end positions 58, 59 the rake 51 is arranged to be transferred by means of the drive unit 30 via the rods 52. The ignition device 28 can also be arranged inside the ash feeder 29, so that the ignition device 28 follows the ash feeder 29 and its forward and backward movements under the fire place 44. The ignition device 28 has a casing 71 with air inlet 72 to blow air from the blowing fan 25.

The drive unit 30, see fig. 3 and 4, includes a fixed front stopper 62 at each rod hole 60, suitably formed by the separating wall 36a between the combustion chamber 16 and the enclosure 53, sliding collars 63, 64 which are arranged movably along said rod 52 and a spring 65, which, in the embodiment shown in fig. 3 and 4 are arranged around each rod 52 between the sliding collars 63, 64, an eccentric 66 which includes a pivot arm 62 and two connecting arms 68, 69 and a fixed rear stop 70 arranged at the rear end of the arm 52. The two connecting arms 68 , 69 of which one 68 is substantially twice as long as the other 69 are pivotally connected to each other at one of their end portions. The other end of the shorter connecting arm 69 is connected to the pivot arm 67 while the other end of the long connecting arm 68 is rotatably connected to the rear sliding collar 64. Furthermore, the drive unit has a motor, not shown, for operating the eccentric 66 via the pivot arm 67 and thereby for the forward and backward movements of the rake 51.

The function and use of the combustion device 3 in accordance with the invention is as follows: With the help of the present electronics for heating the boiler 6 and controlled by the control and monitoring unit 30, the combustion device starts and stops automatically according to the setting on the operative thermostat in the central heating system 1. Before start of the combustion device 3, the ash feeder 29 has been moved to its forward operative position 58, see fig. 4a, so that the bottom 45 of the furnace 44 is closed and the fuel feeder 14 has fed fuel to the dosing device 12, see fig. 1. At start-up, a small amount of fuel is automatically fed with the feed screw 10 into the dosing device 12, see fig. 2, activated by the engine 15, which amount falls down along the feed pipe 17 so that an ignition mixture 49 which is necessary for ignition of the fire bed 46 is formed by the bottom 45 of the fire place 44 and in front of the air holes 57 in the rear limiting wall 37a falls into the ignition device 28, see fig. 4e. The ignition device 28, see fig. 2 and 3, is initiated whereupon the ignition coil 50 is heated significantly to approximately 750-800°C, which takes approximately 2 min. When a correct temperature has been reached for the ignition coil 50, the motor 35 starts the blowing fan 25 so that air is blown in through the air inlet 24 to the rear air chamber 39 and on through the air inlet 72 in the mantle 71 of the ignition device 28 and beyond and past the ignition coil 50. Accordingly, no air is blown during heating of the ignition coil 50, as this would only cool it. Alternatively, fuel can also be fed during the time that the ignition coil 50 is heated to the specified temperature and until an ignition composition 49 with a suitable combustion time is received at the bottom 45 of the furnace 44.

After about two minutes, the blowing fan 25 starts so that short, interrupted bursts of very hot air are forced out and/or up through the ignition assembly 49 through the openings 57 and the holes 43, depending on whether the ignition device 28 is located in the rear (which is shown in Fig. 2-4) or in the lower air chamber 39, 40 (not shown). When the fuel reaches its ignition temperature caused by the high air temperatures, which takes about 1 minute, the ignition composition 49 ignites. More specifically, a primary combustion of fuel takes place at the top of the grate 45, after which the fuel emits combustion gases which are then ignited. Already after approximately 3 minutes, the ignition normally occurs, but the ignition coil 50 is still operated up to the full time (5 minutes) to be sure.

After about 3.5 minutes have passed from the start, the fan 25 is adjusted so that each particular blast of air is longer with shorter interruptions between each blast of air. After ignition of the combustion gases, these are brought to a secondary combustion in the form of a flame out through the outlet 26 formed by the air flow from the blowing fan 25, and with a direction determined by the air chambers 38, 39, 40 and the air channels 41, 42. The operation is then continued of the fact that the control and monitoring unit 32 and the drive thermostat for the heating boiler 6 for the dosing device 12 to dose out sufficient amounts of fuel at a correct interval to achieve a selected temperature. For example, in the case of a full power take-off, well-defined fuel doses are fed into the combustion site 44 at intervals so defined that the fuel bed 46 burns continuously. With a lower power requirement, the burner 16 need not be in continuous operation, after which the fuel bed is allowed to extinguish. Accordingly, the automatic ignition of the ignition composition 49 occurs at the start of the central heating system 1, in certain defined cases during the operation of the said central heating system 1 and after unexpected power interruptions, which ignition is controlled by the control and monitoring unit 32.

After the second combustion of the combustion gases, it is desired that essentially all fuel is transferred to gases with only a small amount of fly ash as a residue, which ash residue follows the gases out into the boiler section 27 and into the ash box 61 which is placed there. However, this is not always the case, as has been explained above. During ignition, the ignition coil 50 reaches about 800°C and the tantalum wire can reach a temperature of about 1100°C. Kantal wire cannot withstand more than 1200°C, as the magnesium oxide in the wire melts if it reaches a temperature above 1200°C. The quenched fuel bed 46 includes unburned fuel, ash and sinter 31, which is formed during the last production period before shutdown, and forms a pile on top of the lower grate 45 in the firebox 44, that is, the rack 51, which pile 31 grows larger as the boiler 6 is used. Each new combustion composition 49 that is dosed down ends up in a smaller pile somewhat further back on the bottom 45 on top of the sinter 31. Thereby the new combustion composition 49 increases the pile 31 and further, it prevents the holes 43 and the openings 57 in addition, after which it becomes more difficult for the hot air flow to get through and start the ignition with each new combustion composition 49. Consequently, the fuel is free from direct contact with the ignition coil 50.

Before a new start and after the ignition coil 50 has cooled down, the drive unit brings the rake 51, which rake is formed both by the bottom 45 for fuel and an ash feeder 29 for sinter products 31, to a back and forth movement, during which movement air is simultaneously blown as that the holes 43 and the openings 57 are not blocked. Inside the heating boiler 6 there is a negative pressure, whereupon air must be forced in by means of the blowing fan 25 to the front part 51 of the ash feeder 29 and then further into the furnace 44 through the grate holes 43 now up through the fuel bed 46. Furthermore, the double walls form 36, 37 in the combustion chamber 16 air channels 41, 42 around the box-shaped grate 51 and through which channels 41, 42 the blowing fan 25 supplies air along the sides 55, 56 of the grate box 51 to the front air chamber 38 and further inwards from the holes 43 in the front air chamber 38, but also through the holes 43 in the long sides 37 in the fire place 44.1 the drive position 58, the grate is completely tight along the inner walls 37 up to the fire place 44, while the grate box 51 is somewhat wider than the inner walls 37 to prevent the fuel from falling outside and to the side of the grate box/rake 51. First, the rake 51 is moved backwards so that the ashes, slag and sinter 31 are scraped off against the rear edge of the inner wall 37a, which serves as hold and down in front of the rake 51 while this is moved backwards to its rear end position, the ash-evacuating position 59. At the ash-evacuating position 59, essentially the entire rake 51 is pulled back inside the rear limiting wall 37a, after which the rake turns and goes back into the front direction of the drive unit 30 and then at least to its drive position 58 or even further, preferably at least to the level of the front outer wall 36 of the combustion chamber 16, while the ash, the sinter products and the unburnt fuel 31 are pushed ahead of the rake and further down to the ash box 61 in the boiler 6. The rake 51 is then pulled back to the first position, that is the drive position 58.

Slag feeding is done when the operation is interrupted; normally approximately every 30 minutes, and after the temperature has been lowered in the combustion chamber 16. When a temperature of 200°C is reached, a first 30 second fan blowing is performed to blow out the fly ash. The slag 31 has then become solid and is left behind. The thermostat switches on and off maybe 6 times in the summer and up to 24 times in the winter, 30 minutes of operation, 30 minutes of cooling, and 24 hours a day.

The more detailed function of the drive unit for the embodiment shown in fig. 3 and 4a-f are as follows: During operation of the combustion device 3, the two connecting arms 68, 69 in the drive unit 30 are brought eccentrically 66 forward and towards the combustion chamber 16. During initiation of an ash evacuation, the control and monitoring unit 32 activates the motor in the drive unit 30, which rotates the pivot arms 67 (in accordance with Fig. 4a) so that the eccentric 66, with the help of the connecting arms 68, 69, pushes the grate box 51 backwards from its forward drive position 58. At the ash evacuation position 59, the two connecting arms 68, 69 are completely directed backwards. The furnace 44 is fully open and the slag products 31, which have been left after blowdown cleaning before the retraction of the rake 51 commenced, are now forward of the rake 54. The pivot arm 67 continues to rotate so as to pull the rod 52 with it in a forward direction, to the original position, that is, the drive position 58 is again taken. By using one or more somewhat longer rods together with the drive unit, in an alternative and not shown embodiment, the axle feeder can be brought all the way forward and in level with the front outer wall of the combustion chamber before the drive position for the rake is taken, and in which position the connecting arms in this particular case have an angle between them that is greater than zero and less than 180°.

If the forward movement of the rake 51 is blocked by too large a pile of slag products and unburnt fuel 31, which has fallen down in front of the rake 51 during the return movement, then the spring 65 allows the eccentric to make a complete rotation, after which the control and monitoring unit 32, or a switch, not shown, ensures that the ash-evacuating movement is repeated until one complete stroke is achieved for the rake 51, that is, the rake 51 is sent back and forth between its maximum end positions 58, 59 which are set by the length of the rods 52 which used.

The invention is not limited to the embodiment shown and it can be varied in various ways within the framework of the requirements. It is assumed, for example, that with a conventional heating boiler 6 is intended, for example, a so-called oil-fired boiler for smaller houses 2 where the normal oil burner is replaced by a burner 16 for solid fuel, preferably pellets, and in which heating system, for example the existing the water-bearing system is used in exactly the same way as with normal oil heating. The pellet burner 16 is installed with a connection to the usual drive thermostat for the boiler 6. Of course, there is no restriction on the use of the combustion device 3, for example for use in already existing boilers 6, while the combustion device can be used in any new installation for use in central heating systems 1.

Claims (23)

1. A device (3) for burning granulated solid fuel, for example wood pellets, tiles and the like, including a combustion chamber (16) which includes outer walls (36) as well as inner limiting walls (37) and an inner bottom (45), which inner limiting walls (37) and inner bottom are placed at a fixed distance from the outer walls (36 ) for dividing the double-walled combustion chamber (16) into a front, a rear and a lower air chamber (38, 39, 40) and two air channels (41, 42) placed along the side of the combustion chamber in the longitudinal direction, which limiting walls (37) and inner bottom (45) encloses an inner part (44) of the combustion chamber (16) which forms a combustion place (44) for the combustion of the fuel, an air inlet (24) with a fan (25) for feeding air to the combustion chamber (16) via the air chambers (38, 39, 40) and the air channels (41, 42) to achieve a predetermined air flow through the combustion chamber (16), a dosing unit (12) for feeding fuel into the combustion chamber (16), an ignition device (28) for igniting the fuel, a control and monitoring unit (32) for operation of the combustion device (3) and of parts of it or that interact with it, an outlet (26) for hot combustion gases from the combustion of fuel from the combustion chamber (16) to a boiler section (27) in a boiler (6) for transferring the heat to the heating system in the boiler (6), for example through water-cooled surfaces in the boiler (6) , a movable ash feeder (29) with a drive unit (30) controlled by the board and the monitoring unit (32) for automatic feeding of ash, unburnt fuel and slag products (31, formed during the combustion of fuel) out of the combustion chamber (16), characterized in that the ash feeder (29) includes a movable front part (51) placed in the lower air chamber (40) and which part includes a perforated bottom which constitutes the above-mentioned inner bottom (45), which front part (51) is placed to be moved by the drive unit (30) between at least one drive position (58), in which the aforementioned front part (51) is placed to close the lower end of the combustion chamber (44) and an ash-evacuating position (59) where the combustion chamber ( 44) is open downwards. 2. Device according to claim 1, characterized in that it is included in a system (1) for central heating of a building (2), which central heating system (1) in addition to the aforementioned boiler (6) with associated heating system includes at least an additional fuel supply (4) and at least one fuel supplier (5) for automatically feeding fuel from the fuel supply (4) to the dosing device (12). 3. Device according to claim 2, characterized in that the combustion device (3), in addition to or instead of the fuel supplier (5) and the fuel supply (4) has a fuel supply (13) which is built into the dosing device (12). 4. Device according to claims 1, 2 or 3, characterized in that the dosing device (12) includes a fuel feeder (14) for dosing fuel from the dosing device (12) and further into the combustion chamber (16) via a feed pipe (17). 5-. Device according to claim 4, characterized in that the feed pipe (17) has the shape of preferably a somewhat inclined fall chute, along which the fuel falls freely a predetermined length to prevent kickback. 6. Device according to claims 4 or 5, characterized in that safety devices are arranged near the feed pipe (17), which consist of a thermal fuse (18) which alarms if the heat spreads in the pipe (17) and/or one or more slide valves (19) to close the feed pipe ( 17). 7. Device according to claim 4 in combination with claim 3, characterized in that the fuel feeder (14) includes a feed screw (20) which is rotatably arranged between and near the upper end (21) of the aforementioned feed pipe (17) at the dosing device, (12) and either an inlet (22) to the dosing device (12) or to the bottom (23) of the built-in fuel supply (13). 8. Device according to any of the preceding claims, characterized in that the blowing fan (25) includes a variable speed controlled motor (35) and is located at the rear part (33) of the combustion chamber (16) to blow and circulate air through said air inlet (24) and forward and further out through the outlet (26) of the front part (34) of the combustion chamber (16). 9. Device according to any of the preceding claims, characterized in that one, several or preferably all of the limiting walls (37) have perforations in the form of smaller openings, holes and/or larger openings (43) for blowing air through. 10. Device according to any of the preceding claims, characterized in that the ignition device (28) is arranged in the rear air chamber (39) at the rear limiting wall (37a). 11. Device according to claims 1 -9, characterized in that the ignition device (28) is arranged in the lower air chamber (39) and is arranged in cooperation with the ash feeder (29). 12. Device according to claims 1-9, characterized in that the ignition device (28) is arranged in the ash feeder (29), where the ignition device (28) follows the reciprocating movements of the ash feeder (29). 13. Device according to claim 10, characterized in that the rear limiting wall (37a) has air holes (37) into the ignition device (28) for blowing air from the blowing fan (25) through the ignition device (28) and further into the combustion place (44). 14. Device according to any of the preceding claims, characterized in that the ignition device (28) includes an ignition coil (50) for electrically heating the ignition device (28). 15. Device according to claim 14, characterized in that the ignition coil (50) is produced as an induction heater. 16. Device according to any of the preceding items, characterized in that the ignition device (28) has a mantle (71) with an air inlet (72) to blow air from the blowing fan (25). 17. Device according to any of the preceding claims, characterized in that the ash feeder (29) includes a front part (51) and one or more elongated rods (52) which are connected at and between the front part (51) and the drive unit (30) for ash feeding. 18. Device according to claim 17, characterized in that the front part (51) and the front end of each rod (52) are arranged in the lower air chamber (40), while the drive unit (30) and the rear end of each rod (52) are arranged in a casing for itself. 19. Device according to claim 18, characterized in that the mantle (53) is arranged outside the heat-insulated combustion chamber (16) at the rear outer wall (36a) and with each rod (52) extending through an opening (60) in said rear outer wall (36a). 20. Device according to any of claims 17-19, characterized in that the front part (51) has the shape of a box on its head, open at the back with three sides (54, 55, 56) and a perforated bottom arranged upwards, which bottom at the same time constitutes the movable inner bottom (45) mentioned above, in which one side (54) constitutes a front edge from which the bottom (45) and the other two sides (55, 56) are arranged in a backward direction towards the drive unit (30) and in which the sides (55, 56) are arranged at a distance from the outer walls (36) in the longitudinal direction of the combustion chamber (16) to form a downward extension of the air ducts (41, 42) mentioned above. 21. Device according to any of claims 17-20, characterized in that the drive unit (30) includes a fixed front stopper (62), two sliding collars (63, 64) which are movable arranged along each rod (52) as a front and a rear sliding collar, and a spring (65), which is arranged between the sliding collars (63, 64), an eccentric (66) and also a fixed rear stop (70) with the rear end part of the rod (52). 22. Device according to claim 21, characterized in that the eccentric (66) includes a pivot arm (67) and two connecting arms (68, 69) of which one (68) is longer than the other (69) and that the two connecting arms (68, 69) are rotatably connected to each other by a common end part, that the other end of the short connecting arm (69) is connected to the pivot arm (67) while the other end of the long connecting arm (68) is rotatably attached to the rear sliding collar (64). 23. Device according to any of claims 21-22, characterized in that the drive unit (30) has a motor for operation of the eccentric (66) by means of the pivot arm (67) and thereby for the forward and backward movements of the front part (51).