The subject of the invention is an apparatus to burn solid fuel according to the preamble of claim 1

Such an apparatus is known from EP 0 039 073 A and US 2 370 067 A.

Today various apparatuses are known to burn solid fuel such as fuel made of wooden material. Usually there is some kind of grate or plate, on which the fuel to be burned is fed, in these burning apparatus or in combustion chambers of their boilers. Disadvantage in this kind of constructions is the possibility for partly burned material to fall under the grate finishing the burning process before the material has completely burned. Another disadvantage is often incomplete and not sufficiently fast combustion.

The purpose of the invention is to provide an apparatus to burn solid fuel by using which disadvantages connected with present apparatus are eliminated. In particular, the purpose of the invention is to provide a burner for solid fuel with good and effective efficiency and in which combustion is as perfect as possible.

The purpose of the invention is achieved by the apparatus to burn solid fuel, which possesses the characteristics presented in the appended claim.

Characteristic to the apparatus according to the invention is that the burner comprises a fuel feeder according to the characterising portion of claim 1. The fuel cone beneath the burner section is narrower in the upper part. Therefore the fuel feeder in the lower part of the burner creates a wall at regular distance from the surface of the fuel cone thus alloying an even flow of air between the fuel cone and the fuel feeder. Therefore the combustion on the surface of the fuel cone is effective and even and the feeding of the fuel is easy to control. Furthermore, because of the strong flow of the air developed this way in the lower part of the burner section combustion is effective also in the burner section placed above the fuel feeder. Effective and perfect combustion in the burner section is caused by the fact that in this kind of burner the flow of the air gets slower when going up, in which case fuel particles of various sizes and in various stages of burning get up in various parts inside the burner. So the material bums relatively exactly to the end before exiting the burner. Furthermore, when the air fan of this kind of apparatus is stopped the partly burned fuel and ash inside the burner and above it fall back on the fuel cone beneath the burner section and the fuel feeder. This way the warm ash on the fuel cone protects and isolates the fuel under it thus keeping the hot fuel under ash warm for some time. Therefore it is possible to light the fuel again after some time just by starting the air fan. Therefore stopping and restarting an apparatus like this (for instance because of maintenance or repairing) can be accomplished in relatively short time when required very simply and with ease.

In the advantageous embodiment of the invention the apparatus consists of a supporting frame reaching down to the lower part of the burner and trough, which the air channels are connected, to the burner. This way the burner can be supported to the combustion chamber and air channels connected to the burner in a functional way simply and advantageously.

In the second advantageous embodiment of the invention the burner is located at a distance from the supporting frame on tubes for the air channel. The attachment realised by connecting the burner to the air channels is simple and this way air flow in the air channels cools the temperature flowing from the burner to the supporting frame, thus preventing the overheating of the supporting frame. Furthermore, air can flow between the air channels from outside the burner inside the burner section and the fuel feeder.

In the third advantageous embodiment of the invention at least a part of the air channels is connected inside the burner mainly at the lower part of the burner section. This way it is possible to increase the strong air flow in the lower part of the burner section thus intensifying further the combustion process at various parts of the burner.

In the fourth advantageous embodiment of the invention in the burner at least a part of the air channels is connected inside the burner mainly at the lower part of the fuel feeder. This way the even combustion process in the fuel feeder can be made to start from the bottom of the fuel conc, thus holding the shape of the fuel cone getting narrower evenly upwards and preventing the blockage of the fuel feeder.

In the fifth advantageous embodiment of the invention at least a part of the air channels is connected inside of the burner mainly at the upper part of the fuel feeder.

This way it is possible to apply an extremely strong flow between the fuel feeder and the burner section, which raises burning fuel to the burner section to be burned effectively and perfectly.

In the sixth advantageous embodiment of the invention at least a part of the air channels is placed in inclined angle parallel to the circumference of the burner, thus making the air inside the burner to rotate. This way it is possible to create extremely sufficient and almost perfect combustion in the combustion chamber, because fuel, ash and flue gases are not able to raise to the flue too quickly and combustion occurs more perfectly and the heat generated during combustion is conducted more certainly to the boiler around the combustion chamber.

In the seventh advantageous embodiment of the invention a feeder is placed inside the supporting frame to feed the fuel through the supporting frame to the lower part of the burner. This makes it possible to feed the fuel in suitable way to the lower part of the fuel feeder in the middle of the fuel cone, alloying the cone keep its shape optimum. While placed inside the supporting frame the fuel feeder doesn't require extra space in the burner. Furthermore, the fuel feeder placed in the supporting frame is functioning as a pre-hcater for fuel without overheating, though, due to the air channels.

In the eighth advantageous embodiment of the invention there is one or more channels reaching through a side wall of the burner section to return the partly burned fuel and air by means of negative pressure produced by the rotating motion and flow of air to the channels back inside the burner section. By circulation of fuel, combustion gases and ash formed this way the combustion in the burner section can be made simply and advantageously more perfect and efficient than combustion that takes place only once.

In the following, the invention is defined in more detail with reference to the attached drawings, in which:

• Figure 1 presents an embodiment of the apparatus according to the invention seen from the side and a cross-section of it and
• Figure 2 presents a cross-section A-A to figure 1,
• Figure 3 presents a cross-section B-B to figure 1,
• Figure 4 presents a cross-section C-C to figure 1,
• Figure 5 presents a cross-section D-D to figure 1, and
• Figure 6 presents a cross-section E-E to figure 1.

In the embodiment according to figures 1 - 6 the boiler consists of a frame 1, inside of which there is a combustion chamber 2. Outside the frame there is a water reservoir 3 and fire tubes 4. Inside the boiler there is placed a burner 5. The burner is a cylindrical object, in lower part of which there is a conical fuel feeder 12 and in the upper part an inverted conical burner 13. In the burner there are also air channels 7 and in the upper part of the inverted conical burner there are return channels 14 for fuel and air. The burner 5 is attached by means of air channels to the supporting frame 10 under it. It consists of a conical fuel feeder 6 reaching outside the combustion chamber and channels for air supply, divided to lower 15, middle 16 and upper 17 sections. In the upper part of the boiler there is a recognised construction of afterburner chamber 8 a flue gas pass, placed between it and combustion chamber. In the boiler there is also a base with a flue gas chamber 18 and a de-ashing hatch for the base and a de-ashing hatch for the combustion chamber, which are not shown in figures 1 - 6. Furthermore, there is a flue gas duct 21 with an adjustable damper 11.

In the embodiment according to figures 1 - 6 the inverted conical burner of the burner is cast out of fireproof silicon carbide mass such that the lower part of it forms a cone contracting downwards. Inverted conical burner can also be made of some other suitable fireproof material in other embodiments of the invention. The middle part between the inverted conical burner and the conical fuel feeder can be removed separately, for instance, for maintenance and a part of different type, where air channels, for instance, may be placed in a different way, can be placed there. The upper part of the inverted conical burner is also changeable separately, because the thermal load in that part is the most and changeability to more thermoduric material must be possible. The shape of the conical burner can also be other than that of a cone; it may be, for example, parabolic or other way broadening upwards.

In the embodiment according to figures 1 - 6 there are twelve tubes, which function as air feeding air channels 7 for the burner from the supporting frame connected to the burner 5. Air channels are tubes made of heat resisting material to be used in circumstances corresponding the situation between the burner and the supporting frame. Tubes are connected inside the burner in groups of four tubes at three various points in vertical direction of the burner. The first four tubes are connected at the lower part of the conical fuel feeder 12, the second group at the upper part of the conical fuel feeder and the third group further above those, at the lower part of the inverted conical burner 13. The nozzles of the tubes are directed radially inside according to cross-sections in figures 3 - 6. As shown in figure 5 the tubes connected to the lower part of the conical fuel feeder are directed radially to the central axis of the conical fuel feeder as viewed from above. The next tubes (figure 4) connected to the upper part of the conical fuel feeder are directed somewhat inclined to the circumference from the radial direction and the tubes connected at the lower part of the inverted conical burner (figure 3) are directed somewhat more than the earlier mentioned to the circumference in inclined angle. The purpose of this arrangement is to make the air rotate while rising upwards. This way negative pressure is created in the return channels 14 in the upper part of the inverted conical burner, creating a flow, which returns flue gases and ash and fuel particles from aside inside the inverted conical burner. Efficient air circulation created this way promotes the most perfect combustion in the inverted conical burner.

Air channels 7 connected to the inverted conical burner at various places are connected to sections in the supporting frame 10. Separate sections of the air channels of the supporting frame are connected each to its air supply device, which are placed outside the boiler. The channels connected to the lower part of the conical fuel feeder 12 are connected to the upper section 17 of the air channels of the supporting frame, the air channels connected to the upper part of the conical fuel feeder are connected to the middle section 16 and the air channels connected to the lower part of the inverted conical burner are connected to the lower section 15. This way different kind of heating of combustion air in various sections of the supporting frame can be divided to various phases of the combustion process in a suitable way.

The supporting frame 10 is constructed of two round tubes with different diameters and placed one inside the other and of two conical gable elements accordingly constructed of two cones connected to it. A gable element is placed under the conical fuel feeder of the burner and the upper part of it is of the same size as the lower part of the conical fuel feeder. This way the gable element forms together with the conical fuel feeder a closed space, where fuel can be fed as demonstrated in figure 1. Inside the inner tube of the part reaching outside the burner there is a feed auger mounted in bearings driven by a recognized drive mechanism. The other end of the feed auger reaches the conical space broadening upwards of the gable part and in the other end of which there is a dropping pass, through which the fuel to be used in the burner can be fed to the auger. There is a space left between the outer and inner tube as well as between the outer and inner conical part of the gable element which is divided into three sections 15, 16 and 17 by means of separating walls. Air channels 7 connected with the burner are connected to these sections as described earlier.

When using the apparatus according to the invention solid fuel is fed to the fuel feeder. This fuel is usually of wooden material, which may be chip, sawdust or their mixture. Advantageous moisture content of the fuel is about 20 - 30 %, but it may vary in various cases. Fuel feeding is realized by dropping the fuel through the dropping pass to the fuel feeder. In this embodiment as a fuel feeder 6 an auger (progressive stoker) is used, but in other embodiments other kind of feeders may be used to transfer the material. The fuel dropped to the spirals of the auger is transferred by means of rotating motions of the auger to the conical fuel feeder 12, placed under the burner. This way a fuel cone is formed in the conical fuel feeder. There is a separate igniter (not shown in figures) functioning in a recognized way in the conical fuel feeder by means of which the fuel is ignited. After the fire has started and combustion is in progress speed of rotation of the drive mechanism of the auger is controlled to be suitable. Control is realized steplessly by means of frequency transformer drive. During the combustion the automatic control of fuel feeder keeps the height of the fuel cone stable in spite of change in combustion power. During the feeding the hot ash dropping to the bottom of the combustion chamber warms the feeder thus warming the combustion air in the air channels of the supporting frame and the fuel in the feeder in order to create as sufficient combustion process as possible.

Combustion air is supplied into the burner 5 from outside the burner through sections 15, 16 and 17 of the air channels of the supporting frame 10 and trough air channels 7 of the burner. The higher combustion air raises inside the supporting frame and burner the more it warms before bursting inside the burner. During combustion air is blown continuously to the fuel cone and to the inverted conical burner 13. This way burning material is provided with a sufficient amount of oxygen all the time. Inside the supporting frame air is transferred inside the three sections placed as stated earlier. The air supplied through the upper 17 and the middle section 16 to the conical fuel feeder 12 is called primary air, and the air supplied through the lower section 15 to the lower part of the inverted conical burner 13 is called secondary air. Primary air of the upper section is supplied to the air channels of the lower part of the conical fuel feeder, primary air of the middle section to the air channels of the upper part of the conical fuel feeder and secondary air of the lower section to the air channels of the lower part of the inverted conical burner. Secondary air warms up inside the supporting frame more than primary air because the lower section inside the supporting frame is closer to the hot bottom of the combustion chamber where the hot ash, which has been able to pass the inverted conical burner, falls. This arrangement is made in order to make the combustion in the inverted conical burner to be as sufficient and perfect as possible.

Air is supplied to the air channels of the supporting frame in the embodiment according to figures 1 - 6 by three fans with frequency transformer drives (not shown in figures) connected to each section of the supporting frame 10. Thus the amount of air supply can be controlled steplessly as the combustion process requires. Alternatively, the amount of air supply can be controlled, for example, by means of dampers fixed in the channels.

Combustion starts inside the conical fuel feeder 12 on the outer surface of the fuel cone and continues through the space between the conical fuel feeder and inverted conical burner to the inverted conical burner 13 and from there further through flue gas pass 9 to afterburner chamber. The wall between the conical fuel feeder and the inverted conical burner glows at the narrowest place at temperature over + 1100°C igniting gases and carbon particles able to burn separated from the fuel. After the narrowest place pre-heated secondary air is supplied to the burning gases and carbon particles, which burns wood gases, and carbon particles completely. Inverted conical burner is designed such that possible wood gases and carbon particles in combustion gases raised to the upper part of the combustion chamber can be ignited by means of glowing, hot walls of the narrow opening and thus burn in the afterburner chamber 8. Temperature of the flame burning above the upper part of the inverted conical burner changes depending on the load of the boiler (on the sphere + 1150 ... 1350°C). Return channels 14 in the lower part of the inverted conical burner return part of the flue gases flowing downwards near the heating surface of the boiler back to the inverted conical burner thus burning the wood gases in the circling gases in good combustion circumstances completely. Outside the inverted conical burner the almost completely burned ash falls into the ash pan in the base of the boiler, where it warms the constructions of the supporting frame and, for instance, the feeding channels of the combustion air.

Flue gases raising from the inverted conical burner flow through flue gas pass 8 to the afterburner chamber 9 constructed in a recognised way, which mixes the air efficiently and where the afterburning takes place. In the afterburner chamber flames and possible carbon particles bump against the glowing ceiling and burn completely. From the afterburner chamber hot gases divide evenly to the fire tubes through which they flow to the ash pan in the base and from there through flue gas ducts to outside. In fire tubes hot flue gases flow downwards and emit their heat to the boiler water in the reservoir 3. In this embodiment fire tubes are straight tubes placed side by side inside the water reservoir, but inside the fire tubes turbulence elements can be fixed to increase the efficiency of heat emission. There are de-ashing hatches in the wall of the flue gas space of the base through which the ash from the ash pan of the boiler and the base can be regularly removed. The ash gathering in the ash pan of the base and the boiler is removed manually with a pusher in smaller boilers. Larger boilers can be equipped with auto-de-ashing equipment. In the flue gas duct 19 from the base of the boiler there is a controlled damper 11. By using damper it is made certain that there is overpressure during the combustion in the combustion chamber and in afterburner chamber, so that combustion would be as effective as possible according to foregoing description. In this embodiment the position of the damper is manually regulated, but can be provided with automatic regulating device in other embodiments.

Heat is transmitted to boiler water in water reservoir 3 straight from the walls of the combustion chamber 2 and through fire tubes 4. Water outlet pipes of the boiler 1 are placed as low as possible to create an effective water circulation inside the boiler and water inlet pipes are placed as up as possible to create an effective water circulation and to avoid boiling of the water in the upper part of the boiler. In the embodiment according to figures 1 - 6 there are 4 fire tubes and the water reservoir around the burner is placed around the burner eccentric such that the fire tubes are inside the water reservoir, at the broadest place of the reservoir. In other embodiments of the boiler according to the invention there can be also more or less fire tubes and the water reservoir can be, for instance, only partly around the boiler or same other way realized.

The construction of various parts of the apparatus according to the invention and the material in them can vary. The combustion chamber, burner with air channels can differ by shape and quantity of various parts from foregoing embodiment. The conical fuel feeder and the inverted conical burner of the burner can be assembled differently from different kind of parts. The quantity and grouping of air channels at different places of the conical fuel feeder and inverted conical burner can vary. Air channels may appear instead of in three groups, for instance, in two or in four groups placed in various places in inverted conical burner. They can be connected also in other way than according to figures 1 - 6 through supporting frame to air feeder. The size and the shape of flue gas pass and afterburner chamber can vary when required. The quantity, the shape, the length and the diameter of the fire tubes from the afterburner chamber can differ from foregoing embodiment. Also the size and the shape of the flue gas space of the base, the ash hatches and the flue gas space can be many various ways realized.

The invention is not limited to the advantageous arrangements shown but can vary within the idea of the invention within the limits set forth in the claims.