EP2087282A1

EP2087282A1 - Method for combusting solid fuel and a heating device

Info

Publication number: EP2087282A1
Application number: EP07823119A
Authority: EP
Inventors: Timo Karjalainen
Original assignee: Individual
Current assignee: KARJALAINEN, TIMO
Priority date: 2006-10-24
Filing date: 2007-10-24
Publication date: 2009-08-12
Also published as: EP2087282A4; WO2008049962A1; FI20060935A0

Abstract

The invention comprises a method for combusting solid fuel and a heating device (20), wherein the method can be applied. In the method - a fuel bed of solid fuel is formed in the first pipe (3), which is at an angle in relation to the horizontal plane and equipped with openings (5), - the fuel bed is combusted in the first pipe (3), - air needed for the combustion comes into the first pipe (3) from the openings (5) and - flue gases are led out from the first pipe (3) via its top part (21). In the method the fuel bed is ignited only at its surface and the fuel bed is combusted only at its surface, so that a combustion zone of a certain height is formed on the surface of the fuel bed. In the heating device (20) according to the invention the combustion advances as a zone in a controlled manner downwards in the fuel bed.

Description

METHOD FOR COMBUSTING SOLID FUEL AND A HEATING DEVICE

TECHNICAL FIELD OF THE INVENTION

The object of the invention is a method for combusting solid fuel, such as pellets, and a heating device according to the preambles of the independent claims presented below. The object of the invention is especially a new manner of producing heating energy by combusting pellets.

PRIOR ART In the Nordic countries the traditional manner of heating is batch combustion. The typical heat source is thus a heat accumulating fireplace. A heat accumulating fireplace is heavy and usually has to be built firmly in its place. It is known to install, various additional structures into stationary fireplaces, which structures provide for combusting pellets in furnaces, which are originally meant for other fuel.

In the Nordic countries the use of pellets has lately become more common for the continuous heating of single-family houses. For example oil heating is often replaced by installing a continuous pellet combustor into a furnace originally equipped with an oil combustor. Such a solution requires for example an electric fuel feeder.

For example the Finnish patent applications Fl 20011053 and Fl 20020152 present solutions for combusting pellets. US 4712491 presents one solution for combusting solid fuel. The known solutions are often complicated and ineffective.

OBJECT AND BRIEF DESCRIPTION OF THE INVENTION An object of the present invention is to reduce or even to eliminate above- mentioned problems appearing in the prior art.

An object of the present invention is to provide a solution, with which solid fuel, especially pellets, can be combusted in a clean, controlled, easy and effective manner. An object of the present invention is to solve the controlled combustion of the low amount of pellets and the combustion gases with a good efficiency.

In order to realize among others the objects mentioned above, the present invention is characterised by what is presented in the characterising parts of the enclosed independent claims.

The embodiment examples and advantages mentioned in this text relate, where applicable, to both the method and the heating device according to the invention, even if this is not always specifically mentioned.

In a typical method according to the invention for combusting solid fuel >

- a fuel bed of solid fuel is formed in the first pipe, which is at an angle in relation to the horizontal plane and equipped with openings, - the fuel bed is combusted in the first pipe,

- the air needed for the combustion comes into the first pipe from the openings and

- flue gases are led out from the first pipe via its top part.

In the method the fuel bed is ignited only at its surface and the fuel bed is combusted only at its surface, so that a combustion zone of a certain height is formed on the surface of the fuel bed. The combustion advances as a zone in a controlled manner downwards in the fuel bed.

It has thus now surprisingly been found that solid fuel, such as pellets, can be combusted in a controlled and simple manner in a so-called zone combustion process. The heating device itself functions as a fuel storage, and fuel is combusted directly in the storage, but only at its surface. The combustion advances during the process in a controlled manner downwards in the fuel storage. The dimensions and structure of the device are easy to adapt so that the desired combustion rate is achieved. For example the location and size of the openings for the combustion air can easily be adjusted. The stove with pipe structure according to the invention is light and inexpensive to manufacture. The fuel can be made to combust rather slowly, whereby heavy accumulating structures are not needed. The heating device can easily be installed almost anywhere and it is easy to move when necessary.

An advantage of the invention is that it can, when desired, be made to function completely without external energy feeding. The heating device according to the invention does not necessarily need electric energy for example for feeding fuel or combustion air.

An advantage of the invention is that the combustion according to the invention in the heating device according to the invention is easy to extinguish ^uiokjy^foπ example in an emergency. The combustion takes place in a restricted pipe and in a combustion zone of a limited height. Thus it is possible to extinguish the fire for example with a small amount of water, for example by pouring water through the fuel feeding hatch into the first pipe.

By dimensioning the heating device suitably and/or adjusting the draft the fuel bed can be made to combust in the pipe at a substantially standard rate. It is also possible to adjust the combustion so that the combusting fuel layer on the surface of the fuel bed stays substantially the same thickness throughout the combustion. The device according to the invention can thus comprise means for adjusting the draft, for example flaps, hatches or doors, which can be opened and closed, can be placed in front of the air openings, with the aid of which flaps, hatches or doors the openings can be closed when necessary.

The solid fuel can be for example pellets, grain such as barley, coal such as coke, small-sized wood such as twigs or woodchips, saw or cutter dust, a combination of the previous.

By pellets is in this text meant granular fuel manufactured at least mainly from wood or another suitable biomass. The pellet can be manufactured for example by pressing sawdust, shavings or other fine-grained wood with high pressure through small holes in a metal disk. Thus elongated pieces are made from the wood. The diameter of the holes and at the same time the diameter of the formed pellet grains can be for example 5-15 mm. The length of a typical pellet grain is for example 10-30 mm. The pellet can also be of another size.

By being in an angle in relation to the horizontal plane is meant that the first pipe is in an essential angle in relation to the horizontal plane. For example the direction of the pipe may be in an angle of at least 10 degrees, at least 45 degrees or at least 80 degrees in relation to the horizontal plane. By adjusting the inclination of the pipe, the course of the combustion can be adjusted. In an embodiment of the invention the fuel bed is formed and the combustion takes place in the substantially vertical first pipe. The vertical first pipe is. in . some, situations the simplest and most reliable solution.

The first pipe can be substantially straight over its entire length, but curves can be arranged in it.

The first pipe or the entire heating device can be manufactured for example from common carbon steel. Other materials are also possible.

The first pipe according to the invention may be lined from the inside for example with a ceramic lining. The first pipe can also be formed out of two metal pipes within each other, which pipes may between themselves be of the same or of different materials. The inner lining or the mentioned double pipe structure insulates the first pipe, so that the combustion temperature of the fuel inside the first pipe can be made higher.

In an embodiment of the invention the air needed for combustion comes into the first pipe from openings on several different heights on the fuel bed. In an embodiment of the invention a part of the air needed for the combustion comes into the first pipe from the combustion zone and a part from below the combustion zone. In an embodiment of the invention a part of the air needed for the combustion comes into the first pipe from above the combustion zone. In an embodiment of the invention the amount of air flowing into the first pipe from the openings is controlled by closing and opening one or more openings partly or completely. The closing and opening of the openings can be carried out for example with particular closures, such as hatches, doors or flaps, which can be arranged in front of the openings. The size of one or more openings can be controlled separately or the closure can be arranged to open and close all the openings at the same time.

In an embodiment of the invention a perforated air duct is arranged inside the first pipe, with which air duct air is brought into the fuel bed. Fuel is substantially not held inside the air duct, but it is typically substantially unobstructed_!. The airxfcuct may open at its end for example under the first pipe or it can be arranged to open through the flank of the first pipe into the side of the first pipe. The air duct may for example be arranged in the middle of the first pipe or attached to the inner edge of the first pipe. The holes in the air duct are typically so small that no fuel can flow into the air duct and that the combustion is not lead downwards in the air duct.

The method according to the invention can be applied in a heating device, which typically comprises a first pipe, wherein a fuel bed for solid fuel is to be formed and wherein the fuel bed is to be combusted. The first pipe is at an angle in relation to the horizontal plane, and open at its top end in order to lead flue gases out of it. Openings have been arranged in the first pipe, from which openings the air needed for the combustion flows into the first pipe. A typical heating device further comprises a substantially vertical second pipe, the top part of which is arranged in gas connection with the top part of the first pipe. The flue gases are led from the first to the second pipe and downwards in the second pipe. In gas connection with the second pipe of the typical heating device is arranged an exhaust pipe, through which flue gases are led out of the heating device.

In an embodiment of the invention the first pipe of the heating device is substantially vertical. Such a heating device is easy to manufacture and use. In an embodiment of the invention an ash pipe has been arranged in the bottom end of and in connection with the second pipe. The ash pipe can be substantially vertical. Ash is separated from the flue gases into the ash pipe.

In an embodiment of the invention the heating device comprises an ash box, which can be opened. In an embodiment of the invention the lower end of the ash pipe and the lower end of the first pipe are in connection with the ash box. The ash pipe and the first pipe can have separate ash boxes or a shared one.

In an embodiment of the invention a filling opening, which can be opened and closed, has been arranged above the first pipe. Thus it is easy to feed fuel from the filling opening into the first pipe. The filling opening can be. situated perpendicularly above the first pipe, whereby fuel can be spilled straight into the first pipe.

In an embodiment of the invention combustion air is brought to the vicinity of the air openings of the first pipe along a pre-heating duct. In the pre-heating duct the air is pre-heated with the aid of the combustion heat from the first pipe. A suitable pre-heating of the combustion air boosts the combustion. The pre-heating duct can be arranged attached to the outer surface of the first pipe, for example substantially along its entire length. It is possible to form the pre-heating duct so that the outer wall of the first pipe functions as one of the walls of the pre-heating duct. In this way the air can be pre-heated directly using the heat led by the first pipe.

In an embodiment of the invention the pre-heating duct is arranged at the site of the device's openings for combustion air. Thus it is easy to arrange even all of the combustion air needed by the heating device to arrive through the pre-heating duct. If the outer wall of the first pipe functions as one of the walls of the pre- heating duct, the air openings in this outer wall then open directly into the preheating duct. The pre-heating duct can be substantially as high as the entire heating boiler. There can be several feeding pipes on different sides of the heating device. It is possible to divide the feeding pipe for example into two separate parts in the vertical direction, so that air is fed to the bottom part of the heating device from the first part and air is fed to the top part of the heating device from the second part. In an embodiment of the invention the pre-heating duct leads upwards air from the level of the bottom part of the heating boiler and even from below it. Thus the preheating duct in a typical embodiment of the invention is substantially vertical. In such a pre-heating duct the air warms up at it travels upwards.

In an embodiment of the invention the air flows in the separate pre-heating ducts in the same heating device can be adjusted independently from each" other. For. example gate valves or other adjustable flow restrictors can be arranged into the pre-heating ducts. The flow restrictor can for example be arranged in the bottom end of the pre-heating duct, whereby the entire air volume passing in the duct can be controlled. The flow restrictor can also be arranged for example between the top and bottom ends of the pre-heating duct, whereby the relationship between the flows of the top and bottom parts to each other can be adjusted.

In an embodiment of the invention the bottom end of the pre-heating pipe is arranged to open into the ash storage, i.e. the ash hatch, in the lower part of the device. Thereby combustion air is taken into the pre-heating pipe through the ash hatch. It is possible that substantially all of the combustion air needed by the device is taken from the ash hatch. In this embodiment it is very easy to adjust the flow of combustion air for example by opening and closing the lid of the ash hatch.

In an embodiment of the invention the inner part of the pre-heating pipe is tapered towards it top end. In this way the air flow in the pre-heating pipe can be kept relatively stable although combustion air exits the pre-heating pipe during the way. If the pipe is much tapered, it is even possible to increase the air flow when moving towards the top end. In an embodiment of the invention the horizontal cross-section of the inner part of the first pipe is substantially circular. A combustion space, which has a circular cross-section, has a structure which is simple and inexpensive to manufacture.

In an embodiment of the invention the air needed for the combustion is led from the openings into the first pipe, substantially in the direction of the tangent of the inner surface of the first pipe. Getting the air into a circulating motion in the combustion space promotes the combustion. This can be realized for example by drilling air holes in the first pipe, slanting in a suitable angle. The holes can also be formed for example by pressing, punching or bending the pipe material at the site of the hole into a flap in a suitable direction.

In an embodiment of the invention the air openings are larger in diameter in the bottom part of the heating device than in the top part.

In an embodiment of the invention the relationship of the length of the inner part of the first pipe to its diameter is at least 3, at least 5 or at least 10, or for example 3- 50, 5-20 or 10-15. When fuel is combusted in such a pipe-like combustion space, the relationship of the thickness of the fuel bed to the diameter of the fuel bed is thus also, at least when the combustion starts at least 3, at least 5 or at least 10, or for example 3-50, 5-20 or 10-15. By diameter is meant the diameter of the cross-section of a pipe, the cross-section of which is approximately the shape of a circle. If the cross-section of the first pipe is shaped other than as a circle, the diameter means the diameter of a circle, the surface area of which would be the same as the surface area of the cross-section in question. If the surface area of the cross-section of the first pipe changes significantly along its length, the diameter means the average diameter.

In an embodiment of the invention glass windows have been arranged in the first pipe in order to discern the amount of fuel from the outside of the device.

In an embodiment of the invention the first pipe consists of two pipes within each other. The inner pipe, the inner surface of which abuts the combustion space, is typically of a material which withstands very high temperatures, for example stainless steel. The outer pipe can be formed of a more inexpensive material, for example common carbon steel. One or more flow obstructers, such as flanges or corrugations, which are substantially horizontal and directed from the inner surface of the pipe towards the combustion space, can be arranged on the inner surface of the inner pipe. The purpose of the flanges is to decelerate the vertical flows which form on the surface of the pipe, and stop or slow down the movement of the particles which possibly travel with the flows. The flange may extend to a distance of for example 5-50 mm from the inner surface of the pipe. Insulating material may be arranged between the mentioned two pipes within each other.

In an embodiment of the invention the first pipe or a part of it is manufactured from two pieces, shaped like a pipe split in its longitudinal direction, by joining these halves to face each other, so that they form a pipe section shaped substantially like a circular cylinder. The connecting points of these two halves are easy to arrange into each other in such a way that the necessary air openings remain between the halves. If for example the halves are joined together by spot welding, the air openings can be arranged in the spaces between the spot weldings. In the above-mentioned manner pipe sections manufactured from pipe halves can be joined two or more subsequently, whereby a first tube of a desired length is obtained.

BRIEF DESCRIPTION OF THE FIGURES The invention is described in more detail below with reference to the enclosed schematic drawing, in which

Figure 1 shows a heating device according to the invention seen from the front,

Figure 2 shows a heating device according to the invention seen from the side,

Figure 3 shows the section A-A of Figure 2, Figure 4 shows the section B-B of Figure 2,

Figure 5 shows the section C-C of Figure 2,

Figure 6 shows another heating device according to the invention seen from the front, Figure 7 shows the heating device of Figure 6 seen from the side,

Figure 8 shows the section AA-AA of Figure 7,

Figure 9 shows the horizontal cross-section of a heating device according to the invention, and Figure 10 shows the section BB-BB of Figure 7 in a magnified view.

DETAILED DESCRIPTION OF THE EXAMPLES OF THE FIGURES For the sake of clarity, the same reference numbers have been used for corresponding parts in different embodiments. Some arrows are used to show certain air flows.

Figures 1-5 show a heating device 20 according to the invention, meant for.< combusting pellets. A vertical steel pipe 3 functions as a furnace and fuel storage for the device. Air openings 5, which pass through the pipe, have been formed on one side of the furnace. The air openings 5 have been formed above each other and evenly spaced, but the placement and dimensioning of the openings can always be adapted as desired. In the example of the Figure, the openings 5 are rectangular gaps, but round openings or openings of another shape are also possible. The size of the rectangular openings 5 can be for example somewhere in the range of 1-3 mm times 10-30 mm. The diameter of the round openings 5 can be for example 4-10 mm or 5-7 mm. The spaces between the openings 5 can be for example 10-100 mm, 20-50 mm or 30-40 mm. The openings 5 can be placed in a straight line or right above each other, as in Figure 1 , but the openings may also be scattered over different parts of the pipe 3.

Below the pipe 3 there is an ash box 6, which is in connection with the pipe and can be opened, wherein the ash, which remains as a remnant of the combustion, flows. A moveable bottom cone 7 has been arranged between the pipe 3 and the ash box 6. The bottom cone 7 can be moved with the aid of a thereto attached lever 10, which extends outside the device 20. By moving the bottom cone the connection between the pipe 3 and the ash box can be opened or closed. The cone 7 can be replaced by some other suitable instrument, for example a hatch that can be turned. A horizontal section 21 , wherein is arranged a filling hatch 1 that can be opened, has been arranged in the top end of the pipe 3 and in gas connection with the pipe. The filling hatch is directly above the pipe, whereby it is easy to drop for example fuel or kindling into the pipe 3 through it. A substantially vertical heat exchanger 2 has been attached to the horizontal section 21 , in gas connection with it. The joint between the heat exchanger 2 and the horizontal section 21 is arranged to be an expansion joint 9 in order to lessen the effects of heat expansion. A substantially horizontal exhaust pipe 4 has been attached in gas connection with the heat exchanger 2. The surface area of the cross-section of the horizontal section 21 can be for example 2-4 or 2.5-3 times as large as the surface area of the cross-section of the pipe 3. If the cross-section of the horizontal section is rectangular, as in the examples of the Figures, its size can be something in the range of 100-350 mm times 80-200 mm.

An essentially vertical ash pipe 11 has been arranged in the bottom end of the heat exchanger 2, below the junction of the exhaust pipe 4 and in gas connection with the heat exchanger 2. The ash pipe 11 is joined to an ash box 6 that can be opened, in order to lead the ash from the heat exchanger 2 to the ash box 6.

In the example of the Figure, the cross-section of both the pipe 3, the heat exchanger 2 and the ash pipe 11 is circular. The diameter of the pipe 3 can be for example 50-120 mm or 70-90 mm and its length can be for example 1000-3000 mm or 1300-1800 mm. The diameter of the heat exchanger 2 can be for example 80-200 mm or 100-140 mm and its length can be for example 400-1500 mm or 500-900 mm. The diameter of the ash pipe 11 can be for example 30-200 mm or 40-60 mm and its length can be for example 400-1500 mm or 500-900 mm.

Figures 2 and 4 show a wire spiral 8. The wire spiral 8 is made of metal wire, which is wound loosely on the inner wall of the heat exchanger 2. The end of the wire spiral 8 comes out of the heating device 20 through an opening in the upper surface of the horizontal section 21. The wire spiral 8 can be rotated manually and in this way the inner surface of the heat exchanger can be sooted. The device shown in the Figures is used as follows. Through the filling hatch 1 fuel, for example wood pellets, are poured into the pipe 3. The pipe 3 is filled to a desired degree of filling, for example halfway or to the level of the highest air opening 5. A fuel bed of a desired height is thus formed in the bottom of the pipe 3. The surface of the fuel bed is ignited for example using some kind of incendiary agent. The air needed for the combustion comes through the openings 5. The combustion advances in a controlled manner downwards in the pipe. Only the zone on the surface of the bed bums at all times. The dimensions of the device 20, for example the dimensions of the pipe 3 and the openings 5 define a certain combustion rate for each fuel quality. The flue gases are led via the top part of the pipe 3 to the horizontal section 21 and onwards to the heat exchanger 2 and onwards to the exhaust pipe 4. The ash passes to the ash pipe 11 and onwards to the ash box 6. The wire spiral 8 can be formed so that it causes a circulating motion in the flue gases, whereby the heat exchanger 2 can be made to function as a cyclone. This way the ash could be collected more efficiently into the ash pipe 11 and the ash box 6.

Figures 6-8 and 10 show another heating device 20 according to the invention. Its function is substantially the same as the device in Figures 1-5, so below mostly the features differing from each other in the embodiments are focused on.

In the examples in Figures 6-8 and 10 the air openings 5 are formed in the sides on the pipe 3 as vertical rows. Onto the air openings 5 are attached vertical pre- heating ducts 13, on both sides of the pipe 3. The pre-heating ducts 13 are made of a steel U channel, the open edge of which is placed against the pipe 3, so that the air openings 5 open directly into the duct 13. The edges of the duct, which are attached against the pipe 3, are attached against the pipe in an airtight manner. The bottom ends of the ducts 13 open into the ash box 6. The top ends of the ducts 13 are closed in an airtight manner. All the air needed by the device 20 for combustion is thus taken from the ash box 6, as seen in Figure 8. By controlling the position of the ash hatch from the opening button 14 of the ash hatch, the amount of air coming into the device 20 can thus be adjusted. The bottom cone 7, which can function as the grate of the device, can be moved with the lever 10. The cone 7 can be manufactured for example out of perforated plate, whereby the ash flows through it into the ash box 6 and the air can pass through it into the first pipe 3. The pre-heating ducts 13 are tapered towards their top end. Thus the air flow in the pre-heating duct can be made to remain relatively constant over the length of the whole device. Small glass windows 19 have been arranged in a vertical row on the front edge of the first pipe 3. From the windows 19 the advancing of the combustion, e.g. the amount of remaining fuel inside the first pipe 3, can be monitored.

Figure 10 shows a horizontal cross-section of the first pipe 3. The Figure shows how the air transfers from the pre-heating duct 13 through the holes 5 into the first pipe 3 approximately in the direction of the tangent of the inner surface of the pipe 3. This has been achieved by bending the material of the pipe 3 at the site of the holes 5 into flaps 23, which turn the air flow coming through the holes 5 in the direction of the inner surface of the pipe.

Figure 7 shows how, after the horizontal section 21 in the upper end of the device, the flue gases pass to the upper end of the front edge of the heat exchanger 2. In the example of the Figure the height of the heat exchanger is about a third of the height of the first pipe, but it can of course be formed to a desired size. Two exhaust pipes start from the rear edge of the heat exchanger, one from the upper edge 4a and one from the lower edge 4b. The exhaust pipes can be closed with gate valves 12a and 12b. An ash hatch (not shown) can when necessary be arranged in the lower edge of the heat exchanger.

Figure 9 shows the horizontal cross-section of the first pipe 3 according to an embodiment of the invention. The pipe 3 consists of two pipes within each other, an outer pipe 15 and an inner pipe 16, in the space 17 between which pipes insulating material can be placed. The pipes are shown in the Figure schematically as a thin line. A flange 18 extending towards the middle of the pipe can be seen on the inside of the inner pipe 16, the task of which flange is to hinder the gases and the solid material, which travel upwards along the inner surface of the inner pipe 6. In this way especially the heavier particles can be made to remain in the furnace for longer and they can be made to burn out better. The first pipe 3 is formed of two halves 3a and 3b, the cross-sections of which are approximately in the shape of a half circle. The halves 3a and 3b are arranged against each other almost to align with each other, so that a gap is formed between the edges, which gap functions as an air opening 5. Into the second vertical edge of both halves has been arranged a fold 22a and 22b, which points perpendicularly away from the pipe, into which folds the pre-heating pipes 13 are attached.

A mantle (not shown) can be formed around the device 20, with the aid of which mantle the design of the device 20 can be made pleasing.

Only one advantageous embodiment of the invention is shown in the Figures. The Figures do not separately show matters that are irrelevant in view of the main idea of the invention, known as such or obvious as such for a person skilled in the art.

It is apparent to a person skilled in the art that the invention is not limited exclusively to the examples described above, but that the invention can vary within the scope of the claims presented below. The dependent claims present some possible embodiments of the invention, and they are not to be considered to restrict the scope of protection of the invention as such.

Claims

1. A method for combusting solid fuel, wherein

- a fuel bed of solid fuel is formed in the first pipe (3), which is at an angle in relation to the horizontal plane and equipped with openings (5),

- the fuel bed is combusted in the first pipe (3),

- air needed for the combustion comes into the first pipe (3) from the openings (5) and

- flue gases are led out from the first pipe (3) via its top part (21 ), characterized in that in the method

- the fuel bed is ignited only at its surface,

- the fuel bed is combusted only at its surface so that a combustion zone of a certain height is formed on the surface of the fuel bed, and

- the combustion advances as a zone in a controlled manner downwards in the fuel bed.

2. A method according to claim 1 , characterized in that the fuel bed is formed and the combustion takes place in a substantially vertical first pipe (3).

3. A method according to claim 1 or 2, characterized in that the air needed for the combustion comes into the first pipe (3) from several openings (5) on different heights on the fuel bed.

4. A method according to claim 3, characterized in that a part of the air needed for the combustion comes into the first pipe (3) at the combustion zone and a part from below the combustion zone.

5. A method according to claim 1, 2, 3 or 4, characterized in that a part of the air needed for the combustion comes into the first pipe (3) from above the combustion zone.

6. A method according to any of the preceding claims, characterized in that - flue gases are led via the top part (21) of the first pipe (3) to a substantially vertical second pipe (2),

- in the second pipe (2) the flue gases are led downwards,

- from the second pipe (2) the flue gases are led into an exhaust pipe (4).

7. A method according to claim 6, characterized in that ash is separated from the flue gases into an ash pipe (11 ) arranged in the bottom end of the second pipe (2).

8. A method according to any of the preceding claims, characterized in that the amount of air flowing from the openings (5) into the first pipe (3) is controlled by closing and opening one or more openings (5) partly or completely.

9. A method according to any of the preceding claims, characterized in that the fuel bed is formed by feeding fuel from the filling opening (1 ) above the first pipe

(3).

10. A method according to any of the preceding claims, characterized in that air is brought to the vicinity of the air openings (5) of the first pipe (3) along a preheating duct, and while passing in said preheating duct the air is preheated with the aid of the combustion heat from the first pipe (3).

11. A method according to claim 10, characterized in that the air passes in the preheating duct along the outer surface of the first pipe (3).

12. A method according to any of the preceding claims, characterized in that the air needed for the combustion is lead from the openings (5) into the first pipe (3) substantially in the direction of the tangent of the inner surface of the first pipe (3).

13. A heating device (20), which is suited for burning solid fuel, which comprises a first pipe (3), wherein a fuel bed of solid fuel is to be formed, which first pipe (3) is

- at an angle in relation to the horizontal plane, - open at its top end in order to lead flue gases out from the first pipe (3) via its top part (21 ),

- equipped with openings (5), from which air needed for the combustion is arranged to flow into the first pipe (3), characterized in that the heating device further comprises

- a substantially vertical second pipe (2), the top part of which is arranged in gas connection with the top part (21 ) of the first pipe in order to lead the flue gases downwards in the second pipe (2),

- an exhaust pipe (4), which is arranged at a junction of the exhaust pipe in gas connection with the second pipe (2) in order to lead the flue gases away from the heating device (20).

14. A heating device (20) according to claim 13, characterized in that the first pipe (3) is substantially vertical.

15. A heating device (20) according to claim 13 or 14, characterized in that the first pipe has openings (5) on several different heights.

16. A heating device (20) according to claim 13, 14 or 15, characterized in that a substantially vertical ash pipe (11 ) for separating ash from the flue gases has been arranged in the bottom end of the second pipe (2), below the junction of the exhaust pipe (4).

17. A heating device (20) according to claim 16, characterized in that it comprises an ash box (6) which can be opened, and that the bottom end of the ash pipe (11 ) and the bottom end of the first pipe (3) are in connection with the ash box (6).

18. A heating device (20) according to any of the preceding claims 13-17, characterized in that it comprises one or more closures for partly or completely closing and opening one or more openings (5) in order to control the amount of air flowing into the first pipe (3) from the openings (5).

19. A heating device (20) according to any of the preceding claims 13-18, characterized in that a filling opening (1) which can be opened and closed has been arranged above the first pipe (3) for feeding fuel into the first pipe (3).

20. A heating device (20) according to any of the preceding claims 13-19, characterized in that it comprises a preheating duct, which leads from outside the heating device (20) to the vicinity of the air openings (5) of the first pipe (3), and the air passing in said preheating duct is arranged to be preheated with the aid of the combustion heat from the first pipe (3).

21. A heating device (20) according to claim 20, characterized in that the preheating duct is arranged in connection with the outer surface of the first pipe (3).

22. A heating device (20) according to claim 20 or 21 , characterized in that the preheating duct is substantially vertical.

23. A heating device (20) according to claim 20, 21 or 22, characterized in that the preheating duct is tapered towards its top end.

24. A heating device (20) according to any of the preceding claims 13-23, characterized in that a horizontal cross-section of the inner part of the first pipe (3) is substantially circular.

25. A heating device (20) according to any of the preceding claims 13-24, characterized in that the relationship between the length of the inner part of the first pipe (3) to its diameter is 3-50, preferably 5-20.