EP4524467A1 - Biomass boiler and method for operating a biomass boiler - Google Patents

Abstract

The invention relates to a biomass heating boiler (1) for a biomass solid fuel (51), in particular pellets and/or wood chips, comprising: a boiler housing (2), a combustion chamber (3), a solid fuel conveying device (4) for feeding the combustion chamber (3) with the biomass solid fuel (51), wherein the solid fuel conveying device (4) has a conveying channel (5) and a conveying unit (6) for conveying the biomass solid fuel (51) within the conveying channel (5), a combustion air supply device (15) within the boiler housing (2) for distributing and supplying combustion air V, in particular primary (VP) and/or secondary (VS) and/or tertiary air (VT), into the combustion chamber 3 and an intake opening (24) for the combustion air (V), wherein the intake opening (24) is provided on the solid fuel conveying device (15) and a Combustion air flow path (25) for the combustion air (V) leads from the intake opening (24) to the conveying channel (5) and further into the combustion air supply device (15), wherein the combustion air flow path (25) is guided at least in sections along the conveying channel (5).The invention further relates to a method for operating a biomass boiler (1).

Description

• ein Kesselgehäuse,
• eine Brennkammer,
• eine Festbrennstoff-Fördereinrichtung zur Beschickung der Brennkammer mit dem Biomasse-Festbrennstoff, wobei die Festbrennstoff-Fördereinrichtung einen Förderkanal und eine Fördereinheit zur Förderung des Biomasse-Festbrennstoffes innerhalb des Förderkanals aufweist,
• eine Verbrennungsluft-Zufuhreinrichtung innerhalb des Kesselgehäuses zur Verteilung und Zuführung von Verbrennungsluft, insbesondere von Primär- und/oder Sekundär- und/oder Tertiärluft, in die Brennkammer und
• eine Ansaugöffnung für Verbrennungsluft.

The invention relates to a biomass boiler for a biomass solid fuel, in particular pellets and/or wood chips, comprising:

• a boiler housing,
• a combustion chamber,
• a solid fuel conveying device for feeding the combustion chamber with the biomass solid fuel, wherein the solid fuel conveying device has a conveying channel and a conveying unit for conveying the biomass solid fuel within the conveying channel,
• a combustion air supply device within the boiler housing for distributing and supplying combustion air, in particular primary and/or secondary and/or tertiary air, into the combustion chamber and
• an intake opening for combustion air.

Furthermore, the invention relates to a method for operating a biomass boiler.

Biomass boilers are used to generate heat. An example of such a biomass boiler is EP 3 495 045 A1 The combustion air required for combustion is drawn in through the intake opening and fed into the combustion chamber via the combustion air supply device, where a multi-stage combustion of the solid biomass fuel takes place. Many biomass boilers have multiple inlet openings in the combustion chamber for efficient and complete combustion, particularly for directing primary and/or secondary and/or tertiary air into the combustion chamber.

The disadvantage of conventional biomass boilers is that the high temperatures in the combustion chamber can cause damage to the solid fuel feed system. This is particularly the case during periods when no new, lower-temperature biomass solid fuel is being fed in.

To prevent damage caused by high temperatures, it is known from the state of the art to use water to cool those parts of the solid fuel conveying system of biomass boilers that are exposed to high temperatures. However, this technique has the disadvantage of being very complex.

Even though modern biomass boilers already achieve high levels of efficiency, development engineers are always keen to further improve the efficiency of biomass boilers.

From the PL 222 523 B1 A different type of burner for central heating boilers for the combustion of fine coal is known. In this burner, the combustion air is directed outside the burner housing across the conveyor channel of a conveyor screw and then directly through an opening into the combustion chamber. The brief heating via the conveyor channel and subsequent direct introduction of the combustion air through the opening only slightly increases the burner's efficiency.

In light of these statements, the object of the present invention is to at least partially mitigate or even completely eliminate the disadvantages of the prior art. Preferably, the object of the invention is to increase the service life of the components, in particular the solid fuel conveying device, of a biomass boiler of the type mentioned above, while simultaneously improving the efficiency.

This object is achieved by a biomass boiler according to claim 1 and a method for operating a biomass boiler according to claim 14.

According to the invention, in a biomass boiler of the type mentioned at the outset, the intake opening is provided on the solid fuel conveying device and a combustion air flow path for the combustion air from the intake opening to the conveying channel and further into the combustion air supply device leads, wherein the combustion air flow path is guided at least in sections along the conveying duct. Advantageously, the combustion air flow path according to the invention heats the combustion air over a longer period of time at the hot parts of the biomass boiler before it enters the combustion chamber, thereby increasing the efficiency of the biomass boiler compared to the prior art. By guiding the combustion air flow path at least in sections along the conveying duct, the solid fuel conveying device, in particular the conveying duct, is advantageously cooled. Furthermore, the combustion air flow path according to the invention can better protect the conveying duct from the heat of the combustion chamber, since the combustion air is not guided directly into the combustion chamber, but via the combustion air supply device. The combustion air supply device is arranged at least partially, preferably completely, within the boiler housing and is designed to direct the combustion air to at least one, preferably several, inlet opening(s) through which the combustion air is guided into the combustion chamber. The combustion air supply device can have a cavity between two walls of the boiler housing. This cavity can also be referred to as a boiler air jacket. The cavity can be formed or delimited, for example, by pipes and/or baffles. The combustion air supply device can extend at least partially around the combustion chamber. In one embodiment of the invention, the combustion air supply device is designed to guide primary and/or secondary and/or tertiary air into the combustion chamber. For this purpose, primary, secondary or tertiary inlet openings, to be described in more detail below, can be provided, in particular on a wall of the boiler housing facing the combustion chamber. The intake opening can be covered by a grille. If primary and/or secondary and/or tertiary air is fed into the combustion chamber using the combustion air supply device, the intake opening can preferably be a common intake opening for primary and/or secondary and/or tertiary air. Multiple intake openings or shared intake openings can also be provided. During operation of the biomass boiler, the ambient air is sucked in from the surroundings of the biomass boiler via the intake opening(s) and then guided as combustion air along the combustion air flow path into the combustion chamber. First, the combustion air travels along the combustion air flow path from the intake opening to the conveying channel of the solid fuel conveying device, thereby cooling it and reducing the risk of damage to the conveying channel. The combustion air is advantageously heated, which increases the efficiency of the biomass boiler. The combustion air flow path preferably runs along an outer wall of the conveying channel, preferably made of metal, on the inside of which the conveying unit is arranged. The combustion air flowing along the combustion air flow path is thus in contact with the outer wall of the conveying channel. The combustion air flow path is preferably guided at least once along the conveying channel transversely to the longitudinal axis of the conveying channel. "Transverse to the longitudinal axis" in this context means a direction that encloses an angle other than 0° to the longitudinal axis. The angle between the direction of the flow path and the longitudinal axis of the conveying channel is preferably at least 45°, preferably at least 70° or at least 80°, and most preferably substantially 90°. After the combustion air has been guided at least partially along the conveying channel, so that the conveying channel is cooled by the drawn-in combustion air, it flows along the combustion air flow path into the combustion air supply device, where it is further heated and then guided into the combustion chamber. The conveying unit for conveying the biomass solid fuel is located within the conveying channel, which is preferably designed as a tube with, for example, a round or n-shaped cross-section. The conveying channel can be designed as a stoker channel. The conveying unit is preferably designed as a screw conveyor. The conveyor unit conveys the biomass solid fuel from a storage area into the combustion chamber. For this purpose, the conveyor channel penetrates the boiler casing. through a through opening. The biomass boiler, for example, can have a heating output between 20 kW and 2000 kW.

In this disclosure, directions and orientations refer to the intended use of a biomass boiler. "Downward" in this context means, for example, in the direction of gravitational acceleration.

In one embodiment of the invention, the intake opening is provided on an underside of the conveying channel. The intake opening is preferably directed downwards, at least in sections. Alternatively, it is also possible to arrange the intake opening on an upper side of the conveying channel, preferably directed upwards. However, a preferably downward-facing intake opening has the advantage that the already heated and therefore rising ambient air can be more easily drawn in, and the interior of the biomass boiler is better protected from contamination.

A particularly advantageous possibility for guiding the combustion air at least in sections along the conveying channel is provided if an outer casing is arranged on, preferably around, the conveying channel, within which the combustion air flow path is guided. The outer casing can preferably completely surround the conveying channel circumferentially, in particular only in a limited longitudinal section of the conveying channel. The outer casing can have the intake opening(s). The outer casing can be made of metal. The outer casing can be fastened to the boiler housing and/or to the conveying channel. The outer casing can be at least partially accommodated in the boiler housing. So that ambient air can reach the intake opening in this case, the boiler housing can have at least one ventilation opening. The combustion air flow path is preferably formed between an inner wall of the outer casing and an outer wall of the conveying channel. For this purpose, the inner wall of the outer casing is spaced radially outwards from the outer wall of the conveying channel, preferably between 30 mm and 120 mm, in particular between 45 mm and 95 mm. In one embodiment of the invention, the combustion air flow path can run on two opposite sides of the conveying channel, preferably between a bottom and a top side of the conveying channel. Alternatively, the combustion air flow path can run in only one direction around the conveying channel, preferably completely around the conveying channel.

It is preferred if the boiler housing has an inlet opening for combustion air and the outer casing is arranged in the region of the inlet opening, in particular flanged to the boiler housing. In this way, the outer casing can guide the combustion air into the boiler housing and thus into the combustion air supply device. The inlet opening can be formed by one or more recesses on an outer wall of the boiler housing.

In one embodiment of the invention, the combustion air flow path leads from a bottom side of the conveying channel to a top side of the conveying channel. Preferably, the combustion air flow path is guided within the outer casing from the bottom side to the top side.

In one embodiment of the invention, the combustion air flow path leads from an upper side of the conveying channel to a lower side of the conveying channel. Preferably, the combustion air flow path is guided within the outer casing from the upper side to the lower side.

The combustion air flow path can initially be guided from a bottom side to a top side of the conveying channel and then via a deflection device back to the bottom side of the conveying channel. In an alternative embodiment, the reverse variant can also be implemented, so that the combustion air flow path is initially guided from a top side to a bottom side of the conveying channel and then via a deflection device back to the top side of the conveying channel. By means of a plurality of deflection devices, the combustion air flow path can also be guided several times between a bottom and a top side of the conveying channel. By guiding the combustion air from the bottom or top side to the top or bottom side, the conveying channel is cooled and the combustion air is heated. It is preferred if the flow path is guided within the outer casing between the bottom and the top side. For this purpose, the outer casing can also have a deflection device and/or corresponding guide plates, as described.

A particularly advantageous design is achieved when the combustion air flow path opens into the combustion air supply device at the bottom of the conveying channel.

To convey the combustion air into the combustion chamber, it is advantageous to provide a fan, particularly a suction fan, for conveying the combustion air. The suction fan is preferably arranged downstream of the heat exchanger in terms of gas flow. In particular, the fan can be arranged at an exhaust gas outlet of the biomass boiler. A fan can also be provided at the combustion air intake opening to convey combustion air into the combustion air flow path.

In one embodiment of the invention, the combustion air supply device is arranged within the boiler housing at least partially around the combustion chamber. This allows the combustion air to be introduced into the combustion chamber at various points.

It is advantageous if the combustion air supply device is configured to distribute the combustion air to one or more inlet openings in the combustion chamber. The one or more inlet openings can be arranged on a wall of the boiler housing facing the combustion chamber.

In one embodiment of the invention, the combustion air supply device can have at least one primary air inlet opening, which is designed to introduce the combustion air preferably directly into a primary combustion zone of the combustion chamber, wherein the at least one primary air inlet opening is preferably arranged below a firing grate in the combustion chamber. In the primary combustion zone, during operation of the biomass boiler, direct combustion of the solid biomass fuel takes place, in particular on the firing grate. The at least one primary air inlet opening can be arranged on a wall of the boiler housing facing the combustion chamber. The at least one primary air inlet opening can have a controllable and/or adjustable air damper in order to regulate and/or control the amount of primary air introduced into the combustion chamber.

In one embodiment of the invention, the combustion air supply device can have at least one secondary air inlet opening, which is designed to introduce the combustion air preferably directly into a secondary combustion zone of the combustion chamber, wherein the at least one secondary air inlet opening is preferably arranged above a firing grate in the combustion chamber. The combustion air introduced by the at least one secondary air inlet opening can also be referred to as secondary air. The at least one secondary air inlet opening can be arranged on a wall of the boiler housing facing the combustion chamber. In the secondary combustion zone, afterburning of the flue gases produced takes place during operation of the biomass boiler. In terms of gas flow, the secondary combustion zone is arranged downstream of the primary combustion zone. The secondary combustion zone is preferably arranged above the primary combustion zone. In an alternative embodiment, it can be provided that ambient air is sucked in through a further intake opening and the ambient air sucked in by the further intake opening enters the combustion chamber as combustion air via the at least one secondary air inlet opening. In this case, the at least A secondary air inlet opening is not part of the combustion air supply device, but receives combustion air exclusively via the additional intake opening, which is independent of the intake opening. The at least one secondary air inlet opening can have a controllable and/or adjustable air flap to regulate and/or control the amount of secondary air introduced into the combustion chamber.

In one embodiment of the invention, the combustion air supply device can have at least one tertiary air inlet opening, which is designed to introduce the combustion air preferably directly into a tertiary combustion zone of the combustion chamber, wherein the at least one tertiary air inlet opening is preferably arranged above a firing grate in the combustion chamber. The combustion air introduced by the at least one tertiary air inlet opening can also be referred to as tertiary air. The tertiary combustion zone can also be referred to as a burnout zone and serves for the further afterburning of the combustion gases. The at least one tertiary air inlet opening can be arranged on a wall of the boiler housing facing the combustion chamber. The tertiary combustion zone is fluidically connected to the secondary combustion zone and is preferably located above the firing grate. In an alternative embodiment, it can be provided that ambient air is sucked in through a further intake opening, and the ambient air sucked in by the further intake opening enters the combustion chamber as tertiary air via the at least one tertiary air inlet opening. In this case, the at least one tertiary air inlet opening is not part of the combustion air supply device, but receives combustion air exclusively via the further intake opening, which is independent of the intake opening. The at least one tertiary air inlet opening can have a controllable and/or adjustable air flap in order to regulate and/or control the amount of tertiary air introduced into the combustion chamber.

The above-mentioned problem is also solved by a method for operating a biomass boiler of the type described. In this method, the combustion air is guided through the combustion air flow path for preheating and/or cooling the conveying channel. The advantages and effects described above in connection with the biomass boiler are transferable to the method according to the invention.

• Fig. 1 eine Schrägansicht auf einen Biomasse-Heizkessel mit einer Festbrennstoff-Fördereinrichtung;
• Fig. 2 einen Querschnitt eines Biomasse-Heizkessels mit einer Festbrennstoff-Fördereinrichtung;
• Fig. 3 eine Schrägansicht auf einen Biomasse-Heizkessel mit einer Festbrennstoff-Fördereinrichtung in aufgeschnittener Darstellung; und
• Fig. 4 eine aufgeschnittene Darstellung eines Biomasse-Heizkessels.

The invention is described in more detail below with reference to figures, to which, however, it is not intended to be limited. They show:
They show:

• Fig. 1 an oblique view of a biomass boiler with a solid fuel conveying device;
• Fig. 2 a cross-section of a biomass boiler with a solid fuel conveying device;
• Fig. 3 an oblique view of a biomass boiler with a solid fuel conveyor in a cutaway view; and
• Fig. 4 a cutaway view of a biomass boiler.

Fig. 1 shows a biomass boiler 1 for a biomass solid fuel 51 (see Fig. 2 ), in particular pellets and/or wood chips. The biomass boiler 1 has a boiler housing 2, inside which a combustion chamber 3 (see Fig. 2 ) is arranged. In order to convey the biomass solid fuel 51 into the combustion chamber 3, the biomass boiler 1 has a solid fuel conveying device 4. The illustrated solid fuel conveying device 4 has a conveying channel 5, in the interior of which a conveying unit 6 in the form of a conveyor screw 7 (see Fig. 2 ) is arranged. A feed opening 8 is provided on the upper side 32 of the conveying channel 5 in the area of the end facing away from the biomass boiler 1. Via a 8 flanged lock unit 9, in particular a rotary valve, the biomass solid fuel 51 enters the interior of the conveying channel 5 and can be conveyed from there towards the combustion chamber 3. The conveying channel 5 is inclined downwards towards the end facing away from the biomass boiler 1.

Fig. 2 shows a longitudinal section of the biomass boiler 1. The conveyor screw 7 is driven by a motor 10 (see Fig. 1 ). The solid biomass fuel 51 is conveyed from the feed opening 8 into the combustion chamber 3 by the spiral 11 along the hollow shaft 12 of the conveyor screw 7. A firing grate 13 is arranged within the combustion chamber 3. The combustion chamber 3 is lined with fireclay bricks 14 for heat protection.

In order to direct combustion air V into the combustion chamber 3, the biomass boiler 1 has a combustion air supply device 15 within the boiler housing 2 for distributing and supplying the combustion air V. In order to suck in the combustion air V, the biomass boiler 1 can have a suction fan 28 (see Fig. 1 ), which is arranged at an exhaust gas outlet opening of the biomass boiler 1. The combustion air supply device 15 can have a cavity 16 between walls 17 of the boiler housing 2. The cavity 16 can, for example, also be delimited by pipes and/or baffles. Combustion air V can be guided via this cavity 16 to one or more primary air inlet openings 18. The one or more primary air inlet openings 18 are arranged below the firing grate 13 in the illustration shown. The combustion air V can also be guided via the combustion air supply device 15, in particular the cavity 16, to one or more secondary air inlet openings 19 and/or one or more tertiary air inlet openings 20 and finally into the combustion chamber 3. Alternatively, at least one further intake opening (not shown) can be provided in the boiler housing 2, through which ambient air U is sucked in and fed to the at least one secondary air inlet opening 19 and/or to the at least one tertiary air inlet opening 20 and finally into the combustion chamber 3. In this case, ambient air U or combustion air V from the combustion air supply device 15 reaches exclusively the primary air inlet openings 18, but not to the at least one secondary air inlet opening 19 and/or to the at least one tertiary air inlet opening 20. In this alternative variant, the at least one secondary air inlet opening 19 and/or the at least one tertiary air inlet opening 20 draws ambient air U exclusively through the at least one further intake opening. The inlet openings 18, 19, 20 can be arranged on a wall of the boiler housing 17 facing the combustion chamber 3. The fireclay bricks 14 can have corresponding recesses 50 for the inlet openings 18, 19, 20. The primary air inlet openings 18 are configured to direct combustion air V as primary combustion air VP, preferably directly into a primary combustion zone 21. In the illustration shown, the primary combustion air VP passes through the firing grate 13 into the primary combustion zone 21. In the primary combustion zone 21, during operation of the biomass boiler 1, direct combustion of the solid biomass fuel 51 takes place. Preferably, the primary air inlet openings 18, as already mentioned, are arranged below the firing grate 13. The secondary air inlet openings 19 are configured to direct combustion air V as secondary combustion air VS, preferably directly into a secondary combustion zone 22. In the secondary combustion zone 22, post-combustion of the resulting combustion gases takes place during operation of the biomass boiler 1. In terms of gas flow, the secondary combustion zone 22 is arranged downstream of the primary combustion zone 21, in particular above the primary combustion zone 21. The tertiary air inlet openings 20 are configured to direct combustion air V as tertiary combustion air VT, preferably directly into a tertiary combustion zone 23. The tertiary combustion zone 23 adjoins the secondary combustion zone 22 in terms of flue gas flow. In the tertiary combustion zone 23, which is also referred to as the burnout zone, further post-combustion of the combustion gases takes place to reduce emissions.

Due to the high temperatures in the combustion chamber 3, which can reach up to 1100 °C, parts of the biomass boiler 1 that are not protected by fireclay or cooled may be damaged. In particular, parts of the solid fuel conveying device 4, such as the conveying channel 5 or the conveyor screw 7, may be damaged due to the heat during phases in which no new biomass solid fuel 51 is being fed.

In order to reduce the risk of damage to the solid fuel conveying device 4, the invention provides that at least one intake opening 24 is provided on the solid fuel conveying device 4 and a combustion air flow path 25 for the combustion air V leads from the intake opening 24 to the conveying channel 5 and further into the combustion air supply device 15. The combustion air flow path 25 is guided at least in sections along the conveying channel 5.

In the illustration shown according to Fig. 2 an outer casing 26 is provided which essentially completely surrounds a longitudinal section of the conveying channel 5. The outer casing 26 is in Fig. 2 at least partially accommodated in the boiler housing 2. On the underside 27 of the conveying channel 5, the outer casing 26 has a plurality of downwardly directed slot-shaped intake openings 24 through which ambient air U can be sucked in as combustion air V. In order for the ambient air U to reach the intake openings 24 located within the boiler housing 2, the boiler housing 2 can have one or more ventilation openings 52, which in the embodiment shown are located below the conveying channel 5. The outer casing 26 is connected to the boiler housing 2 and a flange 29 of the conveying channel 5. The combustion air flow path 25 is formed in the illustration shown between an inner wall 30 of the outer casing 26 and an outer wall 31 of the conveying channel 5. The inner wall 30 and the outer wall 31 are preferably spaced apart from one another by at least 40 mm, in particular at least 45 mm. The combustion air V flowing past is thus in contact with the conveying channel 5.

The combustion air flow path 25 initially runs from the intake openings 24 on the underside 27 of the conveying channel 5 along a first flow path portion 33a of the outer casing 26 to an upper side 32 of the conveying channel 5. At the upper side 32, the outer casing 26 has a deflection device 34, at which the combustion air V is deflected and to which a second flow path portion 33b adjoins, leading from the upper side 32 back to the underside 27 of the conveying channel 5. A partition wall 35 of the outer casing 26 separates the first flow path portion 33a from the second flow path portion 33b. The partition wall 35 has a preferably substantially horizontally oriented opening 36, through which the combustion air V passes from the first flow path portion 33a into the second flow path portion 33b. In terms of flow, the combustion air V in the illustration shown during operation of the biomass boiler 1 therefore flows from the intake openings 28 along the first flow path part 33a upwards, then through the opening 36 in the partition wall 35 and further downwards along the second flow path part 33b. The first 33a and the second flow path part 33b can each run on two opposite sides of the conveying channel 5 (see Fig. 4 ).

At the underside 27 of the conveying channel 5, the combustion air V enters the combustion air supply device 15 through slot-like inlet openings 37 and can, as described above, be supplied to the combustion chamber 3 as primary air VP, secondary air VS and/or tertiary air VT. In this case, the intake openings 24 serve as common intake openings 24 for primary combustion air VP, secondary combustion air VS and/or tertiary combustion air VT. Alternatively, as also described above, the combustion air supply device 15 can only introduce primary air VP into the combustion chamber 3. The secondary air VS and the tertiary air VT can be sucked in via at least one further intake opening (not shown) in the boiler housing 2, which is independent of the intake openings 24.

Claims (14)

Biomass boiler (1) for a biomass solid fuel (51), in particular pellets and/or wood chips, comprising: a boiler housing (2), a combustion chamber (3), a solid fuel conveying device (4) for feeding the combustion chamber (3) with the biomass solid fuel (51), wherein the solid fuel conveying device (4) has a conveying channel (5) and a conveying unit (6) for conveying the biomass solid fuel (51) within the conveying channel (5), a combustion air supply device (15) within the boiler housing (2) for distributing and supplying combustion air (V), in particular primary (VP) and/or secondary (VS) and/or tertiary air (VT), into the combustion chamber (3) and an intake opening (24) for the combustion air (V), characterized in that the intake opening (24) is provided on the solid fuel conveying device (15) and a combustion air flow path (25) for the combustion air (V) leads from the intake opening (24) to the conveying channel (5) and further into the combustion air supply device (15), wherein the combustion air flow path (25) is guided at least in sections on the conveying channel (5). Biomass boiler (1) according to claim 1, characterized in that the suction opening (24) is provided on an underside (27) of the conveying channel (5). Biomass boiler (1) according to claim 1 or 2, characterized in that an outer casing (26) is arranged on, preferably around, the conveying channel (5), within which the combustion air flow path (25) is guided. Biomass boiler (1) according to claim 3, characterized in that the boiler housing (2) has an inlet opening (37) for combustion air (V) and the outer casing (26) in the region the inlet opening, in particular flanged to the boiler housing (2). Biomass boiler (1) according to one of claims 1 to 4, characterized in that the combustion air flow path (25) leads from a bottom side (27) of the conveying channel (5) to a top side (32) of the conveying channel (5). Biomass boiler (1) according to one of claims 1 to 5, characterized in that the combustion air flow path (25) leads from an upper side (32) of the conveying channel (5) to a lower side (27) of the conveying channel (5). Biomass boiler (1) according to one of claims 1 to 6, characterized in that the combustion air flow path (25) opens into the combustion air supply device (15) at the underside (27) of the conveying channel (5). Biomass boiler (1) according to one of claims 1 to 7, characterized in that a fan, in particular a suction fan (28), is provided for conveying the combustion air (V). Biomass boiler (1) according to one of claims 1 to 8, characterized in that the combustion air supply device (15) is arranged within the boiler housing (2) at least partially around the combustion chamber (3). Biomass boiler (1) according to claim 9, characterized in that the combustion air supply device (15) is designed to distribute the combustion air (V) to one or more inlet openings (18, 19, 20) in the combustion chamber (3). Biomass boiler (1) according to claim 10, characterized in that the combustion air supply device (15) has at least one primary inlet opening (18) which is designed to supply the combustion air (V) preferably directly into a primary combustion zone (21) of the combustion chamber (3), wherein the at least one primary inlet opening (18) is preferably arranged below a firing grate (13) in the combustion chamber (3). Biomass boiler (1) according to claim 10 or 11, characterized in that the combustion air supply device (15) has at least one secondary inlet opening (19) which is designed to introduce the combustion air (V) preferably directly into a secondary combustion zone (22) of the combustion chamber (3), wherein the at least one secondary inlet opening (19) is preferably arranged above a firing grate (13) in the combustion chamber (3). Biomass boiler according to one of claims 10 to 12, characterized in that the combustion air supply device (15) has at least one tertiary inlet opening (20) which is designed to introduce the combustion air (V) preferably directly into a tertiary combustion zone (23) of the combustion chamber (3), wherein the at least one tertiary inlet opening (20) is preferably arranged above a firing grate (13) in the combustion chamber (3). Method for operating a biomass boiler (1) according to one of claims 1 to 13, wherein the combustion air (V) is guided through the combustion air flow path (25) for preheating it and/or for cooling the conveying channel (5).

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