Efficient hot water boiler combusting biomass briquette

Abstract

The utility model discloses an efficient hot water boiler combusting biomass briquette, and relates to the technical field of biomass boilers. The utility model relates to a biomass fuel boiler, in particular to a biomass fuel boiler, and aims to solve the problems of low combustion efficiency caused by fuel accumulation and incapability of realizing continuous and stable feeding in the fuel combustion process of the conventional biomass fuel boiler, and low boiler heat efficiency caused by the fact that high-temperature flue gas passing through a hearth is not effectively and fully utilized. The boiler comprises a transmission device (1), an inclined pushing reciprocating grate (2), a hopper (3), a hearth (4), an upper boiler barrel (5), a lower boiler barrel (6), a convection bank (7), a connecting flue (8), an air preheater (9), a primary air system (10) and a secondary air system (11), and the output end of the transmission device (1) is connected with the inclined pushing reciprocating grate (2) and drives the inclined pushing reciprocating grate (2) to feed materials back and forth in a reciprocating mode. The utility model is used in the boiler industry.

Description

Technical Field

[0001] The utility model relates to the technical field of biomass boilers, in particular to a high-efficiency hot water boiler burning biomass briquette fuel. Background Art

[0002] The so-called biomass molded fuel is made from woody plants, herbaceous plants and their waste as raw materials, and is processed into molded fuel with a certain shape (mostly regular shape) and size, high bulk density, and easy transportation and combustion using mechanical processing (such as cutting, crushing, etc.) and dense molding techniques.

[0003] As a renewable energy source, biomass has the unique property of being renewable, and the smoke and sulfur dioxide emissions of its combustion products are much lower than those of burning coal.

[0004] However, existing biomass fuel boilers are prone to fuel accumulation during the fuel combustion process and cannot achieve continuous and stable fuel supply, resulting in low combustion efficiency. At the same time, the high-temperature flue gas after passing through the furnace is not effectively and fully utilized, resulting in low boiler thermal efficiency. Therefore, the current biomass fuel boilers cannot achieve efficient combustion and utilization, resulting in energy loss. Utility Model Content

[0005] In order to solve the problems that the existing biomass fuel boilers are prone to fuel accumulation during the fuel combustion process, cannot achieve continuous and stable feeding, resulting in low combustion efficiency, and the high-temperature flue gas after passing through the furnace is not effectively and fully utilized, resulting in low boiler thermal efficiency, the utility model proposes a high-efficiency hot water boiler that burns biomass molded fuel.

[0006] The technical solution adopted by the utility model to solve the above technical problems is:

[0007] A high-efficiency hot water boiler burning biomass pellet fuel includes a transmission device, an oblique push reciprocating grate, a hopper, a furnace, an upper drum, a lower drum, a convection tube bundle, a connecting flue, an air preheater, a primary air system and a secondary air system. The output end of the transmission device is connected to the oblique push reciprocating grate, and drives the oblique push reciprocating grate to reciprocate forward and backward. The hopper is arranged above the front of the oblique push reciprocating grate, and the furnace is arranged above the oblique push reciprocating grate. The rear of the furnace is connected to the convection tube bundle, and the upper end of the convection tube bundle is connected to the upper drum. The lower end of the convection tube bundle is connected to the lower boiler drum. A group of middle smoke partitions is provided in the middle of the convection tube bundle. A group of side smoke partitions are provided on both sides of the convection tube bundle. The side smoke partitions and the middle smoke partitions are arranged alternately. The rear part of the convection tube bundle is connected to the connecting flue. The end of the connecting flue is connected to the air preheater. The air inlet end of the primary air system is connected to the air outlet end of the air preheater. The air outlet end of the primary air system is connected to the lower air inlet end of the oblique push reciprocating grate. The air outlet end of the secondary air system is connected to the middle and lower part of the furnace.

[0008] Furthermore, two vertical smoke-partitioning plates are arranged in parallel in the convection tube bundle, which divide the convection tube bundle into a central area and two side areas. The upper end of the central area is connected to the furnace, the lower end of the central area is connected to the side area, and the upper end of the side area is connected to the connecting flue. The central smoke-partitioning plate is arranged in the central area, and the side smoke-partitioning plates are arranged in the side areas.

[0009] Furthermore, a group of middle smoke partitions includes two middle smoke partitions arranged in sequence from top to bottom, the upper middle smoke partition is fixedly connected to the front side of the convection tube bundle, and the lower middle smoke partition is fixedly connected to the rear side of the convection tube bundle; a group of side smoke partitions includes two side smoke partitions arranged in sequence from top to bottom, the upper side smoke partition is fixedly connected to the rear side of the convection tube bundle, and the lower side smoke partition is fixedly connected to the front side of the convection tube bundle.

[0010] Furthermore, the middle smoke-isolating plate and the upper side smoke-isolating plates are respectively arranged to tilt upward from front to back, and the lower side smoke-isolating plates are respectively arranged to tilt downward from front to back.

[0011] Furthermore, a front arch is provided at the lower portion of the front wall of the furnace, and a rear arch is provided at the lower portion of the rear wall of the furnace.

[0012] Furthermore, the air outlet end of the secondary air system is respectively connected to a front secondary air outlet nozzle and a rear secondary air outlet nozzle, the front secondary air outlet nozzle is arranged above the front arch, and the rear secondary air outlet nozzle is arranged above the arch head of the rear arch.

[0013] Furthermore, the oblique push reciprocating grate is of a reciprocating inclined type, and the oblique push reciprocating grate is inclined downward from front to back, and the inclination angle is 18°.

[0014] Furthermore, the transmission device includes a reducer and a cam mechanism, the output shaft of the reducer is connected to the cam mechanism, and the reducer realizes linear reciprocating motion of the output end of the transmission device through the cam mechanism.

[0015] Furthermore, a SNCR denitrification system is provided in the lower part of the furnace.

[0016] Furthermore, a dust drop device is provided below the convection tube bundle.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The utility model provides a high-efficiency hot water boiler burning biomass briquette fuel, which has the performance characteristics of high combustion efficiency, high boiler thermal efficiency, low pollution emission, long-term stable output, safe and reliable water circulation, etc.

[0019] This utility model combustion equipment consists of a hopper, an oblique push reciprocating grate, and a transmission device. The hopper is arranged at the front of the boiler, and the worm gear transmission mechanism is used to adjust the opening height of the internal gate, control the material layer thickness and feed rate, and adapt to changes in boiler load and material type.

[0020] The grate of this utility model consists of layered grate plates, brackets, beams, guard plates, and air chambers. The grate plates are mounted on the brackets. Every other row of grate plates is movable, and every other row is fixed. The movable grate plates propel the fuel back and forth, ultimately pushing it into the slag remover. The back-fire surface of the grate is effectively cooled by the primary air supply. To ensure optimal air distribution, the grate is equipped with multiple air chambers, each sealed by a partition. The air pressure in each chamber is controlled by air duct baffles and adjusted according to combustion conditions.

[0021] This utility model utilizes a staged air supply technology, with primary air flow provided below the grate and secondary air flow provided at multiple locations below the furnace. Separate fans supply each primary and secondary air, with high-pressure fans being used for the secondary air. The primary air volume accounts for 70% of the total air volume, while the secondary air volume accounts for 30%, with a pressure of at least 5000 Pa and a speed of approximately 55 m / s.

[0022] The utility model controls the temperature of the flue gas entering the convection tube bundle to be below 780° C. by reasonably arranging the heating surface of the furnace.

[0023] The utility model flushes the flue gas in multiple processes in the convection tube bundle, so that the flue gas filling degree is better and the utilization rate is higher.

[0024] The air preheater of this utility model is made of enamel tube material, which is resistant to low-temperature corrosion and chlorine corrosion. The air preheater can heat the cold air at 20℃ to above 80℃. The high-temperature hot air enters the furnace, which is more conducive to the combustion and burnout of the fuel.

[0025] The water circulation system of this utility model boiler is a mixed circulation system. The furnace and a portion of the convection tube bundles utilize forced circulation, while the remaining convection tube bundles utilize natural circulation. Return water from the heating network is drawn by a circulating water pump through the lower headers of the water-cooled walls on both sides. Connecting pipes distribute the return water to the front and rear lower headers. After rising through the upper, lower, and side water-cooled walls, it enters the upper drum through the outlet pipes of the side upper headers. The front and rear water-cooled walls then directly enter the upper drum. The first row of the convection tube bundle descends, while the second to fifth rows ascend. The remaining convection tube bundles utilize natural circulation. The rising and falling water velocities of the circulation loop ensure safe boiler operation.

[0026] The thermal efficiency of the boiler of the utility model can reach over 88%. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the overall structure of the utility model;

[0028] Figure 2 This is a schematic diagram of the flow direction of smoke in the middle area of the convection tube bundle in the present invention;

[0029] Figure 3 This is a schematic diagram of the flow direction of the flue gas in the lower part of the convection tube bundle in the present invention;

[0030] Figure 4 This is a schematic diagram of the flow direction of smoke in the side area of the convection tube bundle in the present invention;

[0031] Figure 5 It is a top view schematic diagram of the convection tube bundle in the utility model;

[0032] Figure 6 It is a structural schematic diagram of the transmission device and the oblique push reciprocating grate in the utility model. DETAILED DESCRIPTION

[0033] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0034] Specific implementation method 1: Combination Figures 1 to 5The embodiment of the present invention is described as follows: a high-efficiency hot water boiler burning biomass molded fuel includes a transmission device 1, an oblique push reciprocating grate 2, a hopper 3, a furnace 4, an upper drum 5, a lower drum 6, a convection tube bundle 7, a connecting flue 8, an air preheater 9, a primary air system 10 and a secondary air system 11. The output end of the transmission device 1 is connected to the oblique push reciprocating grate 2, and drives the oblique push reciprocating grate 2 to reciprocate forward and backward. The hopper 3 is arranged above the front of the oblique push reciprocating grate 2, and the furnace 4 is arranged above the oblique push reciprocating grate 2. The rear of the furnace 4 is connected to the convection tube bundle 7, and the upper end of the convection tube bundle 7 is connected to the upper The convection tube bundle 7 is connected to the boiler drum 5, and the lower end of the convection tube bundle 7 is connected to the lower boiler drum 6. A group of middle smoke partition plates 7-1 is provided in the middle of the convection tube bundle 7, and a group of side smoke partition plates 7-2 are respectively provided on both sides of the convection tube bundle 7. The side smoke partition plates 7-2 and the middle smoke partition plates 7-1 are staggered. The rear part of the convection tube bundle 7 is connected to the connecting flue 8, and the end of the connecting flue 8 is connected to the air preheater 9. The air inlet end of the primary air system 10 is connected to the air outlet end of the air preheater 9, the air outlet end of the primary air system 10 is connected to the lower air inlet end of the oblique reciprocating grate 2, and the air outlet end of the secondary air system 11 is connected to the middle and lower part of the furnace 4.

[0035] The combustion equipment consists of a hopper, an oblique reciprocating grate, and a transmission device. The hopper is located at the front of the boiler. A worm gear mechanism is used to adjust the opening height of the internal gate, controlling the thickness of the material layer and the feed rate to adapt to changes in boiler load and material type.

[0036] The grate consists of layered grate plates, brackets, beams, guard plates, and air chambers. The grate plates are mounted on the brackets. Every other row of grate plates is movable, and every other row is fixed. The movable grate plates propel the fuel back and forth, ultimately pushing it into the slag remover. The backside of the grate is effectively cooled by the primary air supply. To ensure optimal air distribution, the grate is equipped with multiple air chambers, each sealed by a partition. The air pressure in each chamber is controlled by air duct dampers and adjusted according to combustion conditions.

[0037] A hopper 3 is provided above the front of the obliquely pushed reciprocating grate 2. Fuel is fed through the hopper 3 and falls onto the obliquely pushed reciprocating grate 2.

[0038] The grate plates of the oblique push reciprocating grate 2 are composed of fixed plates and movable plates, and the fixed plates and movable plates are arranged at intervals.

[0039] The furnace adopts a graded air supply technology, with primary air provided under the grate and secondary air provided at multiple locations in the lower part of the furnace. Each of the primary and secondary air is supplied by separate fans, with high-pressure fans being used for the secondary fans. The primary air volume accounts for 70% of the total air volume, while the secondary air volume accounts for 30% of the total air volume, with a pressure of over 5000Pa and a speed of approximately 55m / s.

[0040] The furnace 4 is formed by a front membrane water-cooled wall, a rear membrane water-cooled wall, and two side membrane water-cooled walls.

[0041] The air preheater uses enameled tubes to resist low-temperature and chlorine corrosion. The air preheater heats 20°C cold air to over 80°C. The high-temperature hot air, once entering the furnace, facilitates fuel combustion and burnout.

[0042] The air preheater 9 is connected to dust removal equipment, induced draft fans, chimneys, etc.

[0043] Specific implementation method 2: Combination Figures 1 to 5 This embodiment describes two vertical smoke screens 7-3 arranged side by side within the convection tube bundle 7. These divide the convection tube bundle 7 into a central region and two side regions. The upper end of the central region communicates with the furnace 4, the lower end of the central region communicates with the side regions, and the upper ends of the side regions communicate with the connecting flue 8. The central smoke screen 7-1 is located within the central region, and the side smoke screens 7-2 are located within the side regions. Other components and connection methods are the same as those in the first embodiment.

[0044] The flue gas flushes through multiple processes in the convection tube bundle, making the flue gas fuller and more efficient.

[0045] Specific implementation method three: Combination Figures 1 to 5 To explain this embodiment, a set of central smoke partitions 7-1 includes two central smoke partitions 7-1 arranged sequentially from top to bottom. The upper central smoke partition 7-1 is fixedly connected to the front side of the convection tube bundle 7, and the lower central smoke partition 7-1 is fixedly connected to the rear side of the convection tube bundle 7. A set of side smoke partitions 7-2 includes two side smoke partitions 7-2 arranged sequentially from top to bottom. The upper side smoke partition 7-2 is fixedly connected to the rear side of the convection tube bundle 7, and the lower side smoke partition 7-2 is fixedly connected to the front side of the convection tube bundle 7. Other components and connection methods are the same as those of the second embodiment.

[0046] Specific implementation method four: Combination Figures 1 to 5 In this embodiment, the middle smoke partition plate 7-1 and the upper side smoke partition plates 7-2 are arranged to tilt upward from front to back, while the lower side smoke partition plates 7-2 are arranged to tilt downward from front to back. Other components and connection methods are the same as those of the third embodiment.

[0047] Specific implementation method five: Combination Figure 1 In this embodiment, a front arch 4-1 is provided at the lower portion of the front wall of the furnace 4, and a rear arch 4-2 is provided at the lower portion of the rear wall of the furnace 4. Other components and connection methods are the same as those of the first embodiment.

[0048] The front arch 4 - 1 and the rear arch 4 - 2 are attached to the front arch tube and the rear arch tube by concrete.

[0049] According to the high volatile matter and low ash content of biomass, a reasonable front and rear arch combination is designed, and with the assistance of primary air, it can be burned quickly and completely.

[0050] Specific implementation method six: combination Figure 1 To describe this embodiment, the outlet end of the secondary air system 11 is connected to a front secondary air outlet nozzle 11-1 and a rear secondary air outlet nozzle 11-2. The front secondary air outlet nozzle 11-1 is positioned above the front arch 4-1, while the rear secondary air outlet nozzle 11-2 is positioned above the arch head of the rear arch 4-2. The remaining components and connection methods are the same as those in the fifth embodiment.

[0051] The secondary air system is divided into two parts: the front secondary air and the rear secondary air. Both the front secondary air and the rear secondary are equipped with multiple nozzles.

[0052] Biomass fuels contain over 70% volatile matter, which consists of combustible gases such as methane, hydrogen, carbon monoxide, hydrogen sulfide, and some complex organic compounds. If these volatiles are not promptly burned after analysis, they will result in chemical incomplete combustion losses (q3). The purpose of placing secondary air here is to disrupt the airflow, increase oxygen levels, improve combustion conditions, increase combustion efficiency, and reduce chemical incomplete combustion losses (q3).

[0053] Specific implementation method seven: combination Figure 1 and Figure 6 In this embodiment, the oblique push reciprocating grate 2 is a reciprocating tilting type, and the oblique push reciprocating grate 2 is tilted downward from front to back, and the tilt angle is 18 degrees. Other components and connection methods are the same as those of the specific embodiment 1.

[0054] Specific implementation method eight: combination Figure 1 and Figure 6 This embodiment describes a transmission device 1 comprising a reducer and a cam mechanism. The output shaft of the reducer is connected to the cam mechanism, and the reducer achieves linear reciprocating motion at the output end of the transmission device 1 through the cam mechanism. Other components and connection methods are the same as those of the first embodiment.

[0055] The transmission device 1 is located in front of the entire boiler. The reducer continuously realizes the "forward-backward-forward-backward" movement of the main output shaft through the cam mechanism.

[0056] Specific implementation method nine: Combination Figure 1 In this embodiment, the lower portion of the furnace 4 is provided with an SNCR denitration system 13. Other components and connection methods are the same as those of the first embodiment.

[0057] The SNCR denitrification system 13 can spray urea solution or ammonia solution at this location to reduce the final NOx emissions to below 100 mg / m3.

[0058] Specific implementation method ten: Combination Figure 1 In this embodiment, a dust drop device 12 is provided below the convection tube bundle 7. Other components and connection methods are the same as those in the first embodiment.

[0059] When the flue gas turns in the process of step ④, there is an enhanced centrifugal process, which can drop large particles of dust in the flue gas into the ash collecting device 12 by inertia, and the sedimentation in the furnace reduces the pressure of the environmental dust collector.

[0060] How it works

[0061] The biomass briquette fuel is sent to the hopper 3 through the feeder, and the fuel falls onto the grate pieces of the oblique reciprocating grate 2, and is transported forward by the reciprocating motion of the grate pieces and enters the furnace 4. The primary air 10 is sent upward by the oblique reciprocating grate 2, and is quickly burned on the grate pieces under the reasonable combination of the front and rear arches; the slag produced after combustion continues to be transported forward by the grate pieces and finally falls into the slag trough; the unburned light floating fuel is supplied with air through the secondary air system 11 in the lower middle part of the furnace 4 to increase the oxygen content and enable the fuel to continue to burn; the high-temperature flue gas produced by the final combustion passes through the furnace 4 and enters the middle part of the convection tube bundle 7. In the middle part of the convection tube bundle 7, it follows the process of ①→②→③ as shown in the figure, and then turns from the middle part of the convection tube bundle 7 to the parts on both sides of the convection tube bundle 7 as shown in the figure ④, and circulates in the direction of ⑤→⑥→⑦. Then it passes through the connecting flue 8, enters the air preheater 9, and is finally discharged into the atmosphere; the temperature of the flue gas discharged into the atmosphere is controlled at around 140°C.

[0062] The water circulation in the boiler is a mixed circulation. The furnace and part of the convection tube bundle are forced circulation, while the rest of the convection tube bundle is natural circulation.

[0063] Return water from the heating network is drawn by a circulating water pump through the lower headers of the water-cooled walls on both sides. It is then distributed to the front and rear lower headers via connecting pipes. After rising through the upper, lower, and side water-cooled walls, it enters the upper drum through the outlet pipes of the side water upper headers. The front and rear water-cooled walls directly enter the upper drum. The first row of the convection tube bundle descends, while the second to fifth rows ascend. The remaining convection tube bundles operate in natural circulation, and the rising and falling water velocities in the circulation loop ensure safe boiler operation.

[0064] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and improvements may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and improvements are intended to fall within the scope of the present invention. The scope of protection claimed in this invention is defined by the appended claims and their equivalents.

Claims

1. A high-efficiency hot water boiler burning biomass pellet fuel, characterized by: The invention comprises a transmission device (1), an oblique push reciprocating grate (2), a hopper (3), a furnace (4), an upper drum (5), a lower drum (6), a convection tube bundle (7), a connecting flue (8), an air preheater (9), a primary air system (10) and a secondary air system (11); the output end of the transmission device (1) is connected to the oblique push reciprocating grate (2) and drives the oblique push reciprocating grate (2) to reciprocate forward and backward; the hopper (3) is arranged above the front of the oblique push reciprocating grate (2); the furnace (4) is arranged above the oblique push reciprocating grate (2); the rear of the furnace (4) is connected to the convection tube bundle (7); the upper end of the convection tube bundle (7) is connected to the upper drum (5); the convection tube bundle (7) The lower end of the convection tube bundle (7) is connected to the lower drum (6), a group of middle smoke partitions (7-1) is provided in the middle of the convection tube bundle (7), and a group of side smoke partitions (7-2) are provided on both sides of the convection tube bundle (7), and the side smoke partitions (7-2) and the middle smoke partitions (7-1) are arranged alternately. The rear part of the convection tube bundle (7) is connected to the connecting flue (8), and the end of the connecting flue (8) is connected to the air preheater (9). The air inlet end of the primary air system (10) is connected to the air outlet end of the air preheater (9), the air outlet end of the primary air system (10) is connected to the lower air inlet end of the oblique push reciprocating grate (2), and the air outlet end of the secondary air system (11) is connected to the middle and lower part of the furnace (4).

2. The high-efficiency hot water boiler burning biomass pellet fuel according to claim 1, characterized in that: Two vertical smoke partitions (7-3) are arranged in parallel in the convection tube bundle (7). The two vertical smoke partitions (7-3) divide the convection tube bundle (7) into a central area and two side areas. The upper end of the central area is connected to the furnace (4), the lower end of the central area is connected to the side areas, and the upper end of the side areas is connected to the connecting flue (8). The central smoke partition (7-1) is arranged in the central area, and the side smoke partition (7-2) is arranged in the side areas.

3. The high-efficiency hot water boiler burning biomass pellet fuel according to claim 2, characterized in that: A group of middle smoke-isolating plates (7-1) comprises two middle smoke-isolating plates (7-1) arranged in sequence from top to bottom, wherein the upper middle smoke-isolating plate (7-1) is fixedly connected to the front side of the convection tube bundle (7), and the lower middle smoke-isolating plate (7-1) is fixedly connected to the rear side of the convection tube bundle (7); and a group of side smoke-isolating plates (7-2) comprises two side smoke-isolating plates (7-2) arranged in sequence from top to bottom, wherein the upper side smoke-isolating plate (7-2) is fixedly connected to the rear side of the convection tube bundle (7), and the lower side smoke-isolating plate (7-2) is fixedly connected to the front side of the convection tube bundle (7).

4. The high-efficiency hot water boiler burning biomass pellet fuel according to claim 3, characterized in that: The middle smoke-isolating plate (7-1) and the upper side smoke-isolating plate (7-2) are respectively arranged to tilt upward from front to back, and the lower side smoke-isolating plate (7-2) is respectively arranged to tilt downward from front to back.

5. The high-efficiency hot water boiler burning biomass pellet fuel according to claim 1, characterized in that: A front arch (4-1) is provided at the lower portion of the front wall of the furnace (4), and a rear arch (4-2) is provided at the lower portion of the rear wall of the furnace (4).

6. The high-efficiency hot water boiler burning biomass pellet fuel according to claim 5, characterized in that: The air outlet end of the secondary air system (11) is respectively connected to a front secondary air outlet nozzle (11-1) and a rear secondary air outlet nozzle (11-2); the front secondary air outlet nozzle (11-1) is arranged above the front arch (4-1), and the rear secondary air outlet nozzle (11-2) is arranged above the arch head of the rear arch (4-2).

7. The high-efficiency hot water boiler burning biomass pellet fuel according to claim 1, characterized in that: The oblique push reciprocating grate (2) is of a reciprocating tilting type, and the oblique push reciprocating grate (2) tilts downward from front to back, and the tilting angle is 18°.

8. The high-efficiency hot water boiler burning biomass pellet fuel according to claim 1, characterized in that: The transmission device (1) comprises a reducer and a cam mechanism, wherein the output shaft of the reducer is connected to the cam mechanism, and the reducer realizes linear reciprocating motion of the output end of the transmission device (1) through the cam mechanism.

9. The high-efficiency hot water boiler burning biomass pellet fuel according to claim 1, characterized in that: An SNCR denitration system (13) is provided in the lower part of the furnace (4).

10. The high-efficiency hot water boiler burning biomass pellet fuel according to claim 1, characterized in that: An ash dropping device (12) is provided below the convection tube bundle (7).

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