A method and structure for preventing biomass fuel from coking and affecting combustion

Abstract

The present invention relates to a method and structure for preventing the coking of biomass fuel from affecting combustion, and belongs to the technical field of biomass combustion residue removal. The technical solution is as follows: a plurality of air inlet holes (14) with variable functions are arranged in layers on the side wall of a combustion tube (3); when the combustion tube (3) is inserted into an inner container (2), it becomes a furnace; after a combustion cycle, the combustion tube (3) is pulled out to remove the coke in one go. A combustion layer (16) and a coking layer (17) are provided in the combustion tube (3); the combustion layer (16) is always on top. As the combustion progresses, the coking layer (17) gradually thickens, and the air inlet holes corresponding to the combustion layer also rise dynamically. The coking layer can neither occupy the space of the combustion layer nor block the air inlet holes corresponding to the combustion layer to affect combustion. The positive effect of the present invention is that after the present invention is applied, various biomass boilers, stoves, and burners no longer require a decoking device, can burn stably for a long time under various fire powers, can use high-ash content and cheap fuel, and reduce manufacturing and operating costs.

Description

Technical Field

[0001] The invention relates to a method and a structure for preventing coking of biomass fuel from affecting combustion, belonging to the technical field of biomass combustion residue removal. Background Art

[0002] The prevention and removal of coke formed during the combustion of biomass briquette fuels directly determines the stable operation of furnaces and the ability to utilize more low-cost, high-ash fuels. Existing technologies for addressing biomass coke formation generally employ mechanical intervention to remove it at any time. These include the reciprocating grate mechanical coke removal technology (Patent No. CN201922337782.9), the dual-wheel decoking mechanical rollout technology (Patent No. CN201820962437.7), and the mechanical rotary coke grinding technology (Patent No. CN202111140108.7 (applied by the present applicant). These three decoking technologies share common drawbacks: 1. The furnace volume and height are fixed, limiting their ability to accommodate the rise (thickening) of the coke and combustion layers. If decoking is not timely or the coke formation rate exceeds the decoking rate, the coke layer gradually rises, occupying the combustion layer, causing unstable combustion or flameout. 2. The location and number of air inlets, as well as the ratio of primary air (for combustion of the combustion layer) to secondary air (for combustion of volatiles), are fixed. If decoking is not timely or the coking rate exceeds the decoking rate, the coking layer will gradually grow (thicken) and block the air inlets, causing unstable combustion or flameout. 3. Continuous and stable combustion requires sustained high temperatures. Frequent decoking not only removes the hot coking layer and part of the combustion layer, but also clears the primary air holes, enhancing cooling and lowering the temperature. Operating at low temperatures will result in incomplete combustion, smoke, fuel waste, and low thermal efficiency. 4. The decoking rate is manually set by the controller, while the coking rate is subject to dynamic changes due to various objective factors. In practice, it is difficult to accurately match the two. When the decoking rate is lower than the coking rate, coke residue cannot be effectively removed. When the decoking rate is higher than the coking rate, the combustion layer will be removed as well, resulting in fuel waste and unstable combustion. 5. Low-speed drive motors are constantly exposed to dusty and high-temperature environments, and mechanical transmission mechanisms operate in harsh environments for a long time, making them prone to failure, shortening their lifespan, and sometimes causing excessive noise. Summary of the Invention

[0003] The purpose of the present invention is to provide a method and structure for preventing the coking of biomass fuel from affecting combustion, so that the combustion layer can dynamically avoid the influence of the coking layer. No decoking is required during the entire combustion process. After one combustion cycle, the coke residue is removed at one time to maintain long-term stable combustion. This allows for more use of high-ash content and cheap fuel, thereby solving the above-mentioned technical problems existing in the existing technology.

[0004] The technical solution of the present invention is:

[0005] A structure in which the coking of biomass fuel does not affect combustion comprises a furnace body, an inner liner and a combustion tube. The furnace body is provided with an inner liner, and the combustion tube can be pulled out of and inserted into the inner liner of the furnace body. The combustion tube is movable up and down. The interlayer formed by the inner liner and the combustion tube serves as a positive-pressure air buffer zone, and positive-pressure air is blown into the interlayer. The combustion tube has an open top and a closed bottom at the bottom. The side walls of the combustion tube are layered with multiple air inlet holes, and positive-pressure air enters the combustion tube through the air inlet holes to assist combustion.

[0006] Furthermore, the biomass fuel in the combustion tube forms a combustion layer and a coking layer during the combustion process. The combustion tube is the place where the combustion layer burns, the coking layer is produced, and the coke slag is stored. The combustion layer is always above the coking layer, and the combustion process will not be affected by the coking layer. The coke produced by the biomass fuel during the combustion process does not need to be mechanically removed; after a combustion cycle, the combustion tube is pulled out to remove the coke at one time, and the cleaned combustion tube is inserted into the inner tank again to start a new combustion cycle; the height of the combustion tube is greater than the sum of the heights of the combustion layer and the coking layer at the end of a combustion cycle.

[0007] Furthermore, the inner liner is a cavity located within the furnace body. The bottom of the inner liner is equipped with an air inlet connected to the blower. The top of the inner liner is equipped with an inner liner opening that matches the outer diameter of the combustion tube, allowing for smooth insertion and removal of the combustion tube. Once secured, the combustion tube and the inner liner are coaxial. The shape of the inner liner matches the shape of the combustion tube. The width of the interlayer formed after the combustion tube is inserted into the inner liner matches the air pressure and air volume generated by the blower and air inlet. As air flows from the air inlet into the combustion tube, the air pressure in the interlayer gradually decreases from bottom to top.

[0008] Furthermore, the air inlet holes on the side wall of the combustion tube are arranged in layers, from the first layer of air inlet holes to the Nth layer of air inlet holes from bottom to top, each layer of air inlet holes is composed of several small holes distributed around the combustion tube, and the N layers of air inlet holes are divided into four virtual areas, from bottom to top, they are the used air hole area (blocked by the coking layer), the primary air hole area (generally there is only one layer of air holes), the secondary air hole area and the spare air hole area, which correspond to the used air holes, the primary air holes, the secondary air holes and the spare air holes, respectively.

[0009] Furthermore, the bottom of the combustion tube is not provided with air holes. For low-power stoves, a fixed bottom is provided at the bottom of the combustion tube. The fixed bottom is integrated with the combustion tube, preventing slag from leaking when the tube is pulled out. For high-power stoves, a movable bottom is provided at the bottom of the combustion tube. The movable bottom is a pull-out plate placed on a guide rail, with the upper surface fitting the bottom of the combustion tube. When the pull-out plate is pushed in, it becomes the bottom of the combustion tube. When pulled out, the combustion tube loses its bottom, and the ash and coke fall by gravity. If the falling is not smooth, a tool can be inserted into the combustion tube for manual intervention.

[0010] Furthermore, when the combustion tube uses a movable bottom, a cleaning door communicating with the inner container is provided on the furnace body below the bottom end of the inner container. When the cleaning door is closed, the inner container is kept sealed. When the door is opened, the movable bottom of the combustion tube can be operated to drop ash and coke, which can then be removed using tools.

[0011] Furthermore, an ignition hole is provided at the bottom end of the combustion tube, and the shape of the ignition hole matches the ignition rod tube. When the combustion tube is inserted into the inner tank, the ignition rod tube is embedded in the ignition hole and slightly extends into the combustion tube. An ignition rod is inserted into the ignition rod tube, and the biomass fuel is ignited when the ignition rod is energized.

[0012] Furthermore, a flange is provided at the top opening edge of the combustion tube, which positions and secures the combustion tube to the inner container. The flange covers the gap between the combustion tube and the inner container opening to prevent air leakage. A pulling member is provided on the flange to pull the combustion tube out of the inner container.

[0013] A method for preventing coking of biomass fuel from affecting combustion, wherein a combustion tube can be withdrawn from and inserted into an inner container of a furnace body, the combustion tube having an open top and a closed bottom at the bottom, a plurality of air inlet holes being layered on the side wall of the combustion tube, and positive pressure air entering the combustion tube from the air inlet holes to assist combustion; the biomass fuel in the combustion tube forms a combustion layer and a coking layer during the combustion process, the combustion layer is always above the coking layer, the combustion process is not affected by the coking layer, and the coke generated during the combustion of the biomass fuel does not need to be mechanically removed; after a combustion cycle, the combustion tube is withdrawn to remove the coke at one time, and the cleaned combustion tube is reinserted into the inner container to start a new combustion cycle.

[0014] Furthermore, when a movable bottom is used as the bottom of the combustion tube, the ash cleaning door is opened after one combustion cycle, and the movable bottom is pulled out to allow the coke slag in the combustion tube to fall down and complete one-time decoking.

[0015] Furthermore, the air inlet holes on the side wall of the combustion tube are arranged in layers, from the first layer of air inlet holes to the Nth layer of air inlet holes, from bottom to top. Each layer of air inlet holes is composed of several small holes distributed around the combustion tube, and the N layers of air inlet holes are divided into four virtual zones, from bottom to top, the used air hole zone (blocked by the coking layer), the primary air hole zone (generally only one layer of air holes), the secondary air hole zone and the spare air hole zone, corresponding to the used air holes, the primary air holes, the secondary air holes and the spare air holes, respectively. The positive pressure air in the interlayer is supplied to the combustion tube through the air inlet holes to supply primary and secondary air, corresponding to the primary and secondary air holes in the primary and secondary air hole zones, respectively. During the entire combustion process, the used air hole zone changes from zero to the maximum, and the number of air hole layers gradually increases. The number of layers in the primary and secondary air hole zones is relatively fixed, and their positions gradually rise. The spare air hole zone changes from the maximum to zero, and the number of air hole layers gradually decreases.

[0016] The innovations of the present invention are as follows: 1. The combustion tube is used as the combustion place and the coke slag storage container. During the combustion process, the coke layer gradually accumulates and does not need to be removed by mechanical intervention. It is removed regularly after a combustion cycle. 2. The combustion layer is always above the coke layer. The combustion layer rises dynamically with the coke layer. The coke layer cannot occupy the space of the combustion layer and affect the combustion. 3. The primary air holes and the secondary air holes are generated dynamically following the combustion layer. The coke layer only blocks the used air holes and cannot block the primary air holes and the secondary air holes to affect the combustion. 4. The arrangement of the combustion tube and the inner tank and the air inlet holes are divided into four virtual areas and converted according to a rule, which ensures the rationality of the air used for combustion. 5. The structure is simple and low in cost. There are no driving electrical components and mechanical parts. It does not fail, does not require maintenance, has a long service life, and is noiseless.

[0017] The positive effects of the present invention are as follows: the side walls of the combustion tube are provided with a plurality of air inlet holes with variable functions in layers. When the combustion tube is inserted into the inner tank, it becomes a furnace. After a combustion cycle, the combustion tube is pulled out to remove the coke at one time. There are a combustion layer and a coking layer in the combustion tube, and the combustion layer is always on the top. As the combustion progresses, the coking layer gradually thickens, and the air inlet holes corresponding to the combustion layer will also rise dynamically. The coking layer can neither occupy the space of the combustion layer nor block the air inlet holes corresponding to the combustion layer to affect combustion. After applying the present invention, various biomass boilers, stoves, and burners no longer need decoking devices, can burn stably for a long time under various fire powers, can use high-ash content and cheap fuel, and reduce manufacturing and operating costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a structural diagram of embodiment 1 of the present invention;

[0019] Figure 2 This is a structural diagram of embodiment 2 of the present invention;

[0020] Figure 3 This is a schematic diagram of a combustion tube according to an embodiment of the present invention;

[0021] Figure 4 This is a schematic diagram of the air intake state of the combustion layer when the first layer of air holes is in the embodiment of the present invention;

[0022] Figure 5 This is a schematic diagram of the air inlet state when the combustion layer rises to the second layer of air holes in an embodiment of the present invention;

[0023] Figure 6 This is a schematic diagram of the air intake state at the end of a combustion cycle according to an embodiment of the present invention;

[0024] Figure 7 This is a schematic diagram of the combustion layer state at the start of combustion according to an embodiment of the present invention;

[0025] Figure 8 This is a schematic diagram of the combustion layer and the coking layer in the middle stage of combustion according to an embodiment of the present invention;

[0026] Figure 9 This is a schematic diagram of the combustion layer and the coking layer at the end of combustion in an embodiment of the present invention;

[0027] In the figure: furnace body 1, inner tank 2, combustion tube 3, interlayer 4, blower 5, ignition rod tube 6, chute 7, movable tube bottom 8, guide rail 9, ash cleaning door 10, inner tank opening 11, flange 12, traction piece 13, air inlet 14, ignition hole 15, combustion layer 16, coking layer 17, used air hole 18, primary air hole 19, secondary air hole 20, spare air hole 21. DETAILED DESCRIPTION

[0028] The present invention will be further described below through embodiments with reference to the accompanying drawings.

[0029] A structure in which coking of biomass fuel does not affect combustion comprises a furnace body 1, an inner liner 2 and a combustion tube 3. The furnace body 1 is provided with an inner liner 2, and the combustion tube 3 can be pulled out of and inserted into the inner liner 2 of the furnace body 1. The combustion tube 3 is movable up and down. An interlayer 4 formed by the inner liner 2 and the combustion tube 3 serves as a positive-pressure air buffer, and positive-pressure air is blown into the interlayer 4. The combustion tube 3 has an open top and a closed bottom at the bottom. A plurality of air inlet holes 14 are layered on the side walls of the combustion tube 3, and positive-pressure air enters the combustion tube 3 through the air inlet holes 14 to assist combustion.

[0030] During the combustion process, the biomass fuel in the combustion tube 3 forms a combustion layer 16 and a coking layer 17. The combustion tube 3 is where the combustion layer 16 burns, the coking layer 17 is generated, and the coke residue is stored. The combustion layer 16 is always above the coking layer 17, and the combustion process is not affected by the coking layer 17. The coke generated during the combustion of the biomass fuel does not need to be mechanically removed. After a combustion cycle, the combustion tube 3 is withdrawn to remove the coke in one go. The cleaned combustion tube 3 is then reinserted into the inner liner 2 to begin a new combustion cycle. The height of the combustion tube 3 is greater than the sum of the heights of the combustion layer 16 and the coking layer 17 at the end of a combustion cycle.

[0031] The inner container 2 is a cavity located within the furnace body 1. An air inlet is provided at the bottom of the inner container 2 and is connected to the blower 5. An inner container opening 11 is provided at the top of the inner container 2 and matches the outer diameter of the combustion tube 3, allowing for smooth insertion and removal of the combustion tube 3. Once secured, the combustion tube 3 is coaxial with the inner container 2. The shape of the inner container 2 matches that of the combustion tube 3. The width of the interlayer formed after the combustion tube 3 is inserted into the inner container 2 matches the wind pressure and air volume generated by the blower 5 and the air inlet. As air is drawn into the combustion tube 3 through the air inlet 14, the air pressure within the interlayer 4 gradually decreases from bottom to top.

[0032] The air inlet holes 14 on the side wall of the combustion tube 3 are arranged in layers, from the first layer to the Nth layer of air inlet holes, from bottom to top. Each layer of air inlet holes is composed of several small holes distributed around the combustion tube 3. The N layers of air inlet holes are divided into four virtual zones: from bottom to top, the used air hole zone (blocked by the coking layer), the primary air hole zone (generally only one layer of air holes), the secondary air hole zone, and the spare air hole zone, corresponding to the used air holes 18, the primary air holes 19, the secondary air holes 20, and the spare air holes 21, respectively. The more layers of air inlet holes 14 are arranged, the longer the combustion cycle.

[0033] The bottom of the combustion tube 3 is not provided with an air inlet hole, and biomass fuel is added into the combustion tube 3 through the hopper 7.

[0034] An ignition hole 15 is provided at the bottom end of the combustion tube 3. The shape of the ignition hole 15 matches the ignition rod tube 6. When the combustion tube 3 is inserted into the inner tank 2, the ignition rod tube 6 is embedded in the ignition hole 15 and slightly extends into the combustion tube 3. An ignition rod is inserted into the ignition rod tube 6, and the biomass fuel is ignited when the ignition rod is energized.

[0035] The top opening edge of the combustion tube 3 is provided with a flange 12, which positions and secures the combustion tube 3 to the inner container 2. The flange 12 covers the gap between the combustion tube 3 and the inner container opening 11 to prevent air leakage. The flange 12 is provided with a pulling member 13 for withdrawing the combustion tube 3 from the inner container 2.

[0036] Example 1, refer to the attached Figure 1 For low-power stoves, the bottom end of the combustion tube 3 is welded with a fixed tube bottom, and the fixed tube bottom and the combustion tube 3 become an integrated structure, so that no slag is leaked when it is extracted.

[0037] Example 2, refer to the attached Figure 2 For high-power stoves, a movable tube bottom 8 is provided at the bottom of the combustion tube 3. The movable tube bottom 8 is a pull-out plate placed on a guide rail 9. The upper surface fits the bottom of the combustion tube 3. When the pull-out plate is pushed in, it becomes the bottom of the combustion tube 3. After being pulled out, the combustion tube 3 loses its bottom, and the ash and coke fall by gravity. If the falling is not smooth, tools can be inserted into the combustion tube 3 for manual intervention. When the combustion tube 3 uses the movable tube bottom 8, a cleaning door 10 connected to the inner tank 2 is opened on the furnace body 1 below the bottom end of the inner tank 2. When the cleaning door 10 is closed, the inner tank 2 is kept sealed. When it is opened, the movable tube bottom 8 of the combustion tube 3 can be operated to drop the ash and coke, and then the fallen ash and coke can be removed using tools.

[0038] A method for preventing coking of biomass fuel from affecting combustion, wherein a combustion tube 3 can be withdrawn from and inserted into an inner container 2 of a furnace body 1, wherein the combustion tube 3 is open at the top and provided with a closed bottom at the bottom, and a plurality of air inlet holes 14 are provided in layers on the side walls of the combustion tube 3, and positive pressure air enters the combustion tube 3 from the air inlet holes 14 to assist combustion; during the combustion process, the biomass fuel in the combustion tube 3 forms a combustion layer 16 and a coking layer 17, wherein the combustion layer 16 is always above the coking layer 17, and the combustion process is not affected by the coking layer 17, and the coke generated during the combustion of the biomass fuel does not need to be mechanically removed; after a combustion cycle, the combustion tube 3 is withdrawn to remove the coke at one time, and the cleaned combustion tube 3 is reinserted into the inner container 2 to start a new combustion cycle.

[0039] When the bottom of the combustion tube 3 uses a movable tube bottom 8, after one combustion cycle, the ash cleaning door 10 is opened and the movable tube bottom 8 is pulled out to allow the coke slag in the combustion tube 3 to fall down and complete one-time decoking.

[0040] The air inlet holes 14 on the side wall of the combustion tube 3 are arranged in layers, from the first layer of air inlet holes to the Nth layer of air inlet holes, from bottom to top. Each layer of air inlet holes is composed of several small holes distributed around the combustion tube 3. The N layers of air inlet holes are divided into four virtual areas, from bottom to top, the used air hole area (blocked by the coking layer), the primary air hole area (generally only one layer of air holes), the secondary air hole area and the spare air hole area, corresponding to the used air holes 18, the primary air holes 19, the secondary air holes 20 and the spare air holes 21, respectively. The positive pressure air in the interlayer 4 is supplied to the combustion tube 3 through the air inlet holes 14. The primary air holes 19 and the secondary air holes 20 in the primary air hole area and the secondary air hole area are respectively. During the entire combustion process, the used air hole area changes from zero to the maximum, and the number of air hole layers gradually increases. The number of layers of the primary air hole area and the secondary air hole area is relatively fixed, and their positions gradually rise. The spare air hole area changes from the maximum to zero, and the number of air hole layers gradually decreases.

[0041] The specific combustion process of the present invention is as follows:

[0042] At the beginning of a combustion cycle, the combustion tube 3 after the slag is cleared is inserted into the inner tank 2, and the blower 5 is operated to maintain the positive pressure air in the interlayer 4, and the biomass fuel is introduced until it just submerges the ignition rod tube mouth. The ignition rod is powered to ignite the fuel (manual ignition is performed if no ignition rod is provided); refer to the attached Figure 4 、 7 At the beginning of a cycle, the first layer of air inlet holes is the primary air hole 19, above which are the secondary air hole area and the spare air hole area. At this time, the spare air hole area is the largest and the used air hole area is zero; at the beginning of a combustion cycle, there is only the combustion layer 16, coking has not occurred yet, and there is no coking layer 17.

[0043] Refer to the attached Figure 5 、 8During the combustion process, newly introduced fuel continuously falls onto the combustion layer 16. The biomass fuel is converted into ash through combustion, and part of the ash forms coke slag, forming a stable upper combustion layer 16 and lower coking layer 17. When the feed rate is stable, the thickness of the combustion layer 16 is also relatively stable, and the thickness of the coking layer 17 gradually increases. As the coking layer 17 thickens, the position of the combustion layer 16 gradually rises. However, the coking layer 17 will never squeeze the space of the combustion layer 16 and will not affect the combustion of the combustion layer 16. At the same time, the coking layer 17 has a strong heat preservation ability and can evaporate and output high temperature upward for a considerable period of time, providing a high-temperature environment for stable combustion for the upper combustion layer 16 and maintaining stable combustion; even if the combustion layer 16 is extinguished for a short time, the newly introduced biomass fuel can quickly burn to a stable state in the high-temperature environment. During the combustion process, as the thickness of the coking layer 17 increases and the position of the combustion layer 16 rises, each air hole area changes dynamically. When the combustion layer 16 rises to the second layer of air holes, the first layer of air holes is submerged by the coking layer 17, becoming used air holes from primary air holes. The second layer of air holes, in turn, becomes primary air holes, and one layer of spare air holes is reduced to fill the secondary air holes. Similarly, with each additional air hole layer in the used air hole area, one air hole layer is reduced in the spare air hole area. New primary air holes are constantly generated dynamically in response to the combustion layer, ensuring the primary air required for combustion in the combustion layer 16. As volatiles released from the combustion layer 16 rise above the combustion layer and burn, new secondary air holes are constantly generated above the combustion layer 16 to meet the secondary air requirements for combustion of the volatile gases. The coking layer 17 always blocks the used air holes, never affecting the combustion of the combustion layer 16. During the combustion process, the increasing thickness of the coking layer 17 has little impact on the combustion air configuration. As the coking layer 17 gradually thickens, the number of used air holes gradually increases, the total number of air inlets gradually decreases, and the air speed at each air inlet gradually increases. Since the blower air pressure and air volume are relatively stable, the air intake volume of primary air and secondary air does not change much. Although the ratio of primary air to secondary air changes to a certain extent, it will ensure stable combustion within a vague allowable range.

[0044] Refer to the attached Figure 6 、 9 , a combustion cycle ends, as the coking layer 17 continues to thicken, the position of the combustion layer 16 continues to rise, when there are only secondary air holes above the combustion layer and the spare air holes are zero, a combustion cycle ends.

[0045] In Example 1, the furnace is first turned off, a tool is inserted into the pulling member 13, the burner 3 is pulled out of the inner container 2, and the slag inside is dumped out, completing a one-time decoking. At the same time, the air inlet holes can be cleaned, and finally, the burner tube 3 is inserted into the inner container 2 for the next combustion cycle. If the slag needs to be dumped before the end of the combustion cycle, this method can also be used to complete a one-time decoking midway.

[0046] In Example 2, for a furnace using a movable combustion tube bottom 8, open the ash cleaning door 10, pull out the movable tube bottom 8 to allow the slag in the combustion tube 3 to fall, and then use tools to remove the slag. This method can also be used to complete mid-cycle decoking when slag removal is not required before the end of the combustion cycle.

Claims

1. A structure in which coking of biomass fuel does not affect combustion, characterized in that: The invention comprises a furnace body (1), an inner liner (2) and a combustion tube (3), wherein the furnace body (1) is provided with an inner liner (2), the combustion tube (3) can be drawn out of and inserted into the inner liner (2) of the furnace body (1), and the combustion tube (3) can be moved up and down, and an interlayer (4) formed by the inner liner (2) and the combustion tube (3) serves as a positive pressure air buffer zone, and positive pressure air is blown into the interlayer (4); the combustion tube (3) is open at the top and provided with a closed tube bottom at the bottom, and a plurality of air inlet holes (14) are provided in layers on the side wall of the combustion tube (3), and positive pressure air enters the combustion tube (3) from the air inlet holes (14) to assist combustion; and the tube bottom of the combustion tube (3) is not provided with air holes.

2. The structure according to claim 1, wherein the coking of biomass fuel does not affect combustion, is characterized in that: The biomass fuel in the combustion tube (3) forms a combustion layer (16) and a coking layer (17) during the combustion process. The combustion tube (3) is a place where the combustion layer (16) burns, the coking layer (17) is generated, and coke slag is stored. The combustion layer (16) is always above the coking layer (17).

3. A structure for biomass fuel that does not affect combustion due to coking according to claim 1 or 2, characterized in that: The inner liner (2) is a cavity located inside the furnace body (1). The bottom end of the inner liner (2) is provided with an air inlet and is connected to the blower (5). The top end of the inner liner (2) is provided with an inner liner opening (11) that matches the outer diameter of the combustion tube (3). The combustion tube (3) can be smoothly inserted and withdrawn. After being fixed, the combustion tube (3) and the inner liner (2) are coaxial.

4. A structure for biomass fuel that does not affect combustion due to coking according to claim 1 or 2, characterized in that: The air inlet holes (14) on the side wall of the combustion tube (3) are arranged in layers, from the first layer of air inlet holes to the Nth layer of air inlet holes from bottom to top, each layer of air inlet holes is composed of a number of small holes distributed around the combustion tube (3), and the N layers of air inlet holes are divided into four virtual areas, from bottom to top, which are the used air hole area, the primary air hole area, the secondary air hole area and the spare air hole area, which correspond to the used air hole (18), the primary air hole (19), the secondary air hole (20) and the spare air hole (21), respectively.

5. The structure according to claim 1 wherein coking of biomass fuel does not affect combustion, characterized in that: The tube bottom is a fixed tube bottom and is an integral structure with the combustion tube (3).

6. The structure according to claim 1 wherein the coking of biomass fuel does not affect combustion, characterized in that: The tube bottom is a movable tube bottom (8), which is a pull-out plate placed on a guide rail (9), and the upper surface of which fits the bottom end of the combustion tube (3). When the pull-out plate is pushed in, it becomes the tube bottom of the combustion tube (3), and when it is pulled out, the combustion tube (3) loses its tube bottom.

7. A method for preventing coking of biomass fuel from affecting combustion, characterized in that: The combustion tube (3) can be drawn out and inserted into the inner shell (2) of the furnace body (1). The top end of the combustion tube (3) is open and the bottom end is provided with a closed tube bottom. The side wall of the combustion tube (3) is layered with multiple air inlet holes (14). Positive pressure air enters the combustion tube (3) from the air inlet holes (14) to assist combustion. The biomass fuel in the combustion tube (3) forms a combustion layer (16) and a coking layer (17) during the combustion process. The combustion layer (16) is always above the coking layer (17). The combustion process will not be affected by the coking layer (17). The coking generated by the biomass fuel during the combustion process does not need to be mechanically removed. After a combustion cycle, the combustion tube (3) is drawn out to remove the coking at one time. The cleaned combustion tube (3) is inserted into the inner shell (2) again to start a new combustion cycle.

8. The method for preventing coking of biomass fuel from affecting combustion according to claim 7, characterized in that: When the bottom of the combustion tube (3) uses a movable tube bottom (8), after one combustion cycle, the ash cleaning door (10) is opened and the movable tube bottom (8) is pulled out, so that the coke residue in the combustion tube (3) falls down and completes one-time decoking.

9. The method for preventing coking of biomass fuel from affecting combustion according to claim 7, characterized in that: The air inlet holes (14) on the side wall of the combustion tube (3) are arranged in layers, from bottom to top, they are the first layer of air inlet holes to the Nth layer of air inlet holes, each layer of air inlet holes is composed of a number of small holes distributed around the combustion tube (3), and the N layers of air inlet holes are divided into four virtual areas, from bottom to top, they are the used air hole area, the primary air hole area, the secondary air hole area and the spare air hole area, which correspond to the used air hole (18), the primary air hole (19), the secondary air hole (20) and the spare air hole (21) respectively; the inner liner (2) and the combustion tube (3) are arranged in layers, from bottom to top, they are the used air hole area, the primary air hole area, the secondary air hole area and the spare air hole area, which correspond to the used air hole (18), the primary air hole (19), the secondary air hole (20) and the spare air hole (21) respectively; ) form an interlayer (4) between them, and the positive pressure air in the interlayer (4) is supplied to the combustion tube (3) through the air inlet hole (14) into the primary air and secondary air, which correspond to the primary air holes (19) and secondary air holes (20) in the primary air hole area and the secondary air hole area respectively; during the entire combustion process, the used air hole area changes from zero to the maximum, and the number of air hole layers gradually increases. The number of layers in the primary air hole area and the secondary air hole area is relatively fixed, and the position gradually rises. The spare air hole area changes from the maximum to zero, and the number of air hole layers gradually decreases.

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