Bulk fuel biomass furnace feeding device capable of preventing backfire

Abstract

The invention relates to a backfire-preventing feeding device of a bulk fuel biomass furnace, which can reduce the construction cost of the bulk fuel biomass furnace, and is not exceptional even if fast and inflammable biomass bulk fuel is intermittently operated and used. Biomass bulk fuel is upwards fed into the gasification chamber (1) through a plurality of spiral conveyors (4) with water-cooled walls, and the bulk fuel in a blanking groove (3) arranged at the front parts of the spiral conveyors (4) can realize air tightness by virtue of self weight. The biomass bulk fuel can be sealed through the design of the thread length and angle of a spiral impeller (8) of the spiral conveying machine (4). The tempering safety baffle (5) is installed on the top of the discharging groove (3) and can cut off falling bulk fuel to be closed under the self-weight effect of the tempering safety baffle (5).

Description

Technical Field

[0001] The invention belongs to a feeding device for biomass fuel, in particular to a feeding device for a bulk fuel biomass furnace which can prevent flashback. Background Art

[0002] When relatively dry bulk biomass fuel enters a biomass gasification furnace or direct-fired furnace of a chain grate, water-cooled vibrating grate or circulating fluidized bed type through a feeding system, the risk of flashback during the feeding process is generally increased. The intermittent shutdown of an industrial steam boiler causes the fuel feeding process to be stopped, which may also cause the risk of flashback during the feeding process. The present invention relates to a bulk biomass fuel, particularly a feeding device that can prevent flashback for a biomass furnace that is suitable for chopped crop straw, energy crops and other broken solid waste fuels.

[0003] In order to prevent the flashback of the feeding system, patent CN117167728A shows a device composed of a horizontally arranged screw conveyor, a vertical fuel channel, a wheeled rotating unit gate and a flashback safety valve. In addition, a screw distribution conveyor is also equipped to distribute the fuel laterally within the width of the combustion equipment. Generally, biomass power plants mainly burn undried bulk materials, continuously and continuously at high speed and high temperature. The above technical devices can generally play a flashback prevention function. However, the system has a complex structure, and the screw conveyor, wheeled rotating unit gate, etc. must not be less than the minimum size design even when used in similar small industrial steam boilers to prevent blockage. Therefore, the above devices are difficult to apply to the flashback prevention of small biomass combustion systems.

[0004] According to CN117167728A, since bulk fuel will encounter upward buoyancy resistance when sliding obliquely downward into the combustion chamber, this buoyancy resistance may even push the bulk fuel toward the horizontally arranged screw conveyor. Therefore, the screw conveyor is designed to be two-stage and supplemented by a wheeled rotating unit gate.

[0005] A horizontally arranged screw conveyor as described in CN115654508A, or even a screw conveyor with a certain inclination angle, may also produce flashback, thus affecting the safe operation of the system. Therefore, additional measures such as adding a flashback safety baffle need to be considered. If the flashback safety baffle is arranged at the end of the CN204880191 pipeline, there will be a risk of corrosion. If the CN219341018U flashback safety baffle is installed in the feeding channel, the flashback safety baffle completely passes through the fuel to achieve flashback blocking, which cannot be achieved during the fuel flow process or when the fuel is uneven in size.

[0006] Bulk fuel can only prevent backfire together with the backfire safety baffle installed in the fuel supply pipeline when it is in a dense state. When the fuel is naturally scattered into the fuel supply pipeline and filled with a large amount of air, the fuel cannot play a role in sealing and blocking backfire.

[0007] The gasification of bulk fuel on the mobile grate at a set power requires a certain fuel layer height to ensure that the fuel is delivered. Therefore, a material level signal and feedback are needed to adjust the fuel supply. CN201811060698.0 shows a whole-bundle straw gasifier with a material level sensor arranged in the gasification chamber. However, this sensor can only give a material level signal for the whole bundle of fuel, but cannot give a material level layer height signal for the bulk fuel layer within a range of 0.5-1.5 meters or more.

[0008] Bulk fuels such as chopped straw are often used in small decentralized thermal systems, such as industrial steam biomass boilers with large daytime load changes. When the load decreases or the boiler is shut down, the flashback safety device will also play a role in small industrial steam boilers when the load decreases or the boiler is shut down. When the biomass bulk fuel is relatively dry, the above-mentioned flashback safety needs to be greatly improved, but there is no efficient solution in this regard. Summary of the invention

[0009] The present invention relates to a feeding device for biomass bulk fuel with a screw feeder that can prevent flashback. The device has a simple design and good economic efficiency. It is also applicable to biomass bulk fuel containing irregular fragments. When the fire is stopped, the potential safety hazard caused by flashback can be avoided. The flashback safety baffle in the present invention can be closed quickly and instantly. In addition, the height and width of the bulk fuel level can be controlled and variable without adding additional expensive components.

[0010] The gasification chamber is fed with bulk fuel by more than one screw feeder with water-cooled wall. The screw feeder is lifted upward at an inclined angle and loaded with bulk fuel from above the feed chute arranged in the front of the screw feeder. The feed chute widens in a cone shape from top to bottom and completely covers the front of all screw feeders. The filling height of the bulk fuel in the feed chute is always maintained at more than 4 meters and is connected to the screw feeder in an airtight manner. The bulk fuel in the feed chute continuously falls downward and is compacted due to its own weight, thereby isolating the air from flowing through.

[0011] This sealing effect can prevent fresh air from being sucked into the bulk fuel feeding device through the anti-flashback device by the negative pressure in the biomass furnace. The absence of air can avoid flashback to a certain extent.

[0012] The screw conveyor is lifted upward at an inclined angle, and the bulk fuel entering the screw conveyor slides into the gasification chamber through the downward inclined feeding chamber. In this process, the hot flue gas from the gasification chamber may flow back, so a water-cooled wall is arranged in part of the screw conveyor near the gasification chamber.

[0013] Since the screw conveyor is tilted upward at an angle of not less than 45 degrees, the hot flue gas is blocked from entering the lower area of ​​the screw conveyor to a certain extent, so the downward front half of the screw conveyor will maintain a lower temperature.

[0014] To ensure that even poorly flowing bulk fuels can enter the screw conveyor from above and flow out of the angled top of the screw conveyor by gravity alone, the angle of elevation of the screw conveyor to the horizontal plane should be between 45 and 55 degrees.

[0015] To ensure the tightness of the screw conveyor during operation, the bulk fuel must always be in contact with all sides of the inner surface of the screw conveyor during feeding, so as to close the gap between the spiral wave of the bulk fuel and the inner surface of the screw conveyor. When the screw conveyor rotates, in order to achieve the tightness of the bulk fuel with the upper and lower inner wall surfaces at the same time, it must be ensured that the angle between the screw conveyor and the horizontal plane is greater than 45 degrees, and the length of the screw part of the conveyor is at least 1.7x diameter D. In this way, even if only a certain amount of bulk fuel enters the screw conveyor and the rotation speed of the spiral wave of the bulk fuel is very slow, the bulk fuel can still be pressed on the upper inner surface of the screw conveyor to achieve the tightness of the screw feeding.

[0016] If the above-mentioned angle is 45-55 degrees and the length of the spiral part of the screw conveyor is greater than 2.5xD, the filling and sealing effect of the bulk fuel in the screw conveyor will be better, because at this time the bulk fuel is almost vertically lifted by the screw conveyor, and the gravity of the bulk fuel almost no longer acts to change the position of the bulk fuel, so that the same amount of bulk fuel will be more evenly attached to the upper inner surface of the screw conveyor to achieve sealing.

[0017] Since the temperature and intensity of gasification combustion of bulk fuel are much lower than those of traditional bulk fuel direct combustion equipment, the amount of fuel required in bulk fuel gasifiers is much greater than that in direct combustion furnaces, so bulk fuel gasifiers require larger grate lengths, widths and higher bulk fuel layer heights. Tests and studies have shown that only when the bulk fuel layer height on the grate is above 1 meter can the uniform density of the bulk fuel be guaranteed, and can the bulk fuel on the grate be prevented from burning in places where the bulk fuel layer is too thin.

[0018] In the present invention, one or more screw conveyors are arranged in a fan shape so as to spread the bulk fuel as evenly as possible over the entire grate width of the bulk fuel biomass furnace without adding additional equipment.

[0019] The material level in the bulk fuel gasifier is monitored by one or more material level sensors in the gasifier and sends out signals in a timely manner. The sensing rods of these material level sensors are made of high-temperature resistant stainless steel and are suspended at different depths in the gasifier. The sensing rods rotate when they come into contact with the height change of the moving fuel layer. The screw feeder can adjust the speed of the physical feeder according to the feedback signals of these sensors to adjust the height of the bulk fuel layer.

[0020] During normal operation, the feed trough of the present invention is always filled with fuel, and the density of the fuel increases toward the bottom. The feed trough is tapered and widens from top to bottom, and all side walls of the feed trough are at an angle of 5-8 degrees to the vertical direction, which makes it impossible to bridge the bulk fuel. In this way, it can be ensured that the feed trough has sufficient height so that the bulk fuel can be evenly distributed in the feed trough. When the bulk fuel enters the feed trough from the middle position of the top of the feed trough, the bulk fuel can be distributed to various widths and angles of the feed trough by dripping. In order to realize the dripping and distribution function of the bulk fuel, the drop height of the feed trough should be at least 4 meters.

[0021] The present invention controls the material level in the feed chute according to feedback signals from at least three material level sensors arranged at different heights. Preferably, the material level sensor is a suspended material level sensor, which is suspended at the top to prevent being buried by bulk fuel.

[0022] The bulk fuel is fed into the feed chute from above via a steep-slope feeding belt. The feed opening of the feed chute can be closed at any time with a sealed backfire safety baffle. The backfire safety baffle is preferably fixed at the opening position of the feed opening by an electromagnet and can fall down and close the feed opening completely by its own weight. When the feed opening is closed, the backfire safety baffle falls freely above the feed chute in a direction roughly consistent with the falling flow direction of the bulk fuel and cuts off the bulk fuel flow. Therefore, the continuously flowing bulk fuel will not hinder the closing of the backfire safety baffle, thereby ensuring that backfire will not occur.

[0023] If the bulk fuel discharge chute is overloaded and accumulated due to unexpected circumstances, the bulk fuel accumulated due to the overloading in the discharge chute alone can also achieve the sealing function.

[0024] When the bulk fuel that falls from the top of the discharge chute onto the tempering safety baffle slides back into the steep slope feeding belt through the slide, a movable bottom plate is arranged under the rotating roller at the bottom of the steep slope feeding belt. The flexible carrier plate can pick up the bulk fuel that slides into the movable bottom plate, thereby preventing the flexible carrier plate on the steep slope feeding belt from getting stuck. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The embodiments of the present invention are described in detail below with the help of 7 figures.

[0026] Figure 1 Shown is a side sectional view of a feeding device with an anti-flashback safety device for a chain grate bulk fuel gasification furnace.

[0027] Figure 2 Shown is a side view of the design of the spiral impeller (8) when the bulk fuel cannot be in close contact with all surfaces of the screw conveyor (4) to achieve airtightness.

[0028] Figure 3 Shown is a side view of the design of the spiral impeller (8) when the bulk fuel can effectively be in close contact with all surfaces of the screw conveyor (4) to achieve airtightness.

[0029] Figure 4 Shown is a top view of a portion of a flashback protection safety feeder with three screw conveyors (4) arranged in a fan shape.

[0030] Figure 5 Shown is a side cross-sectional view of the upper half of the feed chute (3) with a flashback safety baffle (5) and a material level sensor (10).

[0031] Figure 6 Shown is a side cross-sectional view of a method for arranging a material level sensor in a gasification chamber (1).

[0032] Figure 7 Shown is a side cross-sectional view of the return of the fallen bulk fuel to the steeply inclined loading belt (2).

[0033] In the figure: 1-gasification chamber, 2-steep slope feeding belt, 3-discharging chute, 4-screw conveyor, 5-tempering safety baffle, 6-water cooling wall, 7-fire water inlet, 8-spiral impeller, 9-electromagnet, 10-level sensor, 11-rotatable sensing rod, 12-fulcrum, 13-retaining ring, 14-maintenance door, 15-bucket loader bottom plate, 16-movable bottom plate, 17-flexible loading plate, 18-lower rotating pivot, 19-counterweight rod, 20-upper rotating pivot. DETAILED DESCRIPTION

[0034] Figure 1 The figure shows a feeding device with a flashback prevention safety device for feeding bulk fuel to the gasification chamber (1). The bulk fuel here is from the upstream fuel drying device of the CN202211552835.9 patent, so it will burn very quickly. If the gasification chamber (1) here is a component of an industrial steam boiler, the industrial steam boiler may often stop or shut down due to discontinuous and irregular steam production. Similar to the above two situations, the safety requirements for preventing flashback in the gasification chamber (1) will be very high.

[0035] When the load demand of the industrial steam boiler mentioned above drops to zero or the screw conveyor (4) stops working or the power is cut off, the bulk fuel accumulated due to overloading in the discharge chute (3) can also be sealed to prevent backfire.

[0036] The steep-slope feeding belt (2) conveys the bulk fuel upward and feeds it into the feeding chute (3) from above. The feeding chute (3) is connected to one or more screw feeders (4) at the bottom. The loading height of the feeding chute (3) arranged in the figure is about 5 meters higher than the screw feeder (4), so that the bulk fuel can be compressed by its own weight and is not easily affected by the flowing air. In this embodiment, the pressure in the gasification chamber (1) is about -90Pa, so it will not affect the airtightness formed by the bulk fuel.

[0037] The design length of the screw conveyor (4) is about 9 meters, and the front half of about 4 meters has a good airtight function. For tempering to occur, the external air must come down from the upper opening of the feed chute (3) and pass through the front half of the screw conveyor (4). It is not easy for the external air to penetrate about 9 meters of bulk material, so tempering will not easily occur.

[0038] However, in some emergency situations, the hot flue gas from the gasification chamber (1) may enter the area of ​​the screw conveyor (4) near the gasification chamber, causing the temperature to rise. Therefore, a water-cooled wall (6) for cooling can be arranged in the area of ​​the screw conveyor (4) near the gasification chamber. The water-cooled wall (6) can effectively prevent the screw conveyor (4) from being damaged when backfire occurs.

[0039] The fire water inlet (7) is an independently controlled safety device. When the temperature in the area of ​​the fire water inlet (7) exceeds the limit value (e.g., 100° C.), the valve of the fire water inlet (7) will automatically open and introduce an appropriate amount of water. When the appropriate amount of water meets high temperature, it will generate steam to squeeze out the air in the area, thereby reliably extinguishing the fire. No electrical equipment is required for fire extinguishing.

[0040] At this time, the feed port at the top of the feed chute (3) will also be automatically closed by the backfire safety baffle (5). The top feed port of the feed device of the present invention is always open when it is working normally, and will only be closed in the case of backfire or emergency. At the same time, the backfire prevention safety feed device will be sealed, and the backfire will be blocked. At this time, the backfire and the fuel in the feed chute (3) are pushed into the gasification chamber (1), or the fire water inlet (7) in the screw conveyor (4) is started to extinguish the backfire in the screw conveyor (4).

[0041] The vertically arranged feed chute (3) is flared outward from top to bottom in a trumpet-shaped manner, and all surfaces of the feed chute (3) are at an angle of 7 degrees to the vertical line of the feed chute (3), which can effectively prevent the bulk fuel from forming a bridge blockage and allow the bulk fuel to be spread evenly and horizontally.

[0042] The conical design of the feed chute (3) means that the surface area for connection with the screw conveyor (4) is very large. In this embodiment, the area for connection between the feed chute (3) and each screw conveyor (4) is about 2.1 square meters. This area or more is very beneficial for conveying bulk fuel containing large pieces of branches and bark.

[0043] The central axis of the screw conveyor (4) in this embodiment forms an angle of 48 degrees with the horizontal plane. The buoyancy generated by the hot flue gas from the gasification chamber (1) can prevent the hot flue gas from further penetrating into the front of the screw conveyor (4).

[0044] Figure 2 The effect of the geometry of the screw conveyor (4) raised at an upward angle and the design of the spiral impeller (8) on the air tightness is shown. The elevation angle of the screw conveyor (4) is 48 degrees. The diameter of the spiral impeller (8) is set to 80 cm or more, so that chopped crop straw, branches or bulk fuel with wood pieces of a certain size are not easy to cause blockage.

[0045] The thread length of the spiral impeller (8) is only 1.2 times the diameter D of the spiral impeller (8). The force F for conveying the bulk fuel cannot counteract the gravity of the bulk fuel, so that the bulk fuel tilts to the left in the figure, toward the bottom of the spiral plastic machine (4), so the bulk fuel at the bottom accounts for a large proportion, while the bulk fuel at the top accounts for a small proportion, so the uneven distribution of the bulk fuel will affect the airtightness during the conveying process.

[0046] Figure 3 The length of the spiral impeller (8) shown is 2.7 times the diameter D of the spiral impeller (8), so the gravity of the bulk fuel is offset and the bulk fuel is no longer offset to one side. At this time, the bulk fuel is in uniform contact with all inner wall surfaces to achieve better airtightness. Therefore, the length of the spiral impeller (8) of the present invention should be at least 2.4 times the length of the spiral impeller (8), and the elevation angle of the screw feeder (4) is preferably 45-55 degrees. In this way, the bulk fuel flow sealing of the screw feeder (4) combined with the feed chute (3) can more effectively prevent backfire, so there is no need for a more complex impeller sealing valve, etc., which makes the equipment structure simple and the cost reasonable.

[0047] Figure 4 The three screw conveyors (4) of the device of the present invention are arranged in a fan-shaped manner on a plane at an elevation angle. The feed chute (3) meets the working condition requirements of the width (1.6 meters) of the steep slope feeding belt (2) and the feed opening width (2.7 meters) of the screw conveyor (4). The fan-shaped arrangement of the screw conveyor (4) enables it to meet the material distribution requirement of the bulk fuel gasification chamber (1) of not less than 5.4 meters without the need for additional cross-conveyor devices.

[0048] like Figure 5A tempering safety baffle (5) is arranged on the top of the feed chute (3) shown. The tempering safety baffle (5) is maintained at the open position of the feed chute (3) by an electromagnet (9). After the signal is triggered, the tempering safety baffle (5) will block the flow of bulk fuel under the action of its own weight and automatically fall to the closed position of the feed chute (3).

[0049] In order to continuously adjust the bulk fuel loading level in the feed chute (3), the present embodiment comprises four height-adjustable level sensors (10). These sensors are designed in a pendulum-type manner, comprising a rotating plate close to the wall and a cover on the top. The fuel feeding speed and feeding amount can be controlled by these level sensors (10). If the actual fuel level exceeds the setting, the flashback safety baffle (5) will fall to the closing position of the feed chute (3).

[0050] Figure 6 The material level sensor (10) in the gasification chamber (1) is shown. The material level sensor mainly consists of a rotatable sensing rod (11) made of refractory stainless steel. The rotatable sensing rod (11) of this embodiment is about 1.7 meters long and can rotate around a fulcrum (12). The operator can set the height of the rotatable sensing rod (11) through a maintenance door (14) and a retaining ring (13).

[0051] according to Figure 1 and Figure 7 When the flashback safety baffle (5) falls down and closes, the bulk fuel will slide onto the bottom plate (15) of the bucket loader and slide down to the bottom of the steep slope feeding belt (2). A movable bottom plate (16) is arranged at the bottom of the steep slope feeding belt (2). When the bulk fuel is blocked, the movable bottom plate (16) will move downward to protect the flexible carrier plate (17) of the steep slope feeding belt (2). Then, the steep slope feeding belt (2) picks up the bulk fuel from above the movable bottom plate (16) and sends it back to the feeding system to ensure the stable operation of the system.

[0052] Obviously, the above embodiments are only examples for clear explanation, and are not intended to limit the implementation methods. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from this are still within the protection scope of the present invention.

Claims

1. A feeding device for a bulk fuel biomass furnace capable of preventing flashback, comprising a gasification chamber, a screw feeder, a feed chute, a steep-slope feeding belt, and a material level sensor; It is characterized in that The gasification chamber (1) is fed with bulk fuel by one or more screw feeders (4) including water-cooled walls. The screw feeders (4) are lifted upward at an elevation angle, and the bulk fuel is loaded from above a feed chute (3) arranged in front of the screw feeders (4). The feed chute (3) widens in a conical shape from top to bottom and completely covers the front of all the screw feeders (4). The filling height of the bulk fuel in the feed chute (3) is always maintained at more than 4 meters and is connected to the screw feeder (4) in an airtight manner.

2. A feeding device for a bulk fuel biomass furnace capable of preventing flashback according to claim 1, It is characterized in that The screw conveyor (4) is arranged in a fan-shaped manner on a fan-shaped plane that is lifted upward at an elevation angle, and the elevation angle between the fan-shaped plane and the horizontal plane is 45-55 degrees.

3. A feeding device for a bulk fuel biomass furnace capable of preventing flashback according to claim 2, It is characterized in that The thread length of the spiral impeller (8) in the screw conveyor (4) is 1.7-2.7 times the diameter of the spiral impeller (8).

4. A feeding device for a bulk fuel biomass furnace capable of preventing flashback according to claim 1, It is characterized in that All side walls of the feed chute (3) are at an angle of 5-8 degrees to the vertical direction, and the bulk fuel filling height in the feed chute (3) can be adjusted by material level sensors (10) arranged at different heights.

5. A feeding device for a bulk fuel biomass furnace capable of preventing flashback according to claim 1, It is characterized in that The top of the feed chute (3) can be closed by a backfire safety baffle (5). After a control signal is triggered, the backfire safety baffle (5) can move in the bulk fuel flow in the feed chute (3) and close under the action of its own weight.

6. A feeding device for a bulk fuel biomass furnace capable of preventing flashback according to claim 1, It is characterized in that One or more material level sensors are arranged in the gasification chamber (1), and the material level sensors are composed of a rotatable sensing rod (11) which can rotate according to the change of the fuel layer height.

7. A feeding device for a bulk fuel biomass furnace capable of preventing flashback according to claim 1, It is characterized in that A movable bottom plate (16) is arranged below the rotating roller at the bottom of the steep-slope feeding belt (2), and a flexible carrier plate (17) can pick up bulk fuel that slides onto the movable bottom plate (16).

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