A downdraft biomass gasifier

Abstract

The present application relates to the technical field related to biomass gasifiers, and discloses a downdraft biomass gasifier, which is mainly composed of a furnace body, a grate, and an ash hopper. The furnace body is provided with an inner tube, an annular space is formed between the inner tube and the furnace body, the side walls of the annular space are provided with spiral baffles, the oxidation layer of the inner tube is provided with an air distributor, the air distributor is used to guide and distribute air, the outer wall of the furnace body is provided with a flow distributor, the flow distributor is connected to the air distributor, an annular closed groove is formed between the annular pipe of the air distributor and the closed tube, a square closed groove is formed between the straight pipe and the closed plate, a slip ring and a slide are slidably installed in the closed groove, and a plurality of stirring rods are provided between adjacent slides. The present invention can evenly distribute air, prevent local burn-through of the oxidation layer, reduce the dust content in the produced biomass gas, and stir the biomass fuel in the oxidation layer to prevent bridging of the oxidation layer and the phenomenon of empty burning.

Description

Technical Field

[0001] The present application relates to the technical field related to biomass gasifiers, and in particular to a downdraft biomass gasifier. Background Art

[0002] Biomass gasification technology involves the thermochemical conversion of biomass fuels. This involves the incomplete combustion of biomass fuels, which results in the cracking of higher molecular weight organic hydrocarbon chains into lower molecular weight combustible gases such as CO, H₂, and CH₄. Biomass gasifiers are the most widely used biomass gasifiers. These gasifiers can be categorized as updraft or downdraft depending on the direction of the gas output.

[0003] In a downdraft biomass gasifier, both raw materials and air enter from the upper end of the furnace body, and the raw materials pass through the drying layer, pyrolysis layer, oxidation layer and reduction layer in the furnace body in turn. However, air enters from the upper end of the furnace body, and the air first contacts the biomass fuel at the upper end. The position where the biomass fuel burns is close to the upper end of the furnace body, and the oxidation layer and reduction layer are easily moved upward, resulting in insufficient oxidation and reduction, thickening of the reduction layer, and increased airflow resistance. The air outlet and ash outlet of the downdraft biomass gasifier are both at the lower end of the furnace body, and the biomass gas is discharged from the ash. It is inevitable that there will be more dust in the biomass gas. In addition, the oxidation layer in the gasifier is the part that burns most completely. There are also pyrolysis layers and drying layers on the upper side of the oxidation layer. After the biomass in the oxidation layer is burned, due to the accumulation and "bridging" phenomenon of the biomass, the biomass is difficult to descend to the oxidation layer. There are large gaps between the biomass in the oxidation layer, resulting in empty burning of the biomass in the oxidation layer and low biomass gas production efficiency. Summary of the Invention

[0004] The present application proposes a downdraft biomass gasifier, which has the advantages of preventing the upward movement of the oxidation layer, reducing the dust content in the biomass gas and preventing the bridging of biomass in the oxidation layer, and is used to solve the problems of low biomass gas yield caused by the upward movement of the oxidation layer, high dust content in the biomass gas and bridging of biomass in the oxidation layer.

[0005] To achieve the above-mentioned purpose, the present application adopts the following technical solutions: a downdraft biomass gasification furnace, comprising a furnace body, a grate and an ash hopper, wherein the grate and the ash hopper are fixedly installed at the lower position of the inner wall of the furnace body, the ash hopper is below the grate, and an inner cylinder is fixedly installed on the upper end of the grate, and an annular space is formed between the inner cylinder and the furnace body, spiral baffles are fixedly installed on the side walls on both sides of the annular space, the inner cylinder is divided into a drying layer, a pyrolysis layer, an oxidation layer and a reduction layer from top to bottom, and two air distributors are fixedly installed on the inner wall of the inner cylinder corresponding to the oxidation layer, and the air distributor is used to guide and distribute the air, and a flow distributor is fixedly installed on the outer wall of the furnace body, and the two air outlets of the flow distributor are respectively connected to the air inlets of the two air distributors.

[0006] Furthermore, the air distributor includes an annular pipe, a straight pipe and air vents. The annular pipe of the air distributor is fixedly installed on the inner wall of the inner tube. A plurality of air vents are provided in an annular array on the inner ring of the annular pipe. A plurality of straight pipes are provided in an annular array on the inner ring of the annular pipe. The straight pipes are connected to the annular pipe. Air vents are equidistantly provided at the lower end of the upper straight pipe, and a plurality of air vents are provided at the upper end of the lower straight pipe.

[0007] Furthermore, the angle formed by the spiral baffle and the axis of the furnace body is less than 45°.

[0008] Furthermore, the air distributor includes an annular pipe, a straight pipe, a closed cylinder and a closed plate. The annular pipe of the air distributor is fixedly installed on the inner wall of the inner cylinder. The outer sides and inner sides of the two annular pipes are respectively fixedly sleeved with closed cylinders. An annular closed groove is formed between the two closed cylinders and the annular pipes. A vent hole connected to the annular closed groove is opened on the annular pipe. A slip ring is slidably installed in the annular closed groove. A plurality of straight pipes are provided in an annular array on the inner ring of the annular pipe. The straight pipes are connected to the annular pipe. A closed plate is fixedly installed on the side wall of the straight pipe. A square is formed between the closed plate and the straight pipe. A closed groove is provided on the straight pipe, and a vent hole connected to the square closed groove is provided. The square closed groove is connected to the annular closed groove. A slide is slidably installed in the square closed groove, and the slide is fixedly installed on the inner wall of the slip ring. Connecting grooves are provided on the closed plates on both sides of the straight pipe, and exhaust holes are provided above and below the connecting grooves of the straight pipe respectively. Two rows of exhaust holes are provided on the inner closed cylinder, and the exhaust holes on the closed cylinder are at the same height as the exhaust holes on the closed plate. Several stirring rods are provided between the two adjacent slides, and the two ends of the stirring rods are fixedly installed on the sides of the two adjacent slides through connecting grooves.

[0009] Furthermore, a hot smoke distributor is fixedly mounted on the inner wall of the inner cylinder, and the hot smoke distributor is located in the pyrolysis layer inside the inner cylinder.

[0010] Furthermore, a screen is fixedly installed in the exhaust hole.

[0011] Furthermore, limit bars are fixedly installed on the top and bottom ends of the inner wall of the square closed groove respectively.

[0012] Furthermore, when not in operation, the slide is placed on the limiting strip at the lower end, and the slide blocks the exhaust holes on the lower side of the closing plate; when the slide slides to the limiting strip at the upper end, the slide blocks the exhaust holes on the upper side of the closing plate.

[0013] 1. The present application provides a downdraft biomass gasifier, in which an inner cylinder is fixedly provided in the furnace body, an annular space is formed between the furnace body and the inner cylinder, an air outlet pipe is opened at the upper end of the outer wall of the furnace body, and a spiral baffle is fixedly installed on the side wall of the annular space. When the downdraft biomass gasifier is in operation, the biomass gas generated in the annular space enters the annular space through the grate and the ash hopper at the lower end. In the process of the biomass gas rising from the lower end of the annular space to the air outlet pipe, the dust in the biomass gas falls into the ash hopper under the obstruction of the spiral baffle and the action of the dust's own gravity, thereby reducing the dust content in the biomass gas.

[0014] 2. The present application provides a downdraft biomass gasifier, in which an upper air distributor is fixedly installed on the oxidation layer in the inner cylinder. The air distributor is connected to the flow distributor through a pipeline. The air inlet of the flow distributor is connected to an air supply device. Air vents are provided on the annular pipe and the straight pipe of the air distributor. When the gasifier is operating, air is introduced into the air distributor through the air supply device and discharged to the oxidation layer through the air vents of the air distributor, so that the air is directly introduced into the oxidation layer of the gasifier, thereby avoiding the phenomenon of the oxidation layer moving up. In addition, the air is evenly distributed by the air distributor, thereby avoiding the different reaction degrees of the oxidation layer due to uneven airflow and the occurrence of local "burn-through" phenomenon.

[0015] 3. The present application provides a downdraft biomass gasifier, which is characterized in that closed cylinders are fixedly installed on both sides of the annular pipe and closed plates are fixedly installed on both sides of the straight pipe to form an annular closed groove and a square closed groove, a slip ring is slidably installed in the annular closed groove, and a slide plate is slidably installed in the square closed groove, the slip ring and the slide plate are fixedly connected, a connecting groove and an exhaust hole are provided on the closed plate, and two adjacent slide plates are fixedly connected to the two ends of the stirring rod. When the gasifier is operating, air is introduced into the air distributor through the air supply device, and after distribution by the flow distributor, the same amount of air is introduced into the annular pipes on the upper and lower sides, and the air in the annular pipes is discharged into the oxidation layer through the annular closed groove and the square closed groove, and the air entering the annular closed groove and the square closed groove pushes the slip ring and the slide plate to move up and down, so that the slide plate drives the stirring rod to move up and down, so that the stirring rod stirs the biomass in the oxidation layer, avoiding the "bridging" phenomenon of the biomass in the oxidation layer, thereby avoiding the biomass from falling during the combustion process, forming an empty burning phenomenon.

[0016] 4. The present application provides a downdraft biomass gasifier, which has a hot smoke distributor fixedly installed on the pyrolysis layer. During operation, exhaust gas containing heat is introduced into the hot smoke distributor, and the exhaust gas contains CO2 gas, which provides heat for the pyrolysis of the pyrolysis layer. Moreover, when CO2 enters the reduction layer, the concentration of the reactants in the reduction layer is increased, thereby increasing the content of CO generated. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments disclosed herein and, together with the description, serve to explain the principles disclosed herein.

[0018] The present application can be more clearly understood from the following detailed description with reference to the accompanying drawings, in which:

[0019] Figure 1 This is a structural diagram of embodiment 1 of the present invention;

[0020] Figure 2 For the present invention Figure 1 Cross-sectional view at AA in the middle;

[0021] Figure 3 This is a structural diagram of embodiment 2 of the present invention;

[0022] Figure 4 For the present invention Figure 3 Schematic diagram of the local structure at B in the middle;

[0023] Figure 5 For the present invention Figure 3 Cross-sectional view at CC;

[0024] Figure 6 For the present invention Figure 5 Cross-sectional view at DD in the middle;

[0025] Figure 7 For the present invention Figure 5 Cross-sectional view at EE.

[0026] In the figure: 1. furnace body; 101. feed pipe; 102. exhaust pipe; 2. grate; 3. ash hopper; 4. screw conveyor; 5. inner cylinder; 6. annular space; 7. spiral baffle; 8. air distributor; 801. annular pipe; 802. straight pipe; 803. vent; 804. closed cylinder; 805. closing plate; 806. annular closed groove; 807. square closed groove; 808. slip ring; 809. slide plate; 810. limit strip; 811. connecting groove; 812. exhaust hole; 813. stirring rod; 9. flow distributor; 10. hot smoke distributor. Implementation Method

[0027] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application. Example

[0028] See also Figure 1 and Figure 2 A downdraft biomass gasification furnace includes a furnace body 1, a grate 2, an ash hopper 3 and a screw conveyor 4. A feed pipe 101 is fixedly installed in the middle position of the top of the furnace body 1, and an air outlet pipe 102 is fixedly installed at the top of one side of the furnace body 1. A grate 2 and an ash hopper 3 are fixedly installed at the lower position of the inner wall of the furnace body 1. The ash hopper 3 is below the grate 2. The grate 2 is used to support biomass fuel, and the ash hopper 3 is used to receive ash falling from the grate 2. A screw conveyor 4 is fixedly installed at the bottom end of the furnace body 1. The feed port of the screw conveyor 4 is connected with the discharge port of the ash hopper 3, and the screw conveyor 4 is used to transport ash.

[0029] An inner tube 5 is provided in the furnace body 1, and the inner tube 5 is fixedly installed on the upper end of the grate 2. An annular space 6 is formed between the furnace body 1 and the inner tube 5. Spiral baffles 7 are fixedly installed on the side walls on both sides of the annular space 6. The spiral baffles 7 are used to guide the biomass gas and separate the dust in the biomass gas. The inner tube 5 is divided into a drying layer, a pyrolysis layer, an oxidation layer and a reduction layer from top to bottom. Two air distributors 8 are fixedly installed on the inner wall of the inner tube 5 corresponding to the oxidation layer. A flow distributor 9 is fixedly installed on the outer wall of the furnace body 1. The two air outlets of the flow distributor 9 are respectively connected to the air inlets of the two air distributors 8. The air distributor 8 is used to guide the air and distribute the air evenly.

[0030] The air distributor 8 includes an annular pipe 801, a straight pipe 802 and an air vent 803. The annular pipe 801 of the air distributor 8 is fixedly installed on the inner wall of the inner tube 5. A plurality of air vents 803 are provided in an annular array on the inner circle of the annular pipe 801. A plurality of straight pipes 802 are provided in an annular array on the inner circle of the annular pipe 801. The straight pipes 802 are connected to the annular pipe 801. The lower end of the straight pipe 802 of the upper air distributor 8 is provided with air vents 803 at equal intervals, and the upper end of the straight pipe 802 of the lower air distributor 8 is provided with a plurality of air vents 803.

[0031] The angle formed between the spiral baffle 7 and the axis of the furnace body 1 is less than 45 degrees. When dust falls on the spiral baffle 7, it slides down under the action of the dust's own gravity, thereby preventing dust from accumulating on the spiral baffle 7.

[0032] The thickness and position of the oxide layer in the inner cylinder 5 can be changed by opening or closing one of the air distributors 8 , and the temperature of the oxide layer can be controlled by controlling the ventilation volume of the air distributor 8 .

[0033] The working principle of the first embodiment of the present invention is as follows:

[0034] See also Figure 1 and Figure 2 Before the downdraft biomass gasifier is operated, the biomass fuel is fed into the inner tube 5 through the feed pipe 101 , and the outside air is fed into the air distributor 8 through the air supply device and the flow distributor 9 .

[0035] During operation, the air entering the air distributor 8 is guided by the annular pipe 801 and the straight pipe 802, and is evenly distributed to the oxidation layer through the air vents 803 on the annular pipe 801 and the straight pipe 802. The position of the oxidation layer is determined by introducing air at a fixed point, thereby avoiding the phenomenon of the oxidation layer moving up due to the introduction of air from above; and the air is evenly distributed by the air distributor 8 so that the air is evenly distributed to the oxidation layer, and the biomass fuel in the oxidation layer can react evenly, thereby preventing the occurrence of violent local reactions and the "burn-through" phenomenon.

[0036] The biomass gas after reacting in the oxidation layer and the reduction layer passes through the grate 2 and enters the ash receiving hopper 3. The biomass gas carries part of the dust in the ash receiving hopper 3 through the grate 2 and enters the annular space 6. During the upward movement of the biomass gas in the annular space 6, the biomass gas and dust are guided by the spiral baffle 7, and the biomass gas moves upward in a rotational manner. Under the action of the spiral baffle 7 and its own gravity, the dust in the biomass gas falls from the annular space 6 to the ash receiving hopper 3, thereby reducing the dust content in the biomass gas. Example

[0037] The difference from the first embodiment is that, please refer to Figure 3 、 Figure 4 、 Figure 5 、 Figure 6 and Figure 7The air distributor 8 includes an annular pipe 801, a straight pipe 802, a closed cylinder 804 and a closed plate 805. The annular pipe 801 of the air distributor 8 is fixedly installed on the inner wall of the inner cylinder 5. The outer and inner sides of the two annular pipes 801 are respectively fixedly sleeved with closed cylinders 804. An annular closed groove 806 is formed between the two closed cylinders 804 and the annular pipe 801. A vent hole 803 is opened on the annular pipe 801 to communicate with the annular closed groove 806. A sliding plate 805 is installed in the annular closed groove 806. A slip ring 808 is installed, and the slip ring 808 is sealed with the side wall of the annular closed groove 806. A plurality of straight pipes 802 are arranged in an annular array on the inner ring of the annular pipe 801. The straight pipes 802 are connected to the annular pipe 801. A closing plate 805 is fixedly installed on the side wall of the straight pipe 802. A square closed groove 807 is formed between the closing plate 805 and the straight pipe 802. A vent hole 803 is opened on the straight pipe 802 to communicate with the square closed groove 807. The square closed groove 807 is connected to the annular closed groove 806. The top and bottom ends of the inner wall of the square closed groove 807 are fixedly installed with limit strips 810, and a slide plate 809 is slidably installed in the square closed groove 807. The slide plate 809 is sealed with the side wall of the square closed groove 807. The slide plate 809 is located between the limit strips 810 at the top and bottom ends. The slide plate 809 is fixedly installed on the inner wall of the slip ring 808. The closing plates 805 on both sides of the straight tube 802 are provided with connecting grooves 811. The connecting grooves 811 are located at the longitudinal center line of the closing plates 805. The straight tube 802 is provided with a plurality of connecting grooves 811. Two rows of exhaust holes 812 are respectively formed on the closing plates 805 on both sides. The two rows of exhaust holes 812 are respectively located on the upper and lower sides of the connecting groove 811. Two rows of exhaust holes 812 are also formed on the inner closing cylinder 804. The exhaust holes 812 on the closing cylinder 804 are at the same height as the exhaust holes 812 on the closing plates 805. A plurality of stirring rods 813 are provided between two adjacent slides 809. The two ends of the stirring rods 813 are fixedly mounted on the sides of the two adjacent slides 809 through the connecting grooves 811.

[0038] When not in operation, the slide plate 809 is placed on the limiting strip 810 at the lower end, and the slide plate 809 blocks the exhaust holes 812 on the lower side of the closing plate 805, and the exhaust holes 812 on the upper side of the closing plate 805 are in a connected state. When the slide plate 809 slides to the limiting strip 810 at the upper end, the slide plate 809 blocks the exhaust holes 812 on the upper side of the closing plate 805, and the exhaust holes 812 on the lower end of the closing plate 805 are in a connected state.

[0039] The pyrolysis layer within the inner tube 5 is provided with a hot smoke distributor 10, which is fixedly mounted on the inner wall of the inner tube 5. The hot smoke distributor 10 is used to introduce hot exhaust gas to provide heat to the pyrolysis layer. In addition, the exhaust gas contains CO2 gas. When the CO2 gas enters the reduction layer, it increases the concentration of the reduction layer reactants and the generated CO content.

[0040] A screen is fixedly installed in the exhaust hole 812 to prevent the biomass fuel burning in the oxidation layer from entering the square closed groove 807 through the exhaust hole 812. In addition, each time the exhaust hole 812 is ventilated, the air passing through the exhaust hole 812 blows off the particles in the screen to prevent the biomass fuel and dust from clogging the screen.

[0041] The working principle of the second embodiment of the present invention is as follows:

[0042] See also Figure 3 、 Figure 4 、 Figure 5 、 Figure 6 and Figure 7 Before the downdraft biomass gasifier is operated, the biomass fuel is fed into the inner tube 5 through the feed pipe 101 , and the outside air is fed into the air distributor 8 through the air supply device and the flow distributor 9 .

[0043] When the air flows through the flow distributor 9, the air is evenly distributed by the flow distributor 9 to the upper and lower annular pipes 801. After the air enters the annular pipe 801 and the straight pipe 802, the air in the upper annular pipe 801 and the straight pipe 802 enters the annular closed groove 806 and the square closed groove 807 through the vent 803. Moreover, the air in the upper annular pipe 801 and the straight pipe 802 is released into the oxide layer through the upper exhaust hole 812. Since the exhaust hole 812 on the lower side is blocked, the air in the lower annular pipe 801 and the straight pipe 802 is not released immediately. The lower annular pipe 801 and the straight pipe 802 continue to take in air, and the amount of air entering the annular closed groove 806 and the square closed groove 807 through the lower annular pipe 801 and the straight pipe 802 gradually increases. The air in the closed groove 806 and the square closed groove 807 pushes the slip ring 808 and the slide plate 809 to move upward until the slide plate 809 moves to the upper end of the exhaust hole 812 on the lower side, so that the air in the lower annular closed groove 806 and the square closed groove 807 flows out through the exhaust hole 812 on the lower side. In the process of the flow distributor 9 evenly ventilating the two air distributors 8, the slip ring 808 and the slide plate 809 move up and down in a cycle. In the process of the movement of the slip ring 808 and the slide plate 809, the slide plate 809 drives the stirring rod 813 to move up and down, so that the stirring rod 813 pushes the biomass fuel in the oxidation layer to move, so that the biomass fuel in the oxidation layer can move while burning, avoiding the "bridging" phenomenon of the biomass fuel in the oxidation layer, thereby avoiding the biomass from falling during the combustion process, forming an empty burning phenomenon.

[0044] During operation, the exhaust gas containing heat is introduced into the hot smoke distributor 10 of the pyrolysis layer through the air intake device, so that the exhaust gas provides heat to the pyrolysis layer. The exhaust gas contains CO2 gas. When the CO2 in the exhaust gas enters the reduction layer, the concentration of the reactants in the reduction layer is increased, thereby increasing the output of CO.

Claims

1. A downdraft biomass gasifier, comprising a furnace body (1), a grate (2) and an ash receiving hopper (3), wherein the grate (2) and the ash receiving hopper (3) are fixedly mounted on the lower portion of the inner wall of the furnace body (1), and the ash receiving hopper (3) is located below the grate (2), and is characterized in that: An inner cylinder (5) is fixedly mounted on the upper end of the grate (2), an annular space (6) is formed between the inner cylinder (5) and the furnace body (1), spiral baffles (7) are fixedly mounted on the side walls on both sides of the annular space (6), the inner cylinder (5) is divided into a drying layer, a pyrolysis layer, an oxidation layer and a reduction layer from top to bottom, two air distributors (8) are fixedly mounted on the inner wall of the inner cylinder (5) corresponding to the oxidation layer, the air distributor (8) is used to guide and distribute the air, a flow distributor (9) is fixedly mounted on the outer wall of the furnace body (1), and two air outlets of the flow distributor (9) are respectively connected to the air inlets of the two air distributors (8); The air distributor (8) comprises an annular pipe (801), a straight pipe (802), a closed cylinder (804) and a closed plate (805). The annular pipe (801) of the air distributor (8) is fixedly mounted on the inner wall of the inner cylinder (5). The outer sides and inner sides of the two annular pipes (801) are respectively fixedly sleeved with closed cylinders (804). An annular closed groove (806) is formed between the two closed cylinders (804) and the annular pipe (801). 1) is provided with a vent hole (803) connected to an annular closed groove (806), a slip ring (808) is slidably installed in the annular closed groove (806), a plurality of straight pipes (802) are provided in an annular array on the inner ring of the annular pipe (801), the straight pipes (802) are connected to the annular pipe (801), a closing plate (805) is fixedly installed on the side wall of the straight pipe (802), and a square closed groove (807) is formed between the closing plate (805) and the straight pipe (802) The straight tube (802) is provided with a vent hole (803) connected to a square closed groove (807), the square closed groove (807) is connected to the annular closed groove (806), a slide plate (809) is slidably installed in the square closed groove (807), and the slide plate (809) is fixedly installed on the inner wall of the slip ring (808), and the closed plates (805) on both sides of the straight tube (802) are provided with connecting grooves (811), and the connecting grooves (811) of the straight tube (802) are connected to the square closed groove (807). Exhaust holes (812) are respectively provided on the top and bottom, and two rows of exhaust holes (812) are provided on the inner closed cylinder (804). The exhaust holes (812) on the closed cylinder (804) and the exhaust holes (812) on the closed plate (805) are at the same height. A plurality of stirring rods (813) are provided between two adjacent slides (809), and both ends of the stirring rods (813) are fixedly mounted on the sides of the two adjacent slides (809) through connecting grooves (811).

2. A downdraft biomass gasifier according to claim 1, characterized in that: The angle formed by the spiral baffle (7) and the axis of the furnace body (1) is less than 45°.

3. The downdraft biomass gasifier according to claim 1, characterized in that: A hot smoke distributor (10) is fixedly mounted on the inner wall of the inner cylinder (5), and the hot smoke distributor (10) is located in the pyrolysis layer inside the inner cylinder (5).

4. The downdraft biomass gasifier according to claim 1, characterized in that: A screen is fixedly installed in the exhaust hole (812).

5. The downdraft biomass gasifier according to claim 1, characterized in that: Limiting bars (810) are fixedly mounted on the top and bottom ends of the inner wall of the square closed groove (807), respectively.

6. The downdraft biomass gasifier according to claim 5, characterized in that: When not in operation, the slide plate (809) is placed on the limiting strip (810) at the lower end, and the slide plate (809) blocks the exhaust hole (812) on the lower side of the closing plate (805); when the slide plate (809) slides to the limiting strip (810) at the upper end, the slide plate (809) blocks the exhaust hole (812) on the upper side of the closing plate (805).

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