Premixing device

Abstract

To provide a premixing device for mixing fuel gas with air to supply an air fuel mixture to a burner through a fan, in which a butterfly valve 8 is provided in an air supply passage on an upstream side of the fan so as to be positioned on the upstream side with respect to a gas suction part to which a downstream end of the gas supply passage is connected, and which can prevent a necessary amount of air from being not secured for a long period of time when the butterfly valve 8 is in a closed position.SOLUTION: A vent opening 82 is formed in a butterfly valve 8, through which air flows from an upstream side to a downstream side of the butterfly valve 8 when the butterfly valve is in a closed posture. Also, a protrusion 84 that protrudes in a thickness direction of the butterfly valve 8 is provided on a side surface 83 of the butterfly valve 8 so as to be located in a portion of a periphery of the vent opening 82 that is on the upstream side when the butterfly valve 8 is in the open posture.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a premixing device that mixes fuel gas with air and supplies the mixture to a burner via a fan. [Background technology]

[0002] Conventionally, as a premixing device of this kind, one in which the downstream end of the gas supply passage is connected to a gas suction section provided in the air supply passage upstream of the fan, and a butterfly valve is provided in a portion of the air supply passage upstream of the gas suction section is known (for example, see Patent Document 1). In this type of premixing device, the butterfly valve is rotatable around a rotation axis along a predetermined diameter direction of the butterfly valve to at least two positions: an open position parallel to the longitudinal direction of the air supply passage, and a closed position perpendicular to the longitudinal direction of the air supply passage. When the butterfly valve is in the closed position, air flows through a gap between the outer periphery of the butterfly valve and the peripheral wall surface of the air supply passage.

[0003] When the butterfly valve is in the closed position, the air that hits the side of the air supply passage facing the upstream side in the closed position of the butterfly valve flows into the gap between the outer periphery of the butterfly valve and the peripheral wall surface of the air supply passage with a large radially outward velocity component. The large radially outward velocity component causes dust contained in the air to strongly collide with the peripheral wall surface of the air supply passage and to easily adhere to the peripheral wall surface. Therefore, dust adheres and accumulates on the peripheral wall surface of the air supply passage in a relatively short period of time, and when the butterfly valve is in the closed position, the gap between the peripheral wall surface of the air supply passage becomes clogged. As a result, the amount of air flowing through this gap decreases, and the required amount of air cannot be secured.

[0004] Therefore, the applicant of the present application previously proposed in Japanese Patent Application No. 2022-141136 a butterfly valve formed with a vent opening through which air flows from the upstream side to the downstream side of the butterfly valve in the closed position. According to this, when the butterfly valve is in the closed position, air flows through the vent opening, so that it is possible to prevent a decrease in the amount of air caused by clogging of the gap between the outer peripheral edge of the butterfly valve and the peripheral wall surface of the air supply passage.

[0005] However, it was found that the prior application also had the following problem: when the butterfly valve was in the open position, part of the air collided strongly with the portion of the periphery of the vent opening that was downstream when the butterfly valve was in the open position, causing dust to adhere to and accumulate on this portion. This reduced the opening area of ​​the vent opening, making it impossible to ensure the required amount of air when the butterfly valve was in the closed position. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2021-25722 Summary of the Invention [Problem to be solved by the invention]

[0007] In view of the above, an object of the present invention is to provide a premixing device that overcomes the problems of the prior application and can prevent, for a long period of time, the inability to secure the required amount of air when the butterfly valve is in a closed position. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention provides a premixing device that mixes fuel gas with air and supplies the mixture to a burner via a fan, the downstream end of a gas supply passage being connected to a gas suction section provided in the air supply passage upstream of the fan, and a butterfly valve being provided in a portion of the air supply passage upstream of the gas suction section, the butterfly valve being rotatable about a rotation axis along a predetermined diameter direction of the butterfly valve to at least two positions: an open position parallel to the longitudinal direction of the air supply passage and a closed position perpendicular to the longitudinal direction of the air supply passage, and the butterfly valve being formed with a vent opening through which air flows from the upstream side to the downstream side of the butterfly valve in the closed position, the butterfly valve being characterized in that a protrusion protruding in the thickness direction of the butterfly valve is provided on each side of the butterfly valve facing the upstream or downstream side in the closed position, located in a portion of the periphery of the vent opening that is upstream in the open position of the butterfly valve.

[0009] According to the present invention, when the butterfly valve is in the open position, the protrusions function as a windbreak wall and can prevent air from strongly colliding with the portion of the circumferential surface of the ventilation opening that is downstream when the butterfly valve is in the open position. This can prevent dust from adhering and accumulating on that portion of the circumferential surface of the ventilation opening, thereby preventing a reduction in the opening area of ​​the ventilation opening. Therefore, when the butterfly valve is in the closed position, a reduction in the opening area of ​​the ventilation opening, which causes a necessary amount of air to be unavailable, can be prevented for a long period of time.

[0010] Furthermore, in the present invention, it is preferable that the portion of the peripheral surface of the ventilation opening that is downstream when the butterfly valve is in the open position is formed as an inclined surface inclined toward the downstream side. In this way, even if dust adheres to the portion of the peripheral surface of the ventilation opening that is downstream when the butterfly valve is in the open position, the effective opening area of ​​the ventilation opening is not reduced. Therefore, it is possible to more effectively prevent the necessary amount of air from being unable to be secured when the butterfly valve is in the closed position.

[0011] In addition, generally, a protuberance that protrudes the most in the thickness direction of the butterfly valve is provided in the center along the rotation axis of each side of the butterfly valve. Then, a vent opening is formed in a part of the butterfly valve located upstream of the protuberance when the butterfly valve is in the open position and in a part of the butterfly valve located downstream of the protuberance when the butterfly valve is in the open position. In this case, it is preferable that the protrusion provided around the vent opening formed in the part of the butterfly valve located upstream of the protuberance when the butterfly valve is in the open position has an extension that extends to the vicinity of the protuberance so as to surround the part of the vent opening that is downstream in the open position of the butterfly valve from both sides in the longitudinal direction of the rotation axis of the butterfly valve. This makes it possible to prevent air from coming around from the rotation axis direction and colliding with the side portion between the part of the protuberance located downstream of the vent opening and the vent opening when the butterfly valve is in the open position. Therefore, it is possible to effectively prevent the substantial opening area of ​​the ventilation opening from being reduced, as described below, due to adhesion of dust caused by air impinging on this side portion.

[0012] In addition, each side of the butterfly valve is generally inclined so that the thickness of the butterfly valve decreases as it moves away from the raised portion. Therefore, when the butterfly valve is in the open position, dust is likely to adhere to the half of each side of the butterfly valve that is located on the upstream side in the open position. If dust adheres to the portion of the side of the butterfly valve near the outer periphery, when the butterfly valve rotates from the open position to the closed position, the dust may get caught between the outer periphery of the butterfly valve and the peripheral wall surface of the air supply passage, making it impossible to rotate the butterfly valve to the closed position. Therefore, in the present invention, it is desirable that the half of each side of the butterfly valve that is located on the upstream side in the open position is inclined in a curved shape so that the inclination angle in the thickness direction of the butterfly valve becomes gentler as it moves away from the raised portion. According to this, when the butterfly valve is in the open position, dust is less likely to adhere to the vicinity of the outer periphery of the upstream half of each side of the butterfly valve. Therefore, the occurrence of the above-mentioned problems can be suppressed. [Brief description of the drawings]

[0013] [Figure 1]FIG. 2 is a cutaway side view illustrating a premixing device according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a perspective view of a butterfly valve provided in the premixing device of the embodiment in an open position. [Diagram 3] FIG. 3 is a cross-sectional side view taken along line III-III in FIG. 2 . [Figure 4] FIG. 4 is a cross-sectional side view taken along line IV-IV in FIG. 2 . DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The combustion device shown in Fig. 1 is a heat source machine equipped with a full primary combustion burner 1, a combustion housing 2 that encloses the combustion space of the air-fuel mixture ejected from the combustion surface 1a of the burner 1, and a heat exchanger 3 arranged inside the combustion housing 2. The combustion gas generated by the combustion of the air-fuel mixture heats the heat exchanger 3 and is then discharged to the outside through an exhaust pipe 4 connected to the end of the combustion housing 2. In addition, a premixing device A according to an embodiment of the present invention mixes fuel gas into air and supplies the mixture to the burner 1 through a fan 5.

[0015] The premixing device A includes a fan 5, an air supply passage 6 upstream of the fan 5, and a gas supply passage 7 for supplying fuel gas. The downstream end of the gas supply passage 7 is connected to a gas suction section 61 provided in the air supply passage 6. A butterfly valve 8, which will be described later, is provided in a portion of the air supply passage 6 upstream of the gas suction section 61. In addition, a venturi section 62 having a smaller diameter than the portion where the butterfly valve 8 is provided in the air supply passage 6, is provided downstream of the portion where the butterfly valve 8 is provided. A portion of the air supply passage 6 adjacent to the downstream side of the venturi section 62 is surrounded by a cylindrical section 63 having a larger diameter than the venturi section 62. The downstream end of the venturi section 62 is inserted into the upstream end of the cylindrical section 63 with a ring-shaped gap, and this gap constitutes the gas suction section 61.

[0016] A gas chamber 71 communicating with the gas suction part 61 is provided at the downstream end of the gas supply passage 7 so as to surround the cylindrical part 63. In addition, a main valve 72, a zero governor 73 for adjusting the secondary gas pressure to atmospheric pressure, and a variable throttle valve 74 are provided in the gas supply passage 7 in this order from the upstream side.

[0017] The amount of fuel gas supplied through the gas suction unit 61 changes according to the pressure difference between the atmospheric pressure, which is the secondary gas pressure, and the negative pressure in the air supply passage 6. Here, the negative pressure in the air supply passage 6 changes according to the rotation speed of the fan 5. Therefore, the amount of fuel gas supplied changes in proportion to the rotation speed of the fan 5, that is, the amount of air supplied. In addition, the ratio of the amount of fuel gas supplied to the amount of air supplied changes according to the opening degree of the combustible throttle valve 74. By setting the opening degree of the variable throttle valve 74 to a predetermined reference opening degree according to the type of gas used, the excess air ratio of the mixture becomes a predetermined appropriate value (for example, 1.3). Then, by controlling the rotation speed of the fan 5 according to the required combustion amount (the amount of combustion necessary to discharge hot water at the set hot water temperature), the mixture is supplied to the burner 1 in an amount according to the required combustion amount with an appropriate excess air ratio.

[0018] In order to prevent exhaust failure caused by wind entering the exhaust pipe 4, that is, to ensure wind resistance, the lower limit rotation speed of the fan 5 cannot be set too low. When the required combustion amount falls below a predetermined value corresponding to the lower limit rotation speed of the fan 5, it becomes impossible to supply the amount of air corresponding to the required combustion amount.

[0019] Therefore, a butterfly valve 8 is arranged in the air supply passage 6 upstream of the gas suction section 61 in order to switch the air flow resistance of the air supply passage 6 between large and small. The butterfly valve 8 is rotated around a rotation axis 8a along a predetermined diameter direction of the butterfly valve 8 to two positions: an open position shown by a virtual line in FIG. 1 parallel to the longitudinal direction of the air supply passage 6, and a closed position shown by a solid line in FIG. 1 perpendicular to the longitudinal direction of the air supply passage 6. A rotating shaft 81 that coincides with the rotation axis 8a and is driven by a motor (not shown) is connected to the butterfly valve 8. When the required combustion amount becomes equal to or less than the predetermined value, the butterfly valve 8 is rotated to the closed position to increase the air flow resistance of the air supply passage 6. This makes it possible to supply an amount of air corresponding to a combustion amount equal to or less than a predetermined value without lowering the rotation speed of the fan 5 below the lower limit rotation speed.

[0020] However, simply increasing the air flow resistance of the air supply passage 6 by closing the butterfly valve 8 increases the negative pressure in the air supply passage 6, causing the amount of fuel gas supplied to be excessive, and causing the excess air ratio of the mixture supplied to the burner 1 to fall below an appropriate value. Therefore, when the required combustion amount is relatively small, the butterfly valve 8 is rotated to the closed position, and the opening of the variable throttle valve 74 is set to a relatively small, low-capacity standard opening that is preset so that the excess air ratio of the mixture becomes an appropriate value with the butterfly valve 8 in the closed position, thereby switching the combustion capacity to a small capacity, and supplying the mixture to the burner 1 in an amount corresponding to a relatively small combustion amount with an appropriate excess air ratio. Furthermore, when the required combustion amount is relatively large, the butterfly valve 8 is rotated to the open position, and the opening of the variable throttle valve 74 is set to a relatively large, large-capacity standard opening that is set in advance so that the air excess ratio of the mixture becomes an appropriate value when the butterfly valve 8 is in the open position, thereby switching the combustion capacity to large capacity and supplying to the burner 1 an amount of mixture corresponding to a relatively large combustion amount and with an appropriate air excess ratio.

[0021] The butterfly valve 8 will be described in detail below with reference to Figs. 2 to 4. The butterfly valve 8 has four ventilation openings 82 at 90° intervals in the circumferential direction, through which air flows from the upstream side to the downstream side of the butterfly valve 8 in the closed position. In addition, in the center along the rotation axis 8a of each side surface 83 of the butterfly valve 8 facing the upstream side or downstream side in the closed position of the butterfly valve 8, a protruding portion 83a that protrudes most in the thickness direction of the butterfly valve 8 is provided in order to form an axial hole 81a into which the rotating shaft 81 is fitted in the butterfly valve 8. Two ventilation openings 82 are formed in each of the part of the butterfly valve 8 located upstream of the protruding portion 83a and the part of the butterfly valve 8 located downstream of the protruding portion 83a in the open position of the butterfly valve 8. If the ventilation openings 82 are formed in the butterfly valve 8 in this way, air flows through the ventilation openings 82 when the butterfly valve 8 is in the closed position. Therefore, a decrease in the amount of air caused by clogging of the gap between the outer circumferential edge of the butterfly valve 8 and the peripheral wall surface 6a of the air supply passage 6 can be prevented.

[0022] However, when the butterfly valve 8 is in the open position, part of the air may strongly collide with a portion of the circumferential surface of the ventilation opening 82 that is downstream when the butterfly valve 8 is in the open position (the upper portion in Figs. 2 and 3), causing dust to adhere and accumulate in this portion. If dust adheres and accumulates, the opening area of ​​the ventilation opening 82 will decrease, and it will become impossible to ensure the required amount of air when the butterfly valve 8 is in the closed position.

[0023] Therefore, in this embodiment, a protrusion 84 is provided on each side surface 83 of the butterfly valve 8, which is located in a portion of the periphery of the ventilation opening 82 that is on the upstream side when the butterfly valve 8 is in the open position (the lower portion in Figs. 2 and 3), more precisely, in a half-circumference portion on the upstream side, and protrudes in the thickness direction of the butterfly valve 8. With this, when the butterfly valve 8 is in the open position, the protrusion 84 functions as a windbreak wall, and it is possible to prevent air from strongly colliding with the portion of the periphery of the ventilation opening 82 that is on the downstream side when the butterfly valve 8 is in the open position. Therefore, it is possible to prevent dust from adhering and accumulating on the portion of the periphery of the ventilation opening 82, which causes the opening area of ​​the ventilation opening 82 to decrease. Therefore, it is possible to prevent the necessary amount of air from being unable to be secured due to the reduction in the opening area of ​​the ventilation opening 82, for a long period of time, when the butterfly valve 8 is in the closed position.

[0024] In this embodiment, the portion of the peripheral surface of the ventilation opening 82 that is downstream when the butterfly valve 8 is in the open position is formed as an inclined surface 82a that is inclined downstream. With this, even if dust adheres to the inclined surface 82a, which is the portion of the peripheral surface of the ventilation opening 82 that is downstream when the butterfly valve 8 is in the open position, the substantial opening area of ​​the ventilation opening 82 is not reduced. Therefore, it is possible to more effectively prevent the necessary amount of air from being unable to be secured when the butterfly valve 8 is in the closed position.

[0025] Furthermore, in this embodiment, the protrusion 84 provided around the ventilation opening 82 formed in the part of the butterfly valve 8 located upstream of the raised part 83a in the open position of the butterfly valve 8 has extension parts 84a, 84a extending to the vicinity of the raised part 83a so as to surround the part of the periphery of the ventilation opening 82 that is downstream in the open position of the butterfly valve 8 from both sides in the longitudinal direction of the rotation axis 8a. This makes it possible to prevent air from going around from the rotation axis direction and colliding with the part of the side surface 83 between the part of the raised part 83a located downstream of the ventilation opening 82 and the ventilation opening 82 when the butterfly valve 8 is in the open position. Here, when air collides with the above part of the side surface 83 of the butterfly valve 8 and dust adheres, the dust accumulates from this point so as to protrude into the ventilation opening 82, and the effective opening area of ​​the ventilation opening 82 is reduced. In contrast, in the present embodiment, it is possible to suppress adhesion of dust due to air collision with the above-mentioned portion of the side surface 83 of the butterfly valve 8. Therefore, it is possible to effectively suppress a reduction in the substantial opening area of ​​the ventilation opening 82 caused by dust adhesion to the above-mentioned portion of the side surface 83 of the butterfly valve 8.

[0026] Incidentally, each side surface 83 of the butterfly valve 8 is inclined so that the thickness of the butterfly valve 8 decreases the farther away from the raised portion 83a. Therefore, when the butterfly valve 8 is in the open position, dust may adhere to the half of each side surface 83 of the butterfly valve 8 that is located on the upstream side in the open position. If dust adheres to the portion near the outer periphery of the side surface 83 of the butterfly valve 8, the dust may get caught between the outer periphery of the butterfly valve 8 and the peripheral wall surface 6a of the air supply passage 6 when the butterfly valve 8 is rotated from the open position to the closed position, and the butterfly valve 8 may not be able to rotate to the closed position.

[0027] Therefore, in this embodiment, the half of each side surface 83 of the butterfly valve 8 located on the upstream side in the open position (hereinafter referred to as the upstream half) is inclined in a curved shape so that the inclination angle in the thickness direction of the butterfly valve 8 becomes gentler as it moves away from the raised portion 83a, as shown in Fig. 4. This makes it difficult for dust to adhere to the vicinity of the outer periphery of the upstream half of each side surface 83 of the butterfly valve 8 when the butterfly valve 8 is in the open position. Therefore, it is possible to effectively prevent dust from getting caught between the outer periphery of the butterfly valve 8 and the peripheral wall surface 6a of the air supply passage 6 when the butterfly valve 8 is rotated from the open position to the closed position, which prevents the butterfly valve 8 from being rotated to the closed position.

[0028] In this embodiment, the half of each side surface 83 of the butterfly valve 8 that is located downstream in the open position (hereinafter referred to as the downstream half) is also inclined in a curved shape. However, because there is a low possibility that dust will adhere to the downstream half of each side surface 83 of the butterfly valve 8 when the butterfly valve 8 is in the open position, the downstream half may be inclined in a linear shape.

[0029] Although the embodiment of the present invention has been described above with reference to the drawings, the present invention is not limited thereto. For example, in the above embodiment, the butterfly valve 8 is rotatable between two positions, an open position and a closed position, but it may be rotatable between three or more positions including positions between the open position and the closed position. In addition, it is also possible to form a single vent opening having an opening area equal to the total opening area of ​​the four vent openings 82 in the above embodiment in the center of the butterfly valve 8, or to form a plurality of vent openings other than four in the butterfly valve 8. [Explanation of symbols]

[0030] A...premixing device, 1...burner, 5...fan, 6...air supply passage, 61...gas suction section, 7...gas supply passage, 8...butterfly valve, 8a...rotation axis, 82...ventilation opening, 82a...inclined surface of downstream portion of circumferential surface of ventilation opening, 83...side surface of butterfly valve, 83a...raised portion, 84...rib, 84a...extension of rib.

Claims

1. A premixing device which mixes fuel gas into air and supplies the mixture to a burner via a fan, the device comprising: a downstream end of a gas supply passage connected to a gas suction section provided in an air supply passage upstream of the fan; a butterfly valve provided in a portion of the air supply passage upstream of the gas suction section; the butterfly valve being rotatable about a rotation axis along a predetermined diameter direction of the butterfly valve to at least two positions, an open position parallel to the longitudinal direction of the air supply passage and a closed position perpendicular to the longitudinal direction of the air supply passage; and a vent opening formed in the butterfly valve through which air flows from the upstream side to the downstream side of the butterfly valve in the closed position, A premixing device characterized in that a protrusion protruding in a thickness direction of the butterfly valve is provided on each side of the butterfly valve facing the upstream or downstream side when the butterfly valve is in a closed position, the protrusion being located in a portion of the periphery of the ventilation opening that is on the upstream side when the butterfly valve is in an open position.

2. 2. The premixing device according to claim 1, wherein a portion of the peripheral surface of the ventilation opening that is on the downstream side when the butterfly valve is in an open position is formed as an inclined surface that is inclined downstream.

3. 2. A premixing device according to claim 1, wherein a raised portion that is the highest in a thickness direction of the butterfly valve is provided in a central portion along the rotation axis of each side surface of the butterfly valve, and the vent openings are formed in a portion of the butterfly valve that is located upstream of the raised portion when the butterfly valve is in an open position and a portion of the butterfly valve that is located downstream of the raised portion when the butterfly valve is in an open position, respectively, and wherein the protrusion provided around the vent opening formed in the portion of the butterfly valve that is located upstream of the raised portion when the butterfly valve is in an open position has an extension portion that extends to the vicinity of the raised portion so as to surround the portion of the periphery of the vent opening that is downstream in the open position of the butterfly valve from both longitudinal sides of the rotation axis.

4. 2. A premixing device according to claim 1, wherein a raised portion that is the highest in a thickness direction of the butterfly valve is provided in a central portion along the rotation axis of each side surface of the butterfly valve, and each side surface of the butterfly valve is inclined so that the thickness of the butterfly valve decreases the further away from the raised portion, and a half of each side surface of the butterfly valve that is located upstream in an open position is inclined in a curved shape so that the inclination angle in the thickness direction of the butterfly valve becomes gentler the further away from the raised portion.

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