POWDER FUEL BURNER

Abstract

A powder fuel burner mounted in a combustion chamber of a boiler includes: a cylindrical air-fuel mixture conveying tube, through which an air-fuel mixture is conveyed and which injects, from a distal end thereof, the air-fuel mixture into the combustion chamber, the air-fuel mixture being a mixture of a powder fuel and conveying air; a swirl vane mounted at the distal end of the air-fuel mixture conveying tube; and a rod-shaped center flow blocker mounted on a center axis of the air-fuel mixture conveying tube at a position upstream of the swirl vane in a conveying direction of the air-fuel mixture, the center flow blocker including a cylindrical surface that is concentric with the air-fuel mixture conveying tube and that extends in a direction of the center axis.

Claims

1. A powder fuel burner mounted in a combustion chamber of a boiler, the powder fuel burner comprising: a cylindrical air-fuel mixture conveying tube, through which an air-fuel mixture is conveyed and which injects, from a distal end thereof, the air-fuel mixture into the combustion chamber, the air-fuel mixture being a mixture of a powder fuel and conveying air; a swirl vane mounted at the distal end of the air-fuel mixture conveying tube; and a rod-shaped center flow blocker mounted on a center axis of the air-fuel mixture conveying tube at a position upstream of the swirl vane in a conveying direction of the air-fuel mixture, the center flow blocker including a cylindrical surface that is concentric with the air-fuel mixture conveying tube and that extends in a direction of the center axis.

2. The powder fuel burner according to claim 1, further comprising: a cylindrical peripheral flow blocker mounted along an inner wall surface of the air-fuel mixture conveying tube, the peripheral flow blocker including a cylindrical inner peripheral surface that faces the cylindrical surface of the center flow blocker and that is spaced apart from the cylindrical surface of the center flow blocker by a predetermined distance.

3. The powder fuel burner according to claim 2, further comprising: an internal cylinder that is concentric with the air-fuel mixture conveying tube and that is, at the distal end of the air-fuel mixture conveying tube, mounted inside the air-fuel mixture conveying tube, wherein the swirl vane is located inside the internal cylinder.

4. The powder fuel burner according to claim 1, wherein the powder fuel is a petroleum residue fuel, a biomass fuel, or a mixed fuel of biomass and pulverized coal.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0010] FIG. 1 is a schematic diagram showing one example of a combustion system including a boiler including powder fuel burners according to an embodiment of the present disclosure.

[0011] FIG. 2 is a schematic sectional view showing one example of a powder fuel burner according to the present embodiment.

[0012] FIG. 3 is a sectional view taken along line A-A of FIG. 2.

[0013] FIG. 4 is a sectional view taken along line B-B of FIG. 2.

[0014] FIG. 5 is a schematic sectional view showing an essential part of another example of the powder fuel burner according to the present embodiment.

DESCRIPTION OF EMBODIMENTS

[0015] Hereinafter, a preferred embodiment of the present disclosure is described with reference to the drawings. In the drawings, the same or corresponding elements are denoted by the same reference signs, and repeating the same descriptions is avoided below. The drawings show each component schematically in order to facilitate the understanding thereof. Therefore, in some cases, the drawings may not display accurate shapes, accurate dimensional ratios, etc.

Embodiment

[0016] FIG. 1 is a schematic diagram showing one example of a combustion system including a boiler including powder fuel burners according to the present embodiment.

[0017] The combustion system shown in FIG. 1 includes a fuel feeder 20 and a boiler 100. The fuel feeder 20 includes a fuel storage tank 21, a weighing feeder 22, and a pulverizer 23. The fuel storage tank 21 stores therein a flame-retardant fuel, for example, a petroleum residue such as petroleum coke. The fuel stored in the fuel storage tank 21 is fed to the weighing feeder 22, and the fuel in a predetermined weight is fed from the weighing feeder 22 to the pulverizer 23. The pulverizer 23 grinds the fuel fed from the weighing feeder 22 into powder, and feeds an air-fuel mixture that is a mixture of the resulting powder fuel and conveying air to powder fuel burners 5 of the boiler 100. An A/F, i.e., an air-fuel ratio, of the air-fuel mixture fed from the pulverizer 23 to the powder fuel burners 5 is about 1.8.

[0018] The boiler 100 is configured as an inverted vertical furnace. The boiler 100 includes; a combustion chamber 1, which is, for example, a cylindrical chamber with a rectangular cross section, and a path 12 connected to the combustion chamber 1 via a gas outlet 11.

[0019] The combustion chamber 1 includes: a high-temperature reducing combustion chamber 2, which is located at the upper end of the combustion chamber 1; a low-temperature oxidizing combustion chamber 3, which is located below the high-temperature reducing combustion chamber 2; and a restrictor 4, which connects the high-temperature reducing combustion chamber 2 and the low-temperature oxidizing combustion chamber 3 to each other.

[0020] The restrictor 4 is a passage at which the horizontal cross sectional area of the combustion chamber 1 is reduced by 20 to 50% compared to the horizontal cross sectional area of the other part of the combustion chamber 1.

[0021] The walls of the high-temperature reducing combustion chamber 2 are covered by a fire-resistant material 6, which can withstand a predetermined internal temperature of a high-temperature furnace. The powder fuel burners 5 are located on each of two side walls of the high-temperature reducing combustion chamber 2, the two side walls facing each other. It this example, a total of eight powder fuel burners 5 are located on these two side walls. The eight burners 5 are located in such a manner that the flame axes of the respective burners do not face each other, but are parallel to each other. In the high-temperature reducing combustion chamber 2, the fuel fed from the burners 5 is subjected to initial-stage combustion in a high-temperature reducing atmosphere. As a result, combustion gas is generated. The amount of generated combustion gas increases due to the fuel being newly fed. Consequently, the generated combustion gas is pushed out from the high-temperature reducing combustion chamber 2, and flows downward through the restrictor 4 to the low-temperature oxidizing combustion chamber 3.

[0022] The side walls of the low-temperature oxidizing combustion chamber 3 have a water-cooled wall structure, by which the high-temperature combustion gas that has flowed downward through the restrictor 4 from the high-temperature reducing combustion chamber 2 is cooled down. In the low-temperature oxidizing combustion chamber 3, a single line of air nozzles 7, or multiple lines of air nozzles 7, are located on a furnace wall that is spaced apart downward from the restrictor 4. The air nozzles 7 are nozzles to feed air for second-stage combustion. In a second-stage combustion region 10 below the air nozzles 7, with the air fed from the air nozzles 7, uncombusted gas in the combustion gas is subjected to second-stage combustion in a low-temperature oxidizing atmosphere. Combustion ash accumulated at the bottom of the furnace is discharged to the outside of the furnace through an ash outlet 8.

[0023] The gas outlet 11, which leads to the path 12, is located on a lower side surface of the second-stage combustion region 10. The flow of combustion gas generated in the second-stage combustion region 10 is inverted in a U shape, and then the combustion gas flows into the path 12. The path 12 includes steam superheater tubes 13 and an economizer 14. The combustion gas that has flowed into the path 12 exchanges heat with boiler water at the steam superheater tubes 13 and the economizer 14, and is then fed to the following treatment step. Combustion ash that flows with the combustion gas is discharged through an ash outlet 15.

[0024] In the boiler 100, the fuel fed from the powder fuel burners 5 is subjected to initial-stage combustion in a high-temperature reducing atmosphere in the high-temperature reducing combustion chamber 2, and then further subjected to second-stage combustion in a low-temperature oxidizing atmosphere in the low-temperature oxidizing combustion chamber 3. Consequently, the amount of NOx generation is reduced.

[0025] FIG. 2 is a schematic sectional view showing one example of a powder fuel burner according to the present embodiment. FIG. 3 is a sectional view take along line A-A of FIG. 2 FIG. 4 is a sectional view taken along line B-B of FIG. 2.

[0026] The powder fuel burner S shown in FIG. 2 includes: a cylindrical air-fuel mixture conveying tube 51, through which the air-fuel mixture fed from the pulverizer 23 is conveyed; and a wind box 52. The wind box 52 includes: a secondary air feeding passage 53, through which secondary air is fed to the high-temperature reducing combustion chamber 2; and a tertiary air feeding passage 54, through which tertiary air swirled by a swirl vane 55 is fed to the high-temperature reducing combustion chamber 2. That is, the air-fuel mixture is injected from the distal end of the air-fuel mixture conveying tube 51 into the high-temperature reducing combustion chamber 2, and the secondary air and the tertiary air, each of which is combustion air, are fed from around the distal end of the air-fuel mixture conveying tube 51 to the high-temperature reducing combustion chamber 2.

[0027] On the distal end of the air-fuel mixture conveying tube 51, there is a flame stabilizing plate 51a, which is integrated with the air-fuel mixture conveying tube 51. A swirl vane 64 and a short internal cylinder 65 are mounted at the distal end of the air-fuel mixture conveying tube 51. The proximal end of the air-fuel mixture conveying tube 51 is connected via an elbow tube 58 to an air-fuel mixture feeding tube 57, through which the air-fuel mixture from the pulverizer 23 is fed. An ignition burner 61, which is a gun-type heavy oil burner or gas burner, is located on a center axis 5a of the air-fuel mixture conveying tube 51.

[0028] The swirl vane 64 is fixed near the distal end of the ignition burner 61. The swirl vane 64 is, as shown in FIG. 4, a well-known swirl vane that includes: a cylindrical structure 64a mounted to the ignition burner 61; and flat-plate vanes 64b. The swirl vane 64 is located inside the internal cylinder 65. The internal cylinder 65 is concentric with the air-fuel mixture conveying tube 51 and mounted inside the air-fuel mixture conveying tube 51. The vanes 64b are mounted to the outer peripheral surface of the cylindrical structure 64a at regular intervals, such that each vane 64b has a predetermined angle relative to the center line of the cylindrical structure 64a. The center line of the cylindrical structure 64a coincides with the center axis 5a, and the cylindrical structure 64a is mounted concentrically with the air-fuel mixture conveying tube 51.

[0029] In the powder fuel burner 5, at the start of the operation of the boiler 100, first, heavy oil or gas injected from the ignition burner 61 is combusted. Then, after the high-temperature reducing combustion chamber 2 is warmed up, the air-fuel mixture is injected from the powder fuel burner 5, and combustion of the powder fuel in the air-fuel mixture is started. Thereafter, the injection of the heavy oil or gas from the ignition burner 61 is stopped at a suitable time, and the combustion of the powder fuel in the air-fuel mixture injected from the powder fuel burner 5 is continued.

[0030] In the powder fuel burner 5 of the present embodiment, at a position upstream of the swirl vane 64 in the conveying direction of the air-fuel mixture, a rod-shaped center flow blocker 62 is mounted on the center axis 5a of the air-fuel mixture conveying tube 51. The center flow blocker 62 includes a cylindrical surface 62a, which is concentric with the air-fuel mixture conveying tube 51 and which extends in the direction of the center axis 5a. Further, a cylindrical peripheral flow blocker 63 is mounted along an inner wall surface 51s of the air-fuel mixture conveying tube 51. The peripheral flow blocker 63 includes a cylindrical inner peripheral surface 63a, which is concentric with the air-fuel mixture conveying tube 51 and which extends in the direction of the center axis 5a. The inner peripheral surface 63a faces the cylindrical surface 62a of the center flow blocker 62, and is spaced apart from the cylindrical surface 62a by a predetermined distance. FIG. 2 shows a range L, within which the cylindrical surface 62a and the inner peripheral surface 63a face each other.

[0031] According to the powder fuel burner 5, when the air-fuel mixture flowing inside the air-fuel mixture conveying tube 51 flows in the region where the center flow blocker 62 and the peripheral flow blocker 63 are mounted, the cross section of the flow passage is a narrow donut shape. Thereafter, the air-fuel mixture flows in a manner to spread over the entire internal space of the tube. Then, the air-fuel mixture is swirled by the swirl vane 64, and injected into the combustion chamber 1. Here, also after the air-fuel mixture traveling straight in the same direction as the direction of the center axis 5a has passed the region where the center flow blocker 62 and the peripheral flow blocker 63 are mounted, the particles of the powder fuel contained in the air-fuel mixture are to travel straight due to the inertial force. Accordingly, as indicated by arrows S2, the air-fuel mixture having a low powder fuel concentration flows near the center and near the tubular wall of the air-fuel mixture conveying tube 51. Also, as indicated by arrows S1, the air-fuel mixture having a high powder fuel concentration flows in the other region of the air-fuel mixture conveying tube 51, and passes through the swirl vane 64 to be injected into an ignition region R1 of the combustion chamber 1. Therefore, even when the air-fuel mixture having a high A/F is fed to the burner 5, the A/F of the air-fuel mixture injected into the combustion chamber 1 can be locally reduced. That is, even when a flame-retardant powder fuel, such as a petroleum residue fuel, having a higher A/F than a suitable A/F for its ignition and combustion is directly fed from the pulverizer 23, the A/F of the air-fuel mixture injected into the combustion chamber 1 can be locally reduced to a suitable A/F for the ignition and combustion of the powder fuel. Consequently, the ignitibility can be improved, and stable combustion can be achieved. In this example, the A/F of the air-fuel mixture fed from the pulverizer 23 is about 1.8. A suitable A/F of the air-fuel mixture for the ignition and combustion of petroleum coke, which is one example of a flame-retardant powder fuel, is preferably less than or equal to 1.5, and more preferably about 1.0.

[0032] In a central part R2 of the swirl vane 64 as shown in FIG. 4, the vanes 64b are densely located. Due to the presence of the center flow blocker 62, the amount of powder fuel particles that collide with the central part R2 of the swirl vane 64 is reduced. Further, a large amount of powder fuel particles pass through the gaps between the vanes 64b outside the central part R2 to be fed to the ignition region R1 of the combustion chamber 1. This also contributes to locally reducing the A/F of the air-fuel mixture injected into the combustion chamber 1.

[0033] FIG. 5 is a schematic sectional view showing an essential part of another example of the powder fuel bumer according to the present embodiment. In a powder fuel burner 5A shown in FIG. 5, the above-described internal cylinder 65 and peripheral flow blocker 63 of the powder fuel burner 5 are absent. The powder fuel burner 5A includes: a swirl vane 64A whose diameter is greater than the diameter of the above-described swirl vane 64; and a center flow blocker 62A whose diameter is greater than the diameter of the center flow blocker 62. The surface of the center flow blocker 62A within the range L is a cylindrical surface. Roughly speaking, the swirl vane 64A is configured such that, in the above-described swirl vane 64, the diameter of the swirl vane 64 is increased by increasing the length of the vanes 64b. The remaining configuration of the powder fuel burner 5A, including the wind box 52 omitted in FIG. 5, is the same as the above-described configuration of the powder fuel burner 5. The burner 5A thus configured provides the same advantageous effects as those provided by the above-described burner 5.

[0034] In the case of the above-described burner 5 shown in FIG. 2, the location where the A/F of the air-fuel mixture injected into the combustion chamber 1 is locally reduced can be adjusted by adjusting the thickness of each of the center flow blocker 62 and the peripheral flow blocker 63.

[0035] In the present embodiment, in a case where the ignition burner 61 is not mounted inside the air-fuel mixture conveying tube 51, but mounted separately, a center axis rod instead of the ignition burner 61 shown in FIG. 2 and FIG. 5 may be mounted on the center axis 5a, and the center flow blocker 62 or 62A and the swirl vane 64 or 64A may be mounted to the center axis rod.

[0036] The flame-retardant powder fuel in the present embodiment may be a petroleum residue fuel, a biomass fuel, or a mixed fuel of biomass and pulverized coal. Each of these fuels is less combustible than pulverized coal.

[0037] From the foregoing description, numerous modifications and other embodiments of the present disclosure are obvious to those skilled in the art. Accordingly, the foregoing description is to be construed as illustrative only, and is provided for the purpose of teaching those skilled in the art the best mode for carrying out the present disclosure. The structural and/or functional details may be substantially modified without departing from the scope of the present disclosure.

Summary

[0038] A powder fuel burner according to one aspect of the present disclosure is a powder fuel bumer mounted in a combustion chamber of a boiler, the powder fuel burner including: a cylindrical air-fuel mixture conveying tube, through which an air-fuel mixture is conveyed and which injects, from a distal end thereof, the air-fuel mixture into the combustion chamber, the air-fuel mixture being a mixture of a powder fuel and conveying air; a swirl vane mounted at the distal end of the air-fuel mixture conveying tube; and a rod-shaped center flow blocker mounted on a center axis of the air-fuel mixture conveying tube at a position upstream of the swirl vane in a conveying direction of the air-fuel mixture, the center flow blocker including a cylindrical surface that is concentric with the air-fuel mixture conveying tube and that extends in a direction of the center axis.

[0039] According to the above configuration, when the air-fuel mixture flowing inside the air-fuel mixture conveying tube flows in the region where the center flow blocker is mounted, the cross section of the flow passage is a narrow donut shape, and thereafter, the air-fuel mixture flows in a manner to spread over the entire internal space of the tube. Then, the air-fuel mixture is swirled by the swirl vane, and injected into the combustion chamber. Here, also after the air-fuel mixture traveling straight in the same direction as the direction of the center axis has passed the region where the center flow blocker is mounted, the particles of the powder fuel contained in the air-fuel mixture are to travel straight due to inertial force. Accordingly, the air-fuel mixture in the state of having a low powder fuel concentration near the center and near the tubular wall of the air-fuel mixture conveying tube and having a high powder fuel concentration in the other region of the air-fuel mixture conveying tube passes through the swirl vane to be injected into the combustion chamber. Therefore, even when the air-fuel mixture having a high A/F is fed to the burner, the A/F of the air-fuel mixture injected into the combustion chamber can be locally reduced. That is, even when a flame-retardant powder fuel, such as a petroleum residue fuel, having a higher A/F than a suitable A/F for its ignition and combustion is directly fed from the pulverizer, the A/F of the air-fuel mixture injected into the combustion chamber can be locally reduced to a suitable A/F for the ignition and combustion of the powder fuel. Consequently, the ignitibility can be improved, and stable combustion can be achieved.

[0040] The powder fuel burner may further include a cylindrical peripheral flow blocker mounted along an inner wall surface of the air-fuel mixture conveying tube, the peripheral flow blocker including a cylindrical inner peripheral surface that faces the cylindrical surface of the center flow blocker and that is spaced apart from the cylindrical surface of the center flow blocker by a predetermined distance. In this case, the location where the A/F of the air-fuel mixture injected into the combustion chamber is locally reduced can be adjusted by adjusting the thickness of each of the center flow blocker and the peripheral flow blocker.

[0041] The powder fuel burner may further include an internal cylinder that is concentric with the air-fuel mixture conveying tube and that is, at the distal end of the air-fuel mixture conveying tube, mounted inside the air-fuel mixture conveying tube. The swirl vane may be located inside the internal cylinder.

[0042] The powder fuel may be a petroleum residue fuel, a biomass fuel, or a mixed fuel of biomass and pulverized coal.

REFERENCE SIGNS LIST

[0043] 1 combustion chamber of a boiler [0044] 5, 5A powder fuel burner [0045] 51 air-fuel mixture conveying tube [0046] 62, 62A center flow blocker [0047] 62a cylindrical surface of the center flow blocker [0048] 63 peripheral flow blocker [0049] 63a inner peripheral surface of the peripheral flow blocker [0050] 64, 64A swirl vane [0051] 65 internal cylinder