Fuel transfer device, fluidized bed combustion device comprising the same, and fuel supply method

Abstract

To prevent backfire to the inside of a fuel transfer pipe.SOLUTION: A fuel transfer device 8 comprises a fuel chute 20 connected to a circulation fluidized bed boiler to transfer fuel to the circulation fluidized bed boiler, a backfire prevention unit attached to the fuel chute 20 to prevent backfire heading toward the fuel chute 20 from the circulation fluidized bed boiler, and seal gas supply pipes 31, 32 feeding seal gas into the fuel chute 20 to prevent the backflow, i.e., a gas flow heading toward the fuel chute 20 from the circulation fluidized bed boiler. The seal gas supply pipes 31, 32 functioning as backfire prevention units supply assist gas so as to gain a flow speed faster than a gas flow speed in the fuel chute 20 attained by the flow of the seal gas preventing the backfire.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a fuel delivery device for supplying fuel to a combustion furnace, a fluidized bed combustion device including the same, and a fuel supply method. [Background technology]

[0002] In combustion furnaces such as fluidized bed boilers, it is known to supply a seal gas to adjust the pressure state in a fuel chute (fuel transport pipe) so that the combustion gas in the combustion furnace does not flow back into the fuel chute (fuel transport pipe) (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-186395 A Summary of the Invention [Problem to be solved by the invention]

[0004] As in Patent Document 1, it is possible to prevent the backflow of gas by making the pressure in the fuel chute higher than the pressure in the combustion furnace. However, when using a fuel with a high combustion rate (fuel containing powder such as wood pellets), even if the backflow of gas is prevented, there is a risk that a flame will propagate from the combustion furnace side toward the fuel in the fuel chute in the opposite direction to the fuel flow. If the flame propagates into the fuel chute, a flame will be formed in the fuel chute, and if the fuel chute is heated, there is a risk that the fuel chute will be damaged, such as by thermal deformation.

[0005] The present disclosure has been made in consideration of the above circumstances, and aims to provide a fuel transport device that can prevent backfire into the inside of a fuel transport pipe, a fluidized bed combustion apparatus equipped with the same, and a fuel supply method. [Means for solving the problem]

[0006] A fuel transport device according to one embodiment of the present disclosure includes a main tube connected to a combustion furnace for transporting fuel to the combustion furnace, and a backfire prevention unit provided in the main tube for obtaining a fuel flow velocity for preventing backfire from the combustion furnace toward the main tube.

[0007] A fluidized bed combustor according to one aspect of the present disclosure includes the above-described fuel delivery device.

[0008] A fuel supply method according to one aspect of the present disclosure is a fuel supply method for supplying fuel to a combustion furnace using a main tube connected to the combustion furnace, in which the fuel is caused to flow at a flow rate sufficient to prevent flashback from the combustion furnace toward the main tube. Effect of the Invention

[0009] It is possible to prevent flashback into the fuel transport pipe. [Brief description of the drawings]

[0010] [Figure 1] 1 is a schematic configuration diagram showing a circulating fluidized bed boiler plant according to a first embodiment of the present disclosure. [Diagram 2] FIG. 2 is a schematic configuration diagram showing the fuel transport device and its surroundings in FIG. [Diagram 3] FIG. 11 is a schematic configuration diagram showing the periphery of a fuel transport device of a circulating fluidized bed boiler plant according to a second embodiment of the present disclosure. [Figure 4] FIG. 11 is a schematic configuration diagram showing the periphery of a fuel transport device of a circulating fluidized bed boiler plant according to a second embodiment of the present disclosure. [Diagram 5] FIG. 5 is a schematic diagram showing the periphery of the throttle unit in FIG. 4. [Figure 6] FIG. 6 is a cross-sectional view of the inclined plate of FIG. 5 as seen from the flow direction. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. [First embodiment] The first embodiment of the present disclosure will be described below.

[0012] <Circulating fluidized bed boiler plant> As shown in FIG. 1, a circulating fluidized bed boiler plant (fluidized bed combustion apparatus) 1 according to this embodiment includes a fuel bunker 2, a circulating fluidized bed boiler (combustion furnace) 3, a cyclone 4, a duct 50, a convective heat transfer section 5, a dust collector 18, and an exhaust gas cooler 60.

[0013] The fuel bunker 2 stores the fuel to be used in the circulating fluidized bed boiler 3. The fuel is, for example, a solid fuel such as biomass fuel, and more specifically, wood pellets are used. Note that waste materials (such as waste tires, dewatered sludge, and urban waste) can also be used as other fuels. When wood pellets are used as fuel, wood powder generated during transportation and storage of the wood pellets may be contained in the fuel.

[0014] The fuel bunker 2 is connected to the circulating fluidized bed boiler 3 via a fuel conveying device 8. The fuel conveying device 8 enables fuel to be supplied from the fuel bunker 2 to the circulating fluidized bed boiler 3. The fuel conveying device 8 is provided with a fuel feeder 19 that promotes the discharge of fuel from the fuel bunker 2 and makes the amount of fuel passing through (the amount of fuel supplied) uniform.

[0015] The circulating fluidized bed boiler 3 is a device that is operated under a pressurized state (pressure higher than atmospheric pressure) inside, and uses a portion of the supplied air (oxidizing gas) as a fluidizing gas to fluidize the fluidizing material and the fuel supplied from the fuel delivery device 8, mix them, and combust them to generate high-temperature combustion gas. Specifically, in the circulating fluidized bed boiler 3, the fluidizing material in the circulating fluidized bed boiler 3 is fluidized by air (fluidizing gas) supplied from a fluidizing nozzle 10 provided at the bottom of the furnace, forming a fluidized bed. The formation of the fluidized bed promotes mixing of the fuel, fluidizing material, and air in the furnace, improving combustion efficiency. For example, particles mainly composed of SiO2, such as silica sand, are used as the fluidizing material.

[0016] The air supplied to the circulating fluidized bed boiler 3 is pressurized by a forced draft fan 16, preheated by heat exchange with the combustion gas in an air preheater 17, and then a portion of the air is supplied as fluidizing gas from a fluidizing nozzle 10, while the remainder is supplied from an air nozzle 11 provided above the fluidized bed formed in the furnace.

[0017] The cyclone 4 is a device for separating the combustion gas from the fluidized material. The cyclone 4 is provided on the outlet side of the circulating fluidized bed boiler 3. The combustion gas separated by the cyclone 4 is supplied to the convection heat transfer section 5 via the duct 50, and the fluidized material is collected in the seal pot 6.

[0018] The fluid material collected in the seal pot 6 is supplied to the external heat exchanger 7 via a line 53 and an ash removal valve 15. The fluid material other than that supplied to the external heat exchanger 7 is returned to the circulating fluidized bed boiler 3 via a line 55.

[0019] The external heat exchanger 7 is a fluidized bed external heat exchanger (FBHE). In the external heat exchanger 7, the fluid material is fluidized by an oxidizing gas such as air supplied from a blower 14. In the external heat exchanger 7, heat is exchanged between the fluid material in a high temperature state and the boiler feed water and steam flowing inside the evaporator 26 and the primary superheater 57, and superheated steam is generated. The external heat exchanger 7 is connected to the furnace bottom of the circulating fluidized bed boiler 3 via a line 24.

[0020] The duct 50 is connected to the gas side outlet of the cyclone 4. A combustion gas passage 51 is formed inside the duct 50. The combustion gas discharged from the circulating fluidized bed boiler 3 and from which the fluidized material has been separated and removed by the cyclone 4 flows through the combustion gas passage 51.

[0021] The convection heat transfer section 5 generates superheated steam by exchanging heat between the combustion gas and the boiler feed water or steam. The convection heat transfer section 5 is provided in the combustion gas flow path 51. The convection heat transfer section 5 has, for example, a coal economizer 12 and a secondary superheater 13. The coal economizer 12 is a device that preheats the boiler feed water using the relatively low-temperature combustion gas in the convection heat transfer section 5 (for example, the combustion gas after heat exchange in the secondary superheater 13, etc.). The secondary superheater 13 is a device that further superheats the superheated steam generated in the external heat exchanger 7 by using the heat of the combustion gas. The superheated steam is supplied to, for example, a steam turbine (not shown) connected to a generator, and is used for power generation, etc.

[0022] The combustion gas that has completed heat exchange in the convection heat transfer section 5 passes through an air preheater 17 and is then supplied to a dust collector 18. The dust collector 18 is a device that collects solid matter such as soot and dust contained in the combustion gas that has completed heat exchange in the convection heat transfer section 5 and the air preheater 17. The dust collector 18 is, for example, a bag filter.

[0023] The exhaust gas cooler 60 is a device that preheats boiler feed water using the combustion gas from which solid matter such as soot and dust has been collected by the dust collector 18. The boiler feed water preheated by the exhaust gas cooler 60 is supplied to the economizer 12.

[0024] The combustion gas that has completed heat exchange in the exhaust gas cooler 60 is discharged into the atmosphere through a chimney (not shown) via a duct 62.

[0025] <Fuel transport device 8> Fig. 2 shows the fuel transport device 8 shown in Fig. 1 and its surroundings. Fuel transport device 8 is equipped with a tubular fuel chute (main pipe) 20 through which fuel passes. The fuel is transported inside fuel chute 20 by gravity and air currents. Fuel chute 20 is equipped with a vertical section 20a extending vertically and an inclined section 20b connected to the lower end of vertical section 20a and extending obliquely downward.

[0026] The vertical section 20a is provided with a first rotary valve 22, a second rotary valve 23, an automatic gate valve 25, an expansion 27, and a manual gate valve 29 in this order from the top. The order in which each component is provided is not limited to this. For example, the manual gate valve 29 may be provided above the automatic gate valve 25, or the expansion 27 may be provided above the automatic gate valve 25. The fuel flow rate is controlled by the fuel feeder 19 (see FIG. 1) in response to a command from a control unit (not shown). The fuel flows in the direction of the arrow A1 (downward). The automatic gate valve 25 is opened and closed in response to a command from a control unit (not shown). The automatic gate valve 25 may be manually operated. The expansion 27 expands and contracts to absorb the thermal expansion difference between the circulating fluidized bed boiler 3 and the fuel chute 20. The manual gate valve 29 is operated by an operator and is fully closed during maintenance, etc., and is fully opened during operation. The manual gate valve 29 may be automatically operated. Also, a pair of flanges or the like may be provided instead of the automatic gate valve or the manual gate valve. In this embodiment, two rotary valves, the first rotary valve 22 and the second rotary valve 23, are provided, but the present invention is not limited to this as long as they have a function of sealing the pressure between the circulating fluidized bed boiler 3 in a pressurized state and the fuel feeder 19 in an atmospheric pressure state. For example, the number of rotary valves may be one or three or more, and a flap damper or the like may be provided instead of the rotary valves.

[0027] Although not shown in Fig. 2, the downstream end of the inclined portion 20b of the fuel chute 20 is connected to a fuel inlet provided in the circulating fluidized bed boiler 3 (see Fig. 1). The inclined portion 20b is installed at a predetermined angle with respect to the horizontal plane. The predetermined angle is, for example, equal to or greater than the angle of repose of the fuel type flowing inside the fuel chute 20.

[0028] A first seal gas supply pipe (seal gas supply unit) 31 is connected between the automatic gate valve 25 and the expansion 27. A seal gas (e.g., air, etc.) is supplied from the first seal gas supply pipe 31 into the fuel chute 20. The flow rate of the seal gas supplied to the first seal gas supply pipe 31 can be adjusted by a valve (not shown). The seal gas is supplied to the first seal gas supply pipe 31 from a seal gas supply source (e.g., a blower, etc.) (not shown).

[0029] A second seal gas supply pipe (seal gas supply unit) 32 is connected to the vertical portion 20a below the manual gate valve 29. A seal gas is supplied from the second seal gas supply pipe 32 into the fuel chute 20. The flow rate of the seal gas supplied to the second seal gas supply pipe 32 can be adjusted by a valve (not shown). The second seal gas supply pipe 32 is supplied with a seal gas from a seal gas supply source (e.g., a blower) (not shown).

[0030] In this embodiment, the seal gas supply pipes 31, 32 are described as being provided below the automatic gate valve 25 and below the manual gate valve 29, respectively, but they may be provided at least between the gate valve provided at the most downstream side in the fuel flow direction in the fuel chute 20 and the circulating fluidized bed boiler 3. This makes it possible to seal the gap between the gate valve and the circulating fluidized bed boiler even when the gate valve is in a closed state.

[0031] The control unit is composed of, for example, a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), and a computer-readable storage medium. A series of processes for realizing various functions is stored in a storage medium or the like in the form of a program, for example, and the CPU reads this program into the RAM or the like and executes information processing and arithmetic processing to realize various functions. The program may be installed in a ROM or other storage medium in advance, may be provided in a state stored in a computer-readable storage medium, or may be distributed via a wired or wireless communication means. The computer-readable storage medium may be a magnetic disk, a magneto-optical disk, a CD-ROM, a DVD-ROM, a semiconductor memory, or the like.

[0032] <Seal gas flow rate setting> Next, setting of the flow rate of the seal gas supplied from the first seal gas supply pipe 31 and the second seal gas supply pipe 32 into the fuel chute 20 will be described.

[0033] The seal gas supplied from the first seal gas supply pipe 31 flows in an upstream direction F11 and a downstream direction F12. The seal gas supplied from the second seal gas supply pipe 32 flows in an upstream direction F21 and a downstream direction F22. In this embodiment, the flow direction of the fuel is referred to as the downstream direction, and the opposite direction is referred to as the upstream direction (or the reverse direction). The flows of the seal gas in the upstream directions F11 and F21 are generated by, for example, leakage flows from gaps between the rotary blades of the rotary valves 22 and 23 and the casing.

[0034] The total flow rate of the seal gas supplied from the first seal gas supply pipe 31 and the second seal gas supply pipe 32 is set so that the pressure in the fuel chute 20 is equal to or higher than a predetermined value so as to prevent the combustion gas in the circulating fluidized bed boiler 3 (see FIG. 1) from flowing back. Specifically, the pressure in the fuel chute 20 is set to be equal to or higher than the pressure in the circulating fluidized bed boiler 3 (more specifically, the pressure in the vicinity of the fuel inlet).

[0035] Furthermore, the total flow rate of the seal gas is set so that the flow rate in the fuel chute 20 downstream of the connection part of the second seal gas supply pipe 32 is equal to or higher than a predetermined value. Specifically, the total flow rate of the seal gas is set so that the flow rate is such that backfire (flame propagation) from the circulating fluidized bed boiler 3 toward the fuel chute 20 is prevented. For example, the total flow rate of the seal gas is set so that the total flow rate of the seal gas is faster than the combustion speed in the environment of the fuel chute 20 of the fuel containing powder made of crumbled wood pellets used as fuel, that is, so that the flame propagation speed of the fuel containing the powder is equal to or lower than 0 (the backfire direction is positive). In this way, the first seal gas supply pipe 31 and the second seal gas supply pipe 32 constitute a backfire prevention unit.

[0036] In relation to the seal gas flow velocity, the flame propagation speed is expressed as follows: (Flame propagation speed) = (Combustion speed) - (Seal gas flow rate)

[0037] The combustion rate can be predicted from the fuel properties (type, concentration, particle size distribution), and the temperature, pressure, and oxygen concentration of the seal gas. The flow velocity of the seal gas to prevent flashback can be calculated from the flame propagation speed relational expression and the predicted burning speed. For example, if the fuel used contains powder generated from woody biomass, the flow velocity is about 4 m / s. As mentioned above, the burning speed varies depending on the fuel properties (type, concentration, particle size distribution), the temperature, pressure, and oxygen concentration of the seal gas, so the flow velocity of the seal gas to prevent flashback is not limited to this.

[0038] In addition, since it is sufficient that the total flow rate of the seal gas is a flow rate that prevents flashback, the assist gas is supplied at a flow rate equal to or greater than the difference between the flow rate that prevents flashback and the flow rate that prevents backflow. The assist gas may be the same gas as the seal gas, and may be supplied into the fuel chute 20 from the first seal gas supply pipe 31 or the second seal gas supply pipe 32, or may be supplied from a gas supply pipe other than the first seal gas supply pipe 31 and the second seal gas supply pipe 32.

[0039] The effects of the present embodiment described above are as follows. In order to prevent flashback from occurring in the fuel chute 20 that transports fuel to the circulating fluidized bed boiler 3, an assist gas is supplied to increase the flow rate of the seal gas. This makes it possible to prevent flashback from occurring in the fuel chute 20 and damage to the fuel chute 20. Specifically, the seal gas is pressurized by supplying it into the fuel chute 20 from the first seal gas supply pipe 31 and the second seal gas supply pipe 32, thereby preventing backflow of the combustion gas from the circulating fluidized bed boiler 3. In addition, in order to prevent flashback toward the fuel chute 20, the assist gas is supplied so that the gas flow velocity formed in the fuel chute 20 is faster than the flame propagation velocity. This makes it possible to prevent the flame propagation in the fuel chute 20 by making the flame propagation velocity in the fuel chute 20 equal to or less than 0 (the flashback direction is positive).

[0040] [Second embodiment] Next, a second embodiment of the present disclosure will be described. This embodiment differs from the first embodiment in that nitrogen gas is used as the assist gas. Therefore, in the following description, the differences will be described, and the description of the matters common to the first embodiment will be omitted.

[0041] As shown in Fig. 3, a nitrogen gas supply pipe (backfire prevention unit) 34 is connected to the fuel chute 20 downstream of the second seal gas supply pipe 32. Note that Fig. 3 shows the downstream side of the manual gate valve 29 in Fig. 2. Therefore, the first seal gas supply pipe 31 and the like are omitted. The nitrogen gas supplied from the nitrogen gas supply pipe 34 flows in the downstream direction F22.

[0042] The effects of the present embodiment described above are as follows. Supplying nitrogen gas from the nitrogen gas supply pipe 34 reduces the oxygen concentration in the fuel chute 20, thereby slowing down the combustion speed of the fuel that may propagate through the fuel chute 20. This makes it possible to reduce the total flow rate of the seal gas required to make the flame propagation speed equal to or less than 0, and therefore makes it possible to reduce the flow rate of the assist gas supplied into the fuel chute 20 to a flow rate that prevents flashback, compared to the case where air is used as the assist gas. Furthermore, by using nitrogen gas, which has a lower water vapor partial pressure than air, it is possible to prevent moisture from being supplied to the system and suppress adhesion and clogging of the fuel chute 20.

[0043] In this embodiment, nitrogen is supplied, but instead, gas having an oxygen concentration lower than that in air, such as exhaust gas from the circulating fluidized bed boiler 3 or steam, may be used. If exhaust gas is used, costs can be reduced compared to using nitrogen gas. If steam is used, equipment costs can be reduced by using steam generated in the plant, and the fuel combustion speed can be reduced compared to using nitrogen gas.

[0044] [Third embodiment] Next, a third embodiment of the present disclosure will be described. This embodiment differs from the first embodiment in that a configuration is provided for narrowing the flow path in the fuel chute 20. Therefore, in the following description, the differences will be described, and descriptions of matters common to the first embodiment will be omitted.

[0045] 4, a throttle portion (flash prevention portion) 38 is provided at the inclined portion 20b of the fuel chute 20. At the throttle portion 38, the flow path cross-sectional area of ​​the fuel flowing inside the fuel chute 20 is reduced.

[0046] As shown in Fig. 5, the throttle section 38 includes an inclined plate 38a, a partition plate 38b, and a downstream plate 38c. The inclined plate 38a is inclined so that the flow passage cross-sectional area gradually decreases toward the downstream side in the longitudinal direction (axial direction) of the inclined section 20b. For example, as shown in Fig. 6, the inclined plate 38a is formed in a substantially semicircular shape so as to close the upper cross section (flow passage) of the fuel chute 20.

[0047] The partition plate 38b has an upstream end connected to the downstream end of the inclined plate 38a and extends parallel to the longitudinal direction (axial direction) of the inclined portion 20b. The partition plate 38b divides the inside of the fuel chute 20 into a lower space (flow path indicated by arrow A5) through which the fuel flows and an upper space through which the fuel does not flow. Note that a steam nozzle (gas injection part) 40 may be provided in the upper space.

[0048] The downstream plate 38c is connected to the downstream end of the partition plate 38b and extends perpendicular to the longitudinal direction of the inclined portion 20b. The downstream plate 38c separates the upper space formed by the inclined plate 38a and the partition plate 38b from the space in the inclined portion 20b through which the fuel flows. Therefore, the upper space separated by the inclined plate 38a, the partition plate 38b, and the downstream plate 38c is a space in the inclined portion 20b through which the fuel does not flow.

[0049] A plurality of steam nozzles 40 are provided, and each downstream end of the steam nozzles 40 is fixed to the downstream plate 38c so as to protrude downstream from the downstream plate 38c. Each upstream end is connected to a steam header 41. Utility steam is guided to the steam header 41 from the surrounding area. Steam is sprayed from the steam nozzles 40 toward the downstream side of the fuel chute 20 at a predetermined timing in response to a command from a control unit (not shown).

[0050] A temperature sensor 43 is provided downstream of the throttle portion 38 of the fuel chute 20. A detection value of the temperature sensor 43 is transmitted to a control unit (not shown).

[0051] The effects of the present embodiment described above are as follows. The flow passage cross-sectional area of ​​the fuel chute 20 is reduced by the throttle section 38, so that the flow velocity of the seal gas containing fuel increases when passing through the throttle section 38. This makes it possible to reduce the total flow rate of the seal gas required to make the flame propagation speed equal to or less than 0, and therefore makes it possible to reduce the flow rate of the assist gas supplied into the fuel chute 20. Even if a flashback occurs inside the fuel chute 20, the throttle section 38 increases the flow rate of the seal gas in the lower space (flow path indicated by arrow A5) through which the fuel flows to above the combustion speed, and the propagation of the flame to the upstream side of the gas flow of the throttle section 38 is suppressed, so that the flashback can be stopped by the throttle section 38. The amount of narrowing of the flow path cross-sectional area by the throttle section 38 can be set arbitrarily. For example, as described in the first embodiment, the required seal gas flow rate can be predicted from the combustion speed of the fuel, and the amount of narrowing can be set so that assist gas is not required based on the flow path cross-sectional area at which the required seal gas flow rate is obtained in the throttle section 38.

[0052] When a flashback occurs in the fuel chute 20, the control unit can detect the flashback before it reaches the throttle section 38 by detecting a temperature rise using the temperature sensor 43. When the control unit detects a flashback based on the detection value of the temperature sensor 43, it injects steam from the steam nozzle 40 toward the downstream side of the throttle section 38. This makes it possible to extinguish the flashback before it reaches the throttle section 38.

[0053] If the throttle portion is provided on the vertical portion 20a of the fuel chute 20, as shown by the arrow A2 in FIG. 5, the fuel falling vertically downward may directly collide with the inclined plate 38a forming the throttle portion 38, causing wear. Therefore, by disposing the throttle portion 38 on the inclined portion 20b, the direct collision of the fuel with the inclined plate 38a of the throttle portion 38 can be suppressed, and the life of the throttle portion 38 can be extended. Specifically, as shown in FIG. 5, the inclined plate 38a is provided on the upper side of the inclined portion 20b, so that the direct collision with the fuel flowing on the lower side of the inclined portion 20b (see the arrow A3) can be suppressed. Even if fuel flows as shown by the arrow A4, the amount is not large, and since it is inclined along the fuel flow direction (the direction of the arrow A4), damage to the inclined plate 38a can be minimized.

[0054] 4, an additional steam supply pipe 45 may be connected below the second seal gas supply pipe 32 and to the vertical section 20a of the fuel chute 20. By supplying steam from the additional steam supply pipe 45 into the fuel chute 20, it may be used as in the second embodiment, or may be used to extinguish a flashback in case of an accident.

[0055] Moreover, the steam nozzle 40 may inject other inert gas (such as nitrogen gas or exhaust gas) instead of steam.

[0056] In addition, the portion provided with the throttling portion 38 may be attached so as to be partially removable from the fuel chute 20 via a flange 47, and partial removal from the fuel chute 20 makes it easy to replace or maintain the throttling portion 38.

[0057] The fuel transport device, the fluidized bed combustor including the same, and the fuel supply method described in each of the above-described embodiments can be understood, for example, as follows.

[0058] The fuel transport device according to the first aspect of the present disclosure includes a main pipe (20) connected to a combustion furnace for transporting fuel to the combustion furnace, and a flashback prevention unit provided in the main pipe for obtaining a flow velocity for preventing flashback from the combustion furnace toward the main pipe.

[0059] The main tube that transports fuel to the combustion furnace is provided with a flashback prevention unit that prevents flashback from the combustion furnace toward the main tube, preventing flashback from occurring inside the main tube and damaging the main tube.

[0060] The fuel conveying device of the second aspect of the present disclosure, in the first aspect, includes a sealing gas supply unit (31, 32) that supplies a sealing gas to the inside of the main tube (20) to prevent backflow, which is a gas flow from the combustion furnace toward the main tube, and the backfire prevention unit supplies an assist gas so as to obtain a flow velocity higher than the gas flow velocity formed inside the main tube by the flow rate of the sealing gas that prevents the backflow.

[0061] The seal gas is pressurized by supplying it from the seal gas supply unit into the main tube to prevent backflow from the combustion furnace. In addition, to prevent flashback toward the main tube, assist gas is supplied so that the gas flow velocity formed in the main tube is faster than the flame propagation speed. This makes it possible to prevent the flame propagation in the main tube by making the flame propagation speed in the main tube 0 or less (flashback direction is positive). The assist gas may be supplied from the seal gas supply unit together with the seal gas, or may be supplied from a position separate from the seal gas supply unit.

[0062] A fuel delivery device according to a third aspect of the present disclosure is the fuel delivery device of the second aspect, wherein the assist gas is a gas having an oxygen concentration lower than that of air.

[0063] Although air can be used as the assist gas, in this embodiment, a gas with an oxygen concentration lower than that of air, such as nitrogen, exhaust gas from a boiler, or steam, is used as the assist gas. This reduces the oxygen concentration, thereby slowing down the combustion speed of the fuel that may propagate inside the main tube, and thus slowing down the flame propagation speed. In addition, since the combustion speed can be reduced, the flow rate of the assist gas can be reduced compared to when air is used.

[0064] A fuel conveying device according to a fourth aspect of the present disclosure is any one of the first to third aspects, wherein the flashback prevention section includes a throttling section (38) that reduces the cross-sectional area of ​​the flow path inside the main pipe (20).

[0065] By providing a constriction that reduces the cross-sectional area of ​​the flow passage inside the main tube, the flow speed in the constriction can be increased, making the flame propagation speed 0 or less (forward flashback direction). As a result, even if a flashback occurs inside the main tube, the flashback can be stopped at the constriction.

[0066] The fuel transport device according to a fifth aspect of the present disclosure is the fuel transport device of the fourth aspect, further including a gas injection section (40) that injects gas downstream of the throttle section (38) in the fuel flow direction.

[0067] By operating the gas injection unit to inject gas toward the downstream side of the throttle, it is possible to extinguish the flashback before it reaches the throttle. As the gas injected from the gas injection unit, for example, a gas with an oxygen concentration lower than that in air is used, and steam is preferable.

[0068] The fuel delivery device of a sixth aspect of the present disclosure is the fuel delivery device of the fifth aspect, further comprising a temperature sensor (43) provided downstream of the throttling portion (38), and a control portion that operates the gas injection portion based on a detection value of the temperature sensor.

[0069] A temperature sensor installed downstream of the constriction allows the control unit to detect flashbacks in the main tube before they reach the constriction. When the control unit detects a flashback based on the temperature sensor's detection value, it operates the gas injection unit to inject gas downstream of the constriction. This allows the flashback to be extinguished before it reaches the constriction.

[0070] The fuel conveying device according to a seventh aspect of the present disclosure is the fuel conveying device of the fourth or fifth aspect, wherein the main pipe (20) has a vertical portion (20a) extending vertically and an inclined portion (20b) connected to the lower end of the vertical portion and extending diagonally downward, and the throttle portion (38) is provided on the inclined portion.

[0071] If the throttle portion is provided on the vertical portion of the main pipe, there is a risk that the fuel will directly collide with the wall portion forming the throttle portion, causing wear. Therefore, by locating the throttle portion on the inclined portion, it is possible to prevent the fuel from directly colliding with the wall portion of the throttle portion, thereby extending the life of the throttle portion.

[0072] A fuel conveying device according to an eighth aspect of the present disclosure is in any one of the first to sixth aspects, wherein the fuel is a solid fuel containing powder.

[0073] The powder contained in the solid fuel is more flammable and burns faster than the solid part, making it more likely to flash back. Therefore, it is effective to prevent flashback inside the main tube using a flashback prevention part.

[0074] A fluidized bed combustion apparatus according to a first aspect of the present disclosure includes the fuel delivery device of any of the above aspects, and the combustion furnace is a fluidized bed combustion furnace.

[0075] A fuel supply method according to a first aspect of the present disclosure is a fuel supply method for supplying fuel to a combustion furnace using a main pipe (20) connected to the combustion furnace, and ensuring a flow velocity sufficient to prevent flashback from the combustion furnace toward the main pipe. [Explanation of symbols]

[0076] 1. Circulating fluidized bed boiler plant (fluidized bed combustion equipment) 2 Fuel bunker 3 Circulating fluidized bed boiler (combustion furnace) 4. Cyclone 5. Convection heat transfer section 6 Seal Pot 7 External heat exchanger 8. Fuel Delivery System 10 Fluidizing nozzle 11 Air nozzle 12 Economizer 13 Secondary superheater 14 Blois 15 Ash removal valve 16 Forced draft fan 17 Air preheater 18 Dust collector 19 Fuel Feeder 20 Fuel chute (main pipe) 20a Vertical section 20b Slope 22 No. 1 rotary valve 23 No. 2 rotary valve 25 Automatic gate valve 27 Expansion 29 Manual Gate Valve 31 First seal gas supply pipe (seal gas supply section, flashback prevention section) 32 Second seal gas supply pipe (seal gas supply section, flashback prevention section) 34 Nitrogen gas supply pipe (flash prevention section) 38 Throttle section (backfire prevention section) 38a inclined plate 38b Partition 38c downstream plate 40 Steam nozzle (gas injection part) 41 Steam Header 43 Temperature Sensor 45 Additional steam supply pipe 47 Flange

Claims

1. a main pipe connected to a combustion furnace for transporting fuel to the combustion furnace; a flashback prevention unit provided in the main body tube and configured to obtain a fuel flow velocity for preventing flashback from the combustion furnace toward the main body tube; A fuel delivery device comprising:

2. a seal gas supply unit that supplies a seal gas to the inside of the main tube to prevent a backflow, which is a gas flow from the combustion furnace toward the main tube; 2. The fuel transport device according to claim 1, wherein the flashback prevention unit supplies the assist gas so as to obtain a flow velocity greater than a gas flow velocity formed inside the main tube by a flow rate of the seal gas that prevents the backflow.

3. 3. The fuel delivery device according to claim 2, wherein the assist gas has an oxygen concentration lower than that of air.

4. 2. The fuel transport device according to claim 1, wherein the flashback prevention portion includes a throttle portion that reduces a cross-sectional area of ​​a flow passage inside the main tube.

5. 5. The fuel transport device according to claim 4, further comprising a gas injection portion that injects gas toward a downstream side of the throttle portion in the fuel flow direction.

6. a temperature sensor provided downstream of the throttle portion; a control unit that operates the gas injection unit based on a detection value of the temperature sensor; 6. The fuel delivery system of claim 5, comprising:

7. The main body pipe includes a vertical portion extending vertically and an inclined portion connected to a lower end of the vertical portion and extending obliquely downward, 7. The fuel transport device according to claim 4, wherein the throttle portion is provided on the inclined portion.

8. 2. The fuel delivery device according to claim 1, wherein the fuel is a solid fuel containing powder.

9. A fuel delivery device according to claim 1, A fluidized bed combustion apparatus, wherein the combustion furnace is a fluidized bed combustion furnace.

10. A fuel supply method for supplying fuel to a combustion furnace using a main pipe connected to the combustion furnace, comprising the steps of: A fuel supply method in which fuel is flowed at a flow rate to prevent flashback from the combustion furnace toward the main tube.

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