JP7386019B2 - Fine fuel fired boiler - Google Patents

Description

The present invention relates to a pulverized fuel-fired boiler that uses pulverized material pulverized by a pulverizer as fuel.

BACKGROUND ART Conventionally, pulverized fuel-fired boilers are known that use pulverized fuel obtained by crushing and drying coal, biomass, petroleum residue, etc. containing low-grade ash with relatively high moisture content such as lignite or sub-bituminous coal. Patent Document 1 discloses this type of boiler.

The boiler disclosed in Patent Document 1 uses a combustion burner to combust pulverized fuel containing pulverized coal obtained by pulverizing coal and pulverized biomass obtained by pulverizing biomass, and recovers the heat generated by this combustion. This boiler includes a furnace extending in the vertical direction, a flue connected to the upper part of the furnace, and a heat exchanger such as a superheater, reheater, and economizer provided in the flue. A plurality of combustion burners are arranged along the circumferential direction on the furnace wall, and are arranged in multiple stages in the vertical direction. These combustion burners include a combustion burner that blows a mixture of pulverized coal and heated air into the furnace, and a combustion burner that blows a mixture of pulverized biomass and heated air into the furnace. Additional air nozzles are provided above the combustion burners to blow additional air into the furnace. The pulverized fuel ignited by the burner combustion air in the furnace is completely combusted by the additional air. Heat is exchanged between the exhaust gas produced by combustion and the water in the heat exchanger, producing steam.

The boiler shown in the first embodiment of Patent Document 1 is provided with a pulverizing dryer for pulverizing and drying biomass. The biomass supplied to the pulverizer/dryer is dried by heated air and pulverized by a mill to become pulverized biomass, which is then airflow-transported to the cyclone along with the heated air. In the cyclone, the pulverized biomass and heated air are separated into pulverized biomass and additional air in the cyclone. The pulverized biomass coming out of the lower part of the cyclone is sent as burner combustion air to the combustion burner of the furnace through the biomass supply line. Additional air exiting the top of the cyclone is routed through an additional air supply line to an additional air nozzle.

Japanese Patent Application Publication No. 2016-95113

The air/fuel ratio between burner combustion air and pulverized fuel supplied to the combustion burner of the furnace is used to control the combustion performance of the furnace. In Patent Document 1, the air-fuel ratio between burner combustion air (carrying air) supplied to a combustion burner of a furnace and pulverized fuel is lowered to an appropriate value by performing solid-gas separation using a cyclone.

In the cyclone of Patent Document 1, solid-gas separation is performed using inflowing air, so if the flow rate of inflowing air decreases during low-load operation, the solid-gas separation ability may decrease. Conversely, if the flow rate of air flowing into the cyclone is increased in order to maintain solid-gas separation performance during low-load operation, the air-fuel ratio of the portion of the furnace into which the exhaust gas from the cyclone flows will increase.

The present invention has been made in view of the above circumstances, and its purpose is to improve the flow rate of the conveying air in a pulverized fuel-fired boiler in which the conveying air and pulverized fuel discharged from a crusher are supplied to a combustion burner via a cyclone. The objective is to maintain the solid-gas separation ability of the cyclone even if the flow rate decreases.

A pulverized fuel-fired boiler according to one aspect of the present invention includes:
a furnace having at least one combustion burner provided in the furnace wall;
A pulverizer that crushes fuel into pulverized fuel and discharges the pulverized fuel on conveying air;
a multi-cyclone that separates the conveying air with the pulverized fuel discharged from the pulverizer into solids and gas;
a flow meter that detects the flow rate of the carrier air accompanied by the pulverized fuel flowing into the multi-cyclone;
a first line that sends the carrier air separated by the multi-cyclone to the furnace;
A second line is connected to the multi-cyclone through a pulverized fuel supply pipe and a valve, and sends the pulverized fuel separated by the multi-cyclone to the combustion burner.
The multi-cyclone includes a plurality of cyclones each having an outer cylinder, an inner cylinder inserted into the outer cylinder, and a guide vane disposed between the outer cylinder and the inner cylinder, and the plurality of cyclones . switching between allowing and blocking inflow of the conveying air for each of the cyclones and a casing having an internal space with an open lower opening of the outer cylinder and including a powder outlet connected to the pulverized fuel supply pipe; A switch for switching between operation and stop of the cyclone, and a switch such that the number of cyclones in operation increases as the flow rate detected by the flow meter increases, and the number of cyclones in operation decreases as the flow rate decreases. , and a controller that controls the switching device.

According to the pulverized fuel-fired boiler, when the flow rate of carrier air supplied to the multi-cyclone increases, the number of cyclones in operation increases, and when the flow rate of carrier air supplied to the multi-cyclone decreases, the number of cyclones in operation decreases. The operating cyclone is supplied with carrier air at a flow rate necessary for solid-gas separation, and the solid-gas separation capability of the operating cyclone can be maintained. In addition, when the flow rate of carrier air supplied to the multi-cyclone decreases, carrier air is not forcibly added, so the air discharged from the multi-cyclone and supplied to the furnace does not increase, and the air in the furnace is It is possible to suppress an increase in the air-fuel ratio in the blown portion.

According to the present invention, in a pulverized fuel-fired boiler in which conveying air and pulverized fuel discharged from a crusher are supplied to a combustion burner via a cyclone, the solid-gas separation capacity of the cyclone can be maintained even if the flow rate of the conveying air is reduced. It becomes possible to maintain.

FIG. 1 is a diagram showing the overall configuration of a pulverized fuel-fired boiler according to an embodiment of the present invention. FIG. 2 is a diagram showing the configuration of a control system for a pulverized fuel-fired boiler. FIG. 3 is a schematic diagram of the multicyclone shown in FIG. 1. FIG. 4 is a schematic configuration diagram of a multi-cyclone according to modification 1.

FIG. 1 is a diagram showing the overall configuration of a pulverized fuel-fired boiler 1 according to a first embodiment of the present invention, and FIG. 2 is a diagram showing the configuration of a control system of the boiler 1. As shown in FIGS. 1 and 2, the pulverized fuel-fired boiler 1 according to the present embodiment includes a boiler body 10, a fuel supply system 30 that supplies fuel to the boiler body 10, and a system that processes exhaust gas from the boiler body 10. It includes an exhaust gas treatment system 60 and a controller 9.

[Configuration of boiler main body 10]
The boiler body 10 burns fuel including pulverized fuel using a combustion burner 21 and recovers the heat generated by this combustion. Pulverized fuel is obtained by drying and pulverizing wet fuel. Wet fuel is a fuel containing water, and includes, for example, biomass, low-grade coal such as sub-bituminous coal and lignite, and solid residue generated during petroleum refining such as oil coke. Furthermore, biomass is defined as renewable organic resources derived from living organisms, excluding fossil resources. Biomass includes, for example, thinned wood, waste wood, driftwood, grass, waste, sludge, tires, and recycled fuels (pellets and chips) made from these materials.

The boiler body 10 includes a multi-stage combustion type furnace 11, a combustion device 12, a flue 41 connected to the furnace 11, and a heat exchanger 15 provided in the flue 41.

The furnace 11 has a body extending in the vertical direction, and has a first combustion area A formed in the lower part of the furnace, and a second combustion area B formed above the first combustion area A. The combustion device 12 is provided on the furnace wall of the furnace 11, and includes at least one combustion burner 21 that blows a mixture of burner-combusted primary air and pulverized fuel into a first-stage combustion area A, and a second-stage combustion burner 21 that blows a mixture of burner-combusted primary air and pulverized fuel into a first-stage combustion area B. at least one two-stage combustion air nozzle 26 for blowing combustion air. In this embodiment, a plurality of combustion burners 21 arranged in the circumferential direction are arranged in one stage, and a set of combustion burners 21 in multiple stages is provided along the vertical direction. Moreover, a plurality of two-stage combustion air nozzles 26 arranged in the circumferential direction are provided above the multiple-stage combustion burner 21 .

A flue 41 is connected to the upper part of the furnace 11, and the heat exchanger 15 recovers heat from the exhaust gas passing through the flue 41. A heat transfer tube 15a through which water or steam flows is provided in the flue 41. The heat exchanger 15 includes a superheater, a reheater, an economizer, and the like.

[Configuration of fuel supply system 30]
The fuel supply system 30 includes a crusher 31 and a multi-cyclone 33 that separates exhaust gas from the crusher 31 into solid and gas. In this embodiment, since wet fuel is used as the fuel, a pulverizer/dryer that pulverizes and dries the wet fuel is employed as the pulverizer 31. However, the pulverizer 31 is not limited to a pulverizer/dryer, but may be any pulverizer in which the pulverized fuel, which is the pulverized powder, is conveyed in an air flow using conveying air. Furthermore, the fuel is not limited to wet fuel, but may be any fuel that is ultimately supplied to the combustion burner 21 in the form of pulverized fuel.

Wet fuel is supplied to the crusher 31 from a fuel supply device 32 . The fuel supply device 32 includes, for example, a constant supply device such as a belt conveyor and a metering device (both not shown), and can adjust the amount of wet fuel supplied to the crusher 31. The fuel supply device 32 transmits the amount of wet fuel supplied to the controller 9. The controller 9 can estimate the amount of pulverized fuel supplied to the furnace 11 from the amount of wet fuel supplied.

Furthermore, a crusher air supply line 35 is connected to the crusher 31 for supplying conveying air to the crusher 31 . The crusher air supply line 35 is supplied with temperature-adjusted conveyance air from the air heating line 34 . The air heating line 34 includes a forced air blower 62 and a gas air heater 61. The amount of air blown from the blower 62 is detected by the airflow meter 46. Air sent from the forced air blower 62 to the air heating line 34 is heated through the gas air heater 61 to become high-temperature conveying air, and is supplied to the crusher 31 through the crusher air supply line 35. The air heating line 34 is provided with a bypass path 39 through which the air sent out from the blower 62 bypasses the gas air heater 61 and flows to the crusher 31. A fourth adjustment device 40 is provided in the bypass path 39. Further, a third adjustment device 37 is provided in a portion of the air heating line 34 that is bypassed by the bypass path 39. Furthermore, a thermometer 43 is provided in the pulverizer air supply line 35, and a thermometer 79 for detecting the temperature of the gas discharged from the pulverizer 31 is provided in the pulverized fuel discharge line 70, which will be described later. The temperature of the conveying air supplied to the crusher 31 through the crusher air supply line 35 is controlled by the adjusting device 37 so that the temperature detected by the thermometer 79 is a predetermined temperature based on the temperature detected by the thermometer 43. , 40.

The crusher air supply line 35 is provided with a booster fan 47 and a regulator 48 . The adjustment device 48 may be, for example, a means for adjusting the flow rate of the conveying air, such as a flow rate adjustment valve or a damper. The flow rate of the conveying air supplied to the crusher 31 through the crusher air supply line 35 is adjusted by the regulating device 48 depending on the amount of fuel supplied to the crusher 31 from the fuel supply device 32 .

A burner combustion air line 36 branches off from the air heating line 34 downstream of the gas air heater 61 . A portion of the air heated in the air heating line 34 is sent directly to the burner through the burner combustion air line 36 without passing through the crusher 31. The burner combustion air line 36 branches at a branch portion 44 into a two-stage combustion air line 36a and a burner combustion secondary air line 36b. A portion of the air sent through the burner combustion air line 36 is sent to the combustion burner 21 as burner combustion secondary air via the burner combustion secondary air line 36b. Additionally, the remainder of the air sent through the burner combustion air line 36 is sent to the two-stage combustion air nozzle 26 as second-stage combustion air through the second-stage combustion air line 36a.

A second-stage combustion air additional line 72, which will be described later, is connected to the second-stage combustion air line 36a at the merging portion 64. A second adjustment device 76 is provided downstream of the confluence section 64 of the two-stage combustion air line 36a. The second adjustment device 76 may be, for example, a flow rate adjustment valve, a damper, or the like. A second pressure gauge 68 and a second two-stage combustion air flow meter 69 are provided downstream of the confluence section 64 of the two-stage combustion air line 36a.

The pulverizer 31 includes a pulverizing table that has a rotation axis extending in the vertical direction and is rotationally driven within a housing, and a plurality of pulverizing rollers that are disposed opposite to each other above the pulverizing table (both are not shown). The wet fuel supplied to the crusher 31 is crushed to a predetermined size between a crushing roller and a crushing table, classified by conveying air, and heated and dried to become pulverized fuel. Although the crusher 31 according to this embodiment is a vertical roller mill, the crusher 31 is not limited to this, and may be a known crusher such as a ball mill or a rod mill, for example.

The pulverized fuel is discharged from the crusher 31 along with the conveying air and flows into the multi-cyclone 33 through the discharge line 70. The discharge line 70 is provided with a conveying air flow meter 63 that detects the flow rate of the conveying air (powder-containing conveying air) accompanied by the pulverized fuel flowing into the multi-cyclone 33 . In the multi-cyclone 33, the powder-containing conveying air is separated into solid (pulverized fuel) and gas (additional two-stage combustion air).

The gas discharge port 33a of the multi-cyclone 33 is connected to the starting end of a two-stage combustion air addition line 72 (corresponding to the "first line" in the claims). The terminal end of the additional second-stage combustion air line 72 is connected to the second-stage combustion air line 36a and reaches the second-stage combustion air nozzle 26. The second stage combustion air addition line 72 is provided with a first adjustment device 75 . In the additional two-stage combustion air line 72, an additional two-stage combustion air flow meter 66 and an additional two-stage combustion air pressure gauge 67 are provided on the upstream or downstream side of the air flow from the first adjustment device 75. . The additional two-stage combustion air flow meter 66 detects the flow rate of the additional two-stage combustion air discharged from the multi-cyclone 33. The additional two-stage combustion air pressure gauge 67 detects the pressure of the additional two-stage combustion air discharged from the multi-cyclone 33.

The lower solid discharge port 33b of the cyclone 33 is connected to a burner combustion primary air line 71 (corresponding to the "second line" in the claims) via a pulverized fuel supply pipe 38. A mixing section 78 for mixing the burner combustion primary air and the pulverized fuel is provided at a connection portion between the pulverized fuel supply pipe 38 and the burner combustion primary air line 71. The terminal end of the burner combustion primary air line 71 is connected to the combustion burner 21 , and burner combustion primary air is sent to the combustion burner 21 through the burner combustion primary air line 71 . The burner combustion primary air line 71 is provided with a booster fan 77 and a burner combustion primary air flow meter 65 . The boost fan 77 adjusts the flow rate and pressure of the burner combustion primary air. Burner combustion primary air flow meter 65 detects the flow rate of burner combustion primary air.

[Configuration of exhaust gas treatment system 60]
An exhaust gas line 49 is connected to the downstream side of the flue 41, through which exhaust gas that has undergone heat exchange in the heat exchanger 15 is discharged. The exhaust gas line 49 is provided with a selective reduction catalyst 50, a gas air heater 61, a dust collector 51, an induced blower 52, and a desulfurization device 53, and a chimney 54 is provided at the downstream end. The gas air heater 61 heats the air flowing through the air heating line 34 by exchanging heat with exhaust gas.

[Configuration of control system of boiler 1]
The controller 9 includes a cyclone control section 96. The controller 9 is a so-called computer, and includes a processor 91 such as a microcontroller, CPU, MPU, PLC, DSP, ASIC, or FPGA, and a memory 92 such as a ROM or RAM. The memory 92 stores programs executed by the processor 91, including a cyclone control program 93. Further, the memory 92 stores data such as the amount of pulverized fuel supplied and the air-fuel ratio, which are used in the processing performed by the processor 91. In the controller 9, a processor 91 reads and executes a program stored in a memory 92, thereby performing processing for functioning as a cyclone control unit 96.

The controller 9 includes an air flow meter 46, a thermometer 43, a carrier air flow meter 63, a burner combustion primary air flow meter 65, an additional two-stage combustion air flow meter 66, an additional two-stage combustion air pressure gauge 67, and a two-stage combustion air pressure meter. Various instruments including a total 68 and a two-stage combustion air flow meter 69 are electrically connected. The controller 9 acquires detection signals from these instruments.

The controller 9 also includes a fuel supply device 32, a first adjustment device 75, a second adjustment device 76, a third adjustment device 37, a fourth adjustment device 40, a blower 62, a boost fan 77, a first rotary valve 81, and , and various devices including the second rotary valve 83 are electrically connected. The controller 9 monitors the operations of these devices and controls the operations of these devices by outputting control signals to these devices.

[Example of operation of boiler 1]
Here, the operation of the boiler 1 having the above configuration will be explained. In the pulverizer 31, the supplied wet fuel is pulverized to a predetermined particle size and dried by conveying air. The pulverized fuel obtained by pulverizing and drying the wet fuel is air-flow-transported to the multi-cyclone 33 along with the transport air. In the multi-cyclone 33, the powder-containing conveying air is solid-gas separated into pulverized fuel and air.

The air discharged from the gas outlet 33a of the multi-cyclone 33 flows out to the additional second-stage combustion air line 72 as additional second-stage combustion air. This additional second-stage combustion air is sent to the second-stage combustion air nozzle 26 together with the second-stage combustion air supplied through the second-stage combustion air line 36a, and is ejected from the second-stage combustion air nozzle 26 into the furnace 11.

The pulverized fuel discharged from the powder outlet 33b of the multi-cyclone 33 flows into the burner combustion primary air line 71 through the pulverized fuel supply pipe 38. The pulverized fuel that has flowed into the burner combustion primary air line 71 is carried by airflow through the burner combustion primary air line 71 and reaches the combustion burner 21 . Here, at least one of the flow rate and pressure of the burner combustion primary air flowing through the burner combustion primary air line 71 is adjusted by the booster fan 77 .

A mixture of pulverized fuel and burner combustion primary air is blown into the furnace 11 from the combustion burner 21, and when it is ignited, a flame is generated in the first stage combustion area A. The combustion gas in the first stage combustion area A rises and reaches the second stage combustion area B. In the second-stage combustion region B, the second-stage combustion air blown out from the second-stage combustion air nozzle 26 completes the oxidation combustion of the pulverized fuel by the reaction between the combustion gas and the second-stage combustion air, and NOx is generated by the combustion of the pulverized fuel. The amount of generation is reduced.

Then, the exhaust gas generated by the combustion exchanges heat with water and/or steam flowing through the heat exchanger tubes 15a of the heat exchanger 15, and the heat is recovered. The steam generated in the heat exchanger tubes 15a is supplied, for example, to a power generation plant (for example, a turbine, etc.) not shown. The exhaust gas flowing out from the flue 41 to the exhaust gas line 49 has harmful substances such as NOx removed by a selective reduction catalyst 50 while passing through the exhaust gas line 49, particulate matter is removed by a dust collector 51, and is removed by a desulfurization device 53. After the sulfur content is removed, it is discharged into the atmosphere from the chimney 54.

Furthermore, the gas air heater 61 is activated by the flow of high temperature exhaust gas into the exhaust gas line 49. That is, the blower 62 is driven, a part of the air from the outside is sent into the air heating line 34, and this air is heated by exchanging heat with the exhaust gas by the gas air heater 61. A part of the air, which has become high in temperature due to heating, is supplied to the crusher 31 through the crusher air supply line 35.

Further, the remainder of the air heated to high temperature by the gas air heater 61 is sent to the combustion burner 21 and the two-stage combustion air nozzle 26 through the burner combustion air line 36 as burner combustion secondary air and second-stage combustion air. Here, at least one of the flow rate and pressure of the second stage combustion air flowing through the second adjustment device 76 is adjusted so that the second stage combustion air does not flow backward through the second stage combustion air additional line 72. Furthermore, the first adjustment device 75 and the second adjustment device are arranged so that the second stage combustion air blown into the furnace from the second stage combustion air nozzle 26 becomes a predetermined ratio of the air flow rate of the blower 62 detected by the air flow meter 46. Device 76 is adjusted. The above predetermined ratio varies depending on the type of fuel and the shape of the furnace, but is about 30% when the pulverized fuel is pulverized biomass, for example.

[Configuration of multi-cyclone 33]
Here, the configuration of the multi-cyclone 33 will be explained in detail. FIG. 3 is a schematic diagram of the multi-cyclone 33.

The multi-cyclone 33 shown in FIG. 3 includes a casing 20 and a plurality of cyclones 22 provided within the casing 20. The casing 20 has a body part 20c, an inlet part 20a connected to the upper part of the body part 20c, and a powder outlet part 20b connected to the lower part of the body part 20c. The inlet portion 20a is connected to a discharge line 70 from the crusher 31. The powder outlet portion 20b is connected to a pulverized fuel supply pipe 38 to the burner combustion primary air line 71.

The plurality of cyclones 22 are housed in the body 20c of the casing 20. Each cyclone 22 has substantially the same structure. That is, each cyclone 22 has an outer cylinder 23 and an inner cylinder 25 inserted into the outer cylinder 23. Guide vanes 24 are provided around the inner cylinder 25 to form a swirling flow inside the outer cylinder 23. The lower end of the inner cylinder 25 is located within the outer cylinder 23, and the upper end of the inner cylinder 25 is connected to a gas outlet pipe 20d penetrating the body 20c of the casing 20. The gas outlet pipe 20d is connected to a two-stage combustion air addition line 72. The powder-containing conveying air that enters from the upper opening of the outer cylinder 23 is accelerated when passing through the guide vanes 24 and generates a strong downward swirling flow within the outer cylinder 23. The pulverized fuel reaches the outer cylinder 23 under strong centrifugal force, descends with a swirling flow, and is discharged from the lower opening of the outer cylinder 23 to the powder outlet portion 20b of the casing 20. The swirling flow reversed at the lower part of the outer cylinder 23 swirls upward in the center of the outer cylinder 23 and enters the lower opening of the inner cylinder 25 . The conveying air exiting from the upper opening of the inner cylinder 25 flows out to the second stage combustion air addition line 72 through the gas outlet pipe 20d.

A switch 27 is provided within the inner cylinder 25 to switch between closing and opening the flow path. The switching device 27 may be of any type as long as it is capable of closing and opening the flow path, such as a valve, shutter, damper, or slide gate. The operation of each switch 27 is controlled by a cyclone control section 96 of the controller 9.

By closing the flow path in the inner cylinder 25 with the switch 27, the powder-containing transport air is prevented from flowing into the cyclone 22. Furthermore, by opening the flow path in the inner cylinder 25 by the switch 27, the powder-containing transport air is allowed to flow into the cyclone 22. In this way, the switch 27 provided in each cyclone 22 switches between allowing and blocking the powder-containing conveying air from flowing into the cyclone 22, thereby switching between operating and stopping the cyclone 22. Note that a cyclone 22 in which the inflow of powder-containing transport air is blocked is referred to as a "stopped cyclone 22", and a cyclone 22 in which the inflow of powder-containing transport air is allowed is referred to as an "operating cyclone 22". .

As described above, in the multi-cyclone 33 having a configuration in which the number of operating cyclones 22 is variable, the number of operating cyclones 22 is adjusted according to the flow rate of powder-containing conveying air detected by the conveying air flow meter 63. Specifically, the cyclone control unit 96 of the controller 9 acquires the flow rate of the powder-containing conveying air detected by the conveying air flow meter 63, determines the number of operating cyclones 22 based on this flow rate, and controls the determined operating number. A switching signal is sent to each switch 27 to operate each switch 27 so that some cyclones 22 are operated and the remaining cyclones 22 are stopped. The number of operating cyclones 22 is determined so that when the flow rate of the powder-containing conveying air is distributed to the operating cyclones 22, the operating cyclones 22 can exhibit a predetermined solid-gas separation ability. Information relating the flow rate of the powder-containing conveyance air to the number of operating cyclones 22 is obtained through experiments, simulations, or calculations and is stored in the controller 9 in advance. Using such information, the cyclone control unit 96 determines the number of operating cyclones 22 from the flow rate of the powder-containing conveying air detected by the conveying air flow meter 63.

As a result of adjusting the number of cyclones 22 in operation as described above, the number of cyclones 22 in operation increases as the flow rate detected by the conveyance air flow meter 63 increases, and as the flow rate detected in the conveyance air flow meter 63 decreases. The number of cyclones 22 in operation will be reduced.

As explained above, the pulverized fuel-fired boiler 1 according to the present embodiment includes a furnace 11 having at least one combustion burner 21 provided on the furnace wall, and a furnace 11 that pulverizes fuel into pulverized fuel and converts the pulverized fuel into powdered fuel. A pulverizer 31 discharges the pulverized fuel on the conveying air, a multi-cyclone 33 that separates the pulverized fuel discharged from the pulverizer 31 into solid and gas, and a pulverized fuel flowing into the multi-cyclone 33. A flow meter 63 that detects the flow rate of the carrier air, a first line (two-stage combustion air additional line 72) that sends the carrier air separated by the multi-cyclone 33 to the furnace 11, and a pulverized fuel separated by the multi-cyclone 33. A second line (burner combustion primary air line 71) is provided to send to the combustion burner 21. The multi-cyclone 33 includes a plurality of cyclones 22, a switch 27 that switches between operating and stopping the cyclone 22 by switching between allowing and blocking the inflow of carrier air for each of the cyclones 22, and a flow rate detected by a flow meter. The controller 9 controls the switch 27 so that the number of cyclones 22 in operation increases as the flow rate increases, and the number of cyclones 22 in operation decreases as the flow rate decreases.

According to the pulverized fuel-fired boiler 1, when the flow rate of the carrier air supplied to the multi-cyclone 33 increases, the number of operating cyclones 22 increases, and when the flow rate of the carrier air supplied to the multi-cyclone 33 decreases, the number of operating cyclones 22 increases. Since the number is reduced, powder-containing conveying air can be supplied to the cyclone 22 during operation at a flow rate necessary for solid-gas separation. This allows the solid-gas separation ability of the cyclone to be maintained during operation. Therefore, even when the flow rate of the conveying air is lower than during steady operation, such as during low load operation of the boiler 1, the solid-gas separation ability of the multi-cyclone 33 can be maintained. As a result, the turndown ratio of boiler 1 (the ratio between the rated gas flow rate of the boiler and the minimum controllable gas flow rate) can be lowered, and since boiler 1 can be operated without stopping even under low load, the purge loss is reduced. This reduces running costs and improves operating efficiency, contributing to a reduction in running costs.

Furthermore, as mentioned above, even during low-load operation, the carrier air introduced into the multi-cyclone 33 is not forcibly added, so the carrier air (two-stage combustion air) is discharged from the multi-cyclone 33 and supplied to the furnace 11. does not increase, and an increase in the air-fuel ratio of the portion of the furnace 11 into which the second-stage combustion air is blown (second-stage combustion region B) can be suppressed.

Although the preferred embodiments of the present invention have been described above, the present invention may include modifications to the specific structure and/or functional details of the above embodiments without departing from the spirit of the present invention. .

For example, the multi-cyclone 33 is not limited to one in which a plurality of cyclones 22 are housed in a single casing 20. FIG. 4 shows a multi-cyclone 33A according to a first modification. The multi-cyclone 33A according to the first modification has a plurality of cyclones 22, which are connected in parallel. The outer cylinder 23 of each cyclone 22 is connected to a discharge line 70, and powder-containing conveying air is supplied from the discharge line 70 to the outer cylinder 23 of each cyclone 22. Further, the inner cylinder 25 of each cyclone 22 is connected to the second stage combustion air addition line 72, and the conveying air flows out from the inner cylinder 25 of each cyclone 22 to the second stage combustion air addition line 72. The lower part of the outer cylinder 23 of each cyclone 22 is connected to a pulverized fuel supply pipe 38, and the pulverized fuel discharged from the outer cylinder 23 of each cyclone 22 is supplied to the burner combustion primary air line 71 through the pulverized fuel supply pipe 38.

In the multi-cyclone 33A having the above configuration, the switch 27A is provided in the branch pipe 70a that connects the discharge line 70 and the outer cylinder 23 of each cyclone 22. This switch 27A is a means for switching between closing and opening the flow path of the branch pipe 70a. The switch 27A switches between allowing and blocking the powder-containing transport air from flowing into the outer cylinder 23 of the cyclone 22, thereby allowing the cyclone 22 to be switched between operating and stopping.

1: Pulverized fuel fired boiler 9: Controller 10: Boiler main body 11: Furnace 12: Combustion device 15: Heat exchanger 20: Casing 21: Combustion burner 22: Cyclone 23: Outer cylinder 24: Guide vane 25: Inner cylinder 26: Two Stage combustion air nozzles 27, 27A: Switcher 30: Fuel supply system 31: Pulverizer 32: Fuel supply device 33, 33A: Multi-cyclone 34: Air heating line 35: Pulverizer air supply line 36: Burner combustion air line 36a: Two-stage combustion air line 36b: Burner combustion secondary air line 37, 40, 75, 76: Adjustment device 38: Powdered fuel supply pipe 39: Bypass path 41: Flue 43: Thermometer 46: Air flow meter 49: Exhaust gas line 50 : Selective reduction catalyst 51 : Dust collector 52 : Induced blower 53 : Desulfurizer 54 : Chimney 60 : Exhaust gas treatment system 61 : Gas air heater 62 : Forced blower 63 : Conveying air flow meter (flow meter)
65: Burner combustion primary air flow meter 66: Additional two-stage combustion air flow meter 67: Additional two-stage combustion air pressure gauge 68: Two-stage combustion air pressure gauge 69: Two-stage combustion air flow meter 70: Discharge line 70a: Branch pipe 71: Burner combustion primary air line (second line)
72: Two-stage combustion air additional line (first line)
77: Boosting fan 81: First rotary valve 82: Intermediate chamber 83: Second rotary valve 91: Processor 92: Memory 93: Cyclone control program 94: Air-fuel ratio adjustment program 96: Cyclone control section

Claims (2)

a furnace having at least one combustion burner provided in the furnace wall;
A pulverizer that crushes fuel into pulverized fuel and discharges the pulverized fuel on conveying air;
a multi-cyclone that separates the conveying air with the pulverized fuel discharged from the pulverizer into solids and gas;
a flow meter that detects the flow rate of the carrier air accompanied by the pulverized fuel flowing into the multi-cyclone;
a first line that sends the carrier air separated by the multi-cyclone to the furnace;
A second line connected to the multi-cyclone via a pulverized fuel supply pipe and a valve and sending the pulverized fuel separated by the multi-cyclone to the combustion burner,
The multi-cyclone includes a plurality of cyclones each having an outer cylinder, an inner cylinder inserted into the outer cylinder, and a guide vane disposed between the outer cylinder and the inner cylinder, and the plurality of cyclones . switching between allowing and blocking inflow of the conveying air for each of the cyclones and a casing having an internal space with an open lower opening of the outer cylinder and including a powder outlet connected to the pulverized fuel supply pipe; A switch for switching between operation and stop of the cyclone, and a switch such that the number of cyclones in operation increases as the flow rate detected by the flow meter increases, and the number of cyclones in operation decreases as the flow rate decreases. , and a controller that controls the switching device. The casing of the multi-cyclone includes a body that accommodates the plurality of cyclones, the powder outlet connected to a lower part of the body, and an inlet connected to an upper part of the body.
The pulverized fuel-fired boiler according to claim 1.

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