JP2007292335A - Thermal power generation plant and pulverized coal supply controlling method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce unburned combustibles of pulverized coal included in a combustion gas generated in combustion in a boiler. <P>SOLUTION: This thermal power generation plant comprises a coal feeder 4 for conveying coal A from a coal bunker 7, a grinder 3 for finely pulverizing the conveyed coal A to produce pulverized coal B, a burner 2 for injecting the pulverized coal B, and the boiler 1 for burning the pulverized coal B injected from the burner 2. The burners 2 are arranged in plural stages in the height direction at a prescribed position of an inner peripheral face of the boiler 1, and the amount of pulverized coal injected from the burner 2 is adjusted by a control device. The control device controls the supply of pulverized coal so that the injection amount of pulverized coal B of the burner 2 at least at the lowermost stage position is more than that of the burner 2 at an upper stage position. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a thermal power plant that generates electricity using combustion of coal and a supply control method for pulverized coal used in the plant.

  Conventionally, there is a thermal power plant using a pulverized coal combustion method as an electric business using coal combustion. In the pulverized coal combustion method, coal is finely pulverized into pulverized coal and burned while being injected into the boiler together with air. This pulverized coal combustion method is currently used in many thermal power plants because it has a large air flow rate in the boiler and requires less excess air, and the coal itself has high combustibility. This pulverized coal combustion system is characterized in that burners for pulverized coal injection are arranged in a plurality of stages in the vertical direction on the side wall in the furnace of the boiler.

Moreover, the pulverized coal combustion system is controlled so that the thermal efficiency of the boiler is maximized by adjusting the amount of pulverized coal injected into the furnace and the amount of air. As such a boiler combustion control method, for example, there is a method disclosed in Patent Document 1. The combustion control method of Patent Document 1 estimates the unburned amount in ash by controlling the amount of trial operation of fuel and air, and corrects the amount of operation of fuel and air so that the boiler thermal efficiency is maximized. A combustion control method for controlling combustion.
JP-A-4-214120

  However, the combustion control method of Patent Document 1 takes into account a number of parameters (for example, mass flow rate, pressure, temperature, calorific value, heat transfer amount, etc.), and the burner at each stage individually controls the operation amounts of fuel and air. Therefore, complicated control operations are required for each device of the thermal power plant. Moreover, in the combustion control method of patent document 1, the expertise for changing the operation amount of pulverized coal is needed also for an operator, and versatility is not high. Furthermore, the combustion control method of Patent Document 1 does not consider the residence time of pulverized coal in the furnace, and does not sufficiently reduce the unburned content contained in the combustion gas of pulverized coal.

  The present invention has been made in view of the above-described circumstances, and in combustion in a boiler of a thermal power plant, the amount of pulverized coal injected from a burner is easily controlled according to the residence time of pulverized coal, and combustion It aims at reducing the unburned part of the pulverized coal contained in gas.

In order to solve the above problems, the thermal power plant of the present invention comprises a boiler that burns pulverized coal injected from a burner inside a furnace to generate steam, and discharges combustion gas from above the furnace. In a thermal power plant having a configuration in which burners are provided at a plurality of height positions on the peripheral wall of the furnace,
Pulverized coal supply control means is provided for controlling the amount of pulverized coal supplied to the burner so that at least the burner provided at the lowermost stage is larger than the burner provided at the uppermost stage.

  Here, the pulverized coal supply control means may be configured to gradually decrease the supply amount of the pulverized coal in a stepwise manner from the burner provided at the lowermost stage toward the burner provided at the uppermost stage.

  Further, the pulverized coal supply control means preferably adjusts the pulverized coal supply amount to each burner without changing the total amount of pulverized coal supply to all burners.

The pulverized coal supply control method of the present invention includes a boiler that burns pulverized coal injected from a burner inside a furnace to generate steam, and discharges combustion gas from above the furnace, and the burner has a furnace peripheral wall. In a thermal power plant having a configuration provided at a plurality of height positions,
The supply amount of pulverized coal to the burner is controlled so that at least the burner provided at the lowermost stage is larger than the burner provided at the uppermost stage.

  Here, the supply amount of pulverized coal can be decreased step by step from the burner provided at the lowermost stage toward the burner provided at the uppermost stage. Moreover, it is preferable to adjust the supply amount of pulverized coal to each burner without changing the total supply amount of pulverized coal to all the burners.

  According to the present invention, by increasing the amount of pulverized coal supplied from the lowermost burner, the residence time of the pulverized coal in the furnace is lengthened and the combustion efficiency is improved. The unburned content of the pulverized coal contained can be reduced.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic diagram showing the overall configuration of a thermal power plant according to an embodiment of the present invention. First, the overall structure of a thermal power plant will be described with reference to FIG.

  As shown in FIG. 1, coal A for burning in the boiler 1 is carried to a coal storage 5 of a thermal power plant by a coal ship or the like. Further, coal A is transported into the plant from the coal storage 5 by the conveyor 6 and stored in the coal bunker 7. Coal A stored in the coal bunker 7 is supplied to the mill 3 (pulverizer) by the coal feeder 4, and is pulverized in the mill 3 to be generated into pulverized coal. The generated pulverized coal is sent from the mill 3 to the burner 2 and is injected into the furnace 1a of the boiler 1 together with the air 100 sent from another route.

  The air 100 injected together with the pulverized coal is taken in from the outside by the forced air blower 8, and partly passes through the air preheater 28, partly to the mill 3 as pulverized coal transport air, and the other directly to the burner 2 as combustion air Led to. Further, a steam pipe 9 is disposed in the boiler 1, and power generation water circulated from the water supply pipe 10 is supplied into the pipe. The supplied water is sent to the turbine 11 as superheated steam by burning pulverized coal in the furnace 1 a of the boiler 1. The turbine 11 is rotated by adiabatic expansion of superheated steam, and the generator 12 generates electric power using this rotation. The superheated steam is cooled by the condenser 13 and returned to water, and is newly supplied to the boiler 1.

  Moreover, the combustion gas of the pulverized coal which burned in the furnace 1a of the boiler 1 and gave heat to water and steam includes soot, NOx, SOx and the like. For this reason, the thermal power plant is provided with a flue gas treatment facility for removing these harmful substances. The combustion gas is discharged from above the furnace 1 a, passes through the flue gas denitration device 14, travels to the dust collector 15, and is separated into coal ash and exhaust gas in the dust collector 15. Further, gypsum is generated from the exhaust gas by the flue gas desulfurization device 16 and the remaining clean exhaust gas is released from the chimney 17 to the atmosphere. By configuring the thermal power plant as described above, it becomes possible to constantly supply electricity.

Next, the configuration related to the pulverized coal supply control method according to the present embodiment will be described in more detail with reference to FIG. 2 and FIG. 3.
FIG. 2 is a schematic view showing a configuration relating to the supply of pulverized coal, and FIG. 3 is a schematic side view showing a burner attached state.
As shown in FIG. 2, the boiler 1 has a furnace 1a for burning the pulverized coal B, and a burner 2 for injecting the pulverized coal B is provided below the furnace 1a. The burner 2 is arranged in a plurality of stages in the height direction on the peripheral wall in the furnace 1 a of the boiler 1. By arranging the burners 2 in a plurality of stages in the height direction in this way, the boiler thermal efficiency in the entire furnace 1a can be stably obtained. Although not described in detail, a plurality of burners are provided on the same plane at each height position where the burners are installed. In the present embodiment, four burners 2 are provided at four height positions a, b, c, and d, respectively.

  In addition, as shown in FIG. 3, a starter fuel burner 20 that injects auxiliary fuel and a pulverized coal burner 21 are disposed in one burner 2 so as to surround the starter fuel burner 20. . The pulverized coal burner 21 communicates with the mill 3 through a coal feeding pipe 22 (see FIG. 2). The burner 2 raises the furnace temperature with the start-up fuel burner 20 at the start of combustion, and then injects the pulverized coal burner 21 to burn the pulverized coal B. An igniting torch 23 is provided above the pulverized coal burner 21 to ignite auxiliary fuel injected from the starting fuel burner 20.

Around the burner 2 is provided an air passage 24 through which the secondary and tertiary combustion air 102 is discharged. A damper 25 and a vane 26 are provided in the air passage 24, and the discharge amount of the secondary and tertiary combustion air 102 can be adjusted. The secondary and tertiary combustion air 102 discharged from the air passage 24 is mixed with the pulverized coal B from the pulverized coal burner 21 and injected into the furnace 1a.
Furthermore, a viewing window 27 for confirming the combustion state in the furnace 1a is provided at the lower part of the pulverized coal burner 21. The combustion state confirmed from the viewing window 27 is obtained as combustion information by an artificial or analysis device.

  The number of mills 3 that pulverize coal A to produce pulverized coal B is the same as the number of stages of burners 2 disposed in the boiler 1. That is, the burner 2a stage is provided with a mill 3a, the burner 2b stage with a mill 3b, the burner 2c stage with a mill 3c, and the burner 2d stage with a mill 3d, respectively. In this configuration, each stage is supplied separately.

  The pulverized coal B produced by the mill 3 is generally adjusted so that the pulverized particle size is 200 mesh (75 μm) or less. The generated pulverized coal B is sent to the burner 2 together with the pulverized coal conveying air 101 of 70 to 80 ° C. supplied from the forced air blower 8. These mills 3 are provided with coal feeders 4a, 4b, 4c, and 4d, respectively, that distribute and supply coal A from the coal bunker 7. The coal feeder 4 is configured such that the supply amount of coal A is individually controlled during conveyance by a driving motor (not shown).

FIG. 4 is a block diagram for explaining the pulverized coal supply control method according to the present embodiment.
As shown in FIG. 4, the thermal power plant is provided with a control device 30 (pulverized coal supply control means) that controls boiler thermal efficiency. The control device 30 includes a CPU 31 (arithmetic device) and a memory 32 (storage device). In addition, an input device 33 capable of inputting data from the outside is connected to the control device 30.

  The control device 30 is connected to the drive motor of the coal feeder 4 and the damper 25 and the vane 26 of the burner 2. The control device 30 connected to the drive motor is configured to automatically adjust the supply amount of coal A. That is, the control device 30 can adjust the generation amount of the pulverized coal B of the mill 3 by controlling the drive motor and operating the supply amount of the coal A. Thereby, the injection amount of the pulverized coal B is adjusted for each stage of the burner 2. Further, the control device 30 connected to the damper 25 and the vane 26 can adjust the discharge amount of the secondary and tertiary combustion air 102 discharged from the burner 2.

FIGS. 5A and 5B are conceptual diagrams showing the combustion state of the burner. FIG. 5A shows a conventional pulverized coal supply control method, and FIG. 5B shows a pulverized coal supply control method according to this embodiment.
As shown to Fig.5 (a), conventionally, the pulverized coal B was supplied to each burner 2 of multiple stages with the same supply amount. However, the pulverized coal B has a difference in the residence time in the furnace 1a after being injected depending on the height position of each stage number of the burner 2. This is because, in the furnace 1a, the injected pulverized coal B flows upward by heat convection and is discharged from above. For example, the pulverized coal B injected from the burner 2a is pulverized coal injected from the burner 2d. The residence time in the furnace 1a is shorter than B. For this reason, the pulverized coal B having a short residence time (that is, injected from a burner at a high position in the furnace 1a) has a high probability of being included in the combustion gas as it is without being burned and discharged. Become.

  In the pulverized coal supply control method of this embodiment, the injection amount of the pulverized coal B is adjusted according to the residence time of each stage of the burner 2 without changing the entire injection amount of the pulverized coal B. In other words, the supply amount of coal A from the coal feeder 4 is controlled by the control device 30 so that the burner 2 installed at the lower position of the furnace 1a increases the injection amount of pulverized coal. Accordingly, in the furnace 1a, as shown in FIG. 5B, the lower the burner 2 is, the stronger the fire is due to combustion.

  Adjustment of the injection quantity of the pulverized coal B for each stage of the burner 2 is performed by control by the control device 30. The control device 30 receives the data of the injection amount and the air amount of the pulverized coal B input to the input device 33 by the worker of the thermal power plant and stores them in the memory 32. During operation, the CPU 31 appropriately calls various data required from the memory 32 and transmits control signals to the drive motor of the coal feeder 4 and the damper 25 and vane 26 of the burner 2. It is preferable that the worker confirms the unburned content contained in the combustion gas at the time of pulverized coal combustion and designates the optimum supply amount of pulverized coal for each stage of the burner 2.

By configuring in this way, for example, the pulverized coal B injected in large quantities from the burner 2d has a long time to move upward in the furnace 1a even if it is not burned at the time of injection. The probability of burning inside increases. Further, the amount of pulverized coal B injected from the burner 2a is limited, and most of it is burned at the time of injection. Therefore, each pulverized coal B injected for each stage of the burner 2 is more reliably combusted within the residence time in the furnace 1a. As a result, unburned pulverized coal B is less included in the combustion gas, and the boiler thermal efficiency can be improved.
Further, by simultaneously adjusting the supply amount of the combustion air 102 together with the injection amount of the pulverized coal B, the residence time in the boiler 1 can be effectively controlled, and higher boiler thermal efficiency can be obtained.

〔Example〕
In order to verify the combustion control method of the present invention, the unburned portion contained in the combustion gas was compared when the injection amount of the pulverized coal B was the same as when the injection amount of the pulverized coal B was changed. Specifically, in the furnace 1a provided with four stages of burners in the height direction, all the conditions in the combustion in the furnace 1a are the same, and the conditions when the injection amount of the pulverized coal B is the same, The supply amount of pulverized coal B for each stage of the burner 2 was set to 12 t / h. On the other hand, as a condition for changing the injection amount of the pulverized coal B, the supply amount of the pulverized coal B is set to 15 t / h only for the lowermost burner 2d, and the other three are the supply amount of the pulverized coal B of the burner 2. Was set to 11 t / h. Therefore, in this embodiment, there is no difference in the total supply amount of the pulverized coal B in the entire burner 2, and the unburned portion of the pulverized coal can be compared purely due to the difference in the position of the burner 2.

In the implementation result of such a configuration, the unburned content of the pulverized coal contained in the combustion gas is 4 when the injection amount of the pulverized coal B is changed as compared with the case where the injection amount of the pulverized coal B is the same. 8% less. That is, by increasing the supply amount of the pulverized coal B of the lowermost burner 2d, the combustion efficiency was further improved and the unburned content could be reduced.
Therefore, in the boiler 1, it turns out that the combustion efficiency of pulverized coal B improves by changing supply_amount | feed_rate of pulverized coal B according to the residence time of internal pulverized coal.

It is the schematic which shows the whole structure of the thermal power plant which concerns on this embodiment. It is the schematic which shows the structure in connection with supply control of the pulverized coal which concerns on this embodiment. It is a side schematic diagram which shows the attachment state of a burner. It is a block diagram for demonstrating the pulverized coal supply control method which concerns on this embodiment. It is the conceptual diagram which showed the combustion state of the burner, (a) is based on the conventional pulverized coal supply control method, (b) is based on the pulverized coal supply control method of this embodiment.

Explanation of symbols

1: boiler, 2: burner, 3: mill, 4: coal feeder, 5: coal storage, 6: conveyor, 7: coal bunker, 8: indenter, 9: steam pipe, 10: water supply pipe, 11: Turbine, 12: generator, 13: condenser, 14: flue gas denitration device, 15: dust collector, 16: flue gas desulfurization device, 17: chimney,
20: Fuel burner for starting, 21: Burner for pulverized coal, 22: Coal pipe, 23: Ignition torch, 24: Air passage, 25: Damper, 26: Vane, 27: Viewing window, 28: Air preheater 30: Control device 31: CPU 32: Memory 33: Input device
100: Air, 101: Air for conveying pulverized coal, 102: Air for combustion A: Coal, B: Pulverized coal

Claims (6)

A configuration in which pulverized coal injected from a burner is combusted inside a furnace to generate steam, a boiler that discharges combustion gas from above the furnace, and the burner is provided at a plurality of height positions on the peripheral wall of the furnace In the thermal power plant of
Thermal power generation comprising pulverized coal supply control means for controlling the amount of pulverized coal supplied to the burner so that at least the burner provided at the lowermost stage is larger than the burner provided at the uppermost stage plant. The pulverized coal supply control means sequentially reduces the supply amount of the pulverized coal stepwise from the burner provided at the lowermost stage toward the burner provided at the uppermost stage. The described thermal power plant. The thermal power plant according to claim 1 or 2, wherein the pulverized coal supply control means adjusts the pulverized coal supply amount to each burner without changing the total amount of pulverized coal supply to all burners. . A configuration in which pulverized coal injected from a burner is combusted inside a furnace to generate steam, a boiler that discharges combustion gas from above the furnace, and the burner is provided at a plurality of height positions on the peripheral wall of the furnace In the thermal power plant of
A method for controlling the supply of pulverized coal, wherein the amount of pulverized coal supplied to the burner is controlled so that at least the burner provided at the lowermost stage is larger than the burner provided at the uppermost stage. The pulverized coal supply control method according to claim 4, wherein the supply amount of pulverized coal is gradually reduced from the burner provided at the lowermost stage toward the burner provided at the uppermost stage. . The pulverized coal supply control method according to claim 4 or 5, wherein the total amount of pulverized coal supplied to all the burners is adjusted without changing the total amount of pulverized coal supplied to each burner.

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