JP2000249331A - Boiler controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten a controlling/regulating period of a boiler and to optimize boiler designing by preventing a change in a gas temperature distribution caused by a difference of coal properties. SOLUTION: The boiler controller calculates a furnace heat absorption ratio in a present operating state of a boiler by a furnace heat absorption ratio calculator 2 based on a measured value from boiler plant data 1, and obtains a deviation from a furnace heat absorption ratio target value at a present value and each load by a deviation calculator 5. A PI calculator 6 conducts a proportional integration control from the deviation obtained by the calculator 5, controls a frequency of an inverter 8 through an automatic/manual switching unit 7, and regulates a fine particle grain size when coal is outputted from a mill by changing a rotational speed of a rotary classifier motor 9. Thus, for example, if the furnace heat absorption ratio is higher than an optimum value, the coal output grain size of the mill is excessively high (excessively fine), and hence is this case, a rotational speed of the motor provided in the mill is decelerated, and controlled so that the coal output grain size from the mill is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a boiler control device, and more particularly to a boiler control device suitable for optimizing control characteristics for a change in coal properties in a pulverized coal-fired boiler.

[0002]

2. Description of the Related Art Coal burning in a pulverized coal-fired boiler greatly differs in coal properties depending on the coal-producing area, and measures to stabilize a pulverized coal-fired boiler by burning a wide range of coal have become an important issue. . Among the coal properties, the components that are particularly important for the combustion characteristics are the volatile component and the fixed coal component constituting the coal, and this property is generally defined as the fuel ratio in the following equation (1). Fuel ratio = fixed carbon weight / volatile component weight (1) Here, the volatile component burns near the burner at a high burning rate, so that the gas temperature in the furnace increases and the fluid is absorbed by the fluid at the furnace wall. Ratio increases. On the other hand, the fixed carbon component has a low burning rate and burns in the upper part or the latter part of the furnace, so that the gas temperature on the superheater side increases, and the heat absorption ratio in the superheater or evaporator increases. Therefore, in the case of coal with a low fuel ratio, the heat absorption ratio on the furnace side increases and the gas temperature in the furnace increases, and on the other hand, in the case of coal with a high fuel ratio, the heat absorption ratio in the latter stage of the furnace increases and the furnace Outlet gas temperature increases.

[0003] Since the gas temperature distribution in the boiler is significantly different due to the difference in fuel ratio, it is very difficult to optimize the design of the heat transfer area of the boiler and to control the temperature on the fluid side. . In particular, in a variable-pressure Benson type boiler with high efficiency at low load, the steam-water separation is performed in the evaporation tube without the steam-water separation drum, so it is necessary to keep the outlet temperature of the evaporation tube above the saturation temperature. The superheater outlet temperature, which is the boiler outlet temperature for turning the turbine, also needs to be constant due to the restrictions on the turbine side.Since the inlet and outlet temperatures on the steam side are constant in this way, there are some differences depending on the steam pressure conditions. Although different, the temperature distribution on the steam side is almost determined. For this reason, in general, when the gas temperature distribution fluctuates due to the fuel ratio of coal or the boiler load, the distribution of the water supply flow rate of the spray water to the furnace side and the superheater side is changed to change the steam side temperature. The distribution is controlled so as to be kept constant.

[0004]

However, in the conventional control method described above, when the fuel ratio is low or the boiler load is low, the heat absorption rate of the furnace increases and the amount of water supplied to the furnace increases. When the spray amount on the superheater side is close to the control lower limit, and conversely, when the fuel ratio is high or the boiler load is high, the rate of furnace heat absorption decreases and the amount of water supplied to the superheater side increases, so the superheater side Has a problem that the control margin is lost in any case. Further, in order to confirm the control characteristics, it is necessary to perform the test operation with several kinds of fuel ratios, and there is a problem that the test operation period is increased. Furthermore, since the gas temperature distribution in the boiler is greatly different, it is difficult to optimize the structural material and size of each part of the boiler, and it is necessary to provide a margin in design, and the total cost of the boiler rises. There was also.

The present invention has been made in view of the above-mentioned circumstances of the prior art, and an object of the present invention is to maintain a constant gas temperature distribution in a furnace even when burning coal having different coal properties, and to control a boiler control period. And to provide an inexpensive boiler apparatus by optimizing the boiler design.

[0006]

As described above, the fuel ratio of coal is closely related to the burning rate. Coal with a low fuel ratio has a fast burning rate, and coal with a high fuel ratio has a slow burning rate. However, the burning rate is also related to the fine particle size of the coal.If the fine particle size is small even for coal with the same fuel ratio, the volatile components in the coal are quickly mixed with air to increase the burning rate, and the apparent fuel The ratio decreases. On the other hand, when the fine powder particle size is large even with coal having the same fuel ratio, the volatile component is gently mixed with the air, so that the combustion speed is reduced, and the apparent fuel ratio is increased.

The present invention focuses on such a phenomenon and controls the apparent fuel ratio of coal by controlling the particle size of coal discharged from a pulverized coal mill to keep the gas temperature distribution in the furnace constant. I did it. With this configuration, the apparent fuel ratio of coal is optimally controlled, so that the gas temperature distribution in the furnace can be kept constant irrespective of differences in coal properties, and the boiler control adjustment period can be shortened. And the boiler design can be improved.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A boiler control apparatus according to the present invention is provided with a pulverized coal mill for pulverizing coal into pulverized coal, and pulverized coal pulverized by the pulverized coal mill is supplied to a burner and burned. , A detecting means for measuring the heat absorption rate of the boiler furnace and a correction means for controlling the particle size of coal discharged from the pulverized coal mill so that the heat absorption rate of the furnace measured by the detecting means become constant.

Further, the boiler control device of the present invention is provided with a pulverized coal mill for pulverizing coal into pulverized coal, and supplying the pulverized coal pulverized by the pulverized coal mill to a burner for combustion. A detection means for measuring the boiler furnace outlet gas temperature and a correction means for controlling the coal exit particle size from the pulverized coal mill so that the furnace outlet gas temperature measured by the detection means is constant.

[0010] The boiler control device of the present invention further includes a pulverized coal mill for pulverizing coal into pulverized coal, and a pulverized coal fired boiler for supplying pulverized coal pulverized by the pulverized coal mill to a burner for combustion. A detecting means for measuring the coal properties and a correcting means for controlling the particle size of coal discharged from the pulverized coal mill according to the coal properties measured by the detecting means are provided. In this case, it is preferable that the detecting means measures the ratio of the volatile component and the fixed carbon component in the coal.

In the above configuration, a fine particle size selecting device using centrifugal force is provided in the pulverized coal mill, and the correcting means controls the number of rotations of the fine particle size selecting device to thereby obtain a predetermined fine particle size. It is preferable to selectively remove coal only, and further, a detecting means for measuring a mill air flow rate and a mill differential pressure is provided, and the correcting means corrects the pressure for coal pulverization based on a measured value from the detecting means. Is preferred.

[0012]

Embodiments will be described with reference to the drawings.
FIG. 1 is a block diagram of a boiler control device according to a first embodiment, in which 1 is boiler plant data, 2 is a furnace heat absorption ratio calculator, and 3 is a boiler load command (MW).
D), 4 is a function generator, 5 is a deviation calculator, 6 is a PI calculator, 7 is an automatic manual switcher, 8 is an inverter, and 9 is a rotary classifier motor.

As shown in FIG. 1, the values of the furnace inlet water supply flow rate, the furnace inlet water supply pressure, the furnace inlet water supply temperature, the furnace outlet fluid pressure, and the furnace outlet temperature are measured based on the boiler plant data 1, and based on these measured values. The furnace heat absorption ratio calculator 2 calculates the furnace heat absorption ratio in the current operation state of the boiler. Further, a furnace heat absorption ratio target value at each load is obtained by the function generator 4 from the boiler load command 3, and a deviation between the current value and the target value at each load is obtained by the deviation calculator 5. As shown in FIG. 2, a curve of the furnace heat absorption ratio which is an optimum steam condition at the time of the boiler operation at each load is set in the function generator 4, and the current operation condition is optimized by the above-described deviation calculation. It is possible to calculate the degree of deviation from driving. Here, when the furnace heat absorption ratio in the current operating condition is deviated from the optimum value, for example, when the furnace heat absorption ratio is higher than the optimum value,
In this case, control the rotation speed of the rotary classifier motor provided in the pulverized coal mill to lower the particle size of the coal output from the pulverized coal mill because the particle size of the coal output from the pulverized coal mill is too high (too fine). I do. In other words, the proportional integral control is performed by the PI calculator 6 based on the deviation obtained by the deviation calculator 5 and the frequency of the inverter 8 is controlled via the automatic manual switch 7 so that the rotation speed of the rotation classifier motor 9 can be reduced. Adjust the particle size of the powder at the time of mill coal release.

As shown in FIG. 3, the pulverized coal mill employed in this embodiment is disposed at a position equally divided in a circumferential direction of the turntable 10 and a turntable 10 disposed at a lower portion of the housing. A plurality of rollers 11 and each roller 11
The turntable 10 is configured to rotate using a motor (not shown) as a driving source. After the coal supplied into the housing is pulverized between the rotating turntable 10 and the roller 11 rotating with the same, the coal is moved up in the housing by the carrier air and adjusted to a predetermined particle size by the rotary classifier 12. The coal is supplied from a pulverized coal mill and supplied to a boiler. The rotary classifier 12 emits only fine powder having a particle size equal to or less than a predetermined value by centrifugal force, and coal larger than the predetermined particle size that has not passed through the rotary classifier 12 falls onto the turntable 10 by its own weight and enters the housing. Pulverized again with freshly supplied coal. The number of rotations of the rotary classifier 12 is controlled by the rotary classifier motor 9,
If the number of rotations of 2 is advanced, coal with a finer particle size can be discharged, and if the number of rotations of the rotary classifier 12 is reduced, coal with a larger particle size can be output.

According to the first embodiment constructed as described above, the fluctuation of the gas temperature distribution in the furnace is calculated by the furnace heat absorption ratio, and this is compared with the furnace heat absorption ratio which is the optimum steam condition. Automatically adjusts the rotation of the rotary classifier of the pulverized coal mill, so that the gas temperature distribution in the furnace can be kept constant regardless of the properties of the coal, and automatic operation under optimal steam conditions becomes possible. .

In the first embodiment, the particle size of coal discharged from the pulverized coal mill is controlled only by the number of revolutions of the rotary classifier. There is a possibility that the crushing ability between the rollers cannot keep up, and relatively coarse fine powder may pass through the rotary classifier. In other words, since the actual pulverizing capacity of the pulverized coal mill is constant, the pulverized coal mill is pulverized when the output of coal is large, in other words, when the transport air flow is large or the retained coal is large (differential pressure is large) The ability may not be able to follow.

In the second embodiment shown in FIG. 4, this point is taken into consideration. In FIG.
4, 15 are adders, 16 is a subtractor, 17 is an automatic manual switcher, 18 is an amplifier, 19 is a mill pressure increasing oil pump,
20 is a mill air flow rate measurement signal, 21 is a mill differential pressure measurement signal, 22 is a mill current measurement signal, and 23, 24, and 25 are function generators.

As shown in FIG. 4, in this embodiment, the following three corrections are applied to the mill pressure (standard setting) command value 13. The first correction is the mill air flow measurement signal 2.
A pressure increase value obtained by the function generator 23 from 0;
As shown in FIG. 5A, a curve of a correction value for an air flow rate equal to or more than a certain value is set in the function generator 23. The correction at the second point is a pressure increase value obtained by the function generator 24 from the mill differential pressure measurement signal 21. As shown in FIG. The curve of the correction value for is set. These pressurizing force increase values are added to the mill pressurizing command value 13 by adders 14 and 15, respectively. The third correction is a reduced correction pressure value obtained from the mill current measurement signal 22 by the function generator 25. As shown in FIG. A curve of the correction value is set, and the reduced correction pressure value is subtracted by the subtractor 16 from the mill pressure command value 13. After the mill pressure command value 13 is thus corrected at three points,
Amplifier 1 for pump operation via automatic / manual switch 19
At 8, a current / voltage is amplified, and a mill pressure increasing pump 19 for applying a pressure to the roller is driven.

According to the second embodiment constructed as described above, since the pressing force of the roller is also corrected, when the coal output is large, that is, the mill air flow is large or the mill differential pressure is large, the roller This has the advantage that the pressing force can be increased and the pulverizing ability can be improved, and the control range of coal particle size can be expanded. Moreover, since the mill current value is detected and the pressing force of the roller is interlocked, it is possible to prevent the pressing force of the roller from excessively increasing.

In the above-described first embodiment, since the rotation speed of the rotary classifier is changed from the current value after detecting the furnace heat absorption ratio, there is a possibility that the furnace heat absorption ratio cannot be changed when the load changes at a high rate. There is. In the third embodiment shown in FIG. 6, this point is taken into consideration. In addition, Nox, which is a constraint condition at the environmental value when the fine particle size is reduced,
The CO value is also taken into account.

In FIG. 6, the control elements added to the first embodiment shown in FIG.
8, adders 29 and 31, subtractor 30, function generator 32,
Mill differential pressure signal 33, function generators 34 and 36, mill current signal 35, adder 37, boiler Nox measuring instrument 38, boiler partial measuring instrument 40, boiler CO measuring instrument 42, function generators 39, 41, 43, The adder 44.

As shown in FIG. 6, in this embodiment, the furnace heat absorption ratio calculator 2 takes in measured values using a pressure gauge 26, a flow meter 27, a thermometer 28 and the like separately from the boiler plant data 1. It has become. The values measured by the pressure gauge 26, the flow meter 27, and the thermometer 28 are used when the furnace heat absorption ratio calculator 2 calculates the furnace heat absorption ratio using data other than the boiler plant data 1. Is the data when measuring online. However, similarly to the first embodiment described above, the furnace heat absorption ratio can be calculated using only the boiler plant data 1, or the boiler plant data 1 and the pressure gauge 26, the flow meter 27, and the thermometer 28 can be calculated. It is also possible to calculate the furnace heat absorption ratio by using data such as these.

As described above, the furnace heat absorption ratio calculator 2 calculates the furnace heat absorption ratio in the current operating state of the boiler,
A furnace heat absorption ratio target value at each load is obtained by the function generator 4 from the boiler load command 3, and a deviation calculator 5 calculates a deviation between the current value and the target value at each load. A correction value is calculated by the PI calculation unit 6 from the deviation obtained by the deviation calculation unit 5, and the interlock from the environmental regulation value and the interlock from the mill operation state are corrected for the correction value. For the interlock from the former environmental regulation value, see Nox
The correction value is calculated by the function generator 39 from the measuring device 38, the correction value is calculated by the function generator 41 from the measurement device 40, and the correction value is calculated by the function generator 43 from the CO measuring device 42.
After these correction values are added by the adder 44, the correction is performed by the adder 29 at the subsequent stage of the PI calculator 6. For the latter interlock from the mill operation state, a correction value is calculated by the function generator 34 from the mill differential pressure signal 33 and a correction value is calculated by the function generator 36 from the mill current signal 35, respectively.
After adding these correction values in the adder 37, the adder 29
The correction is performed by the subtractor 30 in the subsequent stage.

In this manner, the number of revolutions of the rotary classifier required to correct the furnace heat absorption ratio is calculated. Instead of determining the number of revolutions of the rotary classifier motor 9 based on the calculated value, A rotation speed control value is calculated in an adder 31 subsequent to the subtractor 30. That is, the reference target value of the rotary classifier at each load is obtained by the function generator 32 from the boiler load command 3, and this reference target value is used as a preceding value by the adder 3
By giving it to 1, the characteristics at the time of a load change are improved. Then, the rotation speed control value calculated by the adder 31 is converted into a control power signal by the inverter 8 via the automatic manual switching device 7 and the rotation speed of the rotation classifier motor 9 is controlled, so that the mill output is controlled. The particle size of coal is adjusted to control the gas temperature distribution in the furnace.

In the first to third embodiments described above, the case in which the furnace heat absorption ratio is calculated to control the fine particle size is described. However, the furnace outlet gas temperature is calculated instead of the furnace heat absorption ratio to calculate the fine particle size. May be controlled, and an example thereof will be described with reference to a fourth embodiment shown in FIG.

FIG. 7 is different from the third embodiment shown in FIG. 6 in that the furnace outlet gas temperature is measured by a thermometer 45, and a function generator is obtained from the measured value from the thermometer 45 and the boiler load command 3. The deviation from the optimum temperature target value calculated at 29 is obtained directly by the deviation calculator 5, and the other conditions are basically the same. Since the furnace outlet gas temperature is 1000 ° C or higher and cannot be measured with a normal thermocouple thermometer, it may be estimated from the gas temperature at the subsequent stage, or a thermometer using a phenomenon in which the sound transmission speed differs depending on the gas temperature. The measurement may be performed by using the above method. In addition, because the gas temperature in the boiler furnace fluctuates greatly depending on the place and time, for example, because the gas flow in the furnace is not uniform, and the combustion itself has the nature of fluctuations, when measuring the gas temperature at the furnace outlet, Requires processing such as taking the average of a plurality of measurement points.

[0027]

The present invention is embodied in the form described above and has the following effects.

Since the apparent fuel ratio of the coal was controlled by controlling the particle size of coal discharged from the pulverized coal mill to optimize the gas temperature distribution in the furnace, the gas in the furnace was controlled regardless of the coal properties. The temperature distribution can be kept constant, and the boiler control adjustment period can be shortened, the boiler design margin can be improved, and the like.

[Brief description of the drawings]

FIG. 1 is a block diagram of a boiler control device according to a first embodiment.

FIG. 2 is an explanatory diagram of a furnace heat absorption ratio set in a function generator.

FIG. 3 is a configuration diagram of a pulverized coal mill.

FIG. 4 is a block diagram of a boiler control device according to a second embodiment.

FIG. 5 is an explanatory diagram of a correction value set in a function generator.

FIG. 6 is a block diagram of a boiler control device according to a third embodiment.

FIG. 7 is a block diagram of a boiler control device according to a fourth embodiment.

[Explanation of symbols]

1 Boiler plant data 2 Furnace heat absorption ratio calculator 3 Boiler load command 4,23,24,25,32,34,36,39,4
1,43 Function generator 5 Deviation calculator 6 PI calculator 7,17 Automatic manual switch 8 Inverter 9 Rotary classifier motor 10 Turntable 11 Roller 12 Rotary classifier 13 Mill force command 14,15,29,31, 37,44 Adder 16,30 Subtractor 18 Amplifier 19 Mil pressure increasing oil pump 20 Mil air flow rate measurement signal 21 Mill differential pressure measurement signal 22 Mill current measurement signal 26 Pressure gauge 27 Flow meter 28,45 Thermometer 33 Mill differential pressure signal 35 Mill current signal 38 Boiler Nox measuring device 40 Boiler predisposition measuring device 42 Boiler CO measuring device

Claims (6)

[Claims] 1. A pulverized coal-fired boiler having a pulverized coal mill for pulverizing coal into pulverized coal and supplying the pulverized coal pulverized by the pulverized coal mill to a burner and burning the measured coal boiler furnace heat absorption ratio. A boiler control device comprising: a detection unit; and a correction unit that controls a particle size of coal discharged from the pulverized coal mill so that a furnace heat absorption ratio measured by the detection unit is constant. 2. A pulverized coal-fired boiler which is provided with a pulverized coal mill for pulverizing coal into pulverized coal, and supplies the pulverized coal pulverized by the pulverized coal mill to a burner and burns the coal, and measures the gas temperature at the boiler furnace outlet. A boiler control device comprising: a detection unit; and a correction unit that controls a particle size of coal discharged from the pulverized coal mill so that a furnace outlet gas temperature measured by the detection unit is constant. 3. A pulverized coal-fired boiler comprising a pulverized coal mill for pulverizing coal into pulverized coal, and supplying the pulverized coal pulverized by the pulverized coal mill to a burner and burning the coal, and detecting means for measuring coal properties. A boiler control device, further comprising correction means for controlling the particle size of coal discharged from the pulverized coal mill in accordance with the properties of the coal measured by the detection means. 4. The boiler control device according to claim 3, wherein said detecting means measures a ratio between a volatile component and a fixed carbon component in the coal. 5. The pulverized coal mill according to claim 1, wherein the pulverized coal mill is provided with a fine particle size selection device using centrifugal force, and the correction means controls the number of revolutions of the fine particle size selection device. Thus, a boiler control device characterized in that only a predetermined fine particle size is selectively coalesced. 6. The apparatus according to claim 5, further comprising detecting means for measuring a mill air flow rate and a mill differential pressure, wherein the correcting means corrects the pressure for coal pulverization based on a measured value from the detecting means. A boiler control device.