JPS649561B2 - - Google Patents

Description

[Detailed Description of the Invention] In recent coal-fired thermal power plants, it is common to pulverize coal in a mill and transport the pulverized coal to a boiler by air. As with combustion, it is necessary to directly and accurately measure the amount of fuel.

Therefore, conventional methods have been used to determine the amount of pulverized coal input to the boiler from the air pressure difference at the entrance and exit of the coal mill, or to determine the amount of pulverized coal input to the boiler from the amount of coal fed from the coal feeder to the coal mill. . The former calculates the amount of coal fed from the coal feeder to the mill by multiplying the signals obtained by the coal feeder belt load detector and the coal feeder belt speed detector installed inside the coal feeder. This is a detection method. The coal feed amount detected using this method has a major feature of high measurement accuracy, but when this detected amount is applied to a control system, there is a time delay until coal is fed from the coal feeder to the boiler. This makes control difficult and there is a great risk of large fluctuations in steam temperature. In addition, in the latter method of detecting the amount of coal fed from the air pressure difference at the entrance and exit of the coal mill, the measurement point is closer to the boiler side and has a great advantage in terms of improving detection delays, but clogging of pulverized coal in the mill, etc.)
There is a high possibility that detection errors will occur due to Therefore, when this method is applied to a fuel control system, the control deviation increases due to detection errors, which may lead to fluctuations in steam temperature, and as with the former method, there are many problems in terms of protecting the main engine of the plant.

An object of the present invention is to eliminate the drawbacks of the above-mentioned detection method and provide a method and apparatus for accurately detecting the amount of pulverized coal input to a boiler in response to changes in the amount of primary air for conveyance that vary depending on the operation pattern of the coal mill. .

A detailed explanation will be given below with reference to the drawings.

Figure 1 shows an example of a coal mill system. In the figure, coal from a coal storage tank 7 is placed on a rotary table 14 inside the mill selected by a coal feeder belt 9 driven by a motor 8. The coal that is repelled toward the outer circumference by the centrifugal force of the rotary table becomes a ball 13.
It is bitten and crushed. The pulverized coal is conveyed inside the mill by the primary conveying air provided by the fan 16, and is sorted by a classifier and hopper, and only the pulverized coal of a specified particle size or less is conveyed to the fuel pipe 11. Coarse pulverized coal that does not reach the specified particle size is circulated again onto the rotary table. This grinding process is repeated a considerable number of times to reach the specified particle size. Therefore, there is a pulverization delay of the order of minutes before the coal sent from the coal feeder 20 to the mill 10 becomes pulverized coal and reaches the burner 12 in the boiler 4.

FIG. 2 shows a currently used coal feeding amount adjustment and coal feeding amount detection device. The amount of coal to be fed is adjusted by controlling the thyristor 25 using a coal feed command signal 24 and changing the voltage of the coal feeder motor 8 to adjust the speed of the coal feeder belt 9. In FIG. 3, the coal feed amount is detected by calculating a coal feeder belt speed signal 26 and a coal feeder belt load signal 27 using a multiplier 28 to obtain a coal feed amount detection value 29. In addition, the air pressure difference at the mill entrance and exit, which is another conventionally known method for detecting the amount of coal fed, is determined by the oscillator 2 shown in FIG.
It is obtained as the output of 1. The oscillator 22 detects the amount of primary air as a differential pressure across the orifice 23.

FIG. 3 shows a block diagram of the fuel detection method according to the present invention. First, the amount of pulverized coal input to the boiler is calculated from the mill differential pressure 21. The characteristics of mill differential pressure and coal feed amount are the fourth
As shown in Figure a, it is determined from the characteristic data of the actual machine. A function generator 501 creates this characteristic curve a. Furthermore, as shown in FIG. 4, the characteristics of the mill differential pressure and the amount of coal fed change somewhat depending on the ratio b of the amount of coal fed into the coal mill and the amount of conveying air. The primary air amount ratio (mil ratio) b is set, the function generator 504 derives the correction amount of the signal obtained by the function generator 501, and the multiplier 506 multiplies this to input the boiler. Create pulverized coal amount A.

On the other hand, a mill input coal feed amount 29 is calculated by a multiplier 28 from the coal feeder motor rotation speed 26 and the coal feeder belt load 27. This mill input coal feed amount 29 cannot be immediately made into the amount of pulverized coal given to the boiler inlet. Needs to be compensated statically and dynamically. First, regarding static factors, it is necessary to consider the relationship shown in FIG. 5, in which the larger the coal feed command signal, the more the amount of coal fed at the boiler inlet increases. The mill load factor on the horizontal axis in FIG. 5 is equivalent to the coal feed command signal, and in fact, the coal feed command signal given to the thyristor 25 in FIG. 2 is in the form of the mill load factor. Incidentally, since the mill inlet coal feeding amount 29, which is the output of the multiplier 28 in FIG. 3, is the result of being controlled by the mill load factor, the signal 29 is equivalent to the mill load factor. Therefore, by correcting the signal 29 using the function shown in FIG. 5, the boiler inlet coal feeding amount can be obtained. To express the relationship shown in FIG. 5 in other words, this means that the greater the amount of coal fed to the mill, the greater the proportion of pulverized coal.

Next, looking at the dynamic factor, this is the time delay until the coal reaches the boiler from the coal feeder.
More specifically, as shown in Fig. 6, when the mill inlet coal feed amount (coal feed command signal 24) changes in a stepwise manner, the air differential pressure c at the mill inlet and outlet follows with a delay, and as a result, the conveyance The relationship is that the amount of pulverized coal changes. This relationship is used as a coal feeding command signal.
Expressing the equation between Q _CD and the amount of pulverized coal given to the boiler inlet is as shown in equation (1).

Q _C = K ₃・e ^-LS / 1 + K ₁ S + K ₂ S ²・Q _CD ... (1) Here, Q _CD : Coal feed amount command signal S: Laplace operator L: Dead time K ₁ ~ K ₃ : Constant Therefore, the relationship between equation (1) and FIG.
02, the boiler input pulverized coal amount B can be obtained. Next, the boiler input pulverized coal amount A and the boiler input pulverized coal amount B are matched and an adder 508 generates a deviation signal 512. Function generator 503
Then, appropriate correction is performed depending on the magnitude of the output of the deviation signal 512, and the signal D is calculated by the integrator 507 and matched with the boiler input pulverized coal amount A described above using the adder 509 to create the boiler input pulverized coal amount E. do. The above circuit makes it possible to accurately determine the amount of pulverized coal input to the boiler.

In the present invention, the signal A is high-speed and does not include an operation delay time, but it includes a temporal fluctuation factor. Although the signal B is accurate in terms of the amount of coal fed into the mill, there is a large delay in operation. Therefore signals A and B
The difference 512 includes errors due to temporal fluctuation factors and operation delays. Of these, by absorbing the transient fluctuations due to the operation delay with the integrator 507, only the temporal fluctuation factors can be extracted as the signal D and compensated.

According to the present invention, it is possible to detect pulverized coal input to a boiler, which has not been measured in the past. Furthermore, by incorporating this detection circuit into the control system, it becomes possible to improve the dynamic characteristic delay of the coal mill, and it becomes possible to cope with large load changes.

[Brief explanation of the drawing]

Figure 1 shows an example of the configuration of a coal mill, Figure 2 shows an example of the configuration of a coal mill.
The figure shows an example of the configuration of a coal feeder, FIG. 3 is a block diagram of a method for detecting the amount of pulverized coal input to a boiler according to the present invention, FIG. 4 shows a mill differential pressure-coal feed amount characteristic curve, and FIG. This figure shows a characteristic curve of the mill load factor and the amount of coal fed, and FIG. 6 shows the response characteristic of the mill differential pressure to the step change signal of the amount of coal fed. 501-504...Function generator, 28,506
... Multiplier, 508, 509 ... Adder, 507
...integrator.

Claims (1)

[Scope of Claims] 1. In a coal-fired power plant in which coal is made into pulverized coal by a coal mill and the pulverized coal is conveyed by primary air for conveyance and supplied to a boiler, the primary air for conveyance in the coal mill is The amount of pulverized coal input to the boiler, which is determined according to the differential pressure between the inlet and the outlet, and the amount of pulverized coal input to the boiler, which is determined from the amount of coal input into the coal mill, are determined, and the amount of pulverized coal input to the boiler is calculated according to the difference between the amounts of pulverized coal input to both boilers. A fuel amount detection method for a coal-fired power plant, characterized in that a correction value determined by the pressure difference is added to the boiler input pulverized coal amount determined according to the differential pressure to obtain an appropriate boiler input pulverized coal amount. 2. Coal-fired power according to claim 1, wherein the correction value determined according to the difference between the amounts of pulverized coal input to both the boilers is an integral value of the difference between the amounts of pulverized coal input to both the boilers. How to detect the amount of fuel in a plant. 3. In a coal-fired power plant where coal is made into pulverized coal by a coal mill and the pulverized coal is conveyed by primary conveying air and fed to a boiler, the differential pressure between the inlet and outlet of the primary conveying air in the coal mill. means for outputting a boiler input pulverized coal amount signal corresponding to the amount of coal input to the coal mill; means for outputting a boiler input pulverized coal amount signal corresponding to the amount of coal input to the coal mill; and a deviation signal between the two boiler input pulverized coal amount signals. a subtraction means for outputting a subtraction means; a correction means for inputting the deviation signal and outputting a correction signal for correcting a change over time in the boiler input pulverized coal amount signal according to the differential pressure; adding the correction signal to the signal;
1. A fuel amount detection device for a coal-fired power plant, comprising an addition means for outputting an appropriate boiler input pulverized coal amount signal. 4. A fuel amount detection device for a coal-fired power plant, wherein the correction means according to claim 3 is an integrator.