JPH0116926Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a furnace draft control device that appropriately controls the draft in a furnace such as a boiler.

In a general balanced draft boiler, if the pressure inside the furnace rises above atmospheric pressure, there is a danger that high-temperature gas will blow out from inside the furnace, and if the pressure inside the furnace decreases abnormally, External atmospheric pressure may cause damage to the furnace walls, flue, etc. For this reason, furnace draft control is required to maintain the pressure within the furnace at an appropriate value and minimize fluctuations in the draft within the furnace. Conventionally, furnace draft control for balanced draft boilers has been performed by detecting the furnace draft and adjusting the opening degree of the induced draft fan (hereinafter referred to as IDF) inlet damper or vane based on the detected value. . This will be explained with reference to the diagram.

Figure 1 is a flue duct system diagram of a balanced draft boiler. In the figure, 1 is a boiler furnace, and 2 is a forced draft fan (hereinafter referred to as FDF) that supplies combustion air to the boiler furnace 1.
It is called. ) 3 is an inlet damper or vane (hereinafter referred to as an inlet damper) that adjusts the ventilation flow rate of the FDF 2, 4 is an air preheater that preheats the combustion air pushed in from the FDF 2, 5 is an air passage, and 6 is a supply This is a burner wind box that collects the combustion air and sends it from the burner to the boiler furnace. 8 is a reheater, 9 is a superheater, and 10 is an energy saver. Exhaust gas discharged from the economizer 10 is discharged into the atmosphere through a flue 12 via a denitrification device 13, an air preheater 4, an electrostatic precipitator 14, and a desulfurization device 15. Reference numeral 17 indicates an IDF that induces this exhaust gas, and reference numeral 18 indicates an IDF inlet damper or vane (hereinafter referred to as an inlet damper) that is provided at a stage before the IDF 17 and adjusts the ventilation flow rate. 19 is a furnace draft detector that detects the pressure inside the boiler furnace 1.

FIG. 2 is a block diagram of a conventional furnace draft control device. In the figure, 20 is an opening command signal that commands the opening of the FDF inlet damper 3, and 21 is a signal with a predetermined value corresponding to the value of the opening command signal 20 upon input of the opening command signal 20. It is a function generator that outputs. 22 is a furnace draft detector 19
The furnace draft signal 23 is a furnace draft setting device that sets the furnace draft to a predetermined value. 24 is an arithmetic unit which inputs the furnace draft signal 22 and the value set in the furnace draft setter 23 and calculates the deviation between the two, and 25 is a proportional integrator which proportionally integrates the deviation signal from the arithmetic unit 24. 26
27 is an adder that adds the output signal of the proportional integrator 25 and the output signal of the function generator 21, and 27 is a damper control drive that controls the opening degree of the IDF inlet damper 18 based on the output signal of the adder 26.

The draft in the furnace is determined by comparing the value detected by the furnace draft detector 19 with the value determined and set in the furnace draft setting device 23, calculating the deviation between the two by the calculator 24, and calculating the value according to this deviation. It is controlled by adjusting the opening degree of the IDF inlet damper 18. In this case, the draft inside the furnace is naturally
Since it depends on the amount of ventilation of the FDF,
In order to take into account the value corresponding to the FDF inlet damper opening degree command signal as a preceding value, this value is added to the previously mentioned deviation by the adder 26. As a result, if the pressure inside the boiler furnace 1 increases,
The opening degree of the IDF inlet damper 18 is increased, and when the pressure decreases, the opening degree of the IDF inlet damper 18 is controlled to be decreased, thereby maintaining the furnace pressure of the boiler furnace 1 at an appropriate value.

By the way, in the actual operation of a balanced draft boiler, for example, when an excessive draft fluctuation suddenly occurs due to a failure in the power transmission system or a failure in the boiler, turbine, etc. (when the load change becomes large due to MFT, runback, etc.) There is. In such a case, the furnace draft control device shown in FIG.
Due to the response performance of the damper control drive 27, etc., the control of the IDF inlet damper 18 cannot sufficiently follow the draft fluctuation, and therefore,
There was a risk of damage to the boiler furnace, flue, etc. In order to prevent this danger, a pressure relief device has been proposed that opens a door directly connecting the boiler furnace to the atmosphere when the deviation of the furnace draft is large, thereby reducing fluctuations in the furnace draft. However, this device cannot be expected to be as effective because the volume of the furnace is too large.

The present invention was devised in view of the above circumstances, and its purpose is to eliminate the above-mentioned drawbacks of the conventional methods and to solve the problem of excessive and rapid furnace draft fluctuations.
An object of the present invention is to provide a furnace draft control device that can sufficiently follow and control an inlet flow rate adjusting device.

To achieve this objective, the present invention detects the IDF inlet draft, also determines the IDF inlet draft generated in response to the boiler input command signal, and combines this determined IDF inlet draft with the detected actual IDF inlet draft.
The deviation from the IDF inlet draft is calculated, this deviation is added to the deviation between the detected furnace draft and the set furnace draft, and the signal obtained by this addition is used as a signal to control the flow rate adjustment device at the IDF inlet. It is characterized by being used as a.

The present invention will be explained below based on the embodiment shown in FIGS. 3 and 4.

FIG. 3 is a block diagram of a furnace draft control device according to a first embodiment of the present invention. In the figure, parts that are the same as those shown in FIG. 2 are given the same reference numerals, and explanations thereof will be omitted. Note that in this embodiment, the arithmetic unit 24 is referred to as a first arithmetic unit. 28S is an IDF inlet draft detector 28 provided in this embodiment.
Figure 1 shows the IDF inlet draft signal detected at (shown in Figure 1). Further, 29 is a boiler input command signal based on the boiler fuel amount, etc., and 30 is a function generator in which is set an IDF inlet draft that appears in response to the boiler input command when the boiler input command is received. In response to the input of the command signal 29, a value corresponding to the input signal is output. 31 is the detected IDF entrance draft signal 28
This is a second computing unit that computes the deviation between S and the output signal of the function generator 30. 32 is an adder that adds the output signal of the proportional integrator 25 and the output signal of the second arithmetic unit 31; 33 is a proportional integrator that proportionally integrates the output signal of the adder 32; and 34 is the output of the function generator 21. This is an adder that adds the signal and the output signal of the proportional integrator 33.

Next, the operation of this embodiment will be explained. The signal 22 detected by the furnace draft detector 19 is compared with the set value (target value) set in the furnace draft setting device 23 to calculate the deviation between the two, and also corresponds to the FDF inlet damper opening command signal 20. The control mode in which the value is added to the deviation as the preceding value is the same as in the conventional example described above. In this example,
Furthermore, the IDF entrance draft is added to the deviation as a preceding value. That is, the deviation between the IDF entrance draft signal 28S and the output signal of the function generator 30 is calculated by the second calculation unit 31, and this deviation is used as the preceding value.

Now, if we look at the balanced draft boiler shown in Fig. 1, in such a boiler, the boiler furnace 1
The distance from the IDF 17 to the IDF 17 is very long, and as shown in the figure, a denitration device 13, an air preheater 4, an electric precipitator 14, a desulfurization device 15, etc. are interposed therebetween. Therefore, the resistance experienced by the exhaust gases passing through the flue is also increased, and there is a considerable time delay between the furnace draft and the IDF inlet draft. Therefore, even if a sudden and excessive fluctuation occurs in the furnace draft, the fluctuation does not immediately appear as the IDF inlet draft, and the IDF inlet draft remains in the state before the fluctuation. For example, when reducing the load by runback or the like, the amount of fuel supplied is rapidly reduced, so the amount of combustion gas in the boiler furnace 1 is rapidly reduced, and as a result, the pressure inside the furnace suddenly becomes negative, causing the damage described above. There is a risk of an accident. However, when the pressure inside the furnace becomes negative,
The IDF inlet draft shows a pressure that has not yet reached negative pressure, and negative pressure will only appear after a certain period of time.

Therefore, returning to the apparatus shown in FIG. 3 again, the IDF entrance draft signal 28S indicates the actual IDF entrance draft (IDF entrance draft before variation).
On the other hand, since the output signal of the function generator 30 has a value corresponding to the boiler input command signal, it indicates the IDF inlet draft that appears after a certain period of time. Therefore, using the previous example, the boiler input command signal 29 suddenly decreases at the same time as a command to reduce the fuel supply amount by runback or the like is issued.
Correspondingly, the output signal of the function generator 30 also decreases rapidly. However, since the IDF entrance draft is still in the state before the command, the IDF entrance draft signal 28
S has a large value. Therefore, the deviation calculated by the second calculating unit 31 becomes a very large value almost at the same time as the command to narrow down the fuel supply amount is issued. This deviation is added in the adder 32 to a signal obtained by proportionally integrating the deviation between the furnace draft and the target value at that time, and this addition is added to the IDF inlet damper 1.
Works in the direction of closing 8. That is, the second arithmetic unit 31
The signal output from the furnace is a signal that is output almost at the same time as the command to reduce the fuel supply amount is issued, in other words, before the pressure inside the boiler furnace 1 suddenly becomes negative pressure, and the signal is output from the furnace draft. It serves as a signal as a leading value that indicates the magnitude of fluctuation in . The same applies if the furnace draft suddenly rises for some reason. Since the output signal from the adder 32 is a signal added as a preceding value according to the magnitude of the furnace draft fluctuation, it is possible to control the IDF inlet damper 18 in advance in preparation for the furnace draft fluctuation. can.

In this way, in this embodiment, the deviation between the IDF inlet draft signal and the IDF inlet draft signal corresponding to the boiler input command signal is used as the advance value signal, so that excessive and rapid furnace draft fluctuations can be prevented. Also, the IDF inlet damper can be sufficiently tracked and controlled, and the furnace draft can be maintained appropriately.

FIG. 4 is a block diagram of a furnace draft control device according to a second embodiment of the present invention. In the figure, the same parts as in FIG. 3 are given the same reference numerals, and their explanation will be omitted. 35 is a multiplier that multiplies the deviation signal output from the second arithmetic unit 31 by a predetermined coefficient K. 3
6 is an adder, which applies an FDF inlet damper opening degree command to a signal obtained by proportional integration processing of the deviation between the furnace draft signal 22 calculated by the first calculation unit 24 and the target value set in the furnace draft setting device 23. The preceding value signal output from the function generator 21 based on the signal 20 and the preceding value signal output from the multiplier 35 are added. By appropriately selecting the coefficient K of the multiplier 35, the output signal of the second arithmetic unit can be
The degree of influence on the control signal for the IDF inlet damper 18 can be adjusted.

In this way, in this embodiment, the deviation between the IDF inlet draft signal and the IDF inlet draft signal corresponding to the boiler input command signal is used as the advance value signal, so it has the same effect as the previous embodiment, and Since the deviation can be multiplied by an appropriate coefficient, the degree of influence of this deviation on the control signal can be adjusted to an appropriate magnitude.

As described above, in the present invention, the IDF inlet draft is detected, the IDF inlet draft generated in response to the boiler input command signal is determined, and the detected IDF inlet draft is combined with the detected IDF inlet draft.
The deviation from the inlet draft is calculated, this deviation is used as a leading value, and added to the deviation between the detected furnace draft and the set furnace draft, and the signal obtained by this addition is used as the IDF inlet flow rate regulator control signal. Since it is used, the IDF inlet flow rate adjustment device can be sufficiently controlled to follow even in the case of excessive and rapid fluctuations in the furnace draft, and the furnace draft can be maintained appropriately.

[Brief explanation of drawings]

Fig. 1 is a flue duct system diagram of a balanced draft boiler, Fig. 2 is a block diagram of a conventional furnace draft control system, and Figs.
FIG. 2 is a block diagram of a furnace draft control device according to an embodiment and a second embodiment. 17...IDF, 18...IDF entrance damper, 19
...Furnace draft detector, 22...Furnace draft detection signal, 23...Furnace draft setting device, 24...
...First arithmetic unit, 25, 33...Proportional integrator, 2
7...Damper control drive, 28...
IDF inlet draft detector, 28S...IDF inlet draft signal, 29...Boiler input command signal, 30
...Function generator, 31...Second arithmetic unit, 32,
34, 36...adder, 35...multiplier.

Claims (1)

[Scope of utility model registration request] a first detection device that detects a furnace draft; a first calculation means that calculates a deviation between a value detected by the first detection device and a predetermined furnace draft setting value; and a control means for controlling the flow rate adjustment device of the induced draft fan based on the deviation obtained by the means, the furnace draft control device includes a second controller for detecting the induced draft inlet draft.
a detection device, means for determining an induced draft inlet draft in response to a boiler input command signal, and an induced draft inlet draft determined by the means and an induced draft inlet draft detected by the second detection device. a second calculation means for calculating the deviation between the
A furnace draft control device comprising: an addition means for adding the deviation obtained by the second calculation means to the deviation obtained by the first calculation means.