JPS6115355B2 - - Google Patents

Description

[Detailed Description of the Invention] This invention automatically controls the temperature and air inside the furnace during the firing process of a single furnace for the ceramic industry, which is used to bake ceramics, etc., thereby improving the firing yield and reducing the fuel consumption rate. This invention relates to the improvement of automatic control equipment for the purpose of.

To operate a single furnace for ceramics, which is generally used for firing ceramics, heavy oil or LPG (liquefied petroleum gas) is used as fuel, and after igniting the burner, the temperature is raised to around 900℃ in an oxidizing atmosphere (roasting process).
However, when the object to be heated becomes dry of soot, either send excessive fuel or reduce the amount of combustion air to create a reduction atmosphere, and raise the temperature to around 1200℃ (aggressive process). A firing method is used in which the product is aged, then heated to 1300°C in neutral (weakly oxidizing or slightly reducing) air (the simmering process), maintained for about an hour, and then extinguished. The most important and difficult of these processes is the aggressive reduction process mentioned above, which is carried out in the furnace at the temperature at which the ceramic glaze begins to melt, which is around 900℃ (varies depending on the type of firing). Reducing gaseous air such as CO (carbon monoxide) concentration
The timing of switching to a specific state such as VOL. 3.5% and H ₂ (hydrogen) concentration VOL. 2%, and the timing of increasing the temperature by approximately 300°C as described above in a state of incomplete combustion while keeping this reduction concentration constant. The furnace temperature and atmosphere are controlled for 4 to 5 hours (this also varies depending on the fired product). However, in the conventional program-based automatic control device, various measures have been taken to control the timing of reduction and firing switching, and although various measures have been taken to control the temperature, automatic control of the air inside the furnace Sample the internal gas and analyze and detect its CO concentration or _H2 concentration,
Opening and closing the flue damper depending on the difference from the desired concentration (for example, when the concentration is low, open the flue damper, weaken the draft in the furnace, and increase the concentration by reducing the amount of combustion air flowing into the furnace) ). In other words, this is simply a mixture ratio control of the gas component (CO or H ₂ ) generated by fuel combustion and air, and as a result of the fuel supply amount being controlled only by the temperature inside the kiln, the above gas component The absolute amount of air may be insufficient, and the desired concentration may not be obtained with just the amount of air supplied, and the opposite phenomenon to the above may occur, i.e., more fuel is consumed than necessary due to a timing difference between temperature control and concentration control. arise. For this reason, during the reduction firing process, the temperature control side of the program-based temperature and concentration automatic control device is switched to manual mode to maintain the reduction concentration constant, resulting in the consumption of more fuel than necessary and Not only does the yield of products drop due to sudden changes in internal temperature or variations in air quality, but also a drop in thermal efficiency due to wasteful use of fuel has a significant impact on high product costs, and improvements to this are strongly desired in the kiln industry. This is the current situation.

In view of the above-mentioned current situation, this invention improves the reduction firing process of the conventional program-type automatic control device. The so-called override method constantly compares the control deviation (difference in controller output with respect to the target) between the Through control, the reduction concentration is stabilized with the minimum amount of burning fuel consumed, and the quality and thermal efficiency are improved. In other words, in a kiln that burns fuel such as heavy oil and fires ceramics using a program that includes oxidation, reduction, and neutralization in one cycle, the fuel valve opening signal that controls the temperature inside the furnace and the smoke that controls the atmosphere inside the furnace are used. means for converting and comparing the flue damper opening signal into a required combustion fuel supply amount, selecting the signal with the larger supply amount, and selectively controlling the fuel valve opening; and the flue damper opening signal. means for continuously modifying the temperature increase program for the furnace temperature in accordance with the rise in furnace temperature caused by this control when controlling the fuel valve opening, and This invention relates to an automatic control device for a ceramic firing furnace configured to control the gas concentration to a reducing concentration.

This will be explained in detail below with reference to the drawings. Figure 1 is a block diagram of an embodiment of this invention using LPG as fuel.The LPG cylinder is vaporized by a liquefied gas vaporizer, and this LP gas is depressurized by a gas pressure regulator (1) to maintain a constant pressure. The gas is introduced into a burner 4 through an automatic gas amount control valve 2 and a stop valve 3, where it is combusted. When the fired products are loaded onto a trolley and put into the kiln, and the door is closed, combustion air is supplied from around the burner 4 by the draft of the flue. The draft is controlled by a damper 6 that opens and closes a window on the side of the flue using an automatic damper operator 7, but a forced exhaust fan 5 is also used to freely set and stabilize the draft. The temperature control system of this furnace usually uses a thermocouple 8 as the detection end, and inputs the detection signal Ti to the furnace temperature regulator 9, and the regulator 9 uses the signal Ti and the temperature program setting device 10.
The control deviation signal Sa is sent to the electro-pneumatic converter 12 via the high signal selector 11 (the operation of which will be described later). Here, the electrical signal Sc becomes the air signal At, which controls the gas flow valve 13 and the like to control the gas amount automatic control valve 2. Next, the air control system first extracts the air in the furnace at the gas extraction end 14 and passes it through the gas cooling device.
Input the detection signal Ci to the CO concentration regulator 15.
The controller 5 compares the signal Ci with the setting signal Cs of the CO concentration program setting device 16, and sends the control deviation signal Sd to the electro-pneumatic converter 17.
AC controls the damper automatic operating device 7. The forced exhaust fan No. 5 is used in combination to arbitrarily adjust and stabilize the draft. Next, the air exchanger 18 will be explained. Generally, the firing curve for ceramics requires switching between oxidizing, reducing, and neutral air, as shown in Figure 2. In order to automatically perform this switching, the air air switch 18 can be set to any set voltage. When the voltage of the input signal Ti reaches the built-in voltage, the following signals are output.
When the temperature is T ₀ , T ₁ , T ₂ , T ₃ , and T ₄ in Figure 2, each signal is transmitted and the temperature increase rate is changed. S ₂ is a signal to the CO concentration program setting device 16, and Ti is the second signal.
It is transmitted at times T ₁ , T ₂ , T ₃ , and T ₄ in the diagram to change the damper opening program. Air changer 18
The temperature and CO concentration program setters 10 and 16, which are activated by the output signals of S ₁ and S ₂ , are a type of timer, and are activated by any pulse signal during the set time.
Ts and Cs are sent to the pulse motors of the respective regulators 9 and 15, and the adjustment set values are changed according to the program. The above configuration and operation are the basics of the conventional program-type automatic control device.As mentioned above, the opening degree V of the two gas amount automatic control valves in Fig. On the other hand, the opening degree D of the flue damper 6 is operated only by the air control system, and shows the D curve in FIG. 2. In this conventional device, the type of fired product,
Depending on a number of factors such as the shape and the condition of the kiln, the opening degree D of the flue damper alone will cause the difference between ΔH ₁ from the time H ₁ when reduction begins to H ₂ , as shown in the CO concentration characteristic C in Figure 2. A slow rise may occur, which results in a lack of the required reduction concentration, making it impossible to completely reduce the fired product. The purpose of this invention is to improve this drawback, and the block 1 shown in FIG.
Reference numerals 9, 20, 21, and 22 are configurations showing the characteristics of an embodiment of the device of the present invention, and 19 is a balanced amplifier that is turned on and off by the output signal of the monitor switch 20.
When it is OFF, when it is ON, it is either one of the two input signals.
20 has a function similar to a so-called regulator that outputs a correction value that makes one signal equal to the reference value and other signals equal to that reference value. The monitor switch 19 speeds up the output signal when a condition is met, and the signal calculator 21 speeds up the input signal (for example, 4 to 4).
20mADC) converts the ratio, characteristics or bias value, etc. and outputs it. 22 is a signal limiter. Input signals below the set voltage are output as they are, and input signals above that are set to the set voltage as the output voltage. It is. Next, the operation of this embodiment device will be explained first.
This will be explained with reference to FIG. During the oxidation firing control shown in FIG. 2, the block ₁₈ shown in FIG. Operate. Also, even during reduction firing control, when the CO concentration Ci is stable at the predetermined concentration Cs (as after H ₂ of the C characteristic in Fig. 2), the output signal Sd of the signal limiter 22 and the furnace temperature regulator The relationship between the output signal Sa of the output signal 9 and the output signal Sa is such that Sd<Sa, and neither the monitor switch 20 nor the balance amplifier 19 outputs a signal. Therefore, as with conventional program control, the control deviation signal of the furnace temperature controller 9
Sa remains as Sc and controls the gas amount control valve 2, while the damper operating device 7 also receives its control deviation signal Sd.
Each of them has its own control system. However, like the time of ΔH ₁ in Figure 2,
If the CO concentration C rises poorly or the amount of combustion fuel decreases abnormally during reduction firing, the detection signal Ci of the CO concentration detector 14 becomes the set value signal of the regulator 15.
When the control deviation signal Sd becomes smaller than Cs and gradually becomes larger, the signal calculator 21 outputs an output signal.
The output signal Sb until the limiter 22 limits Sb'
is input to the high signal selector 11. 11 compares the two input signals Sa and Sb and outputs the higher signal. If Sb>Sa, the output signal Sc becomes Sb, and the gas flow control valve 2 immediately closes the furnace. It is controlled by the CO concentration in the furnace, regardless of the internal temperature. This is the first point of this invention, and the monitor switch 20 operates under the condition of Sb>Sa, and sends its output signal Sm to the balance amplifier 19, which, as described above, receives the input signal Ti. Signal S ₄ to correct the difference from Ts = Ti−
Ts is transmitted to the block 10, which uses this _S4 to set its output signal as Ts', and the regulator 9
The second requirement of the present invention is a series of control operations in which the signal is sent to the balance amplifier 19 and fed back to the balance amplifier 19. It goes without saying that even during this control operation, the air control system is still controlled by the CO concentration regulator 15 as described above. How the in-furnace air and the in-furnace temperature are controlled by the above-mentioned override control will be explained with reference to FIG. 2. First, the gas valve opening degree V
The CO concentration C rapidly reaches the desired concentration as C' in proportion to the increase in the amount of combustion fuel. Furthermore, as mentioned above, the temperature T in the furnace increases as the fuel increases, reaching a temperature rise rate of T', but as mentioned above, the temperature program setting device 10 follows this temperature rise rate and maintains Ts'. A signal is issued, and the regulator 9 continues to control with a temperature gradient of T'. After this override control is carried out for ΔH ₁ , at time H ₂ the desired concentration is reached, Ci≈Cs, and the control deviation signal Sd decreases, and the two signals Sb and Sa to the monitor switch 20 are
The relationship becomes the original Sa<Sb, and the monitor switch 20
The signal Sm from is stopped, and the balance amplifier 19 also stops.
It turns OFF and returns to normal reduction firing control.
However, the furnace temperature program has a characteristic that moves parallel to the original T from the _H2 point, as shown by T'' in Figure 2, and the temperature _T3 at which switching to neutral firing is _H3 is faster than _H3 by _{ΔH3 .} Also, the signal limiter 22
When the signal Sb increases abnormally, the opening degree of the gas valve 2 is made larger than necessary, which serves to prevent wasted fuel and a sudden rise in firing temperature during reduction firing.
As mentioned above, by appropriately limiting the signal Sb′, the signal Sb
shall be.

The structure and operation of one embodiment of the device of the present invention have been described above, and another embodiment of the device will be explained with reference to FIG. Reference numeral 23 denotes a timer that changes the damper opening degree step by step at each time with a value preset by the flue damper opening degree setting device, and all other devices are configured with the same symbols as in FIG. 1. The operation of this device is 15
The damper opening degree is not controlled by continuous operation of the CO concentration regulator, but the setting device 23 starts with the signal S ₅ of the air switch 18, and the setting device 23 starts as shown above in stages (or continuously). The damper opening degree is set, and its basic program is similar to the D characteristic shown in FIG. On the other hand, the control system for the gas valve 2 of this device is configured to always perform override control of temperature and air, but as explained above, air control is mainly performed during reduction firing, which is an important process. The same thing applies. The difference from Figure 1 is 1.
The control deviation signal of the CO concentration regulator in step 5 is shown in step 2 in Figure 1.
The point is that the Sb signal is used to directly control the gas valve 2 with the same characteristics as the Sa signal without going through the signal calculator 1 and the signal limiter 22. In this case, the controllers 9 and 1
5 is equipped with a signal limiting function to prevent excessive output signals and to prevent fuel wastage. Compared to the above-mentioned embodiments, this device does not require a signal calculator and can be manufactured at low cost, and can be said to be a device that readily meets the gist of the present invention.
Since the present invention is constructed as described above, the air flow control of the conventional program-type automatic control device of the ceramic firing furnace is biased to the control of the mixture ratio of gas components and air simply by opening and closing the flue damper. Therefore, during reduction firing control, it takes time to bring the CO concentration in the furnace air to the desired concentration, and abnormally low concentrations occur, which reduces the yield of fired products. To prevent this, we temporarily switched to manual control to eliminate the disadvantage of consuming more fuel than necessary, and fully automatic control stabilized the reduction firing atmosphere and improved product quality. This device can control combustion with the minimum amount of fuel consumed while suppressing a sudden rise in temperature, and can shorten the reduction firing program, resulting in an apparatus that can improve thermal efficiency.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the configuration of one embodiment of this invention, Fig. 2 is a diagram explaining the basic program for firing ceramics and the effects of the device of this invention, and Fig. 3 is the configuration of another embodiment of the device of this invention. It is a block diagram. 2... Gas amount automatic control valve, 4... Burner, 5...
... Forced ventilation fan, 6... Flue damper, 7... Flue damper operating section, 8... Furnace temperature detection end (thermocouple),
14...Furnace gas extraction end (gas sampling probe), Ti...Furnace temperature detection value, (controlled value), Ts
...Temperature setting value, Ci...Furnace CO concentration detection value, Cs...
...CO concentration set value, Sa'...Temperature control deviation value, Sd
...CO concentration control deviation value, Sb...The above Sd signal converted to the control deviation value of gas valve 2, Sm...Monitor switch output signal, _S4 ...Signal corresponding to the difference between Ti and Ts , Ts'... Revised temperature setting value, ΔH ₁ ... CO concentration shortage period immediately after switching to reduction firing, ΔH ₃ ... Shortening time of reduction firing time, C',
V', T'...Characteristic curves of CO concentration, gas valve opening, and furnace temperature during override control.

Claims (1)

[Claims] 1 Burning fuel such as heavy oil to oxidize and oxidize ceramics.
In a kiln that fires with a program that has one cycle of reduction and neutralization, the fuel valve opening signal that controls the temperature inside the furnace and the flue damper opening signal that controls the air inside the furnace are necessary for supplying fuel for combustion. a means for converting and comparing the signals into supply amounts, selecting the signal with a larger supply amount, and selectively controlling the fuel valve opening; and when the flue damper opening signal controls the fuel valve opening; means for continuously modifying the heating program for the temperature inside the furnace in accordance with the rise in temperature inside the furnace due to the increase in the temperature inside the furnace, and the gas concentration of the air during the reduction firing is controlled to the reduction concentration. Automatic control device for ceramic firing furnace.