JPS59229175A - Method of controlling heating of melting furnace, etc. - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a g0 heating method for a melting furnace, etc., and particularly to a heating control method for an aluminum melting furnace.

In conventional aluminum melting furnaces (reverberatory furnaces), the furnace temperature or exhaust gas temperature and molten metal temperature are controlled by the mass of one or several heavy oil burners or LNG burners. At this time, until molten aluminum is formed in the melting furnace, it is controlled by the furnace temperature or exhaust gas temperature, and after the molten aluminum is formed, it is controlled by the molten metal temperature (see Figure 1).

In this case, the control is based on PID (proportional-integral-derivative) in which the exhaust gas temperature target value and the molten metal temperature target value are set constant.
Control is performed conventionally, but it takes a considerable amount of time to switch between the control and operating systems, and the response of the exhaust gas temperature to the switching is slow, making it impossible to accurately follow the temperature rise diagram that follows the set operating pattern, resulting in hunting. This made effective control difficult. Furthermore, conventional aluminum melting furnaces that operate at a high combustion rate from the initial stage of heating have the following problems.

ti) Aluminum removed immediately after being charged into the melting furnace absorbs radiant heat only on the surface, and the heat absorption efficiency is poor.
The heat from the high-combustion heavy oil burner or LNG burner is used exclusively to raise the exhaust gas temperature, resulting in large heat losses to the exhaust gas.

(2) Because the aluminum removed material is rapidly heated with a burner, the aluminum removed material burns without melting.
Oxidation loss increases.

(3) The heat transfer efficiency is adversely affected by the heat insulation effect of the oxides generated in the melting furnace.

In view of the above-mentioned problems in the prior art, the present applicant has proposed a method for controlling the heating of a melting furnace, etc. equipped with a plurality of combustion devices, in a patent application dated the same date as the present application, which describes Selecting an operation pattern of the combustion device that provides combustion that minimizes the rate of increase in exhaust gas temperature, that is, optimal combustion when the amount of heat generated is constant, and causing the combustion device to burn for a predetermined period of time in the selected operation pattern, We propose a heating control method characterized by minimizing heat loss due to exhaust gas and avoiding rapid heating of the material to be melted, which is the charging material of the melting furnace, from a low temperature. This prevents oxidation loss and achieves optimal thermal efficiency. However, even if this method is carried out until a predetermined exhaust gas temperature is reached, for example near the aluminum hot water temperature target value, and then the switch is made to PID control and rapid heating is performed,
There is a problem in that the total time required for melting becomes long.

By the way, in the case of melting metals such as aluminum, even if only the surface is heated at the beginning and there is a risk of oxidation, as the temperature rises the surface of the material to be melted will melt, so even if heated at a higher speed, oxidation will not occur. The possibility of loss will be reduced.

Therefore, it is desirable for operation to solve the problems of the prior art described above and at the same time to shorten the melting process itself.

In order to achieve these objectives, in the heating control method according to the present invention, the total number of devices in the combustion device is increased stepwise in at least two or more stages, and in each stage of combustion, the total number of devices in the combustion device is increased. A combustion device operation pattern that minimizes the rate of increase in combustion exhaust gas temperature under a constant state is selected, and the combustion device is operated for a predetermined period of time in accordance with the selected operation pattern. The reason for selecting such an operation pattern is that all the combustion equipment is the same and the rate of increase in exhaust gas temperature is the lowest, which means that the rate of heat absorption into the aluminum removed material is the highest and can reduce exhaust gas loss. Because it means.

Furthermore, according to a preferred feature of the present invention, the stepwise increase in all the units of the combustion device while carrying out the operation pattern selection step and the combustion step according to the selected operation pattern in each step is such that the exhaust gas temperature is approximately equal to the molten metal. This is done until the target value is reached. /8 When the hot water temperature is close to the target value, that is, the set value, the outer surface of the charging material is completely melted, and there is no need to worry about oxidation loss of the charging material even if it is rapidly heated by controlling the exhaust gas temperature set value. It is from.

In other words, the present invention prevents oxidation loss of the material to be melted by performing low combustion when the temperature of the furnace body is low, and maintains melting efficiency by increasing combustion in stages as the surface of the H material to be melted melts. It is something.

Preferred embodiments of the present invention will now be described with reference to the accompanying drawings.

FIG. 2 is a schematic diagram of the melting furnace. Burner (reference number 1
~8) are installed in the melting furnace, four each facing each other. Burner 1.3.6.8 has a large capacity (for example, LNG 150 Nrr/hour), and burner 2.4.5.7 has a small capacity (for example, LNG 5ON/hour).
d/waiting time. Burners 1 to 8 are all L
It is an ultra-high-speed burner that uses NG or heavy oil as fuel.

Incidentally, with regard to the application of the present invention, the type of burner and the fuel do not matter. Also, various choices can be made regarding the shape of the melting furnace and the arrangement of the burners.

The aluminum plate is charged into the melting furnace through the material charging door 9, while the gas inside the furnace is exhausted through the flue 10. Further, a thermocouple 11 is installed inside the melting furnace and the flue, and a signal from the thermocouple 11 is input to a control device 12.

In this example, three adjacent large capacity burners 1.3
．． Combination of 6.8 and small capacity burner 2.4.5.7,
That is, burners 1, 2.3, 4.5, 6.7, and 8 constitute four combustion devices.

The control device 12 operates to select one of two types of mass, large and small, for each combustion device. The control device 12 is equipped with arithmetic functions such as a sequencer, a microcomputer, a minicomputer, etc., and controls the operation pattern of the l/'A baking apparatus.

According to the present invention, until exhaust gas temperature set value control is performed,
That is, the heating period of the material until the exhaust gas temperature approaches the set temperature of the molten metal is divided into at least two stages, and the total charge of the combustion device is increased in stages. - As an example, the heating control method of the present invention will be explained in more detail in the case where the heating period until exhaust gas temperature set value control is divided into three stages. Table 1 shows the mass of the combustion device in this case.

Table 1 After loading the painted aluminum into the melting furnace through the door 9, before carrying out the first stage combustion, the initial combustion period is 5 to 10 minutes. The furnace is heated according to the operating pattern of two sets of small combustion. This allows for an appropriate rise in furnace temperature and avoids rapid changes in exhaust gas temperature at the beginning.

Next, the first stage of heating is performed, and in this heating method, four (4C1-4) operation patterns (a) to (d) are shown. and small represent the large combustion and small combustion of the combustion device, respectively.

There are four operating patterns (a) to (a) for such a combustion device.
d) for an appropriate period of time while keeping the total loading of the combustion device constant;
For example, change the settings every 2 minutes and execute them all. At this time 2
The temperature difference between the exhaust gas temperature at the beginning and end of a minute is calculated to find the rate of increase in exhaust gas temperature for each driving pattern. The reason why the time is set at 2 minutes is that the control motor takes about 30 seconds to switch between large and small levels, which is a reasonable time considering the responsiveness of the exhaust gas temperature.

Based on the rate of increase in exhaust gas temperature determined in this way, the operation pattern of the combustion device that minimizes the rate of increase is selected from among (a) to (d). The furnace is heated for a suitable period of time, e.g. 20-30 minutes, according to the operating pattern of the combustion equipment selected.

Next, switch to the second stage of operation.

As is clear from Table 1, this second stage heating is a combination of two sets of combustion device fire combustion and two sets of small combustion. In such a heating method, there are six ways (
4C2=6) driving patterns (a) to (f) are possible. In the second stage of operation, as in the first stage, the combustion equipment operation pattern that minimizes the rate of increase in exhaust gas temperature is selected.
Select from figures (a) to (f).

In other words, there are six operation patterns (a) to (f) of the combustion device.
) are all carried out by keeping the total charge of the combustion device constant and changing it for an appropriate period of time, for example, every two minutes, to find the rate of increase in exhaust gas temperature in each operation pattern. As in the first stage, the furnace is heated for a suitable period of time, for example 20 to 30 minutes, according to the combustion device operating pattern selected.

Finally, switch to the third stage of operation. As is clear from Table 1, this third stage heating is a combination of three sets of combustion device fire combustion and one set of small combustion. In this heating method, four (4C3=4) operation patterns (a) to (d) are possible as shown in Fig. 5. In the third stage of operation, the first and second As in the fifth stage, the combustion equipment operation pattern that minimizes the rate of increase in exhaust gas temperature is
Select from figures (a) to (d).

In other words, there are four operating patterns (a) to (d) of the combustion device.
) are all carried out by keeping the total charge of the combustion device constant and changing it for an appropriate period of time, for example, every two minutes, to find the rate of increase in exhaust gas temperature in each operation pattern. As in the first and second stages, the furnace is heated for a suitable period of time, for example 20 to 30 minutes, according to the selected operating pattern of the combustion equipment.

After the optimum mass combustion in the third stage, the control is switched to exhaust gas temperature set value control, and after the exhaust gas temperature control period has elapsed, hot water temperature control is performed.

FIG. 6 shows a time-temperature diagram of a heating control method for an aluminum melting furnace according to another embodiment of the present invention.

From the start of the melting furnace operation, heating is performed at low combustion rate for a period of time.
After the time T0 has elapsed, the mass is increased and the time (T1+T2
), the mass is kept constant. Immediately after this increase, operation is performed in the optimum operating pattern according to the selection process detailed above, and after time T1 has elapsed, a combustion process is performed again in the optimum pattern selected according to the selection process. After these times T2 have elapsed,
Performing a second stage mass increase according to the present invention, a selection step,
The combustion process in this optimum operation pattern is repeated at the beginning of the increase in mass and after the elapse of time T3. Therefore time (
After T3+T4), that is, when the exhaust gas approaches a predetermined value near the hot water temperature set value, the heating control according to the present invention is terminated, and rapid heating is performed with the exhaust gas temperature target value constant. When the exhaust gas temperature reaches the target set value, the burner is controlled on and off to maintain this set value. Furthermore, when the temperature of the material to be melted reaches the set value (after time T5 has elapsed), the burner is controlled on and off to maintain the water temperature at this set value to ensure complete melting.

As explained above, by following the controlled heating method for a melting furnace according to the present invention, it is possible to reduce exhaust gas loss and oxidation loss at the initial stage of aluminum removal and melting, and to maintain a high level of melting efficiency.

Although the present invention has been described for the case where it is applied to an aluminum melting furnace, it is clear that it can also be applied to a melting furnace (for iron, glass, etc.) using several burners and an incinerator.

[Brief explanation of drawings]

Figure 1 is a graph showing the melting furnace temperature and burner mass according to the conventional heating method, Figure 2 is a schematic diagram of the melting furnace, Figure 3 is a diagram showing the operation pattern of the first stage combustion equipment, FIG. 4 is a diagram showing the operation pattern of the second stage combustion device, FIG. 5 is a diagram showing the operation pattern of the third stage combustion device, and FIG. 6 is a diagram showing the heating of the melting furnace according to one embodiment of the present invention. Figure 3 shows a time-temperature diagram of the control. (Main reference numbers) 1-817. Burner, 901. Material charging door, 10,... Melting furnace flue. 11. ,,,,Thermocouple, 12,,,,,Control device, Applicant: Sumitomo Light Metal Industries Co., Ltd. Agent Patent attorney: Arai Noise stoppage Figure 1 Figure 2 Figure 3 Figure 4 (a) (b) (c ) (d) (e) (f) 6th mouth time

Claims (1)

[Scope of Claims] (1) A method for controlling heating of a melting furnace, etc. equipped with a plurality of combustion devices, wherein all of the combustion devices are
Selecting an operation pattern of the combustion device that provides combustion that minimizes the rate of increase in combustion exhaust gas temperature with all devices in the combustion device being kept constant during each stage of combustion. A heating control method for a melting furnace, etc., characterized in that the combustion device is caused to burn for a predetermined period of time according to the selected operation pattern. (2. The heating control method for a melting furnace, etc. as set forth in claim 1, wherein the operation turn selection step changes the operation pattern of the combustion device at predetermined time intervals, and at the start of each operation pattern. A heating control method for a melting furnace, etc., characterized in that it is carried out by determining the difference in exhaust gas temperature between and at the end, calculating the difference in the determined exhaust gas temperature, and thereby determining the rate of increase in exhaust gas temperature. (3 ) A heating control method for a melting furnace, etc., as set forth in claim 1, characterized in that all of the combustion devices described above are increased in stages until the exhaust gas temperature approaches a predetermined temperature. (4) A heating control method for a melting furnace, etc. according to claim 3, characterized in that the predetermined temperature is a target temperature of hot water for melting interest. (5) A heating control method for a melting furnace, etc. according to claim 1, wherein in any step of increasing the total number of the combustion devices in stages. A heating control method for a melting furnace, etc., characterized in that the operation pattern selection step and the combustion step according to the selected operation pattern are repeatedly performed.