JP5276834B2 - Metal melting and holding furnace and operating method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To resolve disadvantages of an indirect heating type metal melting holding furnace, such as a low melting speed and low heat efficiency, and to prevent waste of fuel by reducing variation of the temperature in the furnace. <P>SOLUTION: A molten metal temperature T1 in a crucible 1 of a metal melting holding furnace body is measured by a first temperature sensor 4, an temperature T2 inside of the furnace body is measured by a second temperature sensor 6, a target value A of the molten metal temperature T1 is set to a first temperature adjuster 5, a measured value of the molten metal temperature T1 is input to the same, a target value B of the temperature T2 in the furnace is output to a second temperature adjuster 7, a measured value of the temperature T2 in the furnace is input to the second temperature adjuster 7, a control signal for adjusting a fuel supply amount and an oxidizing agent supply amount is output to a burner 3 from the second temperature adjuster 7, and the fuel supply amount and the oxidizing agent supply amount to the burner 3 are adjusted on the basis of the control signal. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to an indirect heating type metal melting and holding furnace that melts a metal material such as an ingot such as an aluminum alloy, a zinc alloy, or a magnesium alloy and temporarily stores the molten metal while maintaining a molten metal state, and a method of operating the same. The heat energy required for melting and holding the molten metal can be reduced.

This type of metal melting and holding furnace includes a direct heating furnace and an indirect heating furnace.
FIG. 5 shows an example of a conventional indirect heating furnace.
In this indirect heating furnace, a metal ingot is melted to form a molten metal, a crucible 1 for storing the molten metal while keeping the molten state, a furnace body 2 surrounding the crucible 1, and a crucible 1 provided at the bottom of the furnace body 2. Is generally composed of a burner 3 for heating from the outside.

  In such an indirect heating furnace, since the molten metal is not directly exposed to the flame of the burner 3, the molten metal is less oxidized and lost as a metal oxide, and the molten metal quality is excellent. On the other hand, since it is indirect heating, it has been pointed out that the dissolution rate is low and the thermal efficiency is low.

That is, in the conventional melting and holding furnace, when the molten metal temperature decreases, this is detected by a temperature sensor, and the fuel supply amount and the oxidant supply amount to the burner are controlled on and off based on this detection signal. In the control method, the amount of fuel supplied becomes excessive, resulting in wasted fuel, and much of the heat escapes to the outside, resulting in low thermal efficiency.
JP 2007-232273 A JP 2006-275336 A JP-A-2005-75940

  Accordingly, an object of the present invention is to eliminate the disadvantage of low thermal efficiency in the indirect heating type metal melting and holding furnace and reduce the waste of fuel.

To solve this problem,
The invention according to claim 1 is an operation method of a metal melting and holding furnace provided with an indirect heating furnace main body for melting a metal and maintaining a molten state, and a burner for heating the furnace main body,
Measure the melt temperature in the crucible of the furnace body and the furnace temperature inside the furnace body, set the target value of the melt temperature in the first temperature controller, and input the measured value of the melt temperature to the target of the furnace temperature The value is output to the second temperature controller, the measured value of the furnace temperature is input to the second temperature controller, and the control signal for adjusting the fuel supply amount and the oxidant supply amount from the second temperature controller to the burner is provided. This is a method for operating a metal melting and holding furnace, characterized in that the fuel supply amount and the oxidant supply amount to the burner are adjusted by the output of this control signal.

The invention according to claim 2 detects opening and closing of the crucible lid, and inputs this detection signal to the first temperature controller to increase the target value A of the molten metal temperature by a time corresponding to the opening time of the lid. The method for operating a metal melting and holding furnace according to claim 1.
The invention according to claim 3 is characterized in that the measurement position of the furnace temperature is near the bottom of the furnace body, and the measurement position of the molten metal temperature is about half the depth to the bottom of the crucible. The operation method of the metal melting and holding furnace according to Item 1.

The invention according to claim 4 is a metal melting and holding furnace including an indirect heating furnace main body for melting a metal and maintaining a molten state, and a burner for heating the furnace main body,
A first temperature sensor for measuring the temperature of the molten metal in the crucible of the furnace body, a second temperature sensor for measuring the temperature in the furnace inside the furnace body,
A first temperature controller for setting a target value of the molten metal temperature and inputting a measured value of the molten metal temperature from the first temperature sensor to calculate a target value of the furnace temperature;
Control for adjusting the fuel supply amount and the oxidant supply amount to the burner by inputting the target value of the furnace temperature from the first temperature controller and the measured value of the furnace temperature from the second temperature sensor. A second temperature controller for outputting a signal;
A metal melting and holding furnace having a control means for adjusting a fuel supply amount and an oxidant supply amount to a burner by a control signal from a second temperature controller.

The invention according to claim 5 is the metal melting and holding furnace according to claim 4, further comprising a lid opening / closing sensor that detects opening / closing of the crucible lid and sends a lid opening signal to the first temperature controller. is there.
The invention according to claim 6 is characterized in that the installation position of the first temperature sensor is about half the depth to the bottom of the crucible, and the installation position of the second temperature sensor is near the bottom of the furnace body. The metal melting and holding furnace according to claim 4.

  According to the present invention, as described above, by controlling the fuel supply amount and the oxidant supply amount to the burner using the molten metal temperature as an index, the heat output of the burner can be precisely controlled, and the furnace temperature Will not rise excessively, there will be no wasteful fuel supply to the burner, and fuel consumption can be reduced.

1 and 2 show an example of the melting and holding furnace of the present invention. FIG. 1 shows the metal melting and holding furnace itself, and FIG. 2 shows the temperature control system of the metal melting and holding furnace. 1 and 2, reference numeral 1 denotes a crucible, 2 denotes a furnace body, and 3 denotes a burner.
The crucible 1 has a bowl-like outer shape, in which a metal ingot to be melted is introduced into a space inside thereof and melted, and the generated molten metal is stored in a molten state.
The crucible 1 is in a state surrounded by the furnace body 2.

The furnace body 2 is constructed from a heat-resistant brick, silica board, ceramic fiber, and the like, and includes a circular furnace wall 21, a disk-shaped furnace bottom 22, and a disk-shaped lid 23 that opens and closes the opening of the crucible 1. It is roughly composed.
Also, a burner installation portion 24 for installing the burner 3 is provided at the lower part of the furnace wall 21 so as to protrude outward. Further, a chimney 25 for discharging combustion exhaust gas is provided on the upper portion of the furnace wall 21.

On the inner wall surface of the furnace wall 21, as shown in FIG. 1, a spiral projecting portion 26 projecting like a bowl is formed.
The spiral projecting portion 26 causes the flame or combustion gas of the burner 3 to spirally rise in the furnace body 2 and surround the crucible 1 to heat it efficiently.

The burner 3 is supplied with a fuel composed of a normal hydrocarbon gas such as liquefied petroleum gas (LPG), liquefied natural gas (LNG), propane and butane, and an oxidant composed of an oxygen-containing gas such as air, and burns. It is installed in the burner installation part 24 provided in the furnace wall 21.
The burner 3 is connected to a fuel supply pipe 31 for supplying fuel to the burner 3 and an oxidant supply pipe 32 for supplying oxidant. The fuel supply pipe 31 is connected to a fuel supply source (not shown), and the oxidant supply pipe 32 is connected to the burner 3. It is connected to an oxidant supply source (not shown).

As shown in FIG. 2, the fuel supply pipe 31 has a fuel flow rate adjustment valve 33 for adjusting the fuel supply flow rate, and the oxidant supply pipe 32 has an oxidant flow rate adjustment valve 34 for adjusting the oxidant supply flow rate. Is provided.
As shown in FIGS. 1 and 2, a first temperature sensor 4 for measuring the molten metal temperature is attached to the inside of the crucible 1, and a measured value from the first temperature sensor 4 is sent to the first temperature controller 5. It is supposed to be.
Further, a second temperature sensor 6 for measuring the temperature in the furnace at this position (hereinafter referred to as the furnace temperature) is attached to the lower part of the inner wall of the furnace wall 21 of the furnace body 2. The measurement value measured by the temperature sensor 6 is sent to the second temperature controller 7.

Each of the first and second temperature sensors 4 and 6 is made of a thermocouple, and is housed in a tip portion in a protective tube made of a heat resistant ceramic such as silicon nitride.
In this embodiment, the installation position of the first temperature sensor 4 is in the vicinity of the bottom having a depth of about ½ of the depth of the crucible 1 and is a position protruding from the inner surface of the crucible 1 by 3 to 5 cm. . Since the first temperature sensor 4 is installed in a state immersed in the crucible 1, an L-shaped protective tube is used.
The reason why the first temperature sensor 4 is arranged at this installation position is that a change in the molten metal temperature at this position appears greatly, and the detection speed increases. The molten metal temperature measured by the first temperature sensor 4 at this position is a measured value of the molten metal temperature.

  The installation position of the second temperature sensor 6 is a position 30 to 50 cm above the inner surface of the bottom of the inner surface of the furnace wall, the protective tube penetrates the furnace wall, and the tip of the protective tube protrudes 3 to 5 cm from the inner wall surface. It has become a position. At this installation position, it is difficult to be affected by the flame of the burner 3, and an appropriate furnace temperature can be measured. The furnace temperature measured by the second temperature sensor 6 at this position is a measured value of the furnace temperature.

  The first temperature controller 5 calculates a target value of the furnace temperature based on a preset target value of the molten metal temperature and a measured value of the molten metal temperature input from the first temperature sensor 4. This has a function of sending the calculated target value to the second temperature controller 7 and executes PID control. An upper limit value is set for the calculated target value of the furnace temperature, and the target value of the furnace temperature does not exceed the upper limit value.

Based on the target value of the furnace temperature sent from the first temperature controller 5 and the measured value of the furnace temperature input from the second temperature sensor 6, the second temperature controller 7 It has a function of calculating a control signal for controlling the opening degree of the control valve 33 and outputting this control signal, and executes PID control.
As shown in FIG. 2, the fuel flow rate control signal output from the second temperature controller 7 is once sent to the fuel flow rate regulator 35, and the valve opening degree signal is sent from the fuel flow rate regulator 35 to the fuel flow rate regulating valve 33. Configured to be sent to.

At the same time, a fuel flow rate signal is sent from the fuel flow rate regulator 35 to the oxidant flow rate regulator 36, and the oxidant flow rate regulator 36 calculates an oxidant flow rate corresponding to this based on this fuel flow rate signal. The valve opening degree signal is sent to the oxidant flow rate adjusting valve 34 based on the oxidant flow rate.
To calculate the oxidant flow rate from the fuel flow rate, for example, when the fuel is LNG and the oxidant is air, multiply the theoretical air amount 10.6 Nm ³ / hour per LNG 1 Nm ³ / hour by the air-fuel ratio 1.1. Calculated.
As described above, when the fuel supply amount is determined, the oxidant supply amount corresponding to the fuel supply amount is automatically determined.

  Further, as shown in FIG. 1, a lid opening / closing detection sensor 8 such as a limit switch for detecting opening / closing of the lid 23 is attached to the upper portion of the furnace body 2. An open signal is sent to the first temperature controller 5, and when the open signal from the lid open / close detection sensor 8 is input, the first temperature controller 5 is in a period during which the open signal is input. Correspondingly, it operates to increase the target value of the molten metal temperature by about 1 to 5 ° C.

Next, an operation method of the above metal heating and holding furnace will be described.
First, the target value of the molten metal temperature is set in the first temperature controller 5. The target value when the metal material is an aluminum alloy is set within a temperature range of 660 to 680 ° C.
An appropriate amount of fuel and oxidant are supplied to the burner 2 to start combustion, and a metal material such as an aluminum ingot is introduced into the crucible 1 for melting.

  The molten metal temperature is constantly measured by the first temperature sensor 4 and the furnace temperature is constantly measured by the second temperature sensor 6. The measured value of the molten metal temperature is input to the first temperature controller 5. The first temperature controller 5 uses a response characteristic between the melt temperature and the furnace temperature stored in advance, and based on the target value of the melt temperature and the measured value of the melt temperature, the target value of the furnace temperature. And the target value of the furnace temperature is transmitted to the second temperature controller 7.

  When the metal material is put into the crucible 1, the lid 23 is opened, so that an open signal from the lid open / close detection sensor 8 is sent to the first temperature controller 5. The first temperature controller 5 performs an operation of raising the target value of the molten metal temperature by about 1 to 5 ° C. only during the time when the open signal is sent, so that the calculated target value of the in-furnace temperature also depends on this. Get higher.

  In the second temperature controller 7, based on the target value of the furnace temperature and the measured value of the furnace temperature input from the second temperature sensor 6, the temperature of the furnace in relation to the fuel supply amount to the burner 3 stored in advance is stored. Referring to the response characteristics, a fuel flow control signal that indicates the opening degree of the fuel flow control valve 33 is calculated, and this signal is sent to the fuel flow controller 35.

Based on this fuel flow control signal, the fuel flow controller 35 sends a valve opening signal to the fuel flow adjustment valve 33, adjusts the opening of the valve 33, and controls the amount of fuel supplied to the burner 1.
At the same time, the fuel flow regulator 35 sends a fuel flow signal to the oxidant flow regulator 36. Based on the fuel flow signal, the oxidant flow controller 36 calculates the oxidant flow required according to the fuel flow as described above, sends the valve opening signal to the oxidant flow control valve 34, and burner 3 controls the amount of oxidant supplied to 3.

According to such an operation method, the fuel supply amount and the oxidant supply amount to the burner can be controlled precisely and without excess or shortage even when subjected to disturbances such as ingot charging that fluctuate the molten metal temperature. The fluctuation becomes smaller. This means that excessive supply of fuel to the burner is suppressed, and thermal efficiency is improved.
FIG. 3 is a graph showing temporal changes in the molten metal temperature and the chimney temperature according to the operation method of this embodiment. The chimney temperature is the temperature of the exhaust gas discharged from the chimney, and indicates the amount of heat that is taken out (escapes) from the melting furnace.

In addition, the arrow attached | subjected to the curve which shows the fluctuation | variation of the molten aluminum temperature in FIG. 3 shows the timing which throws the aluminum alloy ingot in the crucible. The molten aluminum temperature is a temperature measured by the first temperature sensor 4.
This graph is obtained when the aluminum alloy ingot is melted, and the target value of the molten metal temperature is set to 680 ° C.

The reason why the temperature fluctuation of the furnace temperature is small is considered as follows.
If the measured value of the molten metal temperature is lower than the target value, the first temperature controller 5 outputs to the second temperature controller 7 so as to increase the target value of the furnace temperature, and the second temperature controller 7 indicates this instruction. Thus, the target value of the furnace temperature is increased, and the fuel supply amount to the burner 3 is increased to increase the furnace temperature so that the measured value of the furnace temperature becomes this target value.
On the other hand, the second temperature controller 7 operates so that when the measured value of the in-furnace temperature is lower than the target value, the amount of fuel supplied to the burner 3 is increased to increase the in-furnace temperature to match the target value. To do.

  When the ingot is put into the crucible 1, the amount of heat transfer from the inside of the furnace to the crucible 1 increases, so that the temperature in the furnace decreases before the temperature of the molten metal decreases. The second temperature controller 7 senses this decrease in the furnace temperature and performs its own control. The control is started prior to the decrease in the molten metal temperature, the response speed is increased, and the temperature fluctuation range is reduced.

  Also, by opening the open signal from the lid open / close detection sensor 8 to the first temperature controller 5 and increasing the target temperature of the furnace before the ingot is charged, the furnace temperature is lowered before the molten metal temperature is lowered due to the ingot being charged. The temperature can be increased. For this reason, the response speed of the entire control system is increased, and as a result, fluctuations in the furnace temperature are reduced.

Moreover, since the upper limit is set to the target value of the furnace temperature output from the first temperature controller 5, even if the molten metal temperature is greatly lowered, the furnace temperature can be increased unnecessarily. Therefore, the fuel supply amount is not excessively supplied to the burner 3, and the fuel supply amount can be suppressed.
As described above, fluctuations in the furnace temperature can be reduced, the amount of fuel supply can be suppressed, and the energy cost can be reduced.

FIG. 4 is a graph showing temporal fluctuations of the molten metal temperature, the furnace temperature, and the chimney temperature in a method of controlling the fuel supply amount and the oxidant supply amount to the burner 3 based on the fluctuation of the conventional molten metal temperature. The temperature measuring position is the same as that of FIG.
Even in this case, the molten metal target value is 680 ° C.
The chimney temperature fluctuates more than that of FIG. This shows that a lot of heat escapes from the chimney and the thermal efficiency is low.

It is a schematic block diagram which shows an example of a structure of the metal melting | dissolving holding furnace itself of this invention. It is a block diagram which shows an example of the temperature control system of the metal melting holding furnace of this invention. It is a graph which shows temporal fluctuations, such as an in-furnace temperature by the present invention. It is a graph which shows temporal fluctuations, such as a furnace temperature, by the conventional thing. It is a schematic block diagram which shows the example of the conventional metal melt | dissolution holding furnace.

Explanation of symbols

1 ··· crucible 2 ··· furnace body 3 · · burner 4 · · 1st temperature sensor 5 · · 1st temperature controller 6 · · 2nd temperature sensor 7 · · 2 temperature controller 8. ・ Land open / close detection sensor

Claims (6)

An indirect heating furnace main body for melting a metal to maintain a molten state, and a method for operating a metal melting and holding furnace including a burner for heating the furnace main body,
Measure the melt temperature in the crucible of the furnace body and the furnace temperature inside the furnace body, set the target value of the melt temperature in the first temperature controller, and input the measured value of the melt temperature to the target of the furnace temperature The value is output to the second temperature controller, the measured value of the furnace temperature is input to the second temperature controller, and the control signal for adjusting the fuel supply amount and the oxidant supply amount from the second temperature controller to the burner is provided. A method for operating a metal melting and holding furnace, which outputs and adjusts a fuel supply amount and an oxidant supply amount to a burner according to the control signal.   The opening and closing of the crucible lid is detected, and this detection signal is input to the first temperature controller to raise the target temperature of the molten metal by a time corresponding to the opening time of the lid. How to operate a metal melting and holding furnace. 2. The metal melting and holding furnace according to claim 1, wherein the measurement position of the furnace temperature is near the bottom of the furnace body, and the measurement position of the molten metal temperature is about half the depth to the bottom of the crucible. Driving method. An indirect heating furnace main body for melting a metal and maintaining a molten state, and a metal melting and holding furnace provided with a burner for heating the furnace main body,
A first temperature sensor for measuring the temperature of the molten metal in the crucible of the furnace body, a second temperature sensor for measuring the temperature in the furnace inside the furnace body,
A first temperature controller for setting a target value of the molten metal temperature and inputting a measured value of the molten metal temperature from the first temperature sensor to calculate a target value of the furnace temperature;
Control for adjusting the fuel supply amount and the oxidant supply amount to the burner by inputting the target value of the furnace temperature from the first temperature controller and the measured value of the furnace temperature from the second temperature sensor. A second temperature controller for outputting a signal;
A metal melting and holding furnace having a control means for adjusting a fuel supply amount and an oxidant supply amount to a burner by a control signal from a second temperature controller.   5. The metal melting and holding furnace according to claim 4, further comprising a lid opening / closing sensor that detects opening / closing of the crucible lid and sends a lid opening signal to the first temperature controller. The metal according to claim 4, wherein the installation position of the first temperature sensor is about half the depth to the bottom of the crucible, and the installation position of the second temperature sensor is near the bottom of the furnace body. Melting and holding furnace.

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