JP7632890B2 - Industrial furnace heating structure - Google Patents

Description

The present invention relates to the heating structure of an industrial furnace used for heat treating metals and non-ferrous metals.

2. Description of the Related Art Electric furnaces that use electricity as a heat source exist as furnaces for heat treating metals and non-ferrous metals (see, for example, Patent Document 1).
The electric furnace shown in Patent Document 1 is provided with a cooling fan on the outside of the furnace body, and this cooling fan has a cooling function of supplying outside air to the inside of the furnace body and dissipating the heated air inside the furnace body to the outside.

As an example of such a conventional electric furnace, the one shown in Figures 4 and 5 is known. The electric furnace shown in Figure 4 has metal heaters 31 on the left and right sides inside the furnace body 30, and a rotating fan 32 in the upper center of the furnace body 30. These metal heaters 31 heat the air inside the furnace body 30, and the heated material T is heated by convection of the heated air by the rotating fan 32.

The electric furnace shown in FIG. 5 has an air heater 41 attached to the outside of the furnace body 40, and external air is heated through the air heater 41 and taken into the furnace body 40, and the heated air heats the material to be heated T. The heated air is discharged to the outside of the furnace body 40.

JP 2015-137781 A

The electric furnaces of the prior art shown in Patent Document 1 and Figures 4 and 5 all use electricity as a heating source, and are therefore highly desirable from the perspective of carbon neutrality.

However, there is a need to further improve the heating efficiency of all of these electric furnaces. In other words, the electric furnace shown in Patent Document 1 has a cooling function using a cooling fan, which naturally reduces the heating efficiency.

In addition, the electric furnace shown in FIG. 4 heats the air inside the furnace body 30 with metal heaters 31 installed on the left and right sides inside the furnace body 30, and then circulates it with a rotating fan 32, so the agitation effect of the heated air is insufficient, and there are issues with heating efficiency. In addition, the heated air always acts on the material T to be heated from a fixed direction, which causes problems with heating efficiency. These are particularly noticeable when the shape of the material T to be heated is complex.

In addition, the rotating fan 32 in this electric furnace is installed inside the furnace body 30, which is at high temperature, so it is prone to damage such as deformation and vibration due to imbalance of the impeller, and there are also problems with its short lifespan.

In addition, the electric furnace shown in FIG. 5 heats the air outside the furnace body 40 (i.e., air at room temperature) with the air heater 41, and then exhausts the heated air after it acts on the material to be heated T. This means that it is necessary to constantly heat the air at room temperature to the required high temperature. This results in a large energy loss and low heating efficiency.

Furthermore, because electric furnaces use electricity as a heat source, there is the problem that it is difficult to use them in cases where high output is required, such as high-temperature heat treatment furnaces or heating furnaces.

The object of the present invention is to provide a heating structure for an industrial furnace that has excellent heating efficiency and a long fan life.

In order to achieve the above object, the heating structure of the industrial furnace of the present invention is an industrial furnace (1) that circulates air inside a furnace body (10) to heat a material (T),
An air heater (11) provided on the outer side of the furnace body (10) for heating the air and blowing it into the furnace body (10);
A burner (21) provided on a side surface of the furnace body (10) for heating the air;
an air blower (60) that takes in room temperature air and sends it to the air heater (11) and the burner (21);
An exhaust passage (51) connecting an exhaust tower (100) provided outside the furnace body (10) and the furnace body (10);
a recuperator (50) provided in the exhaust passage (51) and taking in room temperature air blown from the air blower (60) before it reaches the air heater (11) and the burner (21), and preheating the room temperature air with exhaust heat from the furnace body (10);
a first on-off valve (12) provided between the recuperator (50) and the air heater (11);
a second on-off valve (22) provided between the recuperator (50) and the burner (21);
a third on-off valve (25) provided in a path through which gas fuel is sent to the burner (21);
During low output, the first on-off valve (12) is opened and the second on-off valve (22) and the third on-off valve (25) are closed to heat the material to be heated (T) with air blown from the air heater (11), and during high output, the first on-off valve (12), the second on-off valve (22), and the third on-off valve (25) are opened to add heating by the burner (21).

Here, the symbols in parentheses indicate the corresponding elements or matters described in the drawings and in the detailed description of the invention described below.

The industrial furnace of the present invention uses an air heater at low output and adds a burner heater at high output to create a hybrid heat source, so it can also be used in high-temperature heat treatment furnaces and heating furnaces.

In addition, a recuperator is used to preheat room temperature air using the exhaust heat from the furnace body, and the preheated air is then sent to the air heater and burner, resulting in excellent heating efficiency and energy savings.
Furthermore, since the air blower for blowing air is provided outside the furnace body, breakdowns due to the influence of heat can be reduced and the life of the furnace can be extended, compared to when the air blower is provided inside the furnace body.

This hybrid heat source configuration, which uses an air heater at low output and adds a burner heater at high output, and further utilizes a recuperator, is not described at all in the above-mentioned patent documents.

FIG. 2 is a front view showing the heating structure of the industrial furnace according to the embodiment of the present invention, illustrating the state at low output. FIG. 2 is a front view showing the heating structure of the industrial furnace according to the embodiment of the present invention, illustrating the state at high output. FIG. 4 is a front view showing a heating structure of an industrial furnace according to another embodiment of the present invention. FIG. 1 is a front view showing the configuration of an electric furnace according to a conventional example. FIG. 13 is a front view showing an electric furnace according to another conventional example.

The heating structure of an industrial furnace 1 according to an embodiment of the present invention will be described with reference to Figures 1 and 2. Figure 1 shows the structure at low output, and Figure 2 shows the structure at high output.

The heating structure of the industrial furnace 1 according to this embodiment is a hybrid type heat source that uses electric heating from the air heater 11 and flame heating from the burner 21 as heat sources, and circulates air inside the furnace body 10 to heat the material T placed inside the furnace body 10. The material T may be placed in a fixed state, or it may be placed in a movable state (rotatable, etc.).

The heating structure of this industrial furnace 1 includes an air heater 11, a first on-off valve 12, a burner 21, a second on-off valve 22, a third on-off valve 25, a recuperator 50, an exhaust passage 51, a first passage 52, a second passage 53, a third passage 54, a fourth passage 55, a blower 60, a thermocouple sensor 71, and a temperature indicator/regulator 72.

The air heater 11 is installed on the outside side of the furnace body 10 (here, the right side), and heats the air using electricity and blows it into the furnace body 10. A portion of the room temperature air blown from the air blower 60 is sent to the air heater 11 via the first opening/closing valve 12 as air for the air heater.

The burner 12 is installed on the side (here, the right side) of the furnace body 10 so that a flame is sprayed below the hot air blown into the furnace from the air heater 11, and the air circulating inside the furnace body 10 is heated by the fire. The burner 12 takes in gas as fuel and combustion air, and the gas is connected via a flowmeter 27 that measures the amount of gas, a regulating valve 26, and a third on-off valve 25, while the combustion air is connected via a flowmeter 24 that measures the amount of gas, a regulating valve 23, and a second on-off valve 22. The combustion air is room temperature air blown from the air blower 60, and the air excluding the air for the air heater is sent via the second on-off valve 22.

The exhaust passage 51 connects the exhaust tower 100 provided outside the furnace body 10 to the lower part of the furnace body 10, and a recuperator 50 is provided in the middle of the exhaust passage 51. A furnace pressure damper 56 is provided between the recuperator 50 and the exhaust tower 100.
Room temperature air is sent to the recuperator 50 from an air blower 60 through a first passage 52, and the first passage 52 is provided with a flow meter 63 for measuring the amount of room temperature air blown from the air blower 60, a regulating valve 62, and an air on-off valve 61.
In addition, a second passage 53 is connected to the recuperator 50, and the second passage 53 branches into a third passage 54 which is connected to the air heater 11 side, and a fourth passage 55 which is connected to the burner 21 side (the combustion air supply side).

The recuperator 50 is an exhaust heat recovery heat exchanger, in which room temperature air blown from the air blower 60 through the first passage 52 is taken in before it reaches the air heater 11 and the burner 21. The room temperature air taken in by the recuperator 50 is preheated by the exhaust heat sent from the furnace body 10 through the exhaust passage 51, and the preheated air is sent to the air heater 11 through the second passage 53 and the third passage 54 as air heater air, and to the burner 21 through the second passage 53 and the fourth passage 55 as combustion air.

The thermocouple sensor 71 is a thermometer installed inside the furnace to measure the temperature inside the furnace, and the temperature is sent to a temperature indicator regulator 72 installed outside the furnace, which controls the air heater 11 so that the temperature approaches a pre-input target set value. This control may be a control to turn the air heater 11 on and off, or a proportional control (phase control) that varies the output proportionally, and is not particularly limited.

The heating structure of this industrial furnace 1 uses different heat sources at low and high output. That is, at low output, the heat source is an air heater 11 as shown in FIG. 1, and at high output, the heat source is an air heater 21 as shown in FIG. 2.

(Low power operation)
At low power, the heating structure of the industrial furnace 1 can be operated as follows.
That is, the heating structure of this industrial furnace 1 heats the material T to be heated with air blown from the air heater 11 by opening the first on-off valve 12 and closing the second on-off valve 22 and the third on-off valve 25 .
At this time, room temperature air is not directly sent from the air blower 60 to the air heater 11 as air for the air heater, but the room temperature air is preheated by the exhaust heat from the furnace body 10 using the recuperator 50, and the preheated high temperature air is sent to the air heater 11.
This provides excellent heating efficiency and energy savings.

In addition, because the air blower 60 for blowing air is installed outside the furnace body, it is possible to reduce breakdowns caused by heat and extend the lifespan of the furnace body 10 compared to when it is installed inside the furnace body 10.

(High power operation)
Next, at high power, the heating structure of the industrial furnace 1 can be operated as follows.
That is, in addition to opening the first opening/closing valve 12, the second opening/closing valve 22 and the third opening/closing valve 25 are also opened to add heating by the burner 21, and the heated material T is heated by the flame from the burner 21 in addition to the air blown from the air heater 11.
At this time, the air for the air heater sent to the air heater 11 and the combustion air sent to the burner 21 are not room temperature air sent directly from the air blower 60, but high temperature air that has been preheated by the exhaust heat from the furnace body 10 using the recuperator 50, resulting in excellent heating efficiency and energy savings.

This effectively increases the temperature inside the furnace instantly because the heat from the burner 21 is added to the heat from the air heater 11 when the output is high.

As shown in FIG. 3, the burner 21 may be omitted and the material T may be heated only by the air heater 11.
In this case, too, a recuperator 50 is provided in the exhaust path 51, and room temperature air blown from an air blower 60 is taken in before it reaches the air heater 11, and the room temperature air is preheated by the exhaust heat from the furnace body 10, and the preheated high temperature air is sent through the second passage 53 as air for the air heater.
This makes it possible to provide an industrial furnace with excellent heating efficiency even when heating is performed only by the air heater 11.

REFERENCE SIGNS LIST 1 industrial furnace 10 furnace body 11 air heater 12 first on-off valve 21 burner 22 second on-off valve 23 regulating valve 24 flow meter (for combustion air)
25 Third opening/closing valve 26 Adjustment valve 27 Flow meter (for gas fuel)
30 Furnace body 31 Metal heater 32 Rotary fan 40 Furnace body 41 Air heater 50 Recuperator 51 Exhaust passage 52 First passage 53 Second passage 54 Third passage 55 Fourth passage 56 Furnace pressure damper 60 Air blower 61 Air on-off valve 62 Adjustment valve 63 Flow meter (for room temperature air)
71 Thermocouple sensor (thermometer)
72 Temperature indication controller 100 Exhaust tower

Claims (1)

An industrial furnace in which air is circulated inside the furnace body to heat a material to be heated,
An air heater provided on the outer side of the furnace body to heat the air and blow it into the furnace body;
A burner provided on a side surface of the furnace body for heating the air;
an air blower that takes in room temperature air and blows it to the air heater and the burner;
An exhaust passage connecting an exhaust tower provided outside the furnace body to the furnace body;
A recuperator is provided in the exhaust passage, and takes in room temperature air blown from the air blower before it reaches the air heater and the burner, and preheats the room temperature air with exhaust heat from the furnace body;
A first on-off valve provided between the recuperator and the air heater;
A second on-off valve provided between the recuperator and the burner;
a third on-off valve provided in a path through which gas fuel is sent to the burner;
said first on-off valve being opened and said second on-off valve and said third on-off valve being closed during low output to heat said material to be heated with air blown from said air heater, and said first on-off valve, said second on-off valve and said third on-off valve being opened during high output to additionally heat said material with said burner.

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