JP7135562B2 - heating furnace - Google Patents

Description

The present disclosure relates to furnaces.

2. Description of the Related Art Conventionally, as disclosed in Patent Document 1, for example, a heating furnace having a furnace body for heating objects to be heated such as industrial materials and foods is known. In such a heating furnace, there has been proposed one in which the air in the furnace body is heated by a heating part, and an object to be heated is heated by convective heat transfer from the heated air (for example, Patent Document 1).

JP 2010-286179 A

A heating furnace generally requires a great deal of time from the time it is started until the temperature of the inner wall surface of the furnace body stabilizes. In particular, in a heating furnace with high heat insulation or a heating furnace with a large heat capacity of the furnace body, it takes a longer time to settle down. In a heating furnace that receives radiation not only from the heating part but also from the furnace body to heat the object to be heated, if the inner wall temperature of the furnace body is not stable, the heating amount can be controlled only by controlling the temperature of the heating part. Can not. Therefore, there is a problem that the start-up time (the time until the heating amount can be controlled) becomes long until the heating furnace is actually operated.

In view of such problems, the present disclosure aims to provide a heating furnace capable of shortening the start-up time.

In order to solve the above problems, a heating furnace according to an aspect of the present disclosure includes a furnace body, a heating unit provided in the furnace body, an acquisition unit that acquires parameters related to the amount of heat applied to an object to be heated, and an acquisition Based on the parameters acquired by the heating unit, the heating unit is adjusted so that the total heating amount of the heat amount due to radiation from the furnace body to the object to be heated and the heat amount due to radiation from the heating unit to the object to be heated is constant. and a control unit for controlling the temperature.

The obtaining unit may obtain the temperature of the inner wall surface of the furnace body as the parameter, and the control unit may control the temperature of the heating unit based on the temperature of the inner wall surface of the furnace body obtained by the obtaining unit.

The control unit may derive a target temperature of the heating unit based on the temperature of the inner wall surface of the furnace body acquired by the acquiring unit, and control the temperature of the heating unit so as to achieve the derived target temperature.

According to the present disclosure, the startup time can be shortened.

It is a schematic sectional view of the heating furnace of this embodiment. FIG. 2 is a sectional view taken along the line II-II of FIG. 1; It is a figure explaining the control system of the heating furnace of this embodiment. FIG. 4 is a diagram showing heat fluxes to the object to be heated at different times from start-up; It is a figure explaining the area of a furnace body. It is a figure explaining the temperature of the inner wall surface of a furnace body, the temperature of a heating part, and the target temperature of a heating part. FIG. 7 is a diagram showing a flowchart of heating unit control processing; FIG. 4 is a diagram illustrating a control system of a heating furnace when a heating unit is composed of an electric heater;

Embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. Dimensions, materials, and other specific numerical values shown in the embodiments are merely examples for facilitating understanding, and do not limit the present disclosure unless otherwise specified. In this specification and the drawings, elements having substantially the same functions and configurations are denoted by the same reference numerals, thereby omitting redundant description. Illustrations of elements that are not directly related to the present disclosure are omitted.

Here, a continuous heating furnace will be described as an example of a heating furnace, but the heating furnace described below can be applied to, for example, a batch furnace, a multi-chamber furnace, and the like.

FIG. 1 is a schematic cross-sectional view of a heating furnace 1 of this embodiment. FIG. 2 is a sectional view taken along line II-II of FIG. As shown in FIG. 1, the heating furnace 1 of the present embodiment is configured as a so-called continuous heating furnace that continuously heats the object W to be heated during the transportation process. The heating furnace 1 is continuously provided with a plurality of furnace bodies 10 each having an internal space. In this embodiment, an example in which nine furnace bodies 10 are provided will be described. Note that the furnace body 10 may be any number, for example, one.

As shown in FIG. 2, the furnace body 10 has an internal space surrounded by outer walls (an upper outer wall 10a, a lower outer wall 10b, a left outer wall 10c, and a right outer wall 10d). Further, as shown in FIG. 1, the furnace body 10 extends linearly from the inlet-side opening 10e to the outlet-side opening 10f. The inlet side opening 10e and the outlet side opening 10f of the adjacent furnace bodies 10 are connected to each other.

In the heating furnace 1, a plurality of furnace bodies 10 are divided into a plurality of zones. In this embodiment, three furnace bodies 10 on the upstream side in the transport direction are divided into first zones. Further, the fourth to sixth furnace bodies 10 from the upstream side in the transport direction are divided into the second zone. Further, three furnace bodies 10 on the downstream side in the transport direction are divided into the third zone.

The transport section 20 includes a transport band 20a, rollers 20b, and a motor mechanism 20c. The conveying belt 20a is composed of, for example, an endless belt. The rollers 20b support part of the conveying belt 20a in the furnace body 10 from below vertically. The motor mechanism 20c includes gears and a motor, and rotates the transport band 20a. The conveying belt 20a is rotated by the power of the motor mechanism 20c, and the object to be heated W placed on the conveying belt 20a is moved in the direction of the white arrow in FIG. transport. In this manner, the object W to be heated is carried in from the entrance-side opening 10e of the furnace body 10 on the most upstream side in the transport direction. Then, the object to be heated W is carried out from the outlet side opening 10f of the furnace body 10 on the most downstream side in the carrying direction.

A heating unit 30 composed of a radiant burner is provided in the furnace body 10 . Here, the heating unit 30 is composed of a radiant burner, but the heating unit 30 may be a radiant tube burner, a line burner, an infrared ceramic burner, an electric heater, or the like. In any case, the heating unit 30 may mainly function as a heat source for heating the furnace body 10 . The heating units 30 are provided vertically above and below the conveying belt 20a. That is, the two heating units 30 are positioned so as to vertically sandwich the conveying belt 20a. A plurality of heating units 30 are arranged in the furnace body 10 at predetermined intervals in the transport direction. Note that the heating unit 30 does not need to be entirely operated (heated). In the heating furnace 1, the heating unit 30 to be operated is appropriately selected according to the object W to be heated. For example, in the heating furnace 1 of the present embodiment, in FIG. 1, the black heating unit 30 is in operation, and the white heating unit 30 is inactive.

As shown in FIG. 2, support holes 30a for supporting the heating unit 30 are formed in the left side wall 10c and the right side wall 10d of the furnace body 10, respectively. The support hole 30a penetrates the left side wall 10c or the right side wall 10d, and the heating unit 30 is inserted and removed through the support hole 30a during the manufacturing process and maintenance of the heating furnace 1.

A plate member 50 that holds a heat insulating material 40 between itself and the inner wall of the furnace body 10 is provided in the furnace body 10 . Here, the outer wall of the furnace body 10 is often made of SS material for cost reasons. On the other hand, the plate member 50 serving as the inner wall is made of a metal plate material such as austenitic SUS in consideration of heat resistance and oxidation resistance. The plate member 50 is provided facing each of the upper outer wall 10a, the lower outer wall 10b, the left outer wall 10c, and the right outer wall 10d. Thereby, the plate member 50 constitutes the inner wall surface of the furnace space S in which the object W to be heated is provided. The furnace body 10 is covered with the heat insulating material 40 all around, so that heat radiation from the furnace body 10 is suppressed.

In the heating furnace 1, the temperature of the heating unit 30 is controlled for each area obtained by further dividing the zones, and the object W to be heated is heated in each zone, as will be described later in detail. For example, if the object W to be heated is rice crackers, the moisture in the rice crackers is heated in the first zone until just before vaporization. Subsequently, moisture in the rice cracker is vaporized in the second zone. Then, the rice crackers are browned in the third zone. In addition, although the case where the furnace body 10 is divided into three zones has been described in the present embodiment, the number of zones may be any number. Further, the furnace body 10 may not be divided into zones.

FIG. 3 is a diagram for explaining the control system of the heating furnace 1 of this embodiment. In FIG. 3, the solid line indicates the flow of the signal, and the dashed line indicates the flow of the gas (air, fuel gas).

As shown in FIG. 3, the heating furnace 1 is provided with a control device 60 . The control device 60 is composed of a semiconductor integrated circuit including a CPU (Central Processing Unit). The control device 60 reads programs, parameters, etc. for operating the CPU itself from the ROM. The control device 60 manages and controls the entire heating furnace 1 in cooperation with RAM as a work area and other electronic circuits. In this embodiment, the control device 60 functions as an acquisition section 62 and a control section 64 .

The heating furnace 1 is provided with a temperature sensor 70 and a temperature sensor 72 . The temperature sensor 70 is, for example, a thermocouple and attached to the inner wall surface of the furnace body 10 . The temperature sensor 70 measures the temperature of the inner wall surface of the furnace body 10 and outputs the measurement result to the control device 60 . The temperature sensor 72 is, for example, a thermocouple and attached to the surface of the heating unit 30 in operation. The temperature sensor 72 measures the surface temperature of the heating unit 30 and outputs the measurement result to the control device 60 . At least one temperature sensor 70 is provided for each zone.

The heating furnace 1 is also provided with a blower 82 , a control valve 84 and a gas mixer 86 . Blower 82 is connected to heating section 30 via control valve 84 and gas mixer 86 . The blower 82 supplies air to the heating section 30 . Control valve 84 is electrically connected to controller 60 . The control valve 84 is an electronic control valve whose opening is controlled by the control device 60 .

Gas mixer 86 is supplied with air from blower 82 via control valve 84 . Further, the gas mixer 86 is supplied with fuel gas. The gas mixer 86 supplies the supplied mixture of air and fuel gas to the heating section 30 . The gas mixer 86 draws fuel gas proportional to the amount of air supplied from the blower 82 and supplies it to the heating unit 30 . Therefore, the mixing ratio between the air and the fuel gas supplied from the gas mixer 86 to the heating section 30 is always constant.

In the heating furnace 1 , the amount of air supplied to the heating section 30 can be controlled by controlling the opening degree of the control valve 84 with the control device 60 . The heating unit 30 heats by burning a mixture of air and fuel gas. Therefore, the temperature of the heating unit 30 is controlled by the degree of opening of the control valve 84 .

FIG. 4 is a diagram showing the heat flux with respect to the object to be heated W at different times from the start. In FIG. 4, the horizontal axis represents the time (heating time) during which the object W to be heated is carried into the furnace body 10, and the vertical axis represents the amount of heat or the heat flux with respect to the object W to be heated. In other words, the horizontal axis of FIG. 4 corresponds to the position from the inlet to the outlet of the plurality of furnace bodies 10 as a whole.

In the heating furnace 1 , the object W to be heated is heated by radiation from the heating unit 30 , radiation from the furnace body 10 , heat transfer from the carrier belt 20 a , and heat transfer from the air inside the furnace body 10 . However, since the object to be heated W and the conveying belt 20a are carried into the furnace body 10 at the same time, they have substantially the same temperature. In other words, the transfer of heat between the object to be heated W and the conveying belt 20a is relatively small.

Therefore, the total heat flux to the object to be heated W is due to radiation from the heating section 30 , radiation from the inner wall surface of the furnace body 10 , and heat transfer from the air inside the furnace body 10 . Since the flow velocity of the air in the furnace body 10 is small, the heat transfer from the air in the furnace body 10 to the object W to be heated is relatively small.

Therefore, the total heat flux to the object W to be heated, that is, the amount of heat applied to the object W to be heated, is dominated by radiation from the heating unit 30 and radiation from the inner wall surface of the furnace body 10 .

However, in the heating furnace 1, it takes time for the temperature of the inner wall surface of the furnace body 10 to stabilize after starting, that is, starting to supply the fuel gas to the heating unit 30. FIG. For example, it takes about 5 hours for the temperature of the inner wall surface of the furnace body 10 to stabilize after the heating furnace 1 is started. Note that the term "statically set" refers to a state in which the temperature is stable at a predetermined temperature.

On the other hand, the time required for the heating part 30 to stabilize is shorter than the time required for the temperature of the inner wall surface of the furnace body 10 to stabilize. For example, the temperature of the heating unit 30 stabilizes in about one hour after the heating furnace 1 is started.

Therefore, as shown in FIG. 4, the heat flux with respect to the object W to be heated varies depending on the time until the temperature of the inner wall surface of the furnace body 10 stabilizes. In addition, in FIG. 4 , a plurality of peaks are mainly heat fluxes due to radiation from the heating unit 30 . Moreover, between adjacent peaks is mainly the heat flux due to radiation from the inner wall surface of the furnace body 10 .

As is clear from FIG. 4, when the time after the heating furnace 1 is started is short, the heat from the inner wall surface of the furnace body 10 is greater than when the time is long after the heating furnace 1 is started. The heat flux due to radiation is small. Therefore, until the temperature of the inner wall surface of the furnace body 10 is stabilized, the amount of heat (heating amount) applied to the object to be heated W is reduced.

If the object to be heated W cannot be heated until the temperature of the inner wall surface of the furnace body 10 is stabilized, production efficiency and energy efficiency are reduced accordingly. Therefore, in the heating furnace 1 of the present embodiment, even before the temperature of the inner wall surface of the furnace body 10 is stabilized, the amount of heat (heating amount) applied to the object to be heated W increases to the inner wall surface of the furnace body 10. The temperature of the heating unit 30 is controlled so as to be the same as when the temperature is stabilized. This reduces start-up time and increases productivity and energy efficiency.

FIG. 5 is a diagram for explaining areas of the furnace body 10. As shown in FIG. FIG. 6 is a diagram for explaining the temperature of the inner wall surface of the furnace body 10, the temperature of the heating section 30, and the target temperature of the heating section 30. As shown in FIG. As described above, in the heating furnace 1, a plurality of furnace bodies 10 are continuously arranged. Further, the plurality of furnace bodies 10 are divided into any one of the first zone to the third zone. In this embodiment, the furnace body 10 in each zone is divided into different areas with the transfer belt 20a as a boundary. Then, the control device 60 controls the temperature of the heating section 30 independently for each area.

Specifically, as shown in FIG. 5, the first area is defined as a region provided above the conveying belt 20a in the first zone. In addition, a region provided below the conveying belt 20a in the first zone is referred to as a second area. In the second zone, the area provided above the conveying belt 20a is referred to as the third area. A fourth area is defined as a region provided below the conveying belt 20a in the second zone. A region provided above the conveying belt 20a in the third zone is referred to as a fifth area. A region provided below the conveying belt 20a in the third zone is referred to as a sixth area. Then, the control device 60 independently controls the temperature of the heating section 30 for each of the first to sixth areas.

Here, as described above, the amount of heat applied to the object to be heated W is due to heat transfer from radiation from the heating unit 30, radiation from the inner wall surface of the furnace body 10, and air in the furnace body 10. be. Therefore, the amount of heat (heating amount) Q applied to the object W to be heated in each area is expressed by Equation (1).
Q=a×(Tw ⁴ −To ⁴ )+b×(Th ⁴ −To ⁴ )+c×(Tg−To) (1)
Here, a, b, and c are constants, Tw is the temperature of the inner wall surface of the furnace body 10, To is the temperature (surface temperature) of the object W to be heated, and Th is the heating unit 30 and Tg is the temperature of the air in the furnace body 10 .

As described above, the amount of heat applied to the object to be heated W is dominated by the radiation from the heating unit 30 and the radiation from the inner wall surface of the furnace body 10, so the heating amount Q is constant ( constant), equation (1) can be transformed into equation (2).
Th=(−A×Tw ⁴ +B) ^1/4 −273 (2)
where A and B are constants.

As is clear from Equation (2), the temperature Th of the heating section 30 can be expressed as a function of only the temperature Tw of the inner wall surface of the furnace body 10 .

Therefore, by determining the constants A and B for each area in advance, the target temperature of the heating unit 30 (Th in Equation (2)) when the heating amount Q is applied to the object W to be heated in each area is It can be derived from the temperature Tw of the inner wall surface of the furnace body 10 .

In the heating furnace 1, the heating amount Q in each area, that is, the amount of heat to be applied to the object to be heated W in each area can be determined in advance by experiments or computer analysis. After the heating amount Q in each area is determined, the constants A and B in each area are determined by experiments and computer analysis. Of the constants A and B in each area, the constants A and B for the first area and the second area are determined first. The constants A and B for the third and fourth areas are then determined. Finally, the constants A, B for the fifth and sixth areas are determined.

Constants A and B in each area are stored in advance in the ROM of control device 60 . As a result, the control device 60 controls the temperature of the heating unit 30 for each area, thereby controlling the heating amount of the object W to be heated in each area to be constant. However, if the heating amount is controlled to be constant immediately after the heating furnace 1 is started, even if the heating unit 30 is heated to the maximum, the predetermined heating amount is reduced by the radiation from the heating unit 30 and the furnace body 10. It cannot be added to the object W to be heated. Therefore, as shown in FIG. 6, the control unit 64 operates the control valve 84 so that the maximum amount of air that can be supplied to the heating unit 30 is supplied to the heating unit 30 for a certain period after the heating furnace 1 is started. Control. As a result, the heating unit 30 is fully opened and the temperature rises quickly.

An acquisition unit 62 (see FIG. 3) of the control device 60 acquires the temperature of the furnace body 10 from a temperature sensor 70 provided on the inner wall surface of the furnace body 10 as a parameter related to the amount of heat applied to the object W to be heated. The acquisition unit 62 also acquires the temperature of the heating unit 30 from the temperature sensor 72 provided in the heating unit 30 as a parameter related to the amount of heat applied to the object W to be heated. Then, when the temperature of the inner wall surface of the furnace body 10 obtained from the temperature sensor 70 reaches a preset warm-up determination temperature, the control unit 64 reads the constants A and B of each area from the ROM, and formula (2 ) to derive the target temperature (temperature Th) of the heating unit 30 for each area.

Further, the control unit 64 adjusts the opening degree of the control valve 84 based on the derived target temperature and the temperature of the heating unit 30 acquired from the temperature sensor 72 . Specifically, the control unit 64 adjusts the opening degree of the control valve 84 by feedback control so that the temperature of the heating unit 30 obtained from the temperature sensor 72 becomes the derived target temperature. For example, when the temperature of the heating unit 30 obtained from the temperature sensor 72 is lower than the target temperature, the opening of the control valve 84 is controlled to be increased. As a result, the amount of air supplied to the heating unit 30 increases, the heating unit 30 is heated more, and the temperature of the heating unit 30 rises. Further, when the temperature of the heating unit 30 obtained from the temperature sensor 72 is higher than the target temperature, the opening of the control valve 84 is controlled to be small. As a result, the amount of air supplied to the heating section 30 is reduced, and the temperature of the heating section 30 is lowered.

Thus, the heating furnace 1 controls the temperature of the heating unit 30 so that the total amount of heat generated by the radiation from the heating unit 30 and the amount of heat generated by the radiation from the furnace body 10 is constant. As a result, the heating furnace 1 can control the heating amount of the object W to be heated at an earlier stage than the period in which the temperature of the inner wall surface of the furnace body 10 is stabilized, and can be started up early.

Further, the control unit 64 can derive the target temperature of the heating unit 30 as a function of only the temperature of the inner wall surface of the furnace body 10 by using the equation (2) under the condition that the heating amount is constant. This facilitates control of the heating amount in the heating furnace 1 .

In addition, the control unit 64 derives the target temperature of the heating unit 30 using equation (2), and controls the opening degree of the control valve 84 based on the derived target temperature. This makes it possible to easily control the temperature of the heating unit 30 by feedback control.

FIG. 7 is a diagram showing a flowchart of heating unit control processing in this embodiment. The control device 60 executes the heating unit control process shown in FIG. 7 for each area at predetermined time intervals.

First, the acquisition unit 62 acquires the temperature of the inner wall surface of the furnace body 10 from the temperature sensor 70 . Further, the acquisition unit 62 acquires the temperature of the heating unit 30 from the temperature sensor 72 (S102).

Next, the control unit 64 determines whether the temperature of the inner wall surface of the furnace body 10 acquired by the acquisition unit 62 is higher than the warm-up determination temperature (S104). Then, when the temperature of the inner wall surface of the furnace body 10 is equal to or lower than the warm-up determination temperature (NO in S104), the control section 64 fully opens the heating section 30 (S106), and repeats the processing from S102.

On the other hand, if the temperature of the inner wall surface of the furnace body 10 is higher than the warm-up determination temperature (YES in S104), the control unit 64, based on the temperature of the inner wall surface of the furnace body 10 acquired by the acquisition unit 62, calculates (2) is used to derive the target temperature of the heating unit 30 (S108). After that, the control unit 64 adjusts the opening degree of the control valve 84 based on the derived target temperature and the temperature of the heating unit 30 acquired by the acquisition unit 62, and feedback-controls the temperature of the heating unit 30. (S110).

Although the embodiment has been described above with reference to the accompanying drawings, it goes without saying that the configuration is not limited to the configuration of the above embodiment. It is obvious that a person skilled in the art can conceive of various modifications or modifications within the scope of the claims, and they are naturally within the technical scope.

In the above embodiment, the case where the temperature is acquired as a parameter related to the amount of heat applied to the object W to be heated has been described. However, the parameter related to the amount of heat applied to the object W to be heated may be other than the temperature. For example, the parameter related to the amount of heat applied to the object W to be heated may be heat flux. In this case, the heat flux from the inner wall surface of the furnace body 10 and the heating unit 30 to the object to be heated may be obtained using a heat flux sensor.

Further, in the above embodiment, the temperature control of the heating unit 30 is started when the temperature of the heating unit 30 reaches the warm-up determination temperature after the heating furnace 1 is started. However, the temperature control of the heating unit 30 may be started when a preset warm-up determination period has elapsed after the heating furnace 1 is started.

Moreover, in the above embodiment, the case where the heating furnace 1 is a continuous heating furnace has been described. However, the heating furnace 1 is not limited to a continuous heating furnace.

Moreover, in the above-described embodiment, the case where the heating unit 30 is composed of a radiation burner has been described. However, the heating unit 30 may be composed of an electric heater as described above. A control system when the heating unit 30 is composed of an electric heater will be described below.

FIG. 8 is a diagram for explaining the control system of the heating furnace when the heating unit is composed of an electric heater. As shown in FIG. 8, when the heating unit is composed of an electric heater 102, the heating furnace 1 is provided with an electric heater 102, a transformer 104 and a thyristor . The temperature sensor 72 measures the surface temperature of the electric heater 102 (heating section).

A transformer 104 transforms a voltage supplied from a power supply source (not shown). The thyristor 106 functions as a switch and disconnects and connects between the transformer 104 and the electric heater 102 under the control of the controller 60 .

In the heating furnace 1 , parameters relating to the amount of heat applied to the object W to be heated are acquired by the acquisition unit 162 . Further, in the heating furnace 1 , the power supply to the electric heater 102 , that is, the heating of the electric heater 102 can be controlled by controlling the thyristor 106 with the control unit 164 of the control device 60 .

INDUSTRIAL APPLICABILITY The present disclosure can be used for heating furnaces.

W Object to be heated 1 Heating furnace 10 Furnace body 30 Heating unit 62 Obtaining unit 64 Control unit 162 Obtaining unit 164 Control unit

Claims (3)

a furnace body;
a heating unit provided in the furnace body;
an acquisition unit that acquires a parameter related to the amount of heat applied to the object to be heated;
Based on the parameters acquired by the acquisition unit, the total heating amount of the heat amount by radiation from the furnace body to the object to be heated and the heat amount by radiation from the heating unit to the object to be heated is constant. A control unit that controls the temperature of the heating unit so that
Furnace with The acquisition unit
Obtaining the temperature of the inner wall surface of the furnace body as the parameter,
The control unit
The heating furnace according to claim 1, wherein the temperature of the heating part is controlled based on the temperature of the inner wall surface of the furnace body obtained by the obtaining part. The control unit
A target temperature of the heating unit is derived based on the temperature of the inner wall surface of the furnace body acquired by the acquisition unit, and the temperature of the heating unit is controlled so as to achieve the derived target temperature. Furnace as described.

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