JPH0659443B2 - Optimal combustion control system for exhaust gas recirculation furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Industrial Application) The present invention relates to an optimum combustion control device for an exhaust gas recirculation furnace used in a baking furnace of a continuous coating line, etc. The present invention relates to an optimum combustion control device for an exhaust gas recirculation furnace, which aims to effectively utilize the discharged exhaust gas.

(Prior Art) In a conventional continuous coating line, as shown in FIG. 4, a coating is applied to the surface of a thin metal plate (hereinafter, referred to as a coil) 1 using a coater 2 and the coil 1 after the coating is applied. Is introduced into a baking oven 3, where the coil surface paint is baked.
At this time, a volatile solvent is generated from the paint on the coil surface in the furnace due to the baking temperature. Therefore, the volatile solvent in the furnace is guided to the combustion device 5 by using the exhaust gas fan 4, and the burner 6 is applied from outside to the burner 6. By giving heat quantity of fuel, combustion air, etc., unburned components are completely burned to achieve non-hazardous gasification and deodorization of odor peculiar to organic agents.
In the combustion control of the combustion device 5, the temperature of the combustion device generated gas from the combustion device 5 is detected by the temperature detector 7 and guided to the temperature controller 8, and the temperature detected by the temperature controller 8 is predetermined. This is done by operating the control valve 9 so that the target temperature is reached. Since the combustion device generated gas discharged from the combustion device 5 by this combustion control is generally high in temperature, a part of it is used as a supply gas for the heat source of the baking furnace 3, and the rest is guided to the waste heat boiler 10 to be finally discharged. The waste gas emitted from the waste heat boiler 10 is discharged from the chimney 12 to the atmosphere by the waste gas fan 11.

On the other hand, in order to control the temperature of each zone of the baking furnace 3, a zone cooler side pipeline a and a bypass side pipeline b are arranged in parallel from each zone, and a ratio control valve 13 is provided in each of these pipelines a and b. After the atmosphere gas of a relatively high temperature is cooled from the baking furnace 3 by the zone cooler 14 and merged with the bypass side, the merged atmosphere gas is returned to the furnace using the fan 15. During the return of the gas, the temperature of the atmospheric gas is detected by the temperature detector 16 and introduced into the temperature controller 17, where an operation output such that the deviation between the detected temperature and the predetermined target temperature becomes zero is obtained. The opening of the ratio control valve 13 is controlled based on this operation output so that the temperature in each zone becomes a predetermined temperature.

(Problems to be Solved by the Invention) Therefore, in the exhaust gas recirculation furnace system as described above, the waste heat boiler 10 recovers the heat of the combustion device generated gas discharged from the combustion device 5 to some extent. Since the target temperature of the controllers 8 and 17 is set to a constant value in advance, it is difficult to control the temperature corresponding to changes in the width, thickness, line speed, etc. of the coil 1, and as a result,
The combustion device generated gas is unnecessarily discharged from the chimney 12,
Alternatively, a large amount of heat was wasted from the zone cooler 14 in vain.

The present invention has been made to eliminate the above-mentioned problems, and it can be effectively re-used as a heat source in the furnace without releasing the gas generated in the furnace to the outside while keeping the temperature in the furnace at a predetermined temperature. It is an object of the present invention to provide an optimum combustion control device for an exhaust gas recirculation furnace that realizes energy saving by utilizing it.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the optimum combustion control device for an exhaust gas recirculation furnace according to the present invention guides the exhaust gas generated in the furnace to a combustion device and burns it. In the optimum combustion control device of the exhaust gas recirculation furnace, which controls the inside of the furnace to a predetermined temperature by using the supplied gas to output the obtained combustor-produced gas separately to the supplied gas and the waste gas, The waste gas flow rate control means provided in the output line of the waste gas, the zone cooler or burner for taking in the atmosphere gas in the furnace for each zone of the furnace and discarding the gas heat to the outside, and the bypass The temperature of the ambient gas is detected during the return of the ambient gas to the furnace, and the opening of the valve on the zone cooler side or the valve on the burner side is suppressed based on the detected temperature to adjust the opening of the bypass side valve. Shi Furnace temperature control means for controlling the furnace temperature, and maximum value acquisition means for obtaining the maximum output value from the operation output corresponding to the opening degree of the bypass side valve of each zone obtained by the furnace temperature control means And comparing the maximum output value obtained by the maximum value acquisition means with a predetermined target flow rate range value, and when the maximum output value exceeds the target flow rate range value, the maximum output value falls within the target flow rate range value. The flow rate set value calculating means for changing the target flow rate of the waste gas flow rate control means so as to enter and the nominal flow rate of this waste gas flow rate control means and the value determined by the condition in the furnace are compared, and based on the magnitude relation. And a temperature set value calculation means for increasing or decreasing the target temperature of the combustion device.

(Operation) Therefore, the present invention has taken the above-mentioned means, whereby the opening of the zone cooler side valve is suppressed as much as possible by the temperature controller for each zone, and the inside of the furnace is adjusted while adjusting the opening degree of the bypass side valve. While controlling the temperature, obtain the maximum output value from the operation output corresponding to the opening of the bypass valve by these temperature controllers, compare this maximum output value with the waste gas target flow rate range value, and discard the maximum output value. When the gas flow rate is exceeded,
By controlling the waste gas target flow rate so that the maximum output value falls within the balance range of the waste gas flow rate from the viewpoint of energy saving, the waste gas flow rate in the combustion device generated gas is suppressed as much as possible Make effective use of.

In addition, the waste gas target flow rate is compared with the value set in consideration of the conditions in the furnace such as material, product quality and energy saving, and the target temperature to the temperature controller of the combustion device is increased or decreased depending on the magnitude relationship. It efficiently burns fuel.

(Examples) Before describing the examples of the present invention, first, the basic principle for realizing the present invention will be described. now,
When the amount of heat supplied to the baking furnace 3 is Q, the following relational expression holds: Q = α · F ₂ · T (1) F = F ₁ + F ₂ (2) However, in the above equation, α is a proportional constant, T is a combustion device generated gas temperature, F is a combustion device generated gas flow rate, F ₁ is a waste gas flow rate, and F ₂ is a supply gas flow rate to the baking furnace 3.

Now, if the flow rate F of the gas generated by the combustion device is constant, and the flow rate F ₁ of the waste gas sent to the waste heat boiler 10 is increased, the flow rate F _{2 of the} supply gas decreases from the above equation (2), and accordingly the furnace flow rate F ₂ decreases. The internal heat supply Q decreases. Therefore, the following two conditions are required in order to keep the inside of the furnace at a predetermined temperature and to minimize the energy loss.

One of them is the ratio control valve 1 using the temperature controller 17.
If the zone cooler side pipe line 3 of No. 3 is closed and the bypass side pipe line b is opened, the amount of heat dissipated from the zone cooler 14 to the outside can be reduced.

The other one is that the zone cooler side pipe a of the ratio control valve 13 is fully closed, and the waste gas flow rate F ₁ is decreased and the supply gas flow rate F ₂ is increased when the temperature in the furnace is decreased. If so, the temperature inside the furnace can be raised.

Therefore, as is clear from the above two conditions, if the waste gas flow rate F ₁ is adjusted so that the zone cooler side pipe a of the ratio control valve 13 is always closed, the furnace temperature is controlled to a predetermined value. You can do it. Incidentally, the fact that the waste gas flow rate F ₁ is higher than necessary indicates that the combustion device generated gas temperature is higher than necessary, that is, the burner 6 wastefully consumes fuel. In this case, the target temperature of the temperature controller 8 may be lowered, and instead, the waste gas flow rate F ₁ may be decreased and the supply gas flow rate F ₂ may be increased. That is, the waste gas flow rate F ₁ is controlled so that the zone cooler side pipe a of the ratio control valve 13 is fully closed, and the combustion device generated gas temperature is controlled so that the waste gas flow rate F ₁ is also minimized. Thus, an optimum combustion control system can be realized.

Therefore, the device of the present invention has been realized based on the above basic principle, and one embodiment of the device of the present invention will be described below with reference to FIG. In the figure, the same parts as those of the conventional device (FIG. 4) are designated by the same reference numerals, and detailed description thereof will be omitted. That is, this optimum combustion control device is provided with the furnace temperature control means 21, for each zone of the baking furnace 3.
... are provided, and the plurality of furnace temperature control means 21, ...
The maximum value acquisition means 22 is provided on the operation output side of the temperature controllers 14 ,. This maximum value acquisition means 22 acquires the maximum output value MV _max with the operation output value with the largest opening degree of the bypass side conduit b from the operation outputs of the temperature controllers 17, ... The output value MV _max is sent to the flow rate set value calculation means 23 that determines the target flow rate of the waste gas. The flow rate set value calculation means 23 compares the maximum output value MV _max with a predetermined target flow rate range value (MVH-MVL), and the maximum output value MV is obtained.
_{When max} exceeds the target flow rate range value, it has a function of changing the target flow rate of the waste gas flow rate control means 25 via the switch 24 so that the maximum output value falls within the target flow rate range value. The waste gas flow rate control means 25 has a flow meter 25a and a flow rate adjusting valve 25b installed in the waste gas line, and performs an adjustment calculation based on the deviation between the detected flow rate of the flow meter 25a and the target flow rate to obtain an operation output. A flow controller 25c for obtaining the flow rate is provided. The switch 24 is, for example, manually switched, and is normally closed on the flow rate set value computing means 23 side.

Reference numeral 26 compares the target flow rate FSV of the flow rate controller 25c output from the flow rate setting value calculation means 23 with a value (FSL + DD) determined by the conditions in the furnace, and the target of the combustion temperature controller 8'according to the magnitude relationship. It is a temperature set value calculation means for changing the temperature. Note that FSL is a prescribed value that is determined by the baking state of the baking furnace 3. Specifically, when the waste gas flow rate decreases, the furnace pressure rises, and the dew point rises due to a decrease in the amount of atmospheric air entering the baking furnace 3. When the dew point rises, the quality of the coating film on the coil surface deteriorates. Therefore, the FSL serves as the lower limit of the waste gas flow rate. DD is a value determined from the viewpoint of energy saving in the furnace. Reference numeral 27 is a pressure controller, which does not directly relate to the gist of the present invention, but when the pressure inside the furnace is controlled with the highest priority, the switch 24 is switched to make a cascade connection with the flow controller 25c. The waste gas flow rate is cascade-controlled based on the outputs of the furnace pressure detector 27, the O ₂ concentration detector 28, and the supply gas pressure detector 30.

Next, the operation of the apparatus configured as described above will be described.
The coating is applied to the surface of the coil 1 using the coater 2 and introduced into the baking furnace 3 for baking. At this time, the atmosphere gas of the baking furnace 3 is changed to the zone cooler side conduit a of the furnace temperature control means 21. Also, the gas temperature is taken in through the bypass side conduit b and the gas temperature is detected by the temperature detector 16. Here, the temperature controller 17
Operates the ratio adjusting valve 13 by obtaining an operation output based on the deviation between the detected gas temperature from the temperature detector 16 and the target temperature. At this time, the zone cooler side pipe a is set to the closed state as much as possible, and the bypass is set. The temperature inside the furnace is controlled by adjusting the opening of the side pipe b.

The adjusting operation of the ratio adjusting valves 16, ...
, For each zone, and the operation outputs of the temperature controllers 17, ... Corresponding to the respective openings of the bypass side pipelines b, ... At this time are sent to the maximum value acquisition means 22. The maximum value acquisition means 22 acquires the largest operation output as the maximum output value MV _max from the operation outputs of the plurality of zones,
This maximum output value MV _max is sent to the flow rate setting value calculation means 23. Here, the flow rate set value calculation means 23 uses the maximum output value MV _max and the predetermined target flow rate range value (MV) shown in FIG.
H-MVL), and when the maximum output value MV _max exceeds the target flow rate range value MVH as shown in FIG. 2 (A), it is determined that the flow rate of the supply gas F ₂ is insufficient, and the flow rate set value is set. The calculation means 23 gradually lowers the target flow rate of the flow rate controller 25c.

Then, the supply gas flow rate increases and the atmospheric gas temperature of the baking furnace 3 rises. Therefore, the temperature controller 17 detects the gas temperature and reduces the valve opening of the bypass side conduit b of the ratio control valve 13. . The flow rate setting value calculation means 23 continues to decrease the target flow rate FSV of the flow rate controller 25c until the maximum output value of the bypass side opening obtained from the maximum value calculation means 22 falls below the target flow rate range value MVH, and the target flow rate range is calculated. When the value becomes MVH or less, the target flow rate FSV is held. That is, the change of the target flow rate is stopped when the state shown in FIG. 2A is changed to the state shown in FIG. 2B.

On the contrary, when the maximum output value MV _max exceeds the predetermined target flow rate range value MVL as shown in FIG. 2 (C), the target flow rate FSV is increased until the maximum value MV _max becomes equal to or more than MVL as described above.
Is changed, and when the target flow rate range value (balance range) is entered, the flow rate set value calculation means 23 holds the target flow rate. Therefore, by performing the above-described series of controls, it is possible to effectively use the produced gas obtained in the combustion device 5 while reducing the amount of waste gas released into the atmosphere and the amount of gas from the zone cooler side.

On the other hand, when the waste gas flow rate is too low, the furnace pressure rises, the amount of atmospheric air entering the baking furnace 3 decreases, and the dew point in the furnace rises. When the dew point rises, the quality of the coating film on the coil surface deteriorates. This means that the waste gas flow rate cannot be made lower than the flow rate lower limit value FSL in view of the quality of the coating film.

Therefore, the temperature setting value calculation means 26 has a waste gas flow rate lower limit value FSL in advance, and the flow rate target value F of the flow rate controller 25c.
SV is compared with the flow rate lower limit value FSL + bias value DD (dead band). As shown in FIG. 3, when FSV> FSL + DD, it is determined that the waste gas flow rate F ₁ is too large, and the target temperature of the combustion device 5 is high. Then, the target temperature of the temperature controller 8'is lowered. As a result, the temperature of the gas generated by the combustion device decreases, and therefore, from the above formula (1), the supply gas F ₂
Is increased, and the target flow rate FSV of the flow rate controller 25c is decreased according to the equation (2) and the relationship of FIG. That is, the temperature setting value calculation means 26 keeps lowering the target temperature of the temperature controller 8'until FSV is in the balance region, that is, FSV≤FSL + DD, and FS
Hold the final value when V ≦ FSL + DD,
This value is used as the target temperature of the temperature controller 8 '.

On the contrary, when FSV <FSL + ID (ID is a predetermined value from the product material), it is determined that the target temperature of the combustion device 5 is low, and FSV ≧ FSL + ID
Until the target temperature of the temperature controller 8'is increased. Finally, control is performed so that the balance range shown in FIG. 3 (B) is entered, and the temperature controller 17, the flow rate controller 25c and the temperature controller 8'are controlled in an optimum state to realize energy saving. It becomes possible.

Therefore, according to the configuration of the above embodiment, the in-furnace temperature control means 21 closes the valves of the zone cooler side pipes a, ... While operating, the maximum value of the valve opening of the bypass side pipes b, ..., That is, the maximum output value is obtained from the operation output of each temperature controller 17, ..., and the maximum output value and the predetermined waste gas target flow rate range value are obtained. Since the target flow rate of the waste gas is changed so that the maximum value is within the target flow rate range value while comparing the above, the amount of waste gas in the gas generated by the combustion device is reduced and the supply gas is effectively supplied to the baking furnace 3. The amount of waste gas discharged from the chimney 12 and the amount of furnace atmosphere gas discarded from the zone cooler side can be greatly reduced. In addition, a waste gas flow controller 25c
Since the target temperature of the temperature controller 8'is made variable while comparing the target flow rate of No. 2 and the required condition value in the furnace,
A well-balanced combustion can be performed while considering the waste gas flow rate. Therefore, if the series of controls as described above are performed, the optimum control can be automatically realized without knowing the type of coil 1, the line speed, the size of the baking furnace 3, the O ₂ concentration, the solvent amount, etc. In addition, it can greatly contribute to energy saving. Further, the temperature controller 17 of the baking furnace 3, the waste gas flow rate controller 25c, and the temperature controller 8'of the combustion device 5 '
If the control cycle is increased in this order, optimal control can be performed without causing interference.

In the above embodiment, as a temperature control method for the baking furnace 3, the zone cooler 14 is provided in the zone cooler side pipe a, and the atmospheric gas of a relatively high temperature is taken from the inside of the furnace to cool the zone cooler 14. Although the temperature inside the furnace is controlled while being merged with the atmospheric gas at a high temperature, for example, a burner 41 is provided instead of the zone cooler 14, and the atmospheric gas having a relatively low temperature is taken from the inside of the furnace to control the temperature. The temperature inside the furnace may be controlled by raising the temperature and joining it with the atmospheric gas at a low temperature. Also, the combustion device 5
May be a catalytic combustion device or a fume incinerator, or may be another combustion device. Further, the present invention can be applied to any furnace as long as it recirculates the gas generated by the combustion device. In addition, the present invention can be modified in various ways without departing from the scope of the invention.

[Effects of the Invention] As described in detail above, according to the present invention, an apparatus can be constructed only by a feedback control system without needing various data of a plant, and the gas generated from a furnace causes very little energy loss. It can be recycled to the furnace and used in a small amount, which can greatly contribute to energy saving. Further, the non-interference control can be easily realized by increasing the control cycle in the order of the furnace temperature controller, the waste gas flow controller and the temperature controller of the combustion device.

[Brief description of drawings]

1 to 3 are shown for explaining an embodiment of an optimum combustion control apparatus for an exhaust gas recirculation furnace according to the present invention. FIG. 1 is a block diagram of the apparatus of the present invention, and FIG. FIG. 3 is an explanatory diagram for determining a target flow rate of the waste gas flow rate control means, FIG. 3 is an explanatory diagram for determining a target temperature in the combustion device, and FIG. 4 is a configuration diagram of a conventional device. 1 ... Coil, 2 ... Coater, 3 ... Baking furnace, 5 ... Combustor, 6 ... Burner, 8 '... Temperature controller, 13 ...
Ratio control valve, 14 ... zone cooler, 16 ... temperature detector, 17 ... temperature controller, 21 ... furnace temperature control means,
22 ... Maximum value acquisition means, 23 ... Flow rate set value calculation means, 25 ... Waste gas flow rate control means, 25a ... Flow meter, 25b ... Control valve, 25c ... Flow rate controller, 26 ...
... Temperature setting value calculation means.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical indication location G05D 23/00 F 9132-3H B 9132-3H (72) Inventor Muguruma Nobuyoshi Ishizu Nishimachi, Sakai City, Osaka Prefecture No. 5 Nisshin Steel Co., Ltd. in Sakai Works (72) Inventor Naoki Tohhara No. 5 Ishizu Nishimachi, Sakai City, Osaka Prefecture No. 5 In Niishin Steel Co., Ltd. in Sakai Works (72) Hozumi Akita 4-29 Honmachi, Higashi-ku, Osaka City, Osaka Prefecture House number Toshiba Kansai branch office

Claims (1)

[Claims] 1. An exhaust gas produced in a furnace is introduced into a combustion apparatus and burned, and the resulting combustion apparatus produced gas is divided into a supply gas and a waste gas and output, and the supply gas is used as a heat quantity in a furnace. In an optimal combustion control device for an exhaust gas recirculation furnace that recirculates inside, a waste gas flow rate control means provided in the output line of the exhaust gas, and the ambient gas in the furnace taken in for each zone of the furnace Detecting the temperature of the ambient gas in the middle of returning the ambient gas into the furnace through a burner and a bypass that take in the ambient gas in the furnace or a zone cooler that dissipates heat to the outside, In-furnace temperature control means for controlling the in-furnace temperature while controlling the opening degree of the bypass side valve by suppressing the opening degree of the zone cooler side valve or the burner side valve based on the detected temperature, and the in-furnace temperature Control means Maximum value obtaining means for obtaining the maximum output value from the operation outputs corresponding to the opening degree of the bypass side valve of each zone obtained in step 1, and the maximum output value obtained by this maximum value obtaining means and the predetermined target flow rate. Flow rate set value calculating means for comparing the threshold value and changing the target flow rate of the waste gas flow rate control means so that the maximum output value falls within the target flow rate range value when the maximum output value exceeds the target flow rate range value. And a value FSL + DD (F determined by the target flow rate of the waste gas flow rate control means and the conditions in the furnace.
SL: lower limit value of waste gas flow rate, DD: means a bias value determined from the viewpoint of energy saving in the furnace), and temperature setting value calculating means for increasing / decreasing the target temperature of the combustion apparatus based on the magnitude relationship. An optimum combustion control device for an exhaust gas recirculation furnace, characterized by comprising: