JPH02119972A - Controller for optimum combustion in exhaust gas-recirculation furnace - Google Patents

Abstract

PURPOSE:To reutilize the gaseous product as the heat source in a furnace by providing a means for controlling the flow rate of the waste gas, a means for adjusting the opening degree of a bypass-side valve and controlling the furnace temp., a means for detecting the maximum value of an manipulated output, etc., to the output line of waste gas. CONSTITUTION:A furnace temp. controlling means 21 is provided in each zone of a baking furnace 3 in the optimum combustion controller. A maximum value receiving means 22 is provided on the manipulated output side of a temp. controller 14 constituting a part of the plural furnace temp. controlling means 21. The maximum value receiving means 22 receives the manipulated output value of the highest opening degree of the bypass-side pipeline (b) among the manipulated outputs of a temp. controller 17 in the respective zones as the maximum output value MWmax which is sent to a flow rate set value calculating means 23 for determining the desired flow rate of the waste gas.

Description

Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) The present invention relates to an optimal combustion control device for an exhaust gas recirculation furnace used in a baking furnace of a continuous painting line, and in particular, This invention relates to an optimal combustion control device for an exhaust gas recirculation furnace that makes effective use of the waste gas.

(Prior Art) As shown in FIG. 4, a conventional continuous painting line applies paint to the surface of a thin metal plate (hereinafter referred to as a coil) 1 using a coater 2, and also coats the coil 1 after this application. is led to a baking furnace 3, where the coil surface paint is baked.

At this time, in the furnace, volatile solvent is generated from the paint on the coil surface due to temperature, so the volatile solvent in the furnace is guided to the combustion device 5 using the exhaust gas fan 4, and from there to the burner 6 from the outside. By supplying heat from fuel and combustion air, the unburned components are completely combusted, turned into non-toxic gases, and the odor peculiar to organic agents is deodorized.

In addition, the combustion control of the combustion device 5 is performed by detecting the temperature of the combustion device generated gas from the combustion device 5 with a temperature detector 7 and guiding it to a temperature controller 8. The detected temperature is determined by the temperature controller 8. This is done by operating the control valve 9 so that the target temperature is reached. The combustion device generated gas discharged from the combustion device 5 by this combustion control is generally at a high temperature, so a part of it is used as a supply gas as a heat source for the firing furnace 3, and the rest is led to the waste heat boiler 10 and is finally used as a heat source. The waste gas discharged from the waste heat boiler] 0 is discharged into the atmosphere from a chimney 12 by a 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 conduit a and a bypass side conduit S 4 are provided from each zone, and a ratio control valve 1 is installed in each of these conduits a and b.
3 is provided, and after the atmospheric gas at a relatively high temperature from the baking furnace 3 is cooled by the zone cooler 14 and merged with the bypass side, the combined atmospheric gas is returned to the furnace using the fan 15. , during the return of this atmospheric gas, l! of the atmospheric gas! Detect i degrees with temperature detector 16 and measure temperature 2
7 to obtain an operating output that makes the deviation between the detected temperature and the predetermined target temperature zero, and based on this operating output, control the opening degree of the ratio 21 control valve 13, The temperature is controlled to be a predetermined temperature.

(Problem to be Solved by the Invention) Therefore, in the exhaust gas recirculation furnace system as described above, a certain amount of heat is recovered from the combustion device generated gas discharged from the combustion device 5 by the waste heat boiler 10, but the temperature Since the target temperatures of the controllers 8 and 17 are preset to constant values, it is difficult to control the temperature in response to changes in the width, thickness, line speed, etc. of the coil 1, for example, and as a result,
Combustion device generated gas is wastefully released from the chimney 12,
Alternatively, a large amount of heat from the zone cooler 14 was often wasted.

The present invention was made in order to eliminate the above-mentioned problems, and it is possible to maintain the inside of the furnace at a predetermined temperature and to effectively use the gas generated inside the furnace as a heat source without releasing it to the outside. The objective is to provide an optimal combustion control device for an exhaust gas recirculation furnace that achieves energy savings through reuse.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the optimal 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 an optimal combustion control device for an exhaust gas recirculation furnace, which separates and outputs the collected combustion device generated gas into feed gas and waste gas, and controls the inside of the furnace to a predetermined temperature using the feed gas, A waste gas flow rate control means provided in the output line of the waste gas, and a zone cooler or burner that takes in the atmospheric gas in the furnace and discards the gas heat to the outside for each zone of the furnace, and a bypass. The temperature of the atmospheric gas is detected during the return of the atmospheric gas into the furnace, and based on this detected temperature, the opening degree of the zone cooler side valve or the burner side valve is suppressed, and the opening degree of the bypass side valve is adjusted. Furnace temperature control means that controls the furnace temperature while adjusting it, and a maximum value to obtain the maximum output value from among the operating outputs corresponding to the opening degrees of the bypass side valves of each zone obtained by this furnace temperature control means. An acquisition means compares 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 is determined as the target flow rate range value. and a flow rate setting value calculation means for changing the target value of the waste gas flow rate control means so that the waste gas flow is within the furnace. and temperature setting value calculation means for increasing or decreasing the target temperature of the combustion device based on the magnitude relationship.

(Function) Therefore, by taking the above-mentioned measures, the present invention suppresses the opening degree of the zone cooler side valve as much as possible using the temperature controller for each zone, and controls the opening degree of the bypass side valve while controlling the inside of the furnace. In addition to controlling the temperature, the maximum output value is obtained from the operation output corresponding to the opening degree of the bypass valve by these temperature controllers,
This maximum output value is compared with the waste gas target flow rate range value, and if the maximum output value exceeds the waste gas flow rate range value, the maximum output value is within the waste gas flow rate range value, which is the balance range from an energy saving perspective. By changing and controlling the waste gas target flow rate so that the waste gas flow rate increases, the waste gas flow rate of the combustion device generated gas is suppressed as much as possible, and the supply gas flow rate is effectively utilized.

In addition, the target flow rate of waste gas is compared with the value determined by taking into account the conditions inside the furnace, such as material, product quality, and energy saving aspects, and the target temperature for the temperature controller of the combustion equipment is increased or decreased based on the magnitude relationship. It burns fuel efficiently.

(Example) Below, prior to detailed description of the present invention.

First, the basic principle for realizing the present invention will be explained. Now, if the amount of heat supplied to the baking furnace 3 is Q, then Q-α ・F, @T...
(1) Fs-F, +F2
... The following relational expression (2) holds true. However, in the above equation, α is a proportionality constant, T is the combustion device generated gas; H degrees, F is the combustion device generated gas flow rate, Fl is the waste gas flow rate, and F2 is the supply gas flow rate to the baking furnace 3.

Now, assuming that the combustion device generated gas flow filtF is constant, the waste gas flow sent to the waste heat boiler 10 is F1.If 1 is increased, the supply gas flow rate F2 decreases from equation (2), and accordingly, As a result, the heat EuQ supplied to the furnace decreases.

Therefore, in order to maintain a predetermined temperature in the furnace and to minimize energy loss, the following two conditions are required.

(1) One of them is to use the temperature controller 17 to control the ratio control valve 1.
By closing the zone cooler side pipe line a of No. 3 and opening the bypass side pipe line a, the amount of heat disposed of from the zone cooler 14 to the outside can be reduced.

(2) The other method is to fully open the zone cooler side pipe a of the ratio control valve 13, and when the temperature inside the furnace decreases, the waste gas flow decreases Fl and increases the supply gas flow rate F2. If so, the temperature inside the furnace can be increased.

Therefore, as is clear from the following two conditions, if the waste gas flow W F 1 is adjusted so that the zone cooler side pipe a of the ratio control valve 13 is always closed, the temperature inside the furnace can be maintained at a predetermined value. This means that it can be controlled. Incidentally, the waste gas flow W F
The fact that l is larger than necessary indicates that the combustion device produced gas temperature is higher than the required amount, that is, the burner 6 wastes fuel. In this case, the temperature controller 8
and instead reduce the target temperature of the waste gas flow f:kF1
What is necessary is to increase the supply gas flow ff1F2 by decreasing . In other words, if the waste gas flow ff1F is controlled so that the zone cooler side pipe a of the ratio control valve 13 is fully opened, and the combustion device generated gas temperature is controlled so that this waste gas flow rate F1 is also minimized, An optimal combustion control system can be realized.

Therefore, the apparatus of the present invention has been realized based on the above basic principle, and one embodiment of the apparatus of the present invention will be described below with reference to FIG. In this figure, the same parts as those in the conventional device (FIG. 4) are given the same reference numerals, and detailed explanation thereof will be omitted. In other words, this optimum combustion control device includes furnace temperature control means 21 for each zone of the baking furnace 3.・
... are provided, and these plurality of furnace temperature control means 21.
Temperature controller 14 constituting the negative part of... A maximum value acquisition means 22 is provided on the operation output side of . This maximum value acquisition means 22 calculates the temperature 2fii for each zone.
;; Out of the operating outputs of 117, . . . , the operating output value with the largest opening degree of the bypass side pipe is set as the maximum output value M.
This maximum output value M V wa is obtained as Va+ax.
Flow rate setting value calculation means 2 for determining the target flow rate of waste gas by x
Send to 3. This flow rate setting value calculation means 23 calculates the maximum output value M V ll1ax and a predetermined target flow rate range value (
MVH-MVL), the maximum output value MVIlax
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 limit value when the value exceeds the target flow rate limit value. This waste gas flow rate control means 25 has a flow meter 25a and a flow rate adjustment valve 25b installed in the waste gas line, and performs adjustment calculations based on the deviation between the flow rate detected by the flow meter 25a and the 1'' mark. Flow rate controller 25 for obtaining operational output
c is provided. Note that the switch 24 is switched by manual operation, for example, and is normally closed on the flow rate setting value calculation means 23 side.

Reference numeral 26 compares the target flow rate FSV of the flow rate controller 25c outputted from the flow rate setting value calculating means 23 with a value (FSL+DD) determined by the conditions in the furnace, and determines the target of the combustion temperature 2m meter 8' according to the magnitude relationship. This is temperature set value calculation means for changing the temperature. Note that FSL is a specified value determined by the baking condition of the baking furnace 3, and specifically, when the waste gas flow rate decreases, the furnace pressure increases, and as the amount of air entering the baking furnace 3 decreases, the dew point increases. . As the dew point increases, the quality of the coating on the coil surface deteriorates. Therefore, FSL has a role as a lower limit value of the waste gas flow rate. DD is a value determined from the viewpoint of energy saving in the furnace. Reference numeral 27 denotes a pressure one-week meter, which is not directly related to the gist of the present invention, but when controlling the pressure in the furnace with the highest priority, the switch 24 is switched to control the flow rate controller 25c. The waste gas flow rate is controlled in cascade based on the outputs of the furnace pressure detector 27, concentration detector 28, and supply gas pressure detector 30.

Next, the operation of the apparatus configured as above will be explained.

Coating is applied to the surface of the coil 1 using a coater 2 and then introduced into the baking furnace 3 for baking. The temperature of the gas is detected by the temperature detector 16 taken in through the passage a and the bypass side pipe line S. Here, the temperature controller 17
obtains an operating output based on the deviation between the detected gas temperature from the temperature detector 16 and the target temperature and operates the ratio control valve 13. At this time, the zone cooler side pipe a is set to the closed state as much as possible, and the bypass The temperature inside the furnace is controlled by adjusting the opening of the side pipe.

Ratio control valve 16 as shown in 1- below. The adjustment operations for... are performed for each zone of the baking furnace 3, and at this time, the temperature controllers 17.・
... are respectively sent to the maximum value acquisition means 22. This maximum value acquisition means 22 selects the largest operational output from among the operational outputs of a plurality of zones as a maximum output value M V l
1aX, and sends this maximum output value M V wax to the flow rate setting value calculation means 23. Here, the flow rate setting value calculating means 23 calculates the maximum output value M V ff1aX and the second
When the maximum output value MVa+ax exceeds the target flow rate range value MVH as shown in Figure 2 (A), the supply air F
It is determined that the flow rate of step 2 is insufficient, and the flow rate set value calculation means 23
The target flow rate of the flow rate controller 25c is gradually lowered.

Then, the supply gas flow rate increases and the atmospheric gas temperature in the baking furnace 3 increases, so the temperature controller 17 detects the gas temperature and reduces the valve opening of the bypass side pipe of the ratio control valve 13. . The flow rate setting value calculation means 23 operates the flow rate 1-point meter 25c until the maximum output value of the bypass side pressure obtained from the maximum value calculation means 22 becomes lower than the 11-mark flow barrier value MVH.
Continuing to lower the target flow rate FSV, the target flow rate range value MV
When the target flow W F S V falls below H, the target flow W F S V is held. In other words, the change in target flow rate is stopped when the state changes from FIG. 2(A) to FIG. 2(B).

On the other hand, when the maximum output value MVtrrax exceeds the predetermined target flow rate range value MVL as shown in FIG. Value (balance range)
When the target flow rate is reached, the flow rate setting value calculating means 23 holds the target flow rate. Therefore, by performing a series of controls as described above, it is possible to utilize the generated gas obtained in the combustion device 5 in a Q-effective manner while reducing the amount of waste gas released into the atmosphere and the gas evaporation from the zone cooler side.

-W: If the amount of waste gas is too small, the furnace pressure will decrease and the amount of atmospheric air entering the baking furnace 3 will decrease, increasing the dew point inside the furnace. As the dew point increases, the quality of the coating on the coil surface deteriorates. This means that the waste gas flow rate cannot be lower than the flow rate lower limit value FSL from the viewpoint of coating film quality.

Therefore, the temperature set value calculating 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 25 (
SV is compared with the flow rate lower limit value FSL + bias value DD (dead band), and as shown in FIG. It is determined that the temperature is too high, and the target temperature of the temperature controller 8' is lowered. As a result, the temperature of the combustion device produced gas decreases, so the flow rate of the supply gas F2 increases according to equation (1), and according to the equation (2) above and the relationship shown in FIG. The target flow=psv decreases.In other words, the temperature set value calculation means 26
is the balance range.

In other words, the target temperature of the temperature controller 8' is continued to be lowered until FSV ≦ FSL - DD, and the FS
Hold the final value when V≦FSL+DD,
This value is set as the target temperature of the temperature controller 8'.

Conversely, if FSV<FSL+ID (ID is a predetermined value based on the product material), it is determined that the target temperature of the combustion device 5 is low, and FSV≧FSL+ID.
Increase the temperature at the 11th mark on the temperature controller 8' until the temperature reaches .

Finally, the temperature controller 17. is controlled so as to enter the balance range shown in FIG. 3(B). Both the flow rate controller 25 (and the temperature controller 8') are controlled in an optimal state, making it possible to save energy.

Therefore, according to the configuration of the embodiment described above, the furnace temperature control means 21 closes the valves of the zone cooler side pipes a, . . . as much as possible, and closes the valves of the bypass side pipes a, . While manipulating the valve opening degree, obtain the maximum output value from the maximum value of the valve opening degree of the bypass side pipes 17, . . . , that is, the operation output of each temperature controller 17, . The waste gas target flow rate is changed so that the maximum value falls within the target flow rate range while comparing the target waste gas flow rate with the waste gas target flow rate range.
By reducing the amount of waste gas out of the combustion device generated gas, the gas supplied to the baking furnace 3 can be effectively used, and the amount of furnace atmosphere gas that is discarded from the waste gas outlet from the chimney 12 and the zone cooler side can be reduced. This can be significantly reduced. In addition, the target temperature of the temperature controller 8' is changed by =I while comparing the target flow rate of the waste gas flow rate controller 25c with the required condition value in the furnace, so the waste gas flow rate is taken into consideration. However, it is possible to achieve well-balanced combustion. Therefore, if the above series of controls is performed, especially the type of coil 1.

Optimum control can be automatically achieved without knowing the line speed, the size of the baking furnace 3, the 02 concentration, the amount of solvent, etc., and it can also greatly contribute to energy savings. Also, the temperature controller 17 of the baking furnace 3. By increasing the control period in the order of the waste gas flow rate controller 25C and the temperature controller 8' of the combustion device 5, optimal control can be performed without causing interference with each other.

In the above embodiment, as a temperature control method for the baking furnace 3, a zone cooler 14 is provided in the zone cooler side pipe a, and atmospheric gas at a relatively high temperature is taken in from inside the furnace and cooled by the zone cooler 14. The temperature inside the furnace is controlled by merging the high-temperature atmospheric gas, but for example, a burner 41 is provided in place of the zone cracker 14, and relatively low-temperature atmospheric gas is taken in from inside the furnace and the temperature is controlled by the burner. Alternatively, the temperature inside the furnace may be controlled by raising the temperature to join the lower temperature atmospheric gas. Further, the combustion device 5 may be a catalytic combustion device or a fume insulator, or may be any other combustion device. Further, the present device can be applied to any type of furnace as long as it recirculates the gas produced by the combustion device. In addition, the present invention can be implemented with various modifications without departing from the gist thereof.

[Effects of the Invention] As detailed above, according to the present invention, it is possible to construct a device using only a feedback control system without requiring various plant data, and moreover, it is possible to control the gas generated from the furnace with very little energy loss. It can be recirculated to the furnace in a small amount and can greatly contribute to energy savings. Furthermore, non-interference control can be easily achieved by increasing the control period in the order of the furnace temperature controller, waste gas flow rate controller, and combustion device temperature controller.

[Brief explanation of the drawing]

1 to 3 are shown to explain an embodiment of the optimal combustion control device for an exhaust gas recirculation furnace according to the present invention, and FIG. 1 is a block diagram of the device of the present invention, and FIG. FIG. 3 is an explanatory diagram for determining the target flow rate of the waste gas flow rate control means, FIG. 3 is an explanatory diagram for determining the 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
... Combustion device, 6... Burner, 8'... Temperature controller, 13... Ratio control valve, 14... Zone cooler,
16...Temperature detector, 17...Temperature controller, 2]・
...Furnace temperature control means, 22...Maximum value acquisition means, 2
3... Flow rate setting value calculation means, 25... Waste gas flow rate control means, 25a... Flow meter, 25b... Control valve,
25C...Flow rate controller, 26...Temperature set value calculation means. Applicant's agent Patent attorney Takehiko Suzue

Claims (1)

[Claims] Exhaust gas generated in the furnace is led to a combustion device and combusted, and the resulting combustion device generated gas is divided into supply gas and waste gas and output, and the supply gas is converted into calorific value. An optimal combustion control device for an exhaust gas recirculation furnace that recirculates the exhaust gas into the furnace includes a waste gas flow rate control means provided in the waste gas output line, and a waste gas flow rate control means installed in the output line of the waste gas, and a means for controlling the atmospheric gas in the furnace for each zone of the furnace. The temperature of the atmospheric gas is detected while it is being returned to the furnace via a zone cooler or burner that dissipates the gas heat to the outside and a bypass, and based on this detected temperature, the temperature of the atmospheric gas is detected by the valve or Furnace temperature control means for controlling the furnace temperature while suppressing the opening degree of the burner side valve and adjusting the opening degree of the bypass side valve; Maximum value acquisition means obtains the maximum output value from the operation output corresponding to the opening degree, and the maximum output value obtained by this maximum value acquisition means is compared with a predetermined target flow rate range value, and the maximum output value is determined as the target. The process of 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 limit value when the flow rate limit value is exceeded is controlled by a set value calculation means and a target of the waste gas flow rate control means. Optimal combustion for an exhaust gas recirculation furnace, characterized in that it is equipped with a temperature set value calculating means for comparing the flow rate with a value determined by the conditions in the furnace and increasing or decreasing the target temperature of the combustion device based on the magnitude relationship. Control device.