JPH0556195B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is designed to suck and discharge exhaust gas generated in a paint drying oven to which high-temperature hot air is circulated and supplied at an exhaust amount depending on the exhaust gas concentration. This invention relates to a method of operating a drying device.

[Prior art and its problems]

For example, an automobile paint drying device that heats and reaction-cures the paint film of an automobile body transported through a paint baking drying oven has a drying oven 1 as shown in FIG.
The interior is formed into a plurality of zones, and each zone is provided with a hot air circulation system N that includes a hot air circulation fan 2 and a burner 3. The hot air circulating fan 2 draws hot air from the drying oven 1 into the burner. 3 and then circulated again into the furnace to heat the atmosphere inside the furnace where the objects to be coated, the automobile bodies 4, 4..., are transported to a predetermined baking temperature (usually around 170 to 180 degrees Celsius). That's what I do.

In addition, when the automobile body 4 carried into the furnace is heated, organic solvents such as thinner and toluene, paint resins, hardeners, etc. contained in the paint evaporate from the coating film, and harmful odor components are released into the furnace. If the concentration of harmful malodorous components increases, there is a risk that the drying efficiency of the paint film will deteriorate, quality defects such as yellowing of the paint film occur, and there is a risk of fire. The exhaust gas containing harmful malodorous components is sucked and discharged out of the furnace by an exhaust fan 6 installed in an exhaust duct 5.

In addition, from the viewpoint of pollution prevention, the exhaust gas sucked and discharged through the exhaust duct 5 is sent to a catalytic combustion type deodorizing treatment device 7, and a burner 8 provided in the deodorizing treatment device 7 is heated to a predetermined reaction temperature (usually 300~400
The noxious odor is oxidized and decomposed by passing through a catalyst 9 heated to 15°F (°C) to produce clean deodorized gas, which is then released to the outside.

However, in the past, the exhaust volume of the exhaust fan 6 was adjusted to the maximum exhaust gas concentration expected when the automobile bodies 4, 4... were continuously conveyed through the drying oven 1 at intervals of about 20 m, for example. Since the temperature is set to a constant value, a large amount of exhaust gas will not be exhausted even when the drying device starts to raise the temperature inside the drying oven 1, or when the number of automobile bodies 4 to be conveyed decreases and the amount of exhaust gas generated decreases. More than necessary is being suctioned and discharged from the duct 5. Therefore, the electric power cost of the exhaust fan 6 increases, and at the same time, the heat loss inside the furnace when the temperature rises becomes very large, which increases the cost of gas fuel for the burner 3 that heats the hot air. is sent to the deodorizing treatment device 7, the catalyst 9 cannot be heated by the oxidative combustion heat generated by oxidative decomposition of the combustible components in the exhaust gas, and the catalyst 9 cannot be heated.
There was also a problem in that the cost of gas fuel for the burner 8 for heating the gas to a predetermined reaction temperature increased.

Therefore, in Utility Application No. 59-127031 (Utility Model Application No. 61-44277), the present applicant detected the concentration of exhaust gas in the furnace and variably controlled the rotation speed of the exhaust fan 6 according to the detected concentration of exhaust gas. By doing so, we have proposed a coating drying oven that saves energy by reducing the electricity cost of the exhaust fan 6 and the gas fuel cost of the burner 8 provided in the deodorizing device 7.

However, if the rotational speed of the exhaust fan 6 is simply variably controlled to increase or decrease the exhaust volume according to the exhaust gas concentration in the furnace, the balance of air supply and exhaust in the furnace will be disrupted, causing formation of gas on both sides of the drying furnace 1. A large amount of hot air leaks from the entrance/exit of the drying furnace, causing heat loss, and the surrounding environment is contaminated by harmful odor components contained in the leaked hot air.
A new problem arose: a large amount of cold outside air entered the furnace, disrupting the temperature distribution inside the furnace and impairing the quality of the coating film.

[Purpose of the invention]

Therefore, the present invention aims to reduce the displacement of the exhaust fan that sucks and discharges the exhaust gas in the furnace when the amount of exhaust gas generated in the furnace is very small, such as when the drying device starts to raise the temperature inside the drying furnace. By reducing the amount to a certain level, the electricity cost of the exhaust fan can be reduced and the energy can be increased. Energy saving is achieved by increasing or decreasing the exhaust volume of the exhaust fan according to the exhaust gas concentration, which changes depending on the number of products.In addition, in any case, the balance of air supply and exhaust inside the furnace is maintained, and the air flow from the entrance and exit of the drying furnace is maintained. It is an object of the present invention to provide a method of operating a drying device that can reliably prevent exhaust gas from leaking inside the furnace and outside air from entering the furnace.

[Structure of the invention]

In order to achieve this object, the present invention circulates and supplies hot air heated by a burner into a paint drying oven, and exhausts the exhaust gas generated in the drying oven using an exhaust fan that is rotated at an exhaust amount depending on the exhaust gas concentration. In the operating method of the drying device in which the exhaust gas is sucked and discharged by the burner, when the exhaust gas concentration is below a certain value that does not adversely affect the coating film, the exhaust gas is discharged at an amount equivalent to the amount of combustion air introduced to the burner. When the exhaust fan is rotated and the exhaust gas concentration exceeds the certain value, the displacement of the exhaust fan is increased or decreased in accordance with the change in the exhaust gas concentration, and at the same time the displacement of the exhaust fan that is increased or decreased and the combustion It is characterized by supplying heated fresh air into the furnace in an amount corresponding to the difference between the amount of air introduced and the amount of air introduced.

[Action of the invention]

According to the present invention, when the drying device is started up when the exhaust gas concentration in the drying furnace is below a certain value that does not adversely affect the coating film, the combustion Since the exhaust fan is rotated with a very small displacement corresponding to the amount of air introduced, the electric power cost of the exhaust fan can be significantly reduced, and at the same time, the heat loss of the hot air that heats the inside of the furnace is significantly reduced. In addition, since the supply/exhaust balance between the amount of combustion air supplied to the burner and the exhaust amount of the exhaust fan is maintained, and outside air is prevented from entering, the cost of gas fuel for the burner that heats the hot air can be significantly reduced. It is possible to save money and at the same time to uniformly raise the temperature inside the furnace.

In addition, when the exhaust gas concentration in the furnace exceeds a certain value, the exhaust volume of the exhaust fan can be increased or decreased according to the exhaust gas concentration to save electricity costs etc. of the exhaust fan. Since the amount of heated fresh air is supplied into the furnace in an amount equivalent to the difference between the exhaust volume of the combustion air and the amount of combustion air introduced to the burner that heats the hot air,
Even if the exhaust volume of the exhaust fan is increased or decreased depending on the exhaust gas concentration, the supply and exhaust balance within the furnace is always maintained.

Therefore, it is reliably prevented that the exhaust gas inside the furnace leaks from the entrance and exit of the drying furnace and deteriorates the surrounding environment, and that the outside air enters the drying furnace and disrupts the temperature distribution inside the furnace.

〔Example〕

Embodiments of the present invention will be specifically described below with reference to the drawings.

FIG. 1 is a flow sheet diagram showing an example of a drying apparatus to which the method of the present invention is applied.

Note that parts common to those in FIG. 2 are denoted by the same reference numerals, and detailed description thereof will be omitted.

In FIG. 1, on the inlet 1a side of the drying oven 1,
A dark red zone is provided in which the coating film of the workpiece carried into the furnace is heated by radiant heat radiated from the surfaces of the hot air circulation ducts 10, 10, and from the rear of the dark red zone to the exit of the drying furnace 1. On the 1b side, a convection zone is provided in which hot air is blown directly into the furnace to heat the coating film of the object to be coated.

Each hot air circulation duct 10 installed in the dark red zone
are connected to a hot air circulation system N' having a burner 11 and a hot air circulation fan 12 interposed therein, respectively.

The convection zone is further formed into a plurality of zones, and each zone has a hot air circulation fan 2 and a burner 3.
A hot air circulation system N, N, etc. is provided.

Each of these hot air circulation systems N is configured to heat the hot air inside the furnace drawn through a return duct 13 by a hot air circulation fan 2, heat it with a burner 3, remove dust with a filter 14, and circulate and supply it again into the furnace from a supply duct 15. has been done. Furthermore, combustion air is supplied to the burner 3 from a blower 16, and a purge duct 17 is branch-connected to the supply duct 15, and by switching the purge dampers 18 and 19, the dryer is operated at the start and end of operation. Air inside the furnace is discharged from the purge duct 17 to the outside.

In addition, a purge duct 17' is connected to the hot air circulation system N' as well as the hot air circulation system N', and by switching purge dampers 18' and 19', hot air is supplied from the barge duct 17' at the start and end of operation of the drying equipment. The air in the circulation duct 10 is discharged to the outside.

In addition, between the exhaust duct 5 equipped with an exhaust fan 6 for sucking and discharging the exhaust gas in the furnace and the deodorizing treatment device 7, there is a heat exchanger for preheating the exhaust gas sent from the exhaust duct 5 to the deodorizing treatment device 7. A heat exchanger 20 is installed, and the exhaust gas passing through the heat exchanger 20 is transferred to the burner 8.
The high-temperature deodorized gas is sent to the catalyst 9 heated to a predetermined reaction temperature (usually about 350 to 450 degrees Celsius), and deodorized through the catalyst 9. The high-temperature deodorized gas is sent to the heat exchanger 20 and is then discharged from the exhaust duct 5. It is designed to preheat the exhaust gas to be fed.

In addition, the high-temperature deodorizing gas that has been used to preheat the exhaust gas is passed through the air supply duct 22 that introduces the fresh air sucked by the exhaust fan 21 into the return duct 13 of the hot air circulation system N, N... The fresh air is passed through an installed heat exchanger 23 to heat the fresh air before being discharged to the outside.

Further, a semiconductor gas sensor 24 is provided in the exhaust duct 5 to detect the concentration of hydrocarbon gas, combustible gas, etc. contained in the exhaust gas discharged from the furnace, and a detection signal of the gas sensor 24 is input. The exhaust gas concentration meter 25 is connected to an inverter 27 that continuously changes the rotation speed of the motor 26 that drives the exhaust fan 6, and an inverter 29 that continuously changes the rotation speed of the motor 28 that drives the air supply fan 21. Thus, a control signal is outputted to variably adjust the rotational speed of each motor 26, 28 in accordance with the exhaust gas concentration.

The above is the configuration of the drying device shown in FIG.
Next, the method of the present invention applied to the drying apparatus will be explained.

When starting the operation of the drying equipment, before starting up the entire equipment, first the hot air circulation system N, N...
Open the purge damper 18 interposed therein, close the purge damper 19, and operate the hot air circulation fan 2.
The air inside the furnace is discharged to the outside through the purge duct 17, and the hot air circulation system N' in the dark red zone is
The purge damper 18' interposed in N' is opened, the purge damper 19' is closed, the hot air circulation fan 12 is operated, and the air in the hot air circulation duct 10 is also discharged to the outside through the barge duct 17'.

When all of the air stagnant in the drying oven 1 and the air stagnant in the hot air circulation duct 10 provided in the drying oven 1 are discharged, the entire drying device is started and each purge damper 18, 18' is activated. When the barge dampers 19 and 19' are closed and the barge dampers 19 and 19' are opened, each burner 3 and 11 is ignited, and the hot air heated by the burner 3 is circulated and supplied into the drying furnace 1 by the hot air circulation fan 2 to start heating the atmosphere inside the furnace. At the same time, the hot air heated by the burner 11 is circulated and supplied into the hot air circulation duct 10 provided in the drying furnace 1, and the radiant heat radiated from the duct 10 indirectly heats the atmosphere inside the furnace.

At the same time, the exhaust fan 6 is rotated with a displacement corresponding to the amount of combustion air introduced into the burner 3 from the blower 16, and the combustion air introduced into the furnace via the burner 3 is The same amount of exhaust gas is sucked out.

That is, when the exhaust gas concentration detected by the gas sensor 24 installed in the exhaust duct 5 is below a certain value (usually about 30 ppm or below) that does not adversely affect the coating film of the workpiece carried into the drying oven 1. , the exhaust gas concentration meter 25 outputs a control signal to the inverter 27 to rotate the exhaust fan 6 at an exhaust amount corresponding to the amount of combustion air introduced to be supplied to the burners 3, 3, .

As a result, the low concentration exhaust gas generated by the evaporation of tar-like substances adhering to the walls etc. inside the drying oven 1,
Since it is discharged with a very small amount of exhaust gas equivalent to the amount of combustion air introduced into the burner 3, not only can the electricity cost of the exhaust fan 6 be reduced, but also the heat loss of the hot air that is circulated and supplied to the furnace is significantly reduced. As a result, the gas fuel cost for the burner 3 that heats the hot air can be significantly reduced, and the exhaust gas concentration of the exhaust gas sent to the deodorizing treatment device 7 does not decrease, so the oxidation combustion heat of the exhaust gas is effectively used and the catalyst is heated. Burner 8 that heats 9
Gas fuel costs will also be reduced.

In addition, since the air supply and exhaust inside the drying furnace 1 are well balanced, hot air is prevented from leaking out of the furnace from the entrances and exits 1a and 1b of the drying furnace 1, and cold outside air is prevented from entering the furnace. It is possible to uniformly heat and raise the temperature.

In the drying oven 1 heated and heated in this manner, the amount of exhaust gas generated gradually increases as the temperature rises.

When the temperature inside the furnace rises to, for example, about 150°C and the exhaust gas concentration detected by the gas sensor 24 exceeds a fixed value of 30 ppm, the exhaust gas concentration meter 25 variably adjusts the rotation speed of the exhaust fan 6. A control signal is outputted to the inverter 27 to increase the displacement amount of the exhaust fan 6 in accordance with the rise in exhaust gas concentration.

At the same time, the exhaust gas concentration meter 25 outputs a control signal to start the operation of the air supply fan 21, and the inverter 29 controlled by the exhaust gas concentration meter 25 changes the rotation speed of the air supply fan 21.
The intake air amount is variably adjusted to correspond to the difference between the displacement amount of the exhaust fan 6 and the amount of combustion air introduced into the burners 3, 3, which is increased according to the exhaust gas concentration.

As a result, the same amount of air as the amount of exhaust gas discharged by the exhaust fan 6 is filled into the furnace by the air supply fan 21.
and blowers 16, 16, . . . . Therefore, since the balance of air supply and exhaust inside the oven is not disrupted, the entrances and exits 1a and 1b of the drying oven 1 are
This prevents exhaust gas from leaking out of the furnace and contaminating the surrounding environment, and preventing cold outside air from entering the furnace and disrupting the temperature distribution inside the furnace. In particular, the fresh air fed into the furnace by the air supply fan 21 is
Through the heat exchanger 23 installed in the air supply duct 22, the hot air circulation system N, N...
Since the hot air is introduced into the hot air circulation system N, there is no need to increase the combustion amount of the burner 3 installed in the hot air circulation system N.

That is, the exhaust gas that is suctioned and discharged from the inside of the furnace by the exhaust fan 6 and sent to the deodorizing treatment device 7 is transferred to the burner 8.
The harmful malodorous components are oxidized and decomposed by passing through a catalyst 9 heated to a predetermined reaction temperature (usually 350 to 450°C), and heated to a high temperature of about 450 to 520°C by the heat of oxidation combustion at that time. The deodorized gas is subjected to heat exchange with the exhaust gas discharged from the exhaust duct 5 through the heat exchanger 20, and after preheating the exhaust gas to a temperature close to the reaction temperature of the catalyst 9, for example, about 250 to 300 degrees Celsius, the deodorized gas is transferred to the supply air duct 22. The air is passed through a heat exchanger 23 installed in the air supply fan 21 to exchange heat with fresh air introduced into the return duct 13 of the hot air circulation system N, N... fresh air at e.g. 190℃
The deodorizing gas is heated to a certain degree and then released to the outside, so that the exhaust heat of the deodorizing gas discharged from the deodorizing treatment device 7 is effectively utilized.

Therefore, even if fresh air is introduced into the hot air circulation system N, N... through the air supply duct 22, the thermal load on the burner 3 will not increase, and in some cases, the baking temperature in the furnace or its temperature may increase. The combustion amount of the burner 3 can also be reduced by introducing high-temperature fresh air.

Then, the temperature in the furnace is about the prescribed baking temperature.
When the temperature reaches 150-200℃, the object to be coated is carried into the furnace and the coating film is baked and dried.

At this time, if the object to be coated is conveyed continuously without interruption at a predetermined interval of, for example, 20 m, a large amount of harmful odor components will be generated from the coating film of the object, and the exhaust gas concentration in the furnace will reach a maximum of about 500 ppm. However, the exhaust amount of the exhaust fan 6 is increased according to the exhaust gas concentration as described above.

Further, when the number of objects to be conveyed changes and the exhaust gas concentration changes, the displacement of the exhaust fan 6 is increased or decreased depending on the level of the exhaust gas concentration, and the electric power cost of the exhaust fan 6 is reduced, and the catalyst The cost of gas fuel for the burner 8 that heats the burner 9 is reduced. Also, the displacement of the exhaust fan 6, which is increased or decreased, and the burner 3, 3
Since the air supply fan 21 is rotated with an air supply amount corresponding to the difference between the amount of combustion air introduced to the It is reliably prevented from leaking from the inlet 1a and outlet 1b and contaminating the surrounding environment, or from entering the furnace with outside air and disrupting the temperature distribution inside the furnace.

〔Effect of the invention〕

As described above, according to the method of the present invention, when the exhaust gas concentration is below a certain value that does not affect the coating film, such as when starting the drying equipment that raises the temperature inside the oven, the The exhaust gas is exhausted at a very small amount, which is equivalent to the amount of combustion air introduced to the burner that heats the hot air that is circulated into the furnace, reducing the electricity cost of the exhaust fan that exhausts the exhaust gas. Not only that, but the heat loss of the hot air that is circulated and supplied into the furnace is significantly reduced, and the cost of gas fuel for the burner that heats the hot air can be significantly reduced.

In addition, since the air supply and exhaust inside the drying oven are well balanced, there is no risk of exhaust gas leaking from the entrance or exit of the drying oven, worsening the surrounding environment, or causing outside air to enter the oven and disrupting the temperature distribution inside the oven. can also be reliably prevented.

In addition, when the exhaust gas concentration in the furnace exceeds a certain value, the exhaust volume of the exhaust fan can be increased or decreased according to the exhaust gas concentration to save electricity costs for the exhaust fan, and at the same time, the exhaust volume can be increased or decreased. Since heated fresh air is supplied into the furnace in an amount equivalent to the difference between the amount of combustion air introduced to the burner that heats the hot air, the exhaust volume of the exhaust fan can be adjusted according to the exhaust gas concentration. Even if the temperature is increased or decreased, the air supply and exhaust balance inside the furnace will not be disrupted, and even in this case, the exhaust gas inside the furnace will leak from the entrance and exit of the drying furnace, worsening the surrounding environment, or outside air will enter the furnace, causing damage inside the furnace. This prevents the temperature distribution from being disrupted.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet diagram showing an example of a drying apparatus to which the method of the present invention is applied, and FIG. 2 is a flow sheet diagram of a drying apparatus shown for explaining a conventional method. Explanation of symbols, 1...Drying oven, 2...Hot air circulation fan, 3...Burner, 5...Exhaust duct, 6...
Exhaust fan, 7... Deodorizing device, 8... Burner, 9... Catalyst, 16... Blower, 21... Air supply fan, 22... Air supply duct, 23... Heat exchanger, 24... Gas sensor , 25... gas concentration meter,
26...Motor, 27...Inverter, 28...
Motor, 29...Inverter.

Claims (1)

[Claims] 1. A drying device that circulates and supplies hot air heated by a burner into a paint drying oven, and sucks and discharges exhaust gas generated in the drying oven using an exhaust fan that rotates at an exhaust volume that corresponds to the exhaust gas concentration. In the operating method, when the exhaust gas concentration is below a certain value that does not adversely affect the coating film, the exhaust fan is rotated at a displacement corresponding to the amount of combustion air introduced to be supplied to the burner, and the exhaust gas concentration is When it exceeds a certain value, the displacement of the exhaust fan is increased or decreased in accordance with the change in the exhaust gas concentration, and at the same time, an amount corresponding to the difference between the increased or decreased displacement of the exhaust fan and the amount of combustion air introduced. A method of operating a drying device characterized by supplying heated fresh air into a furnace.