JPH04219119A - Method and device for removing solvent in waste gas of baking finish drying furnace - Google Patents

Abstract

PURPOSE:To absorb a water paint solvent in water and to remove the solvent from the waste gas of a baking finish drying furnace without burning the solvent by colliding the waste gas with a wet filter. CONSTITUTION:The filter chamber 7 of a solvent removing device 5 is provided in the waste gas passage 3 of a baking finish drying furnace. Filters 10 and 11 of expanded metal are set in the chamber 7 in plural stages in opposition to the waste gas current. Water is sprinkled over the filters 10 and 11 from nozzles 16 and 17 on the upstream side. Water is simultaneously dripped from nozzles 18 and 19 at the upper part, hence a thin water film is formed on the filter surface, the waste gas is passed through the filters 18 and 19 and brought into contact with water, and a water-soluble solvent is absorbed in water and removed. The waste gas is further passed through a demister 12 and a flow control damper 22 and discharged from a waste gas duct 6. Meanwhile, the waste gas from the passage 3 is made turbulent by an obliquely projecting baffle 8 and uniformly collided with the filter 10.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for removing solvents from exhaust gas from a paint baking drying oven.

0002

2. Description of the Related Art Generally, in the painting process, the object to be coated is baked and dried in a baking drying oven after painting. for example,
In the can manufacturing process, the inner surface of the can is painted after the can body is formed or in a blank state before the can body is formed, and after painting, the can is sent to a baking drying oven (oven) for baking drying. The exhaust air from paint baking and drying ovens contains harmful solvents emitted from the paint, and the concentration of these solvents is below a specified level.For example, in places with the strictest regulations, the concentration of cellosolve solvents is 10
It is regulated so that it cannot be released into the atmosphere unless it is below ppm. Therefore, the exhaust from the paint baking furnace is
The solvent is discharged into the atmosphere after being subjected to exhaust treatment to bring the concentration below a predetermined value. Conventionally, exhaust gas from paint baking and drying furnaces has been treated by burning the exhaust gas. However, in that case, it is highly dangerous and requires a high level of safety management, and fuel is required to burn the exhaust.
Not only does it have the disadvantage of high operating costs, but it also emits a lot of carbon dioxide gas during combustion, which is undesirable from the perspective of global warming, which has become a problem in recent years. Furthermore, the equipment is large and requires a large installation space.

0003

OBJECTS OF THE INVENTION The present invention aims to solve the above-mentioned drawbacks of the conventional solvent removal treatment in the exhaust gas of paint baking drying ovens. To provide a method and device for removing solvent in the exhaust gas of a paint baking drying oven, which can remove solvent to a level below the regulated value according to local ordinances, and can reduce running costs compared to conventional ones.

0004

[Means for Solving the Problems] In recent years, there has been a trend toward water-based paints for the interior of cans. As a result of repeated research focusing on this point, the inventor of the present invention discovered that the solvent in the exhaust gas can be removed by actively bringing the exhaust gas into contact with water using a wet filter, and has thus arrived at the present invention. be.

That is, the method for removing solvent from the exhaust gas of a paint baking drying oven according to the present invention includes providing a filter chamber in the exhaust passage of the baking drying oven, and disposing a heat-resistant filter in the filter chamber facing the exhaust flow. The solvent in the exhaust gas is converted into water by spraying water onto the filter from the direction of the exhaust flow, and by dripping water from the top of the filter to form a thin water film on the filter and causing the exhaust gas to collide with the water. It is characterized by being absorbed and removed.

[0006] As the filter, a metal filter in the form of an expanded metal is desirable because it is heat resistant and causes less pressure loss in the exhaust gas flow. By providing a plurality of filters at intervals along the direction of the exhaust flow, the solvent can be absorbed more efficiently. In that case, even if the water sprayed and dripped onto the most upstream filter is recovered and used, the removal rate will not decrease compared to when fresh water is used. Since the amount of waste water is small, it is desirable to use recovered water in order to reduce the amount of water used and the amount of sewage. A demister was provided downstream of the last stage filter to remove moisture contained in the exhaust gas after the solvent removal process. Furthermore, a baffle plate that protrudes into the exhaust passage is provided at the entrance of the chamber to provide a rectifying effect on the exhaust flow.

[0007]

[Operation] The present invention makes use of the characteristics of water-based paints, and allows the exhaust air from a paint baking drying oven to pass through a wet filter so that it comes into contact with water, and the solvent is absorbed by the water and removed. The exhaust gas is rectified by a baffle plate at the entrance of the filter chamber, and uniformly impinges on the filter surface provided in the filter chamber. The filter is sprayed with water from upwind, and when it comes into contact with the exhaust gas containing the solvent, the solvent is absorbed by the water. Furthermore, by dripping water from the top of the filter, a thin, uniform water film is formed on the filter surface, and even when exhaust air collides with the filter surface, the solvent is absorbed by the water. Even if filters are provided in multiple stages, the first stage will mainly contribute to solvent removal, but by providing multiple stages, solvents that are not removed in the first stage will be passed through the second stage, making it more reliable. In addition, by providing a second-stage wet filter device, the back pressure causes the exhaust gas to impinge uniformly on the first-stage filter, thereby increasing the removal efficiency.

[0008]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic view of one embodiment of the present invention apparatus, and FIG. 2 is an overall schematic view of the apparatus disposed in a paint baking drying oven when applied to a can manufacturing line. In FIG. 2, reference numeral 1 denotes a paint baking drying oven, in which cans whose inner surfaces have been coated in a previous step are conveyed by a conveyor 2 passing through the oven, baking drying is performed during conveyance, and the cans are conveyed outside the oven. Reference numeral 3 designates an exhaust duct of the baking drying oven, an exhaust fan 4 is provided in the middle of the exhaust duct, and a solvent removing device 5 according to the present invention is provided downstream of the exhaust duct.

As shown in FIG. 1, the solvent removal device 5 has a filter chamber 7 whose inlet side is connected to the inlet duct 3 from the baking drying furnace and whose outlet side is connected to the exhaust duct 6 which is open to the atmosphere. A baffle plate 8 is provided projecting from the bottom wall on the inlet side into the exhaust passage at an angle of approximately 30° to 45° to cause turbulence in the exhaust gas entering the filter chamber from the duct. The exhaust flow impinges uniformly on the filter. Inside the chamber, there are two stages of wet filter devices 10 and 11 along the exhaust direction.
and a demister 12.

The wet filter devices 10 and 11 are made of stainless steel filter plates made of expanded metal, which have relatively coarse mesh, have low pressure loss, and have excellent heat resistance and chemical resistance. It has a plurality of filters 14 and 15 which are combined so as to intersect with each other to increase the collision area with the exhaust gas passing through the filters.Water is dripped from the top of the filter along the filter surface. A thin, uniform water film is formed on the filter by spraying water over the entire filter surface from the upstream side of the filter, that is, from the windward side. For this purpose, 16 and 17 are spray nozzles arranged upstream of the filter, and the amount of spray water can be adjusted individually according to the solvent removal performance with a combination of one nozzle per filter. 18 and 19 are drip nozzles arranged above each filter. In this embodiment, as will be described later, the water used in the first-stage wet filter device 10 is made by storing waste water from the second-stage wet filter device 11 in a tank 20 and utilizing it. 21 is a pump for that purpose. The second stage wet filter device uses fresh water. As fresh water, use discharged water after wastewater treatment or industrial water.

The demister 12 is for collecting water droplets from the exhaust gas that has passed through the wet filter device, and in this embodiment, a stainless steel filter similar to the filter of the wet filter device is used. 22 is a damper for setting the air volume.

Using the above-described apparatus, the following experiment was conducted to confirm the effectiveness of the method of the present invention. The above embodiment device was applied to an exhaust system from a baking drying oven for DI cans whose inner surfaces were coated with water-based paint.
Spray water volume and drip water volume are 2,
The rate was changed to 3 and 4 L/min, respectively, and the change in solvent concentration in the exhaust gas and the pressure loss in each case were measured. The results are shown in Table 1.

[Table 1]

As is clear from the above table, by employing this device, solvents, which are harmful substances in exhaust gas, can be removed with an overall removal efficiency of about 40 to 60%, and the spray By selecting the amount of water and the amount of drip water, it was possible to remove the solvent to a level below the standard concentration that is allowed to be released into the atmosphere, and it was confirmed that this device is fully applicable to removing solvents from exhaust gas. Among the above conditions, it was confirmed that the removal efficiency decreases when the amount of water in spray and drip is too small or too large, and in the case of this experimental device, the removal efficiency was highest at 3.0 L/min. In addition, when comparing the case where fresh water is used in both the first and second stages and the case where the water used in the second stage is recovered and used, in the table above, tests 1 and 4, tests 2 and 5 , 3 and 6 roughly correspond to each other, but except for tests 1 and 4, the removal efficiency is slightly higher in the case of fresh water, but there is no significant difference, and even if the water used in the second stage is used in the first stage. , especially for test 5 BA
, BC, and HC were able to suppress their concentrations to about 10 ppm or less. Therefore, in order to reduce water consumption and wastewater, it is desirable to conduct the test under conditions similar to those in Test 5. Moreover, the pressure loss was 7 to 10 mmAq, which was small. Therefore, the furnace power capacity can also be reduced. In the above experiment, the water used in the first stage was treated as wastewater before being discharged.

Furthermore, as a comparative example, a similar test was conducted three times in the above apparatus without using water, that is, in a dry filter state, and the solvent concentration of the exhaust gas in that case was as shown in Table 2.
It is now shown in

[Table 2] As described above, when using a dry method, almost no solvent is removed, but by using a wet filter as in the present invention, the solvent removal efficiency is significantly increased. It was confirmed that this is an effective method.

FIG. 3 shows another embodiment of the device according to the invention. This embodiment is for a case where the capacity is large, such as a baking drying furnace used in a normal can manufacturing line, and each stage of filters is installed in the filter chamber 29 in multiple stages in the vertical direction and width direction according to the exhaust capacity. It is superimposed on the .

In the figure, 30 is the first stage wet filter device;
31 is a second-stage wet filter device, 32 is a demister device, and each filter 3 is made of stainless steel expanded metal in the vertical direction in the same manner as in the above embodiment.
3, 34, and 35 are stacked in three stages in the illustrated embodiment. and spray nozzles 36, 3 for each filter.
7. Drip nozzles 38 and 39 are provided. In this embodiment, the water dripped at the top stage drips down to the filters at the lower stage, so the amount of dripped water from the nozzle is appropriately adjusted to decrease as the stage goes lower.

40, 41, 42 are respective drainage hoppers, and the water collected in the drainage hoppers 41, 42 is
The water is collected in a tank (not shown) and used again as first-stage spray and drip water. 43 is a baffle plate. The embodiments of the present invention have been described above, but the present invention is not limited to a baking drying oven for painting the inner surface of cans in the can manufacturing process, but can be applied to any form of baking drying oven for coating objects using water-based paints. Needless to say, this method can also be applied to furnaces.

[0018]

Effects of the Invention According to the present invention, the water-based paint solvent in the exhaust gas can be removed to a value below the standard concentration that is allowed to be released into the atmosphere without being burned. There is no need for fuel to burn the fuel, which saves energy and causes no air pollution due to combustion.

[0019] Compared to the conventional exhaust combustion treatment method, there is no danger, and the device has a simple structure, is light in weight, and requires less installation space, so it is possible to save space and the installation work is easy. . Furthermore, since maintenance and management simply involve periodic cleaning of the filter, running costs are low. In addition, since the filter only needs to have a large contact area with the exhaust gas, and a filter with a coarse mesh can be used, there is little pressure loss or clogging, which reduces the exhaust amount, and has little effect on the furnace. Since the water used in the first stage filter can be reused as the water used in the second and subsequent stages, the amount of water used and the amount of wastewater can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a solvent removal device for a paint baking drying furnace according to an embodiment of the present invention.

FIG. 2 is a schematic view of the solvent removal device shown in FIG. 1 placed in a paint baking drying furnace.

FIG. 3 is a schematic diagram of a solvent removal device for a paint baking drying oven according to another embodiment of the present invention.

[Explanation of symbols]

1 Paint baking drying oven 5 Solvent removal device 7, 29 Filter chamber 8, 43 Baffle plate 10, 11, 30, 31 Wet filter device 12, 3
2 Demister 14, 15, 33, 34 Filter

Claims (7)

[Claims] Claim 1: A method for removing solvents from exhaust air from a paint baking drying oven for a workpiece using a water-based paint, comprising:
A filter chamber is installed in the exhaust passage of the baking drying oven.
A heat-resistant filter is provided in the filter chamber facing the exhaust flow, water is sprayed onto the filter from the direction of the exhaust flow, and water is dripped from the top of the filter to form a thin water film on the filter, A method for removing solvents in the exhaust gas of a paint baking drying furnace, characterized in that the solvents in the exhaust gas are absorbed by the water and removed by colliding the exhaust gases with water. 2. A filter chamber provided in an exhaust passage of a paint baking drying furnace, a heat-resistant filter provided in the chamber facing the exhaust flow, and a filter in which water is supplied to the filter from the upstream side in the direction of the exhaust flow. 1. An apparatus for removing solvent in the exhaust gas of a paint baking drying furnace, characterized by comprising a spray nozzle for spraying water and a drip nozzle for dripping water from the upper part of the filter onto the filter surface. 3. The apparatus for removing solvent in the exhaust gas of a paint baking drying furnace according to claim 2, wherein said filter is an expanded metal filter. 4. The apparatus for removing solvent in the exhaust gas of a paint baking drying furnace according to claim 2 or 3, wherein the filters are provided in a plurality of stages at intervals along the direction of the exhaust flow. 5. The apparatus for removing solvent in the exhaust gas of a paint baking drying furnace according to claim 2, further comprising a demister provided downstream of the filter. 6. The water sprayed and dripped on the filter on the most upstream side is recovered from the water sprayed and dripped on the filter on the downstream side for use. Solvent removal equipment. 7. Claims 2, 3, 4, 5, wherein a baffle plate is provided at the entrance of the filter chamber and projects into the exhaust passage.
Or a device for removing solvents in the exhaust gas of a paint baking drying furnace as described in item 6.