JPS62266119A - Apparatus for treating waste gas of painting drying oven - Google Patents

Abstract

PURPOSE:To perfectly remove combustible components by a reduced amount of a catalyst, by a method wherein the exhaust gas from a painting drying oven is oxidized by a primary catalyst and a part of the treated gas is returned to the painting drying oven while the remainder is further oxidized by a secondary catalyst to be discharged out of the system. CONSTITUTION:The waste gas from a painting drying oven 1 is sucked by a fan 2 to be taken in a first flow passage 3 and introduced into a primary catalyst 7 while being heated by a heat exchanger 5 and an auxiliary combustion device 6 to receive oxidation treatment to remove combustion components. Subsequently, the waste gas is heat-exchanged with untreated waste gas through the heat exchanger 5 and introduced into a second flow passage 9 to be returned to the painting drying oven 1 by a recycle fan 11. The remainder of the waste gas passes through a branched third flow passage 10 and further oxidized by a secondary catalyst 8 to be discharged out of the system.

Description

Detailed Description of the Invention [Technical Field] The present invention relates to a paint drying furnace in which exhaust gas containing volatilized solvent components generated in the paint drying furnace is oxidized to be odorless and discharged outside the system. Related to exhaust gas treatment equipment.

[Prior art and its problems] For example, in paint drying ovens used in the steel industry, painted strips are baked through a drying process that evaporates the solvent in the paint and causes the components of the paint film to react. The coating is heated to achieve the required paint film performance. However, as the production volume of steel increases, the concentration of solvent gas in the paint drying oven increases, and if the exhaust gas containing this is discharged directly outside the system, it may cause environmental pollution, so it is necessary to reduce the concentration of solvent gas in the exhaust gas. need to be lower.

For this purpose, exhaust gas containing solvent is taken out of the paint drying oven, passed through a catalyst layer, and combustible components derived from solvents such as ketones, cellosolves, toluene, and xylene are burned to reduce their concentration and create a clean By using a circulation system that returns most of the solvent to the furnace, the concentration of solvent gas in the exhaust gas outside the system can be kept below a predetermined value.

FIG. 2 shows an example of a conventional exhaust gas treatment device for a paint drying oven. That is, a steel material is introduced into the paint drying oven 1 as indicated by the white arrow in the figure, and the solvent in the paint is removed by volatilization in an atmosphere of, for example, about 180°C. The solvent consists of, for example, 50% xylene, 25% ME (methyl ethyl ketone), and 25% ethyl cellosolve, and the concentration in the exhaust gas is, for example, 1250 ρρm of xylene, M
625ppm for E, and 62511m for Chill Cell Solv. Then, the exhaust gas in the paint drying oven 1 is
suction and take it out from the first channel 3. At this time, the damper 4 adjusts the amount of exhaust gas taken out.

The exhaust gas taken out from the first flow path 3 is guided to a cross-flow type heat exchanger 5 and heated there. Furthermore, if necessary, for example, butane-air mixed gas is introduced from the auxiliary combustion bag M6 and combusted to raise the exhaust gas temperature to about 350°C. In this state, the exhaust gas is passed through a catalyst 7 to oxidize combustible components in the exhaust gas.

The element of the catalyst 7 is formed by stacking 10 to 20 sheets of 14-mesh heat-resistant glass cloth and forming it into a pipe shape.
It consists of a 2 micron thick deposited platinum catalyst.

The solvent component in the exhaust gas is oxidized to PA by this platinum catalyst, and the tar mist and combustible dust in the exhaust gas are also adsorbed on the catalyst surface and then reacted and burned away. Incidentally, the non-flammable dust is removed from the exhaust gas by adhering to the catalyst 7 or being filtered out. 8 is the catalyst 7
It is a blind lid that covers one end of the.

The combustion exhaust gas that has passed through the catalyst 7 and has been heated by combustion of combustible components and from which non-flammable dust has been removed passes through the heat exchanger 5 and is cooled by exchanging heat with the exhaust gas before oxidation treatment. ,
A part of it (for example, stream ji of 415) is returned to the coating drying oven 1 through the second flow path 9, and the remaining part (for example, stream ji of 1
15 flow rate) branched from the second flow path.
is discharged from the system through the

The exhaust gas returned through the second flow path 9 is guided to the paint drying oven 1 by a recycling fan 11. Further, a burner 12 is provided next to the recycle fan 11 to raise the temperature of the gas circulating in the furnace. In addition, 13.14
are dampers that respectively adjust the flow rates of the exhaust gas returned to the coating drying furnace 1 and the exhaust gas discharged outside the system.

By the way, by using the above-mentioned exhaust gas treatment equipment M, for example, 99% of the combustible components contained in the exhaust gas, which is 2500 ppm in total, can be removed.
It will be removed to a concentration of 25 ppm and discharged to the outside of the system through the third channel 10. Exhaust gas is to, 000 Nrri'
/h, and at that flow rate, the processing capacity of the catalyst is such that 90% of combustible components can be removed per 1 rri' of catalyst volume. In this case, the combustible components in the exhaust gas are
% removal, the volume of catalyst 7 must be 2rn'. Even if 99% of the combustible components are removed, most of the exhaust gas (for example, 415) is returned to the paint drying furnace 1 through the second flow path 9, so it is once again subjected to oxidation treatment by the catalyst. It turns out.

Therefore, in the above exhaust gas treatment device, the catalyst 7
It is necessary to increase the volume of Therefore, during long-term use, the catalyst's activity gradually decreases due to poisoning by components such as 5Ox (sulfur oxides) and adhesion of dust and tar mist. For this reason, it becomes necessary to replace the catalyst, but since it is made of an expensive noble metal such as platinum, the replacement cost becomes extremely high when the amount of catalyst is large as described above.

[Object of the Invention] An object of the present invention is to provide an exhaust gas treatment device for a paint drying oven that can remove combustible components in exhaust gas with a smaller amount of catalyst.

“Structure of the Invention” The present invention provides a first
a heat exchanger that heats up the exhaust gas introduced from the first flow path, a primary catalyst that oxidizes combustible components in the heated exhaust gas, and a A paint drying furnace comprising a second flow path that returns a portion of the exhaust gas to the paint drying furnace, and a third flow path that branches from the second flow path and discharges the remainder of the exhaust gas to the outside of the system. In the exhaust gas treatment device, a secondary catalyst is provided in the third flow path to further oxidize combustible components remaining in the exhaust gas discharged outside the system.

In this way, by providing the secondary catalyst in the third flow path, even if the removal of combustible components by the primary catalyst is not sufficient,
Combustible components can be removed to a desired value using a secondary catalyst and then discharged from the system. Since the exhaust gas passed through the secondary catalyst is the remainder of the exhaust gas returned to the paint drying oven, the flow rate is reduced, and the amount of secondary catalyst required is correspondingly small. As a result, the total amount of the primary catalyst and the secondary catalyst can be reduced, and expensive catalysts can be used effectively to reduce storage maintenance costs.

"Embodiment of the Invention" FIG. 1 shows an embodiment of an exhaust gas treatment apparatus for a paint drying oven according to the present invention.

The exhaust gas treatment design of this paint drying furnace is basically the same as the device shown in FIG. a heat exchanger 5 that heats up the exhaust gas introduced from the flow path 3; a primary catalyst 17 that oxidizes combustible components in the heated exhaust gas; and a part of the exhaust gas that has been treated with the primary catalyst 17. It mainly consists of a second flow path 9 that returns the exhaust gas to the paint drying oven 1, and a third flow path 10 that branches off from the second flow path 9 and discharges the remainder of the exhaust gas to the outside of the system. .

In the figure, 2 is a fan, 4, 13, 14 is a damper for adjusting the flow rate, 6 is an auxiliary combustion device, 8 is a blind lid, 11 is a recycling fan, and 12 is a bar. The element of the primary catalyst 17 is formed into a pipe shape by stacking 10 to 20 sheets of heat-resistant glass cloth of 14 meshes, for example, in the same way as described above. It consists of a micron-thick platinum catalyst deposited by vapor deposition.

The feature of the present invention is that a secondary catalyst 1 is provided in the third flow path 10.
8 is provided. The elements of this secondary catalyst 18 are also made of the same material as the primary catalyst 17.

In the above configuration, exhaust gas is sucked from the paint drying oven 1 by the fan 2 and taken out through the first flow path 3. At that time, the damper 4 is used to adjust the flow rate to a predetermined level. The exhaust gas is
It is heated in the heat exchanger 5 and further heated in the auxiliary combustion device 6 as needed to raise the temperature to the temperature required to activate the catalyst, and then introduced into the primary catalyst 17. Then, it is oxidized by the primary catalyst 17 and combustible components are removed to some extent. At this time, the temperature of the exhaust gas is raised by combustion of combustible components, and after passing through the heat exchanger 518 and exchanging heat with the exhaust gas that has not been subjected to catalyst treatment, it is introduced into the second flow path 9.

A part of the exhaust gas passes through the second passage 9 and is returned to the paint drying furnace 1 by the recycle fan 11, and the remainder of the exhaust gas passes through the branched third passage 10, passing through the secondary catalyst 18 along the way. After being roughly oxidized, it is discharged from the system. The amount of N in the exhaust gas returned to the coating drying oven 1 and the amount of exhaust gas discharged outside the system are adjusted by dampers 13,14.

So, for example, the solvent is 50% xylene, ME is 25%
%, ethyl cellosolve 2ti%, paint drying oven 1
Assume that the exhaust gas contains 1,250 ppm of xylene, 625 ppm of ME, and 625 ppm of ethyl cellosolve, for a total of 2,500 ppm of combustible components. Then, this exhaust gas is transferred from the paint drying oven 1 to In, 000 Nr.
After being taken out at a flow rate of ri'/h and treated with the primary catalyst 17, it is returned to the 415 8.00 ONrri'/h paint drying oven 1, and the 115 2.000) Lrrf/
h is further treated with the secondary catalyst 18 and then discharged to the outside of the system. In addition, the catalytic capacity is 10.000 Nrr
In treating exhaust gas flowing at a flow rate of i'/h, it is assumed that 90% of combustible components can be removed per catalyst volume 1r+1'.

Under these conditions, when the volume of the primary catalyst 17 is 1 p, 90% of the combustible components are removed by the primary catalyst 17 and 250 p
It becomes pm. Further removes 99% of combustible components from this exhaust gas.
When trying to remove up to 25 ppm and discharge it,
It is necessary to further reduce the combustible components to 1710 by using the secondary catalyst 18. If the flow rate of the exhaust gas flowing into the secondary catalyst 18 is the same, the volume of the secondary catalyst per day must be 1 m. However, in the present invention, since the amount of exhaust gas flowing through the third flow path 10 is 2,00 ONrn'/h, the volume of the secondary catalyst 18 is sufficient to be 0.2 rn'. Therefore, 99% of combustible components can be removed with a total catalyst volume of 1.2 rri', and the amount of catalyst can be significantly reduced compared to conventional exhaust gas treatment devices.

[Effects of the Invention] As explained above, according to the present invention, after the exhaust gas taken out from the paint drying oven is oxidized using the primary catalyst, a part of it is returned to the paint drying oven, and the remaining part is sent to the secondary catalyst. Since the exhaust gas is further oxidized and discharged outside the system, the combustible components in the exhaust gas can be more completely removed and discharged with a small amount of catalyst. Therefore, expensive catalysts can be used effectively and equipment costs and maintenance costs can be reduced.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram showing an embodiment of an exhaust gas treatment device for a paint drying oven according to the present invention, and FIG. 2 is a schematic explanatory diagram showing an example of a conventional exhaust gas treatment device for a paint drying oven. In the figure, 1 is a paint drying oven, 3 is a first passage, 5 is a heat exchanger, 17 is a primary catalyst, 9 is a second passage, 10 is a third passage, and 18 is a secondary catalyst. be. Patent Applicant Kagura Co., Ltd. Sumitomo Metal Industries Co., Ltd. Procedural Negotiations (Spontaneous) July 10, 1986

Claims (1)

[Claims] a first flow path that takes out a predetermined amount of exhaust gas from the paint drying oven;
A heat exchanger that raises the temperature of the exhaust gas introduced from the first flow path, a primary catalyst that oxidizes combustible components in the heated exhaust gas, and a part of the exhaust gas that has been treated with the primary catalyst. In an exhaust gas treatment device for a paint drying furnace, comprising a second flow path that returns to the paint drying furnace, and a third flow path that branches off from the second flow path and discharges the remainder of the exhaust gas to the outside of the system. , an exhaust gas treatment device for a paint drying furnace, characterized in that a secondary catalyst is provided in the third flow path in order to further oxidize combustible components remaining in the exhaust gas discharged outside the system. .