JPH0425048B2 - - Google Patents

Description

Detailed Description of the Invention [Technical Field] The present invention involves oxidizing exhaust gas containing volatilized solvent components generated in a paint drying oven to make it odorless.
This invention relates to an exhaust gas treatment device for a paint drying oven that discharges the gas outside the system.

"Prior art and its problems" For example, in paint drying ovens used in the steel industry, painted strips go through a baking drying process, which evaporates the solvent in the paint and causes the components of the paint film to react. It is heated to achieve the required paint film performance. However, as steel production increases, the concentration of solvent gas in the paint drying oven increases, and if exhaust gas containing this is discharged outside the system, it may cause environmental pollution. 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 is 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 shown 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 mainly consists of ethyl cellosolve, for example, and the concentration in the exhaust gas is
For example, ethyl cellosolve is said to be 2500 ppm.
Then, the exhaust gas in the paint drying oven 1 is sucked in by the fan 2 and taken out from the first flow path 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, a butane-air mixed gas is introduced from the auxiliary combustion device 6 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.

Solvent components in the combustion exhaust gas are oxidized and burned by the catalyst 7, and tar mist and combustible dust in the exhaust gas are also adsorbed on the catalyst surface and then reacted and burned away. In addition, non-flammable dust is
It adheres to the catalyst 7 or is filtered out and removed from the exhaust gas. 8 is a blind lid that closes one end of the catalyst 7.

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 (for example, a flow rate of 4/5) is returned to the coating drying oven 1 through the second flow path 9, and the remainder (for example, a flow rate of 1/5) is returned to the second flow path 9.
It is discharged to the outside of the system through a third flow path 10 branched from the flow path.

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. Note that 13 and 14 are dampers that respectively adjust the flow rates of the exhaust gas to be returned to the coating drying oven 1 and the exhaust gas to be discharged to the outside of the system.

However, in the exhaust gas treatment equipment of this paint drying oven, if the exhaust gas contains catalyst poisoning components such as SOx (sulfur oxides), the poisoning progresses not only to the catalyst surface layer but also to the entire catalyst. The catalyst deteriorates and the purification efficiency decreases. For this reason, combustible components in the exhaust gas cannot be sufficiently removed, causing the environmental pollution mentioned above.Also, when the flexible components generated from the paint drying oven have a bad odor, they may not pass through the catalyst. Because the subsequent concentration of malodorous components is not sufficiently reduced, malodors are generated in the exhaust gas released into the atmosphere and in the paint drying oven.

In addition, combustible dust and tar mist are difficult to purify even if they are adsorbed on the catalyst surface, so they clog the catalyst and increase pressure loss, resulting in poor system pressure matching and the amount of circulating gas. It may be necessary to reduce the amount of water or the operation may become unstable.

Therefore, in order to perform stable operation, it is necessary to constantly monitor the deterioration status of the catalyst and replace it if the catalyst has deteriorated. However, when replacing the catalyst, it is necessary to stop the operation, and since the catalyst element itself supports precious metals, the replacement cost becomes very high.

In addition, in the exhaust gas treatment equipment of this paint drying oven, dust and tar tend to adhere to the heat transfer element of the heat exchanger, and this adhesion causes a decrease in the heat transfer performance of the heat exchanger and an increase in pressure loss. . Therefore, the temperature of the gas flowing into the catalyst decreases, and the purification efficiency of the catalyst deteriorates. Furthermore, the outlet temperature of the catalyst decreases, and the amount of heat exchanged by the heat exchanger further decreases.
Therefore, by reheating with an auxiliary combustion device,
It becomes necessary to compensate for the decrease in the temperature of the gas flowing into the catalyst, which increases fuel costs.

On the other hand, using the above-mentioned exhaust gas treatment device, combustible components present in the exhaust gas at a high concentration of, for example, about 2500 ppm are oxidized and removed by a catalyst to a concentration of, for example, one hundredth or less. At this time, the entire amount of exhaust gas is passed through the catalyst 7 for treatment, and most of the exhaust gas (for example, 4/5) whose combustible component concentration has been greatly reduced by the catalyst treatment is passed through the second flow path 9 again. The paint is then returned to the paint drying oven 1, which is the source of combustible components. Therefore, it is necessary to increase the volume of the expensive catalyst 7, and there is also a waste of recontaminating most of the exhaust gas that has been sufficiently purified thereby.

"Objective of the Invention" The purpose of the present invention is to stabilize the performance of the catalyst for a long time by preventing poisoning of the catalyst by SOx etc. in the exhaust gas, and to prevent dust and tar from adhering to the heat transfer element of the heat exchanger. The paint drying oven is designed to stabilize the performance of the heat exchanger over a long period of time by preventing this, and to remove flammable components (malodorous components) contained in exhaust gas stably over a long period of time with as little catalyst as possible. An object of the present invention is to provide an exhaust gas treatment device.

"Structure of the Invention" The exhaust gas treatment device for a paint drying oven according to the present invention has the following features:
A first flow path for taking out a predetermined amount of exhaust gas from the paint drying oven, and a heat transfer element carrying a primary catalyst to raise the temperature of the exhaust gas introduced from the first flow path to oxidize combustible components. a rotary regenerative heat exchanger for processing, and a second flow path for returning a portion of the exhaust gas oxidized by the primary catalyst to the paint drying furnace;
A third flow path that branches from this second flow path and discharges the remainder of the exhaust gas to the outside of the system, and further oxidizes the flexible components contained in the remainder of the exhaust gas in the middle of this third flow path. It is characterized by comprising a secondary catalyst for treatment.

In this way, in the present invention, by using a rotary regenerative heat exchanger, the heating gas and the gas to be heated periodically flow alternately along the heat transfer element, so that the primary catalyst supported on the heat transfer element Even if it becomes poisoned, it will self-regenerate upon contact with high-temperature heated gas.
In addition, even if termist or dust adheres to the heat transfer element on the heated gas side of a rotary regenerative heat exchanger, it will vaporize or burn when it comes into contact with the high-temperature heated gas, so tar and dust will accumulate on the heat transfer element. It's getting harder to do. Therefore, the activity of the catalyst can be kept stable for a long period of time, gas pressure loss can be suppressed as much as possible, heat transfer performance can be maintained well, and stable operation can be performed for a long period of time.

In addition, by providing a secondary catalyst in the third flow path, even if the primary catalyst does not remove the heatable components (malodorous components) sufficiently, the secondary catalyst can remove the heatable components to the desired value. can be removed and 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 can be reduced accordingly. As a result, the total amount of the primary catalyst and secondary catalyst can be reduced, and expensive catalysts can be used effectively to reduce equipment costs and 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.

This exhaust gas treatment device for a paint drying furnace has a first flow path 29 that extracts exhaust gas from a paint drying furnace 31 by sucking it with a fan 30 while adjusting the flow rate with a damper 32, and the first flow path 29 rotates. It is connected to a regenerative heat exchanger 15.

The rotary regenerative heat exchanger 15 includes a heat transfer element 1
6, and a primary catalyst 17 in which a catalyst component is supported on a similar heat transfer element. Both of these are coaxially connected such that the heat transfer element 16 is located on the first flow path 29 side, and the motor 1
8 rotates as a unit. In the rotation path of the heat transfer element 16 and the primary catalyst 17, one half is a flow path A for the heated gas, and the other half is a flow path B for the heated gas. Therefore,
The exhaust gas introduced from the first flow path 29 flows through the flow path A
The temperature is raised by the heat transfer element 16, and the combustible components are oxidized by the primary catalyst 17, resulting in a high temperature. Then, the exhaust gas reverses and passes through the flow path B, contacts the primary catalyst 17 again, then the heat transfer element 16, is cooled, and flows out.

Note that the rotary regenerative heat exchanger 15 may be configured such that the heat transfer element 16 and the primary catalyst 17 are fixed, and the flow paths A and B rotate relative to them.

The first flow path 29 is provided with a temperature raising auxiliary device 19 that introduces fuel gas or high temperature gas in order to raise the temperature of the exhaust gas to the catalyst activation temperature at the start of operation or the like. Instead of connecting to the first flow path 29, or in addition to this, the temperature raising auxiliary device 19 connects the fuel gas into the reverse flow path of the rotary regenerative heat exchanger 15 as shown by the two-dot chain line in the figure. Alternatively, high-temperature gas may be introduced.

A second flow path 20 is connected to the outflow side of the rotary regenerative heat exchanger 15, and most of the exhaust gas is returned to the coating drying furnace 31 through this flow path 20. Further, a third flow path 21 is provided branching off from the second flow path 20, and the remainder of the exhaust gas is discharged out of the system through this third flow path 21. The amount of exhaust gas returned to the paint drying furnace 31 and the amount of exhaust gas outside the system are controlled by damper 2.
2, 23. A secondary catalyst 24 is provided in the middle of the third flow path 21 to more completely oxidize the combustible components in the exhaust gas discharged to the outside of the system.

The exhaust gas from which combustible components (malodorous components) have been removed in this way exchanges heat with burner preheated air in a heat exchanger 25, and then is released into the outside air. Moreover, the burner preheating air is guided to the burner 27 through the flow path 26 as preheating air. and,
The gas in the paint drying oven 31 is circulated by a fan 28 and heated by a burner 27 at that time.

As the primary catalyst 17 and the secondary catalyst 24, for example, a ceramic honeycomb body supported with platinum, palladium, or a mixture of both is used.

Next, the operation of the exhaust gas treatment device for this paint drying oven will be explained. The paint drying oven 31 contains, for example, 4.2% carbon dioxide, 11.0% water, 74.0% nitrogen, and oxygen.
10.4%, SOx300ppm, ethyl cellosolve
2517ppm, dust concentration 0.1mg/ ^Nm3 , tar concentration
The exhaust gas contains 2.5 mg/Nm ³ and a temperature of 230° C., and this exhaust gas is taken out from the first flow path 29 at a flow rate of 20000 Nm ³ /h.

The exhaust gas flows into the flow path A of the rotary regenerative heat exchanger 15, is heated by the heat transfer element 16 to 300°C at which the catalyst exhibits the required activity, and then passes through the primary catalyst 17 to remove combustible components. (ethyl cellosolve) is oxidized. The catalyst volume of the primary catalyst 17 is such that the purification efficiency is 90% or more. The exhaust gas that has passed through the primary catalyst 17 is heated to 443° C. by the heat of oxidation. Then, the flow is reversed in the upper space of the rotary regenerative heat exchanger 15 and enters the flow path B, and after passing through the primary catalyst 17 again,
The flammable components are further oxidized and the temperature is raised to 488°C. At this time, the concentration of ethyl cellosolve, an odoriferous and flammable component, was 252 ppm. This high-temperature exhaust gas contacts the heat transfer element 16 and is cooled 418
℃. As a result, the heat transfer element 16 becomes high in temperature and obtains heat that raises the temperature of the exhaust gas introduced in the flow path A.

By the way, since the temperature of the exhaust gas that contacts the primary catalyst 17 in the flow path A is 300°C, the primary catalyst 1
7 is temporarily poisoned by SOx, but when it is rotated by the motor 18 and moved to the flow path B side, it comes into contact with exhaust gas at a high temperature of 418° C., so it self-regenerates and recovers its purification performance. In addition, since tar mist and dust also come into contact with the high temperature exhaust gas in the flow path B, they are vaporized or burned, and the heat transfer element 1
6 or the primary catalyst 17.

At the outlet of the rotary regenerative heat exchanger 15, the ethyl cellosolve concentration in the exhaust gas is 365 ppm due to the addition of leakage from the seal, but this exhaust gas flows out through the second flow path 20. Damper 2
The flow rate is adjusted by 2 and 23, of which 17000N
m ³ /h is returned to the paint drying oven 31. The remaining part of the exhaust gas, that is, 3000Nm ³ /h, passes through a third flow path 21 branched from the second flow path 20, is further oxidized by a secondary catalyst 24, and is then oxidized into a heat exchanger 2.
5 and then released to the outside air. The secondary catalyst 24 has a catalyst volume such that the purification efficiency is 99% or more, and ethyl cellosolve, which was contained in the exhaust gas before treatment at 365 ppm, is reduced to 4 ppm.

Therefore, the primary catalyst 17 and the secondary catalyst 24
In total, more than 99.8% of ethyl cellosolve is purified. In this case, since the amount of exhaust gas passing through the secondary catalyst 24 is 3000Nm ³ /h, the volume of the catalyst is relatively small in order to achieve a purification efficiency of 99% or more. can be removed.

"Effects of the Invention" As explained above, according to the present invention, by using a rotary regenerative heat exchanger having a heat transfer element on which a primary catalyst is supported, the primary catalyst is prevented from being poisoned by, for example, SOx. Even if it is exposed to heat, it can self-regenerate when it comes into contact with high-temperature exhaust gas, and even if tar mist or dust adheres to it, it will volatilize or burn when it comes into contact with high-temperature exhaust gas. Therefore, the activity of the catalyst can be kept stable for a long period of time, gas pressure loss can be suppressed as much as possible, heat transfer performance can be maintained well, and stable operation can be performed for a long period of time.

In addition, by providing a secondary catalyst in the third flow path, even if the primary catalyst does not sufficiently remove flammable components (malodorous components), or even if a leak occurs in the rotary regenerative heat exchanger, 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 can be reduced accordingly. As a result, the total amount of the primary catalyst and secondary catalyst can be reduced, and expensive catalysts can be used effectively to reduce equipment costs and maintenance costs.

[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, 15 is a rotary regenerative heat exchanger, 16 is a heat transfer element, 17 is a primary catalyst, 19 is a temperature raising auxiliary device, 20 is a second flow path, 21 is a third flow path, 24
3 is a secondary catalyst, 31 is a paint drying oven, and 29 is a first flow path.

Claims (1)

[Claims] 1. A first device for extracting a predetermined amount of exhaust gas from a paint drying oven.
a rotary regenerative heat exchanger that heats exhaust gas introduced from the first flow path to oxidize combustible components by a heat transfer element carrying a primary catalyst; a second flow path that returns a portion of the exhaust gas oxidized by the catalyst to the paint drying oven; and a third flow path that branches off from this 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, comprising a third flow path and a secondary catalyst that further oxidizes the flexible components contained in the remainder of the exhaust gas in the middle of the third flow path. 2. An exhaust gas treatment device for a paint drying furnace according to claim 1, which is provided with a temperature-raising auxiliary device for introducing fuel gas or high-temperature gas into the first flow path or the rotary regenerative heat exchanger. .