JPH0425051B2 - - 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 transferred to the fan 2.
suction and take out to the first channel 3. At this time, the damper 4 adjusts the amount of exhaust gas taken out.

The exhaust gas taken out into the first flow path 3 is guided to a cross-flow type heat exchanger 5 and heated there. Furthermore, if necessary, fuel such as butane-air mixed gas is inputted from the auxiliary combustion device 6 and combusted.
Raise the exhaust gas temperature to about 350℃, the catalyst activation temperature. In this state, the exhaust gas is passed through the catalyst 7 to oxidize the 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. Reference numeral 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 furnace 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, the symbols 13 and 14 are the paint drying oven 1.
This is a damper that adjusts the flow rates of exhaust gas returned to the system and exhaust gas discharged outside 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 removed sufficiently, causing the environmental pollution mentioned above.Also, when the flammable components generated from the paint drying oven are malodorous, the Because the concentration of malodorous components in the paint 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, when using the above-mentioned exhaust gas treatment device, when trying to remove combustible components present in the exhaust gas at a high concentration of, for example, 2500 ppm, by oxidizing it with a catalyst to a concentration of one hundredth or less. , 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. Then, it is 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 object 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 entering the heat transfer element of the heat exchanger. An object of the present invention is to provide an exhaust gas treatment device for a paint drying oven that prevents pressure loss and deterioration in heat exchange performance due to adhesion and can stably remove flammable components (malodorous components) contained in exhaust gas over a long period of time.

"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, a dust removal filter provided in the first flow path, and a heat-receiving fluid side for raising the temperature of the exhaust gas introduced from the first flow path. A heat exchanger equipped with a flow path and a flow path on the heat-radiating fluid side that lowers the temperature of the exhaust gas after oxidation treatment of combustible components, and the flammability of the exhaust gas introduced from the flow path on the heat-receiving fluid side of this heat exchanger. a rotary catalytic device equipped with a primary catalyst for oxidizing components;
a second flow path for circulating a part of the exhaust gas that has been oxidized by the rotary catalyst device and has passed through the flow path on the heat radiation fluid side of the heat exchanger to the paint drying furnace;
A third flow path that branches off from the flow path and discharges the remainder of the exhaust gas to the outside of the system, and a secondary flow path that further oxidizes combustible components contained in the remainder of the exhaust gas in the middle of this third flow path. It is characterized by being equipped with a catalyst.

In this way, in the present invention, the exhaust gas taken out in the first flow path is introduced into the heat exchanger and the subsequent rotary catalyst device after dust is removed in advance by a dust removal filter placed in the middle of the flow path. be done. Therefore, it is possible to prevent dust from adhering to the heat transfer element of the heat exchanger or the primary catalyst of the rotary catalyst device.

In addition, for the oxidation treatment of combustible components, a rotary catalyst device is used in which heating gas and heated gas flow alternately periodically, and this is connected to the flow path on the heat receiving fluid side and the flow path on the heat dissipating fluid side of the heat exchanger. Therefore, even if the primary catalyst of the rotary catalytic converter is poisoned, it will self-regenerate when it comes into contact with the high-temperature heating gas.Furthermore, even if tar mist or the like adheres to the primary catalyst, that part will be removed from the heating gas side. When this happens, it comes into contact with high-temperature heated gas and is purified, making it difficult for tar and other substances to accumulate on the primary catalyst. Therefore, it is necessary to maintain catalyst activity stably for a long period of time, suppress gas pressure loss, etc. as much as possible.
Good heat transfer performance can be maintained and stable operation can be performed for a long period of time.

Further, by providing the secondary catalyst in the middle of the third flow path, it is possible to further oxidize the low concentration combustible components contained in the remainder of the exhaust gas.
In this way, by treating the exhaust gas discharged outside the system again with the secondary catalyst, combustible components remaining due to leaks in the rotary catalytic converter can be more completely removed. In this case, the exhaust gas flowing into the third flow path is the remainder of the exhaust gas returned to the coating drying furnace, so its flow rate is small, and therefore the required volume of the catalyst is also small.

According to a preferred aspect of the present invention, a temperature-raising auxiliary device for introducing fuel gas or high-temperature gas is provided between the flow path on the heat-receiving fluid side of the heat exchanger and the rotary catalyst device or inside the rotary catalyst device. ing.

According to this, during start-up operation, etc.
The temperature of the exhaust gas decreases due to heat storage in the heat transfer element of the heat exchanger, but as the temperature of the exhaust gas is raised by the fuel gas or high temperature gas, the outlet temperature of the primary catalyst becomes high and the start-up operation time increases. can be shortened. Furthermore, when the primary catalyst is significantly poisoned, the poisoned primary catalyst can be activated by increasing the temperature of the exhaust gas.

"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.

A first flow path 22 for extracting exhaust gas is connected to the paint drying oven 21 . This first flow path 22 is
In the middle of the flow path, there is provided a damper 23 that adjusts the flow rate of exhaust gas, and a fan 24 located downstream of this damper 23 that sucks the exhaust gas. Therefore, the flow rate of the exhaust gas from the paint drying oven 21 is adjusted to a predetermined amount by the damper 23, and the exhaust gas is taken out to the first flow path 22 by the fan 24.

A dust removal filter 25 is arranged on the downstream side of the fan 24 in the middle of the first flow path 22 . This dust removal filter 25 removes dust from the exhaust gas taken out from the first flow path 22, and its filter body is made of porous ceramic material, cloth made of ceramic fiber, glass fiber, etc. It is preferable to use it in order to prevent corrosion caused by SOx. A backwashing mechanism (not shown) is attached to the dust removal filter 25, and by backwashing the filter body at regular intervals, an increase in pressure loss is suppressed.

The first flow path 2 further downstream of the dust removal filter 25
2, a heat exchanger 26 is arranged. The heat exchanger 26 has a built-in heat transfer element (not shown), and this heat transfer element is provided with a flow path on the heat receiving fluid side and a flow path on the heat radiation fluid side. The flow path on the heat-receiving fluid side has a function of raising the temperature of the exhaust gas from the first flow path 22, and is connected to the heated gas flow path A of the rotary catalyst device 28 via the outflow path 27. . Further, the flow path on the heat radiation fluid side has a function of lowering the temperature of the exhaust gas from the rotary catalyst device 28, and is connected to the heated gas flow path B of the rotary catalyst device 28 via the return flow path 29.

The rotary catalyst device 28 includes a primary catalyst 30 that oxidizes combustible components in exhaust gas, has a shaft center fixed to a drive shaft 31, and is rotated by a motor 32. In the rotation path of the primary catalyst 30, half is designated as a heated gas flow path A, and the other half is designated as a heated gas flow path B. Therefore, when the exhaust gas introduced from the heat receiving fluid side flow path of the heat exchanger 26 via the outgoing flow path 27 passes through the flow path A, the combustible components are oxidized by the primary catalyst 30. It becomes high temperature. Then, the exhaust gas is transferred to the inversion space 3
At step 3, the air is reversed, passes through the flow path B, and passes through the primary catalyst 30 again to reach an even higher temperature. The exhaust gas whose combustible components have been oxidized by the primary catalyst 30 is returned to the flow path on the heat radiation fluid side of the heat exchanger 26 via the return flow path 29.

The primary catalyst 30 is preferably one in which platinum, palladium, or a mixture of both is supported on a ceramic honeycomb carrier. This primary catalyst 30 has the property of being able to self-regenerate when low temperature gas flows through it and the poisoned portion comes into contact with high temperature gas.

Note that the rotary catalyst device 28 may be configured such that the primary catalyst 30 is fixed and the flow paths A and B rotate relative to it.

A temperature raising auxiliary device 34 is connected to an outflow path 27 that connects the heat exchanger 26 and the rotary catalyst device 28 .
This temperature raising auxiliary device 34 is used to raise the temperature of exhaust gas to the catalyst activation temperature during start-up operation, or to activate the primary catalyst 30 that has been significantly poisoned, and is used to transport fuel gas and high temperature gas. Channel 2
7 and a valve 36 for controlling the introduction of the gas. Instead of or in addition to being connected to the outgoing flow path 27, such a temperature raising auxiliary device 34 is connected to the rotary catalytic device 28 as shown by the two-dot chain line in the figure. Fuel gas or high temperature gas may be introduced into the reversal space 33.

Further, a second flow path 37 is connected to the flow path on the heat radiation fluid side of the heat exchanger 26 . This second
The flow path 37 circulates most of the oxidized exhaust gas to the coating drying furnace 21, and a damper 38 is provided along the way to adjust the flow rate of the exhaust gas.

A third flow path 39 is provided to branch from the second flow path 37 . This third flow path 39 is for discharging the remaining part of the exhaust gas to the outside of the system, and a damper 40 is provided in the middle thereof to adjust the flow rate of the exhaust gas.

A secondary catalyst 41 is provided in the middle of the third flow path 39 and downstream of the damper 40 . This secondary catalyst 41 is used to more completely oxidize a small amount of combustible components still remaining in the exhaust gas to be discharged outside the system. As the secondary catalyst 41, platinum,
Preferably, it supports palladium or a mixture of both.

An air preheater 42 is connected downstream of the third flow path 39 . This air preheater 42
is for exchanging heat with the burner preheated air for exhaust gas from which combustible components have been completely removed by the secondary catalyst 41, and releasing the exhaust gas to the outside air through the chimney 43. Further, a flow path 44 is connected to the air preheater 42, and burner preheated air is guided to each burner 45 through this flow path 44. The gas within the coating drying oven 21 is circulated by a fan 46 and heated by a burner 45 at that time.

Next, the operation of the exhaust gas treatment device for a paint drying oven according to the present invention will be explained.

For example, carbon dioxide is emitted from inside the paint drying oven 21.
4.2%, water 11.0%, nitrogen 74.0%, oxygen 10.4%, ethyl cellosolve 2500ppm, SOx 300ppm, dust concentration 0.1mg/Nm ³ , tar concentration 2.5mg/Nm ³ , temperature
It is assumed that exhaust gas at 230° C. is taken out to the first flow path 22 at a flow rate of 20000 Nm ³ /h.

The exhaust gas is flown into the first flow path 22 by a fan 24 while the flow rate is adjusted by a damper 23, and dust is removed by a dust removal filter 25. Therefore, it is possible to prevent dust from adhering to the heat transfer element built into the heat exchanger 26 and the primary catalyst 30 of the rotary catalyst device 28. Then, the exhaust gas flows into the flow path on the heat receiving fluid side of the heat exchanger 26, and the primary catalyst 30 has the required activity due to the heat transfer element.
The temperature is raised to 300℃.

In the rotary catalyst device 28, a primary catalyst 30 is rotated by a motor 32 at a predetermined period, and a heat exchanger 2
The exhaust gas heated in step 6 flows into the flow path A of the device 28 via the outgoing flow path 27. In this flow path A, the exhaust gas passes through the primary catalyst 30, and the odorous combustible component (ethyl cellosolve) is oxidized and deodorized. The catalyst volume of the primary catalyst 30 is such that the purification efficiency is 90% or more. The exhaust gas that has passed through the primary catalyst 30 is heated to 443° C. by the heat of oxidation.
Then, the exhaust gas whose flow is reversed in the reversal space 33 of the device 28 enters the flow path B and passes through the primary catalyst 30.
After passing through the exhaust gas again, the remaining odorous and combustible components in the exhaust gas are further oxidized and deodorized, and the temperature is raised to 488°C. At this time, the ethyl cellosolve concentration is
It becomes 250ppm.

This high-temperature exhaust gas is sent to the heat exchanger 26 again via the return flow path 29, passes through the flow path on the heat radiation fluid side of the heat exchanger 26, and is lowered in temperature to 418°C. As a result, the heat transfer element in the heat exchanger 26 reaches a high temperature and obtains heat that raises the temperature of the exhaust gas introduced from the first flow path 22.

By the way, in the flow path A of the rotary catalyst device 28, the temperature of the exhaust gas that contacts the primary catalyst 30 is 300°C.
Due to the low temperature of ℃, the primary catalyst 30 is temporarily poisoned by SOx, but this poisoned portion is moved to the flow path B side by rotation by the motor 32.
It self-regenerates when it comes into contact with high-temperature exhaust gas of 418℃,
Restores its purification performance. Furthermore, tar mist and the like adhering to the primary catalyst 30 in the low-temperature flow path A come into contact with the high-temperature exhaust gas when it rotates to become the flow path B, and are purified by vaporization or combustion.

During start-up operation, the exhaust gas temperature decreases due to heat storage in the heat transfer element in the heat exchanger 26, but in this case, the temperature increase auxiliary device 34 is activated to pump the fuel gas and high-temperature gas back and forth. It is introduced into the rotary catalyst device 28 via the flow path 27. By introducing fuel gas, the concentration of odorous combustible components in the exhaust gas is increased, and the heat of oxidation at the primary catalyst 30 is increased, thereby increasing the temperature of the primary catalyst 30. The temperature is raised and the start-up operation time can be shortened. Even if the primary catalyst 30 is severely poisoned and interferes with self-regeneration,
By activating the temperature raising auxiliary device 34 and introducing fuel gas or high temperature gas, the poisoned primary catalyst 30 can be activated.

At the outlet of the rotary catalytic converter 28, the concentration of ethyl cellosolve in the exhaust gas is 365 ppm due to the addition of leakage from the seal.
It passes through the heat exchanger 26 and the second flow path 37, and the flow rate is adjusted by the damper 38, of which 17000N
m ³ /h is circulated to the coating drying oven 21. Further, the remaining part of the exhaust gas, that is, 3000 Nm ³ /h, branches from the second flow path 37 and passes through the third flow path 39, the flow rate is adjusted by the damper 40, and further oxidized by the secondary catalyst 41. The volume of the secondary catalyst 41 is 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 30 and the secondary catalyst 41
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 41 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.

The exhaust gas purified in this way is sent to the air preheater 4.
After passing through 2 and exchanging heat with the burner preheated air at room temperature, the air is discharged to the atmosphere through a chimney 43. The heated burner preheated air is guided to the burner 45 through the flow path 44 and then introduced into the coating drying oven 21 again.

"Effects of the Invention" As explained above, according to the present invention, the exhaust gas taken out from the paint drying oven is passed through a dust removal filter in advance, and then introduced into the heat transfer element of the heat exchanger and the subsequent rotary catalyst device. I decided to do this, so
Dust can be prevented from adhering to the heat transfer element and catalyst. In addition, for the oxidation and deodorization treatment of exhaust gas, a rotary catalyst device is used in which heated gas and heated gas alternately flow, and this is connected to the flow path on the heat-receiving fluid side and the flow path on the heated fluid side of the heat exchanger. Therefore, even if the primary catalyst of the rotary catalytic converter is poisoned by, for example, SOx, it can self-regenerate when it comes into contact with high-temperature exhaust gas.Furthermore, tar mist, etc. Even if it adheres to the catalyst, it can be purified by 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 exhaust gas can be purified stably 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 odoriferous combustible components sufficiently or even if a leak occurs in the rotary catalytic converter, the secondary catalyst This allows odoriferous and combustible components to be removed to the desired level and discharged from the system.

[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, 21 is a paint drying oven, 22 is a first flow path,
25 is a dust removal filter, 26 is a heat exchanger, 28 is a rotary catalyst device, 30 is a primary catalyst, 34 is a temperature raising auxiliary device, 37 is a second flow path, 39 is a third flow path, 41
is a secondary catalyst, and 42 is an air preheater.

Claims (1)

[Claims] 1. A first device for extracting a predetermined amount of exhaust gas from a paint drying oven.
a flow path, a dust removal filter provided in the first flow path, a flow path on the heat-receiving fluid side that raises the temperature of the exhaust gas introduced from the first flow path, and after the combustible components have been oxidized. A rotary catalyst comprising a heat exchanger equipped with a flow path on the heat-radiating fluid side that lowers the temperature of the exhaust gas, and a primary catalyst that oxidizes combustible components of the exhaust gas introduced from the flow path on the heat-receiving fluid side of the heat exchanger. a second flow path for circulating a part of the exhaust gas that has been oxidized by the rotary catalyst device and has passed through the flow path on the heat radiation fluid side of the heat exchanger to the paint drying furnace; A third flow path that branches off from the exhaust gas and discharges the remainder of the exhaust gas to the outside of the system, and a secondary catalyst that further oxidizes combustible components contained in the remainder of the exhaust gas is provided in the middle of the third flow path. An exhaust gas treatment device for a paint drying oven characterized by: 2. In claim 1, a temperature raising auxiliary device for introducing fuel gas or high-temperature gas is provided between the heat-receiving fluid side flow path of the heat exchanger and the rotary catalyst device or inside the rotary catalyst device. Exhaust gas treatment equipment for paint drying ovens.