JPS5848826B2 - Butupinjiyounoyoubaikicoteingokansousacelhouhoutouchi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates generally to a method and apparatus for performing heating operations that release flammable solvent vapors, and more particularly to a method and apparatus for performing heating operations that release flammable solvent vapors, and more particularly, for the application of solvent-based paint coatings to articles of various forms. Concerning drying method and apparatus.

Solvent-based coatings typically contain 40 to 60 percent organic solvent in the form of aromatic hydrocarbon compounds such as benzene, toluene, xylene, and other highly flammable naphthas derived from coal tar distillates. These solvents evaporate from the paint coating during the drying process.

These solvent vapors are highly flammable and, when mixed with air, form explosive mixtures and pose a potential fire and explosion hazard.

For this reason, safety and fire prevention regulations require that the concentration of solvent in the oven exhaust gas must be less than 25 percent of its lower explosive limit for the safety of open drying exposed to the atmosphere. .

Therefore, in order to comply with these regulations, the solvent vapor generated in such an oven, separate from the heat demands of the drying process, must be rated at 25% of the lower explosive limit before being discharged therefrom.
It must be diluted to a percentage or less.

In conventional paint drying ovens, this dilution is accomplished by introducing into the open at least 2,840,000 liters of air (10,000 cubic feet of air per gallon) per 379 liters of vaporized solvent.

Prior to the enactment of recent pollution control regulations, these solvent-air mixtures containing unwanted contaminants were discharged directly into the atmosphere.

The heat required to carry out such conventional paint drying methods simply brings the paint coated article to the required paint drying temperature, typically 93°C.
．． 3° to 315.6°C' (2000 to 600OF
) It is used not only for heating in the enclosure, but also for heating the diluted air in the open discharge temperature chamber.

The additional thermal energy expended in heating the required large volumes of dilution air accounts for a significant portion of the total fuel requirements of the process and thus adds significant operating costs.

Solvent-air mixtures discharged from conventional paint drying ovens contain significant levels of contaminants, so recently enacted government pollution control regulations no longer allow these mixtures to be released directly into the atmosphere. not allowed.

Therefore, in order to meet these air pollution regulations, it is necessary to equip the paint drying oven with some type of pollution abatement device, the most common form of which is to incinerate the exhaust gases from the paint drying oven. It was a thermal fume incinerator.

The thermal incineration of these open exhaust gases is 676.700 and 7
Temperatures between 75.68C (1250OF and 1450F) are typically required.

In a typical fume incinerator, the fume is used as an auxiliary fuel,
For example, it is mixed with natural gas, and the mixing temperature is 676.7°-775.6°C (1250°-1250°C) to incinerate the fumes.
1450 lower)=1.

With properly designed incinerators, gaseous combustion materials are almost always clean.

That is, there are no air pollutants. The amount of auxiliary fuel required for the incineration process depends on the exhaust fume temperature and initial fume content.

However, in most paint drying equipment that uses such exhaust gas incineration, the amount of combustion consumed during paint drying operations is more than double that used in conventional paint drying equipment that does not include a fume incineration device. To increase.

In order to reduce the fuel consumption of paint drying equipment equipped with such an incinerator, a fume preheater is used to heat the exhaust gas from the incinerator to increase its temperature before entering the incinerator. It has been proposed to use .

However, the addition of such a smoke preheater increases the capital cost of the dryer by an amount comparable to, but not less than, the cost of the incinerator itself.

In many cases, for economic reasons, the efficiency of the preheater is reduced to 50%.
It is impractical to increase it above 60%.

As a result, the extra fuel consumption for the operation of the incinerator remains high.

Another suggestion to further reduce fuel consumption is:
A liquid-to-gas heat exchanger may be used to recover excess heat from the exhaust gas leaving the fume preheater.

However, such equipment is even more expensive and its use is limited to very large installations.

However, even with such sophisticated heat recovery equipment, fuel consumption is more expensive than simple conventional equipment without fume incineration equipment.

Many small to medium sized paint drying facilities cannot justify the use of full heat recovery methods from an economic standpoint.

As a result, these facilities must use considerably more fuel than is conventional in order to operate the required pollution reduction equipment and incinerator.

Additionally, current fuel supply shortages and continuously rising fuel costs threaten the paint drying industry with higher production costs, inadequate fuel allocation, bottlenecks, and production cuts or shutdowns.

As an alternative to using solvent-based coatings, powder coatings and water-based coatings are being considered as an expedient to reduce or eliminate air pollution emissions and therefore excess fuel consumption within the incinerator; however, The use of either of these two alternatives still requires the use of large amounts of fuel in the dry space or heated open.

Furthermore, as currently known, none of these alternative methods have been tried on a large scale in the past, and their ultimate use in large scale coating operations is unlikely for a considerable period of time.

As mentioned above, conventional solvent-based paints are highly flammable, with a cost of between 120,000 and 140,000 B.P. t, u. (30000
40 to 6 with a calorific value of 35,000 kilocalories)
Contains 0% 1 or more organic solvents.

These paints are usually applied as a thin coating or film onto an article or object, and for heavy duty applications, the film thickness is about 0.5 to 2 mils (12.7 to 50.0 mils). 8 microns).

During the drying process, most of these solvents evaporate and the pigments of the paint form a protective coating on the article.

The amount of heat in the solvent vapor vaporized during the paint drying process is typically several times the amount of fuel required in a typical paint drying oven.

Therefore, if paint drying equipment is designed to utilize the thermal energy of this solvent vapor while maintaining basic safety requirements, a pollutant-free exhaust gas, and constant coating or product quality, This would drastically reduce the fuel demand of the paint drying industry.

For conventional paint drying equipment operating in an open atmosphere below the lower explosive limit, the dilution air that must be added to the solvent vapors before exiting the oven to comply with safety regulations is less than the total heat requirement of the equipment. Increase the main part of.

676.7° to 775° to further comply with air pollution regulations.
．． Increasing the exhaust gas temperature at an incineration temperature of 6°C (12,500 to 1,450'F) more than doubles the heat requirements of a system without an oven exhaust incinerator.

If the use of diluted air or the amount of air used can be reduced without compromising the safety requirements of the paint drying equipment, most of the inherent thermal energy in the solvent vapor released from the paint during drying can be absorbed. It can be used to heat the drying oven and the coated articles therein to be dried.

However, in the design of such equipment, the basis for the flammability of the gas mixtures formed in paint drying ovens, with regard to safety and complete combustibility considerations, must be made with reference to the flammability curves established for that purpose. It is necessary to understand.

These curves show that a mixture of hydrogen, carbon monoxide, hydrocarbons, and common paint solvent vapors, as well as common combustible gases containing nitrogen, carbon dioxide, and water vapor, has an oxygen concentration of about 5 percent or less. In some cases, it has been shown to be non-flammable.

Therefore, as an alternative to using small amounts of diluted air to limit potential explosion hazards, the gas-solvent vapor mixture formed in the paint drying oven during drying operations may be If a low atmosphere 1 or inert gas containing little oxygen is maintained in the oven while the solvent is evaporating from the paint coating, there will be no explosion.

In this way, the gas-solvent mixture is well outside the flammable range, i.e. its upper explosive limit (
U. E. L. ), so there is no need to use dilution air at all.

On the other hand, from a safety standpoint, the volume ratio of inert gas to solvent vapor can be any value for such gases; The amount required is far less than the dilution air required in conventional paint drying methods.

The non-explosive gas-solvent mixture or concentrated fumes discharged from the drying oven is incinerated in an incinerator under stoichiometric conditions to incinerate the oven exhaust gases and render them substantially inert and at high temperatures, e.g. 〜898.9℃(1
4000-1650'F) can be used to provide the total heat required for paint drying operations.

Because they are inert, these heated exhaust gases from incinerators
Necessary not only to supply all, or if desired only a portion, of the heat required for the paint drying operation, but also to ensure that the gas-solvent vapor mixture remains above the upper explosive limit at all times during the paint drying operation. In order to supply a sufficient amount of inert gas,
After cooling, it is recirculated.

Since the volume and thermal energy of the exhaust gases generated within the incinerator is significantly greater than that required for paint drying operations within the oven, only a small portion of the total volume of these exhaust gases need be recycled into the oven.

Given their inert and therefore non-polluting nature, the remainder of these exhaust gases may be discharged directly to the atmosphere.

The part of the emitted gas from the heating incinerator that is recirculated to the oven can be supplied by a water heater, an air heater, a low pressure steam boiler, or a low pressure steam boiler.
It can be cooled at the low temperatures required for paint drying operations in ovens by passing it through a suitable heat recovery system enclosure or heat exchanger, such as a metal part of a container or article coating line.

The incinerator is thus used as an energy recovery device and serves a multipurpose function as an inert gas generator, a heat generator or burner, and as a pollution reduction facility.

Additionally, the rod incinerator is equipped with a pilot burner to maintain the required ignition conditions within the incinerator to ensure complete combustion of the solvent vapors entrained in the oven exhaust gas mixture introduced into the incinerator. No auxiliary fuel is required for normal operation other than the very small amount necessary for operation.

It is therefore an object of the present invention to provide a method for drying solvent-based paints and other solvent-containing coatings that increases thermal efficiency.

Another object of the invention is to provide a method for drying solvent-based coatings which is characterized not only by improved thermal efficiency but also by pollution-free exhaust gas emissions.

Yet another object of the present invention is to provide a method of drying a solvent-based coating that is substantially self-sufficient in terms of its fuel energy requirements.

Another object of the present invention is to dry and thaw solvent-based coatings in an inert atmosphere with a substantially oxygen-free residue and low oxygen content that is maintained well above the upper explosive limit during the drying process. The objective is to provide a method for this purpose that complies with standard fire safety regulations.

Yet another object of the present invention is to provide a solvent-based coating in which the potential thermal energy in the solvent vapor evaporated from the coating during a drying operation can be used to supply all or a portion of the heat required for the drying operation. The purpose is to provide a method for drying.

It is another object of the invention that the solvent vapors evaporated from the coating during the drying operation be recirculated during the drying open to provide an inert atmosphere. It is an object of the present invention to provide a method for drying a solvent-based coating that is incinerated to produce an active gaseous combustion product.

Yet another object of the present invention is that there is no need to add dilution air to the gases exhausted from the drying oven during the drying operation in order to keep them outside the explosive limits so as to meet standard fire safety regulations. An object of the present invention is to provide a method for drying a solvent-based coating.

Another object of the present invention is to provide an apparatus for effectively drying solvent-based paints and other coatings by the method described above.

In summary, according to one feature of the present invention, drying solvent-based paints and other similar types of coatings on articles is carried out in such a way that the heated atmosphere is almost always above the upper explosive limit during the drying operation. It is carried out in a drying oven maintained under inert conditions without oxygen or with a low oxygen content.

The solvent vapor that evaporates from the coating and mixes with the inert gas discharged from the drying open is incinerated under stoichiometric conditions in an incinerator to reduce the temperature between 760° and 898.9°.
At elevated temperatures of 14,000 to 1,650 °C (14,000 to 1,650 °F), a substantially oxygen-free, non-polluting inert gas with a low oxygen content is formed which is passed from the dryer directly to the atmosphere as a non-polluting effluent. released.

At least a portion of the released gas is heated between 93.3° and 315.6°C (2000° and 600°C) for coating drying operations.
After cooling in a suitable heat recovery device to the required temperature (see below), it is possible to supply not only all or part of the heat required by the oven for the drying operation, but also to provide an inert atmosphere to the oven. It is recycled back into the drying oven for dispensing.

According to another feature of the invention, the only auxiliary fuel requirement of the coating drying system according to the invention during its normal operation is to ensure complete combustion of the solvent vapor introduced into it from the oven. , only a small amount in it to maintain the required ignition conditions.

Other objects and advantages of the invention will become apparent from the following detailed description of the embodiments and the accompanying drawings.

In the drawings, the invention is illustrated as being implemented in a continuous drying apparatus for solvent-based paint coatings applied to metal strip stock, such as rolled metal strip.

However, the present invention is useful for drying solvent-based paint coatings applied to, for example, automobile bodies, metal cabinets for household appliances, and various other articles; It is to be understood that the present invention is also applicable to other heating methods in which steam with a high calorific value is released, such as those used in the present invention.

Referring to FIG. 1, an oven is indicated at 10 in which heating operations are carried out which result in the release of high calorific flammable vapors.

The illustrated embodiment involves the heating of a metal strip stock 11, such as a strip of steel and aluminum coated on both sides with a layer or film 12 (FIG. 4) of a solvent-based paint.

For continuous metal strip paint coating methods as shown in FIG.
from there into the coating tank 16.
The coating 12 is formed by dipping into a bath of solvent-based paint.

However, it should be understood that the paint coating 12 on the metal strip blank 11 can be applied thereto by methods other than the dip coating method shown, such as by spraying, rolling, etc.

From the coating bath 16, the coated strip 11 is supported between a pair of squeegee rolls 17 which wipe excess coating material from the strip and coat the film 1 of the desired thickness thereon. 12, which is typically 0.5 to 2.0 mils (12.7 to 50.8 microns) thick for conventional paint coatings.

The coating strip 11 enters from the squeegee roll 17 into the interior of the oven 10 or into the drying chamber 18 through an inlet opening 19 in the end face 20 of the oven and, after drying of the coating on the strip 11, from the open chamber 18 outwardly. exits through an outlet opening 21 in the other end wall 22 of.

Strip 11 emerging from oven 10 passes between and is supported by a pair of idler rolls 230 and is then wound onto take-up roll 24.

The oven chamber 18 has a temperature required for the particular drying operation or other heating operation to be carried out therein, such as about 93.3°C when drying a conventional solvent-based paint coating 12.
°~315.6°c (200'~600''
F) Provide a heated atmosphere at a temperature within the range.

As noted above, the heating action performed in the oxygen-containing atmosphere within the oven may result in the generation of flammable and explosive vapors within the oven, such as solvent vapors that evaporate from the solvent-based paint coating 12 during drying. For safe operation of ovens, the safety and fire regulations applicable therein require that the solvent vapors generated therein be removed from the oven during the heating operation before it is vented from the open. 25 of the lower explosive limit of the solvent vapor-containing gas mixture formed in
It requires that it must be diluted by 4%, ie with a sufficiently low value l.

In a conventional paint drying open, this dilution is 2.84 million liters per 3.79 liters of solvent evaporated.
This is done by introducing io'ooo cubic ins per gallon of air into the oven.

Since the dilution air introduced into this oven must necessarily be heated to the temperature 1 necessary for the heating action to take place in the oven, the additional thermal energy expended to heat the dilution air is It accounts for a significant proportion of the total heating fuel requirement in the open and therefore presents significant additional operating costs.

In accordance with the present invention, the need and additional expense for adding such diluting air is eliminated by reducing the need and additional cost of adding such diluent air to the specific gas mixture formed in the oven during the heating operation, instead of the lower explosive limit of the gas mixture traditionally used. can be completely eliminated by drying paint or performing other heating operations in an inert atmosphere with little oxygen or low oxygen content above the upper explosive limit of .

The flammability of any gas mixture is determined with reference to flammability curves established for various gas mixtures.

These curves represent common flammable gases, including hydrogen, carbon monoxide, and vapors of common solvents such as those used in common solvent-based coatings, and inert gases such as nitrogen, carbon dioxide, and water vapor. It has been shown that a mixture with oxidants is flammable if the oxygen concentration in the mixture is less than 5 percent.

Therefore, for purposes of the present invention, oven 10 includes five
A substantially inert gas is supplied with an oxygen concentration of less than 2 percent, preferably less than 2 percent.

Inert gas is supplied to oven 10 from another source.

However, in order to obtain the full benefit of the present invention from an economical standpoint, it is preferred, however, that the inert gas supplied to the oven 10 and the paint drying or other solvents carried out in the open. The heat required for the evaporative heating operation is generated by the exhaust casing from the incinerator 25, which incinerates the mixture of inert gas and solvent vapor discharged from the oven 10 in the manner described below, as shown in the flowchart of FIG. is given by the emitted gas.

At least a portion of these released gases are cooled to a temperature 1 necessary for paint drying 1 and other heating operations to be carried out in the oven 10, and then the inert gas and all of the heat required in the oven 10 are removed. It can be recycled back to the oven for serving in portions or portions.

Thus, a paint dryer or other solvent evaporator in accordance with the present invention is substantially self-sustaining with respect to its fuel energy requirements.

To maintain the desired low oxygen concentration in the open atmosphere at all times during the continuation of paint drying chambers or other heating operations carried out in the open oven 10, the drying chamber 18 of the oven is used to prevent air from escaping into the oven. and it is necessary to isolate the atmosphere therein from the surrounding atmosphere.

For this purpose, the walls of the oven 10 are made of a suitable design so as to be substantially airtight as such.

Therefore, as shown in FIG.
The six buttons and the top and bottom walls 27 and 28 are each formed as a shell or casing 29 of sheet metal, the inside of which is lined with a lining 30 of a suitable refractory material, such as ceramic fiber type block insulation. establish.

Further certainty against the leakage of ambient air into the oven chamber 18 can be achieved by reducing the inert gas atmosphere therein by e.g.
This is achieved by maintaining a slight overpressure on the order of inches (1.27 mm IJ) of water.

1. As shown in Figure 3 for the specific paint drying operation, the workpiece to be processed in the open 10 is connected to the inlet and outlet 19,
21, these openings 19,
21 also needs to be sealed from the exposed outside atmosphere.

For this purpose, the opening 10 is formed with suitably shaped aerodynamic seals 31 at its inlet and outlet openings 19.21.

As shown in more detail in FIG.
If the article is in the form of a continuous strip, such as a continuous strip, or is in the form of an article to be conveyed to and out of an oven on a conveyor belt 1 or similar device, the aerodynamic seal 31 may 11 flat double-sided housing or a curtain of inert gas blown in a direction opposite to the direction of movement of the conveyor device immediately outside each of the openings 19 and 21 of the oven; or a screen 32.

For the gas screen 32 to effectively seal the inlet and outlet openings 19.21 in the oven wall 20.22, these openings must be approximately 6 inches (15.24 centas) high and run through the openings. It may be in the form of a narrow, rectangular slot wide enough to receive the widest strip of material 11 or conveyor with a slight clearance on each side.

Inert gas screen 32 inlet and outlet openings 19 and 21
end walls 20, 22 of the oven so as to be located on either side of the moving strip 11 in positions immediately above and below the
The moving strip 11 is directed in the direction of a conveyor carrying the housing or workpiece from a respective pair of pneumatic chambers 33 and 34 placed on the outside of the strip.

The plenum chambers 33 and 34 are sized to match the width of the inlet and outlet openings 19.21 in the oven wall 20.22 and are provided with opposed flat porous outlet plates 35, which allow the strips 1
1 and arranged oppositely to each other in order to provide an outlet opening for the inert gas forming a gas flow curtain 32.

The outlet plate 35 of the plenum chamber has dimensions of approximately 6 inches (15.24 centimeters) in the longitudinal direction of the advancing strip 11, with a spacing of about 9 inches (22.86 centimeters) between the stubs. approximately 4 from each side of each advancing piece 11
! They are separated by approximately the same distance of 0.2 cm (11.43 cm).

The porous outlet plate 35 has small diameter gas discharge holes 1 or outlet holes (not shown) whose centers are spaced apart by a distance of the diameter of the two outlet holes and are arranged in a staggered pattern in the plate 35. An opening area of approximately 33% may be provided.

In order to prevent leakage of the sealed gas flow 32 at the side ends of the space between the plenum chambers 33 and 34, end plates 36 are provided on the plenum chambers at each end, spanning the plenum chambers and closing the space between them. ing.

The inert gas for the plenum chamber 33.34 opens into the plenum chamber,
It is supplied thereto by respective gas ports or conduits 37 connected to a suitable source of inert gas, namely the exhaust gas from the incinerator 25 according to the invention.

Sufficient inlets 37 to each plenum chamber 33, 34 should be provided to prevent uneven gas distribution therein.

This point is satisfied by providing one lateral inlet 37 per foot (30.48 cm) of chamber length along the width of each slotted inlet 1 or outlet opening 19.21. Get the desired results.

As mentioned above, the openings 19, 21 and the plenum chamber 33 are of specific dimensions.
34, the plenum chambers 33, 34 are closed to provide an effective aerodynamic seal 31 to the open opening 19.21.
The amount of inert gas that needs to be supplied to the incinerator 25
much less than the gas by-products released from

A sufficient surplus of such inert gas from the incinerator 25 is therefore transferred to the inlet and outlet openings 19. of the oven 10.
21 to maintain an aerodynamic seal 31 in the air chamber 33.
, 34 can be used to constantly supply the necessary gas.

In operation of the aerodynamic seal 31, an inert gas stream 32 discharged from the plenum chambers 33, 34 in a direction perpendicular to the advancing strip 11, after impinging on the strip, flows as shown in FIG. As indicated by the arrows, it curves and runs more or less parallel along the strip 11, with part of the gas flow flowing inwardly into the opening 10 and the other part flowing outside thereof.

This flow pattern allows the outside air to enter the oven at the inlet and outlet openings.
9 and 21 into the oven 10, and likewise prevents inert oven atmosphere from escaping into the atmosphere through these openings.

To perform the illustrated paint drying operation, the paint coated strip 11 is passed through the oven outlet opening 21 to the oven chamber 18, depending on the specific operating temperature of the open atmosphere and the thickness and specific composition of the paint coating 12. The strip is passed through an open chamber 18 which is heated to a degree that ensures substantially complete drying of the paint coating 12 on the strip before exiting the strip.

During this paint drying operation, the solvent in the paint coating 12 evaporates therefrom and the resulting solvent vapor mixes with the inert gas maintained within the oven chamber 18.

Since this gas-solvent vapor mixture is maintained below about 5 percent oxygen content at all times during the continuation of the paint drying operation, it is above the upper explosive limit and outside the flammability range of its flammable elements; Therefore, it can be safely discharged directly from the oven 10 without the need for dilution with air, consistent with safety and fire regulations commonly practiced for prior conventional paint drying methods.

As shown, the inert gas-solvent vapor mixture is passed through exhaust conduit 38 (FIG. 1) to the flowchart indicated by line 38a in FIGS. 2 and 3. As shown, from oven chamber 18,
It is preferably discharged near the oven, in the area of its roof behind the opening or at the exit end.

The gas-solvent vapor mixture is suitably evacuated from the open chamber 18, such as by a fan 39 in the evacuation pump 1 and conduit 38, at the required rate to maintain the solvent vapor concentration in the oven atmosphere at a desired level.

In this regard, from the point of view of safety regulations, the volume ratio of inert gas to solvent vapor in the oven atmosphere can be any value, but it is necessary to keep this ratio below a certain value due to vapor condensation and other considerations. .

However, in many cases, the amount of inert gas required per gallon of evaporated solvent is in any case several orders of magnitude less than the diluted air required for conventional solvent-based paint drying methods.

The oven atmosphere is determined by a pressure measuring device 41 in the oven chamber 18.
The pressure is maintained at a pressure slightly above atmospheric pressure of about 0.05 inches (0.127 centimeters) of water by a conventional pressure regulator 40 (FIG. 1) operated by a pressurizer.

The pressure regulator 40 is connected to a damper 42 in the gas exhaust flue 38 from the oven chamber 18 or to an inert gas supply intake 44.
The damper 43 is arranged to adjust the position of either one of the dampers 43 within the damper 43.

Inert gas-solvent vapor mixture, i.e. Open 10
According to another characteristic of the invention, the so-called rich fumes discharged from the incinerator are conducted into a specially designed incinerator 25, known as a rich fume incinerator, where the rich fumes are heated to a temperature of at least 760'C (1400'C). F) is incinerated under approximately stoichiometric conditions at a temperature of clean, i.e. non-polluting, inert gas combustion materials, sulfate or with emitted gases such as nitrogen, carbon dioxide and water vapor; If less than about 5 percent is desired, the special paint drying method shown will convert the gas into an emitted gas that has an oxygen concentration of about 2 percent and is permitted to be released into the atmosphere under current pollution control regulations. be done.

For the purpose of the present invention, the concentrated fume incinerator 25 is
K., H., filed July 24, 1972, and assigned to the assignee of this application. Hem sath and A. C.
It may be of the type described and claimed in Thekdi US Application No. 274,406.

As disclosed therein, the incinerator 25 is arranged inside a refractory brick to conserve heat, and the dense fumes are discharged from the opening 10 into a stack 45 (FIG. 1). generally includes.

Above the generally cylindrical stack 45 is a lower chamber 4.
A housing 46 having an upper part 1 or a combustion chamber 48 is arranged, and the housing 46 is also lined with a human-resistant material.

The lower chamber 47 extends upwardly into and opens into the upper chamber 48;
The stacks 4 are closely surrounded so as to prevent flooding and to form a narrow annular air supply passage 50 between them.
It ends a short distance above the top of 5.

The combustion chamber 48 abruptly closes at the upper end of the narrow passage 49 by means of a stepped shoulder 51 in its wall, which promotes the complete combustion of the dense heat and provides a fire stabilizer that draws the air mixture into the combustion chamber. It is now available.

The lower chamber 47 also has an opening 53 for an air supply pipe 54 equipped with a manual valve 55 .

The air supply pipe 54 supplies the amount of suction air necessary for approximately stoichiometric combustion of the dense fumes in the upper part 1 of the housing 46 or in the combustion chamber 48 .

The intake air directed from the narrow annular passage 50 to the lower end of the combustion chamber 48 is discharged into the combustion chamber at a velocity greater than the velocity of the rich fume exhaust discharged into it from the stack, and thus It acts as an air pump to increase the extraction of concentrated fumes into the combustion chamber.

Furthermore, the suction air from the annular passage 50 promotes homogeneous mixing with the dense fumes discharged from the stack 45 and burns out all combustion products in the dense fumes introduced therein from the oven chamber 18. To ensure complete combustion in a chamber 48.

The upper part of the incinerator 25, i.e. the combustion chamber 48, at its lower end is a region of mutual mixing of the suction air from the passage 50 and the dense fume from the stack 45, tangentially to the combustion chamber and its approximately stoichiometric Several pilot and auxiliary gas burners 56 are provided which are operated by a balanced air and natural gas mixture for proper combustion.

The pilot burner 56 provides a pilot flame residue or ignition source within the combustion chamber 48 and extends the combustion chamber by at least about 760'.
C (1400°F), about 898 in favorable conditions
It helps to maintain a temperature of 9° C. (1650° F.) to ensure that the combustion products in the rich fumes discharged therein from the stack 45 are completely combusted therein.

The supply of combustion air and gas to the pilot burner 56 is as follows:
These are set by manual adjustment of valves 57 and 58 in air line 59 and gas line 60, respectively, to provide an ignition source for the rich fume wicking air mixture directed to the incinerator.

The solvent concentration in the exhaust gas stream or concentrated fume from the oven 10 is significantly lower with the method of the present invention than for conventional paint drying methods because the addition of dilution air to the open exhaust gas is not required. Because of the high temperature, the heat released by solvent vapor combustion within the incinerator 25 typically moves the fume air mixture in the combustion chamber 48 between 760° C. and 898.98° C.
14,000F to 1,650'F).

Thus, for proper operation of the paint drying system according to the invention, the incinerator 25 requires no auxiliary fuel other than a very small amount for the pilot flame from the burner 56.

The fuel requirements of oven 10 are further reduced compared to conventional methods because the inert gas heat load is much less than that required for conventional dilute air paint drying methods.

In order to use the effluent gas from the incinerator 25 as a source for a low oxygen-containing atmosphere, i.e. no more than about 5 percent oxygen content needs to be maintained in the open chamber 18 for the practice of the present invention; It is necessary that the gases emitted from these incinerators contain no more than about 5 percent oxygen.

Because the pilot burners 56 in the incinerator 25 are operated at a near stoichiometric air-to-fuel ratio, they release little oxygen from the incinerator into the exhaust gas.

However, the solvent vapor in the dense fume led from the drying opening 10 into the incinerator 25 requires oxygen for its combustion in the incinerator, and this oxygen is supplied to the suction air led into the lower chamber 47 of the incinerator. Powered by.

Is the solvent concentration in the gas mixture introduced into the incinerator combustion chamber 48 such that the heat generated by the complete, ie, stoichiometric combustion of the solvent vapor in this mixture is due to the complete combustion of the solvent vapor? At least 7 required to maintain JIJV indoors
600 to 898.9°C (14000 to 1650°
F) maintained sufficiently to rise at t.

The suction air supply to the incinerator 25 is designed such that the gas discharged from the incinerator 25 normally contains no more than about 5 percent oxygen, preferably about 2 percent. Manual valve 5 according to solvent vapor release
Set by 5.

In order to maintain the oxygen content in the flue 1 or emission gas from the incinerator 25 at a desired low set point, for example 2 percent, an electrical signal from the temperature control device can be used for this purpose.

The temperature control device includes a thermocouple 61 in the combustion chamber 48 connected by a lead 62 to a temperature measurement and recording device 63.

The signal from the temperature measurement button and recorder 63 is fed via lead 64 to a fuel regulator 65 which in turn actuates a valve 66 in the auxiliary gas supply 67 to the rich fume stack 45.

As mentioned above, the suction air supply source 54 to the incinerator 25 is
It remains constant for a given type of load within oven 10.

This constant suction air flow rate is predetermined by the design requirements for solvent vapor emissions from oven 10.

As the solvent concentration of the concentrated fumes from oven 10 decreases, the temperature of oven 10 also decreases and the evaporation of the solvent therein decreases accordingly, increasing the oxygen concentration of the incinerator flue product. .

When this occurs, a signal from the temperature regulators 61-63 causes the fuel regulator 65 to open the auxiliary gas supply valve 66, causing the incinerator 25 to receive more fuel by combustion with the excess oxygen available therein. This will cause more gaseous fuel and even more heat to be applied, reducing the oxygen content in the incineration flue product.

Since the heat release from the auxiliary fuel replaces the reduction in the amount of solvent vapor in the concentrated fume, and the oxidation size of the solvent vapor and the auxiliary fuel or the oxygen requirement for combustion are all directly proportional,
The rate of temperature rise of the incinerator combustion chamber 48 and its corresponding flue products is substantially the same.

A conventional oxygen indicator 68 with high and low limits, e.g., O to 5.0 percent oxygen content operating range, provides an electrical signal that provides an alarm when the oxygen concentration in the incinerator flue gas falls below a set oxygen concentration limit. It is used for the purpose of supplying air to the equipment, allowing the operator to check for possible problems within the equipment, such as insufficient suction air.

When the oxygen indicator 68 senses an oxygen concentration above its high limit oxygen concentration setting, all equipment automatically closes the all equipment emergency shutoff gas valve (not shown) operated by the oxygen indicator 68. It is stopped by this.

In this case, the oven, the incinerator button and the entire gas recirculation system are automatically cleaned by a suitable supply of an inert gas, such as nitrogen, as a safety measure in the event of an explosion.

However, under normal operating conditions, such as replacement of the paint coating strip 11 or its failure, supplying fuel to the auxiliary gas inlet will reduce the oxygen content in the incinerator flue gas below the maximum set limit. It would be enough to

Incineration of the concentrated fumes from the oven 10 in the incinerator 25 in the manner according to the invention as described above is inert and non-polluting and therefore cannot be released directly to the atmosphere under current pollution control regulations. The so-called clean incinerator flue causes the formation of gases such as nitrogen, carbon dioxide and water vapor that are allowed to escape.

However, in accordance with another aspect of the invention, these emitted gases 1 or by-products from the incinerator 25 are such that they have an inert and substantially oxygen-free composition, i.e., no more than about 5.0 percent; The content, which in the particular case is about 2,0 percent, is recycled at least in part back into the oven chamber 18 by means of a recirculation device comprising an exhaust flue 69 and carried therein to the oven chamber. The inert gas atmosphere and heat necessary to perform the specific solvent evaporation process, such as the solvent-based paint drying process described above, is provided.

Although the recirculated portion of the effluent gas is sufficient to supply a small portion of the total heat and total inert gas requirements of the open 10, economic considerations dictate that a sufficient amount of the effluent gas from the incinerator It is preferable to use the oven 10 to provide all of the heat and inert gas requirements of the oven 10.

The flue gases 1 or discharged gases exiting the incinerator 25 through the flue 69 are typically at a temperature of 760'C (14000F) or higher, and that temperature is sufficient for paint drying or other solvent evaporation operations to take place therein. 2322 required in the oven chamber 18 of
As long as the temperature is significantly higher than 4500 to 600" F., the discharged gas that is recycled back to the oven 10 must first pass through one or more suitable gas recirculation devices. a heat recovery device housing or heat exchanger 70, for example a water or air heater, an oven or a low pressure steam boiler, or a metal strip 1 for applying a paint coating 12;
1 is cooled at a low oven working temperature 1 by passing it through a heater for metal pretreatment solutions used for pretreatment.

The heat thus recovered in heat exchanger 70 can be advantageously used for various other auxiliary heating operations, another economic benefit of the method comprising the present invention.

The flue gas cooled in heat exchanger 70 is discharged, such as by recirculation fan 71 , to inert gas intake 44 of oven 10 , thereby supplying inert gas to oven chamber 18 .

As shown in FIG. 1, the gas intake 44 has a manifold 72.
is formed, from which inert gas from the incinerator 25 is distributed and introduced into the open chamber 18 through a series of gas ports or supply openings 73 in the side wall 26 of the oven 10.

However, the cooled flue gas from the heat exchanger 70 before being led into the open 10 has a better temperature identicality to that of the inert gas led into the oven chamber 18 with what is therein during operation of the device. It is better to first mix it with some of the inert gas already present in the oven chamber 18 in order to ensure its properties.

This mutual mixing is caused by the discharge opening γ in the open 100 side wall 26.
4, by discharging a portion of the inert gas from the oven chamber, the thus evacuated oven atmosphere is conveyed through conduit 75 to a suitable mixing device 76, where it is cooled from the heat exchanger 70. It is achieved by mixing with inert flue gas.

The resulting gas mixture is then circulated by fan 71 through manifold 72 button and gas supply opening 73 in open wall 26 and into oven chamber 18 .

The portion of the cooled inert effluent gas leaving the heat exchanger 70 that is not recycled back to the oven 10 is charged at the inlet and outlet openings 19.21 of the oven 10 to provide an aerodynamic seal to the article. It is supplied to chambers 33 and 34.

Manually set dampers 77. of the respective conduits 79, 80 supplying recirculated cooled inert gas from the heat exchanger 70 to the open 10 button and aerodynamic seal 31, respectively.
78 is from the incinerator 25 to the sealed part 31, to the residual dog air;
It is also used to properly balance the flow of discharged gases recycled to oven 10.

FIG. 3 shows a variation of the invention in which all of the gas released from the incinerator 25 is transferred to the heat requirement of the oven 18, to the residue or to the seal 3.
It is shown that the waste parts not used for 1 are passed through one or more heat exchangers 70 before being discharged to the atmosphere.

In this way, not only from the part that is not emitted,
Heat recovery is provided from all incinerator exhaust gases.

In the particular example illustrated, the heat recovered within heat exchanger 70 is
It is introduced via a conduit 81 into a metal strip pretreatment section 82 of the illustrated strip paint coating line for the purpose of heating a metal pretreatment solution used to pretreat the metal strip 11, for example for applying the paint coating 12. It is shown as a thing.

In this way the overall heat required for the paint coating button and drying process is further reduced.

Upon starting up a paint dryer or other solvent vapor release device according to the present invention, the open 10 must first be cleaned.

For this purpose, e.g. nitrogen, steam, enclosure or burner 5
An inert gas medium, such as a combustion engine from 6 and auxiliary fuel, can be used to clean the oven chamber 18.

The oxygen indicator indicates that the oxygen content of the oven atmosphere is 5.5% before the workpiece to be processed therein is introduced into the open 10. It should be used to indicate when the concentration is below the maximum permissible concentration of, for example, about 2,0 harcents, but not above 0 harcents.

The open seal 31 is actuated before the metal strip 111 or other work conveyor begins to enter the oven.

Burner 56 and auxiliary fuel 67 in incinerator 25 provide heat to bring the device to the required open and incineration temperatures and to provide an inert atmosphere to oven seal 31 .

The auxiliary fuel population 6γ is a supply tube 5 equipped with a manual valve 55.
4 is required during start-up to add a certain set amount of suction air to the incinerator 25 via the incinerator 25.

The incinerator temperature control device 61-63 has an auxiliary fuel population 61
Adjust the fuel input rate to.

Once the working conditions are set, the metal strip 111 or workpiece is moved into the open 10.

The economic advantage of the paint drying method comprising the present invention is that its fuel,
The air and other utility requirements will be readily apparent when compared to conventional solvent-based paint drying methods.

In conventional methods, the drying oven is operated in an atmosphere below the lower explosive limit of the gas mixture formed in the oven during the drying operation, instead of above the upper explosive limit for the method according to the invention.

For example, in a conventional installation used for comparison purposes, which includes a fume incinerator, a preheating recuperator and a heat transfer liquefied medium for total heat recovery, the gas consumption is approximately 410 per hour.
0 0 0 0 0 B. tu-(1033200
0 kilocalories), the thermal conductivity to the workpiece is approximately 7,000,000 B. per hour. t, u, (1,764,000 kilocalories).

For the same heat demand in the paint drying oven 10, a suitably designed paint drying apparatus according to the present invention reduces fuel consumption to 5,000,000 B.B. per hour. t, u. (1260000
kilocalories) or less, i.e. only 12 kilocalories for the same fuel requirement
Reduce to %.

The fresh air requirement of the device according to the invention is only 200
000s. c. f. h. (Standard cubic feet per hour)
The 1,500,000 s. c. f. h. This is approximately 13% of the total.

Furthermore, approximately 525,000 s, c. f,h
, the low fume amount of 1300000 s of the conventional method
．． c. allows the use of discharge fans, pipe systems and the incinerator itself with smaller dimensions compared to f, h,
This makes it even more economical in terms of reduced prices for the equipment required.

Regarding the quality of the finish paint coating, comparative testing of thermoset paint samples showed that the composition of the atmosphere within the drying oven 10 had no effect on the characteristic profile or color properties of the finish paint.

In effect, the inert atmosphere used in the paint drying open 10 according to the present invention retains the paint quality even when the paint is exposed to inert gas for long periods of time, whereas the inert atmosphere used in the drying oven of conventional paint drying equipment In a highly oxygen-containing atmosphere, paint pigments oxidize and become dark colored.

In any case, the drying of solvent-based paint coatings in an inert gas atmosphere according to the present invention actually results in better paint finish and quality.

The present invention can be implemented in the following manner.

1. In accordance with the method defined in claim 1, at least a portion of the remaining portion of the inert emissions from the incinerator that are not recycled back into the drying oven are directly disposed of as non-contaminated emissions. released into the atmosphere.

2. In the method of Claim 1 or Embodiment 1, the cooled effluent gas from the incinerator which is recycled back into the drying oven is substantially free of the coating drying operation. supply all the heat to it.

3. In the method as set forth in Claims and Embodiments, paragraph 1, paragraph 2, l parts of the heated atmosphere are continuously removed and the cooled atmosphere is removed before introducing it into the oven. mixed with the recycled portion of the recycled inert exhaust gas, thereby ensuring temperature equivalence between the recycled exhaust gas and the oven atmosphere.

4. In accordance with the method described in claim 1 and embodiments 1, 2 or 3, the inert effluent gas recycled back into the drying oven is treated in a heat recovery device. It is cooled and the heat thereby recovered is used for supplementary heating equipment.

5. In accordance with the method described in claim 1 and in any of the preceding embodiments, the inert atmosphere in the drying oven is maintained at a slight overpressure.

For the method as claimed in claim 1 and in any of the preceding embodiments, the heat generated by the pilot flame from an auxiliary burner operating in the incinerator under approximately stoichiometric combustion conditions is transferred thereto. Suction air is optionally introduced to maintain the ignition temperature for the solvent vapor in the incinerator by supplying and creating such conditions.

7. For the method as claimed in claim 1 and in any of the preceding embodiments, by adjusting the supply of fuel to the auxiliary fuel inlet to the combustion chamber of the incinerator. maintain an oxygen concentration in the exhaust gas of less than about 5 percent (optionally less than about 2 percent).

8. The apparatus according to claim 2, wherein the recirculation device includes a heat recovery device for cooling the recirculated discharged gas with the temperature drop necessary for the coating drying operation in the oven. Including 70.

The device according to claim 2 1 or embodiment 8, in which the recirculation device for the incinerator emissions 6 9 gases separates said emissions from the part that is not recycled to the oven 10. Includes an outlet for releasing a portion of the gas to the atmosphere as non-polluting emissions.

10 Claim Section 2 Button and Embodiment Section 8 or 9
The apparatus described in Section 1 further includes at least one gas-air pilot burner 56 operating with approximately stoichiometric combustion within the incinerator to maintain an ignition temperature within the combustion chamber portion of the incinerator.

11. The apparatus according to claim 2 and embodiments 8, 9 or 10 further comprises an auxiliary fuel supply 67 to the incinerator for introducing additional fuel thereto.

12 In the apparatus described in Embodiment 11, the incinerator 25 includes a thermocouple 61, and the auxiliary fuel population 6
further comprising a temperature regulating device for regulating the amount of additional fuel introduced into the incinerator by 7, thereby maintaining a temperature within the combustion chamber of the incinerator at the temperature of at least about 760°C (1400°F). .

13. In the apparatus according to claim 2 and embodiment 12, the walls of the oven chamber are used to provide an inert gas screen across the inlet and outlet openings of the articles to seal them from the outside atmosphere. It further includes aerodynamic sealing devices 33,34 at the inlet and outlet openings.

14 Embodiment In accordance with the apparatus described in paragraph 13, the heat recovery device 70 supplies thereto a portion of the cooled effluent gas from the heat recovery device, thereby providing the required inert gas. It is connected to an aerodynamic sealing device 33,34.

15 In the apparatus described in Claim 2 and Embodiment 814, the incinerator 25 is provided with suction air thereto to support the combustion of the solvent vapor led from the oven chamber to the combustion chamber. An air supply 53 to its combustion chamber 47 for supplying and a suction air supply pipe 54 connected to said air inlet to direct the flow of air introduced as necessary for approximately stoichiometric combustion of said solvent vapor. and a valve device V in said suction air supply pipe which is actuated to adjust the amount of suction air.

[Brief explanation of the drawing]

FIG. 1 is a partial vertical sectional view of a paint drying device according to the present invention, FIG. 2 is a flowchart of the basic device shown in FIG. 1, FIG. 3 is a flowchart of a modified paint drying device according to the present invention, and FIG.
Figure 2 is an enlarged longitudinal cross-sectional view of the aerodynamic seal placed at the inlet button and outlet opening of the article in the drying oven shown in Figure 1; In the drawing, 10 is "open", 11 is "metal strip material", 12 is "coating", 13 is "coil",
14 is a "feeding roll", 16 is a "coating tank", 1
7 is "squeegee roll" 18 is "drying room" 19 is "
20 respectively indicate the "inlet opening" and the "oven end wall".

Claims (1)

Claims: 1. A method of drying a solvent-based coating on an article comprising heating the coated article in a heated inert gas atmosphere in a drying oven to evaporate the solvent from the coating and dry it. button to maintain the mixture of inert gas and solvent vapor formed in the oven during the coating drying operation above the explosion limit of the mixture at all times during the coating drying operation, and to open the inert gas-solvent vapor mixture. (e.g. about 76
0° C.) and the inert gas-solvent vapor mixture discharged from the oven in an incinerator (e.g. at a temperature of at least 7° C.).
incineration under approximately stoichiometric conditions (at a temperature of 60° C.) to produce a high temperature, pollution-free inert gas containing low oxygen from the incinerator; said inert emissions from the incinerator; cooling at least a portion of the gas to the temperature required for the coating drying operation in the oven (e.g., below 315.6°C); recycling the cooled inert discharge gas from the button and incinerator into the drying oven; and subjecting the inert gas therein and at least a portion of the heat therein together to a coating drying operation. 2. In an apparatus for drying a solvent-based coating on an article, the apparatus is substantially gas-tight during the coating drying operation and is substantially filled with an inert gas atmosphere at the temperature required for the coating drying operation, and a drying oven 10 having a drying chamber for maintaining the concentrated fume mixture of inert gas-solvent vapor contained in the oven chamber above its explosive limit; and an oven exhaust for discharging the concentrated fume mixture from the open chamber. devices 38, 39;
a rich fume incinerator 25 into which the rich fume mixture is introduced by the oven ejector, the incinerator incinerating the rich fume mixture introduced therein under approximately stoichiometric conditions; , at least about 7
a button on said incinerator for producing a low oxygen-containing inert effluent gas substantially free of air contaminants at a high temperature of 60'C, and further for discharging said effluent gas from said incinerator. An exhaust flue connects the exhaust flue device of the incinerator with the oven chamber to direct at least a portion of the emitted gases from the incinerator to the hot gas atmosphere of the oven chamber and therein. and a recirculation device 69,71 for recycling back into said open chamber to provide at least a portion of the total heat required for the coating drying operation.