HK1037397B - Web dryer with fully intergrated regenerative heat source and method for drying a running web - Google Patents

Description

Foil dryer with fully integrated regenerative heat source and method for drying foil

Background

In view of the possible contamination by impurities and by-products, it is important to control and/or remove these impurities and by-products in various production processes. One conventional method of removing or at least reducing the level of contaminants is thermal oxidation. When impure air containing sufficient oxygen is heated to a sufficiently high temperature and for a sufficiently long time, thermal oxidation will occur to convert the undesirable compounds to harmless gases such as carbon dioxide and water vapor.

The operation of dryers, including air-floating dryers, requires a heat source for heating air to contactlessly support and dry moving foils, such as paper, film or other sheet material, by means of heated air issuing from a set of generally oppositely disposed air nozzles. Thus, the drying process can cause Volatile Organic Compounds (VOCs) to volatilize from the moving foil, particularly when drying ink or the like that is attached to the foil. Legislation dictates that such volatile organic compounds must be treated to convert them into harmless gases before they can be discharged into the environment.

The prior art air flotation dryers are combined with various separate incinerators or afterburners to recover the oxidized hot gases from the exhaust of the thermal oxidizer and return them to the dryer. In fact, this system is not a fully integrated system because the oxidizer and dryer are separate units and additional heating elements need to be provided in the dryer housing. Other prior art systems have integrated thermal oxidizers in the dryer housing and have used the gas volatilized from the foil as fuel. However, such so-called direct-fired systems do not utilize any form of heat recovery device or medium, and therefore require more auxiliary fuel, especially when the concentration of volatile gases is low. Another prior art device is a true combination of an air-float dryer and a so-called recuperative oxidizer. One disadvantage of these systems is that the type of heat exchanger used limits the heat recovery efficiency, thus limiting the possibility of extremely low auxiliary fuel consumption, and often preventing autothermal operation. This limitation in efficiency is due to the high efficiency heat exchanger preheating the inlet air to a sufficiently high temperature to accelerate oxidation of the heat exchange tubes, resulting in tube breakage, leakage, reduced efficiency and volatile decomposition. In general, recuperative devices can reduce the reliability of system components, such as heat exchangers and burners, because the metal is always subjected to high temperatures during operation.

Another fully combined system utilizes a catalytic burner to convert the exhaust gas and possibly provide all of the heat required for the drying process. Oxidation processes can be carried out at low temperatures due to the presence of the catalyst, and therefore this type of system can use highly efficient heat exchangers. However, even a high-efficiency heat exchanger cannot preheat the introduced air to a harmless temperature. However, certain components in the exhaust gas can make the catalytic oxidizer very sensitive to catalyst poisoning, thereby failing to convert these exhaust gases into harmless components. In addition, catalytic systems typically use metal-type heat exchangers to recover the primary heat, which have a limited useful life due to the high temperature conditions at which the heat exchangers operate.

For example, U.S. patent 5,207,008 discloses an air-float dryer with an internal post combustor. The solvent laden air produced by the drying process is passed to a burner where the volatile organic compounds are oxidized. At least a portion of the hot air is then returned to the air nozzle for drying the suspended foil.

Us patent 5,210,961 discloses a foil dryer comprising a burner and a recuperative heat exchanger.

European patent EP- ｃA-0326228 discloses ｃA small heater for ｃA dryer. The heater includes a burner and a combustion chamber having a U-shaped channel therein. And the combustion chamber is connected to a recuperative heat exchanger.

Since the generation of the heat required for oxidation requires a high fuel cost, it is desirable to recover as much heat as possible. For this purpose, us patent 3,870,474 discloses a recuperator type oxidizer comprising three regenerators, two of which are in operation at any time, and the third regenerator receives a small amount of purified air, expels the untreated or contaminated air, and discharges them to a combustion chamber where these contaminants are oxidized. In order to preheat the contaminated air during its passage through the regenerator before it enters the combustion chamber, the flow of the contaminated air through the regenerator is at the end of the first cycle exactly opposite to the flow in which the previously cleaned air was discharged. Heat is recovered in this manner.

Us patent 3,895,918 discloses a rotary regenerative system in which a plurality of discrete non-parallel heat exchange beds are provided towards the periphery of a central high temperature combustion chamber. Each heat exchange bed is packed with heat exchange ceramic members. The exhaust gas from the industrial process is introduced from the inlet and is distributed to selected heat exchange zones according to the opening or closing of the inlet valve of a given zone.

In the air-floating type dryer, the regenerative heat exchange is adopted, so that the heat exchange with high efficiency is realized.

Summary of The Invention

The invention provides a combined foil dryer and regenerative heat exchanger, and a method for drying foil by using the dryer. The apparatus and method of the present invention uses a fully integrated regenerative burner as an integral part of the dryer, heats the air, and converts the volatile organic compounds into harmless gases. In one embodiment, the dryer is an air-float dryer equipped with air-permeable rollers that contactlessly support the running foil with hot air from the oxidizer.

Brief Description of Drawings

FIG. 1 is a schematic diagram of one embodiment of the apparatus and method of the present invention.

FIG. 2 is a perspective view of a monomer bed of the present invention.

Fig. 3 is a schematic diagram of a second embodiment of the present invention.

Fig. 4 is a schematic view of a third embodiment of the present invention.

Fig. 5 is a schematic view of a fourth embodiment of the present invention.

Fig. 6 is a schematic view of a fifth embodiment of the present invention.

FIG. 7 is a schematic diagram of a single bed regenerative oxidizer integrated with a dryer.

Fig. 8 is a schematic view of the single bed regenerative oxidizer of fig. 7.

Detailed Description

An important requirement for achieving a full combination of dryer and regenerative oxidizer is that all of the thermal energy required for the drying process be taken from the conversion of the evolved volatile organic compounds with little or no fuel combustion. According to the invention, an auto-heating or self-sustaining mode of operation can be achieved. Many volatile organic compounds are exothermic in chemical reactions and therefore can be considered as a fuel for a combined system to replace supplemental fuels such as natural gas. The resulting device is heat recovery efficient enough to provide self-heating conditions in a controlled and sustainable manner with highly reliable components, or at least with minimal supply of supplemental fuel, and nearly complete conversion of undesirable volatile exhaust gases to harmless components.

Referring now to fig. 1, there is shown a schematic diagram of a single zone air flotation dryer 10 in combination with a regenerative oxidizer 20. The air-floating dryer 10 comprises a foil inlet slot 11 and a foil outlet slot 12 spaced from the foil inlet slot 11 through which the foil 13 moves. In the dryer 10, the foil in operation is floatingly supported by a plurality of air-permeable rollers 14. Although it is preferred that the air-permeable rollers 14 are arranged in a staggered relationship with respect to each other as shown, one of ordinary skill in the art will recognize that other arrangements may be used. In order to achieve good floating support and high efficiency of heat transfer, it is preferred to use HI-FLOAT commercially available from MEGTEC Systems^An air-permeable roller that floatingly supports the foil 13 along a sinusoidal path through the dryer 10. The drying process can be accelerated by providing a far infrared heating element in the dryer. The upper and lower sets of ventilation rollers are connected to respective manifolds 16, 16', each of which receives heated air via an inlet air blower 17 and directs the heated air to a respective ventilation roller 14. A make-up air buffer plate 25 is connected to the blower 17 to provide make-up air to the system when required. It should be understood by one of ordinary skill in the art that although an air-float dryer is described herein, other dryers that do not require a non-contact support are also within the scope of the present invention.

Preferably, the regenerative oxidizer 20 in combination with the dryer 10 is a dual column oxidizer, although a single column with burners in the inlet plenum (see fig. 7 and 8) or a three or more column or rotary oxidizer may be employed. With the recuperator oxidation technique, the heat transfer zone in each column must be periodically reheated to replenish the heat transfer medium (typically ceramic or saddle-packed bed) in the energy-depleted zone. This can be accomplished by periodically alternating the heat transfer zone through which the cold and hot fluids flow. Specifically, as a hot fluid flows through a heat transfer medium, heat is transferred from the fluid to the heat transfer medium, thereby cooling the fluid and heating the heat transfer medium. Conversely, when a cold fluid flows through a heat transfer medium, heat is transferred from the heat transfer medium to the fluid, whereby the heat transfer medium becomes cold and the fluid becomes hot. Thus, the heat transfer medium receives heat from the hot fluid and stores the heat in relation to a thermal store, and then releases the heat to the cold fluid.

The heat transfer medium can be reheated by alternating heat transfer zones with the aid of suitable changeover valves. In one embodiment of the invention, each heat transfer zone has a switching valve, preferably a pneumatic butterfly valve, with a switching frequency or period that is a function of the volumetric flow rate, and decreasing the flow rate extends the switching period. When the changeover valve regenerates the heat transfer medium, the regeneration itself causes a short period of time for the untreated fluid to be discharged into the atmosphere, reducing the decomposition efficiency of Volatile Organic Compounds (VOC), which in the case of high boiling point VOC, may cause turbidity unless a method of trapping changeover air is employed. It is therefore preferable to increase the efficiency of the device with a trap chamber 90.

Fig. 1 shows a dual column regenerative oxidizer 10. The gas to be treated is introduced from the dryer 10 into the oxidizer 20 by means of an inlet blower 30 and appropriate piping and through an appropriate switching valve or valve set 21 and then into (or out of) one of the recuperative heat exchange columns 15, 15' filled with a heat exchange medium. A combustion zone 18 with combustion supporting heating elements such as one or more gas burners 22 is associated with each of the recuperative heat exchange columns 15, 15 and with the dryer inlet blower 17, the burners 22 in turn having combustion supporting blowers 23 and gas line valves. In theory, it is only at start-up that the combustion zone heating elements need to be operated to bring the combustion zone 18 and the heat exchange columns 15, 15' to operating temperatures. Once the operating temperature is reached, the heating components are preferably turned off (or placed in a "monitoring mode") and self-heating is maintained. Typically, suitable operating temperatures for the combustion zone 18 are in the range of 1400F to 1800F. It will be appreciated by those skilled in the art that while the term "combustion zone" generally refers to the element 18 in the industry, most or all of the combustion occurs in the heat exchange bed, and in fact, little or no combustion occurs in the combustion zone 18. Accordingly, the term in this specification and claims should not be construed to refer to the region where combustion occurs.

Preferably, in order to save space, the heat exchange columns 15, 15' are arranged horizontally (i.e. the gas flows along a horizontal path) in the device. In order to reduce the accumulation of undesirable process gases and to distribute the process gas uniformly over the heat exchange medium, it is preferred to combine a randomly packed medium, in which there are interstices in which the gas flows through the medium particles, with a structured medium. In a preferred embodiment, the voids in the random packing media are larger than the gaps formed between the media particles. If the voids are too small, the gas tends to flow in the interstices without passing through the voids in the particles. The dielectric particles are made of a single material and are characterized by a protrusion or fin extending from the center of the particle. The spaces between the protrusions provide a desirable space for gas to flow through, thereby improving the pressure drop characteristics of the packed heat exchange bed. The randomly packed media may also have a catalyst applied to its surface.

It will be appreciated by those skilled in the art that other suitable shaped media may be used for the random packing media of the present invention, including saddle-shaped media, preferably 1/2 ", and the like.

The second part of the heat exchange medium adopts a monomer structure combined with the random filling medium. Preferably the monolithic structure is about 50 meshes/in²And has laminar flow and pressure drop. With a set of channels or passageways therebetween that allow gas to flow through the structure along predetermined paths. Suitable monolithic structures are commercially available from Frauenthal porcelain products manufacturing company, 40 cells of mullite ceramic honeycomb per element (150 mm outer diameter by 150 mm). In the inventionIn a preferred embodiment, the dimensions of the unitary structure are preferably about 5.91 "by 12.00". These blocks contain a plurality of parallel square channels (40-50 channels per square inch), with the individual channels having cross-sectional dimensions of about 3mm x 3mm and a surrounding wall thickness of about 0.7 mm. From this, it was confirmed that the cross section of the voids was about 60 to 70%, and the specific surface area was about 850-²/m³. Another preferred size block is 5.91 "by 6". In certain cases, a catalyst may also be applied to the surface of the monomer structure.

The random packing medium with high flow resistance is preferably placed at the inlet of the industrial gas to be treated of the heat exchange column, effectively making the gas uniformly distributed over the entire cross section of the column. The monomer medium with the lower flow resistance is preferably placed at the outlet of the random packing medium, where the gas has been distributed. Oxidation occurs inside the regenerative bed, with the fluid temperature at the outlet section of the bed being higher than the fluid temperature at the inlet section. Higher temperatures mean that the pressure drop increases, both by increasing the viscosity of the fluid and by increasing the actual flow rate of the fluid. Therefore, the use of a monomer structure medium with a low intrinsic pressure drop is beneficial for this part of the column.

It will be appreciated by those skilled in the art that the multi-layer bed of heat exchange media may be comprised of more than two different layers of media. The random packing media at the column inlet can consist of saddle media of different sizes, such as 1/2 "for the first layer and 1" for the second layer. And the monomer layer is disposed at the exit of the column. Similarly, for example, the monomer layer may be a first layer which is a monomer layer having a channel cross-section of 3mm by 3mm, and a second layer which is a monomer layer having a channel cross-section of 5mm by 5 mm. In systems that employ only one heat exchange column, the multi-layer media bed may have a first layer of random packing media, a second layer of monomer media, and a third layer of random packing media. It will be appreciated by those skilled in the art that a particular multi-layer bed can be designed based on the desired pressure drop, thermal efficiency and allowable costs.

Most preferably 100% of the monomer structure, as shown in FIG. 2. In the transverse arrangement shown, a plurality of blocks are stacked together to establish a desired flow cross-section and a desired flow length. To build a regenerator with a retention chamber, the dryer is compatible with existing production lines, such as printing lines in the printing field, and therefore requires a small heat exchange bed, preferably a monolith bed. Another design of the monomer bed is to apply a catalyst on the monomer surface. In a 100% cell structure, it is critical for heat exchange performance that the air flow into the cell be uniformly distributed. In fig. 1, a flow divider or distributor 95, such as a perforated plate, is provided at the inlet and outlet of each column to evenly distribute the air over the heat exchange bed. Such a distributor may be optional when a randomly packed media is used, as the randomly packed media can help to evenly distribute the air.

The gas is directed to the atmosphere with a suitable valve 40 or, in order to optimize the decomposition efficiency, blown into an internal device (or lock 90) for purification.

Suitable pressure and/or temperature attenuators 92 are provided as shown to buffer the effects of the switching valves during the recuperative heat exchanger cycle. Switching valves can produce pressure pulses and/or temperature spikes that are detrimental to the drying process. The pressure pulse may enter the dryer through a hot air feed pipe and break the slight negative pressure (relative to atmospheric pressure) in the dryer. Allowing solvent laden air to escape the dryer foil gap. It is difficult to control the temperature of the drying air to a desired set temperature by the temperature fluctuation occurring during the switching. The attenuator 92 reduces the pressure pulses by providing a baffle on the inlet duct of the dryer. By providing a large surface area and high heat capacity component in the flow line of the dryer, the degree of temperature fluctuations can be reduced.

Technically, the oxidizer is combined with a dryer, i.e., the apparatus is very compact and the dryer relies solely on the oxidizer for heating and removing volatile organic compounds. This can be accomplished by enclosing the oxidizer and dryer in a single housing, or by attaching the oxidizer to the dryer, or by placing the oxidizer in close proximity to the dryer. The oxidizer may also be located in thermal isolation from the dryer. Preferably, there is a common wall between the heat exchange bed (or beds) of the dryer and the oxidizer.

In one embodiment of the invention, cool air is withdrawn from the oxidizer and added to the dryer as make-up air. This allows the oxidizer to be cooled while preheating make-up air, improving the efficiency of the system.

Fig. 3 shows an air-float dryer in combination with the regenerative oxidizer shown in fig. 1, except that the dryer consists of two drying zones with hot air return. Each drying zone has a return means 17, 17 ', such as a blower, which supplies hot drying air to the air-permeable rollers by means of suitable lines connected to the air collection ducts 16, 16'. Most of the hot air delivered to the first drying zone comes from the regenerative oxidizer and is regulated by hot air valve 41. The hot air supplied to the second drying zone comes from the return device.

FIG. 4 shows an air flotation dryer combined with the regenerative oxidizer shown in FIG. 1, except that the dryer consists of multiple drying zones (three drying zones are shown) with hot air return features. Each drying zone has a return means 17, 17 ', such as a blower, which supplies hot drying air to the air-permeable rollers 14 by means of suitable lines connected to the air-collecting ducts 16, 16'. However, the hot air received by the dryer sections except the last dryer section is mostly from the regenerative oxidizer and is regulated by hot valve 41. While the hot air supplied to the last drying zone comes from the return device.

FIG. 5 shows an air flotation dryer in combination with the regenerative oxidizer shown in FIG. 1, except that the dryer consists of multiple drying zones (three drying zones are shown) with hot air return, the last drying zone being a conditioning zone. Each drying zone has a return means 17, 17 ', such as a blower, which supplies hot drying air to the air-permeable rollers 14 by means of suitable lines connected to the air-collecting ducts 16, 16'. The combined regulatory regions are described in U.S. patent 5,579,590, the disclosure of which is incorporated herein by reference. The conditioning zone contains air that is substantially free of contaminants and at a temperature low enough to absorb heat from the foil, which effectively reduces the rate of solvent evaporation and slows the condensation of solvent. The device is also provided with pressure control means 45 to prevent volatile solvent from escaping from the dryer housing, and to regulate the supply of ambient air as required by means of regulating means 46.

The embodiment shown in fig. 6 is similar to that of fig. 5, except that the oxidizer to dryer lock (and corresponding valve) purge is eliminated. As shown, a catalytic stack purifier 50 may be used to further decompose volatile organic compounds that are emitted to the atmosphere in order to increase the overall efficiency of the device.

Referring now to fig. 7, fig. 7 shows a single bed oxidizer in combination with a two-zone air-float dryer. Exhaust blower 30 draws solvent laden air from the dryer housing and passes it to the regenerative oxidizer for treatment. A changeover valve (or valve block) 21 directs air to the inlet of the heat exchange media bed 15. (the inlet to the media bed 15 is switched from one side of the bed to the other side of the bed according to a predetermined switching time). The heat exchange medium bed 15 is formed of a single pile of a material that does not occlude the combustion chamber. The combustion zone is located within the bed at a temperature sufficient to convert the various volatile organic compounds into the end products, carbon dioxide and water vapor. The location and size of the combustion zone may vary within the media bed 15 depending on the particular solvent/fuel ratio, air flow rate, and transition time. The heat exchange medium may be composed entirely of any kind of random packing material, or a combination of structural and random packing materials. A preferred embodiment is a media combined in such a way that the structured media is arranged on the so-called cold side of the bed, while the random packing media is arranged in the central area of the bed. Preferably the single bed heat exchanger is stacked in a planar fashion perpendicular to the direction of air flow, first with a layer of structured media, then with a layer of randomly packed media, followed by a second layer of structured media of the same thickness as the first layer. The bed can be oriented perpendicular or parallel to the flow direction, but the flow direction must be perpendicular to the plane of the various media sections.

For initial heating of the exchange bed, a suitable heat source, such as a gas fuel tube or preferably an electric heating element, is arranged centrally, i.e. in the area of the random packing medium. When the solvent and/or fuel is in the bed, the electric heating element is turned off. When an insufficient amount of solvent is available to maintain the desired combustion temperature, it is preferred to pass the combustible fuel, such as natural gas, into the gas to be treated before it enters the heat exchange bed in order to maintain the temperature of the bed.

In order to mix with the air directed to the foil 13 and heat the delivered air, a portion of the combustion gases is withdrawn from the center of the heat exchange bed. Hot gas is extracted from the center of the random packing material zone by means of hot air collection plenum 75 disposed longitudinally along the center of the random packing material zone. The function of the ventilation means is to uniformly draw gas from the cross-section of the exchange media bed to prevent temperature variations within the bed due to non-uniform flow.

The final temperature of the air blown onto the foil 13 depends on the amount of hot air mixed with the return air before the supply blower 17. The amount of hot gas is regulated by a hot air supply valve 4' which is connected to a hot air collection plenum 75 mounted on the heat exchange bed.

The recuperative heat source described above can provide sufficient heat to the dryer in one or more (two as shown) distinct zones divided by respective air supply blowers. Heat from the oxidizer may be directed to one or more drying zones if desired and under process control. The dryer configuration may incorporate one or more cooling zones operating in conjunction with and controlled by the heating zone. The atmosphere in the dryer is effectively controlled by means of a supplementary air buffer plate 25.

Fig. 8 illustrates a preferred embodiment of a heat exchange bed comprised of a single heat exchange material that does not have significant occlusion in the combustion chamber. The combustion zone is disposed within the bed and is distributed about the center of the bed in the direction of flow. The size and location of the combustion zone depends on whether there is a sufficiently large temperature gradient in the bed to cause combustion and volatile gas conversion. An inlet/outlet air distribution plenum 76 is provided to provide a uniform velocity distribution of air over the cold side of the heat exchange bed 15. A perforated plate 77 is placed in front of the cold side in the direction of flow of the air to further homogenize the flow of the air before it enters the heat exchange bed. It is preferable that the heat exchange bed is composed of a structured medium 15A excellent in pressure loss property and a random packing medium 15B which is easy to embed a heat coil therein and can extract a hot gas to heat the supply air of the drying zone. The heating means 60 is preferably an electrical resistance heating element and is controlled by a power regulator 61 to heat the heat exchange bed during start-up. The amount of fuel injected into the exhaust gas is regulated by a gaseous fuel injection valve 9 to maintain a minimum combustion atmosphere within the combustion zone to convert the solvent and fuel to carbon dioxide and water vapor.

To improve the efficiency of decomposition of the volatile organic compounds and eliminate the hazy phenomenon caused by the heat exchange of the substrate reflux, in either embodiment as shown, untreated fluid may be directed from the oxidizer to a "collection vessel" or volatile organic compound collection tank 90. The purpose of the collection tank 90 is to contain the remainder of the untreated fluid, which is generated during the very long substrate reflux heat exchange process, so that most of it can be slowly (that is, at a very low flow rate) refluxed back to the oxidizer inlet for treatment, either sent to the combustion blower 23 as combustion air, or slowly released to the atmosphere through the discharge means. The untreated fluid remaining in the holding tank 90 must be completely drained within a specified time period between matrix reflux heat exchange cycles, as the process is repeated for all subsequent matrix reflux heat exchanges.

In addition to the capacity of the holding tank, the design of the internal components of the holding tank 90 is critical to the ability of the holding tank to contain and return untreated fluid to the oxidizer inlet for treatment during the specified duration of the matrix reflux heat exchange cycle. Any untreated fluid that fails to return during this period will be vented to atmosphere through the air bleed means, which reduces the efficiency of the collection means and reduces the efficiency of the overall oxidizer unit.

For some operating conditions, the amount of volatile solvent in the dryer effluent stream may be less than that required for autothermal operation. To avoid using a burner to supplement the energy, supplemental fuel may be added to the system, such as in the exhaust stream, to provide the required energy. The preferred fuel is natural gas or other conventional gaseous or liquid fuel. The efficiency of the oxidizer is reduced due to the combustion air required for the burner operation and the formation of nitrogen oxides NO_xTherefore, it is preferable to cancel the combustion operation. The gaseous fuel may be introduced by sensing the temperature at a location, such as a heat exchange column. For example, a temperature sensor may be provided in each heat exchange bed, with the location of the sensor in each bed being approximately 18 inches below the top of the heat exchange medium. Once the apparatus has started to operate normally, combustible gas fuel is added to the process gas via the T-junction before the process gas enters the heat exchange column, based on the average of the temperatures sensed by the sensors in each heat exchange bed. If the average of the sensed temperatures is below a predetermined value, additional gaseous fuel may be added to the exhaust stream entering the oxidizer. Similarly, if the average of the detected temperatures is above a predetermined value, the addition of additional gaseous fuel is stopped.

In addition, the temperature of the combustion zone can be indirectly controlled by measuring and controlling the energy of the exhaust air entering the oxidizer. The total solvent and fuel content of the exhaust air was measured at a suitable point downstream of the point of addition of the supplemental fuel using a suitable Low Explosive Limit (LEL) sensor commercially available from Control Instruments Corporation. The measurement is then used to adjust the fuel injection rate by suitable control means to maintain the total fuel content at a predetermined constant concentration, typically in the range of 5-35% of the LEL, preferably in the range of 10-20% of the LEL. If the LEL measured by the sensor is lower than the desired value, the control valve 9 is opened to increase the amount of the supplementary fuel to be injected. If the measured LEL value is higher than the desired value, the flow valve 9 is closed and the injection amount of the supplementary fuel is reduced. When the solvent content from the drying process is higher than the desired LEL even without the injection of fuel, increasing the exhaust flow from the drying process, such as by adjusting the flow of exhaust blower 30, can reduce the LEL. It is well known to those skilled in the art to regulate the exhaust gas flow, preferably by varying the speed of the exhaust blower 30, or by flow regulating dashboards.

If the concentration of combustible components in the gas to be treated is too high, excessive temperatures will occur, causing damage to the apparatus. To avoid excessive temperatures in the high temperature incinerator or combustion zone, the temperature is sensed by suitable thermocouples located in the combustion zone and/or one or more heat exchange columns, which columns are bypassed by the gas that normally passes through the cooled heat exchange column when a predetermined high temperature is reached. When the temperature sensor is placed in the heat exchange column, the specific location of the temperature sensor is not critical; they may be positioned, for example, 6 inches, 12 inches, and 18 inches from the top of the media. Preferably, the sensor is placed approximately 12 to 18 inches from the top of the media. Each sensor is electrically connected to the adjustment member. A thermal bypass/buffer plate receives a regulation signal from a regulation component that regulates the buffer plate to maintain the temperature sensed by the sensor at a predetermined set point. It will be appreciated by those skilled in the art that the actual set point will depend in part on the actual depth of the temperature sensor in the coarse ceramic tube, and the set temperature of the combustion chamber. Suitable set temperatures for the combustion chamber are in the range of about 1600F to 1650F. The bypass gas is vented to the atmosphere, mixed with other gases cooled as a result of passing through a cooling heat exchange column in general, or used for other purposes.

Claims (18)

1. A foil dryer with an integrated regenerative heat source, comprising:

a foil inlet and a foil outlet spaced from the foil inlet;

a plurality of nozzles for drying the foil;

a recuperative heat source comprising at least one heat exchange column, said at least one heat exchange column having a gas inlet and a gas outlet, said at least one heat exchange column being coupled to the combustion zone and having a heat exchange material;

a valve assembly for alternately directing gas exiting said dryer to the inlet of at least one heat exchange column; and

a portion of the gas is directed to a component of the one or more nozzles associated with the combustion zone.

2. The dryer of claim 1 wherein there are at least two heat exchange columns.

3. Dryer according to claim 1, characterized in that at least some of the nozzles of the plurality of nozzles are floating nozzles for floatingly supporting the foil in the housing.

4. The dryer of claim 1, 2 or 3 wherein said heat exchange material is a combination of random packing media and structured media.

5. A dryer according to claim 1, 2 or 3 wherein said heat exchange material is a monolithic material.

6. A dryer according to claim 2 or claim 3 further comprising a trap chamber having an inlet connected to the valve means.

7. The dryer of claim 1, 2 or 3 further comprising means for introducing a combustible fuel into said at least one heat exchange column.

8. The dryer of claim 1, 2 or 3 wherein said heat exchange material comprises a catalyst.

9. The dryer of claim 1, 2 or 3 further comprising an attenuating member associated with said combustion zone.

10. The dryer of claim 9 wherein said attenuating element reduces pressure.

11. The dryer of claim 9 wherein said attenuating element reduces temperature.

12. The dryer according to claim 1 further comprising a temperature sensing element in said recuperative heat source and a bypass element for withdrawing a portion of the gas from said recuperative heat source when said temperature sensing element senses a predetermined temperature.

13. The dryer of claim 1 further comprising a sensor for detecting the concentration of volatile organic solvents in the gas introduced into said inlet.

14. The dryer of claim 7 further comprising a sensor for detecting the concentration of volatile organic solvents in the gas introduced into said inlet, and wherein the amount of combustible fuel introduced is responsive to the detected concentration.

15. A method of drying a running foil material, comprising:

transferring said foil material to a dryer having a dryer atmosphere;

blowing the heated gas onto the foil with a plurality of nozzles;

withdrawing a portion of said dryer atmosphere and introducing into a combined recuperative heat source comprising at least one heat exchange column coupled to a combustion zone and comprising a heat exchange material to heat said portion of the dryer atmosphere;

combusting volatile contaminants contained in the dryer atmosphere in the recuperative heat source; and

a portion of the combustion gases from the recuperative heat source is directed into the one or more nozzles.

16. The method of claim 15, further comprising detecting a concentration of volatile contaminants in the dryer atmosphere.

17. The method of claim 15 or 16, further comprising directing combustible fuel into the at least one heat exchange column.

18. The method of claim 17 wherein the amount of combustible gas fuel added is responsive to the detected concentration of volatile contaminants.