EP0314691B1 - Process and device for drying ceramic hollow bodies - Google Patents

Abstract

A process and a device for drying ceramic hollow bodies (1). The drying energy is supplied by a radiant heating device (21). During the drying process, an air current (19) conditioned according to temperature and humidity is directed mainly through the inner side of the hollow bodies (1). The radiant heat supplied is increased in the direction of the air current (19) so that the drying air remains constantly below the condensation point. Humidity and temperature sensors (8) are provided for the purpose of regulation.

Description

The invention relates to a method for drying ceramic hollow bodies and a drying device therefor with the features in the preambles of the main method and device claim.

Such a drying device is known from the closest US-A-4,439,929. There, a radiant heating unit is combined with a hot air heating unit in one station. The hot air blower drying works at high temperatures between 80 and 150 degrees Celsius and wind speeds between 0.3 and 2.0 m / sec. The radiant heating unit is designed as a high-frequency dryer, with the aim of preventing wet fields from remaining in the molding which cause problems during the subsequent firing. To avoid this, the moldings stand on perforated metal plates. The hot drying air is blown into the molding through the perforations. In addition, the hot air is also blown into the drying chamber from the outside and thereby sweeps over the moldings on the outside.

The prior art technology has some disadvantages for drying hollow ceramic bodies, in particular honeycomb bodies or ceramic catalysts with a large number of fine through-holes. Certain types of ceramic catalysts, depending on the material, only tolerate ceramic catalysts, depending on the material, only relatively low drying temperatures. In addition, a strong release of moisture on the outside of the hollow body is unfavorable, since this can lead to an undesirable and uncontrollable increase in temperature inside the hollow body and to stress cracks. The drying behavior inside the hollow body is also problematic, since if the critical temperature is exceeded and the drying process is too slow, there is a risk of electrical discharges and the destruction of the hollow body.

FR-A 965 166 shows an infrared heater for soft bodies that are sensitive to radiation. In order to avoid deformation of the material here, the distance of the infrared lamps from the dry goods can be varied over the transport length. This device cannot be used for drying ceramic hollow bodies.

From EP-A 145 822 and DE-A-31 19 979 it is known to dry solid ceramic moldings under the action of microwave or high-frequency heating energy and an air flow. The moisture to be expelled migrates from the molded core to the outside and is released into the outside air. This drying process is not suitable for hollow ceramic bodies, in particular honeycomb bodies or ceramic catalysts.

From the documents laid out in DE-C - 17308 it is also known to dry large-volume stoneware pipes by means of hot air passed through them on the inside. This is a convection heater which cannot be used for the ceramic highly sensitive catalysts in question or the like of other honeycomb bodies. The dry hot air would dry out the hollow body too quickly on the inlet side and lead to stress cracks.

Starting from US Pat. No. 4,439,929, it is therefore the object of the present invention to provide a possibility for the quick, safe and controllable drying of hollow ceramic bodies.

The invention solves this problem with the features in the characterizing part of the main method and device claim.

The drying energy is primarily applied by radiant heating, preferably with microwave or high-frequency generators. In contrast, ventilation primarily serves to remove the expelled moisture. The air is conditioned to such an extent that it can absorb the expelled moisture without excessively drying out the hollow body on the inlet side.

With the heating power increasing in the direction of flow, the air flow is continuously heated on its way through the hollow body, as a result of which the relative air humidity drops and the air can therefore still absorb moisture at the end of the body. In this way, cooling of the air below the condensation point is reliably counteracted. On the other hand, this also allows an inflow onto the hollow body on the inlet side with a relatively high and therefore material-friendly air humidity.

The air flow directed specifically through the interior of the hollow body causes not only a rapid removal of the expelled moisture, but also cooling of the ceramic hollow body and a rapid reduction of steam tensions with rapid drying. This is particularly advantageous for ceramic catalysts which have a large number of fine, parallel through-channels or lamellae through which the air flow flows axially.

It is particularly advantageous if the air flow is predominantly guided through the interior of the hollow body. The moisture is transported away, especially in the interior, and the ceramic hollow body dries evenly over the entire cross-section. This results in stress-free drying with even and controllable shrinkage of the material to be dried. The degree of distribution between the inner and outer flow depends on the shape and the material of the ceramic body. In some cases, a pure internal flow is recommended.

Overall, the invention provides the possibility of very rapid drying, which nevertheless allows controlled, uniform shrinkage and thus avoids stress cracks or warpage. The drying times are there very low, for example in the range of an hour or less.

The method according to the invention and the associated drying device can be operated in a stationary or non-stationary manner. For this purpose, various embodiments are specified in the subclaims, which also differ according to hollow bodies transported in the longitudinal or transverse direction. In the case of non-stationary operation, the hollow bodies are preferably transported through a plurality of stationary radiant heaters and are dried in several stages. Between the radiant heaters, different temperatures and degrees of moisture can be compensated for in the hollow bodies in resting stages. The air flow is also maintained during the rest times by ventilation devices that may be moved. However, it can also be switched off in the meantime. At the end of the heating section, the hollow bodies have already dried to the extent that no further shrinkage takes place. The hollow bodies are then insensitive to drying and can only be flowed through with hot air for finished drying.

For the drying process according to the invention, a conscious and controllable flow distribution through the interior of the body and possibly along the outer surface is important. The distribution and influencing of the air flow can take place in different ways, for example by designing the air nozzles, using screens, etc. In addition to or instead of these measures, the hollow bodies can also be dried in a tunnel-like covering which is permeable to the heating radiation and, above all, regulates the degree of flow to the outer surface by varying the gap distance to the hollow body. The covering also permits the joint drying of hollow bodies of different lengths, or the use of a general type of drying device for different types and shapes of hollow bodies.

The casing can be designed differently, for example as a supporting tube that moves along or as a multi-part aperture tunnel comprising a pallet and an aperture cover. Both forms also allow easy adaptation to different hollow body cross sections. The multi-part aperture tunnel can be moved along with the support tube and constantly surround the hollow body. However, it can also be arranged in a stationary manner and thus only function temporarily, which is particularly advantageous for drying devices for drying longitudinally oriented hollow bodies. Stationary coverings can be adapted to the shrinkage of the hollow body, which enables the flow distribution to be kept constant.

Further advantageous refinements of the invention are specified in the subclaims. In particular, the design and function of the ventilation devices can be varied in order to safely regulate and monitor the drying process. Possibilities of influence exist by changing the air conditioning, the flow speed (vapor tension reduction), the transport speed or cycle time and the radiant heating power.

Variations are also possible with regard to the air flow guidance, which can be moved, for example, in a closed circuit separately at each heating stage or in a pass against the transport direction over all stages. The latter variant has the advantage of high economic efficiency and a comparatively simple conditioning, in particular the humidification of the air flow, since this is already loaded with moisture from the previous heating stage. In this embodiment, it is advantageous that the drying device is sealed off on the outside, which prevents the heating radiation and also the air flow from escaping undesirably.

The method according to the invention and the associated drying device are suitable for arbitrarily shaped ceramic hollow bodies. In addition to tubular hollow bodies, hollow bodies with lateral bulges or branches can also be dried. With a suitable number and arrangement of the air nozzles, a continuous air flow can also be generated here, which branches in the hollow body and can be conducted in a closed circuit. Likewise, a plurality of hollow bodies can be acted upon jointly, preferably in parallel, with the step air flow.

The method according to the invention and the associated device can also be used successfully for drying hollow bodies made of other materials, for example wood or the like, in addition to the ceramic area. They are also suitable not only for hollow bodies with one or more axial through channels, but also for porous materials. The most important thing is that a continuous air flow can be achieved inside the hollow body.

• Fig. 1: eine teilweise aufgeschnittene perspektivische Frontansicht einer Trocknungsvorrichtung,
• Fig. 2: eine teilweise aufgeschnittene perspektivische Seitenansicht einer mehrteiligen Trocknungsvorrichtung für Durchlaufbetrieb mit querliegenden Hohlkörpern,
• Fig. 3: eine Stirnansicht der Trocknungsvorrichtung von Fig. 2,
• Fig. 4: eine Trocknungsvorrichtung in Seitenansicht und Variation zu Fig. 2 mit Länsgerichteten Hohlkörpern,
• Fig. 5: eine Draufsicht auf eine Heizstufe,
• Fig. 6: einen Schnitt durch die Heizvorrichtung von Fig. 4 entlang Schnittlinie VI-VI,
• Fig. 7: eine Variation zu Fig. 6,
• Fig. 8: einen Querschnitt durch einen Hohlkörper in einem Stützrohr,
• Fig. 9: eine Stirnansicht eines Trocknungsgerätes in Variation zu Fig. 1 und
• Fig. 10: einen Querschnitt durch einen Hohlkörper im Stützrohr mit Blende in Variation zu Fig. 8.

The invention is shown schematically and by way of example in the drawings. In detail show:

• 1: a partially cutaway perspective front view of a drying device,
• 2: a partially cutaway perspective side view of a multi-part drying device for continuous operation with transverse hollow bodies,
• 3: an end view of the drying device of FIG. 2,
• 4: a drying device in side view and variation to FIG. 2 with longitudinally oriented hollow bodies,
• 5: a plan view of a heating stage,
• 6: a section through the heating device of FIG. 4 along section line VI-VI,
• 7: a variation to FIG. 6,
• 8: a cross section through a hollow body in a support tube,
• 9: an end view of a drying device in variation to FIGS. 1 and
• 10: a cross section through a hollow body in the support tube with an aperture in variation to FIG. 8.

The drawings show a drying device (20) for drying hollow ceramic bodies (1), which essentially consists of one or more radiant heating devices (21) and one or more ventilation devices (16).

The embodiment of Fig. (1) shows a drying device (20) for stationary operation, while the drying devices in Fig. 2, 3 and 4 are designed for continuous operation.

In the exemplary embodiments, the ceramic hollow body (1) is designed as a long ceramic catalyst which has a large number of fine axial passage channels or lamellae. The hollow body (1) is connected to the ventilation device (16) on both end faces, at which the through holes end, which generates an air flow (19) directed axially through the hollow body (1). A flow around the outside of the hollow body (1) with air is avoided in the one exemplary embodiment of FIG. 1 and in the other example FIGS. 4-10 is permitted to a small extent. The decision as to whether or not an external flow should take place depends on the material and the shape of the hollow body (1), in particular also on its outer wall thickness and design. The heating energy required for drying is supplied to the ceramic hollow body (1) in a radiant heater (21) via one or more microwave generators (9) arranged therein. Alternatively, high-frequency generators can also be used in the embodiment of FIGS. 1-7 and 9. A radiation heating wave range of approximately 4 to 2450 MHz is preferred.

In the various exemplary embodiments, a plurality of microwave generators (9) are arranged one behind the other in the roof of the housing (10) in the direction of the air flow (19) and the power can be regulated independently of one another. The hollow body or bodies (1) rest on a floor (11) reflecting the microwaves or on a reflective conveyor belt (11).

In accordance with the increasing moisture content of the air in the direction of flow, the power of the microwave generators (9) is increased in proportion to the water absorption of the air in order to ensure moisture absorption even at the end of the hollow body (1). The air flow is always heated above the condensation point of the moisture that is carried along. With increasing humidity, the efficiency of the radiant heating also increases. The width of the microwave generators (9) can span several hollow bodies (1) or can be arranged in a row in a checkerboard pattern in several rows.

In a variation of the illustrated embodiment, one or more long microwave generators extending along the hollow body can also be provided. The desired increase in heating power is then achieved by increasing the distance to the hollow bodies. The microwave generators are accordingly adjustable in height and tilted cf. 4 and 9.

In a modification of the illustrated embodiment of FIG. 1, the generators can be provided on the bottom or the sides of the hollow body (1) for the application. Likewise, the assignment of the ventilation device (16) can be changed accordingly.

When drying hollow bodies (1) with different dimensions, differences result from varying distances between the microwave generators (9) and the hollow bodies (1). These differences can be compensated for by changing the power of the microwave generator (9) or by changing their distance from the hollow bodies (1). To change the distance, the microwave generators (9) are movably mounted in the housing (10) or the housing parts are in turn movably arranged in relation to their frame.

The ventilation device (16) consists of a recirculation line (3) in which the air flow (19) can be circulated. The air recirculation line (3) has an exhaust air connection (4) and a supply air connection (5), which can be opened and closed via adjustable flaps. An adjustable heating device (6) and a continuously adjustable fan (7) are arranged in the recirculating air line (3). In the flow direction behind the hollow body (1) there is also a sensor (8) in the air recirculation line (3) which detects the temperature and humidity of the air flow (19). The other parts of the regulation are not shown.

During drying, the hollow bodies (1) are acted upon by air conditioned according to the degree of drying. For the drying of ceramic catalysts that come directly from the extrusion press, it is recommended according to the embodiment of FIGS. 1-4, the hollow body (1) first of all with an air temperature of e.g. approx. 40 degrees and a relative humidity of e.g. 95% flow. As a result, the whole of the hollow bodies (1) are carefully heated only by the radiant heating, the drying process already beginning with the removal of the moisture. The heat output gradient ensures that the relative humidity is just below the condensation point.

Only when the operating temperature of the hollow body (1) has been reached is the relative air humidity reduced for the effective removal of the expelled mixing water and the like. Other liquids. In the ventilation circuit of FIGS. 1-3, this can be done by increasing the air temperature in the heater (6) and / or by removing moist air and supplying dry fresh air.

The flexible air recirculation line (3) protrudes from the side into the interior of the radiant heater (21) and is with the hollow body (1) through two ends attachable air nozzles (2) connected. The size of the air nozzles (2) is adapted to the dimensions of the end faces of the hollow body (1), which ensures an airtight fit of the air nozzles (2) on the hollow body (1). As a result, air flow (19) conducted in a circle through line (3) is directed only through the interior of the hollow body (1), but not along its outer sides.

For the simultaneous connection of several hollow bodies (1), which is preferably carried out in parallel, a plurality of recirculated air lines (3) or a recirculated air line with a distributor piece (not shown) for connecting a plurality of air nozzles (2) are provided. For airtight adaptation to different hollow body dimensions, the air nozzles (2) can be designed to be adjustable or to be exchangeably fastened.

In the exemplary embodiment in FIG. 1, the radiant heater (21) consists of a laterally open housing (10), the side opening of which opens access for the air recirculation line (3) and is otherwise secured by a side shield (12) against undesired escape of the radiation. The front opening is also shielded, for example by a chain curtain (13).

In the exemplary embodiment in FIG. 1, the air nozzles (2) are plugged outside the radiation heater (21) onto the hollow body (1), which is then brought into the interior of the radiation heater (21).

In the embodiment of FIG. 2, a drying device (20) is shown, which is designed for continuous operation. A number of ventilation devices (16) and microwave heating devices (21) are provided, which essentially correspond to those of FIG. 1. In the exemplary embodiment in FIG. 2, several batches of hollow bodies (1) are processed simultaneously. Each batch consists of several hollow bodies (1) arranged parallel to one another, which are aligned transversely to the transport direction (33) and are connected together to a ventilation device (16). The hollow bodies (1) are brought to a conveying device (11) at an installation point (17), here in the form of an endless conveyor belt (11) moved by a drive (14) and connected to a ventilation device (16). On their transport route they move the ventilation device (16) while maintaining the connection and the air flow. For this purpose, this is movably mounted on rails (15) via a chassis (22). A stationary radiant heater (21) connects to the scaffolding point (17), to which a quiet zone (18) and in turn a further radiant heater (21) is connected. At the end of this line of equipment there is a disassembly station at which the dried hollow bodies (1) are separated from the ventilation device (16) and removed from the conveyor belt. The empty ventilation device (16) can then drive back to the installation point (17) and be connected to a new batch of hollow bodies (1) there. To shorten the changeover and set-up times, two or more ventilation devices (16) are provided which can run over each other and each run on their own rails (15). In the embodiment of Figure 3, only a single ventilation device (16) is shown.

Variations on the embodiment of FIGS. 1-3 are possible in different ways. On the one hand, an external flow around the hollow body (1) may be desirable in some cases. For this purpose, the air nozzles (2) then do not connect tightly to the end faces of the hollow body (1), but leave a small circumferential gap through which a small part of the air flow emerges, sweep freely along the outer surfaces of the body and then back into the other end Air nozzle (2) can enter. For fastening the air nozzles, small clamping webs can be provided for clamping the hollow body ends on the air nozzles in this case.

Furthermore, changes regarding the flow guidance outside the hollow bodies and the conditioning of the air are possible. In principle, an open ventilation duct is also possible without the recirculation line (3). For this purpose, freshly conditioned air must always be supplied and the moisture-laden air must be completely removed. This is possible in cases where the shape and material of the hollow body do not place high demands on a gentle drying process. In such cases, the conditioned fresh air can consist of the ambient air, which may only be slightly heated in a heater.

In the open as well as in the closed ventilation circuit, the air for generating flow can in principle be blown in at one end of the hollow body (1) or extracted at the other end, or both blown in and extracted. In all cases, it is also possible to vary the flow rate of the air in order to reduce steam tensions in the hollow bodies (1), for example by increasing the flow rate during rapid drying. The degree of moisture removal can also be regulated by changing the flow rate.

The exemplary embodiments in FIGS. 8-10 show further variations of the drying device (20). On the one hand, it is also possible in another way to influence the flow distribution through the interior of the body and along the outer surfaces. For this purpose, the hollow bodies (1) are mounted in a tunnel-like covering (24) which is permeable to the radiant heat and which surrounds the hollow body in tight contact to avoid an external flow or by leaving a gap (32) to adjust the external flow. In the exemplary embodiment in FIG. 8, the casing is designed as a support tube (30) made of ceramic or the like, in which a hollow body (1) of the same or shorter length is mounted. In order to achieve a circumferentially permeable gap (32), the hollow body (1) lies at least in the lower region on a support (29) which has knobs or webs to form longitudinal ventilation channels. The support tube (30) is adapted in this case to the hollow body cross-section, both of which can have any other, for example polygonal, cross-sectional design in addition to the circular shape shown. To fix the position of the support tube, a pallet (28) with adapted recesses is provided, which rests on the floor or the conveyor device (11). Alternatively, the support tube (30) can also have legs or the like. Other fixing means.

The exemplary embodiments 8 and 1 can be combined with one another by plugging the air nozzles (2) onto the support tube (30) with a tight seal on the edge. Fig. 9 shows a further possibility that allows the housing (10) to be completely closed for radiation shielding. The air nozzles (2) are arranged here laterally but outside the housing (10) and are connected to the interior via a respectively inserted panel (31). The diaphragm openings are aligned with each other on both sides and also correspond to the cross section of the hollow bodies (1) which are correspondingly arranged in the housing (10). The hollow body (1) extends at both ends up to the screens (31). The air flowing through the apertures thus reaches the inside of the body without being able to escape laterally. With the same size of the hollow body (1) and aperture opening, an external flow around the hollow body (1) can be avoided. If, on the other hand, this is desired, the diaphragm opening is enlarged according to FIG. 10 to form an edge-side gap (32).

In combination, support tubes (30) or other tunnel-like coverings (24) can also be used. A combination of support tube (30) and screen (31) enables the use of envelopes in standard sizes, which in some cases are larger than the cross-section of the hollow body, since the amount of air flowing along the outside depends on the size of the gap (32) between the aperture opening and the cross-section of the hollow body (1) is set. Fig. 10 illustrates this arrangement and also shows a support (29) arranged only in the lower contact area.

Fig. 4 shows a variant of a multi-part drying device (20), in which the hollow body (1) are aligned along the transport direction (33). The drying device (20) is heat, air and radiation-tight as a closed system. The ventilation devices (16) are arranged here between the individual radiant heating devices (21). They have the shape of domes in cross section and are each connected to the front radiation heater (21) with a conically tapering air nozzle (2) and to the rear radiation heater (21) with the other air nozzle (2).

The ventilation devices (16) each have a fan (7) in the form of a cross-flow fan, which sucks in the air from the air nozzle (2) at the front in the transport direction (33) and blows it into the rear air nozzle (2). As a result, the air flow (19) is guided from the outlet side against the transport direction (33) through the individual drying stages to the inlet side. With this counterflow principle, relatively dry air is introduced at the outlet side, which is harmless given the high degree of dryness of the hollow bodies (1) that have arrived there. By passing from stage to stage, the air flow (19) absorbs more and more moisture and essentially conditions itself to the extent necessary for the degree of drying of the hollow bodies (1).

The ventilation devices (16) each have a supply air connection (5) on the front, suction-side air nozzle for the supply of fresh air. An exhaust duct (4) and then a heater (6) for the air flow (19) are arranged on the pressure-side air nozzle (2) behind the cross-flow fan (7). Both air shafts (4, 5) are equipped with adjustable flaps. In both air nozzles (2), sensors (8) for temperature and humidity are arranged near the radiant heaters (21).

The cross flow fans are arranged in the middle and in the upper area of the domes. Below this there are pivotable partitions (23) which seal the two air nozzles (2) of each ventilation device (16) against each other in such a way that air can only be exchanged via the cross-flow fan (7). This creates closed climatic zones for the radiant heating devices (21) and the air jets (2) of the neighboring ventilation devices (16), which can be controlled independently of one another in the conditioning of the air flow. If the automatic continuation mentioned above is not sufficient, readjustments can be made via the supply and exhaust air ducts (5, 4) and the heater (6) depending on the measured values of the sensor (8). Drying can also be influenced by the flow rate and the length of stay in the respective climate zone. The degree of dryness increases with an increase in these factors.

The hollow bodies (1) are moved in cycles through the various climatic zones or drying levels and gradually dry out in the differently conditioned zones. The pivotable bulkheads (23) can be regulated depending on the conveying movement, so that the hollow bodies (1) can pass underneath. At the end of the drying device (20) there can also be a pure ventilation station, in which the hollow bodies (1) are completely dried with hot air blown through them. Radiant heating is no longer effective given the degree of dryness of the hollow body (1). There is no longer any risk of cracks due to shrinkage.

5, 6 and 7 illustrate, in a system according to FIG. 4 several hollow bodies (1) are dried side by side in tunnel-like coverings (24). In the exemplary embodiment shown, they are stationary and can therefore be adjusted to the respective shrinkage of the hollow body (1) in the individual drying stage. Best in the embodiment of FIG. 6 hen the coverings (24) from between the hollow bodies (1) extending webs (25) which connect to the air nozzles (2). Insulated side walls (26) are provided on the outside, while the underside is formed by a conveyor belt (11) profiled in the longitudinal direction. The upper side is formed by the microwave or high-frequency generators (9) directly or by a support wall arranged below it. These continue in the connection area to the air nozzles (2) in corresponding ceiling parts. The webs (25) become increasingly thicker in the transport direction (33) in accordance with the degree of shrinkage from drying stage to drying stage.

Fig. 7 shows a variant of this, in which the hollow body (1) in a correspondingly shaped pallet (28), possibly over profiled supports (29) are stored. The pallet (28) is moved forward with the conveyor belt (1). The upper part of the tunnel-like covering (24) is formed by a correspondingly designed diaphragm cover (27), with which the size of the gap (32) which may be required is also set. The microwave or high-frequency generators (9) are arranged above the diaphragm cover (27). Lateral walls (26) protrude laterally over the pallets (28) for guidance and sealing.

The panel cover (27) can be moved on the pallet (28) with appropriate support. In principle, this results in a two-part support tube. The cover plate (27) can, however, also be arranged in a stationary manner in each radiant heater (21), the pallets (28) with the hollow bodies (1) moving below them. In the first variant as a moving casing (24), this design can also be used for the ventilation of transverse hollow bodies (1) in an embodiment according to FIG. (2) or (9).

parts list

• (1) hollow body
• (2) air nozzle
• (3) Air recirculation line
• (4) Exhaust port
• (5) Supply air spigot
• (6) heater
• (7) fan
• (8) probe
• (9) Microwave generator, high frequency generator
• (10) housing
• (11) Floor, conveyor, conveyor belt
• (12) side shielding
• (13) chain curtain
• (14) drive
• (15) rail
• (16) ventilation device
• (17) Installation point
• (18) Quiet zone
• (19) Airflow
• (20) Drying device
• (21) Radiant heater
• (22) chassis
• (23) Schott
• (24) tunnel-like cladding
• (25) Bridge
• (26) sidewall
• (27) Cover cover
• (28) pallet
• (29) edition
• (30) support tube
• (31) Aperture
• (32) gap
• (33) Direction of transport

Claims (24)

1. Process for drying ceramic hollow bodies, in particular catalysts, in which the heating is accomplished by radiant energy and the moisture driven out is carried away by a current of air, characterized in that the current of air (19) is conditioned as to temperature and moisture and is directed selectively predominantly through the inside of the hollow bodies (1), and in that the radiant heat output along a hollow body (1) exhibits a rising gradient in the direction of the current of air (19).

2. Process according to Claim 1, characterized in that the drying energy is provided by microwaves or high frequency.

3. Process according to Claim 1 or 2, characterized in that the temperature and the moisture of the current of air (19) are measured (8) at least downstream of the hollow bodies (1) and the input conditioning of the drying air and/or the radiant heat output can be controlled accordingly.

4. Process according to Claim 3, characterized in thatthe hollow bodies (1) are dried in a plurality of stages with hot air conditioned differently according to the degree of drying.

5. Process according to Claim 1 or one of the following claims, characterized in that the current of air (19) is guided in a closed circuit through one or more hollow bodies (1) arranged in parallel next to one another.

6. Process according to Claim 4, characterized in that the hollow bodies (1) are arranged in series, one behind the other, and are dried in a continuous operation having a plurality of stages, the current of air (19) being guided on from stage to stage through the hollow bodies (1) counter to the direction of transport.

7. Process according to Claim 6, characterized in that the speed of transport or the dwell time in the heating stages is controlled in accordance with the moisture of the current of air (19).

8. Process according to Claim 4, 5 or 6, characterized in that, between or downstream of the drying stages, in one or more resting stages, only a conditioned current of air (19) is directed through the hollow bodies (1), without radiant heating.

9. Process according to Claim 1 or one of the following claims, characterized in that the drying air is guided with controllable intensity of flow through the hollow bodies.

10. Process according to Claim 1 or one of the following claims, characterized in that the drying air is blown in at one end of the hollow bodies (1) and sucked off at the other end.

11. Process according to Claim 1, characterized in that, the edges being sealed, the current of air (19) is guided onlythrough the inside of the hollow bodies (1).

12. Drying device for ceramic hollow bodies, in particular catalysts, having at least one radiant heating device (21) and at least one ventilation device (16), which has a device (4, 5, 6, 7) for producing a conditioned current of air (19) directed predominantly through the inside of the hollow bodies (1), characterized in that the current of air (19) is directed byu one or more air nozzles (2), and in that the heat output of the radiant heating device (21) is controllable, the heat output being different along the length of a hollow body and being less at the inflow side of the air (19) than at the outflow side.

13. Drying device according to Claim 12, characterized in that the radiant heating device (21) has one or more microwave or high-frequency producers (9), the output of which can be controlled separately from one another or the distance of which from the material to be dried can be altered.

14. Drying device according to Claim 12, characterized in that the ventilation device (16) has an exhaust-air connection (4) for moist air, a feed connection (5) forfresh air, a heating device (6) and a fan (7), which are controllable in dependence on a sensor (8) which measures temperature and/or moisture of the current of air (19).

15. Drying device according to Claim 12 or 14, characterized in that a plurality of hollow bodies (1) are acted upon in parallel at a ventilation device (16).

16. Drying device according to Claim 12 or one of the following claims, characterized in that the hollow bodies (1) are mounted in a single-or multipart, tunnel-like jacket (24), with airtight contact or with a gap (32) or are at least periodically surrounded by the jacket.

17. Drying device according to Claim 16, characterized in that the hollow bodies (1) rest on a support (29) which leaves free longitudinally extending channels in the gap (32).

18. Drying device according to Claim 14 or 15, characterized in that the ventilaion device (16) has at least one air-recirculation pipe (3) and at least two air nozzles (2) for the production of a closed circuit for the current of air (19) through the hollow body (1).

19. Drying device according to Claim 16,17 or 18, characterized in that the air nozzles (2) protrude into the radiant heating device (21) and, with airtight sealing atthe edges or leaving an all-round gap (32), are releasably attached to the open end faces of the hollow bodies (1) or of the tunnel-like jackets (24).

20. Drying device according to Claim 18, characterized in that the air nozzles (2) have restrictors (31), the openings of which are matched to the contour of the hollow bodies (1) or of the jackets (24).

21. Drying device according to Claim 19, characterized in that for continuous operation with transversely lying hollow bodies (1) one or more laterally open stationary radiant heating devices (21) are provided, throuh which the hollow bodies (1) are transported on a conveying device (11), one or more movable ventilation devices (16) carried along with hollow bodies being provided.

22. Drying device according to Claim 18, characterized in that for continuous operation with transversely lying hollow bodies (1) one or more stationary radiant heating devices (21) having connected stationary ventilation devices (16) with lateral air nozzles (2) are provided, through which the hollow bodies (1) are transported on a conveying device (11).

23. Drying device according to Claim 21 or 22, characterized in that the radiant heating devices (21) are arranged at a distance from one another, forming rest zones (18).

24. Drying device according to one of Claims 12 to 17, characterized in that the drying device for longitudinally oriented hollow bodies (1) is designed as a continuous device having a plurality of radiant heating devices (21), between which ventilation devices (16) having partitions (23) are arranged, which suck the air out of one station, condition it and blow it into the next station counter to the direction of transport (33).

Images