SYSTEM AND METHOD FOR DRYING EXTRUDED HONEYCOMB BODIES

Abstract

A system (2) for extruding and drying an extruded honeycomb body (14) which has channels (18) that extend in a longitudinal direction (L) and which channels (18) are each bounded by first channel walls (20a) that extend in a first direction (A) which is transverse relative to the longitudinal direction (L), and by second channel walls (20b) that extend in a second direction (B) in which is also transverse relative to the longitudinal direction (L) comprises: (i) an extruder (16) having an extrusion head (17) for producing the honeycomb body (14) by extrusion; (ii) a microwave oven (4) comprising an arrangement of a plurality of microwave radiators (6), each microwave radiator being for irradiating the honeycomb body with a directional microwave beam in an irradiation direction (S); and (iii) a feed unit (12) adjoining the extruder (16) for transferring the honeycomb body from the extruder (16) into the microwave oven (4), wherein either: (a) the extrusion head (17) of the extruder is oriented in such a way that during operation of the system the orientation position of the extruded honeycomb body (14) resulting from the extrusion when transferred into the microwave oven (4) is such that the irradiation direction (S) of each microwave radiator (6) is oriented at a predefined irradiation angle (a) which is not zero relative to each of the two transverse directions (A, B) of the first and second channel walls (20a, 20b); GBor (b) the system (2) is designed to sense the orientation of the first and/or second channel walls (20a, 20b) of the honeycomb body produced by the extruder and to move the honeycomb body and/or a microwave radiator (6) into a set point orientation such that the irradiation direction (S) of each microwave radiator (6) is oriented at a predefined irradiation angle (a) which is not zero relative to each of the two transverse directions (A, B) of the first and second channel walls (20a, 20b).

Claims

1. A system for extruding and drying an extruded honeycomb body which has channels that extend in a longitudinal direction and which channels are each bounded by first channel walls that extend in a first direction which is transverse relative to the longitudinal direction, and by second channel walls that extend in a second direction which is also transverse relative to the longitudinal direction, which system comprises: (i) an extruder having an extrusion head for producing the honeycomb body by extrusion; (ii) a microwave oven comprising an arrangement of a plurality of microwave radiators, each microwave radiator being for irradiating the honeycomb body with a directional microwave beam in an irradiation direction; and (iii) a feed unit adjoining the extruder for transferring the honeycomb body from the extruder into the microwave oven, wherein either: (a) the extrusion head of the extruder is oriented in such a way that during operation of the system the orientation position of the extruded honeycomb body resulting from the extrusion when transferred into the microwave oven is such that the irradiation direction of each microwave radiator is oriented at a predefined irradiation angle which is not zero relative to each of the two transverse directions of the first and second channel walls; or (b) the system is designed to sense the orientation of the first and/or second channel walls of the honeycomb body produced by the extruder and to move the honeycomb body and/or a microwave radiator into a set point orientation such that the irradiation direction of each microwave radiator is oriented at a predefined irradiation angle which is not zero relative to each of the two transverse directions of the first and second channel walls.

2. The system according to claim 1, wherein the predefined irradiation angle is in the range from 30 to 60 and is, in particular, 45 with respect to the first or the second transverse direction of the first and second channel walls.

3. The system according to claim 1, wherein a plurality of microwave radiators are arranged within a plane which is transverse relative to the longitudinal direction.

4. The system according to claim 1, wherein the microwave oven comprises an arrangement of four microwave radiators which are each offset by 90 with respect to one another.

5. The system according to claim 3, wherein a plurality of transverse planes which are offset with respect to one another in the longitudinal direction are each provided with a plurality of microwave radiators, in particular four, which are offset by 90 with respect to one another.

6. The system according to claim 1, wherein the individual microwave radiators of the various transverse planes of the first and second channel walls are aligned with one another in the longitudinal direction.

7. The system according to claim 1 which is designed to continuously dry a plurality of honeycomb bodies in a run-through process, and the feed unit is designed to transfer the bodies in a feeding direction which is parallel to the longitudinal direction.

8. The system according to claim 1, wherein during operation the internal pressure in the microwave oven is set to less than 20 mbar, in particular to less than 6 mbar.

9. The system according to claim 1 designed in such a way that during operation the irradiated microwave power is adjusted as a function of the pressure prevailing in the microwave oven.

10. The system according to claim 1, wherein each microwave radiator has its own unit for generating the microwaves.

11. A method of drying extruded honeycomb bodies which have channels that extend in a longitudinal direction and which channels are each bounded by first channel walls that extend in a first direction which is transverse relative to the longitudinal direction, and by second channel walls that extend in a second direction which is also transverse relative to the longitudinal direction, which method comprises: the steps of irradiating the extruded honeycomb bodies in a microwave oven with microwave radiation from a plurality of microwave radiators, each microwave radiator being for irradiating the extruded honeycomb body with a directional microwave beam in an irradiation direction, and ensuring that the irradiation direction of each microwave radiator is oriented at a predefined irradiation angle relative to the two transverse directions of the first and second channel walls which is not zero.

12. The method according to claim 11, wherein the extruded honeycomb bodies are extruded by means of an extruder, and the step of ensuring that the irradiation direction of each microwave radiator is oriented at a predefined irradiation angle relative to the two transverse directions of the first and second channel walls which is not zero is provided by the step of placing the extruded honeycomb body on a feed unit in such an orientation that the condition of the predefined irradiation angle relative to the two transverse directions of the first and second channel walls of the honeycomb body when it is transferred into the microwave over is met.

13. The method according to claim 11, wherein the honeycomb bodies are at a distance of greater than 3 cm and less than 6 cm from one another in the longitudinal direction inside the microwave oven.

Description

[0035] An exemplary embodiment of the invention will now be explained in more detail below with reference to the accompanying drawings, in which:

[0036] FIG. 1 shows a schematic longitudinal sectional illustration of a system for drying honeycomb bodies, and

[0037] FIG. 2 shows a cross-sectional illustration through the microwave oven along the sectional line II, II in FIG. 1.

[0038] In the figures, identically acting parts are provided with the same reference symbols.

[0039] The system 2 which is illustrated in FIG. 1 comprises a microwave oven 4 which extends in a longitudinal direction L and is embodied overall in the manner of an elongated duct. The duct preferably has a circular-round cross section. Alternatively, the cross section of the microwave oven duct is often in the form of a polygon, for example rectangular and, preferably, square. The microwave oven 4 has a plurality of microwave radiators 6. In the exemplary embodiment, the latter are arranged offset with respect to one another in the longitudinal direction L. In addition, a plurality of microwave radiators 6 are each arranged within a transverse plane Q.

[0040] As is apparent, in particular, from FIG. 2, in total four microwave radiators 6 are arranged distributed around the circumference of the microwave oven 4 here, which microwave radiators 6 are each arranged offset with respect to one another by, in particular, 90.

[0041] The microwave radiators 6 are firstly simple microwave waveguides which open into an antenna which is preferably embodied as what is referred to as a horn radiator, as is indicated in FIG. 1. The antennas (horn radiators) are arranged radially on the microwave oven 4 and open into the interior of the microwave oven duct. In order to generate the microwaves, a separate microwave-generating unit is preferably provided for each individual microwave radiator 6 in a way which is not illustrated in more detail here. Said microwave-generating unit therefore outputs the generated microwave radiation into the guide channel of the respective microwave radiator 6.

[0042] In order to set a desired underpressure inside the microwave oven 4, a vacuum system 8 with a vacuum pump 10 is also arranged, said vacuum system 8 setting the internal pressure inside the microwave oven 4 during operation preferably to a value and typically in the range from less than approximately 6 mbar and also holding it there. In addition to the vacuum pump, the condenser/resublimator (not illustrated in more detail here) is arranged for the water which is released during the drying process. On the input or output side of a drying zone of the microwave oven 4, inside which zone the individual microwave radiators 6 are arranged, locks 11 are formed via which the honeycomb bodies 14 are fed into or out of the underpressure region of the microwave oven. Furthermore, in one preferred embodiment a transition zone is formed between the locks 11 and the respectively closest microwave radiator 6, said transition zone having, in the longitudinal direction L, a length of several 10 cm, in particular in the range from at least 30 to 50 cm up to preferably at maximum approximately 1 metre. As a result, (plasma) discharges are reliably avoided.

[0043] The drying zone with the microwave radiators 6 and the two transition zones preferably form a one-storied, preferably tubular, component which is securely adjoined by further components of the system 2, in particular the locks 11, for example via a flange connection.

[0044] Furthermore, inside the microwave oven 4 a feed unit 12 is arranged, on which feed unit 12 a plurality of honeycomb bodies 14 are arranged during operation. The feed unit 12 feeds the individual honeycomb bodies 14 continuously through the microwave oven 4 in the longitudinal direction L in a run-through method. The feed unit 12 therefore feeds the honeycomb bodies 14 in a feed direction F which corresponds to the longitudinal direction L of the microwave oven. The honeycomb bodies 14 have here a distance a in the range of several cm, in particular of more than 3 cm, and preferably in the range from 3 to 6 cm.

[0045] The system 2 also has an extruder 16 comprising an extrusion head 17 on a side oriented to the microwave oven 4. The honeycomb catalysts 14 are generated from a ceramic, pasty mass by means of a shaping process using the extruder 16. Subsequent to the extruder 16, a cutting device is formed (in a way not illustrated here), by means of which the extruded length of material which exits the extrusion head 17 is repeatedly cut, with the result that individual honeycomb bodies 14 are formed.

[0046] The honeycomb bodies 14 have here, for example, a diameter of approximately 5 to 14 inches (12.7 to 35.6 cm) and a length of 5 to 10 inches (12.7 to 25.4 cm).

[0047] The honeycomb bodies 14 are preferably frozen exclusively by means of a suitable reduction in pressure, without an additional cooling device being arranged. The honeycomb bodies 14 are therefore frozen by the low pressure, with the result that the water which is contained in the honeycomb bodies 14 is enclosed in the form of ice.

[0048] It is particularly significant that the entire system 2 is conceived in such a way that the individual honeycomb bodies 14 run through the microwave oven 4 with a defined orientation with respect to the individual microwave radiator 6. For this purpose, in one preferred embodiment the extrusion head 17 is already attached with a suitable orientation, with the result that the generated extrusion strand and therefore the generated honeycomb bodies 14 already have the desired orientation.

[0049] Alternatively, in preferred developments, devices for controlling the desired orientation are integrated, for example a measuring device for checking the desired orientation and/or an orientation unit for bringing about the desired orientation.

[0050] The honeycomb bodies 14 are extruded honeycomb bodies which frequently have a circular cross-sectional shape, that is to say are preferably embodied overall in the form of cylinders. They extend here in the longitudinal direction L and have a plurality of individual channels 18, such as is apparent, in particular, from FIG. 2. These individual channels 18 pass through the honeycomb body 14, preferably completely in the longitudinal direction L and therefore enter and respectively exit at the end sides at inlet and outlet openings. The individual channels 18 are each respectively bounded by first channel walls 20a and second channel walls 20b. The first channel walls 20a extend in a first transverse direction A, and the second channel walls 20b extend in a second transverse direction B. The channel walls 20a, 20b are, in particular, embodied in the manner of a lattice and are perpendicular to one another. Correspondingly, the two transverse directions A, B are also oriented perpendicularly with respect to one another.

[0051] A directional microwave beam is irradiated into the microwave oven 4 during operation in each case in an irradiation direction S by means of the individual microwave radiators 6. Said irradiation direction S is oriented here at an irradiation angle with respect to the two transverse directions A, B. In the exemplary embodiment, the irradiation angle is in each case 45 with respect to the two transverse directions A, B.

[0052] The operation of the system 2 is subject to open-loop and, preferably, also closed-loop control by a control device (not illustrated in more detail here). In order to achieve continuous and efficient operation, the individual honeycomb bodies 14 are guided at a predefined speed in the longitudinal direction L through the microwave oven 4. Sensors, preferably a weight sensor, moisture sensors etc., by means of which, for example, at least indirectly a moisture content of the honeycomb bodies 14 before the entry into the microwave oven 6 is sensed, are preferably arranged inside the system 2. For example the irradiated microwave power is then suitably controlled as a function of the degree of moisture.

[0053] Generally, the irradiated radiation power is suitably adjusted using a control unit, with the result that homogeneous drying which is as uniform as possible to a defined residual moisture content takes place. The adjustment takes place here, in particular, as a function of the internal pressure within the microwave oven 6. The control variable is a desired maximum internal pressure. This ensures that an excessively high sublimation rate does not result in an excessively high mass flow which would bring about an undesired increase in pressure and therefore an undesired rise in temperature, with the risk of (even partial) thawing out.

[0054] The irradiated radiation power per transverse plane Q is here, for example, in the range of several kilowatts. Here, the irradiated radiation power in the front transverse planes Q is usually greater than in the rear transverse planes Q, where pre-drying has already taken place. The irradiation powers of, in particular, the first transverse plane Q are also set, and are regulated, for example, as a function of the properties of the honeycomb body 14 at the entry to the microwave oven 4, in particular as a function of its weight.

[0055] The system described here with the defined orientation of the honeycomb bodies 14 with respect to the radiation direction S permits a particularly suitable, prompt drying method in which the risk of the formation of fractures is low. A further significant aspect is the adjustment of the radiation power with the result that a rise in pressure above a predefined maximum value is avoided.

LIST OF REFERENCE SYMBOLS

[0056] 2 System

[0057] 4 Microwave oven

[0058] 6 Microwave radiator

[0059] 8 Vacuum system

[0060] 10 Vacuum pump

[0061] 11 Lock

[0062] 12 Feed unit

[0063] 14 Honeycomb body

[0064] 16 Extruder

[0065] 17 Extrusion head

[0066] 18 Channels

[0067] 20a First channel wall

[0068] 20b Second channel wall

[0069] L Longitudinal direction

[0070] F Feed direction

[0071] a Distance

[0072] Q Transverse plane

[0073] A First transverse direction

[0074] B Second transverse direction

[0075] S Irradiation direction

[0076] Irradiation angle