WO1998037953A1

WO1998037953A1 - Device for thermal treatment of flowable or pourable solids

Info

Publication number: WO1998037953A1
Application number: PCT/DE1998/000346
Authority: WO
Inventors: Wolfgang Heschel; Dirk MÜLLER
Original assignee: Helsa-Werke Helmut Sandler Gmbh & Co. Kg
Priority date: 1997-02-25
Filing date: 1998-02-05
Publication date: 1998-09-03
Also published as: DE19707438A1

Abstract

The invention relates to a device for thermal treatment of flowable or pourable solids comprising a substantially vertical drum (1), wherein elements (8) for mixing and/or transporting the solids are arranged in said drum. The inventive device further comprises a pivotally mounted shaft (2) inside the drum. The elements (8) for mixing and/or transporting the solids are fixed to the shaft (2).

Description

Device for the thermal treatment of flowable or free-flowing solids

The present invention relates to a device for the thermal treatment of flowable or free-flowing solids with an essentially horizontally arranged drum, wherein elements for mixing and / or transporting the solids are arranged in the drum.

The thermal treatment of granular solids is an essential process step in many production processes. These include heating and cooling, drying, pyrolyzing and gasifying, oxidizing and sintering various inorganic as well as organic, granular to powdery solids. Common

A feature of these processes is that the properties of solids can be specifically changed by treatment at certain temperatures. The thermal treatment can take place in an inert, oxidizing or reducing atmosphere and also in a wide temperature range. It is typical of these processes that substances / substance components pass from the gas phase to the solid or from the solid to the gas phase. In many applications, mass transfer is coupled with chemical reactions between the gas and solid phase or in only one phase (gas or solid). This requires intensive contact between the two phases, devices of the type described in the introduction are generally used as rotary kilns in a wide variety of areas.

In the thermal treatment of solids, the guarantee is an intensive contact of solid and gas, a high contact frequency of the solid particles on heat transfer surfaces for heating or cooling, a sufficient movement impulse on the individual particles with sticky or solids that tend to sinter, a directed transport of the solid and / or gas phase without flow dead spaces in the apparatus or reactor volume, a residence time of all solid particles that is as uniform as possible, a high solid concentration in the reaction space, a high specific throughput and utilization of the device volume as well as low investment and

Operating costs of particular importance. A disadvantage of the devices known from the prior art is that they generally only satisfactorily fulfill some of the above-mentioned points, while most of the other requirements are insufficiently met.

It is therefore an object of the present invention to provide a device of the type described in the introduction, which enriches the prior art with a further device of the aforementioned type, which is the largest possible

Combination of the aforementioned requirements met, this device should have as many possible uses.

The present object is achieved by a device for the thermal treatment of flowable or free-flowing solids of the type described in the introduction in that a rotatably mounted shaft is arranged in the interior of the drum is, and the elements for mixing and / or transport of the solids are attached to the shaft.

Further advantageous embodiments of the present invention are the subject of the dependent claims.

The advantage of the embodiment according to the invention is in particular that the efficiency in mixing and transporting the free-flowing or free-flowing solids is greater with regard to the requirements mentioned at the outset than in the devices known from the prior art.

The transport or mixing elements, which are preferably rigidly attached to the shaft, can differ in shape, number and

Differentiate the angle of attack to the shaft axis and then serve either to mix the solid or to transport it. For example, Alternate so-called mixing elements and transport elements in one plane over the shaft circumference. The angle of attack between the plane of the transport elements and the shaft axis influences the transport speed and direction. The degree of filling in the reaction tube can be changed locally by different angles of attack of the transport elements, which makes it possible to influence the residence time of the solid in certain zones of the reactor. For example, a negative angle of attack can be selected for individual transport paddles, which leads to a local increase in the degree of filling.

The transport elements can also be arranged in an imaginary ascending or descending spiral along the shaft axis. When the spiral rises, the lowest transport speed is reached during the highest transport speed is reached with a descending spiral. Of course, this only applies to otherwise identical settings (e.g. with regard to the speed and the solids throughput).

How often and intensively the solid is mixed depends on the number of mixing elements arranged on the shaft circumference. Since the mixing elements only mix the solid locally to a limited extent, only a small volume of solid is involved, which ensures a practically uniform residence time of the particles and largely prevents longitudinal mixing. The mixing intensity can be influenced regardless of the speed of the shaft via the shape of the mixing elements. The mixing elements can be designed so that they e.g. have a straight or curved surface, which can optionally be provided with slots and / or side edges etc. Because of the variation possibilities mentioned, there is the advantage that materials with the most varied properties can be treated in the device according to the invention. The transport and / or mixing elements can be selected according to the material to be processed and their angle can be adjusted. For example, also for

Material that tends to sintering can be treated or an intensive contact of the material with the gas can be ensured in order to allow certain chemical reactions to take place. In the case of flat and possibly slotted elements, a so-called "stirring effect" prevails and the solid blocks off. A cascade zone is formed, as can also be observed with the movement of solids in slowly moving rotating tubes. Arched or shovel-shaped mixing and / or transport elements promote the Solid across the shaft, forming a strand of particles with intimate contact with the gas phase. This is comparable to the cataract zone with rapidly rotating rotary tubes.

The device according to the invention is heated either indirectly via the tube wall, directly by hot gases or by combustion of gases in the reaction space. Reactions can not only be controlled by the temperature control, but also by the fact that the gaseous reactants are added at various points along the reaction tube. In gas-solid reactions, e.g. when activating carbon-containing materials, this is preferably done from below, because the gases are in intimate contact with the

Solid can occur in the corresponding zone of the reaction space.

When performing homogeneous reactions, i.e. For reactions that take place in the gas phase, the gaseous reactants are preferably introduced from above into the gas space above the solid. This type of gas supply is used, among other things. selected for the internal heating of the reactor by oxidation of flammable gases. The feeding of the solid into the invention

The device is made using generally known metering devices, such as metering plates, cellular wheels and the like, the throughput of the system being able to be set and controlled using the metering device. For a certain geometric design of the device according to the invention, the solids residence time and the mixing intensity, as well as the contact time of the solids on the heated or cooled reactor wall due to the solids throughput, the shaft speed and the inclination of the reaction tube to be influenced. The total dwell time can be increased, for example, if the speed of the shaft is reduced with a constant throughput. The opposite, that is to say the reduction in the total dwell time, can be achieved by increasing the speed of the shaft with a constant throughput. The residence time of the solid in the individual zones of the reactor can also be changed by tilting the tube. A downward slope leads to an increase in the degree of filling in the direction of movement, while an upward slope results in a corresponding decrease. At constant throughput, the residence time of the solid increases with the degree of filling of the reaction tube. With the inclination of the tube, the effective angle of attack of the transport and mixing elements changes at the same time, so that additional influence on the

Mixing and movement of the solid is exercised.

The residence time and / or the degree of filling is also influenced by the geometry of the drum. preferred

Embodiments of the drum therefore have a conical shape or a diameter which increases conically or stepwise in one direction. In these embodiments, it is expedient if the mixing and / or transport elements are each adapted to the drum diameter, so that their effect as such is not impaired.

The invention is explained in more detail below on the basis of exemplary embodiments with reference to the attached figures. Show it:

Figure 1 is a schematic representation of the device according to the invention, wherein the in the Drum arranged shaft is shown without the elements for mixing and / or transport;

Figure 2 shows a cross section of the drum with a

Diameter that increases conically;

Figure 3 shows a cross section of the drum with a gradually increasing diameter;

FIG. 4a shows a section of a shaft of the device according to the invention with elements arranged thereon for mixing and / or transporting the solids;

FIG. 4b shows a view of the detail of the shaft from FIG. 4a rotated by 90 °;

Figure 5a shows a section of the shaft of the device according to the invention with elements for

Mixing and / or transporting the solid, which have a different arrangement compared to FIGS. 4a and 4b;

Figure 5b is a view rotated by 90 ° of the shaft

Figure 5a.

characters

6 and 7 diagrams from which the mean residence time and the mean volume flow in

Depending on the speed of the shaft. FIG. 1 shows a device according to the invention for the thermal treatment of flowable or free-flowing solids with a horizontally arranged drum 1 and a shaft 2 arranged therein. According to the invention, the elements for mixing and / or transporting the

Solids arranged, but in the present Figure 1, the illustration has been omitted for reasons of clarity. The reference number 3 generally designates the casing of the drum consisting of heating elements and insulation. Channels 4 lead through this sheathing, which can serve for the introduction of thermocouples and for the gas supply. The channels 4 can also be designed so that they serve at the same time for the introduction of the thermocouples and for the gas supply. A material supply 5 and a material discharge 6 are located at the ends of the drum, the material supply advantageously being carried out from above and the material discharge downwards. A gas discharge 7 is provided at the end of the drum 1 on which the material discharge 6 is arranged. The gas discharge 7 is expediently directed upwards.

Figure 2 shows a cross section of a drum la with a conically changing diameter. The shaft 2 is arranged in the drum axis, elements 8 for mixing and / or transporting the solids being arranged thereon. In the embodiment shown in FIG. 2, the elements 8 for mixing and / or transporting the solids are of different lengths, their length being adapted to the drum diameter.

A further drum 1b is shown in FIG. 3, the diameter of which increases gradually. Here, too, the shaft 2 is arranged in the drum axis. The elements 8 arranged on the shaft 2 for mixing and / or transport The solids also have different lengths in this embodiment, since their lengths are designed in accordance with the drum diameter.

A section of a shaft 2 is shown in FIGS. 4a and 4b. Figures 4a and 4b differ in that in figure 4b the shaft 2 is rotated by 90 ° with respect to that in figure 4a. A screw 9 is arranged on the shaft 2, as can be provided at the end of the shaft 2 for the supply and / or removal of material. The elements 8 for mixing and / or transporting the solids are shown in FIGS. 4a and 4b in such a way that the elements 8 with a surface running parallel to the shaft axis serve for mixing and the elements 8 with a surface oriented at an angle to the shaft axis for transporting the Solids. The transport elements 8 are arranged offset in an ascending spiral by 90 ° (with the shaft turning to the left). Each transport element 8 is opposed to a mixing element 8, ie on each level on which a transport element 8 is arranged there is a mixing element 8 which is offset by 180 ° with respect to the transport element 8. The angle of attack of the transport elements 8 to the shaft axis is indicated in FIG. 4 and was set to 15 ° in the actual exemplary embodiment. The section of the shaft 2 shown in FIG. 1 shows the positions of the transport and mixing elements 8 in exemplary embodiment 1 on the first two thirds. If solids are now transported through the shaft 2 in the device according to the invention, the solids mass moved by the transport elements 8 remains in a zone for three quarters of a turn and is only mixed in the process. Another embodiment of the shaft 2 of the device according to the invention is shown in FIGS. 5a and 5b, in which in turn a screw 9 is arranged on the shaft 2 and is used for supplying and / or removing goods. The representations in FIGS. 5a and 5b differ in that the shaft 2 in FIG. 5b is rotated by 90 ° with respect to the shaft 2 in FIG. 5a. The elements 8 arranged on the shaft 2 for mixing and transporting the solids are arranged in the embodiment shown in FIGS. 5a and 5b such that some of these elements 8 have a surface alignment with respect to the shaft axis with a negative sign, ie with a negative angle of attack.

In the exemplary embodiment 1, the last third (as seen in the conveying direction) of the shaft 2 had such an arrangement of the transport and mixing elements 8. The transport elements were arranged at an angle of attack of 15 ° to the shaft axis and the mixing elements at an angle of attack of minus 10 °.

With this embodiment, that was

Residence time spectrum of the solid measured with the pipe in a horizontal position. During the measurement, the inclination of the shaft was 0 °, the solids throughput was 1650 cm ³ / h, and the shaft rotated at a speed of 2 rpm. and there was a filling level of 21%. From the measured data, an average residence time of 33 min. with a standard deviation of ± 5.5 min. be determined. A curve fitting performed based on the dispersion model or the cell model (described in: Walas, St.M., Chemical Reaction Engineering Handbook of Solved Problems, Gordon and Breach Publishers 1995) a Bodenstein number of Bo = 90 and an equivalent number of cells of n- = 45.

It can be concluded from the numerical values determined that the movement of solids in the device according to the invention has approximately plug flow, which means an approximately identical residence time for all particles. This ensures uniform product quality and is aimed at in all continuous processes, but is often not achieved.

In embodiment 2, the amount of solids was reduced to half at the same speed of the shaft compared to embodiment 1. The inclination of the shaft was 0 °, the solids throughput was 830 cm ³ / h, and the shaft rotated at a speed of 2 rpm. and there was a filling level of 13%. The average dwell time in embodiment 2 was 46 minutes. with a standard deviation of ± 8 min. determined. A curve fitting carried out as in example 1 gave for example 2 a Bodenstein number of 61 and an equivalent number of cells of 31. From this it follows that a reduction in the throughput with a simultaneously decreasing degree of filling slightly increases the longitudinal mixing of the solid, as in the falling values of Bodenstein number and number of cells can be seen.

In exemplary embodiment 3, the shaft was set with an inclination angle of 1 ° (downward inclination in the conveying direction). In exemplary embodiment 3, the following conditions prevailed: inclination of the shaft 1 °, solids throughput 520 cm ³ / h, speed of the shaft 1 rpm, filling level 13.7% which occurs. The measured residence time distribution gave an average residence time of 64 min. and a standard deviation of ± 9 min.

The same shaft 2 with the same settings for the transport and mixing elements 8 as in embodiment 1 was used for the embodiments 2 and 3.

FIGS. 6 and 7 show the relationship between the average dwell time or volume throughput and the speed of the shaft with the degree of filling as parameters, the values being determined using a test device according to exemplary embodiments 1 to 3.

Claims

claims

1. A device for the thermal treatment of flowable or free-flowing solids with a substantially horizontally arranged drum, wherein elements for mixing and / or for transporting the solids are arranged in the drum, characterized in that ß inside the drum (1; la; lb ) a rotatably mounted shaft (2) is arranged and that the elements for mixing (8) and / or transport (8) of the solids are attached to the shaft (2).

2. Device according to claim 1, d a d u r c h g e k e n n z e i c h n e t, that the drum (1; la; lb) is rotatably mounted.

3. Device according to claim 1 or 2, d a d u r c h g e k e n n z e i c h n e t, that the drum has a horizontal inclination of up to + 15 °.

4. The device according to claim 1 or 2, characterized in that ß the diameter of the drum (1) increases conically or gradually in one direction.

5. The device according to one of claims 1 to 4, where the transport and mixing elements (8) are arranged next to one another on a plane running perpendicular to the shaft axis.

6. The device according to claim 4, d a d u r c h g e k e n n z e i c h n e t d ß each a transport and a mixing element (8) are arranged opposite each other on a plane perpendicular to the shaft axis.

7. Device according to one of claims 1 to 4, d a d u r c h g e k e n n e e c h n e t, d a ß exclusively transport or mixing elements (8) are arranged on a plane running perpendicular to the shaft axis.

8. Device according to one of claims 1 to 4, so that only one transport or mixing element (8) is arranged in each case on a plane running perpendicular to the shaft axis.

9. Device according to one of claims 5 to 8, characterized in that ß the different transport or mixing elements (8) each at an angle of approximately ± 15 to ± 345 °, in particular at an angle of ± 15 °, offset from one another Circumference of the shaft are arranged.

10. Device according to one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t d d ß the transport elements (8) to the shaft axis have an inclination angle of approximately ± 5 to ± 30 °, in particular an inclination angle of approximately ± 15 °.

11. Device according to one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t, that at least some of the mixing elements (8) has an inclination angle of about -5 to -30 °, in particular - 10 °, against the conveying direction.

12. Device according to one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t, d a ß the transport and / or mixing elements (8) are individually and independently adjustable in their angle of attack or inclination.

13. Device according to one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t, d a ß the transport and / or mixing elements (8) each independently have different shapes.

14. Device according to one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t, d a ß the transport and mixing elements are curved (8) and / or slotted.

15. Device according to one of the preceding claims, characterized in that ß transport and / or mixing elements (8) are arranged both on the shaft (2) and on the inner wall of the drum.

16. Device according to one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t, d a ß the shaft (2) has a horizontal inclination of approximately ± 5 to ± 15 °.

17. Device according to one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t, d a ß the length of the transport and / or mixing elements (8) is different.