US20040093759A1

US20040093759A1 - Method and device for the thermally treating a material in pulverulent or granulate form

Info

Publication number: US20040093759A1
Application number: US10/398,181
Authority: US
Inventors: Michael Witt; Thomas Kessler; Karl-Peter Farwerck; Kaspar Evertz
Original assignee: Basell Polyolefine GmbH
Current assignee: Basell Polyolefine GmbH
Priority date: 2000-10-13
Filing date: 2001-10-10
Publication date: 2004-05-20
Also published as: WO2002030555A1; WO2002030555A9; AU2002215934A1; CN1630550A; EP1330304A1; DE10050720A1; JP2004518931A

Abstract

The invention relates to a process and an apparatus for the thermal treatment of powdered or granular solid substances with gas flows (7, 16, 22, 23, 24) by means of a body (2) moved about its axis of rotation (1). In this process, the following process steps are successively carried out:

Firstly, the bulk material held in segments (3) of the moved body (2) is heated by subjecting it to steam (22). Then, the heated bulk material is exposed to a feed of air (23) and/or inert gas (24), taking place in one or more subsequent steps. Finally, removal (17) of the dried or inerted bulk material from the segments (3) of the body (2) moved about its axis of rotation (1) takes place.

Description

The invention relates to a process for the thermal treatment of powdered or granular solid substances by means of gas flows using a body which can move about an axis of rotation.

In many technical processes it is necessary to heat a powdered or granular material. It is particularly cost-effective to use for this the supply of steam which is usually available in production plants and generally represents a particularly low-cost source of energy, in particular in comparison with electrical energy. For heating powdered or granular material, bulk-flow heat exchangers are known, which heat up the product purely by means of heat conduction. The surface areas required for heat conduction are relatively large, so that bulk-flow heat exchangers are of a large overall size and accordingly take up considerable space.

Another possible way of heating up powdered or granular material is to use heated mixers, it being possible for both the surfaces of the housing of a heated mixer and the mixing implements themselves to be heated. On account of the rapidly renewing contact surface, significantly better heat transfers are achieved here in comparison with the bulk-flow heat exchanger, so that altogether smaller overall sizes of apparatus can be achieved. The disadvantage of heated mixers is to be seen in the fact that a not inconsiderable effort has to be devoted to the design of the mixer drive, the control system and the transporting of the product to and from the mixer, so that, for example, retrofitting of existing extrusion systems and extrusion lines is generally not possible or can only be accomplished with considerable effort. If steam is introduced directly for drying or conditioning a powdered or granular solid substance, rapid heating is achieved on account of the high heat of condensation. If, moreover, when heating with steam, saturated steam is used, local overheating of the powder or granules to be heated, and consequently damage to them, can be reliably avoided. The disadvantage of using steam as a temperature control medium can be seen in the fact that the condensate produced can be removed again only with relatively great effort. Therefore, using steam for the selective heating of powdered or granular solid substances, for example pourable solid polymer substances, has so far generally only been possible in those technical processes in which the resulting residual moisture in the heated product does not entail any serious disadvantages in the process steps following the heating process. Subsequent treatment of the heated product to remove the residual moisture would constitute a subsequent step involving considerable effort.

In view of the commonly used processes for drying powdered or granular solid substances and the cited disadvantages accompanying the existing processes, it is an object of the invention to achieve a way of conditioning powdered or granular solid substances which allows both solid substances in which remains of oxygen can stay in the product to be processed and solid substances in which no remains of oxygen can stay in the product to be processed to be directly conditioned by the direct feeding in of steam.

According to the invention, this object is achieved in the case of a process for the thermal treatment of powdered or granular solid substances with gas flows by means of a body moved about an axis of rotation by successively proceeding through the following process steps:

heating the bulk material held in segments of the movable body by subjecting it to steam,

exposing the heated bulk material to a feed of air and/or inert gas, taking place in one or more subsequent steps,

removal of the dried or inerted bulk material from the movable body.

The advantages of the process proposed according to the invention are to be seen in particular in that the product throughput can be specifically set by means of the body moved about its axis of rotation, which contains segmentally configured cells, by automatically controlling the speed of the moved body about its axis of rotation. The moved body is preferably a single cellular wheel containing chambers arranged separately from one another, the chambers of which are open in the radial direction. On account of the very small resultant overall size of the moved body and the substitution of an existing metering device, the process proposed according to the invention can be integrated without any problem as a retrofitting measure into extruding lines or extruding machines in already existing process sequences. In this case, it is immaterial whether the body moved about its axis of rotation is driven in horizontal arrangement or the body moved about its axis of rotation is driven in vertical arrangement.

In an advantageous development of the process proposed according to the invention, in the case of vertical arrangement of the body moved about its axis of rotation, the individual segments of the body of rotation are charged and emptied via the outer circumference. Not only the steam, in particular saturated steam, but also air and an inert gas, for example nitrogen, can be introduced into the individual segments or chambers via the outer circumference of the moved body. For charging with steam, a perforated segment may be provided for example at the outer ring of the body moved about its axis of rotation, designed as a cellular wheel.

According to one implementational variant of the process proposed according to the invention, the bulk material, whether in powdered or granular form, can be fed to the individual segments of the cellular wheel at the outer ring of the moved body, and can be emptied from the individual segments of the body moved about its axis of rotation via the outer ring after almost one revolution. During the operation of a moved body, divided into individual segments, it is possible for both the bulk material to be fed in from the outer circumference and for the air entering from outside to be fed in from outside the moved body. In an advantageous way, both the steam and the gas flow entering via the outer surface can be removed from the individual segments via lines formed in the hub of the cellular wheel. The flow of steam introduced at the outer circumferential surface of the cellular wheel can be collected, together with its content, after it has condensed and flowed through the cells, at the hub of the cellular wheel and from there can be removed from the vane-type cellular wheel via a discharge line running coaxially in relation to the axis of rotation.

In a way assisting the emptying of individual segments of the cellular wheel rotating about its axis of rotation in vertical arrangement, a gas flow, for example a flow of nitrogen, can be introduced from the hub of the cellular wheel rotating about its axis of rotation in vertical arrangement. In the inert-gas supply line, running coaxially in relation to the axis of rotation of the cellular wheel, nitrogen flows from the hub of the cellular wheel, rotating about its axis of rotation, into the individual segments, flows through the bulk material present there and, as a result of the chosen direction of flow from the inside outward, assists the discharge of product at the product discharge point from the individual segment chambers of the cellular wheel. After the individual segment cells on the cellular wheel have been completely emptied, said wheel rotates, for example clockwise, in the direction of the product feed, so that the cells respectively passing the product feed can be charged once again with product to be treated.

To ensure the supply of powdered or granular solid substance into the individual segments of a cellular wheel moved about its horizontally oriented axis of rotation, a bulk-material feed is assigned to the outer circumference of such a cellular wheel. According to an advantageous implementational variant of the process proposed according to the invention, the moved body can also be operated in horizontal arrangement, so that it is possible to subject the bulk material respectively held in the segments to gas flows parallel to the axis of rotation of the body turning about its axis of rotation. In the case of a cellular wheel feeder configured in such a way and operated horizontally, the gases preferably enter the bulk fill from above and flow downward. As this happens, it is possible in an advantageous way for the moisture to be separated out, assisted by the force of gravity. If, in the case of a moved body operated in horizontal arrangement, the individual segments are charged with bulk material, stationarily arranged lines are provided not only for the bulk material but also for the steam, or else in particular for gases or inert gases, and a stationary removal line is provided. The individual segments formed on the moved rotating body configured as a cellular wheel (for example as a vane-type cellular wheel) may be provided in alternating succession with covering surfaces. The covering surfaces can be optionally provided. The alternating succession of the covering surfaces may be chosen differently on the base and on the cover of the cellular wheel operated in horizontal configuration, for example as an inlet or outlet for the bulk material, as covering surfaces without gas passage arranged segmentally in alternating arrangement and segment surfaces permitting gas passage, for example perforated segment surfaces. If a vane-type cellular wheel; is used as the moved body, segments configured in the form of pieces of a pie which are separated from one another by separating walls are produced.

In an advantageous refinement of the process proposed according to the invention, solid substances can be treated in a movable body subdivided into individual cells by segment walls as a cellular wheel in such a way that it is quite possible for remains of oxygen to stay in the solid substance without disturbing further processing. In this variant of the process, the drying can be assisted predominantly by the access of air, so that one air access on the cellular wheel moved about its axis of rotation (in horizontal arrangement) is sufficient.

If, on the other hand, polymers are being processed, for example in the compounding of polyethylenes, where the content of residual oxygen is often a problem and is enormously disruptive in further processing, conditioning of the bulk material contained in the segments of the moved body configured as a cellular wheel takes place by means of steam to heat it up, followed by inerting of said material with inert gases. To facilitate the passage of the gas, while the bulk material is to stay in the segments, the outlet surfaces, and possibly the access surfaces, are formed as a perforated grid arrangement.

The process proposed according to the invention can consequently be used both in the case of solid substances in which a content of residual oxygen may stay and can be carried out equally well on powdered or granular solid substances for which a remaining content of residual oxygen in the solid substance is critical. Allowance is made for this by the number of air or inert-gas inlets or outlets on the cellular wheel, which may be provided as an exemplary embodiment of a moved body.

According to the invention, the object is also achieved by an apparatus for the thermal treatment of powdered or granular solid substances with gas flows by means of a body which can be moved about its axis of rotation and comprises individual segments, coverings which allow bulk material or a gas flow to enter or leave being provided segmentally in the cover and base of the movable body.

A rotating apparatus provided with an external drive allows the product throughput to be set and influenced individually according to the requirements of the installation, for example for supplying raw material to an extruder. The moved device, which is designed such that it rotates about its axis of rotation, whether in vertical arrangement or in horizontal arrangement, may be configured as a cellular wheel, it being possible for the hub of the cellular wheel to have discharge lines for steam condensate and gas and supply lines for gas to assist the emptying of the individual segments over the circumference of the cellular wheel acting as the moved body.

The invention is explained below with reference to the drawing, in which: [0019]
FIG. 1 shows a side view of a moved body operated in vertical arrangement with a product feed and product discharge and a gas feed via the outer circumferential surface, [0020]
FIG. 1[0021] a shows a vane-type cellular wheel,
FIG. 2 shows a cellular wheel arrangement, shown in a perspective representation, with an assigned charging chute, [0022]
FIG. 3 shows a cellular wheel operated in horizontal orientation, rotating about its axis of rotation, with schematically depicted bulk material inlet and outlet and steam or inert-gas feed lines, in stationary arrangement, [0023]
FIG. 4 shows a configuration of the cover of a cellular wheel for drying predominantly with air and subsequent inerting, [0024]
FIG. 4 shows the configuration of the base of a moved body for drying with air according to FIG. 4, with perforated surfaces permitting gas passage and covering segments, [0025]
FIG. 6 shows a configuration of the cover of a cellular wheel acting as a moved body for heating and optionally inerting the product, [0026]
FIG. 7 shows the configuration of the base part of a cellular wheel belonging to the configuration of the base according to FIG. 6. [0027]
The representation shown in FIG. 1 illustrates more closely a side view of a cellular wheel operated in vertical orientation. [0028]
FIG. 1 shows a [0029] cellular wheel 2 rotating about an axis of rotation 1, for example rotating in the clockwise direction 26 about the axis of rotation 1.
The [0030] cellular wheel 2 is subdivided into individual cellular wheel segments 3, the individual segments 3 being formed by segment walls 6 extending from the hub of the cellular wheel 2. The segment arc of a segment is represented by way of example by the designation 3.1. In this configuration, the charging and emptying of the individual segments 3 takes place via the outer circumference, at which both a bulk material feed 4 and a bulk material discharge 5 are indicated in a schematic way, along with a steam inlet 16. The charging of the individual segments 3 of the cellular wheel 2 takes place via the mentioned feed and discharge locations, it being possible for outlet lines for steam condensate occurring or air-discharge lines to be provided coaxially in relation to the axis of rotation 1 in the region of the cellular wheel hub.
While the bulk material can, for example, be fed into the [0031] individual segments 3 of the cellular wheel 2 via the bulk material feed 4, an inert-gas flow generated from the inside radially outward can be produced in each segment 3 of the cellular wheel 2 via a feed line for inert gas likewise running coaxially in relation to the axis of rotation 1 of the cellular wheel 2. In an advantageous way, this direction of inert-gas flow outward in the radial direction can be set directly before or during the time at which the segment arc 3.1 of a segment 3 containing bulk material being treated lies opposite a product discharge 5. At this time, the emptying of the respective segment 3 of treated bulk material is assisted by the inert-gas flow taking place from the inside outward, so that complete emptying of said segment can be ensured. With further turning of the cellular wheel 2 about its axis of rotation 1 in the clockwise direction, untreated bulk material can be newly fed into a segment cell of the cellular wheel 2 emptied in this way, via the bulk material feed 4, entering the emptied cell 3 via the segment arc 3.1.
Once bulk material has been fed in via the [0032] bulk material feed 4, charging with air or an inert gas 23, 24 can take place via the outer ring at the respective segments 3 containing bulk material to be treated by passing the steam inlet 16, the opening of which extends only over a fraction of the segment arc 3.1. Steam 16 or condensate occurring is led away through the mentioned outlet line 8 running coaxially in relation to the axis of rotation 1. An air feed 23, which may optionally be provided, can likewise take place on the outer side of the cellular wheel 2 via the outer surfaces (segment arc 3.1) of the respective segments 3 of the cellular wheel 2. The air flowing from the outside inward, which dries the bulk material contained in the individual segments 3, can likewise be led away from the individual segments 3 via the discharge lines provided in the region of the cellular wheel hub.
By contrast with this, the direction of the inert-gas flow [0033] 9 through the individual cells 3 containing bulk material being treated, i.e. heated and dried bulk material, can be set in the way already mentioned above, so that complete emptying of the individual segments 3 of the cellular wheel 2 opposite the bulk material discharge 5 can be achieved by the inert-gas flow 9 running from the inside outward through the segments 3. FIG. 1a shows the schematic representation of a vane-type cellular wheel.
The vane-type [0034] cellular wheel 2, which is rotatable about its axis of rotation 1 and is preferably used as the moved body, rotates in relation to a bounding surface (not represented here). If fitted in vertical arrangement 28, it rotates with respect to two laterally arranged, stationarily mounted bounding surfaces; if in horizontal arrangement 29, in relation to a base surface and cover surface. With the vane-type cellular wheel in horizontal arrangement as shown in FIG. 1a, an upper covering may be provided, but this is not absolutely necessary. The individual segments 3, open in the region of the segment arc 3.1, are separated from one another by segment walls 6. In the configuration shown in FIGS. 1 and 1a, the direction of rotation of the vane-type cellular wheel 2 used as the moved body corresponds to the clockwise direction; however, with appropriate adaptation of access and outlet surfaces, the direction of rotation can also be reversed.
The perspectively reproduced FIG. 2 illustrates more closely a [0035] cellular wheel 2 in vertical arrangement 28, which is rotatable about its axis of rotation and is charged with bulk material via its outer circumference by means of a bulk material feeding device 10, reproduced in schematic configuration. Although not represented here, above the bulk material chute there is a stock of bulk material, providing a continuous supply of bulk material at the bulk material feeding device 10. The opening of the bulk material chute can be adapted in an advantageous way to the outer curvature of the circumferential surface of the cellular wheel serving as the rotating body 3, and can pass with its opening region 13 over just a fraction of the segment arc 3.1 of a segment 3 of the cellular wheel 2 respectively to be filled or charged. On the other hand, the opening may also pass over the entire segment arc 3.1 between two adjacent segment walls 6.
The bulk material removal point (not represented in any more detail here). is denoted by the designation [0036] 5 (cf. representation shown in FIG. 1).
With [0037] vertical arrangement 28 of the cellular wheel 2 acting as the moved body, the bulk material discharge 5 is preferably located on the underside, to ensure along with the inert-gas flow 9 running in the radial direction from the inside outward through the individual segments 3, an emptying of the individual product-containing cells 3 of the cellular wheel 2 assisted by the force of gravity.
The representation shown in FIG. 3 illustrates more closely in a schematic arrangement a [0038] cellular wheel 2 operated in horizontal orientation. The body configured as cellular wheel 2 and rotating in the clockwise direction 26 about the axis of rotation 1 contains individual segments 3, which are separated from one another by means of segment walls 6 extending in a star-shaped manner via the hub. The height of individual segments 3 of the cellular wheel 2 is indicated by the designation 18. In the upper part of FIG. 3 is the cover system of the cellular wheel 2, which is not represented in any more detail here but is explained more fully further below and, with horizontal arrangement 29, may be optionally provided. In particular the perforated segments allowing gas access are in this case optionally provided. On the underside there is the base region of the cellular wheel 2, which is not represented in any more detail in FIG. 3 but is configured more precisely in FIGS. 5 and 7. The bulk material feed running parallel to the axis of rotation 1 according to the representation in FIG. 3 is indicated by the designation 4. At this location, the powdered or granular bulk material to be treated is introduced into the individual segments 3 of the cellular wheel 2. According to the representation in FIG. 3, a cellular wheel 2 is provided, from which a product discharge, indicated by the designation 17, takes place into a further processing unit (not represented here), an extruder for example. The segment 3 of the cellular wheel 2 that has just been filled with powdered or granular bulk material to be treated rotates according to the representation in FIG. 3 in the clockwise direction 26 about its axis of rotation 1 oriented in the vertical direction. The bulk material respectively contained in the segment cell 3 is heated by the steam feed into the corresponding segment 3 provided in stationary form by designations 16 and 22.
After the feeding of steam to heat the stock of bulk material held in the corresponding [0039] segment 6, drying takes place. The steam feed, inert-gas feed and an air inlet which may optionally be provided can be provided in a stationary manner on the upper side of the cellular wheel 2. It is particularly preferred to carry out the introduction of steam at the segment surfaces configured like pieces of a pie. With the configuration of the moved body operated in horizontal arrangement 29, in the form of the cellular wheel 2, the gas outlet takes place on the underside of the cellular wheel 2. For this purpose, the base region of the cellular wheel 2 shown in FIG. 3 is provided with surfaces allowing gas passage—although not represented in any more detail here.
The representation shown in FIG. 4 illustrates more closely the cover region of a [0040] movable body 2, which is designed as a cellular wheel and essentially serves for drying the powdered or granular solid substance with air.
An optional cellular wheel cover, denoted by the [0041] designation 19, is subdivided in a way according to the representation from FIG. 3 into individual segments 3 by segment walls 6. The product feed to be carried out into the segment 3 is denoted by the designation 4, while the adjacent segment 3, seen in the clockwise direction 26, is closed by a fixed covering 21. The segments 3 appearing as white areas in FIG. 4 represent the segments 3 of the cellular wheel 2, which moves about its axis of rotation 1, mounted in vertical arrangement, in the clockwise direction 26.
Accordingly, solid substance can enter the [0042] segment 3 through the opening of the corresponding segment 3 exposed at 4. In the segment 3 alongside in the clockwise direction 26, the bulk material does not undergo any treatment; in the adjoining segment 3, seen in the clockwise direction 26, steam feeding 22 takes place. The outer arc of the segment 3 is denoted by the designation 3.1. Once steam feeding has taken place, i.e. heating of the stock of bulk material respectively held in the segment 3, the bulk material is fed to an air feed 23, whereby drying takes place.
In FIG. 4, reproducing the [0043] cover region 19 of a cellular wheel 2, the inert-gas feeds are designed as stationarily arranged nitrogen lines 24 and denoted by the designation 24.
In the example represented here of a [0044] cover configuration 19 of a cellular wheel 2, two adjacent segments 3 are open to permit inert gases, such as for example CO₂, to pass through. The white area signifies a corresponding opening or a plate permitting gas passage.
It is obvious that, depending on the nature, heating requirement, degree of moisture and grain size of the powdered or granular bulk material, steam feeding can be carried out at a plurality of [0045] segments 3 and air feeding, assisting the drying, can be carried out at individual segments 3.
The segment surfaces allowing inert-[0046] gas feeding 24 and, here in the representation shown in FIG. 4, lying next to one another in the lower region, of which only 2 are represented here, may also extend over more than 2 segments 3 of the cellular wheel 2.
The representation shown in FIG. 5 illustrates more closely the base region of a [0047] cellular wheel 2, which primarily serves for the drying of a solid substance by feeding air, it being quite permissible for remains of oxygen still to be present in the solid substance to be dried with no adverse effect on the further processing of the solid substance. The segment 3 at which the bulk material held in the segment 3 has undergone a complete treatment cycle during a revolution of the cellular wheel 2 in the clockwise direction 26 of its axis of rotation 1 and leaves the segment 3 at this location is denoted by the designation 17. The product discharge from the respective segment 3 is denoted by the designation 17.
Depending on the design of the cover configuration with respect to passage openings and coverings of the [0048] individual segments 3 holding the bulk material, the base of a cellular wheel 2 serving as the moved body is provided both with a gas passage and with a solid plate 25, preventing bulk material passage, per segment 3, whereas the representation shown in FIG. 5 illustrates that individual segments 3 may be provided with a perforated base or base arranged in the form of a grid, which although it holds back the bulk material in the individual segments 3, which are separated from one another by the indicated segment walls 6 of the cellular wheel 2, readily allows steam, inert gas and drying air to pass through. In this way, moist air for example can leave the cellular wheel 2 downward, parallel to the axis of rotation 1, and steam condensate can be driven out of the individual segments 3 from the bulk material present in the latter. With the segments 3 closed by a solid base surface 25 in the shape of a plate part configured in the form of pieces of a pie, it is not possible for gas to leave downward parallel to the axis of rotation 1 of the cellular wheel 2. The dwell time of the bulk material to be conditioned is a function of the speed of the vane-type cellular wheel 2 about an axis of rotation 1. With given dimensioning of the cellular wheel 2, the effectiveness with respect to heating and drying by the volumes of gas passed through can be varied.
Presented in the representations shown in FIGS. 6 and 7 are configurations of a movable body allowing the treatment of granular or powdered solid substances which, after the treatment, must not contain any disturbing remains of oxygen which could adversely affect further processing. This may be a problem, for example, during the compounding of polyethylenes; in particular whenever the products have been pneumatically conveyed with air and, as a result, have a high oxygen content. [0049]
As distinct from the cover and base configurations according to the configurational variants in FIGS. 4 and 5, in the configurational variants shown in FIGS. 6 and 7 a greater proportion of [0050] segments 3 on the cellular wheel 2 are subjected to nitrogen inert-gas inlets 24.1, 24.2, 24.3 and 24.4, whereas there is no air feeding at all in the individual segments according to the cover configuration 19 in FIG. 6.
Accordingly, only the inert gas, for example nitrogen, fed in at [0051] 4 segments 3 on the circumference of the cellular wheel 2 serves for drying, since separate feeding of air according to the cover configuration in FIG. 4 would further increase the oxygen content of the granular or powdered solid substance, which is specifically not desired.
Accordingly, the base side according to the representation from FIG. 4 of a [0052] cellular wheel 2 used in such a way is also differently designed in comparison with the representation of the base region shown in FIG. 5. In the case of the base region represented in FIG. 7, the bases of the individual segments 3 are designed specifically in such a way that the bulk material stays in them, but inerting of the bulk material contained in them remains possible. The base designed in the form of a grid or wire mesh, or else perforated, on the one hand allows retention of the bulk material to be conditioned in the segments 3 of the cellular wheel 2; on the other hand, the openings provided in the base allow gas passage to be achieved. The representation shown in FIG. 7 illustrates that individual base segments 27.1, 27.2, 27.3, 27.4, 27.5, 27.6 and 27.7 lie next to one another in the direction of rotation 26, i.e. in the clockwise direction. At 17, the product discharge, which takes place parallel to the axis of rotation 1 of the cellular wheel 2 and at which the product leaves the segments 3 of the cellular wheel 2, is possible. With a cellular wheel 2 operated in such a way in horizontal arrangement 29, oxygen can be driven out of the granular or powdered solid substance very efficiently by introducing steam directly at the cover side 19 of the cellular wheel 2 and by subsequent feeding in of inert gas at a plurality of locations lying one behind the other.
The driving out of oxygen is necessary for example to prevent degradation to the greatest extent. A low oxygen content in the feed flow and in the polymer melt means a higher-grade product, which can for example be given a higher quality classification with regard to the yellowness index. [0053]
Along with a significant improvement in product quality in the case of extrusion where a material fed in only comes into contact with oxygen, for example in the case of pneumatic feeds, the process proposed according to the invention has still further advantages: [0054]
1. [0055]
A large part of the energy to be introduced into the product to be processed by heating can be saved at the extruder with respect to the electrical energy to be fed to it. Since steam is generally available at production sites, a considerable reduction in the feeding in of energy at the extruder is obtained. [0056]
2. [0057]
With the same product throughputs on the extruders, less electrical energy is required for preheating the polymer granules; the mechanical loading of the extruder is reduced. This means advantages-with regard to the service life of the extruder and advantages with regard to maintenance cycles. [0058]
3. [0059]
In the event that the mechanical drive power available for the extruder represents a constraint on a planned increase in throughput, the material throughput can be significantly increased. [0060]
On the basis of an example, process parameters obtained and the dimensioning of a cellular wheel configured according to the invention are explained in more detail below: [0061]
With a mass flow of 6 t per hour of polyethylene granules and an assumed rotational speed of the cellular wheel of one revolution per minute, a throughput through the [0062] cellular wheel 2 of 100 kg of polyethylene granules per minute is produced. 10 segments or chambers 3 are assumed per cellular wheel 2, i.e. each segment holds approximately 10 kg of polyethylene, i.e. a volume corresponding to 20 l. The total volume of the cellular wheel 2 must therefore be designed for a capacity of 200 l of material.
Assuming a [0063] cellular wheel 2 with a diameter of 1.5 m, which corresponds to a surface area of 1.76 m², an overall height 18 of the cellular wheel 2 of approximately 11.3 cm is obtained.

For the heating of the polyethylene granules or the granular or powdered bulk material from 20 to 100° C., 0.5 t of steam per hour is required, which corresponds to approximately 800 m ³per hour. It follows from this that a throughput of 13 m³per minute through the cellular wheel 2 can be obtained. This corresponds to a volumetric flow of 200 l of steam per second. At an assumed flow velocity of the steam of approximately 4.5 km/h, an average dwell time of the powdered or granular material in the steam flow of approximately 6 seconds is obtained.



1		Axis of rotation
2		Cellular wheel
3		Cellular wheel segment
3.1		Segment arc
4		Bulk material feed
5		Bulk material discharge
6		Segment wall
7		Air inlet
8		Outlet
9		Direction of inert-gas flow
10		Bulk material feed chute
11		Bulk material stock
12		Bulk material outlet
13		Opening region
14		Cellular wheel width
15		Extent of outlet opening
16		Steam inlet
17		Bulk material removal
18		Cellular wheel height
19		Cellular wheel cover
20		Cellular wheel base
21		Closed segment
22		Steam feed
23		Air feed
24		Inert gas feed
24.1
24.2
24.3	{close oversize brace}	Inert gas segments
24.4
25		Plate
26		Direction of rotation
27		Perforated segment bases
27.1
27.2
27.3
27.4	{close oversize brace}	Gas outlet segments
27.5
27.6
27.7
28		Vertical arrangement
29		Horizontal arrangement

Claims

We claim:

1. A process for the thermal treatment of powdered or granular solid substances with gas flows (7, 16, 22, 23, 24) by means of a body (2) moved about an axis of rotation (1), with the following process steps to be successively carried out:

heating the bulk material held in segments (3) of the body (2) by subjecting it to steam (22),

exposing the heated bulk material to a feed of air (23) and/or inert gas (24), taking place in one or more subsequent steps,

removal (17) of the dried or inerted bulk material from the moved body (2).

2. A process as claimed in claim 1, wherein the segments (3) of a moved body of rotation (2) operated in vertical arrangement (28) are charged/emptied via the outer circumference of said body.

3. A process as claimed in claim 2, wherein bulk material is fed to the segments (3) at the outer ring of the moved body (2) and said segments are emptied at the outer ring of the movable body (2).

4. A process as claimed in claim 1, wherein inert gases (24) and/or steam (16, 22) laterally enter the segments (3) of the body (2) moved about its axis of rotation (1).

5. A process as claimed in claim 2, wherein the entry of steam and air (7) takes place at the outer circumference of the movable body (3).

6. A process as claimed in claim 5, wherein steam, air and inert gas leave at the hub (8) of the moved body (2) in the radial direction after flowing through the segments (3).

7. A process as claimed in claim 2, wherein the segments (3) are subjected to gas in the radial direction (9) from the inside outward.

8. A process as claimed in claim 2, wherein a bulk material feed (10, 11, 12) is assigned to the outer circumference of the body (2) for supplying the segments (3) of the body (2).

9. A process as claimed in claim 1, wherein the segments (3) of a moved body (2), operated in horizontal arrangement (29), are subjected to gas flows (4, 16, 22, 23 and 24) parallel to the axis of rotation (1) of the moved body (2).

10. A process as claimed in claim 9, wherein the moved body (2) is provided on the cover side (19) with surfaces (25) covering the segments (3) in alternating succession.

11. A process as claimed in claim 9, wherein the moved body (2) is provided on the base side (20) with segments (3, 17) with an outlet for the treated bulk material and segmentally arranged covering surfaces (25) and also with segment surfaces (27) permitting gas outlet.

12. A process as claimed in claim 9, wherein, in horizontal arrangement (29) of the moved body (2), the driving out of moisture in the direction parallel to the axis of rotation (1) is assisted.

13. A process as claimed in claim 9, wherein the bulk material held in the segments (3) undergoes drying by air (7, 23) with a permissible residual oxygen content of the bulk material.

14. A process as claimed in claim 9, wherein the bulk material to be freed of oxygen is inerted by direct introduction of steam (22) and feeding in of inert gas (24).

15. An apparatus for the thermal treatment of powdered or granular solid substances with gas flows (7, 16, 22, 23, 24) by means of a cellular wheel (2) which is moved about its axis of rotation (1) and has individual segments (3), wherein coverings (21, 25, 27) which allow bulk material or gas flows (22, 23, 24) to enter or leave are provided segmentally in the cover (19) and base (20) of the moved cellular wheel (2).

16. An apparatus as claimed in claim 15, wherein the moved body (2) is designed as a cellular wheel which is movable about its axis of rotation (1) and discharge lines (8) for steam condensate and air and supply lines for inert gas to assist the emptying of the segments (3) are provided in the hub of the cellular wheel.

17. An apparatus as claimed in claim 15, wherein a cover (19) allowing stationary gas access and the access of bulk material is mounted above the cellular wheel (2) rotating about its axis of rotation (1), and a stationary cover (20) with bulk material removal (17) and segments (27) allowing gas passage is mounted below the cellular wheel (2) rotating about its axis of rotation (1).

18. An apparatus as claimed in claim 15, wherein the segments (3) of the moved body (2) are flowed through in the vertical direction.

19. An apparatus as claimed in claim 15, wherein the segments (3) of the moved body (2) are flowed through by steam, air, inert or drying gas from the outside inward or from the inside outward.