Patent Application
20090286193
The present invention relates to rotary tube furnaces for high temperature treatment of various materials and, more particularly, to an overhung rotary tube furnace.
Rotary tube furnaces within direct heating are commonly used for physical and chemical conversions of both solids and powders. U.S. Pat. No. 6,042,370 discloses a furnace having a graphite tube inside an oxygen free chamber with graphite heating elements capable of heating to temperatures as high as 2800° C. It is known that graphite may be used as one of the construction materials in such furnaces. It is also known that furnaces operating at extreme temperatures frequently require that the treatment of the material being processed be carried out in an inert atmosphere, such as a non-oxidizing atmosphere, to avoid undesired reactions. In addition, when graphite is used as part of the furnace, it may also react with the oxygen and air at extremely high temperatures. Thus, it is known to provide an inert atmosphere enveloping the graphite furnace equipment as well as the material being processed.
With parenthetical reference to corresponding parts, portions or surfaces of the disclosed embodiment, merely for the purposes of illustration and not by way of limitation, the present invention provides a rotary tube furnace (1) comprising an insulated heating chamber (4), the insulated heating chamber having a product discharge outlet (21) and a process tube inlet (39), a heating element (14) operatively arranged to selectively heat the heating chamber, a generally horizontally extending process tube (2) supported for rotation relative to the heating chamber, the process tube having a first portion (36) generally arranged outside of the heating chamber and a cantilevered second portion (37) extending from the first portion into the heating chamber and terminating at a discharge end (38) within the heating chamber, a feed mechanism (40) configured and arranged to feed product into the process tube, and a bearing assembly operating between a support frame (34) and the first portion of the process tube and configured and arranged to support the process tube and transmit rotational torque to the process tube.
The heating chamber may comprise an outer shell (10), a heat conductive muffle (15), and an insulation layer (11) between the outer shell and the muffle. The heating chamber may comprise a gas inlet (16) and a gas outlet (20) operatively arranged to maintain a selected gas atmosphere around the process tube in the heating chamber. The product discharge outlet may comprise a discharge chute (22) and a discharge heating element (25) operatively arranged to selectively heat the discharge chute. The heating element may be operatively arranged to selectively heat the heating chamber to at least 1200 degrees Celsius and the heating element may be operatively arranged to selectively heat the heating chamber to about 2600 degrees Celsius. The heating element may be a graphite resistance heating element or the heating element may comprise an induction coil (30) and a graphite susceptor (31). The process tube may be graphite or quartz. The process tube may comprise a liner (3) and the liner may be quartz or ceramic. The process tube may comprise two or more tube sections. The feed mechanism may comprise a feeder (7) communicating with a feeder tube (6) that extends into the process tube. The feeder tube may extend through the first portion of the process tube and may terminate at a feed discharge end (42) within the heating chamber. The furnace may further comprise an insulating baffle (13) between the feeder tube and the process tube. The feeder tube may comprise a gas port (17) operatively arranged to selectively provide a co-current or counter-current flow of gas through the process tube. The bearing assembly may comprise a drive motor (35), an inner flexible collar (26) extending around the first portion of the process tube, an outer cylindrical member (5) connected to the collar and the drive motor, and a pair of rollers (9) supporting the cylindrical member, wherein the cylindrical member provides counterbalance to the cantilevered second portion of the process tube. The process tube may be inclined from the discharge end to the first portion.
In another aspect, the invention provides a rotary tube furnace comprising a heating zone (48) comprising an insulated heating chamber having a product discharge outlet and a process tube inlet, a heating element operatively arranged to selectively heat the heating zone, a generally horizontally extending process tube supported for rotation relative to the heating chamber and having an feed entrance end (43) and a product discharge end (38), a feed mechanism configured and arranged to feed product into the process tube, a bearing assembly operating between a support member and the process tube and configured and arranged to support the process tube and transmit rotational torque to the process tube, and the process tube and the bearing assembly configured and arranged such that the product discharge end is within the heating zone.
In another aspect the invention provides a rotary tube furnace comprising an insulated heating chamber, the insulated heating chamber having a product discharge outlet and a process tube inlet, a heating element operatively arranged to selectively heat the heating chamber, a generally horizontally extending process tube supported for rotation relative to the heating chamber and having a feed entrance end portion and a product discharge end portion, a feed mechanism configured and arranged to feed product into the process tube, the feed mechanism comprising a feeder communicating with a feeder tube that extends through the process tube inlet of the heating chamber, the feeder tube comprising an end portion that extends into the heating chamber and terminates within the heating chamber, the feeder tube having a thermal barrier (27) at said end portion, and a bearing assembly operating between a support member and the process tube and configured and arranged to support the process tube and transmit rotational torque to the process tube.
One object is to provide an improved rotary tube furnace that provides the materials being processed without premature melting.
Another object is to provide an improved rotary tube furnace that discharges the materials being processed without premature freezing.
Another object is to provide an improved rotary tube furnace that processes materials at high temperatures without the material adhering to the processing equipment.
Another object is to provide an improved rotary tube furnace where material flow is not blocked by undesired material build-up.
These and other objects and advantages will become apparent from the foregoing and ongoing written specification, the drawings, and the claims.
At the outset, it should be clearly understood that like reference numerals are intended to identify the same structural elements, portions or surfaces consistently throughout the several drawing figures, as such elements, portions or surfaces may be further described or explained by the entire written specification, of which this detailed description is an integral part. Unless otherwise indicated, the drawings are intended to be read (e.g., cross-hatching, arrangement of parts, proportion, degree, etc.) together with the specification, and are to be considered a portion of the entire written description of this invention. As used in the following description, the terms “horizontal”, “vertical”, “left”, “right”, “up ” and “down”, as well as adjectival and adverbial derivatives thereof (e.g., “horizontally”, “rightwardly”, “upwardly”, etc.), simply refer to the orientation of the illustrated structure as the particular drawing figure faces the reader. Similarly, the terms “inwardly” and “outwardly” generally refer to the orientation of a surface relative to its axis of elongation, or axis of rotation, as appropriate.
Referring now to the drawings, and more particularly to
As shown in
Thermally insulated heating chamber 4 surrounds the portion of tube 2 being heated with at least one zone of control and at least one element per zone of control. However, while furnace 1 is shown as having a single heating zone, heating chamber 4 may be divided into multiple temperature zones separated by insulation barriers to allow for greater temperature definition. Thus, heating elements 14 may be powered and positioned as desired to provide a constant temperature throughout the heating zone or to provide multiple temperature zones for thermal profiling.
Heating chamber 4 includes a number of ports or vents. Material being processed exits the floor of heating chamber 4 through discharge assembly 21. Discharge assembly 21 comprises a chute heating chamber 24 within a chute insulation enclosure 46. Chute heating elements 25 heat chute heating chamber 24. Discharge chute 22 passes through chute heating chamber 25 and is thus separately heated. A liner 23 may be provided in discharge chute 22 to facilitate movement of material being processed. Accordingly, discharge chute 22 is separately heated to prevent melted material exiting process tube 2 from prematurely cooling and sticking to discharge chute 22 or its liner 23. Discharge chute 22 may feed a solidification unit or some other conventional collection device.
Process tube 2 extends into heating chamber 4 through process tube inlet 39. Process tube 2 is generally a cylindrical graphite or quartz member elongated along axis x-x and adapted to rotate about axis x-x. As shown, process tube 2 extends from the entrance or drive section 47 of furnace 1 into heating chamber 4 of the heating section 48 of furnace 1. While shown as extending horizontally, under normal operating conditions process tube 2 is tilted from horizontal to aid the movement of materials through process tube 2. In addition, while process tube 2 is shown as being formed of a single tubular unit, it may be formed from two or more interconnected sections of tube, depending on various considerations, such as the total length required and the specific requirements of each section of the tube. Also, the materials used to form the sections of tube may vary depending on their position in the furnace, with the sections of tube 2 upstream of insulating plug 13 being metal rather than graphite sections. In the preferred embodiment, tube 2 includes an inner liner 3. In the preferred embodiment, liner 3 is a quartz tube. However, it is contemplated that this inner or second tube may be formed of graphite or ceramic, such as silicon carbide, alumina or mullite, depending on considerations such as the materials being processed. Liner 3 may be a second piece of sacrificial graphite.
As shown in
The length of feeder tube 6 may vary as desired. For example, in the embodiment shown in
As shown, process tube 2 is supported from its entrance end and has a cantilevered portion 37 that extends freely through inlet 39 into heating chamber 4. Thus, heating tube 2 has a first portion 36 generally arranged outside of heating chamber 4 and a cantilevered second portion 37 extending from the first portion through inlet 39 into heating chamber 4 and terminating at a discharge end 38 within heating chamber 4. This provides a number of unexpected benefits. With cantilevered tube 2, furnace 1 is suitable for partially melting material in a continuous feed system without causing premature melting. In addition, because the material is discharged from discharge end 38 of tube 2 into the hot zone of the furnace, the material is discharged without premature freezing. With feeder tube 6, the backflow of heat from heating chamber 4 does not melt material being processed, thereby causing it to stick together or to the walls of process tube 2. Likewise, discharging from cantilevered portion 37 in heating chamber 4 reduces the likelihood of material sticking together or to the tube walls or downstream surfaces, thereby blocking material flow.
As shown in
As shown on
In operation at high temperatures, it is often preferred to maintain a non-oxidizing atmosphere, such as a nitrogen or argon gas atmosphere, in heating chamber 4 and process tube 2. In this embodiment, entrance 43 of process tube 2 is enclosed in, or surrounded by, a chamber for the containment of atmosphere, dust and light. Heating chamber 4, this entrance chamber, and discharge assembly 21 form an enclosure to maintain the selected atmosphere around and within process tube 2. The interior atmosphere of process tube 2 may be controlled by passing a non-oxidizing gas, such as nitrogen for example, through it. If a co-current gas flow is desired, gas is provided through port 17 of feeder tube 6 and exits heating chamber 4 through process vent 20. If counter flow is desired, the direction of flow can be reversed. A counter flow of non-oxidizing gas in discharge chute 22 may also be provided. Furthermore, a non-oxidizing atmosphere may be provided in heating chamber 4 by maintaining a positive pressure of gas through heating chamber 4 using gas passageways 16 into heating chamber 4. In addition, a desired atmosphere may be provided in feed mechanism 41 using inlet 18 in hopper 12. Similarly, a desired atmosphere in entrance or drive section 47 may be provided through drive area gas port 19. Thus, multiple alternate atmospheres and alternate current flows may be employed in furnace 1.
Overhung graphite rotary tube furnace 1 may be used to process various types of feed material, including particulate material. For example, furnace 1 may be used to process silicon particulate material, with the silicon particulate material melting inside quartz lined process tube 2 and exiting through discharge assembly 21 as a liquid. Furnace 1 is generally suitable for the treatment of particulate material which melts at temperatures as high as 2600° C. The preferred temperature range of furnace 1 is from about 1200° C.-2200° C. For silicon processing the preferred temperature is about 1500° C. and the material may be fed directly into the heated and cantilevered section 37 of processing tube 2 to melt.
The present invention contemplates that many changes and modifications may be made. Therefore, while the presently-preferred form of the improved furnace has been shown and described, and a number of alternatives discussed, persons skilled in this art will readily appreciate that various additional changes and modifications may be made without departing from the spirit of the invention, as defined and differentiated by the following claims.
This application claims the benefit of U.S. Provisional Patent Application No. 61/127,423, filed May 13, 2008. The entire content of such application is incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 61127423 | May 2008 | US |
