Patent GB-786170-A (GB)
Title: Processes for treating fusible material
IPC: B01J6/00
Filed: 1954-12-07
Abstract: <PICT:0786170/III/1> <PICT:0786170/III/2> <PICT:0786170/III/3> <PICT:0786170/III/4> <PICT:0786170/III/5> <PICT:0786170/III/6> A process of treating a fusible material comprising at least two ingredients in a column includes the steps of causing alternately spaced molten and solid regions in the material to progress in one direction from one end of the column to the other, removing from at least one end of the column an amount of treated material less than that contained in a molten region each time a molten region reaches that end and adding at a point in the column an amount of feed material equal to the amount of treated material removed. The removal of the treated material may form a void in the material in the column, which void is filled with feed material. The process is particularly applicable to the redistribution of ingredients in solvent-solute systems, e.g. semi-conductor materials such as silicon containing conductivity-determining impurities.  An apparatus for treating such solvent-solute systems by the process is shown in Fig. 3 and comprises a column 13 containing the material to be treated, vertically movable heaters 14 forming molten regions 14a and solid regions 15 in the material, a feed inlet 17 and a re-entrant product outlet tube 121.  If the column is to be used as an enriching section, i.e. the product is to be richer in solvent, the heaters are moved continuously upwards and continuously moving voids 16 are formed in the material by the intermittent discharge of product from the tube 121.  If the column is to be used as a stripping section, i.e. the product is to be richer in solute, the heaters are moved continuously downwards and intermittently moving voids are formed in the material by the intermittent discharge of product from the tube 121.  The voids may be evacuated or contain material of lower specific gravity than the treated material in which case the void motion is upwards or the voids may contain material of higher specific gravity than the treated material in which case the void motion is downwards and the feed inlet is located below, and not above as shown, the product outlets.  Instead of the heater motion being continuous, the heaters may be moved in one direction for an integral number of heater lengths and then returned to their original position at such a rate that the state of the material in the column is substantially unchanged.  This type of heater motion forms the subject-matter of Specification 786,171.  Fig. 4A shows a column comprising an enriching section 18 and a stripping section 19 fed from a common feed tank 122 in which the heater motion is of this type.  Fig. 5 shows an inverted Y-shaped column forming enriching and stripping sections fed from a common feed tank 42 and having void generators 38, 39.  The heaters 34 are attached to a continuously rotating member 35.  Alternatively the heater motion may be of the reciprocating type.  Fig. 9A shows a spiral-type column comprising an enriching section 81 and a stripping section 80 both fed from 82 and both rotated in the same direction as shown by the arrows.  Void generators (not shown) are fitted to the outer ends of the sections. A stationary heater 85 is fitted behind the enriching section and another stationary heater 85a is fitted in front of the stripping section.  Other positions for the heaters, according to the "hand" of the spirals and their direction of rotation, are also referred to. The spiral-type column may also be in the form of a drum having a spiral ramp between inner and outer concentric cylinders.  A drum-type enriching section formed by concentric cylinders 92, 93 with a spiral ramp (not shown) between them is shown in section in Fig. 10.  The heater is in the form of a heating bath 88, an outlet tube 90 fixed with respect to the drum constitutes the void generator and the drum is rotated in a counter-clockwise direction.  A drum-type stripping section is shown in Fig. 11B, the heating bath in this case being replaced by a stationary heater 96 and the drum being rotated in a clockwise direction. Many forms of tube void generators are described and it is also stated that the void generators may be in the form of valves or separate, stationary heating windings actuated by the moving heaters.  If a normally liquid material is to be treated the heaters may represent positions not occupied by cooling elements.