CRYSTAL REFINING APPARATUS

Abstract: A crystal refining apparatus of a vertical type, wherein a plurality of screw vanes are provided, the screw vanes have crystal refining tubes rotating in directions opposite to each other, and contained solid crystalline materials are refined and transferred upwardly. The apparatus provides a high reflux ratio of quantity of an impurity-containing separated solution to the flow rate of the solid crystalline materials thus obtaining a highly pure product. Chambers for removing the impurity-containing separated solution are provided for removing the impurity containing separated solution at the bottom ends and/or the sides of the crystal refining tubes, this or these chambers for removing the impurity-containing separated solution have means for connecting the chambers to a depressurized line, thereby offering a high reflux ratio.

Description: BACKGROUND OF THE INVENTION FIELD OF THE INVENTION This invention relates to an improved crystal refining apparatus. PRIOR ART In the crystal refining apparatus of the prior arts, for instance, disclosed in the Japanese laid open 87-244402(Kokai Sho 62-244402), an amount of the separated liquid containing impurities extracted from the refining column is merely dependent on the head difference between the inside and the outside of the refining column, so that the amount of the separated liquid by extraction is limited to the certain extent, accordingly a value of a reflux ratio (defined as descending return flow rate inside the refining column / upflow rate of the solid crystal inside the refining column) can not be large enough and consequently it is very difficult to obtain highly refined crystal. The object of this invention, therefore, is to solve the afore mentioned defects of the conventional crystal refining apparatus and to provide a refining apparatus having a high reflux ratio (defined as descending return flow rate inside the refining column / upflow rate of the solid crystal inside the refining column) for obtaining highly refined crystal. Additionally this invention provides a crystal refining apparatus which simultaneously serves washing, sweating and recrystalization when needed, for obtaining highly refined crystal from crude crystal in short period of time. The object of the invention is solved by a crystal refining apparatus having the features of claim 1. BRIEF DESCRIPTION OF DRAWINGS Fig. 1 is an elevation view and a part of which is a schematic section view of the refining apparatus of this invention. Fig. 2 is an overview and a part of which is a schematic section view of the refining apparatus. Fig. 3 is a side elevation view and a part of which is a schematic section view of the refining apparatus. Fig. 4 is a schematic view of a separated liquid extraction system. THE BEST MODE OF THE INVENTION This invention is more specifically explained with the embodiment of this invention referring to the figures attached to the specification. Preferred embodiment of this invention is as follows. Fig. 1 is an elevation view and a part of which is a schematic section view of the refining apparatus of this invention. Fig. 2 is an overview and a part of which is a schimatic section view of the refining apparatus. Fig. 3 is a side elevation view and a part of which is a schematic section view of the refining apparatus. Fig. 4 is a schematic view of a separated liquid extraction system. Referring to figure 1 to 4, it is seen that a refining column 1 of this crystal refining apparatus consists of two vertical cylinders which form, for instance, a cocoon like shape and two parallel driving shafts 3, 3' are disposed inside said cylinders which are driven by a driving unit 2 disposed at top of said refining column 1. Screw blades 4, 4' disposed around said shafts 3, 3' are arranged such that they partly overlap each other and the pitch of each screw blade is made to be in opposite direction. Screw blades 4,4' are rotated by said driving unit 2 in the opposite direction to each other and preferably at the same speed whereby carrying solid crystals constantly from the bottom to the top of the refining column 1 where a refined crystal outlet 7 is disposed. A crude crystal inlet 6 is disposed at the one side of the refining column (left side in Fig. 1) where the each screw blade 4,4' moves apart and any place between the solid-liquid separation plate 5 and said refined crystal outlet 7. A solid-liquid separation plate 5 consisting of a net like plate or a plate having a plurality of apertures is located at the bottom part of the refining column 1, which allows separated liquid containing impurities (referred to as separated liquid hereinafter) flow therethrough and the separated liquid extraction chamber 15 is disposed under said solid-liquid separation plate 5. A separated liquid extractor 8 is connected to said liquid extraction chamber 15 and said separated liquid extractor 8 is connected to a separated liquid extraction system 9. The separated liquid extraction system 9 comprises a receiving tank 10 which receives the separated liquid containing impurities, a pump 11 and a pressure reduction pipe 12 connected to the said receiving tank to reduce the pressure in said separated liquid extraction chamber 15. Said pressure reduction pipe 12 is connected to a pressure reduction line which enables to lower the pressure at an arbitrary value down to about -0,1MPa (-760 mmHg(G)), accordingly it is possible to extract separated liquid from any place of said refining column. A plurality of solid-liquid separation plates 14-1, 14-2, 14-3, -----, 14-n, consisting of a plate having apertures or a net plate, are disposed at one side of said refining column 1, which are on the opposite side of said crude crystal inlet 6 (right side in Fig. 1) where the substantially pararelled screw blades approach each other, and located between said solid-liquid separation plate 5 and refined crystal outlet 7. Small chambers 15-1, 15-2, 15-3, -------, 15-n are formed outside said solid-liquid separation plate 14-1, 14-2, 14-3, ----, 14-n. And it is desirable to treat the liquid in a thermally insulated condition for preventing deposition of the crystal inside said small chambers 15-1, 15-2, 15-3, -------, 15-n, so that heaters and/or coolers can be installed to said small chambers if necessary. Each small chamber 15-1, 15-2, 15-3, -------, 15-n has its own separated liquid outlet 16-1, 16-2, 16-3, -------, 16-n and each separated liquid outlet is connected to its separated liquid extraction system 9-1, 9-2, 9-3, -------, 9-n. Said each separated liquid extraction system 9-1, 9-2, 9-3, -------, 9-n is as shown in Fig. 4 is constructed as same as said separated liquid extraction system 9, comprising receiving tanks 10-1, 10-2, 10-3, -------, 10-n, pumps 11-1, 11-2, 11-3, -------, 11-n, and a pressure reduction pipe 12. Said each separated liquid extraction system 9-1, 9-2, 9-3, -------, 9-n, and/or separated liquid extraction system 9 is preferably equipped with a heater for preventing deposition or solidification of said crystal. Separated liquid containing impurities in each receiving tank 10-1, 10-2, 10-3, -------, 10-n, is withdrawn by each pump 11-1, 11-2, 11-3, -------, 11-n, and may be returned to said refining column 1 for recycling through schematically indicated each conduit 17-1, 17-2, 17-3, -------, 17-n, each cooler and/or heater 18-1, 18-2, 18-3, -------, 18-n, each conduit 19-1, 19-2, 19-3, -------, 19-n and each return inlet 20-1, 20-2, 20-3, -------, 20-n each of which is disposed at the opposite side of said each small chambers 15-1, 15-2, 15-3, -------, 15-n where each screw blade recedes and at a slightly lower location of said each small chambers 15-1, 15-2, 15-3, -------, 15-n respectively. The mixture of the liquid containing impurities and isolated crystal, which is like sherbet, produced by heating or cooling if necessary is recycled for continuous refining. Said each small chambers 15-1, 15-2, 15-3, -------, 15-n is also connected to the pressure reduction line and the pressure of the each small chamber is reduced simultaneously or independently. If necessary coolers and/or heaters 13-1, 13-2, 13-3, -------, 13-n are installed inside or outside said refining column 1 to form a temperature gradient inside said refining column. In this embodiment, said refining column 1 as shown in figure 1 is a vertical one but may also be inclined and is formed like a cocoon shape, consisting of two cylinders, but said column may consist of more than three cylinders. As to the screw blade, either a continuous screw blade type or a discrete screw blade type is applicable to this invention. And in case the refining column is a vertical type as indicated in Fig. 1 or Fig. 3, the position where the each blade moves inwardly is indicated at the face side of the drawing sheet in Fig. 3, but it is also allowed that the position where the each blade moves inwardly is located at the back side of the drawing sheet. In case the position where the each blade moves inwardly is located at the lower part of the drawing sheet, the crude crystal inlet, the small chamber, and the separated liquid extractor or the like nay all disposed at the opposite side of the refining column of that of the case that the position where the each blade moves inwardly is located at the face side of the drawing. As to said heater or cooler, an electric heater, a steam heater or any kind of coolant is applicable to this invention for keeping the temperature gradient of said refining column at a desired gradient depending on materials subjected to refining. Said heater or cooler, may be installed inside the driving shafts and/or inside the screw blades if desired. As to said solid-liquid separation plate 5. and/or solid-liquid separation plate 14-1, 14-2, 14-3, -------, 14-n, the diameter of apertures or net void of said solid-liquid separation plate is preferably from 0.05mm to 5mm. FUNCTION OF THE INVENTION Now function of the construction of this invention is more specifically explained hereinafter. A crude crystal raw material which is subjected to refining is introduced into said refining column 1 from said crude crystal inlet 6. Said driving unit 2 drives said shafts 3, 3' in opposite direction each other, one in clockwise and the other in anti-clockwise direction as viewed from the top of said refining column, and preferably at the same speed. Screw blades 4, 4' disposed around said shafts 3, 3' are arranged partly overlap and the pitch of each screw is opposite direction. Screw blades 4, 4' are rotated by said driving unit 2 in the opposite direction whereby causing a pressure between the wall of said refining column and said screw blades which move inwardly, disintegrating said crude crystal raw material and carrying them to the top of said refining column 1 where a refined crystal outlet 7 is disposed. At the same time, the separated liquid rich in impurities flows out through the plurality of solid-liquid separation plate 14-1, 14-2, 14-3, -----, 14-n which are disposed at the side of said refining column 1 and/or said solid-liquid separation plate 5 which is disposed at the bottom of said refining column 1 into the sectioned small chambers 15-1, 15-2, 15-3, -------, 15-n, and the separated liquid extraction chamber 15 respectively and then into the separated liquid extraction system 9-1, 9-2, 9-3, -------, 9-n and/ or the separated liquid extraction system 9. Separated liquid containing impurities in the receiving tanks 10-1, 10-2, 10-3, -------, 10-n of the extraction system 9-1, 9-2, 9-3, -------, 9-n respectively and/or in the separated liquid extraction chamber 10 of the separated liquid extraction system 9, is then extracted promptly by the aid of lowered pressure in the receiving tanks 10-1, 10-2, 10-3, -------, 10-n and the separated liquid extraction chamber 10 caused by the vaccum pump (not shown) which is connected to the pressure reduction line through reduction pipe 12, as the pressure can be lowered down to about -0.1MPa (-760 mmHg(G)) depending on the predetermined condition. Receiving tanks 10-1, 10-2, 10-3, -------, 10-n and the tank 10 can be heated by the heater (not shown) thereby preventing deposition of the crystal and sticking to the wall. Said extracted separated liquid is subjected to other treatment for instance, disposal, or recycled by the pumps 11-1, 11-2, 11-3, ------- , 11-n. To make the temperature gradient according to the desired condition, a heater or a cooler 13-1, 13- 2, 13-3, -------, 13-n may be equipped outside or inside of said refining column 1. In some cases it is possible to install a heater and/or a cooler outside or inside of said purification column 1 to adjust the temperature gradient. In a certain condition, the temperature at the raw material inlet 6 is kept at the lowest and the temperature at the refined crystal outlet 7 is kept at the highest depending on the materials subjected to refining. Consequently, the crystal in the crude raw material is continuously recrystalized and the refined crystal will be obtained. The separated liquid containing impurities extracted from the small chamber 15-1 is then introduced into the heater and/or cooler 18-1, via the outlet 16 1, the receiving tank 10-1, the pump 11-1, and the conduit 17-1, forming crystals in the outflow and come to the mixture of the crystal and liquid containing impurities which is in some case a slurry like liquid. Then the mixture is returned to the refining column 1 through a single or more than two return inlets, for instance, a return inlet 20-1 in Fig. 1, which is located below the small chamber 15-1 and near the raw material inlet 6 via conduit 19-1 for further refining. The separated liquid containing impurities extracted from the small chamber 15-2 same as described above, is also introduced into the heater and/or cooler 18-2, via the outlet 16-2, the receiving tank 10-2, the pump 11-2, and the conduit 17-2, forming crystals in the outflow of separated liquid containing impurities, and further the outflow is returned to the refining column 1 through the return inlet 20-2 in Fig. 1, via conduit 19-2 for further refining. As described above from every small chamber 15-3, ----, 15n, separated liquid is taken out and returned to the refining column 1, the refined crystal is taken out from the crystal outlet 7 and the residue liquid which contains a comparatively much impurities is taken out continuously from the outlet 8. Therefore, according to this invention, an amount of return liquid flowing up the refining column, in other word, a ratio of the amount of return liquid and an amount of solid refined crystal flowing up the refining column which is referred to as reflux ratio, could be larger than the crystal refining apparatus of the prior arts. Consequently inside the refining column 1, the crystal flowing up and moving toward the outlet 7, and the highly refined return molten liquid generated by heating or cooling or introduced from the top of the refining column 1 flowing down inside the refining column flow in the opposite direction each other, and they contact while flowing so that the surface of said crystal is cleaned by said return liquid, which is referred to as cleaning, impurities included inside the crystal is extracted by heating or cooling apparatus, referred to as sweating, and further molten crystal is recrystalized while contacting the solid crystal flowing up inside the refining column, referred to as recrystalization, these three operations take place simultaneously in the refining column. According to this invention, crystal component is carried to said refined crystal outlet 7 while being refined and at the same time separated liquid is taken out through the solid-liquid separation plate 14-1, 14-2, 14-3, ----, 14-n and/or 5 into the small chambers 15-1, 15-2, 15-3, ----, 15-n and separated liquid extraction chamber 15. Then the separated liquid is taken out from the outlets 16-1, 16-2, 16-3, ----, 16-n and/or 8 and is subjected to disposal, recycling or other treatment via pump 11-1, 11-2, 11-3, ----, 11-n and/or 11 of the extraction system 9-1, 9-2, 9-3, ----, 9-n and/or 9. According to this invention, the separated liquid is extracted from the refining column at comparatively large rate because the pressure difference generated by the pressure reduction line connected to the small chambers 15-1, 15-2, 15-3, ----, 15-n and separated liquid extraction chamber 15 to reduce the pressure therein and increased pressure caused by the double screw blade rotating opposite direction between the blades and the separation plate 14-1, 14-2, 14-3, ----, 14-n disposed one side of the refining column. According to this invention, a ratio of the amount of return liquid and the amount of solid crystal flowing up in the refining column that is reflux ratio, could be larger than 2, more specifically, from 2 to 10, which is considerably larger than values of the crystal refining apparatus of the prior arts, which were merely from, 0.7 to 0.8. It is the advantages of this invention that it has not been known to utilize a pressure reduction system and pressure caused by the double screw blade for obtaining highly refined crystal at a high rate. EMBODIMENT Two cylinders having the diameter of 76.2cm and the hight of 3 m respectively composes a cocoon like refining column for refining apparatus and a driving shaft is installed inside said each cylinder as shown in Fig. 1 to Fig. 4. The diameter of apertures of a solid-liquid separation plate disposed at the side wall of said refining column is 2mm. A crude naphthalene containing 10% of thianaphthene was subjected to refining utilizing above described refining apparatus. The temperature of supplied crude crystal is kept at 20°C, and the temperature of at refined crystal outlet 7 is kept at 80°C, and supplying said crude naphthalin at a rate of 300kg/hr. The pressure of said extraction system is lowered to -0.04MPa (-300 mmHg(G)) and the reflux ratio of this embodiment is 3. Consequently, refined naphthalene having the purity of 99.9% was obtained at a high rate of 250kg/Hr from said refined crystal outlet 7. Comparative Example On the other hand, the same refining apparatus which is same in size as described above but has no side wall solid-liquid separation plate and pressure reduction system and the separated liquid is extracted only from the separation plate disposed at the bottom of the refining column was used for comparative experiment. The extraction rate is dependent only on the head difference of the material then the yield of the obtained crystal of the same purity as in the example is 80 kg/Hr and the reflux ratio is 0.8. ADVANTAGES OF THE INVENTION According to this invention extraction rate of separated liquid has become some ten to hundred times as much of that of conventional refining apparatus and high reflux ratio is obtained. Because the pressure reduction system and/or pressure causing means inside the refining column is adapted to the refining apparatus of this invention. Consequently, in case the amount of production of the crystal is constant, the refining apparatus of this invention can provide a high purity crystal than any conventional refining apparatus. On the other hand in case the purity of the products is constant, the refining apparatus of this invention can provide a high production rate than conventional refining apparatus which may be a great help to the industry. Further the apparatus of this invention is also applicable as a liquid removing apparatus, such as dehydrater, having high removal rate. INDUSTRIAL APPLICATION The crystal refining apparatus of this invention is constructed such that it is possible to use this refining apparatus for purifying for example, paradichloro benzene when chlorination of benzene, purifying naphthalene containing thianaphthene, refining para-xylene containing ethylbenzene. Refined materials are occasionally washed with solvent, such as , aceton, methanol, propanol, or the like if desired. The crystal refining apparatus of this invention is also used as a liquid removing apparatus, such as dehydrater. The crystal refining apparatus of this invention is used not only for refining of organic materials but also for refining of industrial salt, production of fruit juice by freezed concentration and for dehydration of sludges.

Claims: A crystal refining apparatus comprising a refining column (1) including double shafts (3,3') having partly overlapping screw blades (4,4') therearound, the pitch of said screws being oppositely arranged to each other and rotated in opposite directions, thereby carrying solid contents upwardly inside said refining column, said apparatus comprising a crude material inlet (6) disposed at said refining column, a refined crystal outlet (7) disposed at the upper part of said refining column, a plurality of solid-liquid separation plates (14-n) disposed along the side wall of the refining column and associated with a plurality of corresponding small chambers(15-n), extraction systems (9-n) and return inlets (20-n) to the column, respectively, whereby each extraction system (9-n) comprises an outlet (16-n) leading from the column to a receiving tank (10-n) connected to a pressure reduction line (12) and a pump (11-n) for recirculating the separated liquid via conduits (17-n, 19-n) to a corresponding return inlet (20-n) located below the small chamber (15-n) of the column, and a separated liquid extraction chamber (15) disposed at the bottom of the refining column receiving the separated liquid containing impurities from a solid-liquid separation plate (5) consisting of a plate having a plurality of apertures or of a net-like plate through which separated liquid flows down to said separated liquid extraction chamber (15), said separated liquid extraction chamber having an outlet (8) for separated liquid and being connected to said pressure reduction line (12).

Inventors: SAITOH SHIGERU, SAITOH, SHIGERU
Applicants: SAITOH SHIGERU, SAITOH, SHIGERU
Application year: 1990
Main classification: B01D9
IPC codes: B01D9, C30B7