TECHNICAL FIELD The present invention relates to an apparatus for continuously separating from each other two different substances- preferably sulphuric acid and water, in a liquid solution/mixture by heating the liquid to boil¬ ing at atmospheric pressure.

STATE OF THE ART An apparatus for concentrating by evaporation a continuously supplied sulphuric acid in a vertical quartz tube is disclosed in Swedish published applica¬ tion 416,042. The quartz tube is heated externally in a furnace by hot flue gases. The evaporated liquid is not cooled until it has passed a collecting tank provided below the quartz tube. Evaporation and recti- fication are performed by means of packings which in the packed state fill the entire quartz tube.

The drawbacks of this apparatus are numerous. The sealing at the lower end of the quartz tube, i.e. between furnace, collecting tank and quartz tube, is exposed to heavy stresses because of the hot sulphuric acid and is liable to break the brittle quartz tube, and so its design necessarily is complicated, requiring that the quartz tube have a special shoulder surface. The non-uniform heating of the quartz tube and the packings often entails that the packings get jammed by expanding in the quartz tube. These jammed packings may crack the quartz tube when it contracts upon cooling. The presence of packings further prevents a continuous falling film from developing on the inner side of the qμartz tube.

BRIEF DESCRIPTION OF THE INVENTION In order to realize the inventive concept to overcome these problems, there are provided, according

to one aspect of the invention, in a continuous vertical outer tube of quartz an upper plate column section for stripping and/or rectifying the water from an aqueous sulphuric acid solution and, below the plate column section, a heated reboiler or evaporator section, the plates of the plate column section being arranged on holder means which form part of the lateral boundary wall of the outer tube that belongs to the plate column section, or are supported by a top or a bottom connec- tion to the outer tube. The lateral wall of the outer tube that belongs to the reboiler/evaporator section is designed on its inside for allowing falling film reboiling/evaporation. For wetting said inside, inlet means on the holder means or the lateral wall of the tube are adapted to guide sulphuric acid from the plate column section to the reboiler/evaporator section. In both of these sections, the outer tube is completely free from packings.

Also, in order to realize the above-mentioned inventive concept, there are provided, according to another aspect of the invention, in a continuous verti¬ cal-outer tube of quartz, an upper column section for stripping and/or rectifying the water from an aqueous sulphuric acid solution, the column arrangement optio- nally being of the type defined above, a subjacent, heated reboiler/evaporator section, and a lower cooling section for cooling the bottom product which flows down from the reboiler/evaporator section. In this instance, too, the outer tube is completely free from packings. The apparatus according to the invention thus has no packings in the quartz tube. In order to ensure the stripping/rectification process, use is instead made of column plates with such a holder arrangement therefor that neither the plates nor the holder arrangement will run the risk of expanding against the inside of the outer tube. Cooling of the bottom product takes place in a section of the lower end of the outer tube, whereby

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the seals between the lower end of the outer tube -and the bottom connection will be protected from exposure to hot sulphuric acid and may have a less complicated and less expensive design. DETAILED DESCRIPTION OF THE INVENTION

In the foregoing, sulphuric acid concentration has been indicated as the field of application of the appa¬ ratus according to the invention. The following descrip¬ tion will also be concerned with this field of appϋca- tion, but it is obvious to anyone skilled in the art that the field of use of the apparatus according to the invention is not restricted to the concentration of sul¬ phuric acid but encompasses in general boiling point separation of two substances in a liquid mixture or solution. Quartz here is the preferred tube material . for sulphuric acid concentration, but other types of glass or ceramic material may instead be used. Plate column section

The above-mentioned plate column section may be constructed in several ways, while observing however that the plates or their holders should be sufficiently spaced apart from the inner wall of the outer tube in order, at expected changes of temperature in the plate column section, not to enter into contact with this inner wall, which would give rise to stresses causing breakage.

For example, the lateral wall portion of the outer tube that surrounds the plate column section may be thermoformed with inwardly directed projections of the Vigreux type forming plates, said lateral wall portion itself forming the holder for the plates. Alternatively, the plate column section may consist of one or more separate quartz tubes which are suspended in the upper, top connection of the tube and extend downwards into the portion of the outer tube that surrounds the plate column section, or which rest on the bottom connection to the outer tube, and which, in the plate column sec-

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^{' " '} 4 ^{" " "} tion of the tube, have projections of the Vigreux type which serve as plates, said separate tubes forming the holder means for the plates. Said Vigreux type projec¬ tions need not necessarily form the plates, but may instead form supports for separate, perforated plates of quartz freely placed thereon.

In the use of several separate tubes which are arranged hanging from the top connection of the outer " tube, the number of these tubes is such that the largest possible amount of vapour from the subjacent portions of the outer tube cavity will pass through the tubes, which may additionally be ensured by the use of throttle means interposed between the tubes.

The feed inlet to the quartz tube may open exter- nally of these smaller tubes whereby the feed will wet the tubes exteriorly, so that vapour is stripped from the feed and/or vapour is condensed in the smaller tubes. . . Reboiler/evaporator section The reboiler/evaporator section of the outer tube is also delimited in its entirety by the outer tube and is also free of packings. This section of the outer tube is supplied from outside with the heat required for reboiling/evaporation and column plate activity, for instance by means of a furnace which encloses the outside of the outer tube in this section and is supplied with hot flue gases. The inside of the outer tube in this reboiler/evaporator section can be designed for receiving falling film of sulphuric acid which is sup- plied tσ the reboiler/evaporator section from the plate column section. In this instance, said inside is advan¬ tageously provided with one or more recesses, for in¬ stance formed by etching, which serve to retard and prolong the path of the falling film through the reboiler/ evaporator section, thus promoting the separation in this section of sulphuric acid and water, to which also contributes the heating of the falling film in this

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recess by the adjacent dry portions of the outer tube. A suitable recess has the form of a helix. The recess need not be pronounced. A finish or surface processing of the inside of the tube in this reboiler/evaporator section, for instance by slight etching or grinding, will suffice to retard the falling film.

In the reboiler/evaporator arrangement of the type now described, there are provided between the plate column section and the reboiler/evaporator sec- tion inlet means for guiding liquid from the former to the latter, such that falling film can develop on the inner wall of the outer tube. The inlet means may be thermoformed on the outer tube itself, for instance like Vigreux projections and/or as internal shoulders and/oron said separate stripping/rectifying tubes sup¬ ported by the top connection of the outer tube, which may then, for instance, have their lower portions de¬ flected obliquely downwards.towards the inside of the outer tube. it is evident that this falling film type ^' evapo¬ rator can be readily modified for "kettle reboiling" or"kettle evaporation" by varying a back pressure provided at the bottom connection of the outer tube, for instance with the assistance of a throttle valve disposed in the outlet of the outer tube.

Another usable reboiler/evaporator arrangement in the now-discussed section of the outer tube operates by thermosiphon action. In this case, a separate tube is concentrically arranged in the outer tube, rests on the bottom connection of the outer tube and extends upwards through the reboiler/evaporator section and, in its cylindrical wall, has openings on a level with the upper and the lower portion of that section, thus permitting vapour to enter through the lower openings and entrain liquid in the gap between the tubes upwardly to the upper openings through which the vapour rises in the outer tube and sulphuric acid descends in the inner

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tube.

Cooler section

The lower portion of the outer tube is, as men¬ tioned above, preferably arranged for cooling the bottom product. The purpose of the cooling is to protect the seals between the lower end of the outer tube and the bottom connection from hot bottom product. Examples of cooling arrangements in the cooling section of the outer tube are blowing cold air against the outside of the outer tube in this section and employing a cooling coil, for instance of teflon, which is introduced in the cooling section through the bottom connection of the tube _. . A third example of such a cooling arrangement comprises a separate tube to which the bottom product is supplied from the reboiler/evaporator section and which extends from below up into the cooling section of the outer tube concentrically therewith and, in its wall, has openings through which colder sulphuric acid supplied from outside to the gap between the tubes will flow and mix with the bottom product in the sepa¬ rate tube for cooling thereof.

As sealing material both at the lower end of the outer tube and at the upper end of the outer tube, ppoollyytteettrraafluoroethylene, such as TEFLON , is preferably selected.

EMBODIMENTS OF THE INVENTION The invention will be described in greater detail hereinbelow with reference to the accompanying drawings. Fig. 1. in longitudinal section, shows a first embodi- ment of the invention, and Fig. 2, in longitudinal sec¬ tion, shows a second embodiment of the invention, it being worth noting that the figures are not according to scale but are drawn so as to clearly show the essen¬ tial components of the apparatus according to the inven- tion.

In Fig. 1, there is shown an installation for stripping water from a mixture of water and sulphuric

acid. To a furnace 1 which can be heated, there are supplied hot flue gases through a f rnace port 2 , ahd cooled flue gases leave the furnace through another furnace port 3. An outer tube 4 of clear quartz extends through the furnace. In the shown embodiment, the length of the outer tube is about 4 m but may in principle be varied between for instance 1 and 8 m. Further,the inner diameter of the outer tube is about 150 mm but may range from for instance 80 to 300 mm. At its upper end the outer tube has a connecting top 5 with an inlet 6 for a feed consisting of a mixture of water and sulphu¬ ric acid. An outlet 7 in the top 5 is intended for strip¬ es) ped water vapour. A gasket 8 of TEFLON ^' is disposed between the upper end 9 of the outer tube and a top connection 22 for the outer tube. The top 5 rests on the top connection 22 through a gasket.

Said upper end 9 is slightly cup-shaped in order to maintain the gasket 8 in place.

Spaced apart disks 10 and 11 of refractory steel enclose the outer tube 4 and support each a ring seal 12 and 13, respectively, delimiting the space for the hot gases in the furnace. The seals 12 and 13 include a ceramic mat and an underlying gasket of "Trito Board" . The seals 12 and 13 are so designed that they allow a certain longitudinal displacement of the outer tube 4 but at the same time ensure such stability for the outer tube 4 that it does not risk entering into contact with the disk 10 or the disk 11.

The top connection plate 22 is of quartz, and Vigreux columns 24 which are arranged in a ring and extend down through the plate column section BS of the outer tube 4 are hanging from the top connection plate in spherical grindings. In the columns 24, water is stripped and sulphuric acid is condensed. On top of the quartz plate 22, a distributor 25 for the feed has been placed within the top 5.

The columns 24 have a laterally bent lower portion

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26 which opens in the vicinity of the inner wall of the outer tube and guides sulphuric acid from the columns 24 to that inner wall, in an .area of transition between the plate column section BS and a falling film evapora- - tor section ES of the outer tube. In this transition or inlet area to the evaporator section, the tube 4 may have a circumferential tapering portion or shoulder 27 which ensures the distribution of the sulphuric acid • supplied through the bends 26, to the evaporator section, In this transition area, as a complement to or an alter¬ native of the taper 27 or the bends 26, inwardly direc¬ ted projections 28 may be thermoformed in the outer tube and thus serve to intercept and guide downwardly falling sulphuric acid to the inner wall of the outer tube 4 which is situated in the evaporator section. Further, as another complement or additional alternative, inward¬ ly directed projections 29- may be provided in this tran¬ sition area in the tube 4. These projections support a freely placed, perforated cap 30 of quartz which intercepts and guides downwardly falling sulphuric acid to the inside of the outer tube 4.

The evaporator section ES advantageously has on the inside of the outer tube 4 a helical recess 30a, formed by etching, which retards the falling film for more effective evaporation of the sulphuric acid in the portion ES of the outer tube 4 that is surrounded by the furnace 1.

In the lower portion of the outer tube 4 , there is preferably provided a channel 31 through which a flow of cold air cools the lowermost portion 32 of the outer tube 4. The lowermost portion 32 is part of a cooling section CS of the outer tube for cooling the concentra¬ ted sulphuric acid received from the evaporator section. Thanks to the cooling of the bottom product, the gasket 33 at the lower end of the outer tube 4 may consist of a less temperature-resistant material, for instance TEFLON^. By the provision of a back pressure in the

bottom connection 34 of the outer tube, the liquid in the tube 4 is kept at a suitable level in respect of cooling. The outer tube 4, over the gasket 33, rests with its entire weight on the bottom connection 34 which has an outlet 35 for cold concentrated sulphuric acid.

In Fig. 2, there is shown another apparatus for the concentration of sulphuric acid. The same reference numerals as in Fig. 1 have been employed for equivalent parts which, therefore, will not be described in greater detail here. A suitable inner diameter of the outer tube 4 is about 200 mm, and this inner diameter may be varied for instance between 100 mm and 400 mm. The inlet 6 for the feed opens outside the Vigreux columns 24, such that they will be exteriorly wetted by ejected feed, water being stripped from the feed and sulphuric acid being condensed in the lower portion of the Vigreux columns 24. In this example, the columns 24 ex±end a certain distance above the suspension plate or top connection 22 and can be cooled in these portions for partial condensation of vapour from the columns 24.

The tube 4 rests via the gasket 33-with its entire weight on the flange of a bottom connection 34, here consisting of tantalum. By a gasket 36, a narrower vertical quartz tube 37 concentrically disposed in the outer tube 4 rests with its entire weight on the flange of the bottom connection 34, and the tube 37 is sealed at its upper end with respect to the plate 22 by means of a gasket 38. In the evaporator section ES of the outer tube 4 , the tube 37 in its longitudinal direc¬ tion has spaced apart holes 39, 40 which produce a thermosiphon effect with liquid and vapour streaming on the outside and liquid streaming downwards on the inside of the tube 37. Quartz tubes 41 and 42 define the flow space between the tubes 4 and 37, the upper tube 41 having a flange which is disposed between the gasket 8 for the outer tube ^" 4 and a gasket 43 adjacent

the plate 22 carrying the columns 24. The lower tube 42 rests by a gasket 44 on the flange of the bottom connec¬ tion 34. Through an inlet 45 in the bottom connection 34, externally cooled bottom product is fed into the outer tube 4. In the lower end of this tube which be¬ longs to the cooling section CS thereof, there is pro¬ vided a concentrically mounted quartz dome 46 in the lateral wall of which openings 47 are formed. The cold bottom product from the inlet 45 will flow in the gap between the tube 37 and the dome 46 and, through the openings 47, into the interior of the dome 46 , where it is mixed with hot bottom product coming from the evapo¬ rator section ES. The dome 46 has a lower flange, by means of which the dome, via gaskets 49 and 50, is mounted in the outer tube 4 and on an outlet member 48. In an alternative embodiment with respect to the arrangements in Figs. 1 and 2, inlets for the feed may be so arranged that the feed will cool the. bottom product. In the embodiment according to Fig. 1, an inlet is so provided for half of the feed that it ex¬ tends through the bottom connection 34 and the lower portion 32 of the outer tube 4 to open on a level v/ith the seal 13.

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