US3616835A

US3616835A - Evaporators having hollow platelike vertical heat transfer elements and overhead nozzles

Info

Publication number: US3616835A
Application number: US798339A
Authority: US
Inventors: Francois Laurenty
Original assignee: C O C E I
Current assignee: C O C E I
Priority date: 1968-02-20
Filing date: 1969-02-11
Publication date: 1971-11-02
Anticipated expiration: 1988-11-02
Also published as: DE1908252A1; FR1583698A; GB1247771A; AT309391B; FR2028623A6; CH491657A; BE728588A; NL6902624A

Abstract

AN INSTALLATION FOR THE CONTINUOUS EVAPORATION OF A SOLVENT AND THE CONTINUOUS CONCENTRATION OF AT LEAST ONE SUBSTANCE IN SOLUTION IN THE SAID SOLVENT, COMPRISING A HEAT-EXCHANGER WHICH SERVES AT THE SAME TIME AS A HEATER AND AS CONCENTRATION DEVICE, THE HEAT-EXCHANGER COMPRISING A PLURALITY OF PARALLEL EXCHANGE ELEMENTS OVER WHICH A DISTRIBUTOR UNIT CAUSES THE SOLUTION TO BE TREATED TO STREAM, SAID UNIT BEING PROVIDED FOR THE PURPOSE WITH AS MANY NOZZLES AS THERE ARE EXCHANGE ELEMENTS.

Description

F. I AURENTY 3,616,835 EVAPORATORS HAVING HOLLOW, PLATELIKE, VERTICAL HEAT Nov. 2, 19H

TRANSFER ELEMENTS AND OVERHEAD NOZZLES 6 Sheets-Sheet 1 Filed Feb. ll, 1969 Nov. 2, 19'71- 3,616,835 PLATELIKE, VERTICAL HEAT F. LAURENTY EVAPORATORS HAVING HOLLOW,

TRANSFER ELEMENTS AND OVERHEAD NOZZLES Filed Feb. 11, 1969 6 Sheets-Sheet f3 mvenor: :Franois Lcuueniu 33: q 4.2m@ ttornegs NOV. 2, 1971 F AURENTY 3,616,835

EVAPORATORS HAVING HOLLOW, PLAlELIKE, VERTICAL HEAT TRANSFER ELEMENTS AND OVERHEAD NOZZLES Filed Feb. ll, 1969 6 Sheets-Sheet .'5

FIGS

FEGIIOA FIGOB .TX N315/ 1,/

I l E l l P 1X1 M I A 130 |31 133 '134 Qttorvmgs Nov. 2, 1971 F. L AURENTY 3,616,835

EVAPORATORS HAVING HOLLOW, LLA'IELIKE, VERTICAL HEAT TRANSFER ELEMENTS AND OVERHEAD NOZZLIIS Filed Feb. ll, 1969 6 Sheets-Sheet Il [meezit/'aff' mvanor: ranoLe Lomnuj 35: ,Biowwz 2 20.164,

Httornes Nov. 2, 1971 F. LAUREN-ry 3,616,835

EVAPORATORS HAVING HOLLOW, PLA'lELIKE, VERTICAL HEAT TRANSFER ELEMENTS AND OVERHEAD NOZZLES Filed Feb. ll, 1969 6 Sheets-Sheet 5 H514 F/GJS F/G.76

F/G,78 F/G.79

Wwencov: :Franois Lauvwuj Qhtomegs Nov. 2, 1971 F. LAURENTY 3,616,835

EvAPoRATORs HAVING HOLLOW, ELATELIHE, VERTICAL HEAT TRANSFER ELEMENTS AND OVERHEAD NOzzLEs Filed Feb. 11, 1969 e sheets-sheet e XXI Ze'll l'rmyw' 275 Aww/Qur 77 fIi' 272 t wd 262 265i Z Anm/aff )gaie invencor; Tra-Cols Lomvenkg 35= sgpww i 4.1m#

Qttornes United States Patent O 3,616,835 EVAPORATORS HAVING HOLLOW, PLATELIKE, VERTICAL HEAT TRANSFER ELEMENTS AND OVERHEAD NOZZLES Francois Laurenty, Le Touquet, France, assignor of fractional part interest to C.O.C.E.I. S.A., Paris, France Filed Feb. 11, 1969, Ser. No. 798,339 Claims priority, application France, Feb. 20, 1968, 140,468; Jan. 8, 1969, 6900106 Int. Cl. B01d 1/22 U.S. Cl. 159-13 B 22 Claims ABSTRACT OF THE DISCLOSURE An installation for the continuous evaporation of a solvent and the continuous concentration of at least one substance in solution in the said solvent, comprising a heat-exchanger which serves at the same time as a heater and as a concentration device, the heat-exchanger comprising a plurality of parallel exchange elements over which a distributor unit causes the solution to be treated to stream, said unit being provided for that purpose with as many nozzles as there are exchange elements.

The present invention relates to installations provided for the continuous evaporation of a solvent of any kind and/ or for the continuous concentration of at least one substance in solution in a solvent, with or without extraction of the said substance.

A conventional installation for the continuous evaporation and/or concentration comprises generally, in a closed circuit, a circulation pump, a heater, an evaporator independent of the said heater, and connecting pipe-work. An intake pipe introduces into this circuit the liquor to be thickened and an outlet piping system for the extraction of the thickened liquor. The whole assembly forms a treatment stage.

In order to economize heat, these installations most frequently comprise a number of stages in cascade. The condensed liquor in a first stage supplies -a second stage heated by the steam formed in the first stage, and so on.

In certain installations, the condensed liquor is the end product desired or obtained; in others, there is crystallization of one or more substances, and the crystals thus formed which constitute the finished product desired or obtained, are extracted either in drying circuits individually associated with the various stages of the installation, or in a terminal drying circuit common to all the stages of the installation.

These installations all have numerous disadvantages.

In the first place, the heating of the liquor in the heater is not uniform; there is a formation of bubbles of vapour even inside the said liquor. This is also true for the evaporator, especially due to the large thickness of liquid to which, in a conventional apparatus, is applied the heat necessary for producing the desired evaporation. The bubbles thus formed burst and cause the production of droplets of liquid which are mechanically carried away by the vapour thus liberated. This phenomenon, known as leading, adversely affects the efficiency of the installation and may result in the elimination of a not-negligible quantity of liquor.

In addition, the existence of these bubbles causes local superheating between them and the walls, which may result in a degradation of the materials, and especially of their taste, such as caramelization.

In installations comprising a number of stages, the temperature difference existing between the primary and the secondary fluids is substantial, of the order of 5 to C., both for a heater and for an evaporator, so

ICC

that the temperature loss resulting from one stage inevitably amounts to 10 to 20 C.

The present invention has for its object an installation for the continuous evaporation of any particular solvent and for the continuous concentration of at least one substance in solution in the said solvent, which is free from the above drawbacks and which furthermore offers other advantages.

The installation according to the invention, which comprises a heat exchanger in which circulate, on the one hand, the solution to be treated and, on the other hand, a heat-exchange fluid, is characterized in that the said heat exchanger comprises a body, a plurality of similar exchange elements arranged in parallel at a distance from each other inside the said body and each formed by two thin walls arranged at a small distance from each other, a primary intake introducing the said exchange fluid between the said Walls and a secondary intake causing the said solution to stream over the said walls, the said secondary intake comprising as many outlet nozzles as there are exchange elements, and each of the said nozzles being arranged directly above one of the said exchange elements.

The heating of the solution and its partial evaporation are effected, in accordance with the invenition, and contrary to the usual installations, in a single apparatus, namely the heat exchanger, which already eliminates one of the causes of bubbling and therefore of overheating and leading or priming.

In addition, by virtue of the structure of this exchanger, the introduction of heat is effected through a very small thickness of solution and therefore the evaporation of the solution is also effected without bubbling and therefore without priming.

Furthermore, other things being equal, this structure has the advantages of permitting conjointly an increase in surface area of the exchanger walls and a reduction of the thdickness of the walls and, in consequence, a substantial reduction of the variation of temperature introduced by any particular stage of treatment.

It is therefore possible, in an installation of given characteristcs, to provide the arrangement of a greater number of stages or effects and therefore to improve the productivity of this installation.

The characteristic features and advantages of the invention will furthermore be brought out in the description which follows below, given by way of example reference being made to the accompanying diagrammatic drawings, in which:

FIG. 1 is a general view with parts broken away of a crystallization installation in accordance with the invention;

FIG. 2 is a view in cross-section taken along the line lI-II of FIG. 1, of an evaporator utilized in this installation;

FIG. 3 is a view in transverse section, to a larger scale, of one of the unitary elements of this evaporator;

FIG. 4 is a view in elevation with parts broken away, of a dryer employed in the installation according to the invention;

FIG. 5 is a half-view in cross-section of this dryer, taken along the line V-V of FIG. 4;

FIG. 6 is a general View of an installation with several stages, according to the invention;

FIG. 7 is a view similar to FIG. 2 and relates to an alternative form of construction;

FIG. 8 is a view in elevation of this alternative form, partly dismantled;

FIG. 9 is a view in cross-section taken along the line IX-lX of FIG. 8, of one of the elements of this alternative construction;

FIGS. 10A, 10B are partial views in cross-section, to a larger scale, taken respectively along the lines XA-XA and XB-XB of FIG. 9;

FIG. 11 is a partial view in cross-section, to a different scale, taken along the line XI-XI of FIG. 10A;

FIG. l2 shows a crystallization diagram, given by way of example;

FIG. 13 is an elevational view similar to FIG. 8 and relates to another alternative form of heat exchanger in accordance with the invention;

FIG. 14 is an end view of the exchanger shown in FIG. 13, looking in the direction of the arrow XIV of this ligure;

FIG. l is a view in transverse section of this exchanger, taken along the line XV-XV of FIG. 13;

FIG. 16 is a detail plan View of one of the components of this exchanger, looking in the direction of the arrow XVI of FIG. 13;

FIG. 17 is a partial, elevational, cross-sectional view, to a larger scale, of this exchanger;

FIG. 18 is a detail View, in elevation of another alternative form of construction, shown in elevation;

FIG. 19 is a detail, elevational, cross-sectional view of another alternative form of construction;

FIG. 20 is a view in axial section of a dryer capable of being utilized in an installation according to the invention;

FIG. 21 is a half-view plan of this dryer taken along the line XXI-XXI of FIG. 20;

FIG. 22 is similar to FIG. 21 and concerns an alternative form of construction.

In conformity with the form of embodiment chosen and shown in FIG. 1, an installation according to the invention, applicable for example to the crystallization of hyposulphite, comprises an evaporation circuit and a drying circuit 11.

The evaporation circuit 10 comprises a single heat exchanger 12, described in detail below, and a centrifugal separation chamber 13 in which rotates a circulating pump with a wheel, helix or the like, driven by a motor 14.

The exchanger 12 is coupled to the separation chamber 13, on the one hand by a pipe and on the other hand by a conduit 16, on which there may be mounted, as shown, a crystallizer 17. In practice, this latter is constituted by a simple section of diameter larger than the pipe 16, and can also be interposed equally well in the same way on the pipe 15.

In the body of the exchanger 12 are mounted a plurality of similar exchange elements 21, arranged parallel to each other and at a small distance from each other.

Each element 21 is as shown in FIG. 3 composed of two thin walls 22A, 22B, each having a depression zone of small depth, 23A, 23B respectively, limited by a

peripheral edge

24A, 24B respectively. The walls 22A, 22B are faced by their

peripheral edges

24A, 24B, and these edges are rigidly iixed in a fluid-tight manner to each other, for example by welding.

In addition, the walls 22A, 22B are provided here and there with

stiening bosses

122A, 122B respectively, supported in pairs between one wall and the other, and ixed to each other rigidly if so required.

These walls 22A, 22B may be made of metal or synthetic material. They form conjointly an elongated pocket of which two main coplanar dimensions are substantially greater than the corresponding transverse dimension.

The exchange elements 21 are arranged vertically in the body 20 and this latter is slightly inclined to the horizontal, so that the upper edge of each of the elements 21 is slightly inclined to the horizontal.

`0n the upper edge of each of the elements 21 is engaged a distributor pipe 25 provided for that purpose at its lower portion with a slot 26 formed along a generator line.

The pipes 25 are horizontal or inclined to the horizontal at an angle diierent from that of the body 20, so that they are engaged more and more deeply over the upper edges of the element 21, in the direction of the free extremities of these latter. The pipes 25 are coupled in parallel to the conduit 16 leading from the separation chamber 13.

At its upper portion, the body 20 of the exchanger 12 is provided with a collecting cone 27 coupled by a pipe 28 to a compression vessel 29.

This compression vessel 29 is connected at its base by a pipe 30 to a vacuum pump 31, which may be for example of the liquid-ring type.

The compression vessel 29 is further connected by a discharge nozzle 32 to the various exchange elements 21 of the exchanger 12 by nozzles 35 (FIG. 3), connected in parallel and each discharging into the upper portion of a respective one of the said elements. In the discharge nozzle 32 is engaged a pipe 37 fed with live steam and controlled by a regulating valve 38. It would of course be possible to use any other type of steam compressor, mechanical or the like..

At its lower portion, each exchange element 21 of the exchanger 12 is connected by a pipe 39 to the vacuum pump 31.

Furthermore, for reasons which will be explained below,

pipes

33 and 34 are branched to the elbows of the conduit 16.

The drying circuit 11, shown in FIG. 1, comprises a circulating pump 40, the suction of which is connected by a pipe 41 to the separation vessel `13 at the base of this latter, while the delivery side of the pump supplies a separation hydro-cyclone 43 through a pipe 42. The delivery side of the pump 40 is also connected to the separation vessel 13 by a return pipe 44 controlled by a valve 45.

In practice, the valve 45 is preferably always slightly open. This arrangement maintains a desirable agitation in the bottom of the separation vessel 13. In addition, it enables part of the delivery of the pump 40 tol be absorbed, this delivery being in general greater than that of the drying circuit 11.

The hydro-cyclone sends a liquor, which is saturated but free from crystals, to the separation vessel '13, through a pipe y416.

The dryer 48 is shown in detail in FIGS. 4 and 5. It comprises, in known manner, a conical sieve 52 rotatably mounted in a chamber or tank 54. The liquor to` be dried is from hydro-cyclone 43 at 47 along the axis of the sieve 52 and this latter ensures the separation or sifting of the desired crystals, which fall at 53, from a practically liquid paste forming the drying reflux, the latter being evacuated from the chamber 54 by a conduit 58. There is diagrammatically shown at 57 the Scrapers which may be employed if so desired, in drying machines of this type.

With the sieve 52 of the drying machine are associated one or more fixed spraying racks 60, arranged in proximity to the external wall of the sieve, parallel to the generator line of this latter. This rack or racks is coupled to a supply pipe 61 through which the under-saturated dense -filtered liquor is introduced into the installation.

`On this pipe 61 is connected, as shown in FIG. 1, a branch pipe 62 controlled by a valve 63 and providing a counter-flow within the conduit 518 up to the point where conduit A58 opens into the chamber 54.

This conduit 58 connects the dryer 48 to the separation vessel 13 in which, after the junction of conduit 58 with the pipe 46, the outlet of conduit 58 forms the intake 70 for previously established crystals, as will be explained below; this intake 70 is preferably arranged as close as possible to the point at which the conduit 15 opens into the separation vessel 13, so as to take advantage of the high upward speed resulting from the large flow-rate in this latter conduit.

In addition, in the conduit 58 is interposed a fractionating means 65 for crystals, which for example may be a ball grinding mill or preferably a simple mixer of the type utilized for example for domestic purposes. It is also possible to place any other fractionating means at any other point of the installation which contains crystals.

The operation of the installation is as follows:

The liquor contained in the evaporation circuit 1'0 carries crystals, the latter being introduced at 70` into the separation vessel 13 as will be explained below. This liquor is kept in continuous circulation in the circuit by the pump of the vessel 13v and, after passing into the crystallizer 17, this liquor is distributed by the pipes 25 over the elements 21 of the exchanger 12; it constitutes the secondary fluid of this exchanger, the primary heating fluid of which is steam introduced into the elements 21, as will be explained below.

As will have already been noted, and by reason of the inclination of the exchanger 12 relative to pipes 25, the cross section available for the passage of liquid in pipes 25 is smaller at their downstream extremities, as indicated in FIGS. l and 3, and this advantageously compensates for the quantity already discharged upstream of the said extremities.

The pipes 25 should preferably be constructed in such manner as to comply with the two following essential features:

The distribution of the liquid to be spread over the elements 21 must be as uniform as possible over each element and no crystal should be capable of blocking the slots 26, shown in FIG. 3.

In contact with the elements 21, along the walls of which it streams in a very thin film, as shown diagrammatically at 75 in FIG. 3, the distributed liquor is subjected to a partial vaporization but, as has been explained above, this vaporization is advantageously carried out without bubbling, and therefore without priming and without local overheating. This vaporization results in a concentration of the liquor and, if this concentration is carried sufficiently far, causes a subsequent increase in size of the previously formed crystals which are carried by the said liquor, as will be explained below. 'Such increase 1n size may also be produced upstream and/or downstream of the heat exchanger, for example in the crvstallizer 17.

The non-vaporized liquor is taken by the conduit and returned to the separation vessel 13.

The vapour liberated in the exchanger 12 above the treated liquid is collected by the cone 27 and dlrected by this latter to the compression vessel 29; then, by means of the discharge nozzle 32 and conjointly with a pressurized solvent vapour coming-in through the pipe 37, it is introduced into the elements 2.1 of the exchanger 12, of which it constitutes the primary fluid.

The condensed solvent vapour is removed by the pump 31.

In the separation vessel 13, the crystals are classified, or sorted, due especially to the rising ilow induced 1n this vessel by the pump which it contains. At the bottorn of the vessel 13, the concentrated liquor loaded with crystals is taken by the pump 40 of the drying circuit 11 and is directed by this pump to the hydro-cyclone 43.

The spent liquor can be extracted by the pipe 33 and/ or by the pipe '34, this liquor being easily separated from the large crystals by the hydro-cyclone 43 for example, by the cyclone action resulting from the connection of these tubes in the elbows of the conduit 16, or by appropriate filtration. This spent liquor returns to the associated preparation unit, preferably after ltration.

The thick mass of crystals leaving the hydrocyclone 43 passes into the drying apparatus which removes the largest crystals by sifting; these crystals fall at 53 and constitute in the present case the lfinal product.

The liquid paste which passes through the basket of the drying apparatus, and which still contains crystals of small size, is directed through the conduit 58 to the separation vessel 13 of the evaporation circuit. The crystals conveyed by this paste constitute for this circuit, a source of supply of pre-formed crystals.

As they pass through, these crystals are brought to the desired dimensions by the fractionating means 65. These dimensions may for example be of the order of 1D0/i. According to the invention, the use of crystals split-up in this way is of particular advantage, since experience has shown that such crystals generally grow faster than naturally-formed crystals.

The fresh liquor is the concentrated 4filtered under-saturated liquor introduced into the drying apparatus 48 by the

pipes

61 and 62. The corresponding points of introduction of this liquor as described above have been chosen so as to ensure a systematic elimination of the nuclei, which without this arrangement, would have a tendency to develop spontaneously in the vicinity of these points. In addition, the liquor introduced through the pipe 62 mechanically carries away the crystals which would have a tendency to be decanted in the tank 54 of the drying apparatus shown in FIG. 4.

A similar arrangement, namely the introduction of under-saturated liquor, is preferably adopted for all the points of the installation at which a nucleation of this kind would have a tendency to take place spontaneously, due to the favourable heat or mechanical conditions.

As this nucleation is most frequently prolific, and as the average individual mass of the crystals for a given hourly production is inversely proportional to the number of nuclei formed, the crystals obtained in the usual crystallization installations only rarely attain a substantial size.

As will be readily understood, the controlled preferential growth of pre-formed crystals, as Carried out in the installation according to the invention, enables, by a judiciously arranged extraction, a production of crystals of the desired size and in particular large crystals.

Experience has in fact shown that in a saturated liquor, the large crystals develop at the expense of the nuclei and even of the small crystals, and in addition, contrary to generally accepted opinion, the speed of crystallization increases, within certain limits, with the size of the crystals.

Now, as is well known for reasons of facility of water removal and drying without dust removal, of ease of storage without setting into a solid mass and without formation of arches, of facility of handling without going into lumps, of economy of transport without sticking to the walls, together with other advantages, it is of the greatest value to obtain crystals which are as large as possible, and this is the economic basis of the installation according to the invention.

lIn addition, it has been established that crystals so obtained by the growth of pre-formed crystals are, other conditions being equal, purer than the crystals developed in the traditional manner from. nuclei.

The number, as large as possible, and the size of the pre-formed crystals introduced into the treated solution, are of course chosen in such manner that the presence of these crystals is compatible with a suitable circulation of the product in question.

In the manner described above, the fresh solution is introduced into the drying apparatus 48.

The advantages of this arrangement will be better understood by referring now to lFIG. l2 which is a concentration-temperature diagram, on which there has been transferred a typical solubility curve C1 of the products for which the solubility of the crystals increases with the temperature-in most cases these are hydrated crystals-and a typical solubility curve C2 of the products for which the solubility of the crystals diminishes with increasing temperature, and in most cases these are anhydrous crystals. These curves intersect at D on a vertical line having an abscissa tD.

There will be assumed, by way of example, the case in which the crystals have a solubility curve of the type C1.

A newly-formed fresh solution `which is slightly undersaturated has its characteristic point at S1, having an ordinate c1, corresponding to a concentration which is as high as possible; its temperature is t1, which is relatively high.

According to the invention, this fresh solution is introduced into the centrifuge, with the following advantages:

Elimination of heat by the centrifuged crystals, and therefore cooling of the entering solution;

Heating of the outgoing centrifuged crystals, which facilitates their subsequent drying and economizes the heat necessary for this drying;

`Centrifuging of the crystals in the presence of the purest liquid phase, the entering solution being necessarily purer than the solution in circuit, since the impurities are successively re-cycled into this circuit and therefore accumulate there;

Elimination by dissolving of the nuclei which would have a tendency to be formed in an undesirable manner in the centrifuge.

The advantages are found in a symmetrical manner with respect to the vertical line tD, in the case in which the solubility curve of the crystals is of the type shown by the curve C2.

F or the reasons given above, the under-saturated liquor conveyed by the pipe 62 axially through, but isolated from the suspension outlet conduit 58 of the centrifuge attacks the nuclei first in tank 54 in preference to the crystals which are located in this conduit after having passed through the basket of the centrifuge.

However, in the case where the liquor circulating in this conduit does not have any crystals or only comprises an insucient number, the supply of pre-formed crystals to the vessel 13 would be ensured, either by increasing the flow taken by the valve 45 from the delivery of the pump 40, or by connecting the said delivery to the inlet 70 through a regulating valve 76 interposed on a branch circuit 77 on the one hand, as shown in broken lines in *FIG. 1, and on the other hand through the fractionating means 65.

This fractionating means has the purpose of maintaining constant the number of crystals'contained in the crystallization unit and of replacing the number of crystals extracted by an equal number of broken crystals introduced into this crystallization unit.

It should furthermore be noted that, in accordance with the invention, the fractionating means is operative in the liquid phase.

FIG. 6 relates, by way of example, to an installation with three stages or eifects A, B and C. In this figure, the elements previously described have been given the same reference numbers, to which is added however the letter A, B, or C corresponding to the effect or stage to which they belong. Each effect A, B and C comprises an

evaporation circuit

10A, 10B, 10C respectively; in order to simplify the drawing, it has been assumed that a single product is crystallized in the installation, and there is therefore only a single centrifuge circuit 11.

The fresh solvent vapour coming in through the pipe 37 is directed inside the elements 21A of the exchanger 12A of the effect A or first effects; the secondary vapour collected by the cone 27A of this exchanger 12A is directed inside the elements 21B of the exchanger 12B of the effect B, or second effect; and then similarly, the tertiary vapour collected by the cone 27B of the exchanger 12B is directed inside the elements 21C of the exchanger 12C of the effect C, or third effect; finally, the fourth vapour collected by the cone 27C of the exchanger 12C is directed over a condenser 80 connected by a conduit 31 to a vacuum pump (not shown). This same conduit 81 also collects the vapours condensed in the various exchangers.

'Ihe treated liquor circulates in the opposite direction. It passes at 61 into the centrifuge 48', as previously, and then after being charged with the crystals passing through the basket of the centrifuge and passing into the fractionating means 65, it is sent by the pump 40 into the distribution pipes 25C of the exchanger 12C.

After collection by a pump C, it is delivered by this latter to the distribution pipes 25B of the exchanger 12B, Finally, after a similar passage into the exchanger 12A, it is collected by a pump 85A and delivered by this latter to the hydro-cyclone 43.

The spent liquor passes out at 146 and can for example be conveyed to a cooling circuit for the subsequent deposit of another solid.

FIGS. 7 to 1l relate to an alternative form of construction of the heat exchanger 12 according to the invention.

Following this alternative, the body 1.20 of this exchanger is as shown in FIGS. 7 and 8 horizontal and is provided laterally with rollers 121 intended to roll on rails 122. This arrangement makes it possible to have very easy access to the exchange elements 21 in case of need.

The body terminates in ange 123 intended for fixing it rigidly, for example by bolting, to a cover 124 to which are connected the vapour outlet 13.2 with a discharge nozzle or the like, and the evacuation pipe 13-9.

The arrangement also includes steam inlet 142 and condensate outlet 143.

The distributor pipes 25 of the previous embodiment are replaced in this alternative form by a unit 125 in the form of a comb (FIGS. 7-10).

This unit 125 is shown in FIGS. 9, 10A, 10B and ll to comprise an upper closure plate 126 and a plurality of parallel channels 1,27. Each channel 127 is convergent horizontally between an inlet 1.28 at one end of unit 125 and an outlet 129 arranged at the other end thereof, but has always the same dimension in the vertical direction.

Each channel 127 is formed by two

vertical Walls

130, 131, which Agradually approach each otherand which are directed towards each other by

horizontal returns

133, 134 respectively, forming conjointly a slot 135 of constant width.

The slots 135 of the unit 125 are engaged over the upper edges of the exchange elements 21 and substantially overlap these latter.

A unit of this -kind ensures a very uniform distribution and permits a considerable delivery of vapour. Any liquid which is delivered to unit 125 and which does not leave via slots 135, simply exits via outlet 129, falls to the bottom of body 120, and is removed with the other liquid.

It will be understood that the heat exchanger described above may equally serve as a cooler in the case especially where a crystallization is desired and this crystallization necessitates a cooling action.

FIGS. 13 to 17 relate to an alternative form of construction of this exchanger.

As previously, this latter comprises as shown in FIGS. 13 and 15 a cylindrical body or casing 220` with a horizontal axis, provided laterally with rollers 221 for moving on rails 222. 'Ihe body 220` is terminated by a flange 223 for fixing, for example by bolting, to a cover 224.

In FIG. 13, the body 220 is shown removed from the cover 224 to a distance from this latter, in order to show the nest of tubes 225 of the exchange elements 226 which the body is intended to protect.

Each of the heat exchange elements 226 has, in a plane perpendicular to the axis of body 120, a substantially rectangular contour (see FIGS. 14 and l5) and in prole an undulating contour as shown in FIGS. 13 and 17. It is composed of two similar

thin walls

227, 228, which are spaced uniformly apart by a distance D. Each of these walls has corrugations, the period, amplitude and number of which are chosen so that, taking account of its thickness, it is capable of resisting without permanent deformation, the difference in pressures capable of existing on each side. These

walls

227, 228 are then simply welded to each other at their periphery without mutual intermediate supports.

At their upper portion, the walls 227, 2281 of an element 226 are provided with a sharp edge 229, the purpose of which will become apparent below. This edge may be added, for example by welding.

The exchange elements 226 extend transversely with respect to the longitudinal axis of the body 220, so that when the latter is withdrawn the edges of elements 2.26 are on the outside. This arrangement facilitates cleaning of these elements by a jet of water, and also provides for the possible addition of supplementary elements at the end of those previously incorporated, with the corresponding addition of a cylindrical portion to the body 2.20.

As indicated in a diagrammatic manner in FIGS. 14 and 15, the assembly of the elements 226 permits the formation peripherally between them and the body 220I of the chambers V1, V2, V3` and V4, the chamber V1 being the extreme left-hand chamber on the said figures and the chambers V2 to V4 being then spaced apart and distributed around elements 226 in the clockwise direction.

The exchange elements 226 are mounted to project in the same way as the teeth of a comb (see FIG. 16) from a common vertical distribution casing 230i arranged inside the chamber V1 defined above. The internal volume of this casing communicates with the internal space 231 of each element, In FIG. 16, the elements 226 are shown in a rectilinear manner, detached from each other for the sake of clearness of the drawing. However, as shown in FIG. 17, these elements are preferably slightly reentrant in each other.

The distribution casing `230 is provided with a supply conduit 232 which passes through the cover 224, and at the same time the elements 226 are connected together at their lower portion by an evacuation conduit 233, which also passes through the cover 224, as shown in FIGS. 13 and 16. The assembly can easily be made dismantlable.

With the elements 226 is associated a distributor unit 235, mounted above the units in the chamber V2, as defined above. This distributor unit, which is preferably but not necessarily of the same type as that described in French Patent No. 1,531,361, comprises a respective transverse discharge nozzle 236 (FIGS. 13 and 17) located vertically above the sharp edge 229 of each element 226.

This distribution unit 2315 which advantageously ensures a smooth projection of the treated solution and not a spraying effect, is coupled to a supply pipe 237 which passes through the cover 224, preferably in a removable manner.

This cover 224 is also traversed by a vapor removal conduit 2381 opening into chamber V3 which is at right angles to the chamber V2, and by a concentrate removal conduit 239 leading from chamber V4.

As previously stated, an exchanger of this kind may also serve as a crystallization body, whether this crystallization is effected by cooling or by evaporation.

In the following text it will be assumed that it is effected by evaporation.

The distribution unit 235, supplied from the pipe 237, causes the mother solution to stream in thin dilms over the walls of the exchange elements 226, the sharp edges of these latter ensuring a good distribution of this solution over each of their walls. The elements 226 are supplied with live steam by the pipe 232 and the distribution casing 230. The steam condensed at 231 in the elements 2126 is evacuated by the pipe 233, while the solution which has streamed over the elements 226 is collected in the chamber V4, from which it is evacuated by the pipe 2-39. In contact with the elements 226, the solution treated becomes concentrated under the most favorable conditions of micro-agitation, advantageously avoiding any excess heating. This micro-agitation is due to the turbulent streaming of the solution over the elements 226 and is facilitated by the corrugated profile of these latter, or more generally, by the changes in slope of the said profile.

With regard to the vapour liberated by the solution treated, this is collected in the chamber V3 and evacuated by the tube 238, for example towards a condenser or a. vacuum ejector.

There should be noted the particularly rational use of the internal space of an exchanger of this kind, this use being made possible by the arrangement according to the invention, of a nest of exchange elements placed trans versely in the interior of a cylindrical body.

According to an arrangement which is not shown in FIG. 17, the most upstream nozzle 236, that is to say the nozzle 236 which is nearest to the co'ver 224, is preferably wider than the others so as to permit the passage of all the crystals which may travel into the pipe 237, thus avoiding a possible obstruction of the other nozzles.

In accordance with the alternative form of construction shown diagrammatically in FIG. 18, the exchange elements 226 may equally well have a zig-zag profile.

Following an arrangement which is not shown in the drawings, spacing members are preferably provided at the overhanging extremities of the elements 226. These spacing members which are preferably adjustable, have a double purpose: on the one hand to compensate for the effects of the differential expansion of the two longitudinal walls of the casing 230, and on the other hand to regulate the positions of the sharp edges 229 of the elements 226 in the axes of the corresponding nozzles 236 of the distribution unit 235.

FIG. 19 relates to an alternative form, in which the sharp edge 229 of an element 226 is formed by an extension of one of the

walls

227, 228 of this element to form a tongue, this extension being preferably deformable with respect to its connection or coupling line to the other wall. The spacing members referred to above enable the regulation by deformation of the position of this extension with respect to the associated nozzle 236 (not shown in the drawing), as indicated in broken lines.

In the foregoing description, it has been assumed that the crystallization concerned was effected by evaporation. -ln the case where this crystallization is effected by cooling, that 1s to say in the case where the heat exchanger accordmg to the invention is utilized as a cooler, the refrigerating fluid necessary may be introduced through the pipe 232 and passes out heated through the pipe 233, although it is preferable from the thermal point of view to introduce it at 233 and to evacuate it at 232.

For the reasons explained above, the introduction of the fresh solution into the centrifuge of the installation according to the invention has a number of advantages.

It will be understood that in the case where the above advantages are not sought for automatically, the fresh solution may be introduced at a point other than into the centrifuge,

This is especially the case when special arrangements are made in addition, to avoid the formation of nuclei in the centrifuge.

There will now be described, with reference to FIGS. 20 and 21, a centrifuge 260 provided in accordance with the invention with arrangements adopted precisely for that purpose.

The perforated basket 26'1 of this centrifuge is carried by a skirt 262 keyed for rotation on a driving shaft 263. In a manner known per se, there is associated therewith one or a plurality of helical Scrapers 264 carried by a support 265, and this support is keyed for rotation with a shaft 266 mounted in the interior of the shaft 263 and coaxial therewith. The shaft 266 may be fixed or it may rotate at the same speed as the basket 261 or it may rotate at a different speed by braking or by a motor.

The crystals to be centrifuged are introduced into the mouth 267 of the basket 261, and, after sliding along the internal wall of this backet under the control of the v11 scraper or scrapers 264, they are evacuated at 268.

This arrangement is well known.

It has however the disadvantage that any undesired ventilation produced through the sieve by the relative rotary movements of the basket 261 and the scraper or scrapers 264, is favourable to the formation of nuclei and causes blocking-up of the basket 261 and also causes the crystals to set in a mass during the course of centrifuging.

According -to the invention, the basket 261 is extended laterally by a plate 270 and is capped by a bell 271.

Between this bell 271 and the basket 261 there is only left a small space 275 which opens to the exterior through an annular slot 276 at the extremity of the plate 270.

The dimensions of this slot are adjusted so that its flow-rate is at most equal to the theoretical liquid flowrate of the centrifuge.

By this means, the space 275 is lled with liquid and any circulation of air through it is impossible, which eliminates the drawbacks referred to above.

In the embodiment shown in FIG. 2l, the outlet of liquid is effected along a ring, as shown diagrammatically at 277.

In an alternative form shown diagrammatically in FIG. 22, the above outlet slot 276 is replaced by a plurality of peripheral nozzles 278 oriented tangentially and uniformly spaced apart around the periphery.

These nozzles make it possible to recover from the liquid a part of `the energy of rotation which has been given to them by the basket 261 and therefore economically reduces the energy necessary for the rotation of this basket 261.

It Awill of course be understood that the present invention is not limited to the forms of construction described above, but includes all its alternative forms of execution, especially as regards the plan contour of the exchange elements which could equally well be curviliner or zig-zag.

What I claim is:

1. An installation for the continuous evaporation of any solvent and for the continuous concentration of at least one substance in solution in said solvent, of the kind comprising an indirect heat exchanger through which circulate, on the one hand, the solution to be treated and, on the other hand, a heat exchange uid, in which said heat exchanger comprises a housing body, a plurality of similar exchange elements arranged in parallel and spaced apart from each other inside said body, each said element being closed and composed of two substantially vertical thin walls disposed at a short distance from each other, a primary heating vapor intake adapted to introduce said exchange fluid between said Walls, and a secondary solution intake causing said solution to stream over said walls, said secondary intake comprising as many substantially horizontal elongate discharge outlet nozzles as there are heat exchange elements, and each of said nozzles being arranged directly above the upper edge of a respective one of said exchange elements, said secondary intake being constituted by a unit having the shape of a comb and comprising a plurality of elongate channels converging in their longitudinal direction and longitudinally slit at their lower portions to provide said nozzles, said heat exchange elements being embraced by the nozzles formed in said channels over the associated exchange elements.

2. An installation as claimed in claim 1, in which said heat-exchanger serves at the same time as a heater and as an evaporator device.

3. An installation as claimed in claim 1, in which the walls of said exchange elements are provided with transverse stiifening bosses.

4. An installation as claimed in claim 1, in which the walls of a said exchange element have a profile presenting changes of slope.

5. An installation as claimed in claim 1, in which each of said exchange elements is provided with a tapering edge 12 facing the corresponding outlet nozzle of the intake for said solution.

6. An installation as claimed in claim 5, in which said tapered edge is constituted by an extension of one of the Walls of said exchange element.

7. An installation as claimed in claim 6, in which said wall extension is deformable with respect to its line of coupling to the other wall of said exchange element.

8. An installation for the continuous evaporation of any solvent and for the continuous concentration of at least one substance in solution in said solvent, of the kind comprising an indirect heat exchanger through which circulate, on the one hand, the solution to be treated, and on the other hand, a heat-exchange fluid, in which said heat exchanger comprises a housing body in the form of a circular cylinder having a substantially horizontal axis, a plurality of similar, vertical exchange elements arranged in parallel, spaced apart from each other inside said body, and disposed transversely with respect to the axis of said body, each said element being closed and composed of two thin substantially vertical walls disposed at a short distance from each other, a primary heating vapor intake adapted to introduce said exchange uid between said walls, and a secondary solution intake causing said solution to stream over said walls, said secondary intake comprising as many outlet nozzles as there are exchange elements, and each of said nozzles being arranged directly above the upper edge of one of said exchange elements.

`9. An installation as claimed in claim 8, in which said exchange elements have a rectangular outline and are adapted to form four adjoining peripheral chambers with the cylindrical body in which they are contained, one said chamber comprising the primary intake for said exchange Huid, a second chamber comprising the secondary intake for said solution, a third chamber comprising an outlet for the solution vapour formed, and a fourth chamber comprising an outlet for the remainder of the nonevaporated solution, a further outlet being provided for the evacuation of the fluid condensed in said exchange elements.

110. An installation as claimed in claim 8, in which said exchange elements are mounted in a cantilever position on a distribution casing, the internal space of said casing being adapted to communicate, on the one hand, with the internal space of each of said elements and, on the other hand, with the primary intake provided for said exchange fluid.

11. An installation for the continuous evaporation of any solvent and for the continuous concentration of at least one substance in solution in said solvent, of the kind comprising an indirect heat exchanger through which circulate, on the one hand, the solution to be treated and, on the other hand, a heat-exchange uid, in which said heat exchanger comprises a housing body, a plurality of similar exchange elements arranged in parallel and spaced apart from each other inside said body, each said element being closed and composed of two substantially vertical thin walls disposed at a short distance from each other, a primary heating vapor intake adapted to introduce said exchange fluid between said walls, and a secondary solution intake causing said solution to stream over said walls, said secondary intake comprising a distributor unit having its bottom provided with as many elongate discharge outlet nozzles as there are exchange elements, each of said nozzles being arranged directly above and parallel to the upper edge of a respective one of said exchange elements, said distributor conveying solution in a direction transverse to said nozzles, and that one of said secondary solution nozzles which is in the farthest upstream position with respect to the direction of solution flow being wider than the succeeding nozzles.

12. An installation as claimed in claim 11, in which said secondary intake of the exchanger is constituted by a plurality of tubes each slit along a generator line and having the slot thus formed embracing the upper edge of the associated exchange element.

13'. An installation as claimed in claim 12, in which the axis of each of said tubes is inclined with respect to the general direction of the said upper edge of the associated exchange element.

14. An installation for the continuous evaporation of any solvent and for the continuous concentration of at least one substance in solution in said solvent and the extraction of crystals of said substance, of the `kind comprising an indirect heat exchanger through which circulate, on the one hand, the solution to be treated and, on the other hand, a heat-exchange fluid, in which said heat exchanger comprises a housing body, a plurality of similar exchange elements arranged in parallel and spaced apart from each other inside said body, each said element being composed of two substantially vertical thin walls disposed at a short distance from each other, a primary heating vapor intake adapted to introduce said exchange iluid between said walls, and a secondary solution intake causing said solution to stream over said Walls, to cause part of said solution to be evaporated by thermal exchange with said exchange fluid and the remainder of said uid to remain in its liquid state and to fall to the bottom of the interior of said body after traversing said walls, said secondary intake comprising as many elongate discharge outlet nozzles as there are exchange elements, and each of said nozzles being arranged directly above the upper edge of one of said exchange elements, said installation further comprising: a centrifugal separation device for circulating a liquid and having a rst inlet in communication with the bottom of the interior of said body for receiving the liquid thereat and an outlet in communication with said secondary intake for delivering solution thereto, said heat exchanger and said separation device forming an evaporation circuit, said centrifugal separation device further having a second inlet; means connected to said second inlet for delivering pre-formed crystals of said substance to said centrifugal separation device; and a centrifugal liquid-solid separation circuit connected in parallel with said evaporation circuit, said separation circuit comprising a liquid-solid separating centrifuge having a centrifuging basket and having a rst inlet connected to receive from said centrifugal separation device, via a pump, a crystal bearing concentrated solution which is delivered to the interior of said basket, and a second inlet connected to receive a supply of undersaturated fresh solution delivered to the exterior of said basket.

15. An installation as claimed in claim 14, in which said centrifuge is fed by a hydro-cyclone.

16. An installation as claimed in claim 14, and further comprising a plurality of evaporation circuits arranged in cascade.

17. An installation as claimed in claim 14, in which said basket of said centrifuge rotates in a chamber connected by a delivery pipe to said second inlet of said separation device of said evaporation circuit.

18. An installation as claimed in claim 17, in which said delivery pipe encloses a counter-110W intake pipe for undersaturated solution, opening into said chamber.

19. An installation as claimed in claim 14, and further comprising crystal-fractionating means provided at any point of sai dinstallation, said means being constituted by a mixer, grinder or the like.

20. An installation as claimed in claim 19, in which said fractionating means operate in the liquid phase.

211. An installation for the continuous evaporation of any solvent and for the continuous concentration of at least one substance in solution in said solvent and the extraction of crystals of said substance, of the kind comprising an indirect heat exchanger through which circulate, on the one hand, the solution to be treated and, on the other hand, a heat-exchange fluid, in which said heat exchanger comprises a housing body, a plurality of similar exchange elements arranged in parallel and spaced apart from each other inside said body, each said element being composed of two substantially vertical thin Walls disposed at a short distance from each other, a primary heating vapor intake adapted to introduce said exchange fluid between said Walls, and a secondary solution intake causing said solution to stream over said walls, to cause part of said solution to be evaporated by thermal exchange with said exchange fluid and the remainder of said Huid to remain in its liquid state and to fall to the bottom of the interior of said body after traversing said walls, said secondary intake comprising as many elongate discharge outlet nozzles as there are exchange elements, and each of said nozzles being arranged directly above the upper edge of one of said exchange elements, said installation further comprising: a centrifugal separation device for circulating a liquid and having a first inlet in communication with the bottom of the interior of said body for receiving the liquid thereat and an outlet in communication with said secondary intake for delivering solution thereto, said heat exchanger and said centrifugal separation device forming an evaporation circuit, said centrifugal separation device forming an evaporation circuit, said centrifugal separation device further having a second inlet; means connected to said second inlet for delivering pre-formed crystals of said substance to said centrifugal separation device; and a centrifugal liquid-solid separation circuit connected in parallel with said evaporation circuit, said centrifugal separation circuit comprising a centrifuge having a perforate basket capped by a bell spaced a small distance from said basket, the space between said basket and said bell being provided with liquid discharge openings dimensioned to permit a maximum rate of flow which is equal to the theoretical liquid outflow rate of said centrifuge. 22. An installation as claimed in claim 21, in which said liquid discharge openings are formed as nozzles disposed tangentially to the basket periphery and perpendicularly skew to the axis of rotation of said basket.

References Cited UNITED STATES PATENTS 743,352 11/1903 Trump 159-27 A X 1,501,646 7/1924 Brown 159-1218 C 2,194,014 3/194() Ehrman 1165--115 2,343,886 3/1944 Cornell, Ir 159--3 X 2,739,044 3/1956 Ashley et al 23,-302 2,805,557 9/1957 Hilger 165-115 X 3,351,119 11/1967 Rosenblad 159-13 B 3,371,709 3/11968 Rosenblad 159-28 X FOREIGN PATENTS 1,003,479 3/1952 France.

NORMAN YUDKOFF, Primary Examiner J. SOFER, Assistant Examiner U.S. Cl. X.R.