FI98198C - Process for concentration of liquid and evaporation unit for concentration of liquid - Google Patents

Description

- 98198

Method and evaporation unit for concentrating the liquid

The present invention relates to a method for concentrating a liquid, the method comprising the steps of passing the liquid through a heat exchanger section from an inlet end to an outlet end; heating the liquid passed through the heat exchanger section to produce steam and concentrate the liquid; circulating the steam produced by heating the liquid in the heat exchanger section from the outlet end of the heat exchanger section to its inlet end to introduce steam into the liquid at the inlet end to increase the velocity of the liquid.

The invention further relates to an evaporation unit for concentrating liquids, which unit comprises a heat exchanger dinosaur; liquid inlet means connected to the inlet end of the heat exchanger section for conveying the liquid to be concentrated to the heat exchanger section; liquid and steam outlet means connected to the opposite end of the heat exchanger section for removing and separating the concentrated liquid and steam from the heat exchanger section; heating means located adjacent the heat exchanger section for heating the liquid passed through the heat exchanger section; steam recirculation means connected to the outlet end and the inlet end for recirculating steam from the outlet end. 25 to mix the inlet end and the steam coming from the outlet end at the inlet end of the liquid through the heat exchanger section to increase the velocity of the liquid and steam conveyed.

• · · • · · * Upstream or downstream systems correspond to two classic types of evaporation. Downstream system- • · c '• i.' 30 The liquid is forced to flow vertically substantially along the vertical exchange surfaces, which generates liquid vapor which flows together with the liquid. The direction of the flow is obtained by gravity and by the difference in • pressure between the upper feed housing and the bottom evaporation housing, both acting in the same direction.

On the other hand, in the upflow type, the liquid rises due to the effect of the pressure difference, acting against gravity, which generates steam from the evaporation of the liquid as the former and the latter flow in the same direction.

In both the downstream and upstream system 5, the heat exchange surfaces may consist of plates or tubes with a heat medium such as steam flowing between the heat transfer walls.

Examples of downstream evaporation systems equipped with tubes are described in detail in U.S. Patents 4,076,576 and 4,641,706, which are incorporated herein by reference. U.S. Patent 4,586,565 describes in detail a downstream system that uses plates as heat transfer means and is also incorporated herein by reference.

15 One of the most serious problems encountered in evaporation equipment is the precipitation of solid particles which remain adhered to the heat exchange surfaces. As the liquid evaporates, the dissolved solid particles concentrate until they reach a solubility coefficient of 20 for each component, exceeding this, whereupon the dissolved solid particles begin to precipitate into a crystalline or amorphous state or in the form of rubber or polymers. Similarly, on the other hand, what: the higher concentration of solid particles in the solution is,; the higher the viscosity so that when the water va-. .25 evaporation by evaporation continues, the liquid solution tends to move • · · · slower and thus the precipitated salts or • · "rubbers" begin to adhere to the walls of the heat exchange surfaces. Technically, this precipitate on the surfaces is called "scale".

• 1 · * 30 Once these precipitated particles have started to adhere to the walls of the heat exchanger, the extra crystals and particles: * ·. · Continue to adhere at an exponential type of staining rate.

The precipitate or scale corresponds to a useful

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'·' '35 reduction in the transfer area, i.e. due to this the amount of heat exchanged per unit of time is reduced.

This precipitate or scale, after reducing the evaporation capacity per unit time, may cause the need to stop the operation for cleaning and start it again when this is completed. Thus, all designers and / or manufacturers of concentrators have invested heavily in solving this serious problem.

Accordingly, it is an object of the present invention to provide a method and concentration unit or apparatus in which vapors from a liquid exposed to evaporation flow at a rate sufficient to prevent the precipitated particles from adhering to the walls of the heat exchange surfaces.

Another object of the present invention is to provide a concentrator which continuously prevents the formation of fines without the need to stop the evaporation function of the apparatus.

Yet another object is to provide an evaporator unit which, as a result of the system used, has a higher heat transfer coefficient than similar corresponding evaporator units provided with completely similar walls or exchange surfaces.

Said objects are achieved by the method according to the invention, which is characterized in that the steam is recirculated so that the velocity of the liquid increases so that the liquid becomes droplets which strike the heat exchanger part against the heat exchanger surface with sufficient energy. · * .T ^ 30 gial so as to prevent the deposition of the precipitated particles *. * 'Or to remove the particles.

The evaporator unit according to the invention, in turn, is characterized in that the evaporator unit is a downstream evaporator unit, the inlet end being the upper end of the heat exchanger part and the outlet end being the lower end of the heat exchanger unit; and that the steam recirculation means are arranged to circulate steam during operation of the evaporator unit so that the velocity of the liquid increases so that the liquid turns into droplets which strike the heat exchanger surface of the heat exchanger part with sufficient energy to prevent or precipitate particles.

Other significant objects, advantages and features of the present invention will become apparent from the accompanying drawings, in which Figure 1 corresponds to a partial view of an evaporator unit according to a first object of the present invention; Figure 2 corresponds to a schematic perspective view of the evaporator unit of Figure 1. Fig. 3 corresponds to a sectional plan view of Fig. 3.3, Fig. 4 is a partial view according to a second unit of the present invention, and Fig. 5 corresponds to a partial view of a third unit 20 of the present invention.

Referring first to Figure 1, an evaporation unit is shown in accordance with the present invention; :: and comprises a shell 12 having an inlet end 14 at the upper end for receiving the liquid to be evaporated; a heat exchanger 16 located below the housing 14, through which the liquid is evaporated and the suspension in solution is concentrated; a bottom housing or base 18 below the exchanger 16 for receiving a partially concentrated solution or a solution of its final concentration, depending on the corresponding evaporation step, together with the vapors from the evaporation; and a base 20 connected below 18 to support the unit. The evaporator unit 10 also comprises a device 22, shown in Figure 2, for the flow of vapors from the evaporator, which is rigidly connected, for example by welding, between the upper housing or head 14 and the base housing; and a fluid flow device 24 rigidly connected to the housing 12.

Vapors flowing through the tubular unit 22 - usually water vapor generated by evaporation of the liquid passing through the heat exchanger 16 and penetrating the head 14, mixing with the liquid in such a way that the mixture passes through the exchanger at a rate sufficient to prevent the precipitated particles from adhering -topintoihin. At high velocities, the liquid changes into droplets, which strike the surfaces of the exchanger with sufficient energy, thus repelling or removing the precipitated particles.

The evaporator unit 10 may consist of a simple step or may be used in conjunction with a plurality of units 15 to form a multi-effect evaporator system. Likewise, the unit 10 may correspond to a downstream or upstream evaporation type or some other suitable evaporation unit.

However, for the sake of simplification, only the simple effect downstream evaporation unit will be described in detail. The object of the invention would be kept unchanged and valid for all types of : for evaporators equipped with exchanger surfaces of any type, ·, ·.

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. The head or feed housing 14 is retained by the lid 26, the first tubular plate 28 and a portion of the cylindrical wall 30 of the circular shell 12 extending between the lid 26 and the first tubular plate 28.

As can be seen in Figures 2 and 3, the head 14 is divided into four equal supply housings 31, 32, 33 and 34 V 'by baffles 36. The baffles 36 are rigidly connected to the first tubular plate 28 and cover 26 to form watertight housings for separating feed fluid in each feed fluid. in the housing 31-34 to the other parts in such a way that the liquids cannot mix with each other. The supply pipes 38, 39, 40 and 41 are rigidly connected to the cover 26 98198 6 to lead the solution to be concentrated from the supply pipes 38, 39, 40 and 41 to be fed to the housings 31, 32, 33 and 34, respectively.

The heat exchanger 16 is defined by a portion of the cylindrical wall 30 of the cylindrical shell 5 12 extending between the first tubular plate 28 and the second tubular plate 44. The heat exchanger tubes 46 are rigidly connected - for example by welding or expansion - to form watertight housings between the tubular plates 28 and 44 10, allowing free contact and medium communication between the inlet housing 14 and the outlet 18 while preventing any contact between the heat medium and the solution or evaporating liquid. between the vapors generated.

In particular, the first tubular plate 28 has various openings aligned with the upper end of a tube group 46 of a heat exchanger so that the feed liquid in each portion 31-34 can be passed through the tubes of the heat exchanger 46.

The second circular tubular plate 44 has the same number of openings positioned in the same geometric position as aligned with the heat exchanger tube assembly 46, allowing concentrated liquid and vapor to exit to the outlet housing or substrate 18.

25 The area of the exchange tubes 46 between the first tubular plate 28 and the second plate • · · * · * · defines the evaporative:. *. dutusalueen. Thus, the longer the exchange tubes 46, the larger the evaporation range. The exchanger tube group 46 is divided into four parts. The first sector or part is connected or in free communication with the liquid supply assembly. to the roll 31, the second is freely connected to the feed housing • · · 32, the third is freely connected to the feed housing 33 and «· · the fourth is freely connected to the feed housing 34.

The heat medium inlet hose 48 is connected “• 35 fixedly to the cylindrical outer shell 30 of the heat medium,. such as to supply fresh steam to the exchanger section 16 for heating the four sectors of the exchanger group 46. Each of the four sectors of the exchanger group 46 is heated with steam or a thermal medium of the same or completely similar quality, i.e., having the same thermo-5 dynamic properties. Thus, when the tube array is heated by a thermal medium, heat is transferred to the liquid passing through the exchanger tube array 46 to effect concentration of the solids in the solution by evaporation and thereby generating vapors. The exchanger portion 16 10 is also provided with an unsealed gas outlet hose 49 connected to the cylindrical wall 30 and placed adjacent to the first tubular plate 28 for transferring it to the condenser; and a hose 49a connected to the cylindrical wall 30 adjacent the second tubular plate 15 for removing condensate from the steam.

It will be appreciated that the exchanger assembly 46 may consist of other types of exchanger surfaces such as plates instead of tubes.

The discharge housing or base 18 is defined as a portion of the cylindrical wall 30 of the outer shell 20 12 extending from the second circular tubular plate 44 and the third circular base plate 50. The guide plates 55 form four discharge ports. part 51, 52, 53 and 54 inside the discharge housing 18, where! ’! from the exchanger tube group 46 come the required intermediate or; \ 25 Liquids and vapors of the final concentration are separated. Each of the four »· * · ** sections 51-54 is provided with outlets 56, 57, 58 and 59 for removing the final concentration fluid or the intermediate concentration fluid, respectively. The housings 51-53 • ·· ♦ are fixedly connected and freely connected to the steam flow system 22 of the flow pipes 70, respectively; 72 and 74 to remove vapors from the previous one as • · · .’1 *. described below.

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On the other hand, the vapors from the total evaporation produced by the exchanger are blown out of the section 54 through the outlet hose 60 and from there towards the next stage 98198 8 or towards the condenser by the pipes 65a if it was the last stage.

Thus, the following steps may use vapors, usually water vapor, produced in the previous step as a thermal medium to concentrate the solids in the solution in the next step. That is, in the multiple stage, the second stage heat medium inlet hose 48 is connected to the first stage steam separator outlet pipe 65a to use the vapors generated by the first stage evaporation concentration in this second stage; likewise, in the third stage, the heat medium supply hose 48 is connected to the second 65a to use the vapors generated in the second stage evaporation, to concentrate the solids in the third stage, and so on.

The liquid flow device 24 is provided with four discharge drain tubes 61, 62, 63 and 64 rigidly connected to the openings 56-59 of the third plate or round base 50 20, respectively, for removing the concentrated liquid from the parts 51-54, respectively, and for sending it to either the next part. or final concentration receiving precipitate. or towards the next stage by means of pumps 66, 67, 68 and 69 • /._. In particular, the pump 66 leads from the liquid outlet housing 51 through the pipe 66a and the supply pipe 39 to the supply housing • · · ** ** 32.

• The pump 67 sends the solution from the outlet housing 52 through the pipe 67a and from the supply pipe 40 to the alignment housing 33.

The pump 68 sends the solution from the outlet housing 53 through the pipes 68a 30 and from the inlet pipe 41 to the supply housing 34.

: The pump 69 sends a solution from the discharge outlet 54 to the pipe «« ·; * t *; through 69a to the storage tank of the concentrated solution for final concentration or the next step.

As can be seen in Figures 2 and 3, the steam flow system 22 comprises three flow pipes 70, 72 and 74 for conducting steam from evaporation from the outlet housing of one exchanger group part 46 to the feed housing of another exchanger group part 46. Although the tubes 70, 72 and 74 are shown inside the shell 12 in the figures, it is obvious that they can also be located outside.

The first flow tube 70 extends from the outlet housing 51 of the discharge tray 18 to the second supply housing 32 of the head 14 to conduct vapors from the first outlet housing 51 to the second supply housing 32. The vapors flow at a rate high enough to prevent precipitated particles from adhering to the exchange surfaces of the tubular heat exchanger 46. At high speeds, the flow vapors divide the liquid into droplets that act as hammers or scrapers on the exchanger surface of the exchanger to continuously remove or remove particles that tend to form scale. In particular, the bottom end of this first tube 70 is rigidly connected, for example by welding, to the opening 76 of the third base plate 50 and its upper end is rigidly connected to the opening 78 in the guide plate 36 so that the vapors of the outlet housing 51 are in free contact with the supply housing 32.

The second flow tube 72 communicates the second outlet housing 52 freely with the third supply housing 33 to conduct vapors therethrough. In particular, the bottom end of this second tube 72 is rigidly connected, for example by hit-25, to the opening 80 in the third base plate 50 and its upper end is rigidly connected to the opening in the guide plate 36 so that the vapors of the outlet housing 52 are in free ** 'connection to supply housing 33.

A The third flow tube 74 freely communicates with the third outlet housing 53 with the fourth supply housing 34 to conduct vapors therethrough. In particular, the bottom end of this third tube 74 is rigidly connected, for example by welding, to an opening 83 in the third base plate 50 and its upper end is rigidly connected to an opening 84 in the guide plate '35 36 so that vapors communicate freely from the outlet housing 53 to the supply housing 34.

98198 10

Although the evaporator unit 10 is shown with the four sectors in the exchanger group 46, it will be appreciated that the evaporator unit could consist of a smaller number or more sectors or portions in all modifications of the arrangements or arrangements. And further, although the evaporator unit 10 is shown with parts of the exchanger having the same dimensions and number of tubes, it is obvious that the evaporator unit could consist of a group of exchanger sectors or parts of different sizes, each with a different number of tubes at the exchanger surface. with different materials or different shapes of the exchanger, or that each exchanger part has its own shell instead of all the parts being inside a single shell 12, other than in a vertical position or other aspects.

Referring to Figures 1 and 2, the feed fluid flowing through the tube 37 initially penetrates the evaporator unit (10) through the feed tube 38 in the feed housing 31 of the head 14. The fluid then passes through a first sector or portion of the tubular heat exchanger assembly 46 communicating with the feed housing 20, and begins to evaporate, generating vapors and thus increasing the concentration of solids in solution or liquid. The liquid evaporates and the solids concentrate so • ·, thus under the influence of the heat medium that circulates! ! through the heat exchanger tubes 16 outside of the heating; 25 tubes of the exchanger group 46 and a liquid or solution circulating through the tube group 46. The liquid then exits the first part of the tubular exchanger 46 and penetrates the outlet housing 51, where the partially concentrated solution and the vapors generated are separated.

30 The ab-:; *: cellular pressure difference between the supply housings 31 and 32 causes the vapors to flow from the discharge housing- ···. * T *. through the flow pipe 70 towards the supply housing 32.

The partially concentrated solution is sent by the pump 66 through the discharge drain pipe 61 from the outlet housing 51 and through the supply pipe 39 to the supply housing 32. The flow of partially concentrated liquid or solution flowing from the outlet housing 51 to the supply housing 32 is automatically controlled by a control valve 89 which maintains a constant level of liquid inside the discharge housing 51. The flow vapors are mixed with the partially concentrated liquid or solution in the feed-5 housing 32, then passed through another sector or portion of the tubular exchanger 46 at a rate and pressure sufficient to increase the velocity of the partially concentrated liquid and prevent the precipitated particles or fines from adhering. In particular, the mixing of the partially concentrated liquid and steam is passed to another sector or section of the tube exchanger 46 connected to the inlet housing 32 and the outlet housing 52 to achieve concentration and thus to generate additional evaporation vapors.

At high velocities, the flow vapors divide the liquid into droplets which act as scrapers to remove and remove precipitated particles and sediments that tend to form scale on the surfaces of the tube exchanger 46. Partially concentrated liquid a partially concentrated solution or liquid and the vapor generated by evaporation • · is separated.

The absolute pressure difference ab-25 between the supply housings 32 and 33 causes the vapors to flow from the discharge housing 52 through the flow pipe 72 to the supply housing 33.

· * · | The partially concentrated solution is sent by pump 67 * 'through discharge pipe 62 from outlet housing 52 and through supply pipe 40 to supply housing 33. The flow of the partially concentrated liquid or solution flowing from the outlet housing 52 to the supply housing 33 is automatically controlled by a control valve 90 which maintains a constant level of liquid inside the outlet housing 52. The flow vapors are mixed with the partially concentrated liquid or solution in the feed housing 35, then passed through the third sector or portion of the tubular exchanger 46 at a rate and pressure 98198 12 sufficient to increase the rate of the partially concentrated liquid and to trap the precipitated particles or deposits. In particular, the mixture of partially concentrated liquid and steam is introduced into a third sector or part of the tube exchanger 46 connected to the inlet housing 33 and the outlet housing 53 to achieve concentration and thus to generate additional evaporative vapors.

The third sector or portion 10 of the tubular exchanger assembly 46 is considered descaled due to the high rate of mixing of the liquid and the recycled vapors as mentioned above. The partially concentrated liquid and the vapors generated in the first, second and third sectors or parts of the tube exchanger 46 penetrate the outlet-15 housing 53, where the partially concentrated liquid or solution and the vapor generated by evaporation are separated.

The absolute pressure difference between the supply housings 33 and 34 causes the vapors to flow from the outlet housing 53 through the flow pipe 74 to the supply housing 34.

The partially concentrated solution is sent by the pump 68 through the discharge drain pipe 63 from the outlet housing 53 and through the supply pipe 41 to the supply housing 34. The flow of the partially concentrated liquid or solution flowing from the outlet housing 53 to the supply housing 34 is automatically controlled by a control valve 91 which keeps the liquid constant within the outlet housing 53. The flow vapors are mixed with the · partially concentrated liquid or solution in the feed housing 34, then passed through a fourth sector or section of the tubular exchanger 46 at a rate and pressure 30 sufficient to increase the rate of the partially concentrated liquid and to allow the precipitated particles or · * «fines are prevented from adhering to the exchange surfaces. In particular, the mixture of partially concentrated liquid and steam is introduced into the fourth sector or part of the tube exchanger 46, which is connected to the inlet housing 34 and the outlet housing 54 4 · • «* it utu uin nu ja. s 98198 13 to achieve concentration and thus to generate additional evaporative vapors.

The fourth sector or portion of the tubular exchanger assembly 46 is considered to be descaled due to the high rate of mixing of the liquid and the recycled vapors as mentioned above. The partially concentrated liquid and the vapors generated in the first, second, third and fourth sectors or portions of the tube exchanger 46 penetrate the outlet housing 54, where the partially concentrated liquid 10 or solution and the vapor generated by evaporation are separated.

The total amount of steam generated by the fourth sector of the tubular exchanger array 46 exits the evaporator unit 10 through the steam outlet 60 toward the separator 65 and from there to the next stage or condenser.

The vapors flow from the separator to the next stage or to the condenser, pushed or forced by the absolute pressure difference between the separator 65 and the next stage or condenser. The concentrated solution is sent to the next stage by means of pump 69 through pur-20 drain pipe 64.

The flow of concentrated solution exiting the outlet housing 54 is automatically controlled by a level control valve 92 which maintains a constant level outlet housing 54. indoors.

Fig. 4 shows an evaporation unit 110 according to another object of the present invention.

• · · · The evaporator unit 110 is substantially similar 1 to the evaporator unit 110 with the exception that the steam • «· J .; : the flow device 22 has been replaced by a flow device 122, the flow device 24 of the liquid 30 has been replaced by a flow device 124, the supply pipes 38-41 have been replaced by a single supply pipe

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· 1 · 1: 138 and baffles 36 and 56 have been removed. Thus, the evaporator 110 will not be explained in detail.

The evaporator 110 comprises an outer shell 112, at the upper end 35 of which a feed housing 114 is arranged to receive the solution or liquid to be concentrated on one side and 98198 14 recyclable vapors on the other, a heat exchanger portion 116 located below the feed housing 114 by evaporation 5, a receiving housing 118 for receiving a partially concentrated liquid or a liquid at a final concentration together with evaporating gases and a bottom housing or base 120 located below the discharge housing 118. The evaporator unit 110 also includes a steam recirculation system 122 and a liquid flow device 124.

The steam recirculation device 122 drives a compressor 180 to generate steam in the tubular exchanger 116 to flow at the desired rate. Compressor 180 communicates freely with supply housing 114 and discharge housing 15 through outlet pipe 160, steam separator 154, and flow pipes 182 and 184. The steam generated in the heat exchanger section 116 is recirculated by the recirculation system or device 122 toward the supply housing 114 to increase the velocity of the solution flowing through the exchanger tubes 146 20 sufficiently to prevent precipitates from adhering to the exchanger surfaces of the tubes 146.

· The recirculation pipe 182 may include an automatic or manual valve 190 for controlling the flow of water vapor from the compressor 180.

»I * · * · Valves such as 190 are conventional and therefore • · ·’ ··· · are not explained in detail here.

The fluid flow device 124 includes a pump 166 connected to an outlet pipe 161 and a liquid recirculation pipe 188 connected to the pump 166 and the inlet; between the working tube 138 to recirculate the concentrated solution again through the heat exchanger 116. The flow device • · · 124 can be removed because the evaporator unit 110 can operate without recirculation.

The operation of the evaporator unit 110 is as follows:

The solution to be evaporated penetrates through the tube 138 98198 15 into the feed box 114 alone or mixed with a partially concentrated solution or a solution at its final required concentration. The liquid passes to the heat exchanger section 146 through the tube assembly 146. The liquid is evaporated and the solids are thus concentrated by the heat transferred by its heat transfer medium, which penetrates the shell 112 through the supply pipe 148, heating the pipes 146. Uncondensed gases of the heat medium are removed from the heat exchanger housing 116 to The condensed vapors of the heat exchanger are discharged from the heat exchanger 116 through the outlet pipe 149a. The solution, which is at a partial concentration or the required final concentration, then exits the tube assembly 146 and penetrates the outlet housing 118 where the vapors are separated from the liquid. The flow of the recycled solution is controlled manually or automatically by means of a valve 196, the solution is recirculated by means of device 124 through line 188, and injected again by means of supply line 138.

The remaining part of the liquid, known as the process liquid, is removed by the same system 124 through the discharge pipe 169a for the next operation or for the next step. The control valve 192 in the tube 159 in the tube 169a maintains a constant level in the outlet roll 25.

* · "On the other hand, the steam is sent through a pipe 160 to a steam separator 165. The desired steam flow is adjusted manually or automatically by a valve 190 and recirculated to the supply housing 114 towards the steam recirculation device 122. The remaining vapors, the process vapors, are sent to the next stage or condenser via line 189.

Figure 5 illustrates a third object of the present invention corresponding to an evaporator unit 210. It is substantially similar to a liquid flow system 24 replaced by a liquid flow device 224. Thus, the evaporator unit 210 will not be described in detail.

Referring to FIG. 218 to receive a partially concentrated or final concentration solution, along with vapors from evaporation, to vertically support the outer shell 212 of the substrate 220 located below the outlet housing 218. The evaporator unit likewise includes a steam flow device 222 fixedly connected between the supply housing 214 and the outlet housing 218, as well as a liquid supply device or system 224 rigidly or fixedly connected to the circular housing 212.

The water vapor flow device 222 is provided with three pipes 270, 272 and 274 through which the steam flows from the outlet housing of the sector of the heat exchanger tube group 246 to the supply housing of the second sector or part of the exchanger tube group 246.

The liquid flow device or system 224 is provided with four discharge drain tubes 261, 262, 263 and * · * · 264 fixedly connected, respectively, to the outlets 256-259 in the third circular plate 250 to remove the concentrated solution from each of them. • · «: from the corresponding outlet housing and to send the concentrated solution to the next exchange part or to recycle it; again to the same exchange part or to send it to the storage tank or to remove it for the next step by means of pumps 266, 267, 268 and 269. In particular, the pump 266 sends the first portion of the liquid or process liquid through the tube 266a from the first outlet housing to the supply tube 239 of the second supply box and the second part through its recirculated tube 285 from the first outlet housing to the supply tube 238 of the first supply box.

The pump 267 sends the liquid or process liquid 5 through the first portion of the tube 267a from the second outlet housing to the third supply box supply tube 240 and the second recycled portion through the tube 286 from the second outlet housing to the second supply box supply tube 239.

The pump 268 delivers liquid or process fluid through a first portion of line 268a from the third outlet housing to the fourth feed box supply tube 241 and a second recycled portion through line 287 from the third outlet housing to the third feed box supply tube 15 240.

Pump 269 delivers the first portion of liquid or process liquid through line 269a from the fourth outlet housing to the storage tank or the next stage and the second recycled portion through line 288 from the four to 20 outlet boxes to the fourth feed box supply tube 241.

The solution flows through tubes 266a, 267a, 268a which are adjusted to the required flow by means of valves 289, 290, 291 and 292, respectively, which maintain a constant level 25 in the outlet housing of the evaporator unit 210.

* · * '· The evaporation operation of unit 210 is substantially the same as that of evaporator unit 10, with the exception 1 that the variable liquid flow can be recirculated • # · V; to the same supply housing via pipes 285-288 and control valves 293-296.

Although only three objects have been described to illustrate the invention, one of ordinary skill in the art will appreciate that changes and modifications may be made without departing from the scope of the invention as defined in the following claims.

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Claims (13)

98198 A method for concentrating a liquid, the method comprising the steps of: 5. passing a liquid through a heat exchanger section (16, 116, 216) from an inlet end (14, 118, 214) to an outlet end (18, 118, 218); - heating a liquid conveyed through the heat exchanger section to produce steam 10. circulating the liquid produced in the heat exchanger section (16, 116, 216) from the outlet end (18, 118, 218) of the heat exchanger section to its inlet end (14, 114, 214) to mix the steam with the liquid at the inlet end (14, 114); 214) to increase the velocity of the liquid, characterized in that - the steam is recirculated so that the velocity of the liquid increases so that the liquid turns into droplets which strike the heat exchanger part (16, 116, 216) against the heat exchanger surface with sufficient energy to prevent deposition of precipitated particles or removal of particles. Method according to claim 1, characterized in that the heat exchanger part (16, 116, 216) is divided into a plurality of evaporation parts (31, 32, 33, 34), each of which has an inlet and an outlet end and which are connected. . * work in fluid contact with each other so that they take • · · * ·· | successively against the liquid to be concentrated. Method according to Claim 1, characterized in that the steam is recycled through the heat exchanger section (16, 116, 216). A method according to claim 2, characterized in that the steam recirculation is carried out by means of pipes located outside the heat exchanger section (16, 116, 216). '35 Method according to one of the preceding claims, characterized in that the evaporation is direct; ; downstream principle. 98198 Method according to one of the preceding claims, characterized in that a compressor (180) is used for circulating steam from the outlet end (18, 118, 218) to the inlet end (14, 114, 214) at the desired speed. Method according to one of the preceding claims, characterized in that the heating comprises conveying the heating liquid next to the evaporation zone of the heat exchanger part (16, 116, 216) to indirectly heat the liquid 10 to be concentrated. An evaporation unit for concentrating liquids, the unit comprising - a heat exchanger section (16, 116, 216); - liquid inlet means (38, 39, 40, 41, 238, 15 239, 240, 241) connected to the inlet end of the heat exchanger part (16, 116, 216) for conveying the liquid to be concentrated to the heat exchanger part (16, 116, 216); - liquid and steam outlet means (51, 52, 53, 54) connected to the opposite end 20 of the heat exchanger section (16, 116, 216) for removing and separating the concentrated liquid and steam from the heat exchanger section (16, 116, 216); - heating means arranged next to the heat exchanger part (16, 116, 216) for heating the liquid conveyed through the heat exchanger part (16, 216); * .1 - steam recirculation means (70, 72, 74, 180, 182, • # · · 272, 274) connected to the outlet end and the inlet end 1 for circulating steam from the outlet end to the * · «* mixing head and the steam coming out of the outlet end. To increase the velocity of the liquid and steam conveyed through the heat exchanger section (16,; 116, 216) at the liquid inlet end by 1: 1; to boost its business; characterized in that - the evaporation unit is a downstream evaporation unit, the inlet end being the upper end of the heat exchanger part (16, 116, 216) and the outlet end being the lower end of the heat exchanger unit (16, 116, 216); and that ii «98198 - the steam recirculation means (70, 72, 74, 180, 182, 270, 272, 274) are arranged to recirculate the steam during the operation of the evaporator unit so that the velocity of the liquid increases so that the liquid turns into droplets impinging on the heat exchanger part 5. (16, 116, 216) against the heat exchanger surface with sufficient energy to prevent deposition of the precipitated particles or to remove the particles. Evaporation unit according to claim 8, characterized in that the heat exchanger unit (16, 116, 216) is divided into a plurality of evaporation sections (31, 32, 33, 34), each of which has an inlet and an outlet end and which are connected in fluid communication with each other, so that they sequentially receive the liquid to be concentrated, and that the steam recirculation means (70, 72, 74, 270, 272, 274) are connected so that steam circulates from each of the preceding outlets of the evaporating section (31, 32, 33) to the next evaporating section (32, 33). , 34) input. Evaporation unit according to claim 9, characterized in that the steam recirculation means (70, 72, 74, 270, 272, 274) are located inside the heat exchanger part (16, 116, 216). Evaporation unit according to claim 9, characterized in that the steam recirculation means 25 (70, 72, 74, 270, 272, 274) are located outside the heat exchanger part ** / (16, 116, 216). • · · • · ί 1 Evaporation unit according to claim 8, characterized in that the steam recirculation means s. · (180, 182) comprise a compressor (180). Evaporation unit according to one of Claims 8 to 12, characterized in that it comprises a «« f · * ♦ *; means for conveying the heating liquid indirectly next to the evaporation zone of the heat exchanger section (16, 116, 216) to heat the liquid to be concentrated. (t: 35 98198