RU2040314C1 - Aggregate for membrane distillation - Google Patents

Abstract

FIELD: liquid dissolved component extraction. SUBSTANCE: aggregate has: chambers for cooling liquid circulation, walls of which are made of waterproof heat-conducting material; chambers for hot solution circulation, walls of which are hydrophobic microporous membranes; chambers for distillate collection, located between chambers for cooling liquid circulation and for hot solution circulation. One of walls of chambers for distillate collection is heat conducting wall of a neighboring chamber, in which cooling liquid is circulating, and another wall of chambers for distillate collection is hydrophobic microporous membrane of a neighboring chamber, in which hot solution is circulating. Chambers for cooling liquid circulation and chambers for hot solution circulation are provided with longitudinal partitions, dividing them for two half-cells, connected by a canal. In the case canal for cooling liquid feeding and removing, half-cells, connecting them canals of all chambers, in which cooling liquid is circulating, are in series communicating with each other, forming united canal; canal of hot solution feeding and removing, half-cells, connecting them canals of all chambers, in which hot solution is circulating, also are in series connected to each other, forming united canal; Longitudinal partitions, dividing chambers, in which hot solution is circulating, for two half-cells, as a version, are provided with transverse partitions, located on their planes in staggered order. The design of aggregate allows to create good conditions for heat-exchange of heat carriers, facilitating membrane process and as a result of it, to increase aggregate productivity at least by 30 EFFECT: aggregate for membrane distillation is used for liquid dissolved component extraction. 2 cl, 9 dwg

Description

 The invention relates to membrane distillation, and more specifically to devices for separating a dissolved component from a liquid using a vapor-permeable membrane and subsequent condensation of steam on a wall cooled by a circulating liquid.

 The invention can be used to obtain pure water from saline solutions, including from sea water, to concentrate saline solutions, including water-soluble thermolabile substances, to obtain ultrapure water, including operant water.

 A known installation for the separation of the dissolved component using a vapor-permeable membrane and subsequent condensation of steam on the cooled wall. The installation consists of a chamber, closed on both sides by a membrane, passing only solvent vapor. A hot liquid stream circulates through it, from which the desired component, for example water vapor, must be isolated. The installation also contains a chamber closed on both sides by a waterproof heat-conducting wall. Coolant circulates through this chamber, which can be used as the fluid to be processed.

 Between these chambers there is a distillate collection chamber, one wall of which is a specified membrane that transmits steam, and the other is a specified waterproof heat-conducting wall on which steam condenses.

 Hot and cold liquid flows from distribution pipelines connected respectively to a heat exchanger and a cold water pump are supplied in parallel flows to each respective chamber and circulate countercurrently in them. (U.S. Patent No. 3,563,860, B 01 D 1/22, 1971).

 The disadvantage of this installation is the low heat exchange efficiency associated with the organization of parallel circulation of hot and cold fluid flows.

 With this organization of circulation, a drop in the flow rate occurs at the moment of supply from the distribution pipeline to the chambers. This is especially noticeable if the installation has a high productivity, consists of a large number of circulation chambers of hot and cold flow. The farther from the source of flow (pump) the chamber is separated, the lower the flow velocity in it. A decrease in the coolant velocity leads to the appearance of such an undesirable effect as temperature polarization, i.e. to a decrease in temperature near the membrane surface compared to the volumetric flow temperature. The result of this effect is a worsening of the membrane process, namely a decrease in the amount of steam passing through the membrane and, consequently, a decrease in the amount of distillate, i.e. installation performance.

 To avoid temperature polarization, it is necessary to increase the flow rate of the coolant into the chambers, and this requires powerful pumping equipment and, consequently, high energy costs. On the other hand, in order to obtain high productivity, given the low heat transfer efficiency, it is necessary to increase the number of chambers, which leads to an increase in size and capital costs.

 The aim of the invention is the creation of a plant for membrane distillation, devoid of these disadvantages.

 This is achieved by the fact that in an installation containing chambers for circulating coolant, the walls of which are made of waterproof heat-conducting material, chambers for circulating hot solution, the walls of which are hydrophobic microporous membranes, chambers for collecting distillate located between these chambers and one of the walls of which is a waterproof heat-conducting wall of an adjacent chamber for circulating coolant, and another hydrophobic microporous membrane of an adjacent chamber for qi circulation of a hot solution, as well as channels for supplying and discharging a coolant, channels for supplying and discharging a hot solution and a channel for draining condensate, according to the invention, chambers for circulating a coolant and chambers for circulating a hot solution are provided with longitudinal partitions dividing them into two half cells, connected by a channel, while the channels for supplying and discharging coolant, the half-cells connecting their channels of all chambers for the circulation of coolant are successively communicated with each other, yn single channel, and the channels supplying and discharging the hot solution half-cell, all channels interconnecting chambers for circulating the hot solution and sequentially communicated with each other, forming a single channel.

 The longitudinal partitions dividing the chambers for circulating the hot solution into two half-cells can be provided with transverse partitions staggered on their planes.

 The proposed installation differs from the well-known structural design of the chambers for the circulation of hot solution and coolant, which, together with the well-known features, provides a new organization of circulation of the coolant, in which the flow of hot solution from the supply source and to exit the system passes sequentially through each chamber of the hot solution circulation and the coolant flow also from the supply source and until the unit exits the system sequentially passes through each cooling circuit waiting fluid.

 The proposed constructive design of the chambers for the circulation of the coolant allows to prevent a drop in its flow rate at the entrance to the chambers and to ensure the same flow rate in all half cells, which avoids temperature polarization and, accordingly, eliminates concentration polarization, and this favorably affects the membrane process.

 The supply of the longitudinal partitions dividing the chambers for circulating the hot solution into two half-cells with transverse partitions staggered on their planes provides additional flow turbulence, which also improves the conditions for the transfer of water vapor through the membrane.

 In FIG. 1 shows the proposed installation; in FIG. 2 frame of the chamber for the circulation of coolant in a perspective view; in FIG. 3 frame of the chamber for circulation of a hot solution in a perspective view; in FIG. 4, section AA in FIG. 2; in FIG. 5 and 6, the disassembled installation module with elements depicted in a perspective view; in FIG. 7 is a graph of module performance versus input temperature of a hot solution stream; in FIG. 8 is a graph of the temperature dependence of the flows of the hot solution, coolant and distillate leaving the installation during the organization of parallel circulation of the coolant on the temperature of the hot solution flow; in FIG. 9 is a graph of the temperature dependence of the hot solution, coolant and distillate leaving the installation during the organization of sequential coolant circulation on the temperature of the hot solution stream.

 Installation for membrane distillation consists of chambers 1 for circulating coolant, chambers 2 for circulating hot solution to be processed, and chambers 3 for collecting distillate located between them.

 Consider a module consisting of two chambers 1 for circulating coolant, a chamber 2 for circulating a hot solution, and two chambers 3 for collecting distillate placed between chambers 1 and 2. The installation, depending on the desired performance, is assembled from a package of such modules. As the coolant can be used cold solution to be processed.

 The cooling fluid circulation chamber 1 comprises a frame 4 with a cavity 5 closed on both sides by a waterproof heat-conducting wall 6. The frame 4 is provided with a longitudinal partition 7 dividing the cavity 5 into two half cells 8 and 9 connected by a channel 10. There are holes 11 and 11 in the frame 12 for supplying and discharging coolant. The holes 11 and 12 of the channels 13 and 14 are connected respectively with half-cells 8 and 9.

 The chamber 2 for circulating a hot solution contains a frame 15 with a cavity 16 closed on both sides by a hydrophobic microporous membrane 17. The cavity 16 is divided by a longitudinal partition 18 into two half-cells 19 and 20 connected by a channel 21 located opposite to the channel 10 in the chamber 1 of the coolant. The frame 15 has openings 22 and 23 for supplying and discharging a hot solution, connected via channels 24 and 25, respectively, with half-cells 19 and 20.

 The longitudinal partition 18 for turbulization of the flow of hot solution passing along it may be provided with transverse partitions 26 placed on its planes in a checkerboard pattern.

 The distillate collection chamber 3 is formed from a frame 27, the contour of which is hermetically connected on one side to a waterproof heat-conducting wall 6, and on the other to a hydrophobic microporous membrane 17. There are openings 28 for removing the distillate in the frame 27.

 To organize the movement of flows of hot solution and coolant in a waterproof heat-conducting wall 6, frame 4, frame 27, hydrophobic microporous membrane 17 and frame 15, which are structural elements from which the module is assembled in accordance with the technological process, holes are made that form channels for supply and the removal of the hot solution, the inlet and outlet of the coolant, as well as the removal of distillate.

 The channel for circulating the hot solution in the module is formed by holes 29, 30, 31, 32 and 22 (Fig. 5), channel 24 (Fig. 3), half-cell 20, channel 21, half-cell 19 (Fig. 1), channel 25 (Fig. . 3), holes 23, 33 (Fig. 5), 34, 35, 36 and 37 (Fig. 6).

 The channel for the circulation of coolant in the module is formed by holes 38 and 11 (Fig. 6), channel 13 (Fig. 4), half-cell 8, channel 10, half-cell 9 (Figs. 1 and 4), channel 14 (Fig. 4), holes 12, 39, 40 (Fig. 6), 41, 42, 43, 44, 45, 11 (Fig. 5), channel 13 (Fig. 4), half-cell 8, channel 10, half-cell 9 (Fig. 1 and 4), channel 14 (Fig. 4), holes 12 and 46 (Fig. 5).

 The channel for distillate removal from the module is formed by holes 47, 48, 49 and 28, chamber cavity 3, holes 28, 50, 51, 52 (Fig. 5), 28, chamber cavity 3, holes 28, 53, 54 and 55 (FIG. . 6).

 The module works as follows.

 The stream I of the hot solution to be processed from the heater (not shown) through the holes 29-32 (Fig. 5), forming the channel for supplying the hot solution, enters the hole 22 (Fig. 5) and through the channel 24 (Fig. 3) into the half-cell 19 Washing the longitudinal partition 18 through the channel 21, the stream I enters the half-cell 20, and from there through the channel 25 (Fig. 3), openings 23, 33 (Fig. 5), 34, 35, 36 and 37 (Fig. 6), forming the channel for draining the hot solution enters the next chamber 2 for circulation of the hot solution and so sequentially passes through each chamber 2 available in the installation.

 The flow of coolant II, which is used in this example, the cooled solution to be processed, from the opposite end of the module through the holes 38 and 11 (Fig. 6) and channel 13 (Fig. 4), forming a channel for supplying coolant, enters the half-cell 9, washes the longitudinal partition 7 and through the channel 10 enters the half-cell 9. From the half-cell 9, the cooling fluid through the channel 14 (Fig. 4), openings 12, 39, 40 (Fig. 6), 41-45 (Fig. 5), simultaneously forming a channel for draining coolant from one chamber 2 of the module and a channel for supplying and it into the next chamber 2, enters the hole 11 of the next chamber 2 of the module and from there through the channel 13 (Fig. 4) it enters its half-cell 8, washes the partition 7, through the channel 10 enters the half-cell 9 and from there through the channel 14 (Fig. 4) and openings 12 and 46 (Fig. 5) in each subsequent chamber 2 for the circulation of coolant available in the installation.

 The flow of coolant passing through the chamber 1 cools the waterproof heat-conducting wall 6 separating the chamber 1 from the distillate collection chamber 3. When the flow of the hot solution passes through the chamber 2, the vapor phase is transferred through the membrane 17 to the chamber 3. The vapor phase, upon contact with the cold wall 6, condenses to form a distillate, which in the form of a finished product (in the drawings, the distillate stream is denoted by Roman numeral III) is removed from the installation . On the presented module, stream III is discharged through openings 47, 48, 49, 28, chamber cavity 3, openings 28, 50, 51, 52 (Fig. 5), 28 and then, connecting to the distillate stream III from the next chamber 3 through opening 28 located at the opposite end of the chamber 3 passes through holes 53, 54 and 55 (FIG. 6), forming a distillate discharge channel.

 The direction of flow of the coolant and distillate in the drawings is shown by arrows.

 The presence of transverse partitions 26 on the planes of the partition 18 allows the movement of the hot solution along the half-cells 19 and 20 to create a turbulization of the flow and thereby increase the efficiency of transfer of the vapor phase through the membrane 17.

 This is achieved as follows. The flow of the hot solution, falling into the half-cells 19 and 20, by the transverse partitions 26 is divided into several streams flowing along the channels between the transverse partitions 26. Since the transverse partitions 26 are staggered, each new stream again encounters an obstacle and also breaks into new streams . In this case, vortices are formed in the horizontal direction. The gap between the transverse baffle 26 and the membrane 17 allows another stream of hot solution to form and creates turbulization in the vertical direction. In this way, conditions are achieved that ensure maximum contact of the flowing stream of the hot solution with the hydrophobic microporous membrane, resulting in an increase in productivity and maximum heat recovery.

 Tests were carried out using the well-known organization of parallel circulation of coolants and the proposed organization of sequential circulation of coolants in the membrane distillation module. The test results are shown in FIG. 7-9.

Let us compare the graphs of the temperature changes emerging from the module flows of hot solution, coolant and distillate with parallel circulation of coolants (Fig. 8) and with the organization of sequential circulation of coolants (Fig. 9). The following notation is used on the graphs: T _n temperature of the hot stream; T _x coolant temperature; T _{d the} temperature of the distillate. Common to both cases is the same volumetric flow rate, and temperature of the cooling liquid entering the module, which is equal in both examples, 10 ^{° C} and the hot solution flow temperature equal to 50, 60 and 70 ° ^C (in the plots not shown).

As can be seen from the graph in FIG. 8, the temperature T _H of the hot solution exiting the module at the organization of the parallel circulation was T _H1 = 32 ^{° C,} T _2n = 36 ^C and T _H3 = 42 ^{° C,} and for organizing a coherent circulating T _n was equal to T _'H1 = 28 ^о С, Т _'н2 = 32 ^о С, Т _{' н3} = 36 ^о С (Fig. 9).

When the temperature T _x of the effluent in the organization of the parallel circulation equal to T _x1 = 31 ^{° C,} T _x2 = 35 ^{° C,} T _x3 = ⁴⁰ ° C (Fig. 8), and for organizing a coherent circulating T _'x1 = 36 ^{° C} , T _{', x2} = 42 ^C and T' _x3 = 46 ^{° C} (Fig. 9).

 The indicated difference in temperatures of the coolant flows leaving the module is explained by the fact that, when organizing parallel circulation in a known installation, the hot solution flow passes a length of the path equal to the length of the chamber, and, not having time to give maximum heat to the coolant flow, leaves the chamber with a sufficiently high temperature. However, this heat carried away by the effluent does not take part in the further membrane process, which is the actual heat loss.

 When organizing a sequential circulation of the coolant flow, they leave the module, passing through all the chambers included in its composition, gradually losing its heat. In this case, heat is used most efficiently.

As for the temperature T _d of the distillate outlet stream, then, as can be seen from FIG. 8, it is _Tg = 24 ^{° C,} T _d2 = 26 ^C and T _g3 = 27 ^{° C,} and for organizing a coherent circulation of coolant (FIG. 9) it is respectively T _'d1 = 22 ^{° C,} T' _d2 = 23 ^o C, T ' _d3 = 24 ^o C, which indicates that the amount of heat carried away by the distillate in the proposed installation is also less.

Thus, in the proposed installation, the best heat transfer conditions are created, as a result of which the productivity of the installation is increased by at least 30%, which is clearly seen from the graph presented in FIG. 7, where the curve denoted by I ₂ shows how the productivity of the installation changes depending on the inlet temperature T _{n of the} hot solution during the organization of parallel circulation of heat carriers, and the curve denoted by I ₁ during the organization of sequential circulation of heat carriers.

Claims (2)

 1. INSTALLATION FOR MEMBRANE DISTILLATION, containing chambers for circulating coolant, the walls of which are made of waterproof heat-conducting material, chambers for circulating hot solution, the walls of which are hydrophobic microporous membranes, chambers for collecting distillate located between them, one of the walls of which is waterproof heat-conducting the wall of the adjacent chamber for circulation of the coolant, and the other wall is the hydrophobic microporous membrane of the adjacent chamber for i circulation of the hot solution, as well as channels for supplying and discharging the coolant, channels for supplying and discharging the hot solution, and a channel for draining the distillate, characterized in that the chambers for circulating the coolant and the chambers for circulating the hot solution are provided with longitudinal partitions dividing them into two half-cells connected by a channel, while the channels for supplying and discharging coolant, the half-cells connecting their channels of all chambers for the circulation of coolant are in series communicated with each other by means of a single channel, and channels for supplying and discharging hot solution, half-cells connecting their channels of all chambers for circulating hot solution are successively communicated with each other through a single channel.  2. The apparatus according to claim 1, characterized in that the longitudinal partitions dividing the chambers for circulating the hot solution into two half-cells are provided with transverse partitions staggered on their planes.

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