Thermal water purification system and method for operating said system

Abstract

A thermal water purification system and a related method including distilling units consecutively flowed through by raw feed liquid, each having a boiling liquid section and a vapor section, and including a heat exchanger cavity adapted to transfer thermal energy to the raw feed liquid before entering the boiling liquid section of a first distilling unit. Heat exchanger tubes in fluidic communication with the heat exchanger cavity extend through the boiling liquid section of the first distilling unit to transfer thermal energy from a medium in the tubes to cause the raw feed liquid to boil. Preheating tubes extend through the vapor section of each distilling unit to heat the raw feed liquid before entering the boiling sections using thermal energy from vapor condensing against external surfaces of the preheating tubes, which produces the distillate liquid that flows through a discharge port and a conduit supplying a storage tank.

Claims

1. A thermal water purification system for producing a distillate liquid from a raw feed liquid, comprising: a plurality of distilling units which are consecutively flowed through by the raw feed liquid, wherein the plurality of distilling units includes a first distilling unit and a plurality of consecutive distilling units; wherein each distilling unit comprises a boiling liquid section and a vapor section adjacent thereto; wherein the boiling liquid section of each distilling unit comprises a plurality of inlet ports and outlet ports, through which respectively enters and exits the raw feed liquid; and wherein any two consecutive distilling units, respectively an upstream distilling unit and a downstream distilling unit, are implemented such that the boiling liquid section of the downstream distilling unit is separated from the vapor section of the upstream distilling unit by a liquid-tight and vapor-tight separation plate, and separated from the vapor section of the downstream distilling unit by a liquid-tight and vapor-permeable membrane; a heat exchanger cavity adapted to transfer thermal energy to the raw feed liquid before the raw feed liquid enters into the boiling liquid section of the first distilling unit; a plurality of heat exchanger tubes in fluidic communication with the heat exchanger cavity and extending through the boiling liquid section of said first distilling unit, said heat exchanger tubes being configured to transfer thermal energy from a hot medium contained thereinside to the raw feed liquid flowing thereoutside, thus leading the raw feed liquid to boil inside the boiling liquid section of the first distilling unit; a plurality of preheating tubes extending through the vapor section of each distilling unit, said preheating tubes being consecutively flowed through by the raw feed liquid before said raw feed liquid flows inside the boiling liquid sections of the distilling units and being configured to heat the raw feed liquid contained thereinside by using thermal energy transferred by vapor contained inside the vapor sections of the distilling units when said vapor condenses against external surfaces of the preheating tubes, thus producing a distillate liquid that flows outside of the vapor section of each distilling unit, each distilling unit having a distillate discharge port through which the distillate liquid flows; and a distillate conduit in fluidic communication with each distillate discharge port, said distillate conduit supplying a storage tank with the distillate liquid.

2. The thermal water purification system according to claim 1, wherein said first distilling unit is positioned upstream from the plurality of consecutive distilling units of the thermal water purification system, thus leading to a decrease of the temperature of the raw feed liquid when it flows from said first distilling unit to said plurality of consecutive distilling units.

3. The thermal water purification system according to claim 1, wherein a plurality of heat exchanger tubes further extends through each boiling section of i further consecutive distilling units amongst the plurality of consecutive distilling units, i being an integer greater than 0.

4. The thermal water purification system according to claim 1, wherein any two consecutive distilling units, respectively an upstream distilling unit and a downstream distilling unit, are implemented such that the inlet ports of the boiling liquid section of the downstream distilling unit are in fluidic communication with the outlet ports of the boiling liquid section of the upstream distilling unit.

5. The thermal water purification system according to claim 1, wherein any two consecutive distilling units, respectively an upstream distilling unit and a downstream distilling unit, are implemented such that the outlet ports of the boiling liquid section of the upstream distilling unit are in fluidic communication with at least one internal boiling tube extending through the vapor section of said upstream distilling unit and such that the inlet ports of the boiling liquid section of the downstream distilling unit are in fluidic communication with said at least one internal boiling tube.

6. The thermal water purification system according to claim 1, wherein the separation plate separating the vapor section of an upstream distilling unit from the boiling liquid section of a downstream distilling unit is configured to heat the raw feed liquid contained inside said boiling liquid section by using thermal energy transferred by the vapor contained inside said vapor section when said vapor condenses against a condensation surface of said separation plate, thus leading the raw feed liquid to boil inside said boiling liquid section.

7. The thermal water purification system according to claim 1, wherein the preheating tubes are provided with projecting fins and ribs arranged along their periphery, said fins and ribs enhancing the heat transfer between the outside of each preheating tube and the inside thereof.

8. The thermal water purification system according to claim 3, wherein i+1 represents less than 40% of the total number of the distilling units of the thermal water purification system.

9. The thermal water purification system according to claim 4, wherein the inlet ports of the boiling liquid section of the downstream distilling unit are in fluidic communication with the outlet ports of the boiling liquid section of the upstream distilling unit via a throttle or flash valve.

10. The thermal water purification system according to claim 5, wherein the inlet ports of the boiling liquid section of the downstream distilling unit are in fluidic communication with said at least one internal boiling tube via a throttle or flash valve.

11. A method for operating the thermal water purification system according to claim 1, comprising the steps of: a) channeling the raw feed liquid having initially a first temperature towards the boiling liquid section of the first distilling unit through the plurality of preheating tubes so as to increase the temperature of the raw feed liquid from said first temperature to a second temperature; b) channeling the raw feed liquid having initially said second temperature towards the boiling liquid section of said first distilling unit through the heat exchanger cavity so as to increase the temperature of the raw feed liquid from said second temperature to a third temperature using the thermal energy transferred from the hot medium; c) channeling the raw feed liquid having initially said third temperature, or a temperature slightly lower than said third temperature, into the boiling liquid section of said first distilling unit and, thereafter, into the boiling liquid sections of the plurality of consecutive distilling units; d) heating said raw feed liquid with the plurality of heat exchanger tubes extending through the boiling liquid section of said first distilling unit, so as to boil the raw feed liquid flowing inside the boiling liquid section of the first distilling unit, with a decrease in the temperature of the raw feed liquid due to the drop of pressure inside the boiling liquid section of the first distilling unit from the inlet ports thereof to the outlet ports thereof; e) passing the vapor produced by the raw feed liquid boiling in the boiling liquid section of each distilling unit through the liquid-tight and vapor-permeable membrane into the vapor section adjacent thereto; f) condensing said vapor into said vapor section to produce the distillate liquid; and g) channeling said distillate liquid into the storage tank.

12. The method according to claim 11, further comprising, simultaneously to step c), a step c) including in channeling the raw feed liquid exiting from the outlet ports of the boiling liquid section of an upstream distilling unit into the vapor section thereof through at least one internal boiling tube before channeling said raw feed liquid into the boiling liquid section of a downstream distilling unit, said upstream and downstream distilling units being any two consecutive distilling units of the thermal water purification system.

13. The method according to claim 11, wherein, during step c), the raw feed liquid is boiling.

14. The method according to claim 11, wherein, during step f), the condensation of the vapor occurs against external surfaces of the preheating tubes and against a condensation surface of each of the separation plates of the thermal water purification system.

15. The method according to claim 11, wherein step d) further includes heating said row feed liquid with a plurality of heat exchanger tubes extending through each boiling section of i further consecutive distilling units amongst the plurality of consecutive distilling units, i being an integer greater than 0.

16. The method according to claim 12, wherein, during step f), the condensation of the vapor occurs against external surfaces of the preheating tubes and against a condensation surface of each of the separation plates of the thermal water purification system, as well as against an external surface of said at least one internal boiling tube.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other features and advantages of the present invention will appear more clearly from the detailed description of one embodiment of the invention which is presented solely by way of a non-restricted example and illustrated by the attached drawings in which:

(2) FIG. 1 is a schematic perspective view of a thermal water purification system according to an exemplary embodiment of the present invention, with four consecutive distilling units;

(3) FIG. 2 is a schematic top view of two consecutive distilling units of the system illustrated in FIG. 1;

(4) FIG. 3 is a schematic side view of the distilling units illustrated in FIG. 2;

(5) FIG. 4 is a schematic side view of a vapor section of a distilling unit in a further embodiment of the present invention;

(6) FIG. 5 is a schematic top view of a thermal water purification system similar to the one illustrated in FIG. 1, but with eight consecutive distilling units;

(7) FIG. 6 is a view similar to FIG. 5, except that the temperatures of the liquid or vapor at each step of the purification process is shown;

(8) FIG. 7 is a schematic front view of a vapor section of the distilling units illustrated in FIG. 2;

(9) FIG. 8 is a schematic front view of the vapor section illustrated in FIG. 4;

(10) FIG. 9 is a perspective view of an exemplary embodiment of a boiling liquid section of the system of the present invention;

(11) FIG. 10 is a perspective view of a first exemplary embodiment of a vapor section of the system of the present invention;

(12) FIG. 11 is a perspective view of a second exemplary embodiment of a vapor section of the system of the present invention;

(13) FIG. 12 is a perspective view of a third exemplary embodiment of a vapor section of the system of the present invention;

(14) FIG. 13 is a exploded perspective view of an exemplary embodiment of a distilling unit of the system of the present invention;

(15) FIG. 14 is a front view of the boiling liquid section illustrated in FIG. 9, the elements surrounding the heat exchanger tubes being seen by transparency;

(16) FIG. 15 is a front view of the vapor section illustrated in FIG. 10, the elements surrounding the preheating tubes being seen by transparency.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(17) In reference to FIG. 1, there is shown an exemplary embodiment of the thermal water purification system according to the present invention.

(18) In this embodiment, the thermal water purification system 10 comprises first to fourth adjacent distilling units 1a, 1b, 1c and 1d which are consecutively flowed by the raw feed liquid to be concentrated. This raw feed liquid can be brackish water, seawater or industrial process wastewater for example. This raw feed liquid flows inside the system according to a specific flow circuit and flow direction illustrated in FIG. 1 by two types of arrows. The first type of arrows corresponds to conduits, pipes or conducts for transporting the raw feed liquid L.sub.P from the fourth distilling unit 1d to the first distilling unit 1a. As detailed in the following paragraphs, the raw feed liquid L.sub.P is thus preheated before flowing through a heat exchanger cavity, which is adapted to increase the temperature of the raw feed liquid L.sub.P till said raw feed liquid is partially boiling or close to its boiling point. In the following paragraphs, to better distinguish the raw feed liquid exiting from the heat exchanger cavity, the term boiling raw feed liquid and the reference L.sub.B will be used in replacement of the term raw feed liquid and the reference L.sub.P. Further heat exchanger elements may advantageously be provided to heat the boiling raw feed liquid L.sub.B. Such heat exchanger elements may consist in a plurality of heat exchanger tubes, through which is flowing a hot medium H.sub.M, such as hot water or steam. As illustrated in FIG. 1, these heat exchanger tubes are partially integrated to one or more distilling units, thus optimizing the space occupied by the system and limiting the thermal losses during the transport of the fluid. The second type of arrows corresponds to conduits, pipes or conducts for transporting the boiling raw feed liquid L.sub.B from the first distilling unit 1a to the fourth distilling unit 1d. During this transport, the vapor phase of said boiling raw feed liquid L.sub.B is separated from the liquid phase thereof, said vapor phase being afterwards condensed against cold surfaces of the system and collected as a distillate liquid.

(19) In reference to FIGS. 2 and 3, there is shown two consecutive, i.e. first and second, distilling units 1a, 1b of the system 10 shown in FIG. 1.

(20) Each distilling unit comprises one boiling liquid section 2 and one vapor section 3 adjacent thereto, said sections 2, 3 being separated by a liquid-tight and vapor-permeable membrane 7. This membrane 7 is configured to, on the one hand, prevent that the liquid phase of the boiling raw feed liquid L.sub.B flowing inside the boiling liquid section 2 to flow across to the vapor section 3, and, on the other hand, permit the evaporation of the boiling raw feed liquid L.sub.B on its surface 7a and allow the vapor phase of said boiling raw feed liquid L.sub.B to diffuse across into the vapor section 3 through its pores. The boiling liquid section 2 of the second distilling unit 1b is separated from the vapor section 3 of the first distilling unit 1a by a liquid-tight and vapor-tight separation plate 6, which may advantageously be provided with enhanced micro-structures such as micro-cavities or micro-projecting fins. This plate 6 is configured to prevent any fluid circulation between the two adjacent sections and permit the film wise condensation of the vapor phase of the boiling raw feed liquid L.sub.B flowing inside the vapor section 3 on the surface 6a that is oriented towards said vapor section. Furthermore, this plate 6, which is heated during the condensation process, has a hotter surface 6b that is oriented towards the boiling liquid section 2 of the second distilling unit 1b. This hotter surface 6b, which is in contact with the boiling raw feed liquid L.sub.B flowing inside said boiling liquid section 2, may lead to flow boiling of said boiling raw feed liquid on surface 6b. To improve again the production of vapor in the boiling liquid section 2, a plurality of heat exchanger tubes 8 advantageously extend through said boiling liquid section 2. These heat exchanger tubes 8, which are flowed through by the hot medium H.sub.M, transfer thermal energy via their external surfaces 8a to the boiling raw feed liquid L.sub.B flowing inside the boiling liquid section 2 so that this boiling raw feed liquid L.sub.B boils in contact to said external surfaces 8a. The heat exchanger tubes 8 may advantageously be provided with internally and externally enhanced structures such as projecting fins arranged along their external surfaces 8a and internal ribs so as to enhance the thermal transfer occurring between the outside of said tubes and the inside thereof, thus enhancing the boiling of the boiling raw feed liquid L.sub.B against the external surfaces of the said heat exchanger tubes 8.

(21) The boiling raw feed liquid L.sub.B successively enters in the boiling liquid section 2 of the first distilling unit 1a through inlet ports 4, is partially vaporized via boiling and evaporation in said boiling liquid section 2, the vapor phase being diffused across the membrane 7 and the liquid phase exiting the boiling liquid section 2 through outlet ports 5. Thereafter, this liquid phase is channeled via conduits to the inlet ports 4 of the boiling liquid section 2 of the second distilling unit 1b. Throttle or flash valves 14 may advantageously be disposed along the conduits between the outlet ports 5 and the inlet ports 4 so as to reduce the pressure of the boiling raw feed liquid L.sub.B. This process may be repeated for the second distilling unit 1b, and, thereafter, for each successive distilling unit of the system 10.

(22) To preheat the raw feed liquid, the system 10 comprises a plurality of preheating tubes 9 extending through the vapor sections 3 of the distilling units 1a-1d, said preheating tubes 9 being consecutively flowed through by the raw feed liquid before said raw feed liquid flows through the heat exchanger cavity and, thereafter, through the boiling liquid sections 2 of said distilling units 1a-1d. These preheating tubes 9 permit to preheat the raw feed liquid contained thereinside by using thermal energy transferred by the condensing vapor contained in the vapor sections 3 of the distilling units 1a-1d when said vapor condenses against external surfaces 9a of the preheating tubes 9. To enhance the thermal transfer occurring between the outside of said tubes and the inside thereof, said tubes 9 may advantageously be provided with projecting fins arranged along their external surfaces 9a and internal rib structures.

(23) In the embodiment shown in FIGS. 2, 3 and 7, three vertically spaced-apart preheating tubes 9 with the raw feed liquid L.sub.P to be preheated flowing thereinside are disposed in each vapor section 3 of the distilling units 1a-1d. The distillate liquid produced by the condensation of the vapor against external surfaces 9a of said preheating tubes 9 and against surfaces 6a of the separation plate 6 flows downwards in the bottom part of said vapor sections 3 and exits therefrom through distillate discharge ports 11 provided in a bottom side of said vapor sections. Thereafter, this distillate liquid is channeled towards a storage tank via a distillate conduit that is in fluidic communication with the distillate discharge ports 11.

(24) In the alternative embodiment shown in FIGS. 4 and 8, two vertically spaced-apart preheating tubes 9 are disposed in the bottom part of each vapor section 3 of the distilling units 1a-1d and two vertically spaced-apart internal boiling tubes 15 are disposed in the top part of each vapor section 3. These internal boiling tubes 15 are flowed through by the boiling raw feed liquid L.sub.B exiting from the outlet port 5 of the boiling liquid section 2 disposed upstream thereof relative to the flow direction of said boiling raw feed liquid L.sub.S and are in fluidic communication with the inlet port 4 of the boiling liquid section 2 disposed downstream relative to the flow direction of said boiling raw feed liquid L.sub.B, preferably via a throttle or flash valve. The vapor contained in the vapor sections 3 condenses against the peripheral external surfaces of both said preheating tubes 9 and said internal boiling tubes 15, which induces flow boiling inside said internal boiling tubes 15. The distillate liquid produced by the condensation of the vapor against the external surfaces of the internal boiling tubes 15 may advantageously have a higher temperature than the raw feed liquid L.sub.P flowing inside the preheating tubes 9, thus advantageously preheating said raw feed liquid L.sub.P.

(25) In the embodiment shown in FIGS. 5 and 6, the system 10 comprises eight consecutive distilling units 1a to 1h, said distilling units having substantially the same structure as the distilling units illustrated in FIG. 1. However, in this embodiment, the heat exchanger tubes 8 extend only through the boiling liquid sections 2 of the first, second and third distilling units 1a, 1b and 1c. These heat exchanger tubes 8 are positioned downstream of a heat exchanger cavity 16 that composes an insulation wall 17 and a heat transfer plate 18 horizontally spaced-apart therefrom, said heat transfer plate 18 being horizontally spaced-apart from the first separation plate 6 bordering the boiling liquid section 2 of the first distilling unit 1a. The insulation wall 17 and the heat transfer plate 18 define a first flow path for the preheated raw feed liquid L.sub.P exiting from the preheating tubes 9 of the first distilling unit 1a and the heat transfer plate 18 and the first separation plate 6 define a second flow path for the hot medium H.sub.M. Thus configured, the heat exchanger cavity 16 permits to heat the raw feed liquid L.sub.P flowing through the first flow path via the heat transfer plate 18. As shown in FIG. 6, due to the higher temperature T_HM of the hot medium H.sub.M relative to the temperature T10.sub.LP of the raw feed liquid L.sub.P exiting from the preheating tubes 9 of the first distilling unit 1a, the temperature of the raw feed liquid L.sub.P increases to reach temperature T11.sub.LP at the exit of the first flow path and before said raw feed liquid L.sub.P is channeled via conduits towards the boiling liquid section 2 of said first distilling unit 1a. This final temperature T11.sub.LP is substantially equal to or slightly higher than the initial temperature T1.sub.LB of the boiling raw feed liquid L.sub.B that flows through the successive boiling liquid sections 2 of the distilling units 1a to 1h. Therefore, this final temperature T11.sub.LP may advantageously be equal to the boiling point of the raw feed liquid L.sub.B so that the boiling process occurs almost immediately when the boiling raw feed liquid L.sub.B enters in the boiling section 2 of the first distilling unit 1a.

(26) The system 10 illustrated in FIGS. 5 and 6 also comprises a preheating chamber 20 disposed upstream of the last distilling unit 1h relative to the flow direction of the raw feed liquid L.sub.P. This preheating chamber 20 comprises an insulation wall 17 and a heat transfer plate 18 horizontally spaced-apart therefrom, said heat transfer plate 18 bordering the vapor section 3 of the last distilling unit 1h. The insulation wall 17 and the heat transfer plate 18 define a first flow path for the raw feed liquid L.sub.P supplied from a raw liquid source 23. Thus configured, the preheating chamber 20 permits to heat the raw feed liquid L.sub.P via the heat transfer plate 18 due to the higher temperature T8.sub.VAPOR of the vapor flowing inside the vapor section 3 of the last distilling unit 1h relative to the temperature T1.sub.LP of the taw feed liquid L.sub.P of the first flow path. Thus, the temperature of the raw feed liquid L.sub.P increases to reach a final temperature T2.sub.LP of said first flow path and before said raw feed liquid L.sub.P is channeled via conduits inside the preheating tubes 9 of the last distilling unit 1h.

(27) As illustrated in FIG. 5, the system 10 may advantageously comprise a distillate conduit 12 in fluidic communication with the distillate discharge ports 11 of the distilling units 1a to 1h, said distillate conduit 12 channeling the distillate liquid towards a storage tank 13 via a plurality of constrictions 19, said constrictions 19 permitting to isolate the varying pressures occurring inside the distillate conduit 12. Indeed, from the first distilling unit 1a to the last distilling unit 1h, the pressure of the distillate liquid tends to decrease. The system 10 may also comprise a brine discharge 21 for collecting the concentrated boiling raw feed liquid L.sub.B exiting from the boiling liquid section 2 of the last distilling unit 1h and a non-condensable gas line 22 for collecting the non-condensable gasses exiting from the vapor sections 3 of the distilling units 1a to 1h.

(28) Thus, the operating steps of the system 10 shown in FIGS. 5 and 6 are successively:

(29) a) channeling the raw feed liquid L.sub.P having initially a first temperature T1.sub.LP towards the boiling liquid section 2 of a first distilling unit 1a through a plurality of preheating tubes 9 adapted to increase the temperature T(n).sub.LP of the raw feed liquid L.sub.P from said first temperature T1.sub.LP to a second temperature T11.sub.LP;
b) channeling the boiling raw feed liquid L.sub.B having initially a temperature T1.sub.LB, said temperature T1.sub.LB being equal to or slightly lower than said second temperature T11.sub.LP, into the boiling liquid sections 2 of said first distilling unit 1a and, thereafter, of the consecutive distilling units 1b to 1h;
c) heating said boiling raw feed liquid L.sub.B with a plurality of heat exchanger tubes 8 extending through the boiling liquid sections 2 of said first distilling unit 1a and two further consecutive distilling units, 1b and 1c, so as to boil the raw feed liquid L.sub.B flowing inside said boiling liquid sections 2, with a decrease in the temperature T(n).sub.LB of the boiling raw feed liquid L.sub.B in each boiling liquid section 2 due to the drop of pressure inside each boiling liquid section 2 from the inlet port 4 thereof to the outlet port 5 thereof;
d) passing the vapor produced by the boiling raw feed liquid L.sub.B boiling in the boiling liquid section 2 of each distilling unit through the liquid-tight and vapor-permeable membrane 7 into the vapor section 3 adjacent thereto;
e) condensing said vapor into said vapor section 3 to produce a distillate liquid;
f) channeling said distillate liquid into the storage tank 13.

(30) As defined in independent claim 8, these operating steps can be adapted to any systems 10 having at least one distilling unit.

(31) Furthermore, these operating steps can be adapted to a system 10 having the specific embodiment illustrated in FIG. 4. Thus, simultaneously to step b), a further step b) may consist in channeling the boiling raw feed liquid L.sub.B exiting from the outlet ports 5 of the boiling liquid section 2 of an upstream distilling unit into the vapor section 3 thereof through at least one internal boiling tube 15 before channeling said boiling raw feed liquid L.sub.B into the boiling liquid section 2 of a downstream distilling unit, said upstream and downstream distilling units being any two consecutive distilling units of the system.

(32) FIGS. 9 and 14 illustrate a boiling liquid section 2 comprising five vertically oriented and horizontally spaced-apart heat exchanger tubes 8, and several inlet ports 4 and outlet ports 5. The flow directions of hot medium H.sub.M and boiling raw feed liquid L.sub.B is shown in the same figures.

(33) FIGS. 10 and 15 illustrate a vapor section 3 comprising five horizontally oriented and vertically spaced-apart integrated preheating tubes 9, and a distillate discharge port 11. The flow direction of the raw feed liquid L.sub.P is shown in the same figures.

(34) FIG. 11 illustrates a vapor section 3 comprising two horizontally oriented and vertically spaced-apart integrated internally boiling tubes 15 positioned at the top part of said vapor section and three horizontally oriented and vertically spaced-apart preheating tubes 9 positioned at the bottom part of said vapor section. Distillate discharge port 11, the raw feed liquid L.sub.P and the boiling raw feed liquid to are also shown in the same figure.

(35) FIG. 12 illustrates a vapor section 3 comprising an array of internally boiling tubes 15 positioned at the top part of said vapor section, an array of preheating tubes 9 positioned at the bottom part of said vapor section and a distillate conduit 12 in fluidic communication with the distillate discharge ports 11 of said vapor section.

(36) FIG. 13 illustrates a distilling unit comprising a micro-structured condensation surface 6a positioned in front of the boiling liquid section 2 illustrated in FIG. 9, and the vapor section 3 illustrated in FIG. 10 positioned in front of condensation surface 6a with hotter surface 6b located on the opposite side of condensation surface 6a, said boiling liquid section 2 and said vapor section 3 being separated by a liquid-tight and vapor-permeable membrane 7. Flow boiling in the boiling liquid section 2 occurs on the external surface 8a of the heat-exchanger tubes 8 while vapor condensation in the vapor section 3 occurs on the external surface 9a of the preheating tubes 9 and condensation surface 6a.

(37) The above detailed description with reference to the drawings illustrates rather than limits the invention. There are numerous alternatives, which fall within the scope of the appended claims. In particular, in a further embodiment of the present invention, the thermal water purification system may include a plurality of consecutive modules, each module comprising several consecutive distilling units and being in a fluidic communication with an adjacent module via bifurcating flow configuration for the boiling raw feed liquid flowing inside the boiling liquid sections. The raw feed liquid flowing inside the preheating tubes can advantageously be in a bifurcating flow configuration.

(38) Three examples are given below to compare the performance simulation of the current invention (Example 3) with MD systems from known prior arts (Examples 1 and 2).

(39) System Parameters:

(40) i) Thermal source=30 kW, II) Assumed system efficiency, n=80%, III) T.sub.feed.in=25 C., IV) T.sub.feed.final=70 C., V) Feed flow rate, V.sub.feed=7 l/min. VI) Latent heat, H.sub.LV=2,333 kJ/kg (assumed constant for water at 70 C.), VII) Assumed specific membrane flux, N=10 L/min. VIII) Membrane area/per effect, A.sub.m=0.5 m.sup.2, IX) density, p=1 kg/liter and, X) No. of effects=8.
Note: US 2010/0072135 A1 claimed an optimum specific flux measurement of 1.910.sup.10 m.sup.3/m.sup.2s-Pa. Assuming a nominal driving force, P3.5 kPa (0.035 bar), the specific membrane flux achieved is 2.4 L/m.sup.2-hr. Partial vapor for water at T=70 C. (P.sub.v=31.2 kPa) and T=25 C. (P.sub.v=3.17 kPa). Hence, assumed nominal driving force of 35 kPa in each module is evaluated as (31.2-3.17)/8-effect. Zhao et al. (2013) obtained a specific membrane flux of 3.0-8.7 L/m.sup.2-hr from their experiments. The assumption of 10 L/m.sup.2-hr for this simulation is to provide an unbiased comparison with MD inventions from known prior arts.

Example 1: 8-Effect MD System with Vapor Transmission Lines but without Feed Preheating

(41) TABLE-US-00001 Total membrane area (A.sub.m 8-effect) 4.0 m.sup.2 First module thermal energy consumption for 3.24 kW MD evaporation (N A.sub.m H.sub.LV/3600 s) Total distillate produced (N A.sub.m 8-effect ) 32 L/hr Total output equivalent thermal energy (Total 20.74 kW distillate produced/3600 s H.sub.LV)
The first effect (steam riser) of the MD system can only consume 3.24 KW (10.8%) out of the total available thermal energy of 30 kW. To consume the total thermal load of 30 kW, the membrane area would have to be enlarged by 9.26 times to 4.63 m.sup.2/effect and a total system membrane area to 37.04 m.sup.2. No condensation losses in the transmission lines were assumed in the simulation.

Example 2: 8-Effect MD System with Vapor Transmission Lines and Feed Preheating

(42) TABLE-US-00002 First module thermal energy consumption for 3.24 kW MD evaporation (N A.sub.m H.sub.LV/3600) First module thermal energy consumption for 3.44 kW feed preheating (V.sub.feed/60 (T.sub.feed,final T.sub.feed,in) Cp (4189 kJ/kg-K)/(8-effect )) First module thermal energy consumption (N 6.68 kW A.sub.R H.sub.LV/3600) Total membrane area required to implement 1.03 m.sup.2 MD and feed preheating, A.sub.R Total distillate produced (N A.sub.R 8-effect ) 65.9 L/hr Total output equivalent thermal energy (Total 42.72 kW distillate produced/3600 s H.sub.LV) Total membrane area (A.sub.R 8-effect) 8.24 m.sup.2
With feed preheating, the first membrane module is capable of consuming 6.68 kW (22.3%) of the total available thermal energy of 30 kW. However, the membrane area will have to be increased from 0.5 m.sup.2 to 1.03 m.sup.2 to produce enough vapor to accommodate feed preheating. The total system membrane area has now increased to 8.24 m.sup.2. No condensation losses in the transmission lines were assumed in the simulation. Due to the presence of vapor transmission lines, no performance enhancement in the MD process was taken into account.

Example 3

(43) Current invention as per the embodiment shown in FIG. 5 with direct condensation and internal flow boiling tubes implemented into the first three modules. An equal distribution of thermal energy for flow boiling in the three modules is assumed for this simulation. In practical applications, the first effect can preferably be imposed a much higher thermal load to increase distillate production and thermal efficiency.

(44) TABLE-US-00003 Total membrane area (A.sub.m 8-effect) 4.0 m.sup.2 First module thermal energy consumption for 3.24 kW MD evaporation (N A.sub.m H.sub.LV/3600) Thermal energy required for raw feed 3.44 kW preheating/effect Thermal energy consumption via tube boiling 8.92 kW (First distilling effect) .fwdarw. (30 kW 3.24 kW)/ 3-effects Thermal energy consumption via tube boiling 8.92 kW (Second distilling effect) .fwdarw. (30 kW 3.24 kW)/3-effects Thermal energy consumption via tube boiling 8.92 kW (Third distilling effect) .fwdarw. (30 kW 3.24 kW)/ 3-effects Estimated MD performance enhancement 10 % due to direct condensation and internal flow boiling Total distillate produced via MD (N A.sub.m 8- 35.2 L/hr effect 1.1) Total distillate produced via boiling in first 66.1 L/hr effect .fwdarw. (8920/H.sub.LV 3600) + ((8920 3440)/H.sub.LV 3600 7-effect ) Total distillate produced via boiling in first 54.4 L/hr effect .fwdarw. (8920/H.sub.LV 3600) + ((8920 3440)/H.sub.LV 3600 6-effect ) Total distillate produced via boiling in first 47.6 L/hr effect .fwdarw. (8920/H.sub.LV 3600) + ((8920 3440)/H.sub.LV 3600 5-effect ) Total distilate produced via MD and boiling 203.3 L/hr Total output equivalent thermal energy (Total 131.75 kW distillate produced/3600 s H.sub.LV)
The thermal energy required for MD is 3.24 kW while the remaining 27.76 kW being distributed into the heat exchanger boiling tubes in the first three (3) effects, i.e. 8.92 kW for boiling/effect. A total thermal load of 30 kW is consumed for vaporization of liquid to produce distillate and raw liquid feed preheating while maintaining the membrane area at 0.5 m.sup.2 per effect, i.e. total system membrane area of 4.0 m.sup.2. Simulated performance indicated a 4.76 times increase m distillate production capacity when compared to MD system with preheating features while 6.35 times more distillate production was encountered when compared to a MD system without feed preheating.