WO2008067096A2

WO2008067096A2 - An evaporator

Info

Publication number: WO2008067096A2
Application number: PCT/US2007/082846
Authority: WO
Inventors: Jean-Claude Gallot; Daniel Bidon
Original assignee: Otv S.A.
Priority date: 2006-11-28
Filing date: 2007-10-29
Publication date: 2008-06-05
Also published as: US20080121379A1; WO2008067096A3

Abstract

The present invention comprises an apparatus and method for evaporating a liquid to produce a product liquid and a vapor. Liquid is evaporated under the influence of a heat transfer medium in a heat exchanger comprised of a bank of tube plates formed from corrugated sheets. Vapor produced is separated from product liquid by a vapor collector which causes vapor to flow upward and into the collector from a downward-flowing product liquid and vapor stream. Backsplash entrainment into the vapor collector is prevented by an anti-backsplash device disposed between the vapor collector and a reservoir into which product liquid flows.

Description

AN EVAPORATOR FIELD OF THE INVENTION

[0001] The invention relates to evaporating a liquid to produce a product liquid and vapor and to separate the product liquid from the vapor.

BACKGROUND OF THE INVENTION

[0002] Evaporators, or devices to evaporate liquids, generally include heat exchangers to transfer heat between a heat transfer medium, often steam, and the liquid. Various forms and types of heat exchanger designs exist, and they include a variety of means of promoting heat transfer between the medium and the liquid. Forms and types of heat exchangers available for these purposes are generally complicated and expensive.

[0003] The production of high quality vapor and product liquid yield are prime objectives of processes employing evaporators. Producing high quality vapor requires effectively separating the vapor from the product liquid. Various kinds of vapor separation approaches exist which generally use a vacuum or reduced pressure to extract the vapor into a vapor collection system. In many designs, it is common for part of the product liquid to be captured with the vapor in the process of vapor separation. This can occur in at least two ways. First, some of the product liquid in the liquid-vapor mix flowing from the heat exchanger comprises drops which can easily be drawn into the vapor collection system. Second, as product liquid falls into a reservoir which is normally positioned below the vapor collection area, backsplash generates droplets which may be entrained into the vapor collector. When product liquid is drawn into the vapor collection system, the vapor quality and product liquid yield are reduced. Some vapor collection systems include further separation of the vapor and entrained product liquid, but these operations add significant complexity and cost. They also result in increased system footprint.

[0004] There are many different situations in which evaporators are useful for generating vapor and product liquid from a given liquid. A wide range of operating conditions and requirements require a large variety of throughput capacities and separation efficiencies. Designing tailored systems for particular situations is costly. Cost advantages can be realized when relatively inexpensive packaged systems are made available in a modularized form in which multiple units can be assembled together to produce a system suitable for a particular application.

SUMMARY OF THE INVENTION x [0005] The present invention comprises an evaporator for evaporating a liquid.

The evaporator includes a housing which facilitates the assembly of the evaporator and provides an integrated package for the evaporator. A heat exchanger is included in an upper portion of the housing to transfer heat from a heat transfer medium, usually steam, to the liquid supplied to the heat exchanger. Positioned below the heat exchanger and substantially within the housing is a vapor collector which includes a vapor inlet having a downward-facing portion. Product liquid and vapor produced in the heat exchanger flows downwardly, passing an upper portion of the vapor collector. Vapor flows upwardly into the vapor inlet and product liquid flows to a reservoir.

[0006] In another embodiment, the present invention comprises an evaporator with a housing, a heat exchanger for evaporating a liquid and generating a product liquid and vapor, a vapor outlet disposed below the heat exchanger for permitting vapor to exit the housing, and a reservoir located below the vapor outlet to receive the product liquid. An anti-splash device is disposed between the vapor outlet and the reservoir for preventing backsplash of product liquid from the reservoir into the vapor outlet.

[0007] In yet another embodiment, the present invention includes housing, a heat exchanger for evaporating a liquid to produce a product liquid and vapor, and a vapor outlet located substantially below the heat exchanger. The heat exchanger is comprised of a bank of spaced-apart tube plates, and each tube plate includes a pair of corrugated sheets secured together. Each corrugated sheet is formed as series of alternating concave and convex segments with adjacent segments being mirror images of each other. A tube plate is formed by aligning the pair of sheets so that each concave segment of one sheet faces a concave segment of the other sheet forming a generally elongated tubular opening there between. Likewise, opposing each convex segment of one sheet is a convex segment of the other, the sheets contacting each other along a line. The sheets are secured together along lines of contact, and tubular openings are thus formed and bounded by the opposing concave segments. [0008] Other objects and advantages of the present invention will become apparent and obvious from a study of the following description and the accompanying drawings which are merely illustrative of such invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a sectional view of the evaporator of the present invention showing the heat exchanger, vapor collector, and anti-splash device. [0010] Figure 2 is a perspective cutaway view of the heat exchanger plate. [0011] Figure 3 is a horizontal sectional view of the evaporator.

[0012] Figure 4 is an exploded view of a tube plate that forms a part of the heat exchanger of the evaporator.

[0013] Figure 5 is a perspective view of a tube plate.

[0014] Figure 6 is an enlarged view of the encircled area shown in Figure 3 and indicated by Vl.

[0015] Figure 7 is a schematic diagram of an evaporator made up of a series of modules in a multiple effect arrangement.

[0016] Figure 8 is a schematic diagram of an evaporator made up of a series of modules in an alternative multiple effect arrangement.

[0017] Figure 9 is a schematic of an evaporator made up of a series of modules in a single effect arrangement.

DESCRIPTION OF THE INVENTION

[0018] The present invention is directed at an evaporator to evaporate a liquid L and produce a product liquid PL and a vapor V. As shown in Figure 1 , the evaporator, indicated generally by the numeral 10, comprises a housing 20 that contains components of the evaporator and facilitates connections to some of the components. A heat exchanger 30 is disposed within housing 20 for evaporating the liquid L, generating a mixed-phase stream including product liquid PL and vapor V. Disposed generally beneath heat exchanger 30 is a vapor collector 40, a portion of which in one embodiment extends across housing 20. A reservoir 50 is positioned beneath vapor collector 40 to receive product liquid PL. Disposed between vapor collector 40 and reservoir 50 is an anti-splash device 60 for preventing backsplash from entering the vapor collector. [0019] As further illustrated in Figures 1-3, housing 20 comprises a tubular structure which is elongated and generally oriented in a vertical direction. Housing 20 includes a wall 22 that encloses an interior area 25, and end flanges 23. Housing 20 may comprise segments adapted to be connected together using flanges 23. Moreover, flanges 23 permit coupling evaporator 10 to other components of a system of which the evaporator is a part, including modular arrangements which will be discussed later in this description. A liquid container 21 , disposed in upper portion 22 of housing 20, holds liquid L and fluidly connects to heat exchanger 30 for facilitating flow of the liquid into the heat exchanger. Heat transfer medium inlet 22a and heat transfer medium outlet 22b are disposed in wall 22 to provide for the flow of a heat transfer medium HTM, commonly steam, to and from heat exchanger 30. Housing 20 can be made of various suitable materials compatible with typical operating conditions of evaporators. In one embodiment, housing 20 is comprised of a stainless steel pipe with flanges 23, made of the same material, threaded or welded thereto. [0020] Turning now to heat exchanger 30 and considering its structure in detail, the heat exchanger comprises a bank of spaced-apart tube plates 32 as illustrated in Figures 1-3. As seen particularly in Figures 2 and 3, the bank of tube plates 32 forms an array of elongated tubes 33 including openings 33a through which liquid L may flow. An upper portion of tubes 33 form the heat exchanger liquid inlet, and a lower portion forms the heat exchanger product liquid and vapor outlet. Tube plates 32 are formed into a unitary structure disposed within housing 20 and interconnected by plates 38a, 38b, and 38c. Plates 38a, 38b, and 38c each include one or more openings 38s formed to receive tube plates 32 and to secure the tube plates in a desired configuration. [0021] Each tube plate 32 is fabricated from a pair of corrugated sheets 34 and 35 as illustrated in Figures 4 and 5. It is useful to consider in some detail the morphology of the pair of corrugated sheets 34 and 35 more particularly shown in Figure 4. Each corrugated sheet 34 and 35 is of a generally undulating, or wavy, structure with a series of alternating concave segments 34a, 35a and convex segments 34b, 35b forming a series of valleys and ridges. Viewed interiorly of sheets 34 and 35 in Figure 4, concave segment 34a forms a valley in sheet 34, and convex segment 34b forms an adjacent ridge. In corrugated sheet 35, shown opposite sheet 34 in Figure 4, concave segment 35a forms a valley in sheet 35 and convex segment 35b forms an adjacent ridge. Corrugated sheets 34 and 35 are aligned and brought into contact with each other by moving, for example, sheet 35 in the direction indicated by the arrows in Figure 4 so that opposed valleys formed by concave segments 34a and 35a form tubes 33 with openings 33a bounded in part by abutting convex segments 34b and 35b as shown in Figure 5. It is appreciated that any number of tubes 33 of various sizes may comprise a tube plate 32, depending on the size and spacing of the segments 34a, 35a, 34b, and 35b which may be selected for corrugated sheets 34 and 35. Corrugated sheets 34 and 35 are welded or otherwise sealed and secured together at sides or edges 36a and 36b. Plates 38a, 38b, and 38c, discussed below, along with the pressure of heat transfer medium HTM passing between the tube plates 32 tend to urge the convex segments 34b, 35b together. (See Figure 6) Corrugated sheets 34 and 35 may be of any material suitable for the environment and operating conditions of the evaporator 10, and in one embodiment comprises stainless steel. [0022] As can be appreciated from an examination of Figures 2, 3, and 6, tube plates 32 are held in a spaced-apart arrangement by plates 38a, 38b, and 38c. The spacing between adjacent tube plates 32 forms passageways 36 through which the heat transfer medium HTM flows. Moreover, plates 38a, 38b, and 38c with tube plates brace the tube plates 32 so as to maintain the shape of the tubes when exposed to pressure. Each plate 38a, 38b, and 38c, in one embodiment, is formed from generally flat sheet material similar in composition and thickness to that of corrugated sheets 34 and 35 of the tube plates 32, although the plates are not limited to this material and thickness. Moreover, additional plates of similar design may be used, depending on the length of the tube plates 32 . Factors considered in selecting the material for plates 38a, 38b, and 38c and in determining the need for additional plates may include the operating pressures and manner of connecting the plates to tube plates 32 and to wall 22 where appropriate. Each plate 38a, 38b, 38c includes a series of spaced apart and shaped slots 38s (see Figure 2) wherein each slot is shaped so that it will fit the undulations of a tube plate 32, allowing space for thermal expansion. In a common manufacturing arrangement, these slots 38s can be made using a CNC f machining process. Likewise, the plates 38a, 38b, and 38c may, in one embodiment, be welded to the tube plates 32 using CNC welding based on the same template as that used to machine slots 38s. In this way, relatively thin material may be used for plates 38a, 38b, and 38c and tube plates 32. [0023] End plates 38a and 38c along with housing wall 22 effectively enclose the interior 25 of the housing where heat exchanger 30 is disposed and through which the heat transfer medium HTM flows. End plates 38a and 38b are secured and sealed to wall 22 of housing 20 by any of a number of conventional means. It is appreciated that the pressure within interior 25 is greater that the pressure within tubes 33 and this difference in pressure tends to urge sheets 34 and 35 of each tube plate 32 together. In one embodiment the intermediate plate 38b may assume an alternate design. In this case the plate is provided with a relatively large central opening that receives and holds the entire bank of tube plates 32. Here, each tube plate is not completely surrounded with an opening 38s. Rather, plate 38b tends to engage each tube plate 32 about opposite ends 36a and 36b. Furthermore, with this alternate design, plate 38b may be connected to wall 22 of the housing 20.

[0024] Focusing now on the vapor collector, indicated generally by the numeral 40, as shown in Figures 1 and 3, the vapor collector comprises a duct structure 42 extending at least partially underneath heat exchanger 30. A vapor inlet 42c is disposed in a lower portion of duct structure 42 with at least a portion thereof generally facing downward. Duct structure 42 forms a vapor outlet 44 which is operably connected to a source of reduced pressure 46 which may comprise a vacuum pump, blower, or other device to provide a reduced pressure to draw vapor V from the evaporator 10. In one embodiment of the present invention, a portion of the duct structure 42 may be omitted and a vapor outlet provided in the wall 22 of housing 20. In this case, vapor V emitted by the heat exchanger 30 is drawn from the evaporator 10 via the vapor outlet.

[0025] A reservoir 50 is disposed beneath vapor collector 40 to collect product liquid PL. Conventional means are used to remove collected product liquid PL for further processing, end use, or disposal. In one embodiment, multiple evaporators 10 are operated in a modular application, to be described below, and reservoir 50 associated with one evaporator is fluidly connected to liquid container 21 of another evaporator.

[0026] An anti-splash device 60 is disposed between vapor collector 40 and reservoir 50. In one embodiment, anti-splash device 60 comprises a chevron-type structure including a series of steeply-angled plates 62 as illustrated in Figure 1. Each angled plate 62 is angled at a relatively small angle with respect to the general direction of flow of product liquid PL. The angle and spacing of the angled plates in this embodiment are such that in general there is no vertical line-of-sight from within reservoir 50 through anti-splash device 60. Other forms of an anti- splash device 60 can be utilized. Principally, the anti-splash device 60 functions to permit product liquid PL drops to pass there through under the influence of gravity, but interfere with or deflect product liquid droplets (backsplash) that splash upwardly from the surface of the product liquid in reservoir 50 and prevent such backsplash droplets from being entrained in the vapor stream being induced into the vapor collector 40.

[0027] As has been mentioned above, two or more evaporators 10 may be arranged and interconnected in a modular fashion. Connecting evaporators 10 in a modular fashion provides economies of design and manufacture associated with producing overall evaporator designs to meet a wide range of needs. In one embodiment, illustrated schematically in Figure 7, three evaporator modules EMA, EMB, and EMc are connected in an example of a multiple effect arrangement. Module EM_A, EMB, and EMc are supplied in parallel with heat transfer medium HTM. Liquid L is supplied to evaporator module EMA which produces vapor VA and product liquid PLA- Vapor VA is collected and product liquid PLA flows through an anti-splash device to evaporator module EMB. Product liquid PLA is evaporated in evaporator module B producing vapor VB and product liquid PL_B. Vapor VB is collected from evaporator module EMB and product liquid PLB flows through an anti-splash device to evaporator module EMc where it is further evaporated producing vapor Vc and product liquid PLc- Vapor Vc is collected from evaporator module EMc and product liquid PLc flows through an anti-splash device into a reservoir and is the final product liquid output of the modular arrangement. Another embodiment of a multiple effect arrangement is shown in Figure 8 showing an example of three evaporator modules connected in a different manner. Heat transfer medium HTM is supplied only to evaporator module EM_A while vapor V_A is used as the heat transfer medium for evaporator module EM₆. Similarly, vapor V_B is used as the heat transfer medium for evaporator module EM_C. It is appreciated that in this embodiment as well, an anti- splash device is employed with each vapor collector to prevent backsplash as product liquid PL flows from one evaporator module to another. A further embodiment comprises a single effect modular arrangement. In a single effect arrangement, multiple heat exchangers are stacked such that product liquid and vapor generated by one heat exchanger are supplied together to a next heat exchanger for further evaporation prior to vapor separation. Figure 9 shows an example of this embodiment in a case of using three heat exchangers in series Liquid L is supplied to heat exchanger module HE_A. Heat transfer medium HTM flowing through heat exchanger HE_A evaporates a portion of liquid L producing a mixed-phase flow of product liquid PL_A and vapor V_A. The mixed-phase flow from heat exchanger HE_A is supplied to heat exchanger HE_B where PL_A is further evaporated and product liquid PLB and vapor VB are produced. The mixed product liquid PL_B and vapor V₆ are supplied to heat exchanger HE_C from which product liquid PLc and vapor Vc are produced. The final product liquid-vapor stream is supplied to a vapor collector and anti-splash device to separate out vapor Vc and deposit product liquid PLc-

[0028] An example of typical modules in terms of the tube plates used is represented in Table 1. This example shows seven modules ranging from Module I consisting of 5 tube plates with two tubes per plate. Module I is 0.8 ft in diameter (largest cross section) at 1 ft in length providing 5.4 ft² of heat transfer area. The example modules I-VII range from 5.4 to 12,500 ft² of heat transfer area. Module IV, for example, is comprised of 22 tube plates, each plate having 10 tubes. The overall diameter, or module diameter, of the bank of tube plates in module IV is 3.3 feet, and the module is 2.6 feet long and comprises 340 ft² of heat transfer area.

Table 1. Exam le tube late bank modules

[0029] As shown in Table 2 below, evaporation of up to 500,000 Ibs/hr of water with heat flux between 15,000 and 2,250 BTU/hr,sq.ft. can be achieved with a limited number of modules by stacking up to four modules in a single effect arrangement. For example, to evaporate of 25,000 Ib/hr of water requires2 8,750,000 BTU/hr heat duty. Using a heat flux of 9,000 BTU/hr ft², for example, a heat transfer area of 2,972 ft² is required. From Table 1 , it is seen that three V modules will provide 1 ,333 ft² each for a total of 3,999 ft². Thus, three V modules would be selected as the combination formed from among the seven modules giving the smallest and therefore least expensive modular assembly providing the required area

Table 2. Modular Selection for ranges of water evaporation rates and heat fluxes

[0030] Considering now the general operation of evaporator 10 and referring to the figures, especially Figure 1 , a liquid L to be evaporated is supplied to liquid container 21. Liquid L is caused to flow into openings 33a of tubes 33 by grdvity or other means to assure adequate film development on the interior surfaces of tubes 33. Heat transfer medium HTM is supplied to inlet 22a and flows more or less continuously within and through interior 25 of housing 20, within the heat exchanger, and out outlet 22b. As heat transfer medium HTM flows within heat exchanger 30, the medium flows through passageways 36 (Figure 6) between tube plates 32 heating liquid L and producing vapor V and product liquid PL. Vapor V is drawn downward by the action of reduced pressure source 46 such that product liquid PL and vapor V together flow downward, out of heat exchanger 30 and towards vapor collector 40. In one embodiment, product liquid PL and vapor V flow around and downwardly past an upper portion 42a of vapor collector 40. Vapor V is drawn upwardly into vapor inlet 42c by the reduced pressure developed by reduced pressure source 46 while product liquid PL continues to fall towards reservoir 50. Vapor V is thus collected. In another embodiment, the portion of duct structure 42 of vapor collector extending across housing 20 is omitted. In this embodiment, vapor V is drawn laterally through a vapor outlet formed in the housing 20 under the influence of reduced pressure source 46. Product liquid PL flows through anti-splash device 60 and into reservoir 50. Droplets of backsplash may be caused by drops of product liquid PL impacting the surface of the product liquid PL in the reservoir 50. Because the reduced pressure source 46 creates a relatively low pressure in the vapor collector 40, droplets of backsplash tend to become entrained in the vapor being induced into the vapor collector. However, the presence of anti-splash device 60 tends to deflect the backsplash droplets and cause them to fall back and settle into reservoir 50. More specifically, drops of product liquid PL falling from heat exchanger 30 pass through the openings between plates 62, while droplets of backsplash contain insufficient mechanical energy to pass upwardly through anti- splash device 60 and are diverted by plates 62 and caused to settle back into reservoir 50. [0031] The present invention may, of course, be carried out in other specific ways than those herein set forth without departing from the scope and the essential characteristics of the invention. The present embodiments are therefore to be construed in all aspects as illustrative and not restrictive and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.

Claims

1 . An evaporator for evaporating a liquid, comprising: a. a housing; b. a heat exchanger for transferring heat from a heat transfer medium to the liquid and producing a vapor and a product liquid; c. a vapor collector disposed substantially within the housing and including a vapor inlet having a downward-facing portion; and d. wherein the vapor produced by the heat exchanger flows downwardly past an upper portion of the vapor collector and upwardly into the vapor inlet.

2. The evaporator of claim 1 wherein the heat exchanger includes a liquid inlet, an outlet for product liquid and vapor, and a bank of tube plates with each tube plate including a pair of corrugated sheets secured together wherein each corrugated sheet includes a series of alternating concave and convex segments with adjacent segments being generally mirror images of each other, and wherein the corrugated sheets comprising each tube plate are disposed such that each concave segment of one sheet faces a concave segment of the other sheet, and wherein each convex segment of one sheet contacts or lies closely adjacent a convex segment of the other sheet and wherein the tube plates are spaced apart and spacing the tube plates includes bracing the tube plates with two or more plates with each plate having openings shaped to generally conform to the tube plates and thereby adapted to retain the shape of each tube plate when exposed to pressure.

3. The evaporator of claim 1 comprising a reservoir disposed below the vapor collector to receive the product liquid, and an anti-splash device disposed between the vapor collector and the reservoir for preventing backsplash of product liquid from a surface of the product liquid in the reservoir into the vapor collector.

4. The evaporator of claim 3 wherein the heat exchanger includes a liquid inlet, an outlet for product liquid and vapor, and a bank of tube plates with each tube plate including a pair of corrugated sheets secured together wherein each corrugated sheet includes a series of alternating concave and convex segments with adjacent segments being generally mirror images of each other, and wherein the corrugated sheets comprising each tube plate are disposed such that each concave segment of one sheet faces a concave segment of the other sheet, and wherein each convex segment of one sheet contacts or lies closely adjacent a convex segment of the other sheet

5. The evaporator of claim 1 wherein the heat exchanger comprises a plurality of tube plates with each tube plate being adapted to receive the liquid; and, wherein the tube plates are spaced apart to form a series of passageways for permitting the heat transfer medium to flow there between.

6. The evaporator of claim 5 wherein each tube plate includes a pair of corrugated sheets secured together so as to form a series of elongated tubes oriented vertically therein.

7. The evaporator of claim 1 wherein the vapor collector includes a duct that extends transversely below the heat exchanger.

8. The evaporator of claim 1 wherein a source of reduced pressure is operatively connected to the vapor collector for maintaining a fluid pressure within the vapor collector less than a fluid pressure within the heat exchanger.

9. The evaporator of claim 1 wherein the evaporator includes a series of modules with each module including at least a heat exchanger.

0. The evaporator of claim 9 wherein the modules are stacked one above another in a generally vertical arrangement. 1 .An evaporator for evaporating a liquid, comprising: a. a housing; b. a heat exchanger for evaporating a portion of the liquid and generating a product liquid and a vapor; c. a vapor outlet disposed below at least a portion of the heat exchanger for permitting vapor to exit the housing; d. a reservoir disposed below the vapor outlet to receive the product liquid; and, e. an anti-splash device disposed between the vapor outlet and the reservoir for preventing backsplash of product liquid from a surface of the product liquid in the reservoir into the vapor outlet.

12. The evaporator of claim 11 wherein the heat exchanger includes a liquid inlet, an outlet for the product liquid and vapor, and a bank of tube plates with each tube plate including a pair of corrugated sheets secured together wherein each corrugated sheet includes a series of alternating concave and convex segments with adjacent segments being generally mirror images of each other, and wherein the corrugated sheets comprising each tube plate are disposed such that each concave segment of one sheet faces a concave segment of the other sheet, and wherein each convex segment of one sheet contacts or lies closely adjacent a convex segment of the other sheet.

13. The evaporator of claim 11 including a vapor collector disposed generally between the heat exchanger and the reservoir and including a vapor inlet having a downward-facing portion.

14. The evaporator of claim 11 including a vapor collector extending transversely within the housing and between the heat exchanger and the reservoir and wherein the vapor collector includes a vapor inlet including a downward facing portion. .

15. The evaporator of claim 11 wherein the anti-splash device comprises a series of spaced-apart plates.

16. The evaporator of claim 15 wherein the plates are disposed in a parallel relationship and slightly angled with respect to the general direction of product liquid flow.

17. The evaporator of claim 11 wherein the anti-splash device comprises a mesh structure.

18. The evaporator of claim 11 wherein the vapor outlet forms a part of a vapor collector disposed substantially within the housing and above the anti-splash device.

19. The evaporator of claim 18 wherein the vapor collector includes a vapor inlet having a downward-facing portion and communicating fluidly with the vapor outlet.

20.An evaporator for evaporating a liquid, comprising: a. a housing; b. a heat exchanger to evaporate a portion of a liquid to produce a product liquid and a vapor; c. a vapor outlet disposed below a substantial portion of the heat exchanger; d. wherein the heat exchanger includes: i) a liquid inlet; ii) an outlet for product liquid and vapor; iii) a bank of spaced-apart tube plates with each tube plate including a pair of corrugated sheets secured together; iv) each corrugated sheet including a series of alternating concave and convex segments with adjacent segments being generally mirror images of each other; v) wherein the corrugated sheets are disposed such that each concave segment of one sheet faces a concave segment of the other sheet, wherein each convex segment of one sheet contacts or lies closely adjacent a convex segment of the other sheet; and vi) wherein the heat exchanger includes one or more vertically spaced- apart horizontal plates, each plate having one or more openings for receiving the tube plates.

21 .The evaporator of claim 20 including a vapor collector disposed substantially within the housing and including a vapor inlet having a downward-facing portion.

22. The evaporator of claim 20 comprising a reservoir disposed below the vapor outlet to receive the product liquid and an anti-splash device disposed between the vapor outlet and the reservoir for preventing backsplash of product liquid from a surface of the product liquid in the reservoir into the vapor outlet.

23. The evaporator of claim 20 including a vapor collector including a vapor inlet having a downward-facing portion and the vapor collector disposed substantially within the housing, a reservoir disposed below the vapor collector to receive the product liquid, and an anti-splash device disposed between the vapor collector and the reservoir for preventing backsplash of product liquid from a surface of the product liquid in the reservoir into the vapor collector.

24. The evaporator of claim 20 wherein the inlet is disposed at a top portion of the heat exchanger and the outlet is disposed at a bottom portion of the heat exchanger; and, wherein the elongated tubes extend between the top and bottom portions.

25. The evaporator of claim 20 including at least a pair of spaced apart plates with each plate having a series of openings therein for receiving the tube plates, and wherein the openings within the plates maintain the tube plates in spaced apart relationship so as to define passageways between the tube plates for permitting the heat transfer medium to flow.

26. The evaporator claim 20 wherein one or more plates interconnect the tube plates and form a unitary structure.

27. The evaporator of claim 20 including a pair of vertically spaced-apart horizontal plates with each plate including one or more openings shaped to generally conform to the tube plates and thereby adapted to retain the shape of the tube plates when exposed to pressure.

28. The evaporator of claim 20 wherein a first plate is disposed at a top portion of the heat exchanger and is secured to the tube plates and to a wall of the housing; and, wherein a second plate is disposed at a bottom portion of the heat exchanger and is secured to the tube plates and to the wall of the housing, thereby forming a closed space between the first and second plates and within the housing.

29. The evaporator of claim 20 wherein the housing includes a heat transfer medium inlet and a heat transfer medium outlet for accommodating the flow of the heat transfer medium within the heat exchanger.

30. The evaporator of claim 20 wherein the vapor outlet forms a part of a vapor collector disposed substantially within the housing.

31 .The evaporator of claim 30 wherein the vapor collector is communicatively connected to the vapor outlet and includes a vapor inlet having a downward- facing portion.

32. The evaporator of claim 30 including a reservoir disposed below the vapor collector for receiving the product liquid.

33. The evaporator of claim 32 including an anti-splash device disposed between the vapor collector and the reservoir for preventing product liquid from splashing from the reservoir into the vapor outlet.

34. A method of evaporating a liquid comprising: a. flowing the liquid through an evaporator comprising a housing, a heat exchanger, and a vapor collector; b. heating the liquid by flowing a heat transfer medium through the heat exchanger and producing a product liquid and a vapor; and c. directing the product liquid and vapor downwardly past an upper portion of the vapor collector and inducing the vapor upwardly into the vapor collector.

35. The method of claim 34 wherein inducing the vapor upwardly into the vapor collector includes providing a reduced pressure source to reduce the pressure in the vapor collector and draw the vapor through a downward-facing vapor inlet disposed in the vapor collector.

36. A method of evaporating a liquid comprising: a. flowing the liquid into a heat exchanger; b. heating the fluid by flowing a heat transfer medium through the heat exchanger and producing a product liquid and a vapor with the product liquid falling into an underlying reservoir; c. inducing the vapor through a vapor outlet associated with the evaporator; and d. preventing product liquid backsplash droplets from being entrained with the vapor and entering the vapor outlet.

37. The method of claim 36 wherein preventing backsplash droplets from entering the vapor outlet includes deflecting the droplets by an anti-splash device and causing the droplets to settle back into reservoir.

38.A method of fabricating an evaporator comprising: a. constructing a heat exchanger having a bank of spaced-apart tube plates with each tube plate including two corrugated sheets with each sheet having alternating concave and convex segments, b. securing the two corrugated sheets of each tube plate together by aligning the concave and convex segments and affixing and sealing opposite edges of the two corrugated sheets together such that the convex segments abut or lie in close proximity to each other and the concave segments form tubes for generally containing a product liquid and a vapor; c. spacing adjacent formed tube plates so as to define passageways there between for permitting a heat transfer medium to move between the tube plates; and, d. wherein spacing adjacent formed tube plates includes bracing the tube plates with two or more plates with each plate having openings shaped to generally conform to the tube plates and thereby retain the shape of each tube plate when exposed to pressure

39. The method of claim 38 including disposing a vapor collector, in the form of a duct transversely below the heat exchanger wherein the duct includes a closed end, open end, and a downward-facing vapor inlet.

40. The method of claim 38 including positioning an anti-splashback device below a vapor collector for preventing backsplash droplets of the liquid product from entering the vapor collector which is disposed between the heat exchanger and a reservoir.