US3155565A

US3155565A - Flat film evaporation liquid concentration method

Info

Publication number: US3155565A
Application number: US56450A
Authority: US
Inventors: Goodman Hugh Frederick
Original assignee: APV Corp Ltd
Current assignee: SPX Flow Technology Crawley Ltd
Priority date: 1956-03-21
Filing date: 1960-09-16
Publication date: 1964-11-03
Anticipated expiration: 1981-11-03
Also published as: FR1173083A; CH346206A; NL107643C; DE1095785B; US2960160A; NL215577A

Description

Nov. 3, 1964 H. F. GOODMAN 3,155,565

FLAT FILM EVAPORATION LIQUID CONCENTRATION METHOD 3 Sheets-Sheet 1 Filed Sept. 16. 1960 I nvenlor Z x/ WW y a Attorney:

Nov. 3, 1964 H. F. GOODMAN 3,155,565

FLAT FILM EVAPORATION LIQUID CONCENTRATION METHOD Filed Sept. 16. 1960 s Sheets-Sheet 2 A Home Nov. 3, 1964 H. F. GOODMAN 3,155,565

FLAT FILM EVAPORATION LIQUID CONCENTRATION METHOD 3 Sheets-Sheet 3 Filed Sept. 16, 1960 I nventor W 1 WWW By 5% 2729M A ttorneys United States Patent 3,155,565 FLAT FILM EVAPORATHQN LIQUID CONCENTRATION METHOD Hugh Frederick Goodman, London, England, assignor to ARV. Company Limited, Crawley, England Filed Sept. 16, 1960, Ser. No. 56,450 Claims priority, application Great Britain, Mar. 21, 1956, 8,842/ 56 2 Claims. Cl. 159-46) This invention relates to flat film evaporation liquid concentration method.

This application is a continuation-in-part of the copending application of Hugh Frederick Goodman, Serial No. 647,380, now Patent No. 2,960,160, filed March 20, 1957.

An object of the invention is to provide an improved method of concentrating liquid products, and more particularly a method of concentrating liquid products by flat film evaporation.

Another object of the invention is to provide such a method in which a liquid product to be concentrated is caused to flow through a series of flow path components of substantially flat, very thin cross section in comparison to the substantially fiat facial areas of the flow path components, while being heated, and is exhausted from the flow path components under low pressure conditions controlled to enable evaporation of the product while flowing in flat, thin film form, whereby the product discharged from the several flow path components will include both vapour and concentrated liquid phases.

Other objects of the invention will become apparent from a reading of the following description, the appended claims, and the accompanying drawings.

The aforesaid co-pending application Serial No. 647,380 discloses, in common with the present application, a flat film evaporator apparatus well suited for use in practicing the method of this invention. The evaporator comprises an assemblage of plates in spaced relationship to provide flow channels or paths at least one of which (termed a heating channel) is connected to an inlet and an outlet for a heating medium, and at least two others of which (termed liquid channels) are connected at corresponding ends across an intermediate heating channel and at their other ends respectively to an inlet for the liquid to be evaporated and an outlet for the concentrated liquid.

A number of heating channels and a number of sets of liquid channels connected in the manner referred to are provided in a single assemblage of plates constituting an evaporator, the heating channels and the sets of liquid channels being arranged in parallel with one another across inlet and outlet lines for the heating medium and the liquid and its concentrate.

With this arrangement, the connected liquid channels provide a total length of flow path which can be accommodated more conveniently and compactly than would be possible with a single flow passage of equivalent length, the liquid moving in one direction in one of the connected liquid channels and then in the other direction in the other connected channel.

It is desirable for the plates to be more or less vertical, with the additional advantage that the connections can be arranged to cause the liquid to have a rising flow in one of the connected liquid channels and a falling flow in the other. This enables an even distribution of the supply of liquid to the connected liquid channels to be efiected easily. When the falling flow is passing to the outlet, high concentration in the product is promoted. Such an evaporator may be used in performing a method according to this invention on the principle generally known as film evaporation in which the liquid to be Patented Nov. 3, 1964 concentrated passes once through the evaporator so that its actual time of subjection to heating is low. This results in improvement in the quality of the final product. Such film evaporators are recognised as being sensitive to control, and to ensure uniform distribution through a number of surfaces in parallel is difiicult. The invention enables difliculties previously encountered to be overcome by virtue of the rising and falling flow in flat film form and the ability to vary the cross-sectional area of the liquid channels in the direction of flow to suit requirements.

This variation of the cross-sectional area can be obtained in a number of ways. Thus, the gap between or the form of the plates providing the liquid flow channels may be arranged to give channels of different cross-sectional area regarded in the direction of flow. For example, the gap and/ or the width of the channels for the falling flow can be smaller or larger than for the rising flow channels as may be found necessary to suit conditions. Moreover, each liquid passage may have in its own length variation in its cross-sectional area, such variation being obtained by variation in the gap and/or by variation in the width of the channel.

It is also possible to constitute one or both of the connected liquid channels by the gaps between a number of plates so that the channels are in eifect constituted by the sum of two or more branches in parallel. This arrangement lends itself to providing one connected liquid channel with a different cross-section from that of the other by selection of the number of plates to provide the one channel as compared with the other.

Moreover, each flow channel can extend across the entire width of the plates or provision can be made to subdivide the width of the plates into a number of (say two) liquid flow channels extending side-by-side. These subdivided flow channels can be of similar width throughout their length but they can be of a varying width, i.e., tapered to give the varying cross-sectional area referred to.

In the drawings illustrating preferred forms of apparatus for use in practicing the invention, FIGURE 1 is a perspective view of an evaporator installation in an opened position, FIGURE 2 is an exploded perspective view showing the various plates separated, FIGURES 3 and 4 are views similar to FIGURE 2 but showing plates of a modified form, FIGURES 5 and 6 are vertical sections through two arrangements of an assemblage of plates, FIGURE 7 is a local vertical section, and FIGURE 8 is a local perspective view of a metering device.

Referring to the drawings and considering firstly FIG- URE 1, the evaporator comprises an assemblage of plates P which are disposed face-to-face and are clamped between pressure heads H which can be drawn together by screws S, the heads and the plates being held in a frame F which also supports at one end a separator unit U to separate vapours from the treated evaporated liquid.

Referring now to FIGURE 2, this figure shows a number of plates forming a single unit for the liquid to be concentrated, the various plates being indicated by the references P P P P and P All of the plates are formed with openings which, when the plates are pressed face-to-face with one another, register with one another and with openings in the head H as shown. These openings provide inlet passages for the liquid to be evaporated and outlet passages for the concentr-ated product, and passages for the inlet and outlet of a heating fluid (or its condensate) which in most cases would be steam.

Thus, each plate has two openings 1 and the various openings register to provide inlet passages for the liquid to be evaporated, the openings 1 in the end plate P registering with supply ducts 2 in the head H. The aligned openings 1 provide fluid inlets passing straight through U the plates. Each plate has also an opening 3 and the various openings 3 register to provide an outlet trunk passage for the concentrated liquid, and the liberated vapour, the outlet for the liquid passing straight through the plates and registering with an outlet opening 4 in the head H.

In addition, each plate has an opening 5, and the various openings register to provide a supply trunk for a heating medium, which would normally be steam, which registers with a supply opening 6 in the head H. Each plate also has an opening 7 and the various openings register to provide an outlet duct for the heating medium or its condensate, the duct registering with an outlet duct 8 in the head H. The heating medium inlet and outlet also pass straight through the plates.

Thus, when the plates are pressed together with gaskets 9 interposed between them, the various openings provide parallel passages for the liquid to be treated which is supplied by the two ducts 2 and returns as a concentrated product via the trunk openings 3, and for the steam which is supplied by the trunk openings 6 and returns as a condensate via the openings 7. The liquid flow is indicated by dot and peck lines in FIGURE 2 and the steam flow by dashed lines.

Now for the purpose of this invention, certain of the plates, i.e., the plates P F for convenience termed primary plates, cooperate with adjacent plates P P and P for convenience termed secondary plates, to provide liquid flow channel components LF which are spaced apart; and the plates P P and P cooperate with the head H and with the plates P P to provide steam flow channel components SF which are disposed at each side of and between the liquid flow channels. These liquid and steam flow channels are defined by the gaskets 9 which are disposed between the adjacent faces of the adjacent pairs of plates. In the case of the plate P its gasket is shaped to connect the base of the liquid flow space LF of that plate to the openings 1 so establishing a connection to the liquid inlet ducts formed by the registered openings 2: this plate at its upper end is formed with a transfer opening 10 which registers with a transfer opening 11 at the upper end of the plate P and this opening in its turn registers with the upper end of the plate P within its gasket 9. This plate P has the opening 3 formed at its lower end.

The openings 10 and 11 interconnect one, the upper, set of closely adjacent ends of the liquid flow channels LF and LF provided respectively between the plates P and P and the intervening heating channel SF, the interconnection being across the heating channel SF. The other (lower) ends of these two liquid flow channels LF are connected respectively to the inlet 1 for liquid to be concentrated and to the outlet 3 for concentrated liquid. Thus the liquid flow is from the two inlet or supply ducts formed by the registered openings 1 up the plate P across the top of the plate P and down the plate P to the outlet duct formed by the registered openings 3.

In the case of the plates P P P the steam passes from the inlet or supply duct formed by the registered openings 5 at the side, down the plates to the condensate outlet passage formed by the registered openings 7. As shown, these plates are fitted or formed with batile strips 12 to compel the steam to follow a tortuous path.

The actual formation of the flow paths can best be seen by reference to FIGURE 5.

In the formation shown in FIGURE 5, the rising and falling channels LF have the same cross-sectional area and both have a width approximating to the width of the plates. FIGURE 7 shows a liquid flow deilector at the bottom of the rightmost or downllow channel LF.

This invention lends itself to varying the cross-sectional area in the direction of flow of the liquid. For example, the arrangement shown in FIGURE 6 can be adopted to give an increasing cross-section to the falling flow as it 4 passes to the return opening 3. In this case, the falling flow gap between the plates P P is made gr at the rising flow gap between the plates P P In the arrangement shown in FIGURE 2, a single composite liquid flow path or channel is provided between the our plates P -P which form a set or unit. It is however possible to divide the plates by suitable shaping of the gaskets 9 to provide two or more liquid flow channels LF side by side. Thus, in FIGURE 3 two flow channels LF and LF are provided by the expedient of forming the gaskets 9 with a dividing strip 9 the two halves of the liquid flow channels taking their supply from the passages formed by registered openings 1 at opposite sides of the plate, and the two channels both discharging to the trunk formed by the registered openings 3.

In FIGURE 3, the two side-by-side channels have the same width throughout their length. To give a varying cross-section, they can have different depth as in the arrangement shown in FIGURE 6. Alternatively or in addition, they can have a varying width as is shown in FIGURE 4, and to enable the width of the plates to be used to advantage, the one flow channel is laid with its increasing width against the decreasing width of the other, this being achieved by forming the gaskets 9 of the plates P P and P with a sloping partition rib 9 In such a case, the inlet to one channel LP is taken as shown from one supply passage formed by the registered openings 1 so as to pass in one direction through that channel, while the supply to the other channel LF is taken from the other supply line formed by the other set of registred openings 1 so as to pass through that channel in the opposite direction.

It will be obvious that the number of sets of plates can be increased within the limits of the frame F of the machine. In this way, common supply and return ducts for the liquid and the steam are provided by the various registered

openings

1, 3, 5 and 7, and the liquid and steam flow channels formed by the different sets of plates are effectively in parallel across those ducts.

It will also now be clear how either or both the rising and falling liquid flow channels LE can be formed by the gaps between more than one pair of plates. Thus, referring to FIGURE 5, two plates P may be employed to provide three parallel branches to the falling flow channel LF, so providing a greater cross-sectional area (as in FIGURE 6) for the falling flow.

In some cases, particularly when a high degree of concentration is required, it may be desirable to fit a metering device at each entry feed port for each set of plates. Such a device is shown in FIGURE 8 as comprising an insert 13 having a metering orifice 14, this insert being fitted to the gasket 9 of a plate where the gasket is cut away to connect the liquid flow channel LF to the common supply duct 1. This device operates to ensure an even distribution of the liquid flow over the different sets of plates, all of which take their supply from the same supply duct.

The evaporator shown gives a single effect. As will be well understood by those versed in the art, units such as described can be combined to form a multiple etfect evaporator, the vapour formed in one effect after separation from the partially concentrated liquid being taken to the heating passages of other effects, whereby economy in heating is made possible. Other expedients such as forward or reverse feed can also be used, and where desirable a proportion of the concentrated product can be recirculated with the feed.

The apparatus described above is representative of apparatuses of one kind suited for use in practicing the method of the present invention. It is, however, apparent that apparatuses of various constructions may be used, providing only that they enable the carrying out of a concentrating procedure in which, essentially, a liquid product to be concentrated is caused to flow through a plurality, tag, a series of flow path components which are of substantially flat, very thin cross section, transverse to the direction of flow of the product, in comparison to the substantially flat facial area of the flow path components parallel to the direction of flow. The method according to the invention further includes applying heat to the liquid product, as by surface contact and conduction from a flowing fluid heating medium isolated from the liquid flow path components. The heat is applied to the product while the latter is flowing through the flow path components and, importantly, the exhausting of the product from the flow path components under low pressure conditions is controlled to enable evaporation of the product while flowing through the thin, substantially flat flow path components. By following this procedure, the liquid product will be discharged from the flow path components in both liquid and vapour phases.

As practiced in connection with the illustrated form of apparatus, the liquid product to be concentrated is introduced through the inlet passages 2, 2 so as to enter directly from these passages into the lower ends of alternate liquid flow channels as represented by the channel or path LP of the plate P The liquid product flows upwardly through this component, then across the space or separation between two adjacent liquid flow channels LF as permitted by the transfer openings and 11, and then reversely or downwardly through intervening channels as represented by the channel LF provided by the plate P While the liquid is flowing through the liquid flow channel or path components in substantially flat very thin form, it is concentrated by evaporation within the components so as to provide both a liquid and a vapour phase. The evaporation while the liquid is flowing in the narrow flow path components is made possible by exhausting the heated product containing both liquid and vapour phases directly from the intervening flow channels, as represented by the channel LF provided by the plate P into and out through the relatively large outlet passage 3. The passage 3 has a cross sectional area transverse to the direction of flow so large in comparison to the cross sections of the inlet passages 2 and the liquid flow path components as to enable the product to flow from the components under very low pressure, with little or no significant back pressure.

The particular sizes of flow paths and inlet and outlet passages, while being dictated by the principle of the invention as outlined above, will be varied in relation to one another in accordance with factors such as the overall size and capacity of the apparatus used for performing the method, and the characteristics of the liquid product which is to be concentrated. By way of example, the apparatus shown in the drawings may be constructed and proportioned in a manner to carry out the invention by providing liquid flow path components LF 1'9" wide and 2'6 high, giving a total length of product travel with reference to two adjacent plates P and P of 5, up, over and down about the interposed heating channel SF. By providlng flow paths of this size, the total heating surface of a group or unit of flow paths provided by the plates P P P and P is approximately 17 /2 square feet. The liquid product to be evaporated is subjected to this heating area on four surfaces of the four plates forming a unit. The space between the plates provided by the gaskets 9, and hence the cross section of the flow paths may vary, according to the nature of the product to be evaporated. Generally, for evaporating a more viscous product, the spacing may be of the order of Ms", whereas in a process in which the amount of vapour to be liberated is very large, the spacing may be of the order of /2". The liquid product is discharged from intervening liquid flow path components as represented by the component LF provided by the plate P all along a slit or port in the form of a narrow band extending the full width, i.e., the entire cross section, of the flow path component, discharging directly into the large outlet 3 which may have a cross sectional area of approximately 1.3 square feet, being for example 1'9" wide and 9" deep.

With a flow path component thickness of /s the ratio of the cross sectional area of the outlet opening 3 to the cross sectional area of the flow channel components is approximately 72: 1; whereas with a flow path component thickness of /2", this ratio is approximately 18:1. In general, for products normally classified as quite viscous as compared to products in which the amount of vapour to be liberated is very large, the ratio of these cross sectional areas should be approximately within the range 72:1 to 18:1.

In some cases, the invention may be used to advantage by carrying out the evaporative concentration in two phases or effects for example by serially employing two apparatuses of the kind described with reference to the drawings, one for each effect. In the evaporation of whole milk by such a double effect process, with both effects Working under Vacuum, the evaporating temperatures are approximately 160 F. in the first effect and F. in the second effect. With the first eflect being accomplished in an apparatus having 21 units each consisting of plates P P P and P and the second effect apparatus having 26 such units, it is possible to evaporate twelve thousand pounds of water per hour from twenty thousand pounds of whole milk per hour. The original product is concentrated from 12% total solids to 30% total solids, both effects operating with a temperature difference of 30 F. to 35 F.

When the liquid being evaporated becomes increasingly concentrated and therefore more viscous, it may be advantageous to reduce the cross sectional area of the liquid flow path components in the sense of the direction of the flow. This enables the maintaining of the flow of the concentrated liquid at the velocity required for obtaining optimum results.

While control of the process may vary, according to factors such as the quality of liquid to be concentrated per hour and the physical characteristics of the product, e.g., its viscosity and solids content, it is essential that the controls be so co-related that evaporation shall take place While the product is flowing in substantially flat thin film form, so as to be discharged from the flat thin path components while in mixed vapour and liquid form, without being flashed substantially into vapour when so discharged.

I claim:

1. In a method of concentrating liquid products by film evaporation, flowing a liquid product to be concentrated in confined, determinate substantially flat thin film form over a plurality of spaced substantially flat parallel heating surfaces; flowing a heating medium between adjacent heating surfaces isolated from the flow of said product over said surfaces for heating said product through said surfaces and evaporating a fraction of said liquid product while flowing in said confined, determinate substantially flat thin film form; and exhausing concen trated liquid and liberated vapour in a long narrow confined determinate band directly from the path of thin film flow thereof over said heating surfaces into and out through an outlet passage large in relation to the cross section of the thin film flow.

2. In a method of concentrating liquid products by film evaporation, flowing a liquid product to be concentrated in confined, determinate substantially flat thin film form over a plurality of spaced substantially flat parallel heating surfaces; flowing a heating medium between adjacent heating surfaces isolated from the flow of said product over said surfaces for heating said product through said surfaces and evaporating a fraction of said liquid product while flowing in said confined, determinate substantially flat thin film form; and exhausting concentrated liquid and liberated vapour in a long narrow confined, determinate band directly from the path of thin film flow thereof over said heating surfaces into and out through an outlet passage having a sectional area transverse to the direction of flow therethrough in the ratio of about 18:1 to about 72:1 to the sectional area of said long narrow bands.

References Cited in the file of this patent UNITED STATES PATENTS Dunn July 8, 1913 Kestner Mar. 17, 1914 Sandberg Oct. 24, 1922 Peebles at al Aug. 24, 1937 Prestage Jan. 21, 1941 8 Peebles Sept. 30, 1941 Cornell Mar. 14, 1944 Henszey June 27, 1950 Strelzoff May 1, 1951 Risberg July 31, 1951 Bassett et al June 7, 1955 Goodman Nov. 15, 1960 Palrnason Jan. 15, 1963 FOREIGN PATENTS Great Britain June 11, 1958

Claims

1. IN A METHOD OF CONCENTRATING LIQUID PRODUCTS BY FILM EVAPORATION, FLOWING A LIQUID PRODUCT TO BE CONCENTRATED IN CONFINED, DETERMINATE SUBATANTIALLY FLAT THIN FILM FORM OVER A PLURALITY OF SPACED SUBSTANTIALLY FLAT PARALLEL HEATING SURFACES; FLOWING A HEATING MEDIUM BETWEEN ADJACENT HEATING SURFACES ISOLATED FROM THE FLOW OF SAID PRODUCT OVER SAID SURFACES FOR HEATING SAID PRODUCT THROUGH SAID SURFACES AND EVAPORATING A FRACTION OF SAID LIQUID PRODUCT WHILE FLOWING IN SAID CONFINED, DETERMINATE SUBSTANTIALLY FLAT THIN FILM FORM; AND EXHAUSING CONCENTRATED LIQUID AND LIBERATED VAPOUR IN A LONG NARROW CONFINED DETERMINATE BAND DIRECTLY FROM THE PATH OF THIN FILM FLOW THEREOF OVER SAID HEATING SURFACES INTO AND OUT THROUGH AN OUTLET PASSAGE LARGE IN RELATION TO THE CROSS SECTION OF THE THIN FILM FLOW.