Thin film down flow type concentrator

A thin film downward flow type plate concentrator suitable for concentration of liquids which are highly heat-sensitive, wherein preheating channels (19), distributing portions (23), pool portions (24) and heating channels (18) which are formed in heat transfer plates (10) are improved to provide efficient concentration of a raw liquid in one-pass. These various portions are given respective channel shapes most suitable for their respective roles with respect to the raw liquid; thus, the total heat transfer performance is improved.

TECHNICAL FIELD 
This invention relates to a thin film down flow type concentrator suitable 
for use for concentration of highly heat-sensitive liquids, for example, 
various fruit juices, extracts of vegetables, herbs and other agricultural 
products, extracts of domestic animal bones, extracts of crabs, shrimps, 
shellfishes, fishes, seaweeds and other marine products, dairy products 
and fermented products. 
BACKGROUND ART 
To concentrate a highly heat-sensitive liquid, it is necessary to effect 
concentration in a thermal contact state at low temperature and in a short 
period of time. To this end, it is required that a raw liquid supplied to 
a concentrator be withdrawn in one pass as a concentrate. In the case of 
withdrawal in one pass, the amount of liquid decreases with concentration; 
thus, how to uniformly distribute this decreasing liquid over a heat 
transfer surface is an important point. Heretofore, a concentrator which 
is a long-tube version of the heat transfer tube system has been used. 
With this system, however, a uniform distribution of raw liquid over a 
heat transfer surface can hardly be attained; for example, there has been 
a drawback that the flow of raw liquid deviates to one side of the heat 
transfer tube, considerably decreasing the heat transfer efficiency. 
Another drawback is that cleaning is not easy. 
A concentrator based on the heat transfer plate system is also known. In 
this system also, the distribution of raw liquid is insufficient and the 
plate is short in length for its width; therefore, in the case where the 
amount of liquid is small, the plate surface dries, resulting in the 
scorching of the raw liquid, leading to a deterioration in quality. 
To remedy the above drawbacks, we have proposed the following. 
We have proposed an apparatus which operates on the principle of forming a 
preheating channel along the longitudinal center line of a heat transfer 
plate in which a raw liquid ascends, while forming heating channels on 
both sides of said preheating channel in which the raw liquid flows down 
in thin film form, preheating the raw liquid while the latter is 
ascending, distributing the raw liquid to both sides from the upper end of 
said preheating channel, and heating the raw liquid during this flow so as 
to evaporate and separate the moisture, thereby providing a concentrated 
liquid (see Japanese Patent Application Laid-Open Specification No. 
22990/1987, dated Jan. 31, 1987, published by the Japanese Patent Office). 
The above proposal is capable of contributing to the remedy of the 
drawbacks involved in using the conventional concentrator based on the 
heat transfer plate system, but much remains to be improved in connection 
with improving the performance in such regions in the heat transfer plate 
as the preheating channel, distributing region and heating channels. 
This invention has been proposed in view of the above problems in the prior 
art, and an object thereof is to improve the performance in such regions 
in the heat transfer plate as the preheating channel, distributing region 
and heating channels. 
DISCLOSURE OF THE INVENTION 
To achieve said object, this invention, in the preheating channel, uses an 
arrangement wherein the channel cross-section comprises a repetition of 
wide and narrow portions, thereby promoting the turbulence of a raw liquid 
and improving the performance of heat transfer in the preheating process. 
Further, in the distributing region, the raw liquid making a U-turn from 
the upper end of the preheating channel to the heating channels on both 
sides is fed to the heating channels in such a manner that the liquid film 
thickness is made uniform. This is attained by forming a plurality of 
narrow portion forming ridges extending at right angles to the liquid film 
flow and spaced in the direction of flow of the raw liquid, systematically 
disposing distributing projections between said narrow portion forming 
ridges and in an outlet region from a distributing portion, said 
projections serving for uniform distribution of a raw liquid, forming a 
recessed pool portion at the terminal end of the distributing portion 
extending at right angles to the direction of downward flow of the raw 
liquid and serving to increase the liquid film thickness, said pool 
portion ensuring that the film thickness of the raw liquid fed to the 
heating channels is retained uniform at all times throughout the width of 
the channels. 
Further, in the heating channels, a number of longitudinal grooves extend 
in wave form in the direction of downward flow of the raw liquid at a 
regular pitch in the direction of the width of the heating channels, said 
longitudinal grooves serving to guide and control the direction of 
downward flow of the raw liquid to ensure regular flow, preventing 
deviation of the raw liquid flow and the drying of the plate surface, 
ensuring uniform evaporation and gradual decrease of the thickness of the 
liquid film. Further, the array pitch of said longitudinal grooves and the 
groove corner curvature have predetermined values. On one heat transfer 
plate surface associated with the heating steam, the condensate drain is 
collected in the groove bottom by surface tension, while the raised 
portions are exposed to prevent deterioration of the film heat transfer 
performance caused by the film form sticking of condensate drain. On the 
other heat transfer plate surface associated with the raw liquid, the raw 
liquid is likewise collected in the groove bottom by surface tension to 
decrease the thickness of the liquid film on the raised portions, thereby 
improving the film heat transfer performance. These and other features of 
the invention will become more apparent from the following description to 
be given with reference to the accompanying drawings.

BEST MODE OF EMBODYING THE INVENTION 
In FIGS. 1A and 1B, the numeral 10 collectively denotes a heat transfer 
plate according to the present invention, having a heating steam inlet 11 
in the upper portion and in the lower portion a raw liquid inlet 12, an 
outlet 13 for concentrate and separated steam, and a drain outlet 14, the 
ratio between the length and the width being about 9:1. 
In the heat transfer plate 10, a steam plate 10a shown in FIG. 7 is formed 
by mounting a heating steam channel forming gasket 15 shown in FIG. 2A. 
Further, by mounting a raw liquid channel forming gasket 16 shown in FIG. 
2B, a raw liquid plate 10b shown in FIG. 7 is formed. 
The heating steam channel forming gasket 15 comprises an outer frame 15a 
surrounding the plate periphery extending from the upper portion of the 
heating steam inlet 11 to a drain outlet 14 in the upper portion so as to 
form a heating steam channel 17, and an inner frame 15b surrounding the 
raw liquid inlet 12 and the outlet 13 for concentrate and separated steam. 
Therefore, in the heat transfer plate 10a shown in FIG. 7, the heating 
steam flowing in through the heating steam inlet 11 is condensed as it 
flows through the heating steam channel 17, becoming the drain which is 
discharged through the drain outlet 14, so that the raw liquid and the 
concentrate and separated steam only pass along the plate. 
The raw liquid channel forming gasket 16 comprises an outer frame 16a 
surrounding the heating steam inlet 11 and drain outlet 14 and surrounding 
the plate periphery extending from the lower portion of the heating steam 
inlet 11 to the lower portion of the outlet 13 for concentrate and 
separated steam so as to form a heating channel 18 for the raw liquid, and 
an inner frame 16b, substantially U-shaped, which forms a raw liquid 
preheating channel 19 and by which the raw liquid flowing in through the 
raw liquid inlet 12 ascends close to the heating steam inlet 11 and makes 
a U-turn to the heating channels 18 on both sides. Therefore, as shown in 
FIG. 7, in the raw liquid plate 10b, the raw liquid flowing in through the 
raw liquid inlet 12 ascends through the raw liquid preheating channel 19, 
during which time it is preheated and flows down, making a U-turn from the 
upper end of the raw liquid preheating channel 19 to the heating channels 
18 on both sides, and flows down the heating channels 18, during which 
time it is heated so that the moisture in the raw liquid is separated as 
it evaporates, the separated steam and concentrate being discharged 
through the outlet 13; the heating steam and drain only pass along the 
plate. 
Steam plates 10a and raw liquid plates 10b, as shown in FIG. 7, are paired 
to form a plurality of pairs, which are positioned between two end plates 
20 and 21 and tightened in the laminating direction by bolts or the like, 
so that a concentrator 22 is assembled, as shown in FIGS. 8 and 9. 
The arrangement of the various portions of the raw liquid plate 10b will 
now be described with reference to FIGS. 1A and 1B and FIGS. 3 through 6. 
In the region extending from the upper end of the raw liquid plate 10b to 
the heating channels 18 on both sides, distributing portions 23 are 
formed, and pool portions 24 are formed between the distributing portions 
23 and the heating channels 18. 
The raw liquid inlet 12, as shown in FIG. 1B, is located immediately above 
the outlet 13 for concentrate and separated steam and on the longitudinal 
center line of the heat transfer plate 10 and is formed in the vicinity of 
the lower end of the heat transfer plate 10. In addition, the drain 
outlets 14 are formed in the lower portion of the outlet 13 for 
concentrate and separated steam and in both corners of the lower portion 
of the heat transfer plate 10. 
The raw liquid preheating channel 19, as shown in FIGS. 1A, 1B and 3, is 
constructed by forming the raw liquid plate 10b with projections 19a at 
equal or suitable intervals to provide a repetition of wide and narrow 
regions in the channel cross-section. In addition, in the position of the 
projection 19a, the raw liquid passes while bypassing both sides; at this 
time the raw liquid passes along the narrow portion and when it passes 
over the projection, it comes in the wide portion; in this manner, it 
passes alternately across the wide and narrow portions, thereby forming a 
turbulent flow, improving the heat transfer performance in the preheating 
process. 
The distributing portions 23, as shown in FIGS. 1A and 4, comprise a 
plurality of narrow portion forming ridges 23a formed on the heat transfer 
plate 10 and extending at right angles to the liquid film flow and spaced 
in the direction of the flow of the raw liquid so that the raw liquid 
making a U-turn from the upper end of the raw liquid preheating channel to 
the heating channels 18 on both sides is fed to the heating channels while 
the liquid film thickness is made uniform, and a number of regularly 
disposed distributing portions 23b for uniformly distributing the raw 
liquid between the narrow portion forming ridges 23a and on the heat 
transfer plate 10 at the distributing portion outlet. 
The pool portion 24, as shown in FIGS. 1A and 5, is a recessed liquid 
reservoir portion formed in the rearmost regions of the distributing 
portions 23 and extending at right angles to the direction of downward 
flow of the raw liquid, whereby the film thickness of the raw liquid fed 
to the heating channels 18 via the distributing portions 23 is maintained 
uniform throughout the width of the heating channels 18 at all times. 
Further, in the heating channels 18, as shown in FIGS. 1A, 1B and 6, a 
number of longitudinal grooves 18a extending in wave form in the direction 
of downward flow of the raw liquid are formed at a regular pitch in the 
direction of the width of the heating channels 18 in the heat transfer 
plate 10, whereby the direction of downward flow of the raw liquid flowing 
down is guided and controlled to prevent deviation of the raw liquid 
flowing down and the drying of the plate surface, thus ensuring uniform 
evaporation and gradual thinning of the liquid film thickness. Further, 
the array pitch P and the groove corner curvature R have predetermined 
values; for example, P=4.5-9.0 mm and R= not more than 3.0 mm, preferably 
P=6.5 mm and R=1.6 mm. Thereby, in the heating steam channel 17, the 
condensate drain is collected in the groove bottom of each longitudinal 
groove 18a by surface tension to expose the raised portion and prevent 
deterioration of the film heat transfer performance. Similarly, in the raw 
liquid heating channels 18, the raw liquid is collected in the bottom of 
each longitudinal groove 18a to reduce the liquid film thickness in the 
raised portion, thereby improving the film heat transfer performance. 
In addition, in FIGS. 1A and 1B, the reference character 18b denotes 
reinforcing projections suitably disposed in the heating channels 18; 25 
denotes a gasket groove for receiving the outer frame 16a therein; 26 
denotes a gasket groove for receiving the inner frame 16b therein; 27 
denotes distributing and reinforcing projections disposed in the heating 
steam inlet 11; 28 denotes reinforcing projections disposed in the outlet 
13 for concentrate and separated steam; 29 denotes reinforcing projections 
disposed in the raw liquid preheating channel 19; and 30 denotes 
reinforcing uneven surface region formed around the entire peripheral edge 
of the heat transfer plate 10. 
In the above embodiment, the pitch P and groove corner curvature R in the 
longitudinal grooves 18a in the raw liquid heating channels 18 are 
P=4.0-9.0 mm and R= not more than 3.0 mm. If the pitch P is less than 4.0 
mm, the probability of the plate rupturing during press working for 
pressing the longitudinal grooves 18a to a predetermined depth becomes 
higher, while if it exceeds 9.0 mm, the probability of dry surface 
occurring on the side associated with the raw liquid becomes higher and on 
the side associated with the heating steam the probability of the 
condensate drain in the raised portion being drawn into the groove bottoms 
is decreased. Further, if the groove corner curvature R is not more than 
3.0 mm, the condensate drain and the like can be arrested within the width 
of the longitudinal grooves 18a by surface tension; however, if it exceeds 
3.0 mm, since the effective range of surface tension is exceeded, the 
probability of arrest lowers. 
As for the pitch P and corner curvature R of said longitudinal groove 18a, 
optimum design values will be set within said range with respect to their 
correlation to the respective surface tensions of the raw liquid and 
heating steam condensate drain. 
FIG. 10 is a flowsheet for a concentrating apparatus constructed by using 
heat transfer plates according to the present invention. The numeral 31 
denotes a first concentrator; 32 denotes a second concentrator; 33 denotes 
a third concentrator; 34 denotes a first separator; 35 denotes a second 
separator; 36 denotes a third separator; 37 denotes a plate type 
condenser; 38 and 39 denote plate type preheaters; 40 denotes a water 
tank; 41 denotes a balance tank; 42 denotes a steam injector; 43 denotes a 
drain pot; 44 denotes a water injector; 45 denotes a first liquid feed 
pump; 46 denotes a second liquid feed pump; 47 denotes a third liquid feed 
pump; 48 denotes an extraction pump; 49 denotes a first drain pump; 50 
denotes a second drain pump; 51 denotes a third drain pump; 52 denotes a 
fourth drain pump; and 53 denotes a vacuum pump. 
The raw liquid is fed from a liquid feed pipe 54 at the left-hand end in 
FIG. 10 to the balance tank 41, wherefrom it is passed by the first liquid 
feed pump 45 successively through the preheater 38, the liquid feed pipe 
55, the preheater 39 and the liquid feed pipe 56 to each raw liquid plate 
of the first concentrator 31, where it is uniformly distributed in thin 
film form over the heat transfer surface and flows from the top to the 
bottom. The steam plate of the first concentrator 31 is fed with heating 
steam from the steam injector 42, while the condensate drain from the 
drain pot 43 is extracted by the first drain pump 49 and fed as a 
preheating medium to the first preheater. Part of the heating steam 
extracted from the upstream region of the steam injector 42 is utilized as 
a preheating medium for the second preheater 39. 
The raw liquid fed to the first concentrator 31 is concentrated while 
flowing down in thin film form across the heat transfer surface of each 
raw liquid plate, the concentrate and the separated steam being separated 
from each other in the first separator 34. The steam separated in the 
first separator 34 is fed as a heating medium to the second concentrator 
32, while the concentrate is fed to each raw liquid plate of the second 
concentrator 32 and further concentrated. The concentrate from the second 
concentrator 32 and the separated steam are separated from each other by 
the second separator 35. And the steam separated in the second separator 
35 is fed as a heating medium to the third concentrator 33; thus, this is 
a system having multiple utility. On the other hand, the concentrate 
separated in the second separator 35 is fed by the third liquid feed pump 
47 to the third concentrator 33, where it is fed to each raw liquid plate 
and further concentrated, and the product of predetermined concentration 
is taken out of the third separator to the outside of the apparatus by the 
extraction pump 48. In this manner, the raw liquid is concentrated on the 
basis of one pass flow through the concentrators 31, 32 and 33 without 
being circulated. 
The steam separated in the third separator 36 is condensed in the condenser 
37, the drain being fed as a heating medium to the first preheater 38 by 
the fourth drain pump 52. 
The condensate drains produced in the concentrators 31, 32 and 33 are drawn 
out by the drain pumps 49, 50 and 51, respectively, and fed as heating 
medium to the first preheater 38. 
In addition, the cleaning of the apparatus is effected by stopping the feed 
of the raw liquid to the balance tank 41 and, instead, feeding cleaning 
water or cleaning chemical liquid to the balance tank 41, driving the 
liquid feed pumps 45, 46, 47 and 48 to pass the cleaning agent 
successively through the first concentrator 31, the first separator 34, 
the second concentrator 32, the second separator 35, the third 
concentrator 33, the third separator 36 and the balance tank 41, in the 
same manner as in the case of the raw liquid, whereby circulatory cleaning 
using the cleaning water or cleaning chemical liquid is carried out. This 
is referred to as CIP (Cleaning In Place). 
According to the above embodiment apparatus, the following merits are 
obtained: Since concentration is effected in one pass from the inlet to 
the outlet of the apparatus, the heat contact time for the raw liquid is 
short. As a result, there is no deterioration of quality; thus, a 
concentrate of high quality can be obtained. And because of the short heat 
contact time and the possibility of low temperature concentration, large 
amounts of volatile of sweet-smelling components contained in the raw 
liquid remain, so that when the concentrate is diluted, the added value of 
the product can be enhanced. 
Further, since the hold volume of the entire apparatus is small, the 
following merits are obtained. 
(a) Concentration is possible even if the amount of raw liquid is small. 
(b) Change of the type of raw liquid is easy. 
(c) During CIP cleaning, the cleaning agent can be saved and the amount of 
discharge thereof is small. 
(d) The yield of liquid increases. 
Because of the feature of non-circulation, the liquid 
feed pumps used are small-sized and so is the amount of electric power 
consumption. Further, the employment of the multiple effect evaporation 
system, steam injectors and preheaters provides a saving of steam 
consumption and requires a smaller amount of cooling water. Further, even 
a foamable liquid can be prevented from foaming in the narrow clearance 
between the plates, ensuring little loss of the liquid due to splash 
accompaniment or the like and stabilized operation. As for CIP effects, 
because of the long plate type, even a low flow rate of cleaning agent 
provides a high speed in the plates, ensuring complete cleaning and 
satisfactory hygiene. Furthermore, the apparatus has no moving parts and 
is of the stationary type and compact; thus, the initial cost is low. 
FIG. 11 is a table of comparison of overall coefficient of heat transfer 
between the present inventive concentrator A and other concentrators B 
through F. It is seen that the present inventive concentrator A has high 
performance as compared with the other concentrators B through F. Although 
the force circulation type B exhibits high performance, it cannot be 
utilized for a one-pass concentrating apparatus which handles highly 
heat-sensitive liquids. 
Examples of data on the quality of concentrated products are described 
below. 
First, concentrated liquids from oranges, pineapples, which are typical 
concentrated juices, and soybean protein concentrate will be considered. 
As is clear from Tables 1, 2 and 3, a comparison between raw liquid and 
concentrate components shows almost no change and it can be said that 
there is no deterioration of quality. 
Table 4 shows the test results of various concentrates obtained by the 
concentrating apparatus of the invention. In this table, Bx is the unit 
for saccharose weight percentage. 
TABLE 1 
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Results of Analysis of Unshu Orange Concentrated Juice 
Measured Raw First utility 
Second utility 
Final 
item liquid concentrate 
concentrate 
concentrate 
______________________________________ 
1 Bx 11.6 20.7 36.1 60.5 
2 Acid 1.05 1.05 1.05 1.05 
3 PH 3.36 3.36 3.36 3.36 
4 V--C 35.28 35.28 35.27 35.26 
(mg %) 
5 A--N 35.44 35.37 35.23 35.02 
(mg %) 
6 L 51.9 50.0 49.8 49.8 
7 a 4.9 7.5 7.7 7.2 
8 b 31.5 29.8 29.8 29.6 
9 Pulp 5.6 4.5 4.5 4.4 
(V/V %) 
10 Degree 0.114 0.144 0.144 0.144 
of brown 
______________________________________ 
* Analyzed values of acid, et seq. indicate values when adjusted to a Bx 
value of 11.6. 
TABLE 2 
______________________________________ 
Results of Analysis of Pineapple Concentrated Juice 
Measured item Raw liquid 
Concentrate 
______________________________________ 
1 Bx 6.9 50.0 
2 Acid 0.99 0.95 
3 PH 3.32 3.35 
4 V--C (mg %) 18.62 16.04 
5 Pulp 0.8 1.0 
______________________________________ 
* Analyzed values of acid, et seq. indicate values when adjusted to a Bx 
value of 11.6. 
TABLE 3 
______________________________________ 
Results of Analysis of Soybean Protein Concentrate 
Concentrate 
Concentrate 
Measured item 
Raw liquid 
(Sample 1) (Sample 2) 
______________________________________ 
1 Concentration 
4.6 32.2 48.6 
of liquid WT % WT % WT % 
(Dry Matter) 
2 Degree of 1.06 1.04 1.00 
turbidity of 
5% liquid 
Color tone of 
20% liquid 
3 L value 81.5 80.8 81.4 
(brightness) 
4 a value 0.8 0.7 0.7 
(reddish tinge) 
5 b value 39.1 39.5 39.9 
(yellowish tinge) 
6 .DELTA.E value 
36.7 37.3 37.5 
(degree of 
transparency) 
______________________________________ 
TABLE 4 
______________________________________ 
Example of Test Results 
Concentration of 
Concentration of 
raw liquid concentrate 
______________________________________ 
Juices 
Unshu orange 11 Bx 57 Bx 
Pineapple 10 Bx 58 Bx 
Apple 7 Bx 43 Bx 
Sudati (Japanese 
6 Bx 61 Bx 
especially sour orange) 
Prune 10 Bx 70 Bx 
Soybean milks 5 Bx 49 Bx 
Soybean protein 
Sugar liquids 41 Bx 77 Bx 
Honey 
Bone extracts 3 Bx 35 Bx 
Poultry bean soup 
Fish extracts 1 Bx 41 Bx 
Bonito soup 
Yeasts 1 Bx 35 Bx 
Beer yeast 
Medicines 4 Bx 10 Bx 
Malt extract 
______________________________________ 
The present inventive apparatus has perfect one-pass performance, as 
described above, and can be said to be a concentrating apparatus most 
suitable for concentration of highly heat-sensitive materials. However, in 
view of its energy saving, maintenanceability, compactness and low cost, 
the present inventive apparatus is considered to be also effective for 
concentration of ordinary materials not so sensitive to heat, as compared 
with other types of concentrating apparatus.