US 3399708 A
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Sept 3, 1968 J. D. Usl-1ER ETAL 3,399,708
PARALLEL FLOW PASSAGE, PLA-TE TYPE EVAPORATORS Filed April 7, 196e s sheets-sheet 1 Sept. 3, 1968 J. D. usi-IER ETAL 3,399,708
PARALLEL FLOW PASSAGE, PLATE TYPE EVAPORATORS 3 Sheets-Shed 2 Filed April '7, 1966 J. D. USHER ETAL Sept. 3, 1968 PARALLEL FLow PASSAGE, PLATE TYPE EvAPoRAToRs 3 Sheets-Sheet 5 Filed April ,7, 196e 3,399,708 PARALLEL FLOW PASSAGE, PLATE TYPE EVAPORATORS John Dennis Usher, Redhill, and Ronald Hugh Linsdell, Crawley, England, assignors to The A.P.V. Company Limited, Crawley, England, a British company Filed Apr. 7, 1966, Ser. No. 540,879 Claims priority, application Great Britain, Apr. 8, 1965,
15,011/65 8 Claims. (Cl. 159-28) ABSTRACT OF THE DISCLOSURE This invention relates to a plate evaporator in which the plates are arranged in one or more units, each unit providing a parallel llow path for the liquid in process and comprising plates dening alternating liquid boiling passages and steam heating passages. The number of rising boiling passages in a unit exceeds the number of falling boiling passages.
This invention relates to plate type evaporators.
United Kingdom patent specification 859,876 describes `an arrangement wherein vertical plates are arranged in units of four to comprise four flow passages, two of which contain the boiling liquid, and the other two the heating medium such as steam. The boiling7 and heating passages alternate and the boiling liquid rises to the top of one passage where it enters the top of the next boiling passage through a transfer duct and falls to the bottom of this passage where it enters the discharge duet. These units of four plates are assembled in parallel in a number to give the required evaporating duty. Boiling actually occurs in the boiling passages between the plates. The discharge duct feeds into a separator.
It is necessary to maintain a minimum liquid flow rate through the boiling passages since otherwise the liquid may burn on the plates and cause deposition of scale, which atiects the efciency of the plate and may also be detrimental to the flavour or other property of the product. A reduction below the minimum is liable to occur in cases where high concentration ratios are required and it is conventional practice to recirculate part of the product to ensure that the tlow rate is above the acceptable minimum. Where heat sensitive liquids are being evaporated, however, the introduction of recirculation increases the time taken for the product to pass through the evaporator and this may result in degradation of the product or a deterioration in its quality.
An object of this invention is to avoid the need for recirculation while at the same time retaining adequate liquid flow.
The invention accordingly consists in a plate evaporator in which tthe plates are arranged in one or more units in parallel each unit comprising plates defining alternating boiling passages -and heating passages, the boiling passages including two or more rising passages in parallel feeding a transfer port leading to one or more falling boiling passages feeding a discharge duct.
In general there will be only one falling boiling passage per unit and this will take the output of two or more rising boiling passages so that a considerable increase in the liquid ilow rate in the falling passages is achieved and the tendency to burning on the plate can be eliminated by 3,399,708 Patented Sept. 3, 1968 choice of the number of rising boiling plates per unit to suit the duty.
The rising boiling passages in a unit may all be one side of the falling boiling passage or they may be divided into two sections, one at each side thereof.
With an arrangement according to the invention it may be possible, where the concentration ratio is sulciently high, for the liquid ow rate at the top of the rising boiling passages to be insuliicient to avoid burning of the product, and to avoid this the rising boiling passages may be tapered towards their top exit in order to reduce the width of the liquid passage in the direction of flow, thereby ensuring sutlicient liquid flow over the reduced width to avoid burning. The exits of the rising boiling passages would therefore be of reduced width in relation to the entry to the falling boiling passage, but these exits would be staggered in relationship to `one another so that the entire width of the falling boiling passage would be fed with liquid.
Alternatively the rising boiling passages could be of a parallel width and the falling boiling passage could be tapered towards its exit, or both could be tapered according to the degree of concentration required.
In cases where the assymetrical nature of the rising passage might give rise to maldistribution of the process liquid it is possible to taper the rising passages from both sides of the plate, thus giving a symmetrical reduction in ow area.
The falling passage can then -be formed of a parallel section equal in width to the outlet section at the top of the rising passage or it can be tapered down from this width if required to give even greater liquid wetting effect.
A further variation relates to the spacing of the plates, which can be adjusted according to the vapour conditions existing within the boiling passages. For instance, the falling boiling passage will be carrying the vapour generated in a number of rising boiling passages and this may result in a high vapour velocity which could give rise to an excessive pressure drop. In such a case the spacing of the plates defining the falling boiling passage could be increased in order to reduce the magnitude of the vapour velocity.
The invention will be further described with reference to the accompanying drawings.
In the drawings:
FIGURE 1 is a diagrammatic side elevation showing the ow in a single unit of ten plates;
FIGURE 2 is an exploded view illustrating the ows between the plates themselves;
FIGURE 3 shows an alternative form of some of the plates of FIGURE 2;
FIGURE 4 shows a further alternative form of the plate of FIGURE 2; and
FIGURE 5 shows a still further variation for one of the plates of FIGURE 4.
As shown in FIGURES 1 and 2 the evaporator comprises a head H which is rigidly secured in a frame (not shown) and a plurality of gasketed plates clamped in the frame between the head and a follower (not shown). The plates are arranged in units of ten in the embodiment illustrated and in FIGURES 1 and 2 the plates S1 to S5 and P1 to P5, of one complete unit, together with the head H and a single plate S1 of the adjacent unit, are illustrated. Alternate plates which carry gaskets to control steam (or vapour from a previous effect) fiow will be called steam plates and are designated by S numbers. The intervening P plates are gasketed to control product flow and will be called product plates. The plates S1 and P5 at the ends of the units will be designated end plates In each of the steam plates the steam tiows from a rectangular steam inlet conduit formed by aligned apertures A in the plates and head, through a serpentine path defined by the gasket and steam spacers to a condensate outlet formed by apertures B. Plates S2 to S5 and P1 to P4 each include an aperture T forming part of a transfer passage extending through but not out of thevunit for passing product and vapour from up product plates P1, P2, P4 and P5 (rising boiling plates) to down product plate P (falling boiling plate). The end plates S1 and P5 do not have apertures T. Thus, in each of the up product plates P1, P2, P4 and P5 the product passes up the plate through a reducing width passage from twin product inlet C to the transfer passage. In plate P3 the product and vapour passes down a passage from the transfer passage to a concentrate and vapour outlet conduit D.
The yrising boiling passages defined by the up plates P1 and P2 are arranged to discharge into one half of the falling boiling passage in plate P3 whilst those defined the plates P4, and P5 are arranged to discharge into the other half of the falling boiling passage in plate P3, thus giving uniform distribution in the falling section.
In FIGURE 3 there is shown an alternative arrangement of the up product plates P1', P2', P4 and P5' wherein the transfer passage T is twinned into two parts T1' and T2' so that the falling boiling passage in plate P3 is fed across its whole width from yboth sides. The steam plates must also be modified somewhat as regards the transfer passage.
In a further alternative arrangement, the up plates can have parallel flow .passages and the down plate can be tapered as shown dotted in FIGURE 2 or any combination of tapered or parallel plates can be used according to the material being handled.
FIGURE 4 shows plates S1 to S5 with modified faces of product plates P1" to P5". The up plates P1, P2", P4" and P5 are formed with tapered product flow passages leading to a narrow transfer passage T adjacent the centre of the top of the plate pack. The plate P3" has a parallel sided passage the same width as passage T providing communication linking the passage T" and the outlet conduit D.
FIGURE 5 shows a further alternative form of plate P5" to replace plate P5". The difference is that the ow passage is tapered from the transfer passage T.
The following numerical example is intended to illu'strate how the invention may be applied and is not given by way of limitation.
The `example is concerned with the six-fold concentration of orange juice. A one up/one down -plate unit according to the prior art would be capable of concentrating 600 lb./hour to 100 lb./hour of liquid. This flow would probably be insufficient to prevent burning of the plates, as some 250 lb./hour are required as a minimum ow.
However, if each unit is increased to four rising passages feeding a single falling passage, with intervening steam passages, the plate heating area is increased by a factor 21/2 so that the total liquid feed rate may be increased to 1500 lb./hour and the product feed rate will be 250 lb./ hour. This will ensure an adequate liquid feed rate at all parts of the falling passage without resort to recirculation.
Various modifications may be made within the scope of the invention. It is not of course necessary to confine the invention to a single falling passage, as the numbers of rising and falling passages in a single unit can be adjusted according to the liquid and vapour loading.
1. A plate evaporator comprising a puck of apertured plates and sandwiched peripheral gaskets defining flow passages therebetween, the apertures being aligned to form ducts through the pack, a first set of apertures defining a heating medium inlet duct, a second set of apertures dening a heating medium discharge duct, a third set of apertures defining a feed inlet duct and a fourth set of apertures defining a concentrate and vapor discharge duct; alternate fiow passages between adjacent plates being for the flow of heating medium, and the intervening pas sages forming boiling passages for the fiow of feed and vapor in heat exchange with the heating medium to boil the feed, said boiling passages being either rising boiling passages or falling boiling passages; the plates in the pack being grouped into a series of units, each unit defining with its gaskets a parallel ow path for the liquid in process between the feed inlet duct and the concentrate and vapor discharge duct through a rising boiling passage, a transfer duct and a falling boiling passage; all plates but the end plates of each unit having apertures defining at least one transfer duct; gaskets isolating the various fiow medium flow passages from each other, the gaskets also sealing the heating medium flow passages allowing communication between the heating medium flow passage and the heating medium inlet and discharge ducts while sealing the heating medium flow passages from the feed inlet duct and the feed and vapor discharge duct and from the transfer ducts; the gaskets defining the rising boiling passages allowing communication between one transfer duct and the feed inlet duct via said rising boiling passage, and the gaskets defining the falling boiling passages allowing communication between said transfer duct and the concentrate and vapor discharge duct via said falling boiling passage; the gaskets sealing all the boiling passages isolating the boiling passages from both the heating medium inlet and discharge ducts; the evaporator having the improvement that each unit includes at least two rising boiling passages separated by a heating passage and defined between distinct .pairs of adjacent plates and in parallel from the feed inlet duct to one of said at least one transfer duct, and at least one falling boiling passage from one of said at least one transfer duct to the concentrate and vapor discharge duct; the number of rising boiling passages in any unit exceeding the number of falling boiling passages in said unit, said falling boiling passages accommodating the partially processed liquid and its vapor from rising boiling passages arriving from opposite sides and directions toward the falling boiling passage.
2. A plate evaporator as claimed in claim 1, in which each falling boiling passage in a unit tapers downwardly towards its outlet to the discharge duct.
3. A plate evaporator as claimed in claim 1, in which the plates defining the rising and falling boiling passages are located at different distances apart so that the depth of the rising and falling boiling passages differs.
4. A plate evaporator as claimed in claim 1, wherein the rising boiling passages are tapered towards their upper downstream ends into their respective transfer duct.
5, A .plate evaporator as claimed in claim 4, including one falling boiling passage per unit, the rising boiling passages in a unit being divided into two Sections, one section lying at each side of the said one falling boiling passage, in which the outlets of the rising boiling passages in a unit are staggered in such a manner that the rising -boiling passages in one section feed a transfer duct leading to one transverse duct line near one edge of the falling boiling passage and the rising boiling passages in the other section feed a second transfer duct line near the opposite edge ofthe falling boiling passage.
6. A plate evaporator as claimed in claim 4, including one falling boiling passage per unit, the rising boiling passages in a unit being divided into two sections, one section lying at each side of the said one falling boiling passage, comprising two laterally separate transfer ducts associated with each section. the upper end of the rising boiling passages in each section being staggered to provide 2,334,959 11/1943 Rosenblad 159-13 feed to their respective transfer duct. 2,562,739 7/1951 Risberg 159--28 X 7. A plate evaporator as claimed in claim 4, wherein 2,764,233 9/1956 Skinner 159-13 the rising boiling passages feed to a single transfer duct 2,960,160 11/1960 Goodman 159-28 X of a width equal to the width of the outlets of the rising 5 3,073,380 1/ 1963 Palmason 159-49 boiling passages and feeding to the falling boiling pas- 3,155,565 11/1964 Goodman 159-28 X sages, which has an inlet of a similar width.
8. A plate evaporator as claimed in claim 4, in which FOREIGN PATENTS each falling boiling passage in a unit tapers downwardly 935,542 8/ 1963 Great Britaintowards its outlet to the discharge duct, 10
NORMAN YUDKOFF, Primary Examiner.
References Cited I. SOFER, Assistant Examiner.
UNITED STATES PATENTS 1,200,996 10/1916 Soderlund et al. 159-13