Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to an apparatus for the
desalination of sea water, with automatic regulation of the
levels of the fresh and the salted water.
More particularly, the present invention relates to an
automatic device for regulating the levels of fresh water and
brine in the multistage desalination process.
From U.S. Patent No. 3,961,658, an apparatus is known
for carrying out a multistage distillation process for sea
water.
Such apparatus may be briefly described as an
apparatus for desalinating sea water that is composed by
a vertically positioned column subdivided into a plurality
of cylindrical sections, each of which comprises the following
component parts:
(a) a film-evaporator in a tube bundle vertical arrangement
having preferably a circular cross-sectional outline, without
any outer casing;
(b) a tub or basin which is connected at the bottom portion
with a top tube plate of the.evaporator of the same cylindrical `.section, the tub or basin in the last section being deprived of
the evaporator and being connected to the brine-discharge tube,
and connected at the top with a bottom tube plateof theevaporator
of the overlying section, the tub or basin being connected, in
the first cylindrical section, to the sea water feeding tube;
; (c) a lamination system or restriction arranged at the
bottom of the tub or basin and having the purpose of allowing
the flow of the brine from the tub or basin to the underlying
tube plate by dissipating the positive pressure differential
obtained between the tub or basin and the tube plates;
(d).openings formed through the upper sidewall of the
tub or basin except that of the first cylindrical section;
(e) one or more siphoning tubes for taking the
condensate collected at the bottom of each cylindrical
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section to recycle the condensate at intermediate points of the
subsequent cylindrical section;
(f) a preheater housed in a throughtube having a circular
of elliptical or rectangular cross-section, the tube being
diametrically passed through the tube and welded thereto, the
heating means being the steam produced in every cylindrical
section, and the steam of the last section being condensed.
The Applicant's attention has been directed to the
device which is intended both for transferring the brine from
the tub of any section to the tube plate of the film evaporator
of the next section, and for transferring the fresh water or
the brine from a stage to the next one, a device which in the
above-mentioned patent, was shown as a submerged overfall,
other devices being equally well suited for this use and
particularly valves, especially of the floater type.
A particular static device (self-regulating siphon) has
now been found, which, by properly exploiting the "flashing"
phenomenon (with evolution of vapor) which takes place during
the expansion of the liquid from a stage to the next, permits a
self-regulation of the levels in a simple and reliable way,
by avoiding the ùse of moving component parts. Such a transfer
device consists of a tube (fall tubel inserted in the end portion
of another tube (riser) having a larger size and coaxial with
the first and having specially provided slots, preferably in
the cylindrical portion for causing the liquid to merge from
the top portion. The cross-section of the tube can also be
other than circular, since it is possible to provide elliptical,
rectangular tubes and so on. The cross-section of these slots
is calculated in such a way that, during the normal run, the
overall load acting on the slots is ~ Hl+ P , wherein AH
is the liquid head in the fall tube and ~P is the pressure
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differential between two consecutive stages, expressed in
terms of height of liquid column.
Under these conditions, the expansion of the liquid
takes place only at the outflow and the riser will not contain
any water vapor.
A device according to the subject invention will now
be described in greater details with reference to the appended
drawings, this description being anyhow intended as being
merely an illustration and not a limitation of this invention.
FIGURE 1 shows an example of transfer of the liquid
(fresh water or brine) from a stage at a pressure P to the
subsequent stage at a pressure P - ~P, wherein the two stages
are separated by specially provided plates 1 and 1'. In this
case, that is, during the normal run, the load acting upon the
slots 2 is ~Hl ~ ~P and under these conditions the expansion of
the liquid takes place only at the outflow and the riser 3
will consequently contain no water vapor.
FIGURE 2 shows an example of the case in which the rate
of flow of the liquid is reduced and the fall tube 4 will
, consequently tend to become emptied and the hydraulic head ~Hl
will become negative relative to the outlet slots 2. The overall
load acting upon the slots 2 will thus be ~P - ~Hl.
The result is that the liquid will undergo a flash-
ing in the interior of the riser 3 and will evolve steam which,
due to its larger specific volume, will drastically reduce the
flow cross-section of the liquid and will prevent the fall tube
4 from being totally emptied and thus also from transferring
stcam from a stage to the next one.
FIGURE 3 shows an example of the case in which, less
frequently, a rate of flow increase over the nominal value
is experienced. In such a case there is an increase of the
level of the liquid in the fall tube 4 and the degree of
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flexibility will be bound to tlle length of said tube. The
insertion of an appropriate overflow tube 10 could prevent
an exceedingly large accumulation of liquid in the several
stages, whenever it is not possible to provide for an
adequately long fall tube. As an alternative to the overflow tube
10, the self-regulating siphon can be designed for a rate of flow
greater than the nominal one and if so, obviously, the siphon
will work during the normal run under flashing conditions in the
riser, as shown in FIGURE 2.
FIGURE 4 gives an example of a portion of the column
with a complete stage which comprises the two evaporators S
placed side by side and the central preheater 6.
The condensates coming from the stage "n" are passed
to the stage "n + 1" through the fall tube 4. Since the space
occupied by a stage is about 4 to 5 meters, the fall tube can
be long enough as to permit wide fluctuations of the level in
the tube without giving rise to accumulation problems. In
addition,the brine coming from the film evaporators 5 is
collected in the relative tubs 7 and the liquid level in
each tub is regulated by the self-regulating siphon E, which has
the vertical fall tube 8 fastened to a plate H, the latter being
internal to the tub and in communication on the one side with
the liquid vapor boundary area and, in addition, has its other end
enclosed by a cylindrical sleeve 9, which is coaxial with the fall
tube and has a larger diameter than the same, is closed at one
end and equipped in the cylindrical portion with slots 2 which
give a preselected pressure drop.
Inasmuch as the fall tube cannot be, in this case,
long anough as to permit the flow of rates of flow larger than
the nominal one, it can be provided so as to have the siphon
to operate under flash conditions in the riser portion, as
outlined above.
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