Note: Descriptions are shown in the official language in which they were submitted.
~ ~5~994
EVAPORATOR ENTRAINMENT SEPARATOR
BACKGROUND OF THE INVENTION
_ield of the Invention
This invention relates generally to evaporator appara-
tus, and is concerned with eliminating entrained droplets of
liquid from vapor generated in an evaporator.
Stat-e of the Art
Evaporators are used in various industrial applications
(e.g., sugar processing, paper manufacturing, chemical
production and mineral extraction) to recover valuable
constituents in waste liquors by removing water in the form
of vapor from the liquors. Industrial evaporators typically
include separator devices for eliminating liquid droplets
that become entrained in the vapor generated by the evapor-
ation process.
A discussion of various louver-type droplet separators
can be found in an article by H. Chilton entitled "Elimin-
ation of Carryover From Packed Towers With Special Reference
- To Natural Draught Water Cooling Towers," published in
Transactions of ~he Institution of Chemical Engineers,
Volume 30, (1952), pages 235-251. Droplet separators are
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also described in the IJ.S. paterlt literature, e.g., in
paterlts 3,070,937, 3,33~,035; and 3,~27,030.
In practice, vanes used in the prior art as
droplet separators for indus-trial evaporators have been
arran~ed in ensembles of generally rectangular configuration,
because separator manufacturers have u-tilized vane ensembles
of the kind designed primarily for mounting in rectangularly
configured orifices of air flow ducts of air conditioning
systems. In the prior art, the spacing between adjacent
vanes has generally been constant along the vapor flow path
in droplet separators for industrial evaporators.
It is an object Gf the present invention to
provide an evaporator having an improved means for separating
entrained liquid droplets from vapor generated in the
evaporator.
It is a further object of the present invention
to provide an improved separator for mounting at the vapor
outlet of an evaporator in order to eliminate entrained
liquid droplets from vapor generated in the evaporator.
According to the present invention there is
provided an evaporator having means for generating a vapor
in which liquid droplets may be en-trained, a vapor dome
supported above the vapor generating means to collect the
vapor and the entrained liquid droplets, the vapor dome
defining an outlet through which vapor passes in leaving
the evaporator, and droplet separator means. The droplet
separator means includes a support member defining an
aperture, the support member being secured to the vapor
dome so that the aperture of the support member is aligned
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~5~999L
with the~ outlet of the vapox dome. A plurality of
corrugated vanes is secured to the support member and
arranged spaced apart from each other to form a vane
ensemble having a holl.ow configuration. Each vane has
a first edge and a second edge, an outer wall of the
vane ensemble being defined by the first edges of the
vanes and an inner wall of the vane ensemble being defined
by the second edges of the vanes. The spacing between
adjacent vanes of the ensemble is such as to prevent
line-of-sight passage of vapor between adjacent vanes
in a direction from the outer wall to the inner wall. A
closure member is secured to each of the vanes, the
closure member and the support member being configured
to prevent vapor from leaving the evaporator except via
a tortuous path between adjacent vanes in a direction from
the oùter wall to the inner wall, so that liquid droplets
entrained in the vapor impinge on the vanes.
A particular advantage of the present invention
is that a droplet separator according to the principles of
this invention ca~ be fabricated using vanes that are
commercially available at the present time for use as
scrubbers and mist eliminators in air flow devices such as
air conditioning equipment.
Other features and advantages of the present
invention will become apparent upon perusal of the
description of the preferred embodiment in conjunction
with the accompanying drawing.
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DESCRIPTION OF' THE DRAWING
FIG. 1 is a cross-sectional view of a vapor
dome and upper portion of a tube trunk of an evaporator
according to the present invention.
FIG. 2 i.s an enlarged cross-sectional view of a
droplet separator mounted at the outlet of the vapor dome
of an evaporator according to the present ivention, as
shown within line 2-2 of FIG. 1.
FIG. 3 is a plan view of the droplet separator
taken along line 3 - 3 of FIG. 2.
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s~/ ' '
5~9~4 ,
. 4
FIG. 4 is a fragmentary plan view of an alternative
configuration or the vanes of a droplet separator as shown
within line 4-4 of FIG. 3.
DESCRIPTION OF P~EFERRED EMBODIMENT
As shown in FI&. 1, a vapor dome 10 is mounted atop and
in vapor communication with a tube trunk 11 of a long-tube
vertical evaporator. A large number, typically hundreds or
even thousands, of vertically rising tubes may be housed
within the tube trunk 11. The vapor dome 10 comprises a
housing 20, which defines an expansion region 21 in which
droplet-laden vapor generated in the verically rising tubes
can be expanded and collected. The housing 20 is of gener-
ally cylindrical configuration in the preferred embodiment,
although the configuration of the housing is not material to
the inventiOn.
For a long-tube vertical evaporator of conventional
design, the bottom ends (not shown) of the tubes in the tube
trunk 11 are immersed in a pool of waste liquor that is fed
into a liquor box at the bottom of the trunk 11, and the top
ends of the tubes extend into the vapor expansion region 21.
The tubes in the trunk 11 are externally heated, as by
exposure to steam, in order to draw boiling liquid up into
the tubes from the liquor box at the bottom of the trunk 11.
In a typical long-tube vertical evaporator, the tubes may be
in the range from 20 to 28 feet in length and have a dia-
meter from 1-1/2 to 2 inches. The heat transfer area of the
tubes of a typical installation might be as high as 40,000
square feet.
In operation, liquid rising in the tubes (collectively
referred to as the tube bundle~ boils at an ever-increasing
rate as the liquid rises. The resulting vapor, which tends
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to be laden with droplets of liquid, is discharged at a high
veloclty into the vapor expansion region 21 of the vapor
dome 10. The tube bundle and the liquor box may be of
conventional design, and hence are not shown in the draw-
in~.
As shown in FIG. 1, and in enlarged view in FIG. 2, anoutlet 22 is provided at the top of the housing 20 to
permit exit of vapor from the expansion region 21 of the
evaporator. Mounted at the outlet 22 is a separator assem--
bly 30 comprising a plurality of spaced-apart corrugated
vanes 31.which are secured to a generally annular support
member 32 and arranged to form a hollow ensemble of vanes.
In the preferred embodiment, the outlet 22 is circular and
the ensemble of vanes 31 is of right circular cylindrical
configuration. However, in applications where a non-circular
outlet 22 would be advantageous, the ensemble of vanes 31
could correspondingly be cylindrical but of a configuration
other than right circular. -
Referring to the preferred embodiment shown in the
drawing, the vanes 31 are secured to the annular support
member 32 to form a hollow right circular cylindrical en-
semble, with the individual vanes 31 being in generally
radial disposition with respect to the cylindrical axis of
the ensemble. The annular support member 32 is secured to
the inside wall of the housing 20 at a location circumjacent
the outlet 22, thereby providing a mounting for the separ-
ator assembly 30 at the outlet 22 such that the assembly 30
extends downward into the expansion region 21. Attachment:
of the individual vanes 31 to the support member 32, and
attachment of the support member 32 to the housing 20, may
be accomplished by conventional means (e.g., by welding).
- As shown in plan view in FIG. 3, the hollow cylindrical
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ensemble of vanes 31 of the separator assembly 30 has an
outer wall 33 and an inner wall 34, with the contour of the
outer wall 33 being defined by the radially outward ends of
the vanes 31 and the contour of the inner wall 34 being
defined by the radially inward ends of the vanes 31.
The non-apertured portion of the support member 32
covers the upper end of the ensemble of vanes 31, with the
hollow interior of the ensemble being aligned with the
aperture of the support member 32. Preferably, the aper-
10 ture of the support member 32 has approximately the samediameter as ths hollow interior of the ensemble of vanes 31.
The separator assembly 30 also includes a closure member 40,
which is attached to the lower end of each of the vanes 31
to cover the lower end of the ensemble. The support member
15 32 at the top of the vane ensemble and the closure member 40
at the bottom of the vane ensemble prevent vapor from leav-
ing the expansion region 21 via any path other than between
adjacent vanes 31 in a direction from the outer wall 33 to
the inner wall 34 leading into the interior of the hollow
20 separator assembly 30.
It is not necessary that the ensemble of vanes 31 be
precisely cylindrical. In particular applications it might
be advantageous for one or more of the vanes 31 to be dimen-
sioned differently from the other vanes, so that the hollow
ensemble could assume a bulge or indentation on its outer
wall 33 and/or inner wall 34 and thus acquire an overall
non-cylindrical aspect. In certain applications, it might
be advantageous for either the outer wall 33 or the inner
wall 34, or both the outer and inner walls, of the ensemble
of vanes 31 to assume a truncated conical configuration. In
such applications, however, the vane ensemble would never-
theless be mounted at the outlet 22 in such a way that vapor
could exit from the expansion region 21 only by passing
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between adjacent vanes 31 in a direction from the outer wall
33 to the inner wall 34.
Each vane 31 is corrugated in a direction parallel lo
the cylindrical axis of the ensemble. Corrugated vanes that
are commercially available for use as scrubbers and mist
eliminators in air conditioning systems are quite suitable
for fabricating the droplet separator assembly 30 of the
present invention. The spacing between adjacent vanes 31 is
such as to preclude line-of-sight passage of vapor between
adjacent vanes, so that any droplets entrained in vapor
passing between adjacent vanes-31 must necessarily impinge
upon one of the vanes as the vapor passes through the sepa-
rator assembly 30.
In the preferred embodiment, the distance separating
15 adjacent vanes 31 along any radius between the outer wall 33
and the inner wall 34 is substantially the same for any two
adjacent vanes of the ensemble. The corrugation of the
vanes 31 could advantageously be sinusoidal with constant
pitch and amplitude, although vanes providing a radially
20 changing pitch and/or amplitude could be used provided that
line-of-sight passage of vapor between adjacent vanes is
precluded.
Each vane 31 as shown in FIG. 3 has curved segments ly-
ing between alternating ridges of maximum and minimum ampli-
25 tude so as to assume an overall sinusoidal configuration.It is not necessary to the invention, however, that the cor-
rugated vanes 31 have a sinusoidal configuration. The vanes
31 could instead be chevron-shaped, as shown in FIG. 4, and
still be within the scope of the invention. Each vane in
30 the embodiment shown in FIG. 4 has a series of flat seg-
ments, with any two adjacent flat segments meeting in a
somewhat rounded crease. The creases at the junctions of
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adjacent flat se~ents need not be rounded, however, but
could be quite sharp.
With the right circular cylindrical disposition of the
vanes 31 of the preferred embodiment as shown in the draw
ing, the spacing between adjacent vanes decreases in the
radially inward direction from the outer wall 33 to the
inner wall 34. Consequently, according to Bernoulli's
principle, the velocity of vapor passing through the sepa.-
rator assembly 30 increases in the direction from the outer
wall 33 to the inner wall 34. This increase in vapor flow
velocity through the separator assembly 30 has been found to
. enhance the efficiency with which droplets that impinge upon
the vanes 31 are separated from the vapor, provided that the
vapor flow velocity is not so great that the fast-flowing
vapor can shear de-entrained liquid from the surfaces of the
vanes 31 and thereby re-entrain the liquid as droplets in
the vapor.
For a right circular cylindrical separator assembly 30,
the difference between the vapor velocity at the inner wall
34 and the vapor velocity at the outer wall 33 is determined
by the ratio of the outer diameter to the inner diameter of
the vane ensemble. Thus, the increase in velocity for vapor
passing through the separator assembly 30 can be controlled
by appropriate selection of the inner and outer radial
lengths of the vanes 31 in order to prevent the occurrence
of such shearing of the liquid from the surfaces of the
vanes.
Liquid depositing upon the surfaces of the vanes 31 as
the result of the impingement of droplets thereon runs do~m-
ward along the vanes 31 and collects on the underlying covermember 40. As shown in the drawing, the cover member 40 is
horizontal. However, in particular applications the cover
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member 40 could be sloped ~o facilitate the concentration of
liquid collected thereon. A drain 50 may advantageously be
provided in communication with the cover member 40 to remove
the collected liquid to the exterior of the housing 20.
.
This invention has been described above in terms cf
specific structural details which are to be construed as
illustrative rather than limiting. It should be recognized
that various changes and modifications in the design of the
preferred embodiment could be made by workers skilled in the
art in order to facilitate adaption of this invention to
particular applications without departing from the funda-
mental teachings of this invention. The scope of the in-
vention is defined by the following claims and their equiv-
alents.
