Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF TH~'INYENTION
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Field o the Invention
... . . .... .
~ he invention relates to the condensation of vapor
in industrial processes, by means of a plate type condenser.
-Descript-ion of the Prior Art
.. . . . . ..
In many industrial applicatisns, the vapor or steam
produced in an evaporator is subsequently condensed for
removal from the system, re-use o~ water or for some other
reason. For example, sur~ce condensers used in evaporator
systems in the pulp and paper industry allow re-use of warm
condenser water reco~ered from steam.
When steam or other vapor to be condensed carries
components in the vapor phase that are more volatile than the
water or other substances comprising the principal constitu-
ent to be recovered by condensation, one way to treat the
vapor is to fully condense everything, including the more
highly volatile materials, often, by subcooling to a con-
siderable degree.
Evaporator and condenser systems of several ki~ds
have been illustrated in Fig. 11-17 at page 11-25 of Perry's
Chemical En~ineer's Handbook, Fourth Edition, 1963.
.. . . . . .. _ . _ . . . . . . ... .
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U.S. Patent No. 3,788,954 to Cantrell relates to
a distillation process and shows a condensation section having
upper and lo~er condensation chaI~ers separated by a horizontal
wall or baffle intended to separate less volatile from more
volatile components of vapor being condensed. U.S. Patent
No. 3,261,392 shows an evaporator having a vertically disposed
~affle dividing a heating space; and plate type heat exchang-
ers have been desc~ibed in C. F. Rosenblad's U.S. Patent No.
3,332,469.
There is considerable experience and other published
information relating to industrial heat exchange technology in
general, and more particularly to surface condensers of various
kinds. Yet no fully satisfactory system for the effective
separation of condensate in a plate type heat exchanger to
concentrate the more volatile components of steam or other
vapor being condensed from those that are less volatile has
achieved wide industrial acceptance. The present invention
overcomes difficulties of prior art systems and provides a
highly effective method and apparatus for selective condensa-
tion.
SUMWARY OF THE INVENTION
~ ~ _ . . . . ..
The condenser of the invention comprises a housing
enclosing a plurality of heat exchange elements outside of
which elements a coolant fluid passes to condense vapor within
the elements. Preferably the heat exchange elements are
formed o~ pairs of broad plates secured together around their
peripheries with an opening to the intarior of each element
at the top and bottom of each element. A header communicat~s
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with all of the elements at theix upper ends so that vapor
can pass freely from one element to another for condensation
within the elements. A bottom header opens on to each
elemen~, but there is a barrier closing off one end portion
of the bottom header ~rom the other end thereof.
Vapor to be condensed is fed to the interiors of
all those heat exchange elements at one side of the header
barrier. The vapo~r rises within those elements and is
partially condensed therein. The condensate formed comprises
the more easily condensed constituents of the vapor.
Thé more volatile components o the vapor are not
so readily condensed and pass on through the upper header to
the heat exchange elements whose bottoms open to the lower
header on the other side of the barrier from the vapor entry
area. Further cooling condenses the more volatile components
and the co~densate containing these contaminant substances
collects at the bottom of the conde~ser at the other side of
~he barrier from the cleaner condensate, and the contam~na~ed
condensate is withd~awn as a sQparate stream from the clean
liquid. Noncondensible and vent gas~s exit from the same
sïde of the barrier as the contaminated condensate.
Most of the heat exchange elements communicate with
the vapor entry side of the lower header, and most of the
condensate is withdrawn from that side. ~he vapor passes
upwards through this majority of the heat exchange elements.
The smaller number of heat exchange elements where~
in the more volatile suhstances are condensed carry the vapor
downward so thclt vent and noncondensible gases can exit at
these elements 1l lower ends. The vent gases can subse~uently
~e condensed ~ld their heat recovered in subsequent treatment~
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The foregoinq description has followed the vapor
being condensed, but the coolant flow should also be consider-
ed. The cooling medium can be a continuous supply of cooling
water which is heated while condensing the vapor; or cooling
water that is recycled ~y means o~ a circulation pump and
cooled by means of evaporative cooling outsid~ the system
shown before return to the condenser as coolan~; or liquid
which is to be evaporated. In the latter case, where water
or other liquid to be evaporated is employed as the coolant
medium for condensing the ~apor inside the heat exchange
elements, the flow of liquid as a thin film down the outside
surfaces of the heat exchange elements results in evaporation
of a considerable amount o~ the coolant liquid. Thus, while
the interior spaces within the heat exchange elements are
working as a condenser, the exterior space outside the heat
exchange elements and within the housing, functions a~ an
evaporator.
Pilot plant trials have been made by condensing
steam contaminated by substances that are malodorous and ha~e
high biochemical oxygen demand ~BOD~. About 90% of the
cond~nsate is formed during the upward pass of steam through
the heat exchange elements on the steam entry side of the
barrier, but the condensate produced in this pass and discharg- -
ed from th~ bottom header carries less than 20~ of the contam-
inants. The remaining 80~ af the contaminant substances go
over to the downward flowing stream in ~he elements whose
bottoms communicate with the lower header on the other side of
the barriex. The 20~ of the total condensate produced and
collected on that side of the barrier and the vent gases dis-
charged on the dirty condensate side together carry over 80%
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of the total contamlnants.
T~e relatiYely clear condensate stream from the
majority of the elements i5 esseIltially odor free and can be
recycled to the mill or plant without further treatment.
The separated stream o contaminated water can be
passed on for further treatment in a stripping column or the
like.
These and othex objects and advantages of the
selective condensation system of the in~ention will be more
fully understood from the following detailed d~scription of
tha invention, especially when- that description is rsad with
reference to the ~ccompanying drawing.
Brief Description of ~he Drawing
In the drawing, in which like reference characters-
indicate like parts throughout: -
~ Fig. 1 is a sectional view through apparatus
according to the invention;
- Fig. 2 is a view in section taken along lines 2-2
of Fig. 1, looking perpendicular to the view of Fig. 1 in the
direction of the arrows and showing the clean condensate-side
of the apparatus;
Fig. 3 is a view similar to that of Fig. 2, but
showing the foul condensate side of the apparatus;
Fig. 4 is a ~iew in section taken along lines 4-4
of Fig. 1 and looking downward, with the path of flow through
the upper part of the apparatus-shown;
Fig. 5 is a view in section taken along lines 5-S
of Fig. 1 showing the flow at the Iower part of the apparatus;
~8~ 0
Fig. 6 is a view in perspectiYe of apparatus o~
Figs. 1-5 with some parts broken away and some parts illus-
trated by dashed lines, and
Fig. 7 is a view in section of apparatus according
-~ to the invention for producing several separate condensate
streams.
DETAILE~ DESCRIPTION OF A PRE~ERRED EMBODIMæNT
. .
In the drawings the condenser of the invention,
generally designated 10, has a housing 11 with generally
vertically extending ront and back walls 12 and 13 respect-
ively and a pair of side walls 14. Within the housing 11
there is an array of spaced, parallel falling film heat
-exchanger elements 15. The heat exchange elements 15 are o~
the type formed-by pairs of spaced parallel broad flat plates
secured together around their peripheries to provide enclosed
- spaces within the elements 15. A preerred method of manu-
facturing plate-heat exchange elements is disclosed in my
prior U.S. Patent ~o. 3,512,239 granted ~ay 19, 1970. As -
those familiar with the art will understand, the elements 15 ~-
can be employed to condense steam or other vapors passing
within the elements 15 by indirect heat exchange with a coolant
medium, such as water ~lowing as a thin film down the outer
surfaces of th~e elements 15.
Mea.ns for introducing coolant liquid into the
housing 11 and distributing the liquid evenly over the sur-
faces of heat e~change elements 11 are shown in Figs. 1, 2
and 3. A perforated, generally horizontally disposed tray 16
is mounted across the interior of the housing 11, abo~e and
spaced from the heat exchange elements 15. Water or other
coolant liquid flows through the per~orations of the tray 16
to run down the outer surfaces of the heat exchange element~
15 as illustrated in the several drawing figures. Prefexably
the cooling liquid is not poured directly onto the tray 16,
~ut is fed to an upwardly open box 17 spaced above the tray
16 to overflow the box 17 and thus distribute liquid more
evenly. When very large amounts of liquid coolant are used,
the box 17 is not ~eeded. Pipe 18 is shown in Eigs. 2 and 3
leading to the box 17 for supplying cooling liquid thereto.
` Water or oth~r cooling liquid that has traversed
the vertical length of the heat exchange elements 15 is shown
in Figs. 1, 2, 3, and 6 to be collected at the bottom of the
housing 11, where inwardly converging bottom portions 22 and
23 of the front and back walls 12 and 13 form a trough 24.
Liquid is discharged from the trough 24 through an outlet
conduit 25. The inlet pipe 18 can supply additional resh
coolant liquid as needed to the tray 16. If racycling of the
coolant liquid is desired, a pump and means for cooling the
liquid before recycling can be used.
- The preferred structure related to flow of liquid
externally of the heat exchange elements has as one result
the provision of a uniform and effective flow of cooIant
along the outer surfaces of the heat exchange elements 15 to
condense steam or other vapor within the elements 15.
Ste,~m or other vapor to be condensed entexs through
the front wall 12 of the housing 11 by way of a conduit 26
as best shown in Figs. 2, 5 and 6 of the drawing. A baf1e
(not shown) can be provided to promote better distribution of
the vapor. The conduit 26 is located at the lower part of the
condenser 10 adjacent the lower ends of the heat exchange
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elements 15. It will be seen that the lower front corner of
each heat exchange element 15 has a cutout area as shown at
27 in Figs. 2, 5 and 6; that is, the peripheries of the plates
rorming the plate type heat exchange elements 15 are not
sealed togather at the elements' lower front corners. Alter-
nately inlet and outlet boxes could be welded on the elements
15, or some other method of fabrication could be employed.
The cutouts or openings 27 all communicate with a bottom head-
er B that extends across the front of the housing 11 as shown
in Fig. 1. It will be seen that the bottom header B has a
top wall 28 and a bottom wall 29, that the front wall 12 of
the housing ~orms a front wall o~ the header B, and that
except for the openings 27 into the interiors of the heat
exchange elements 15, the header B is closed at its rear by a
back wall 30. Thus, nothing can pass to or from the bottom
header B to the space within the housing ll where cooling
liquid circulates, and the header B communicates with the
interior spaces of the heat exchange elements 15 through the
openings 27,
Steam or other vapor to be condensed enters the
bottom header B through the conduit 26 and thence passes to
the heat exchange elements 15 via openings 27 to be condensed
as it passes upward as shown in Fig. 2.
The header B is not open and continuous along the
entire length c~f the ront of the housing 11, but is inter-
rupted by a bar.rier 31, as shown in Figs. 1, 5 and 6. Vapor
entering the header B through the conduit 26 can only pass
directly to some of the heat exchange elements 1~, the openings
27 o~-the other elements 15 being separated from the conduit
26 by the barrier 31.
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It has been found that the barrier 31 should pre-
ferably be positioned to divide the bottom header B into a
relati~ely longer section 32 and a relatively shorter section
33. This- permits direct communication of most o~ the heat
exch nge elements lS with the vapor entering through the
conduit 26 by way oi the longer header section 32 as seen in
Figs. 5 and 6.
Attentibn is now directed to the upper front area
of the heat exchange elements where an upper header ~ i5
shown to extend within the housing 11 to interconnect the
upper front ends of all of the heat exchange elements 15.
The upper header H extends u~obstructed across the entire
array of heat exchange elements 15, which elements 15 all
have cutout or unjoined areas at 37 opening on to the upper
header ~. Except for the openings 37 communicating with the
i~teriors of all of the heat exchange elements 15, the upper
header is enclosed by a top wall 38, bottom wall 39, rear
wall ~0 and by the housing front wall 1~.
The structure of the headers B and ~, and the ~ .
arrangement of heat exchange elements 15 which have openings
only at 27 and 37, thus constrains vapor to ~low upward-
through those elements 15 which communicate with the header
B at the portion 32 and to flow downward through those
elements 15 which communicate with the area 33 of the bottom
header B on the other side of the barrier 31. These flow
paths will be :more fully apparent from Figs. 4, 5, and 6.
Conde~sate formed within the heat exchange elements
15 is discharged by way of two condensate outlets 41 and 42,
shown in Figs. 2, 3 and 6. The condensate outlet 41 drains
the portion 32 of the bottom header B and the condensate out-
let 42 ser~es to drain the shorter portion 33 of the bottom
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header B~ Thus the outlet 41 ls located below the vapor
inlet conduit 26 and the outlet 42 is located below the vent
and noncondensible outlet conduit 36. As shown in Fig. 6,
the lower wall of the bottom header B can be formed to
facilitate condensate discharge.
The barrier 31 splits the bottom header B into two
une~ual sections 32 and 33 as already indicated. Thus ~apor
such as steam to be condensed is passing upward ~hrough most
of the heat exchange elements 15. The relationship between
the amounts o heating surface provided by the sections 32
and 33 depends upon the fluid to be condensed. As an example,
for a pre-evapoxator for spent liquor from the kraft pulping
process, it is presently preferred that about 90% o~ the heat
exchange elements 1~ be in commun.ication with the steam entry
portion 32 of the bottom header B, the remaining elements 15
communicating with the vent outlet area 33 of the header B.
For other services, a ratio other than 9 to 1 can be efect-
ively employed.
- In the typical case, of the pre-evaporator for spent
kraft pulping liquor where steam is to be condensed, about g0%~ -
of the steam is condensed duxing the upward pass through the
majority of the heat exchange elements 15, lea~ing only about -
10~ of the steam to travel along the upper header H for the
downward passage through heat exchange elements 15 that commu-
nicate with the outlet 36. How2ver this 10~ of the steam is
very rich in the lower boiling point or volatile conta~inant
substances. The condensate formed du.ring the downward p~ss
and discharged through the outlet 42 is much richer in malo-
dorous compounds and BOD-producing components than the con-
densate discharged on the steam entry side through the outlet
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pipe 41. Pilot plant trials have produced a yield of less
than 20% of the BOD and malodorous condensate in the 90% of
the condensate formed during the upward pass of the steam,
and over 80~ of the BOD and foul~smelling components ha~e
appeared in the condensate and vent gases exiting at the vent
36 and condensate outlet 42.
The foregoing discussion has treated the flow of
vapor through the interiors of the heat exchange elemen~s 15
and has treated the li~uid coolant flowing down the exterior
~urfaces o~ ~he heat exchange elements only as a coolant for
the vapor to be condensed. However, it is also important to
consider evaporation of this coolant liquid by heat transer
from the condensing vapor. As the water or other coolant
liquid flows down the heat exchange elements lS as a film, a
considerable amount o~ the liquid will evaporate. This
result can be ad~antageously used by`employing as the coolant
a liquid which is to ba evaporated. Thus, while the interior
spaces o the heat exchange elements lS are working as a
condenser, the ext~rior space outslde the elements 15 and
within the housing 11 works as an evaporator.
For example, liquor re-circulated to the tray 16 by
the pump P is mixed with liquor to be evaporated whi~h is
introduced through the pipe 18 and ~oiled off vapors pass
-outward from ~nong the heat exchange elements 15 as the liquor-
is heated by the hot vapor within the elements 15. The vapor
boiled of rises to thP upper part of the apparatus, above the
tray 16. Fig. 6 of the drawing illustrates how the housing
wall- 13 can be spaced from the nearest heat exchan~e element -
15 to permit outward and upward flow of boiled-off vapor with-
in the housing 11. ~his vapor can then be allowed to pass
upward either through space provided alongside th~ tray 16 or
- 12 -
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through a conduit to the top o~ the housing 11, where an
entrainment separator or the like (not shown in the drawing)
can be provided ~or trea~ment of the vapor generated by
evaporation o the liquid coolant. Figs. 1-3 show the housing
11 as vented centrally at its top at ~0, but it will be under- -
stood by those familiar with the art that an entrainment
separator can be provided at the location shown by the refer-
ence numeral 50 to capture droplets of li~uid carried by the
flow of vapor.
The system for selective condensate separation
according to the invention is not limited to the separation
of two condensate streams, but can be extended to the separa-
tion of three or more streams of condensate with di~ferent
degrees of purity. Fig. 7 shows an arr~ngement for selec~ive
condensation of four condansate streams, indicatad as con-
densates I through IV, of which condensate stream I i~ made
up of the most raadily condensed portion of the feed and
- -condensate stream IV contains the most dificult to condense
of the substances that are condensed within the apparatus~
It will be seen that the appar tus of Fig. 7 has
a housing like that of the previously discussed embodiment,-
with side walls 114 corresponding generally to the walls 14
in Fig. 1, a liquid distribution tray 116 similar to the tray
16, heat exchange elements 115 like the elements 15, and so
on. The apparatus of Fig. 7 difers from the embodiment shown
in the other drawing features in that it is sectionalized to
separate the several condensates. The spaced parallel heat
exchange elements 115 have their lower openings 127 and upper
openings 137 axranged in four groups. Vapor to be condensed
- - is fed to a chamber or compartment 100 communicating with a
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number (7 shown) of the heat exchange elements 115 at their
lower openings 127 for the condensation of some o~ the vapor
within ~hose elements 115 as the vapor rises up~ardly within
the interior spaces of the elemenks. Vapor not condensed in
passage upward through the elements 115 of this first group
emerges into a chamber 101 at the upper end of ths elements
115 of the first group. Condensate formed in the elements
of the first group~is relatively free of hard-to-condense
substances, and is drawn off from the bottoms o~ the elements
115 as condensate I.
The chamber lCl is closed except for the openings
137 of the firs~ group of heat exchange elem,ents and a conduit
C 1 shown in dashed lines as C 1 which leads uncondensed vapor
from the chamber 101 to a chamber 10~ that opens on to a second
group of elements 115 at the lower openings 127. The vapor
passes upwards through the interior spaces o this second ~roup
of elements 115 wherein some is condensed to be drawn off as
condensate II while the uncondensed remainder em2rges into a
chamber 103 at the uppex ends of the elements. The process is
repeated as vapor is passed downward through conduit C 2 to,a
chamber 102 and thence upwards through the interior spaces of
a third group o heat exchange elements 115 wherein further
condensation oc:curs. Vapor emerging into the upper chamber,
105 is passed c[own to the final lower chamber 10~ by way of
conduit C 3 ancl the final upward passage through several heat
exchange elements 115 (three shown) condenses volatile compon-
ents to produce condensate stream IV which contains the most
dif~icult to condense of the YaporS that are condensed in the
system. Vent gas and remaining uncondensed ~apors exit from
chamber 107 at the top of the last group of heat exchange
- 14 -
``~ 3~31 1~7~S
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elements 115 as shown at the ~pper right in Fig. 7.
- Embodiments separating two and four di~ferent
- - condensates have been illustrated, but it will be clear that
three condensates, or more than four could also be differen-
tiated in apparatus according to the invention
. ~arious modifications, applications, substitutions
of parts and structural variations of the method and apparatus
- described in terms o~ a presently preferred embodiment will
suggest themselves to those familiar with heat exchange
techniques and are considered to be wlthin the spiri~ and
scope of the invention.
B ~L~T I~ CL~IM~D IS~ - _
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