Note: Descriptions are shown in the official language in which they were submitted.
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,
DISTILLATION SYSTEM AND PROCESS
This invention relates to a distillation system
and process ~or recovering vaporizable components from
an aqueous medium.
In commercial distillation processes, i.e.,
stripping, fractionation and rectification processes,
steam is used to vaporize and expel volatile components
from water containing other elements, salts or
compounds. A substantial quantity of steam is consumed
in such conventional processes, increasing the
operating costs of such processes. In a basic
distillation process, for example, in a stripping
system, the industry has continued to seek further
optimization in terms of lower energy requirements,
lower capital expenditures, i.e., reduction in the
number of pieces and size of required apparatuses and a
reduction of solution flow rates while maintaining high
throughput.
It is desired in this invention to provide an
improvement in a process for removing vaporizable
components from an aqueous medium containing a mixture
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o~ vaporizable components and other salts, elements and
compounds whereby steam consumption is mi.nimized.
More particularly the present invention resides
in a distillation system for removing vaporizable
components from an aqueous medium comprising:
(a) a distillation column adapted ko receive
an aqueous medium containing vaporizable components and
passing steam therethrough ko directly contact the
aqueous medium within the steam and vaporize at least a
0 portion of the vaporizable components,
(b) at least one condenser in communication
with the distlllation column for condensing at least a
portion of the vapors received from the distillation
column,
(c) a separator in communication with the
condenser and adapted for separating vapor from liquid
in a recirculation fluid received from the condenser,
and
(d) a thermal compressor connected to the
separator and the column for removing vapors from the
separator and for injecting exhaust motive steam into
the column.
Additionally, the present invention resides in
a distillation process for removing vaporizable
components from an aqueous medium comprising:
(a) introducing an aqueous medium containing
vaporizable components in a distillation column for
3 removing a portion of the vaporizable components Erom
the aqueous medium,
(b) passing through the aqueous medium a
current of steam from a thermal compressor to vaporize
at least a portion of the vaporizable components,
(c) passing at least a portion of the vapors
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from the distillation column through a first space of
at least one condenser having a first and a second
space to condense at least a portion of the vapors to a
condensate,
(d) passing a recirculation liquid to the
second space of the condenser and from the condenser to
a separator to separate steam from aqueous liquid, and
(e) passing the steam from the separator
through the thermal compressor to form steam for
introducing into the distillation column.
Figure 1 is a schematic representation of one
embodiment of a system useful in practicing the present
process.
Figure 2 is a schematic representation of
another embodiment of a system useful in practicing the
present process.
Figure 3 is a schematic representation of
another embodiment of a system useful in practicing the
present process.
Figure 4 is a schematic representation of yet
another embodiment of a system useful in practicing the
present proceSS-
The present distillation system and process as
illustrated in the drawirgs and as described below may
be useful for removing any vaporizable component(s)
3 from an aqueous medium.
By "aqueous medium" it is meant (1) water
containing a vaporizable component or mixture of
vaporizable components, or (2) water containing a
vaporizable component or ~ixture of vaporizable
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components in combination with other salts, elements or
compounds dissolved or dispersed in the water.
By "vaporizable components" it is meant
components with a relative volatility to water greater
~ 5 than 1.0 when they are dissolved in water. For
example, vaporizable components may include
trichloroethane, propylene chlorohydrin, bromine,
methylene chloride, benzene, toluene and mixtures
thereof.
The vaporizable components in the aqueous
medium are vaporized with steam by contacting the
aqueous medium with the steam at conditions sufficient
to vaporize at least a portion of the vaporizable
components. Steam may be used as the vaporizing gas,
for example, at a temperature of from 10C to 120C and
a pressure of from 9 to 1500 mm Hg. Preferably, steam
at a temperature of from 50C to 100C and a pressure of
from 90 to 7~0 mm Hg is used. Contacting the
vaporizable components in the aqueous medium with steam
is preferably carried out by countercurrent flow.
Referring now to Figure 1, an aqueous medium
feed material containing a vaporizable component(s) is
introduced, through a conduit 120, into an evaporation
apparatus 110 such as a column or tank wherein the
aqueous medium feed material is contacted with a stream
or current of vaporizing gas such as steam to vaporize
vaporizable components in the feed material. The
apparatus 110, herein referred to as a distillation
column may be a stripping column, a fractionation
column or rectification column. The current of steam
is introduced into column 110 through a conduit 121
from the discharge section 111a of a thermal compressor
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111. The steam contacts the feed material under
process conditions sufficient to vaporize substantially
all of the vaporizable components in the feed material.
Preferably, the contacting of feed material with the
steam is carried out in a counter-current fashion.
An aqueous liquid material leaves the column
110 through a conduit 122 located near the bottom of
the column llO to a use point. Vapors, i.e., the
vapors containing the vaporizable components, formed in
0 the column llO pass through a conduit 123 located near
the top of the column 110 to a condenser 112 adapted
for condensing at least a portion of the vapors to an
aqueous cond2nsate. A conventional condenser, for
example, a shell and tube-type heat exchanger may be
used. Preferably, the vapors are passed throu~h the
shell-side of the condenser 112 and a "recirculated
fluid" adapted for use as a cooling fluid for cooling
at least a portion of the vapors in the condenser 112
is passed through the tube-side of the condenser 112
such that at least a portion of the vapors in the
shell-side of the condenser 112 are condensed to a
liquid condensate. By "recirculated fluid~' in the
present invention it is meant a substantially aqueous
stream such as water or water mixed with salts~
elements and other compounds. The recirculated fluid
may be in the form of a llquid or a mixture of liquid
and vapor. The recirculated fluid is preferably
maintained at a temperature of from 0C to 8C lower
than the column 110 overhead vapor stream in conduit
123.
As shown in Figure l, the recirculated fluid is
passed through the condenser 112 through conduit 124
from a separator 113 and exits the condenser 112
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through a conduit 125. Any noncondensable gases and
uncondensed vapors in the shell side of the condenser
112 exit the condenser 112 and are passed to a use
point or to a point for further processing through a
conduit 126. In addition to the uncondensed vapors
exiting the ~ondenser 112 through the conduit 126, at
least a portion of the condensed vapors or liquid
condensate referred to herein as the overhead
distillate, may be transferred to a use point or to a
point for further processing through the conduit 126.
The recirculated fluid, in the conduit 125, may
contain vapor as steam and liquid as water. The
recirculated fluid passes through the conduit 125 to a
separator 113 to separate the vapor from the liquid.
In addition, the separator 113 serves as a flash tank
for flashing at least a portion of the liquid into
steam herein referred to as "flash steam". The
recirculated fluid in the separator 113 exits the
separator 113 through a conduit 127 as a liquid and is
pumped through the conduit 124 to the tube-side of the
condenser 112 by a pump 114. The recirculated fluid
may be supplemented, as required, with makeup
recirculated fluid supplied through a conduit 12~ from
any source to the separator 113. For example, a stream
of hot water may be introduced to the separator 113.
Although the water is introduced into the separator
113, the makeup water may be introduced at any point of
the "recirculated fluid loop" consisting of the conduit
124, the conduit 125 and the conduit 127.
Any flash ~team present in the separator 113 is
passed through a conduit 129 o the thermal compressor
111 and taken up by the suction inlet 11lb of the
thermal compressor 111. The actuating gas for the
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thermal compressor is motive steam passing through a
conduit 130 to the actuating gas inlet 111c of the
thermal compressor 111. The motive steam may be
supplied from any source. Typically, steam at from 30
to 100 psig (3.13 to 1003 kg/cm2) is used. The
discharge section 11la of thermal compressor 111 is in
communication with the conduit 121 which, in turn, is
connected to column 11 0 to supply the steam used in the
column 110 for contacting the aqueous medium and
vaporizing the vaporizable components in the aqueous
medium.
With reference to Figure 2, there is shown
another embodiment of a distillation system according
to the present invention which is particularly useful
for stripping and enriching miscible compounds from
water containing other compounds. Other compounds may
include, for example, those which tend to increase the
boiling point of the water, for example, salt9 sulfuric
aoid or caustic. The distillation system shown in
Figure 2 may also be useful for stripping and enriching
miscible compounds from water that contains low
volatility corrosive compounds such as, for example,
bromine and iodine.
Since the distillation system of Figure 2 is,
to a major extent, identical to that of Figure 1, it
will not be described herein again. The reference
numbers in Figure 2 denoting the same structural
3 features of Figure 1 are used in the same order except
that they are numbered in the 200 range.
In Figure 2, the noncondensable gases,
uncondensed vapors and at least a portion of the
condensed vapors in the shell side of the condenser 212
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IL3q~7Z3~2
are passed through a conduit 225 to a second condenser
216 to condense substantially all the vapors to a
liquid condensate. The condenser 215 may also 3e a
conventional shell and tube-type heat exchanger. Any
conventional cooling fluid, such as cooling tower water
may be passed through the conduit 235 and 236 and used
for cooling the vapors in the condenser 216. The
condensed vapor or liquid condensate, referred to
herein as the overhead distillate, is passed through a
conduit 232, and preferably, at least a portion of the
overhead distillate is refluxed or recycled back to the
column 210 through a conduit 233. Optionally, the
overhead distillate from the conduit 232 may be
combined with a portion of the condensed vapors of the
condenser 212 (not shown). In this instance, at least
a portion of the overhead distillate from the conduit
232 may be transferred to a use point or to a point for
further processing through a conduit 234.
Although not shown in Figure 2, the bottoms
exiting through the conduit 222 may be used to preheat
the feed material via a heater exchanger means
preferably, made of corrosion resistant material. The
heat exchanger means may be, for example, a shell and
tube-type heat exchanger. For example, the feed
material may be preheated by introducing the feed
material into the tube-side of the heat exchanger and
substantially simultaneously introducing the bottoms of
column 210 into the shell-side of the heat exchanger
sufficient to preheat the feed material. The preheated
material existing the exchanger may then be introduced
into the distillation column 210 via the conduit 220.
Although not shown in Figure 2, at least a portion of
the condensed vapors from the condenser 212 may be
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refluxed back to the column 210 near the top of the
column 210.
Another embodiment of a distillation system
according to the present invention is shown in
~ 5 Figure 3. Since the distillation system of Figure 3
is, to a major extent, identical to that of Figure 1?
it will not be described herein again. The reference
numbers in Figure 3 denoting the same structural
features of Figure 1 are used in the same order except
that they are numbered in the 300 range.
The system of Figure 3 is particularlv useful
for stripping and enriching partially miscible
components from an aqueous medium containing other
dissolved compounds such as salt, sulfuric acid or
caustic which increase the boiling point of the aqueous
medium above pure water. In the distillation system of
Figure 3, an aqueous medium feed material containing
vaporizable components is introduced into a
distillation column 310 through the conduit 320 near
the top of the column and a decanter 317 is used for
decanting at least a portion of at least one liquid
stream from another liquid stream.
The condensed vapors or liquid condensate,
herein referred to as the overhead distillate, in
condenser 316 is passed from the condenser 316 through
a conduit 332 to the decanter 317 for decanting an
overhead distillate product from an aqueous stream.
Although not shown in Figure 3, at least a portion of
the condensed vapors from the condenser 312 and at
least a portion of the overhead distillate from the
condenser 316 may be combined in one conduit and passed
to the decanter 317. At least a portion of the
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overhead distillate product and at least a portion of
the aqueous stream are separated in the decanter 317.
The aqueous stream is passed through a conduit 338 and
at least a portion o~ the aqueous stream is refluxed
back to the column 310 through a conduit 339. At least
a portion of the aqueous stream is passed to a use
point through a conduit 340. The overhead distillate
product from the decanter 317 is passed to a use point
through a conduit 337. A valve 315 and a conduit 331
are used for removing at least a portion of the
recirculated fluid from the conduit 324.
Another embodiment of the distillation system
similar to the system illustrated in Figures 2 and 3 is
shown in Figure 4. Since the distillation system of
Figure 4 is, to a major extent, identical to that of
Figure 1, it will not be described herein again. The
reference numbers in Figure 4 denoting the same
structural features of Figure 1 are used in the same
order except that they are numbered in the 400 range.
The system of Figure 4 is particularly useful
for distilling miscible components from an aqueous
medium such as water when the column 410 bottom
temperature is within about 15C or less, (i.e., from 0
to 15C) of the overhead vapors in conduit 423
temperature. An aqueous medium feed material
containing vaporizable components is introduced,
through a conduit 444 into a preheater 418 for
3 preheating the feed material prior to introducing the
feed material into the column 410. In this instance~
the preheater 418 may be a conventional heat exchanger
of the shell and tube-type. The aqueous medium feed
material is passed through the conduit 444 and through
the tube-side of the preheater 418. The preheated feed
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material exits the preheater 418 and passes through a
conduit 420 into the column 410. A liquid for heating
the feed material is passed through a conduit 442 and
through the shell-side of the preheater 418. The
liquid, preferably, is at a temperature sufficient to
heat the aqueous feed material from 0 to 20C below
boiling point of the feed materlal and preferably from
0 to 8C below the boiling point of the feed material.
Preferably, at least a portion or side stream of the
recirculated fluid stream in the conduit 424 being
pumped from the separator 413 is taken through a valve
415 and the conduit 442 and used as the heating liquid
for the preheater 418. The side stream of the
recirculated fluid enters the shell-side of the
preheater 418 and exits through a conduit 443 to a use
point.
The following examples are to illustrate the
present invention and the invention is not to be
limited thereby.
ExamDle 1
This example may be carried out using a
distillation system as described in Figure 2. ~n this
example, a concentration of 4 percent by weight (wt~)
propylene chlorohydrin is stripped from an aqueous feed
mixture of propylene chlorohydrin, water and
hydrochloric acid and enriched to a concentration of 40
wt% propylene chlorohydrin in water. ~he feed mixture
is fed to the center of a distillation column. As
liquid feed moves down the column, it is stripped
substantially free of propylene chlorohydrin by a
rising flow of steam. The vapors leaving the feed
point of the column are enriched in propylene
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chlorohydrin and contain some hydrochloric acid vapor,
but the hydrochloric acid is kept down in the column by
the descending flow of liquid in the upper section of
the column. The vapors leaving the top of the column
are rich in propylene chlorohydrin and substantially
free of hydrochloric acid. The vapors pass through the
shell-side of a partial condenser and leave a stream of
vapor that is enriched even further in propylene
chlorohydrin. The liquid in the shell-side of the
partial condenser may be refluxed back to the top of
the distillation column. Cooling on the partial
condenser is brought about by the flash evaporation of
water inside the tube-side of the condenser at a
reduced pressure that is approximately 0.5 times the
column pressure. The flash steam and water from the
tube-side of the partial condenser are separated in a
vapor-liquid separator tank, and the water from the
tank is recirculated to the tube-side of the partial
condenser. Hot condensate water is added to the
circulating water to maintain a liquid level in the
vapor liquid separator tank. The reduced pressure on
the separator tank is produced by a thermal compressor
which draws the flash steam out of the vapor-liquid
separator and mixes the flash steam with the motive
steam going to the bottom of the distillation column.
The vapors leaving the partial condenser are conducted
to a total condenser. Part of the liquid condensate
from the total condenser is refluxed to the column, and
the rest is taken out of the process as enriched
propylene chlorohydrin in water. The pres ure on the
column is controlled by the pressure of the vacuum
after the total condenser. This process produces a
propylene chlorohydrin containing a reduced amount of
water and hydrochloric acid and minimizes the steam
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consumption that is required to perform this
separation.
Example 2
-- 5 This example may be carried out using a
distillation system as described in Figure 3. A
concentration of 0. 8 wt% phenol and 20 wt% sodium
chloride in water, herein referred to as the brine
feed, is fed near the top of a stripping column and
distributed over a packing in the column at a rate of
8,ooo pounds per hour (lb/hr) (3629 kg/hr). Steam is
introduced into the column near the bottom of the
column at a r~te of 2,000 lb/hr (907 kg/hr). The steam
flows up the column counter current through the flow of
brine feed~ The phenol is stripped from the brine feed
and enriched in the overhead vapor leaving the top of
the column at a rate of 1,120 lb/hr (508 kg/hr).
The rest of the steam condenses in the column
to heat the brine feed to its boiling pointO The
overhead vapor entering a first condenser is partially
condensed, approximately 600 lb/hr (272 kg/hr) and the
remainder of the vapor9 520 lb/hr (236 kg/hr) is
condensed in a second condenser. All of the condensate
from the second condenser is cooled to approximately
60C or lower to cause the formation of two liquid
layers. An aqueous layer is returned to the top of the
stripping column to be mixed with the brine feed to be
stripped free from phenol. The brine leaving the
bottom of the column contains approximately 50 parts
per million phenol. The 2,000 lb/hr (907 kg/hr) of
steam entering the bottom of the column contains l,~00
lb/hr (635 kg/hr) of motive steam and 600 lb/hr (272
kg/hr) of flash steam. The flash steam is produced by
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drawing a vacuum on a flash ~istillation chamber. The
pressure of the diameter is at about one half of the
pressure that is on the column. The vacuum is produced
by the motive steam passing through a thermal
compressor before enterin~ the column. The vacuum
flash distillation reduces the temperature of the water
in the flash chamber so that the water can be used to
remove heat in the partial condenser on the overhead
vapor stream. The amount of water used to generate
flash steam is made up with hot condensate that is
available from the other processes condense steam for
heat. The overall process improvement is in the
requirement of only 1,400 lb/hr (635 kg/hr) of boiler
steam instead of the 2,000 lb/hr (906 kg/hr) that is
required without this improved process.
Example 3
This example is the same as Example 2 except
that residual monomers are removed from polymer latex
emulsions or suspensions. In this example, styrene and
butadiene removed from a styrene/butadiene latex. In
this example, a latex feed of 109000 lb/hr (4536 kg/hr)
is stripped with 3,000 lb/hr (1361 kg/hr) of steam
wherein 2,000 lb/hr (gO7 kg/hr) is motive steam and
1,000 lb/hr (454 kg/hr) is recovered as flash steam.
The hot condensate used îs condensate that is generated
by partial condensation of the overhead vapor.
Example 4
This example may be carried out using the
system as described in Figure 4. In this example
1 weight percent concentration of phenol in water is
stripped from water and enriched to a concentration of
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9 percent phenol which is the concentration near the
azeotropic concentration. A feed stream of 600 lb/hr
(272 kg/hr) of water containing 1 percent phenol enters
the distillation column and the phenol is stripped out
with 1000 lb/hr (454 kg/hr) of steam wherein 700 lb/hr
(317.5 kg/hr) is motive steam and 300 lb/hr (138 kg/hr)
is flash steam. The flash steam is produced by drawing
a vacuum on a flash distillation chamber. The pressure
at the flash chamber is about one half of the pressure
that is on the column. The vacuum is produced by the
motive steam passing through a thermal compressor
before entering the column. The vacuum flash
distillation reduces the temperature of the water in
the flash chamber so that the water can be used to
remove heat in the partial condenser on the overhead
vapor stream. The water used to generate the flash
steam comes from the column bottoms stream which is
allowed to pass to the flash distillation chamber to be
separated into flash steam and recirculation liquid.
The overhead vapor from the column containing
9 percent phenol flows at a rate of about 888 lb/hr
(403 kg/hr). The vapor is partiall~ condensed in the
shell-side of the first condenser with recirculation
liquid passing through the tube-side of the condenser.
The remainder of the vapors is condensed in the shell-
side of a second condenser with cooling tower water
passing through the tube-side of the second condenser.
About 821 lb/hr (372 kg/hr) of the overheads condensate
from the first and second condensers is refluxed back
to the column while 67 lb/hr (30.4 kg/hr) is taken off
as overheads condensate.
28,777-F 15
