Note: Descriptions are shown in the official language in which they were submitted.
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CHLORINE DIOXIDE GENERATOR
The present invention relates to novel chlorine
dioxide generators and to the production of chlorine dioxide
using such generators.
Chlorine dioxide is utilized in a variety of blea~h-
ing operations, particularly in the bleaching of cellulosic
fibrous material, such as, wood pulp. In U.S~ Patents Nos.
3,895,100 and 3,975,506 assigned to the asSi~nee of this
: application, there is disclosed a chlorine dioxide
lQ generating process and equipment therefor wherein chlorine
dioxide is formed in a genexally cylindrical upright reaction
vessel by reduction of an alkali metal chlorate, usually
sodium chlorate, with chloride ions in an aqueous acid
reaction medium, in accordance with the equation:
C103 + Cl + 2H _~ C102 ~ 1/2 C12 + H20
: The reaction medium in the generator is maintained
at its boiling point, generally about 25 to about 90C,
: ~ under a subatmospheric pressure, generally about 20 to about
400 mm Hg, to cause the deposition of a by product salt
20 from the reaction medium in the generation vessel once
saturation has been achieved after start-up and to remove
i~ the chlorine dioxide and chlorine in gaseous admixture with
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steam. ~
The by-product salt which is precipitated depends
on the acid used in the reaction medium, the by-product
being a sodium sulphate when sulphuric acid is used and
sodium chloride and/or hydrogen chloride provide the chloride
ion reducing agent, and the by-product being sodium chloride
when hydrochloric acid is used and also provides the
reducing agent.
When sulphuric acid is used, the sodium sulphate may
be in an acidic or neutral form dependiny on the total
acid normality of the generator, with a neutral salt gener-
ally being obtainecl at total acid normalities o~ about 2 to
about 5 normal and acid salts ~eing obtained at higher
values usually up to about 12 normal.
When the total acid normality of a sulphuric acid
based system is such as to produce neutral sodium sulphate,
it is preferred to use a reaction temperature above about
30C in order to obtain the anhydrous salt.
When hydrochloric acid is used, the actual hydrogen
ion concentration in the reaction medium is maintained in
the range of about 0.05 to about 0.3 normalO The term
"actual hydrogen ion concentration", as used herein, is the
value determined by a pH meter calibrated on an 0.1 normal
solution of hydrochloric acid on the assumption that such a
solution is 100~ dissociated at this concentration.
As described in the above-mentioned patents, the
solid by-product is removed as a slurry in reaction medium
from the generatox vessel, sodium chlorate solution is mixed
therewith, the mixture is recycled through a reboiler
wherein the mixture is heated to the reaction temperature
and ~orwarded to the reaction vessel after the addition of
acid to the heated mixture. A portion of the slurry is
withdrawn prior to the reboiler for crystal separation.
The heated mixture from the reboiler is passed
through a venturi-like pipe which exerts sufficient back
pressure on the mixture in the reboiler to prevent boiling
therein, acid in concentrated form is introduced to the
collar of the venturi and the resultant reaction mixture
is allowed to expand at low acceleration to permit boiling
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and gaseous product formation to occur evenly and graauall~
'` and thereby avoid bumping and vibration, so that a fluid
mixture of solid phase, liquid phase and gaseous phase is
formed and this fluid mixture enters the generator generally
radially of the generator above the liquid level therein
through a curved pipe joining the downstream end of the
venturi-like pipe and the generation vessel inlet
While this prior art procedure represents an
excellent commercially-viable chlorine dioxide generating
system having many advantages over prior art arrangements,
as described in the above-mentioned patents, it has been
fou~d that entrainment of liquid and solid phases in the
gaseous phase occurs~ necessitating a considerable vapor
space in the generator to achieve separation of the
entrained material by the action of gravitational forces,
otherwise the entrained material passes out of the generator
with the removed gases, presenting problems in later-
processing of the gases and is considered undesirable.~
Additionally, it has been found that the radial
entry of the fluid mixture causes considerable splashing
of reaction medium and entrainment of gaseous material in
the reaction medium.` A considerable reaction medium volume
is required to permit the entrained gaseous material to
disengage from the reaction medium, otherwise chlorine diox-
ide and chlorine exit the generator in the by-product
slurry stream and cause considerable difficulties upon
; exposure to atmosphere at the solid by-product filier.
At the time of the making-of the inventions of the
above-mentioned U.S. Patents Nos. 3,~95,100 and 3,975,506
chlorine dio~ide generators were constructed from glass
; fibre reinforced plastics (F~P's) and typical dimensions
of a 10 ton per day chlorine dio~ide generator were a
diameter-of about 9 ft, a vapor height of about 10 ft, and
an overall height of about 35 ft, giving a total volume
of about 2000 cu. ft and a vapor space volume of about
650 ~u~ ft. These dimensions were adequate to permit the
desired disentrainments.
However, ~'s have ~een found not to be wholly satisfactory
as a material of construction for chlorine dioxide generators owing to
40 unsatisfactory wear characteristics and titanium has replaoed FFP's as
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the material of construction,as a result of its high
corrosion and wear resistance and excellent constructional
qualities. In view of the high C05t of this metal,
there has been a distinct trend to provide smaller volume
5 chlorine dioxide generators and design parameters for a
10 ton/day chlorine dioxide generator constructed of
titanium typically result in a diameter of about 7 ft, an
overall height of about 20 ft and a vapor space height of
` about 6 ft. The overall volume of the generator thereby
lQ is decreased to about 750 cu. ft and the vapor space volume
is decreased to about 230 cu. ft, i.e., approximately 1/3rd
of the respective volumes of the same capacity generator con-
structed of FRP.
The large decrease in vapor spac~ ~nd reaction
15 medium volumes renders the gas-liquid entrainment pro~lems
noted above acute and no longer permits the radial-typ~
entry of recycled fluid mixture to the generator without
encountering the difficuities of passage out of the
generator of entrained reaction medium with gaseous phase ;-
20 and passage out of the generator of entrained gaseous phase
with reaction medium.
One prior art suggestion for overcoming the problem
of entrainment of liquid phase in gaseous phase without the
use of excessive vapor space is to use an internal demister,
25 as described, for example, in U.S. Patent No. 4,079,123,
but such demisters, consisting usually of wire mesh through
which the vapor phase passes and on which the liquid
droplets impinge, are prone to clogging especially since
the solid phase is also present, and hence must be cleaned
30 frequently if chlorine dioxide production is to be
sustained. As far as we are aware there have been no prior
art sug~estions for overcoming the problem of entrainment
of gaseous phase in the reaction medium without the use of
exessive reaction medium volume.
In accordance with one aspect of the present inven-
tion, there is provided a chlorine dioxide generator comprising:
a generally cylindrical body having upper and lower end
closures, gaseous outlet means located in or adjacent to the
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upper end closure and slurry outlet means located in or
adjacent to the lower end closure; inlet means arranged
tangentially to the cylindrical body terminating at its down-
stream end in communication with the interior of the body
above the in~ended liquid level therein and below the gaseous
outlet means for projection of reaction mixture into the body
generally tangentially thereo, and baffle means projecting
substantially horizontally inwardly from the internal wall
of the cylindrical body and extending through 360 of turn,
1.0 the baffle means being arranged to be located above the flow
path of the reaction mixture entering the generator.
In accordance with another aspect of the present
:invention, there is provided in a continuous method for the
production of chlorine dioxide, which comprises: continuously
maintaining a chlorine dioxide-producing reaction medium in an
enclosed upright cylindrical reaction zone having a vapor space
located above the liquid level of the reaction medium in the
reaction zone, the reaction medium containing an alkali
metal chlorate, a reducing agent capable of reducing the
alkali metal chlorate to chlorine dioxide and chlorine, and
a strong mineral acid; continuously generating chlorine
dioxide and chlorine from the reaction medium and continuously
evaporating water from the reaction medium at substantially
the boiling point thereof while the reaction zone is maintained
un~er a subatmospheric pressure; continuously removing from
the reaction zone a gaseous mixture of the generated chlorine
; dioxide and chlorine and evaporated water through a gaseous
outlet located in communication with the vapor space in the
reaction zone; continuously depositing in the reaction zone
an alkali metal salt of the anion of the strong acid,
removing from a lower portion of the reaction zone deposited
alkali metal salt and recovering at least part of the removed
alkali metal salt; forming a single reactants feed stream
comprising an alkali metal chlorate, a strong mineral acid and
;35 a reducing agent when the strong mineral acid does not con-
stitute the reducing agent; and feeding the reactants feed
stream into the vapor space; the improvement which comprises
effecting the feeding of the reactants feed stream into the
vapor space generally tangentially of the internal wall of the
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reaction zone; and inducing the gaseous material to move
radially inwardly of the internal wall of the reaction zone
before moving upwardly through the reaction zone towards
the gaseous outlet.
The present invention preferably involves modifica-
tions to the generation system described in our U.S. Patent
No. 3,895,100 which areeffected in order to decrease entrainment
of liquid and solid in the vapor phase and entrainment of
vapor phase in the reaction medium and thereby permit a
decrease in the vapor space volume without the need to use
mesh or other type demisters and a decrease in ihe reaction
medium volume.
One such modification involves provision of tangen-
tial entry for recycled fluid to the vapor space. Such
tangential entry causes the recycled fluid mixture to pass
around the interior wall of the generator and to lose
velocity before it encounters the reaction medium. Gas
phase and liquid phase separation is permitted to a certain
degree prior to the mixture encountering the reaction
medium, whereby entrainment is decreasedO
An additional modification is the provision of
baffle means projecting from the internal wall of the
generator substantially through 360 of turn above the
theoretical trajectory of liquor tangentially entering the
generator and passing around the internal wall. The
baffle means deflects the gas phase separating from thé
liquid phase radially inwardly of generator wall to enhance
the separation.
The tangential entry of the recycled mixture and the
provision of the baffle means permit a smaller diameter
vessel of lesser vapor space and reaction medium volume to
be us~dwithout encountering the prior art problems noted
above. Provision of a smaller diameter generator results
in less material of construction being necessary for the
generator.
While the latter modifications are effected in this
invention with particular reference to the arrangement out-
lined in the aforementioned U.S. Patents Nos. 3,895,100 and3,975,506 in view of the benefits that are derived by the
use of the venturi arrangement described therein and are
described hereinafter with respect thereto, the invention is
applicable to any configuration of feed of reactants as a
single stream to the reaction zone.
The tangential entry of the recycled fluid mixture
of solid phase, liquid phase and gaseous phase into the
vapor space, in accordance with this invention, and
subsequent entry of the solid and liquid phases into the
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reaction medium imparts spin to the body of reaction medium.
Centrifugal forces resulting from such spin cause the
reaction medium surface to assume an approximately parabolic c
shape and the reaction medium to climb the internal genera-
tor wall. The baffle means used in this invention, in
addition to enhancing gas and liquid phase separation as
described above, also serves to limit the upward extent of
climb of reaction medium.
The invention is described further, by way of illus- ,-
tration, with reference to the accompanying drawings, in
which~
Figure l is a perspective view with parts cut away
of a chlorine dioxide generator constructed in accordance
with one preferred embodiment of the invention;
Figure 2 is a view from below of the generator .
sf Figure l,
Figure 3 is a detail view of part of the generator
of Figure 1 with the entry pipe removed;
Figure 4 is a perspective view, with parts cut f
away, of part of a chlorine dioxide generator utilizing
~;~ an alternative mode of entry of the recycled liquor to the
vapor space and constructed in accordance with a second .
embodiment of the inventlon; and
Figure 5 is a perspective view, with parts cut ~way,
of a chlorine dioxide generator utilizing an alternative
baffle structure and a further alternative mode of entry of
recycled liquor to the vapor space, and constructed in
accordance with a third embodiment of the invention.
- Referring first to Figures l to 3 of thë drawings,
a chlorine dioxide ~enerator 10 constructed in accordance
with a preferred embodiment of the invention comprises a
generally cylindrical upright vessel 12 fabricated of any
convenient corrosion-and wear-resistant material, preferably
titanium.
The generator vessel 12 con~ains liquid reaction
medium 14 which produces a gaseous mixture of chlorine
dioxide, chlorine and steam which is removed from the vapor
space 16 above the liquid level through a gaseous outlet
18 located in a top closure 20.
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The reaction medium 14 is maintained at its boilin~
point under a subatmospheric pressure applied to the vap~r
space 16 through the gaseous outlet 18. In continuous
operation, a solid by~product salt precipitates from the
liquid reaction 14 and is removed through a solid outlet 22
located at the lower end of the vessel 12 in communication
with a conical bottom closure element 24 as a slurry with
reaction medium. The slurry then is processed to remove
part of the solid phase and a recycle heated reaction
mixture is formed, as described in detail in U.S. Patent
No. 3,895,100, referred to above.
As set forth therein, means de~ining a recycle path
from the slurry outlet 22 to an inlet pipe 28 is provided in-
cluding pump means for pumping liquor around the recycle flow
path, heat exchanger means for heating recycled liquor to the
boiling temperature of the reaction medium under a subatmos-
pheric pressure, first frusto-conical pipe means located
. downstream of the pump means and the heat exchanger means and
having a decreasing cross-sectional dimension in the direction
; 20 Of liquid flow for exerting a back pressure on the recycling
liquor to prevent boiling of the same in the recycle flow path
upstream of the first frusto-conical pipe means, collar pipe
means located downstream of the first frusto-conical pipe
means and having acid inlet means for injection of strong
mineral acid reactant into liquor passing through the collar
: pipe means, and second frusto-conical pipe means located down-
stream of the collar pipe means and having an increasing
cross-sectional dimension in the direction of fluid flow to
permit expansion of gases at low acceleration, the downstream
end of the second frusto-conical pipe means communicating
with the inlet pipe 28, and means for feeding alkali metal
chlorate reactant to the recycle flow path.
In a preferred embodiment of the latter structure, the
re~ycle flow path comprises first elongate conduit means
extending downwardly from the slurry outlet 22 parallel to
the axis of or coaxial with the generator vessel 12, inlet
means to the first conduit means constituting the means for
feeding alkali metal chlorate reactant, the pump means being
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located at the lower end of the first conduit means, and
conduit means in fluid flow communication with the first
conduit means for removal of part of the slurry from the
recycle flow path, the heat exchanger means-being located
extending ~om the discharge side of the pump means to the
inlet side of the first frusto-conical pipe means in gener-
ally parallel relation to the first conduit means.
A vortex breaker element 26, consisting of mutually
~ perpendicularly arranged baffles, is located in the bottom
closure 24 adjacent the slurry outlet 22 to break up
rotational movement of the reaction medium 14 adjacent the
slurry outlet 22.
The heated reactlon mixture recycle pipe illustrated
in U.S. Patent No. 3/8~5,100 communicates with the horizontally-
:~ 15 directed inlet pipe 28 which increases in cross-sectional
area in the direction of flow of the reaction mixture and
terminates in a rectangular opening 30 in the side wall of
the generator vessel 12 ahove the level of the reaction
medium 14. The inlet pipe 28 extends generally tangentially
20 to the vessel wall so that recycled heated reaction mixture
enters the vapor space 16 generally tangentially to the
: internal wall of the generator vessel 12, in contrast to
the radial entry illustrated in the above-mentioned U.S.
Patent.
The recycled heated reaction mixture contains
crystalline by-product salt which is abrasive in character.
Although titanium is a highly wear-resistant material, it is
preferred to construct the vessel 12 with a titanium liner
32 at least in the initial region of movement of the recycled
30 heated reaction mixture between its entry to the vesseL 12
and the reaction medium 14. In the event of excessive wear,
the liner 32 may be replaced.
Extending horizontally inwardly from the-internal
wall of the vessel 12 is a baffle 34. In the embodiment of
35 Figures 1 to 3, the baffle 34 extends in generally helical
manner from a location just above the inlet opening 30
through 360 of turn to terminate just belo~7 the levcl of
the inlet opening 30. The baffle 34 may extend ~urther, if
desired, into the reaction medium 14.
5 The baffle 34 approximates but is located above the
intended trajectory of the recycled reaction mixture along
the internal wall of the vessel 12 to the reaction medium
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The location of the ba~fle 34 above the intended
trajectory ~revents impingement o~ the mixture thereon which
may impair liquid separation and cause liquid to climb up
the internal wall of the generator vessel 12. The baffle
34 also prevents lic~uor from the spinning vortex of
~ reaction medium from rising along the internal wall past the
: 15 height of the baffle in the vessel 12.
Any liquor which does rise up the internal wall of
. the generator vessel 12 above the ba~le 34 is prevented
from entering the outlet pipe 18 ~y the downward projection
of the cylindrical outlet pipe 18 into the vapor space 16 of
the generator vessel 12 and below the top closure 20, as
: illustrated.
The baffle 34 prevents the gaseous phase in the
recycled reaction mixture entering through opening 30, which
is a fluid mixture o~ liquid phase, solid phase and gaseous
phase as described in U.S. Patent NoO 3,~95,100, from
proceeding upwardly in the vapor space 16, taking with it
entrained liquid and solid phases. Instead, the baffle 34
forces the gaseous phase initially to follow the trajectory
of the liquid and solid phases and to move effectively
radially of the internal wall of the vessel 12 before
moving upwardly in the vapor space 16 when it clears the
radially inner edge of the baffle 34O
This gaseous phase motion causes separation from
the liquid and solid phases which tend to remain in the same
trajectory and hence entrainment of these materials in the
gaseous phase is decreased, permitting the cross-sectional
area o~ the generator vessel 12 to be decreased, as
compared with the radial-entry and no-baffle arrangement
illustrated in U.S. Patent No. 3,895,100. As already
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noted, for example, for a given rea-tion vessel o~ a given
chlorine dioxide production capacity and operating under
the same conditions and flow rates, the overall generakor
vessel 12 cross-sectional area may be decreased by about
5 40% through the use of this invention. The tangential entry
of the recycled mixture and the formation of a spinning
vortex oE reaction medium 14 in the generator 12 also
considerably decrease entrainment of gaseous phase in the
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reaction medium.
For ease of fabrication of the baffle 34, it is
usually constructed, as illustrated, of a plurality of
segments which are joined to form a continuous baffle, each
segment typically extending for 9Q of turn or a multiple -
thereof with its slope being rectilinear ~rom end to end
and approximating the average of the trajectory of the
liquid passing around the internal wall in the particular
curvilinear region of location of the ~affle segment.
Alternatively, the baffle 34 may be provided as a
continuous baffle which is continuously shaped along its
length to approximate at any given location the trajectory
of the liquid passing around the internal wall of the
generator vessel 12
The required location and slope of the baffle 34
depends on a number of factors, including the velocity of
the fluid entering the port 30 and the internal diameter
of the generator vessel 12, and can be readily calculated
using conventional engineering principles.
The transverse dimension, or width, of the baffle
34 may vary widely and is generally related to the width of
the rectangular inlet port 30. Preferably, the width of
the baffle 34 is about 30 to a~out 60 percent of the width
of the rectangular inlet port 3~, and most preferably about
one-half of the width, since the most efficient separation
of entrained material occurs at this dimension.
The rectangular inlet port 30 is dimensioned in
relationship to the internal diameter of the generator
vessel 12, so that the width is less than, and preferably
approximately equal to, about 25 percent of the internal
diameter of the vessel 12, since liquid separation from the
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gaseous phase is generally less satisfactory at hiyher
values.
The inlet port 30 is illustrated as rectangular in
shape, but any other desired shape may be used, for example,
circular or oval. An oval inlet port is illustrated in
Figure 5 discussed below. The actual shape of the inlet
port 30 has little effect on the operatlon o~ the generator.
Referring now to Figure 4, wherein there is disclosed
an alternative recycled heated reaction mix~ure entry
arrangementJ the same reference numerals are used to identi-
fy the same parts as are described above in connection
with the embodiment of Fîgures 1 to 3.
- In the embodiment of Figure 4, instead o~ the inlet
pipe 28 terminating at a rectangular or other snaped
; 15 opening 30 in the wall of the vessel 12 to achieve tangen-
tial entry, the pipe 28 passes through an opening 36 in the
wall of the vessel 12 in sealing relationship therewith and
then follows the internal wall of the vessel 12 to terminate
in a rectangularly-shaped opening 38 to establish the
tangential entry. The baffle 34 commencas immediately at
the termination of the inlet pipe 28.
The dimensional relationships described above with
respect to Figures 1 to 3 between the baffle 34 and the
rectangular opening 30 apply in connection with the embodi-
ment of Figure 4 as between the baffle 34 and therectangular opening 38.
While the rectangular opening 38 and the passageway
leading thereto in the increasing cross-sectional area of
the inlet pipe 28 may be enclosed on four sides, it is
30 prefexred, as illustrated, to omit the bottom wall.
In the embodiment of Figure 5, the complex helical
baffle 34 of the embodiments of FigureS 1 to 4 is replaoed by
a con~inuous ring baffle 50 projecting from the inner wall
of the vessel 12 above the level of the inlet port 30. The
35 circular baffle 50 is effective to enhance vapor-liquid
separation and prevent reaction medium climb, in similar
manner to helical baffle 34.
The inlet port 30 in this embodiment has an oval
shape as the result of the tangential arrangement of
circularly cross-sectioned inlet pipe 28 to the generator
vessel 12. The inlet arrangement is less complicated than
the rectangular arrangement shown in Figures 1 to 4, in
that shaping of the downstream end of the inlet pipe 28 is
not required.
The tangential entry of recycled reaction mixture
to the generator vessel 12 under the influence of energy
imparted thereto by expanding steam in the recycle pipe
causes the reaction medium 14 to rotate in the generator
vessel and to acquire the steam-imparted energy. In place
of breaking this motion at the outlet port 22 using the
vortex breaker 26 as illustrated, a tangential outlet may
be provided adjacent a suitably-designed bottom closure
and the motion energy of the exiting reaction medium may
be used to replace part of the pumping energy required for
recirculation, so that the overall energy requirements of
the system are decreased.
Exam~
, Chlorine dioxide was produced from a chlorine di-
oxide generator having the structure shown in Figures 1 to 3
having a capacity of 14 tons/day. The chlorine dioxide was
p~oduced from reactants sodium chlorate, sodium chloride and
sulphuric acid at the boiling point of the reaction medium
(about 70C) under a subatmospheric pressure (about 190 mm Hg)
and anhydrous sodium sulphate was precipitated from the reac-
tion medium in the vessel.
The vessel had a diameter of 7 ft. and the baffle
was made up of four sections each extending for 90 of turn
from the rectangular entrance port. The baffle had a width
of 10 1/2 inches and the entrance port was dimensioned 1'9"
wide by 3'6" high. The first 90 section of the baffle had
a slope of 1:20, the second 90 section had a slope of 1:10,
the third 90 section had a slope of 1:4 and the fourth 90
section had a slope of 1:2.
The mass vapor velocity of the chlorine dioxide,
chlorine ~nd steam leaving the gaseous outlet was 142 lb/hr./
sq.ft. and it was determined that the liquor entrainment in
the gaseous product stream was 5.5 lb~hr.
In a parallel operation, a 14 ton/day chlorine di-
z~ l
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oxide generator having the structure illustrated in U S.
Patent No. 3,895,100, namely with the recycle pipe arranged
radially of the generator, in place of the tanyential entry
and baffle arrangement of Figures 1 to 3. In this instance,
5 the generator had a diameter of 9 feet but otherwise was dimen-
~- sioned the same and produced chlorine dioxide from the same
reactants under the same conditions.
At the mass vapor velocity of chlorine dioxide,
chlorine and steam leaving the gaseous outlet of 142 lb/hr.
10 sq.ft.~ the amount of liquor entrained in the product stream
was found to be 49.22 lb/hr. It will be seen from the
results that, despite decreasing the diameter of the genera-
tor vessel, a considerable decrease in entrainment of-liquid
in the gaseous phase was achieved using the structure of
15 Figures l to 3, as compared to the prior art radial baffle-
less entry.
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In summary of this disclosure, the present inven-
tion, therefore, provides a chlorine dioxide generator
having advantages over other prior art equipment wherein a
fluid recycle stream consisting of a recycle mixture of
gaseous phase, solid phase and liquid phase enters the vapor
space of the generator. Modifications are possible within
the scope of the invention.
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