Note: Descriptions are shown in the official language in which they were submitted.
~ ~88~ ~ C-6429
This lnventlon relates to granular calclum hypochlorite
parkicles which resist dusting and degradation during handllngJ
and which are highly stable when contacted with lighted
cigarettes or organic materials.
In most methods for the commercial manu~acture o~
calcium hypochlorite a slurry 18 obtained containlng crystals
o~ calcium hypochlorite dihydrate in a cool aqueous solution
o~ calcium hypochlorite and sodium chloride or other inorganic
halide. The slurry is filtered to produce a cake containlng
~rom about 42 to about 48 percent by weight o~ water. When
this cake i8 dried, a very light, porous cake is obtained
whlch breaks down to an undeslrable ~lne, dusty powder. The
crystals in the cake lack a natural cohesive tendency. I~
the ~ilter cake is compressed, the resulting cake is harder
but ~ragments into flaky granules with ~ragile edges. These
are easily abraded and ~orm an unsatis~actory, dusty product.
Thus, the wet cake has been partially dried, compressed into
a sheet between heavy rolls which i~ broken up and ~urther
dried as in U.S. Patent No. 2,195J754, which issued April,
1940 to H.L. Robson et al. This product has a highly
irregular shape with ~ragile edges and will break down into
a flne dust when crushed or submitted to severe handling
conditlons.
U.S. Patent No. 2,195,756, which issued April 2, 1940
to Maurice C. Taylor, describes a process ~or preparing
calclum hypochlorlte particles by admixing the wet cake of
calcium hypochlorite in a cutting type mixer with dry ~ines
in ~u~flcient proportlon to decrease the water content from
the 42 to 48 percent level down to about the 20 to 30 percent
3 level. No water is evaporated during this mixing step,
but instead the molst particles are dried in a separate step
_ ~ _
lQ48868 C-6~2g
under carefully controlled conditions to avoid any sub-
stantial crushing o~ the materlal. Granule compression
pressures are less in the mlxer than by rolls and Taylor's gran-
ules are there~ore softer. Although granular materlal i8 pro-
duced by this technique, the integrity of the granular
partlcles 18 not strong enough to resist dustlng when sub-
~ected to severe handling conditions.
Similar granulatlon technigues are described ln U.S.
Patent Nos. 2,195,755 and 2,195,757, which lssued to Homer
L. Robson et al on April 2, 1940. In each o~ these gran-
ulatlon techniques, care must be taken to dry the granulated
material under conditlons which avold substantial crushing
or abraslon. The problem with the products o~ these ~-
techniques 18 that excesslve dusting occurs when the product
is dried under severely agitated conditions.
In each of the ~our above-described calcium hypochlorite
granulation techniquesJ drying is carried out under gentle
handling condltions ln a rotary vacuum dryer or the Wyssmont
type tray dryer, which is commonly used to minlmize dust
formation and entrainment ln the drylng atmosphere. Drylng
rates ln th~e types o~ driers are relatlvely sloW. Because
of the sensltivity o~ calclum hypochlorite to thermal
degradatlon, the losses o~ actlve hypochlorite are relatively
high in these types of dryers.
In the process o~ U.S. Patent No. 2,347,402, which
issued on April 25, 1944 to George Gerald Day, a plastlc and
unsprayable slurry of calcium hypochlorite is sub~ected
simultaneously to evaporation and agitatlon untll the water
content is ~rom about 25 to 35 percent and the sollds form
3 loosely bonded aggregates. ~he drylng o~ the above-descrlbed
product preferably takes place while the product is main-
tained in a relative quiescent condltion, i.e. with little
_ 4 --
~ 886~ C-6429
or no agitation until the moisture content is reduced to
about 2 percent or less.
U.S. Patent No. 2,901,435 which issued to H.L. Robson
on August 25, 1959, discloses spray-drying o~ calcium hypo-
chlorite slurries to avoid ~iltration and drying problems
and to minimize loss o~ hypochlorite by reduction o~ the
drying time. However, the product is hollow, highly porouq
particles of low density which cannot withstand severe
handling conditons without severe dusting.
~he spray graining technique has been used to prepare
granular solids from various aqueous solutions and aqueous
slurries. For example, British Patent No. 576,557 relates
to the dehydration o~ aluminum sul~ate by spraying a solution
thereo~ onto a rotating bed of pre~ormed crystals at a tem-
perature ~rom about 80C. to about 95C. (176-203F. )
whlle passing hot gases in contact with the solid to remove
water. Due to its high viscosity and tendency to ~orm
hydrated salts, aluminum sulfate solutions cannot readily
be concentrated beyond a 50 percent to 60 percent by weight
o~ A12(S04)3. It iB not sub~ect to thermal degradation hence
relatively high temperatures and long retention time can be
used to volatlliz,e water ~rom the granular solid. In
addition, U.S. Patent No. 2,926,079, which lssued to B.G.
Smith on February 23. 1960, relates to the production o~
~ertilizer pellets by spraying a slurry of ~ertilizer solids
onto a shower of individualized ~ertilizer particles in a
stream of hot gase~ in a flighted granulator. Fertilizers
solids are usually clay-like in texture with good cohesive
properties. Therefore, they can be easily bonded lnto
3 granules ln a moist condition. Bonding moisture is also
easily removed at elevated temperatures over suitable
-- 5 --
8~8
periods of time because fertilizer salts still have good
thermal stability at temperatures which induce rapid vola-
tilization of water. Screening, crushing and recycling
of the solid particles are disclosed by Smith,
Canadian Patent No. 592,240, which issued February 9,
1960, discloses spraying ammonium sulfate solutions onto a
shower of crystals in a rotary grainer. Rigid crystalline
materials of this type are readily formed into granular
particles of high integrity in such a process. Ammonium
sulfate is a fertilizer salt of sufficient thermal stability
to permit water volatilization at high temperatures over
long periods of time.
In contrast to the foregoing cases, calcium hypochlorite
is subject to rapid chemical decomposition in the presence
of moisture at temperatures only slightly in excess of
ambient room temperatures. The experimentally measured
decomposition rate at 30C. for a slurry of calcium hypo-
chlorite in water was 1 percent loss of active chlorine
per hour. For every 10C. elevation in slurry temperature,
the decomposition rate doubles approximately and reaches
about 4 percent per hour at 50C. At 90C. - a temperature
still below the boiling point of water - the decomposition ~ -
rate exceeds 50 percent per hour. Thermal stability of
calcium hypochlorite improves as the water content is reduced.
Thus, anhydrous calcium hypochlorite has good stability
even at temperatures near 100C. Stability improvement
becomes more rapid as water is reduced below about 17 percent
at which point residual moisture exists mainly as the water
of hydration of the dihydrate of calcium hypochlorite. In
view of this interrelation of hypochlorite stability with
~ 48~8 C-6429
molsture and temperature, water removal must be rapid and
at a low temperature to minlmize the degradation o~ the
product durlng the granulatlon and clrying ~teps of the process.
Also, ~ince crystals in hypochlorlte slurry are very weak
ln coheslve tendency as ~upported by earlier patent ark
cited above, this rapid, low-temperature drying must also
be done under clrcumstances where su~icient cohesive bonding
is induced in the granule to ~orm smooth, rounded hard gralns
not easlly sub~ect to breakage or abra~ion during the normal
handllng o~ the product in commerce.
There ls a need at the present time for improved
calclum hypochlorite granules which have a high level o~
integrity and reslst dustlng when sub~ected to severe
handllng condltons.
It is a primary ob~ect o~ this lnvention to provide
improved granular calclum hypochlorite particles which have
a hlgh level o~ integrlty and reslst dusting when sub~ected
to crushing under severe handling conditions.
Another ob~ect o~ this inventlon is to provlde an im-
proved method for producing a novel granular calcium hypo-
chlorite material having a high level o~ integrity which
resists crushing when sub~ected to severe handling conditions.
It is another ob~ect o~ this invention to provide an
lmproved method ~or recovering calcium hypochlorite from
aqueous slurrles thereo~ to produce a partlculate product
of controlled size, available chlorlne content and molsture
content.
A ~urther ob~ect o~ thls lnvention is to provide a
method ~or produclng calclum hypochlorite from aqueous
3 slurries thereo~ at relatively low reaction and drylng
temperatures to produce a particulate product with reduced
- 7 -
,
8~68 C-6429
losses o~ available chlorine caused by decomposition.
It i8 another ob~ect o~ thls invention to provlde a
process ~or accelerating the volatilization of water ~rom
moist and hydrated calcium hypochlorite at relatively low
temperatures to reduce the quantity of calcium hypochlorite
present in process equipment and thus minimize potential
manufacturing hazards which could result from accidental
ignition and decomposition of this material.
Another ob~ect o~ the invention is to provide a method
~or producing smooth-surfaced, r~ounded granular calcium
hypochlorite particles free o~ sharp, fragile edges which are
sub~ect to abrasion and dust ~ormation during handling.
Still another ob~ect o~ this inventlon is to provide
novel granular calcium hypochlorite particles having an
inner portion o~ calcium hypochlorite and an outer portion o~
a di~ferent calcium hypochlorite with a di~erent available
chlorine conaentration or di~erent moisture content and a
process ~or producing them.
It is another ob~ect o~ this invention to provide novel
granular calcium hypochlorite particles having an inner portion
o~ calcium hypochlorite coated with an outer portion of an
inorganic salt other than calcium hypochlorite.
These and other ob~ects of the invention will be
apparent from the following detailed description o~ the
inventlon.
The novel composition o~ this invention is a rounded
granular calcium hypochlorite comprised o~ a core o~ calcium
hypochlorite encapsulated with a plurality of rounded layers
o~ calclum hypochlorite, wherein the core o~ each par~icle
~ generally has a diameter which ranges ~rom about 200 to
about 2,000 microns and the novel coated granules have a
~ 1~48868 C-6429
dlameter ranging from about ~00 to about 5JOOO microns.
The novel rounded granules o~ this inventlon are formed
from a pumpable and ~prayable aqueous slurry o~ calcium
hypochlorite in a process which comprises:
(a) maintaining a moving bed o~ solid calcium hypochlorite
particles containing from about 5 to about 30
percent by weight o~ water in the lower part o~
a distributing zone having an upper part and a
~- lower part,
(b) li~ting a portion of the moving bed o~ particles to
; the upper part of the distributing zone and releasing
: the li~ted partlcles to ~all downwardly through the
upper portion o~ the distributing zone to said moving
bed in the lower portion thereo~,
(c) spraying onto said falling particles a pumpable
and sprayable aqueous slurry of calcium hypo-
chlorite containing ~rom about ~5 to about 90
percent by weight of water,
: (d) maintaining a temperature in said distributlng zone
su~iciently high to simultaneously evaporate and
remove water ~rom the slurry on said ~alling particles,
;~ whereby the resultlng particles after water removal
are coated with a layer o~ solid calcium hypochlorite
and the water content of the resulting coated
particle is maintained in the range ~rom ab~ut
: 5 to about 30 percent by weight, and
te) removlng at least a portion of the resulting
coated solid calcium hypo¢hlorite particles
~rom the distrlbuting zone.
. .
- ,
138~
Lack of cohesiveness between crystals of calcium
hypochlorite is counteracted in the structure and growth
of the novel granular hypochlorite of this invention in
that freshly deposited, pliable moist layers of new hypo-
chlorite solids are packed and pounded onto the dried
hardened underlaying seed substrate by innumerable impacts
as the grains cascade in the drum or are otherwise forced
into violent collision with one another. Where crystalline
particles are too large to submit to hardening by collision
impact, these may retain individual identity as nuclei to
seed the bed or they may be collected in a dry dust collector,
pulverized and returned in more finely divided form, more
susceptible to cohesion and hardening by collision impact.
If desired, the coated particles removed from the dis-
tributing zone can be further dried to reduce the water
content to a lower level. Alternatively, the coated particles
removed from the distributing zone can be conveyed to a second
distributing zone where they are sprayed with another solu-
tion of calcium hypochlorite of a lower available chlorine
concentration than the slurry utilized in the first dis-
tributing zone. In another embodiment of the invention, the
coated particles removed from the distributing zone can
be sprayed with an aqueous solution of an inorganic salt or
certain molten hydrated inorganic salts to form a plurality
of layers of salt other than calcium hypochlorite on the
exterior of the novel calcium hypochlorite particles. Sizing
of the portion of coated calcium hypochlorite particles
separated from the first distributing zone can be accomplished
prior or subsequent to drying or other treatment.
.,
~ 8~68 C-6429
The novel rounded granular calcium hypochlorite
particles prepared in accordance with the process o~ this
invention have a high level o~ integrity and resist dusting
and degradation when sub~ected to ~evere handling conditions.
For example, irregularly shaped granules o~ commercial hypo-
chlorite break easily along the thin ~ragile edges when sub-
~ected to pressure and abrasion. The fragmented edges form
~ine dust easily dispersed in ambient atmosphere and results
in severe respiratorg irritatlon, discom~ort and health
hazards. Fragile edges are absent on the novel rounded
grain of this invention and hence dusting cannot occur.
Even if this novel grain ~ractures under pressure,
~ragments remain su~iciently large to escape entrainment
in ambient air during normal handling o~ the product. As
a result, even though the novel calcium hypochlorite particles
of this invention may be ~ractured under severe handling
conditions during shipment, nevertheless, a minimum o~ ~inely
divided particles are ~ormed. Also, as a result, a more
uniform di~tribution o~ the calcium hypochlorite in the
water being treated can be obtained and respiratory irrita-
tion and discom~ort ~rom entrained hypochlorite dust in air
is greatly minimized. In addition, when the proper level
of moisture ¢ontent is obtained or when the particles
have a coating o~ an anhydrous or hydrated inorganic salt
on the exterior layers to encapsulate the active hypochlorite
in an inert shell, there i9 a high degree o~ resistance to
ignition by lighted cigarettes or the reaction caused when
contacted with organic materials.
Figure 1 shows two embodiments of the invention which
3 utillze a spray grainer as a distributing æor,e, with recycle
o~ ~ines and crushed oversize. In one embodiment, the product
~raction is conveyed to a coating drum and without recycle,
is then drled to the desired water level in a separate dryer.
-- 11 --
, : ,
1048868
In the second embodiment, the product fraction is conveyed
directly to the separate dryer. -~
Figure 2 is a cross-sectional view of the spray
grainer of Figure 1 through the lines 2-2.
Figure 3 is a cross-sectional view of the dryer of -
Figure 1 through the lines 3-3 of Figure 1.
Figure 4 shows a schematic diagram of an embodiment of
the invention in which a fluidized bed is used as the distribu-
tion zone.
Figure 5 is a photograph of known calcium hypochlorite
particles magnified five times.
Figure 6 is a photograph of calcium hypochlorite
particles, of the present invention, magnified five times.
More in detail, as shown in Figure 1, a calcium hypo-
chlorite process slurry of the type formed in a commerical
calcium hypochlorite process is conveyed to filter 10. Calcium
hypochlorite slurry is separated into filtrate 11, which is
recycled or otherwise processed, and filter cake 12, which is
admixed with a liquid such as water fed through liquid line 13
into slurry mixer 14 to produce a pumpable and sprayable slurry
of calcium hypochlorite. This slurry is conveyed from slurry
mixer 14 through mixer discharge line 15 by means of slurry
pump 16 through slurry feed line 17 to spray grainer 18.
Spray grainer 18 has a distributing zone 19 with an
upper portion 20 and a lower portion 21, a feed end 22 and an
opposite discharge end 23. Spray grainer 18 is provided with
exterior tires 24 secured to the exterior thereof which are
adapted to rotate in trunnions 25, exterior tires 24 being
driven by a suitable motor driven rotation means 26 to effect ~-
rotation of spray grainer 18 within the desired speed range.
-12-
:: ~
.' ~ ' ' , ~ .
1~88613
As shown in Figure 2, a bed of solid calcium
hypochlorite particles is placed in lower portion 21 of
distributing zone 19 to form, when spray grainer 18 is rotated,
a moving bed of particulate solids which gradually progresses
from feed
B -12a- .
. ~. - . , . :., . , :
8 - /~3 -
end 22 to discharge end 23 of spray grainer 18. Transport
of the feed from the feed end to the discharge end can be
solely by interaction with a co-current flow of drying
gases (as described below) or by a combination of gas
induced transpor~ aided or retarded by positive or negative
slope of the drum axis. Bed transport can also be aided
or detained by used of inclined vanes and dam rings attached
to the interior of the drum wall.
As described further in Figure 2, a series of lifters
27 are positioned around the interior circumference of spray
grainer 18 to lift the particles of calcium hypochlorite
from the moving bed in lower portion 21 to the upper portion
20 of distributing zone 19. As spray grainer 18 rotates,
the particles gradually fall from lifters 27 as they approach the
top of upper portion 20 and fall through distributing
zone 19 to lower portion 21 into the moving bed of solid
calcium hypochlorite particles. While the solid particles
are falling from lifters 27 from upper portion 20 to lower
portion 21 of distributing zone 19, slurry pump 16 is
continuously conveying through slurry feed line 17 the pump-
able and sprayable calcium hypochlorite slurry to a plurality
of spray nozzles 28. Compressed air is conveyed through
compressed air feed line 29 to nozzles 28 in order to
disperse the slurry as fine droplets from the spray nozzles
and to effect the spraying of these fine droplets of slurry
onto the falling particles of calcium hypochlorite.
~ eated air or other inert gas contacts the calcium
hypochlorite particles wetted with the slurry to simultan-
eously evaporate and remove water and to deposit a thin
solid layer of the calcium hypochlorite-containing component
of the slurry on the surface of the wetted particles. The
coated particles fall to the moving bed and continue to be
lifted, dropped and coated until they are discharged from spray
grainer 18. Any convenient heating techni~ue may be em-
~V4~ 4-
ployed. For example, heated air is preferably conveyed
concurrently with the flow of the moving bed of solids through
heated air line 30. Air is conveyed by blower 31 to heat
exchanger 32 which is heated hy steam conveyed through steam
feed line 33 to heat exchanger 32. The heated air produced
in heat exchanger 32 is conveyed through heated air line 30
by blower 31 into feed end 22 through spray grainer 18, and
passed out discharge end 23. The hea ed air fed to spray
grainer 18 is generally at a temperature in the range from
about 85C. to about 250C. to effect simultaneous evapor-
ation and removal of water from the falling particles. The
steam condensate from heat exchanger 32 is discharged
through steam discharge line 34.
At feed end 22 a feed retaining flange 35 is secured
to the exterior wall of spray grainer 18 in order to retain
the moving bed of particles within spray grainer 18. Simi-
larly, at discharge end 23 a discharge retaining flange
36 is secured to the interior wall of spray grainer 18
in order to retain most of the moving bed of particles
within spray grainer 18. Feed retaining flange 35 and dis-
charge retaining flange 36 each have an opening in the center,
preferably of circular shape. The diameter of the opening
in discharge retaining flange 36 is preferably greater than
the diameter of the opening of feed retaining flange 35
in order to insure that particles are discharged from spray
grainer 18 at discharge end 23 rather than at feed end 22.
For co-current air flow bed transport is primarily by inter-
action of the cascading bed with the air stream. Positive or ~
negative axial slope can be used to aid or retard air trans- ~ ~-
port. Also, internal dam rings (not shown) can be used to re-
tard flow by increasing bed depth. Also, slanted vanes (not
shown) can be mounted to inner walls of spray grainer 18 to
aid or retard bed transport.
1~4~868 C-642g
As the number and slze o~ ¢alcium hypochlorite granule~
lncreases, the moving bed builds up behind dlscharge retaining
~lange 36 until a level is reached where the partlcles ~all
out through the opening ln discharge retaining ~lange 36 into
solids collection zone 37. Granules ~rom solids collection
zone 37 are conveyed by sultable conveying means to a suitable
size classi~ication apparatus. For example, a solids conveying
means such as a chute 38, elevator 39 and lnclined trsugh 40
convey all or part o~ the solids to screens 41 which are pre-
ferably heated to minimlze bllnding. However, other apparatus
such as an air classl~ler may be used to separate the partlcles
into an over_slze ~raction, an under-size ~raction and a
product ~ractlon. By_pass line 122 returns solids in excess
o~ the feed rate to spray grainer 18. Screens 41 contain an
over-size screen 42 and an under-size screen 43 which separate
over-slze partlcles and under-size particle~ ~rom the product
~raction. Generally, any desired particle size can be obtained.
In a typical separatlon, the over-size screen 42 has a me~h
slze in the range ~rom about 4 to about 24 mesh and the under-
slze screen 43 has a mesh size in the range ~rom about 16 to
- about 70 mesh. Under-slze screen 43 always has a mesh opening
smaller than over-size screen 42. A typlcal product ~racti~n
ranges ~rom about 8 to +30 mesh, but the size range can be
varled as desired. Over-~lzed partlcles retained by over-slzed
screen 42 are conveyed through over-slze particle condult 44
to roll crusher 45 where t~e over-size particles are crushed
to pass through over-size screen 42 and then conveyed through
cru3hed over-slze partlcle conduit 46 to chute 38 where the
crushed particles are recycled through elevator 39 to ~creen~
41. Under-slze particles whlch pass through under-size screen
43 are conveyed by means of under-sized particle conduit 47
to the ~eed end o~ spray gralner 18, where they serve as
- 15 -
8~8
core particles or nuclei for the formation of additional
granules of calcium hypochlorite. A product fraction of
rounded granular calcium hypochlorite is collected in product
conduit 48 and processed as described more fully below.
Bxhaust fan 49 is used to withdraw moist air having
finely divided particles of calcium hypochlorite suspended
therein from solids collection zone 37 through a series of
conduits and apparatus. The solid-laden moist air is withdrawn
from solids collection zone 37 through conduit 50 to dust
collector feed line 51 and into dry dust collector 52, pre-
ferably of the cyclone type. Air exhausted from the top of
dry dust collector 52 is conveyed through air discharge
line 53 to wet scrubber 54 for more effectual cleaning. Liquid
such as water or a dilute calcium hypochlorite solution
which may be produced as a by-product in the preparation
of the calcium hypochlorite filter cake, is fed through liquid
feed line 55 to the top of wet scrubber 54 where it contacts
the moist air and removes the bulk of fine solid particles
retained in the air. The resulting dust laden slurry is
removed from the bottom of scrubber 54 through slurry dis-
charge line 56 by means of scrubber pump 57. A portion of
slurry discharged from scrubber pump 57 is conveyed to calcium
hypochlorite slurry mixer 14 through slurry recycle line 58.
The remainder of the slurry from slurry recycle line 58 is
recycled to the top of scrubber 54 through slurry feed line
59 and then sprayed through scrubber nozzle 60 onto the rising
dust laden air fed into the bottom of wet scrubber 54. Con-
tact between the ~lurry and air removes substantially all
of the suspended solids from the air. The resulting gases
depleted of dust are conveyed through exhaust conduit 61 and
exhaust fan 49, and discharged through air exhaust line 62
into the atmosphere, or are otherwise treated.
- : .
:. ' ' . .- ' - ' . .' ~ :'
1~8868 C-6429
Dry dust collector 52 also separates dry particles o~
calcium hypochlorite from the moist air ~ed in through dust
collector ~eed line 51. These dry particle~ are generally
too coarse to ~orm hard cohesive granules, particularly if
recycled to spray grainer 18; Cohesion o~ the particles is
improved by intensive pulverization. Thus, the dust particles
are discharged ~rom dry dust collector 52 through solids
discharge line 63 into pulverizor 64. The solid particles
are comminuted to a diameter of generally les~ than about
40 microns and then conveyed through pulverized particle
line 65 to solids recycle line 66 which recycle~ the pul-
verized solids to spray grainer 18. I~ desired, a portion
or all o~ the pulverized sollds may be recycled to slurry
mixer 14 through mixer recycle llne 67.
The product ~raction of rounded granular calclum hypo-
chlorite particles which do not pass through under-size
screen 43 are conveyed through product conduit 48 to the
next processing step. Generally the moisture content of
the product ~raction o~ screens 41 ranges ~rom about 5 to
about 30 percent, and pre~erably ~rom about 15 to about 27
percent by weight. When the moisture content of calcium
- hypochlorite ranges from about 0.5 percent to about 10 percent,
the calclum hypochlorlte granules possess suf~icient chemical
stability to be used as a commercial product, and may be
conveyed to packaging. I~ the mositure content is above
about 10 percent by weight and if it is desired to produce
a material having less than about 10 percent moisture by
weight, the product fraction is conveyed through product
conduit 48 to a suitable dryer such as rotary dryer 68 through
3 dryer ~eed condult 69, as shown in Figure 1.
17
1~81368
Rotary dryer 68 is provided with at least two dryer tires
70 preferably constructed of metal, positioned at two mechani-
cally-suitable locations near the extremity of rotary dryer
6B. Dryer tires 70 rotate in dryer tire trunnions 71 and
rotary dryer 68 is rotated by a suitable dryer motor drive
means 72 which acts upon one of the dryer tires 70 to effect
rotation of rotary dryer 68.
Rotary dryer 68 is1provided with a dryer feed end 73
and a dryer discharge end 74. Dryer feed end 73 is provided
with a retaining flange 75 and dryer discharge end 74 is
provided with a discharge retaining flange 76 in order to
maintain a moving bed of solids in rotary dryer 68. Retaining
flange 75 and discharge retaining flange 76 are each provided :~
with a circular opening in the center to permit entrance
and exit of particles being dried. Heated air is fed into
feed end 73 of rotary dryer 68 through heated air conduit 77. ~
The heated air is provided by blowing atmospheric air through :
dryer ~lower 78 into heat exchanger 79 which is heated by . -
exchange with steam fed to steam inlet 80. The heated air is -
conveyed to heated air conduit 77. The steam condensate is :~
discharged from heat exchanger 79 through condensate dis-
charge line 81.
Figure 3 is a cross-sectional view of rotary dryer 68
through 3-3 of Figure 1. As indicated in Figures 1 and 3,
rotary dryer 68 is provided with an air exhaust bustle 82
which communicates with dry dust collector 52 by means of gas
discharge conduit 83 from dryer 68 to dust collector feed
line 51. Exhaust fan 49 withdraws the hot gases which have
increased in moisture content within rotary dryer 68 as
well as cool air which is drawn into discharge end 74 of
dryer 68 through cool air feed line 84. The hot moisture
laden gases from the feed end 73 and the cool moist gases
18
- : . - .
.
,.
.
1~48868 C-6~129
~rom the discharge end 74 are withdrawn khrough tubes 85
located around the periphery o~ the internal wall o~ rotary
dryer 68. Tubes 85 communicate with a chamber located in
bustle 82. Gas discharge conduit 83 positloned in bustle
82 conveys the mixture o~ gas and any ~lnely divided calcium
hypochlorite that may be present in the chamber within bustle
82 to dry dust collector 52 where lt is processed in the
same manner as the moist air containing ~inely divided calcium
hypochlorite which i8 conveyed by conduit 50 f'rom sollds
collection zone 37 to dry dust collector 52. Figure 3
also shows retention o~ the movlng bed of solids in dryer 68
by means of discharge retaining ~lange 76. Granular calclum
hypochlorite particles which have been dried in dryer 68 pass
over discharge retaining ~lange 76 into product collection
line 86 where they are conveyed to storage or other proce3sing.
Bed transport towards the discharge end 74 is induced
by interaction of cascadlng solids wlth the co-current ~low
o~ drying gases. If de~lred, rotary dryer 68 may be set at
a positive or negative ~lope ~rom dryer feed end 7~ toward~
dryer dlscharge end 74 to ald or retard bed transport due
to co-current air ~low. The particles of calciwm hypochlorite
are thereby moved at a controlled rate ~rom the ~eed end 73
towards the discharge end 74 as rotary dryer 68 i~ rotated.
In addltlon, inclined vanes, ~not ~hown) may be mounted on
the interior walls o~ the rotary dryer 68 in di~charge end
74 to aid ln the ~orward transport of the bed through the
counter-current air ~low zones. Bed depth in discharge end.
74 o~ rotary dryer 68 can be limited by sel~ction o~ a
suitable diameter ~or retaining flange 76 in di~charge end 74.
,.,, -- 19 _
~z, ,A
10~8868
Rotary dryer 68 may be provided with internal flights
similar to lifters 27 of spray grainer 18 in order to move
a substantial portion of the particles to be dried to the
upper portion of rotary dryer 68 and thereby increase the ~-
degree of contact between the particles and the drying air
as well as the cooling air. Little or no dusting occurs.
Conventional granular calcium hypochlorite particles
are in the form of irregular sharp-edged flakes which must ~ -
be prepared and dried under substantially quiescent condi-
tions with a minimum of agitation because of the sensi-
tivity of the fragile edges to attrition and a high level
of dusting. Unlike conventional granular calcium hypochlorite
the rounded granular calcium hypochlorite particles of ~
this invention can be subjected to severe conditions of ~-
agitation and crushing during granulation and drying without
the formation of excessive quantities of dust because sharp,
fragile edges are totally absent.
Without being bound by theory, it is believed that the
improved structure of the calcium hypochlorite particles
of this invention are a result of the formation of pliable
moist layers of new clacium hypochlorite solids which are
packed and pounded onto the dried hardened underla~ing core or
seed substrate by innumerable impacts as the particles
cascade in the distribution zone or are otherwise forced
into violent collision with one another during processing.
As the solids progress through the distribution zone,
layer upon layer of calcium hypochlorite is formed on the
seed particles in an onion-like manner, each layer imparting
strength to the particles.
The novel granules of this invention have a high
degree of integrity and when subjected to a severe pressing
force will fracture into integral particles of the granule,
-20-
. . .
.
1~4~3~68
rather than decompose into dust, which occurs with conven-
tional granular calcium hypochlorite particles under the
same conditions.
In order to improve ~he storage stability of the rounded
granular calcium hypochlorite particles produced by the process
of this invention, as well as particles produced by conven-
tional calcium hypochlorite processes, it is desirable to
coat these particles with a protective coating of an inor-
ganic salt. In one embodiment, the protective coating may
be applied after drying in rotary dryer 68. In another
emobdiment, the protective coating is applied to calcium
hypochlorite particles before final drying if the moisture
content of the coating solution slurry exceeds the molsture
to be allowed in the final product. Excess moisture from
the coating slurry is then volatilized with the water of
hydration of the calcium hypoChlorite in the final drying
step. The particle size of the uncoated calcium hypochlorite
particles to be coated generally corresponds to that of
the product produced in spray grainer 18 which is discharged
through product conduit 48 from screens 41 in Figure 1.
In the first of these embodiments, rotary dryer 68
may be provided with a spray nozzle 87 which is connected
to spray feed line 88 which provides a solution, slurry,
or melt of an additional coating composition such as a
surface conditioning agent or a molten hydrated salt which
may be applied in small proportions to the dried particles
to improve flowability, prevent caking or in order to form
additional exterior layers of a flame resistant material which
will protect the encapsulated calcium hypochlorite from
ignition when contacted with lighted cigarettes, organic
liquids and the like. When the calcium hypochlorite granules
are coated in this manner, gas discharge conduit 83 does not
-21-
104~8f~B
convey the hot gases containing suspended solids to dry dust
collector 52, but instead conveys the gases from air exhaust
bustle 82 to a separate dry or wet dust collection system (not
shown) where solid particles are separated and recycled to
the bed or coating composition make-up vessel (not shown~ and
fed through spray feed line 88 to dryer 68. This technique
prevents recycle of the coating composition to the beginning
of the process and prevents contamination of the calcium hypo-
chlorite cores with the particles of coating composition.
In the second of these embodiments, as shown in Figure
1, a coating composition in solution or slurry form is prepared
in spray feed tank 90 by addition of the inorganic salt through
inorganic salt feed line 91 and water through water feed line
92. If desired, calcium hypochlorite may be employed as the
coating composition by utilizing a portion of filtrate 11 from
filter 10 which is fed to spray feed tank 90 by filtrate feed
line 93. The components of the coating composition are admixed
in spray feed tank 90 to form a pumpable and sprayable
solution or slurry of the inorganic salt. This slurry is
conveyed from spray feed tank 90 through feed tank discharge
line 94 by means of coating pump 95 through coating feed line
96 to second spray grainer 89.
Second spray grainer 89 has a coating distributing zone
97 with an upper portion 98 and a lower portion 99, a feed ~-
end 100 and an opposite discharge end 101. Spray grainer 89
is provided with exterior tires 102 secured to the exterior
thereof which are adapted to rotate in trunnions 103,
exterior tires 102 being driven by a suitable motor driven
rotation means 104 to effect rotation of second spray grainer
89 within the desired speed range. A cross sectional area
of second spray grainer 89 corresponds to that of spray
grainer 18 of Figure 2. In the operation of second spray
10~868
grainer 89, a bed of solid calcium hypochlorite particles
to be coated is placed in lower portion 99 of coating dis-
tributing zone 97 to form, when spray grainer 89 is rotated,
a moving bed of particulate solids which gradually progresses
from feed end 100 to discharge end 101 of second spray
grainer 89. Transport of the feed from the feed end to the
discharge end can be solely by interaction with a co-current
flow of drying gases (as described below) or by a combination
of gas induced transport aided or retarded by positive or
negative slope of the axis of second spray grainer 89. Bed
transport can also be aided or detained by use of inclined
vanes and dam rings attached to the interior of the drum wall. -
As described further in Figure 1, a series of lifters
105 are positioned around the interior circumference of
second spray grainer 89 to lift the particles of calcium
hypochlorite from the moving bed in lower portion 99 to
upper portion 98 of coating distributing zone 97. As second
spray grainer 89 rotates, the particles gradually fall from
lifters lOS as they approach the top of upper portion 98
and fall through coating distributing zone 97 to lower
portion 99 into the moving bed of solid calcium hypochlorite
particles. While the solid calcium hypochlorite particles
-- are falling from listers 105 in upper portion 98 to lower
portion 99, coating pump 9S is continuously conveying through
coating feed line 96 the pumpable and sprayable coating
composition to at least one coating spray nozzle 106. Com-
pressed air is conveyed through compressed air feed line
107 to nozzle 106 in order to disperse the coating composi-
tion as fine droplets from the coating spray nozzle 106
and to effect the spraying of these fine droplets of coating
composition onto the falling particles of calcium hypochlorite.
~ ~3 ~
10~t~8f~3
Heated air or other inert gas contacts the calcium ~ -
hypochlorite particles wetted with the solution or slurry
of coating composition to simultaneously evaporate and
remove water, and to deposit a thin layer of the solid
coating composition on the surface of the calcium hypochlorite
particles. The coated particles fall to the moving bed, and
continue to be lifted, dropped and coated until they are
discharged from second spray grainer 89. As the solids
progress through the distribution zone, layer upon layer
of the coating composition forms on the calcium hypochlorite
particles and encapsulates the calcium hypochlorite particles
with the coating composition to improve the chemical and
thermal stability of these particles. Any convenient heating
technique may be employed. For example, heated air is
preferably conveyed concurrently with the flow of the moving
bed of solids through heated air line 108. Air is conveyed
by blower 109 to heat exchanger 110 which is heated by steam
conveyed through steam feed line 111 to heat exchanger
110. The heated air produced in heat exchanger 110 is con-
veyed through heated air line 108 by blower 109 into feed
.. .
end 100 through second spray grainer 89,and passed out dis-
charge end 101. The heated air fed to second spray grainer
89 is generally at a temperature in the range from about 85C.
to about 250C. to effect simultaneous evaporation and
removal of water from the falling particles. The steam
condensation from heat exchanger 110 is discharged through
steam discharge line 112.
At feed end 100 a feed retaining flange 113 is secured
to the exterior wall of second spray grainer 89 in order
to retain the moving bed of particles. Similarly, at dis-
charge end 101, a discharge retaining flange 114 is secured
to the interior wall of second spray grainer 89 in order to
-24-
;. . ' ' . : :, ': '
' ' ' ' : :
1~48~368
retain most of the moving bed of particles. Feed retaining
flange 113 and discharge retaining flange 114 each have
an opening in the center, preferably of circular shape.
The diameter of the opening in discharge retaining flange
114 is preferably greater than the diameter of the opening
of feed retaining flange 113 in order to insure that particles
are discharged from second spray grainer 89 at discharge end
101 rather than at feed end 100. As in spray grainer 18, co-
current air flow bed transport is primarily by interaction
of the cascading bed with the heated air stream provided
by heated air line 108. Positive or negative axial slope
can be used to aid or retard air transport. Also, internal
dam rings (not shown) can be used to retard flow by increasing
bed depth. Also, slanted vanes (not shown) can be mounted
to inner walls of second spray grainer 89 to aid or retard
bed transport.
As the number and size of calcium hypochlorite granules
coated with the coating composition increases, the moving
bed builds up behind discharge retaining flange 114 until a
level is reached where the particles fall out through the
opening in discharge retaining flange 114 into coated solids
collection zone llS. Coated calcium hypochlorite granules
from solids collection zone 115 are conveyed to dryer feed
conduit 69 of rotary dryer 68 by means of coated solids
conveying means 116, or are otherwise processed. Size
classification of the product of second spray grainer 89
can be effected, if desired, with recycle of the undersize
and crushed oversize fractions, but generally this size
separation is not necessary.
-25-
~488~ C-6429
I~ desired, another coating composition in liquid or
slurry form ma~ be applied over the coating composition pro-
vided through coating ~eed line 96. In this embodiment,
the second coating composition is placed in second coating
tank 117 and pumped by means o~ second coating pump 118
through second coating ~eed line 119 to at least one second
coating spray nozzle 120. Compressed air (not shown) may
be provided to disperse the second coating composition into
~lne droplets ~or better contact with the calcium hypo-
chlorite particles.
A separate dust recovery system (not shown), employing
an exhaust ~an such as exhaust ~an 49 is u~ed to withdraw
moist air having finely divided particles o~ calcium hypo-
chlorite suspended therein from solids collection zone 115
through conduit 121 to dust collector feed line 51 and lnto
a dry dust collector like dry dust collector 52, and a wet
scrubber like wet scrubber 54 in the same manner as moist
air is withdrawn ~rom spray grainer 18. Recovered solids
are recycled as ~eed to second spray grainer 89.
The coated product o~ second spray grainer 89 are
rounded, granular calcium hypochlorite particles-coated
with the coating composition. Generally, the moisture
content o~ the coated particles ranges ~rom about 5 to about
30 percent, and preferably ~rom about 15 to about 27 percent
by weight. When the moisture content of the coated calcium
hypochlorite range~ from about 0.5 percent to about 10 percent,
it possesses suf~icient chemical stability to be used as
a commercial product, and may be conveyed to packaging. I~
the mol~ture content is above about 10 percent by welght
3 and i~ lt is desired to produce a material having less than
about 10 percent moisture by weight, the coated particles
are conveyed through product conduit 116 to rotary dryer 68
_ 26 -
.
~8868 C-6~29
through dryer feed conduit 69, as shown in Figure 1.
Figure 4 shows an embodiment of this lnvention in which
a fluidized bed technique is used as the distribution zone.
Fluidized bed apparatus 130 is comprised of an upper tower
131 in the upper portion and a lower frusto-conical section
132 in the lower portion. A moving bed of solid particles
of calcium hypochlorite 133 iB suspended within fluidized
bed apparatus 130 by means of a suitable gas such as air
or nitrogen, which is fed by means of gas feed line 134 into
heat exchanger 135 and heated with steam fed into steam inlet
136 and discharged through condensate line 137. Heated air
or nitrogen from heat exchanger 135 is conveyed through
heated gas line 138 into the bottom of frusto-conical section
132 into diffuser grid 139. Heated air or nitrogen is fed
through the diffuser grld 139 under su~ficient pressure and
velocity to maintain the moving bed of solid calcium hypo-
chlorite particles 133 suspended within fluidized bed
apparatus 130. Solids in the moving bed have substantially
- the same composition at start-up as the moving bed employed
in spray grainer 18 of Figures 1, 2, and 3. These feed
particles of caleium hypochlorlte generally have a particle
size in the range ~rom about 200 to about 2,000 microns,
and pre~erably from about 400 to about 1,000 microns in
diameter. They may be obtained by crushlng commercial
granular calcium hypochlorite to the desired particle size,
by utilizing a more finely divided product produced in
conventional calcium hypochlorite processes, or by recycling
fines ~rom another or the same fluidized bed operation.
The~e ~inely divided seed particles are conveyed through
3 solids conveying means 140 to hopper 141 which is provided
with rotary feed means 142 for controlling the rate of feed
of the ~olid particles to the upper portion of upper tower
_ 27 -
1~8868 C-6429
131 by means of controlled solid ~eed line 143.
Calcium hypochlorite slurry from calcium hypochlorlte
slurry mixer 1~ (not shown) of Figure 1 is conveyed through
mixer discharge line 15 to slurry pump 16 which conveys the
calcium hypochlorite through slurry feed line 17 to fluidized
bed slurry feed line 144 and into at least one spray head 145
to the upper portion of upper tower 131. The calcium hypo- ~:
chlorite slurry is sprayed through spray head 145 on to the
suspended partlcles in the moving bed of calcium hypochlorite
133 maintained in fluidized bed apparatus 130. As the cal-
cium hypochlorite slurry coats the surfaces of seed particles
of calclum hypochlorite, the heated air or nitrogen gas in
the bed simultaneously removes and evaporates the water
component of the slurry, leaving a thin layer of solid
calcium hypochlorite on the seed particles of calcium
hypochlorite initially fed into the suspended bed. Freshly
deposited pliable solids are compacted and hardened with the
hard dry seed particles by collision impacting of the grains
against one another. This coating technique is continued
as the particles contact additional spray of calcium hypo-
chlorlte slurry. Although the heated air or nitrogen gas
is fed through heated gas line 138 at suf~icient pressure
and velocity to maintain substantiallg all of the solid
particles in suspension, there is a tendency for the lighter
particles to gravitate to the upper portion of the moving
bed in upper tower 131 and for the heavier particles to
gravitate to the frusto-conical section 132 in the lower part
of fluidlzed bed apparatus 130. An appropriate discharge ~ .
line 146 is positioned in lower frusto-conical section 132
3 to remove at least a portion o~ the suspended particles in
the moving bed during the continuous operation of fluidized
bed apparatus 130. This portion o~ the calcium hypochlorite
_ 28 -
~0~8868
particles removed through discharge line 146 generally has
a particle size in ~he range from about 400 to about 5,000,
and preferably from about 500 to about 2,500 microns. In
addition, the moisture content of these calcium hypochlorite
particles is in the range from about 15 to about 30 percent,
and preferably from about 20 to about 25 percent by weight.
If desired, the calcium hypochlorite particles separated
in discharge line 146 are conveyed to a size classification
apparatus such as screens 41 (not shown) wherein the under-
sized and oversize fractions are obtained along with the
product size fraction. Undersize fraction from the screens
is recycled to hopper 141 as seed particles of calcium hypo-
chlorite for the fluidized bed apparatus 130. Oversize
fraction is crushed and then recycled to the screens~
The product fraction, which generally has a particle
size in the range from about 400 to about 3,000, and preferably
from about 600 to about 2,000 microns, may be stored for use as a
sanitizing agent, or may be further dried in a dryer of
the type shown in Figures 1 and 3, as rotary dryer 68
Exhaust gases are conveyed from the top of upper tower
131 through gas discharge line 147 to a suitable dust col-
lection and scrubbing system such as cyclone 52 and scrubber
54 in Figure 1 which scrubs the exhaust gases in a suitable
liquid to remove the finely divided particles of calcium
hypochlorite entrained therein. The resulting slurry is
recycled to slurry mixer 14 of Figure 1.
If desired, compressed air may be fed into spray head
145 through compressed air feed line 148 in order to produce
a finely divided spray of calcium hypochlorite slurry as
discharge from spray head 145.
-29-
.
1$~8868
C-642g
More in detailJ with respect to the process of this
invention, any pumpable and sprayable calclum hypochlorite
slurry containing ~rom about 45 to about 90 percent by
weight of water, and preferably from about 50 to about 60
percent by weight o~ water may be employed in the process ~ -
o~ this invention. Generally, this slurry is prepared by
admixing water with the filter cake o~ calcium hypochlorlte
produced in conventional commercial calcium hypochlorite
processes o~ the type described in U.S. Patent Nos. 2,195,75~-7,
described above.
Although water is normally used to make up the slurry,
any suitable recycle liquid such as a portion o~ the filtrate
produced in commercial calcium hypochlorite processes, scrubber
liquor, or other aqueous mediums that are inert to calcium
hypochlorite may be employed. I~ the water concentration
o~ the slurry is below about 45 percent by weight, the
resulting slurry is extremely di~ficult to pump and spray.
On the other hand, when the water concentration is above
about 90 percent by weight, an extremely large amount of
water must be evaporated, and as a result the ~eed rate must
be reduced, and ~he production rate is reduced. In addition,
there is excessive decomposition o~ available chlorine when
the moist calclum hypochlorite particles are exposed to the
heated atmosphere ~or the extended periods which are neces-
sary to e~ect evaporation of such large quantities o~ water.
Other processes for preparing suitable calcium hypo-
chlorite filter cakes are described in EncycloPedia o~
Chemical Technology, Kirk and Othmer, Second Edition, Volume ~,
pp 21?~.
-- ~0 --
104886~
More recently, another technique for preparing
calcium hypochlorite filter cake and subsequent drying
by conventional techniques is described in U.S. Patent No.
3,895,099, issued July 19, 1975. The filter cake of this
process may also be used to prepare the calcium hypochlorite
slurry used in the process of this invention. If desired,
dry finely divided, pulverized particles of calcium hypo-
chlorite, such as dust recovered in the dry dust collector may
be admixed with an appropriate liquid, or dilute solutions or
slurries of calcium hypochlorite may be evaporated to form a
slurry having a calcium hypochlorite concentration within the
above defined ranges and used as a starting slurry in the
process of this invention.
The proportion of impurities in the calcium hypo-
chlorite slurry will vary with the type of process employed
to prepare the calcium hypochlorite filter cake and also
with the nature of the lime initially used to prepare the
calcium hypochlorite. A typical analysis of a calcium
hypochlorite filter cake prepared by a commercial process
and a typical preferred analysis range for the calcium hypo-
chlorite slurry useful as a starting material in the process
of this invention are as follows:
-31-
c-6~
1~48~68
Typical Filter Typical ~a~e
Cake Analysi~ Analysis Range, - -
Com~onent Percent By Weight ~rcG~ V ~c~:-b~
Calcium hypochlorite45.43 42-~8
Calcium chloride o.44 o.0-1.5
Calcium chlorate 0. 02 0.0-1.5
Calcium hydroxide o.24 0.2_2.0
Calcium carbonate 0. 44 o.1-2.0
Sodium chloride 7.75 6 . o-8 . o
Water (Dlf~erence)45. 68 40-50
A suitable rate o~ ~eed o~ the ~lurry o~ calcium hypo-
chlorite particles will depend upon a number o~ ~actors such
as size of the distribution zone J the relative size o~ the
; moving bed, the solids concentration of the slurry, the
temperature and velocity of the drying gases, the rate o~
discharge, and the number o~ spray nozzles positioned in the
spray grainer 18 or ~luidized bed apparatus 130 as the case
may be. Generally, the slurry ~eed rate ~or a slurry con-
taining about 55 percent by weight of water ranges ~rom about
100 to about 500 pounds per hour in a spray grainer 18 having
a diameter of about 3 ~eet. In a ~luidized bed apparatus
of about 3 feet diameter, the ~eed rate of slurry ranges
from about 20 to about 100 pounds per hour.
- Faster or slower ~eed rates may be employed, 1~ de~ired.
The hold-up time ln the distribution zone should be
maintalned at a minlmum since excesslve exposure o~ calcium
hypochlorlte particles to elevated temperature causes a
substantial reduction in the available chlorine concentratlon.
Thus, the total hold-up tlme ln the distribution zone generally
ranges ~rom about 30 to about 300 minutes and pre~erably from
about 30 to about 90 mlnutes. Under conditions o~ restrlcted
heat lnput, hold-up tlme may range up to about 150 to 300
minutes. Dryer hold-up tlme generally ranges ~rom about 5
to about 50 minutes and pre~erably ~rom about 10 to about 25
minutes.
_ 32 -
868
The rate of feed or input will have to correspond to
the rate of discharge of products in order to prevent buildup
or depletion of the moving bed to an undesirable degree. The
number and size of spray nozzles 28, 106, or 145 will depend
upon the length of spray grainer 18 or 89, or the cross sectional
area of fluidized bed apparatus 130, as the case may be.
The spray is utilized in order to obtain maximum dispersion
and contact of finely divided droplets of the slurry of
calcium hypochlorite or coating composition with the moving
particles of calcium hypochlorite in the apparatus being
employed. In view of the solids content of the aqueous s7urry
of calcium hypochlorite, it is necessary to use spray nozzles
that are provided with openings of sufficient diameter to
prevent clogging of the spray nozzles.
The rate of slurry feed through the spray must be in
balance with the local heat transfer rate in the drum. Since
this declines exponentially as the temperature differential
declines the spray rate through two or more sequential nozzles
should also be in the same exponential proportion.
In order to obtain the desired dispersion of the calcium
hypochlorite slurry in the distribution zone, air, nitrogen
or other suitable gas which is inert to calcium hypochlorite
is compressed and used to disperse the a~ueous slurry through
the spray nozzle heads. In spray grainer 18 of Figure 1,
it is desired to position spray nozzles 28 in upper portion
20 of the distribution zone 19, as indicated in Figure 2, on
the side opposite from the cascading stream of falling par-
ticles. The nozzles should be positioned as close as pos-
sible to the falling particles to insure that the slurry
contacts the falling particles before the heated gases are
capable of evaporating water from the droplets. It is per-
' ~ ', ' : ' '
~48861~
missable for each spray to be in contact with the cascading
stream of falling particles of ca~cium hypochlorite provided
the force of the stream is not strong enough to block the
discharge of the spray of calcium hypochlorite slurry from
spray nozzles 28. Spray nozzles 106 and 120 are positioned in
second spray grainer 89 in the same manner as shown in Figure 2.
Axial rotation of spray grainers 18 and 89 is preferably
within the range from about 10 rpm to about 45 rpm when the
diameter of the drum of spray grainer 18 or 89 ranges from
about 1 foot to about 12 feet. These rotation speeds are
determined in accordance with the formula:
~ .
rpm = 20 V 3/D(ft.), where D = drum diameter
Lower speeds are also practical in accordance with the
formula:
r --
rpm = 5 V 3/D(ft.)
Other speeds between and beyond these limits are also
permissable.
Rotation of spray grainers 18 and 89 and rotary dryer 68
is effected by any convenient motor driven means such as
electric motors with chain or gear drives.
Evaporation of the liquid component of the slurry is
effected in spray grainers 18 or 89, or fluidized bed apparatus
130 by any suitable heating means such as by means of a heated
gas such as air or nitrogen or other gas which is inert to
calcium hypochlorite. The gas may be heated indirectly in
a heat exchanger, with steam, hot combustion gases or any
other suitable manner. Gases which contain relatively large
proportions of carbon dioxide and water vapor are not suitable
for drying the liquid components from the slurry in spray
-34-
~4~8~;~
grainers 18 or 89 or fluidized bed apparatus 130 since the
water component and the carbon dioxide component react with
the calcium hypochlorite particles to form undesirable by-
products. However, combustion gases or other heating means
may be used to externally heat spray grainers 18 or 89 or
fluidized bed apparatus 130 in order to maintain a temperature
within spray grainers 18 or 89 or fluidized bed apparatus
130 which is sufficiently high to effect the removal and
evaporation of liquid from the slurry of calcium hypo-
chlorite without excessive decomposition of the resultingsolid calcium hypochlorite granules. Other suitable heating
means include external heating of the distribution zone with
combustion gaseR, liquid or solid fuels impinging on the
drum walls, electrical heat, direct flame or other direct
heating source being applied to the exterior of fluidized
bed apparatus 130 or spray grainers 18 or 89.
As indicated in Figures 1 and 4, evaporation and removal
of the water from the surface of the coated calcium hypochlorite
particles is effected by passing a stream of heated gas, such
as air, nitrogen or other inert gas con-currently through
spray grainer 18 or 89, or fluidized bed apparatus 130, as
the case may be. If external means are utilized to heat the
distribution zone, it is still necessary to maintain a flow
of gas through the distribution zone in order to remove the
humidified atmosphere that is formed by evaporation and
removal of the water from the slurry on the coated particles.
The temperature of the distribution zone is maintained in
the range from about 40 to about 70C., and preferably from
about 45 ot about 60C., by means of the heated gas which
is passed through the distribution zone. It is preferred to
pass the air con-current to the flow of the moving bed of
-35-
.
~0~68
solids in spray grainers 18 or 89, but counter-current flow
may also be employed, if desired. The temperature and volume
of the gas fed to the distribution zone are correlated with -
the rate of feed of the slurry, recycle solids, water content
and residence time in order to maintain a suitable bed
temperature and also effect the desired degree of evaporation
of moisture from the calcium hypochlorite particles. In order
to maintain the temperature of the distribution zone within
the above defined ranges, it is generally necessary to feed
heated gas into the feed end of spray grainers 18 or 89, or the
frusto conical section of fluidized bed apparatus 130 at a
temperature in the range from about 85C. to about 250C., and
preferably from about 100 to about 200C. The higher tempera-
tures are suitable with short residence times and higher bed
temperatures and the lower temperatures are employed with the
longer residence times at lower bed temperatures in order to
minimize excessive decomposition of the available chlorine
component of the calcium hypochlorite particles due to over-
heating.
The calcium hyprochlorite particles removed from
solids collection zone 37 of Figure 1, and discharge line 146
of Figure 4 generally have a moisture content in the range
from about 5 to about 30 percent and preferably from about
15 to about 27 percent by weight of water. The available
chlorine content (on a dry basis) generally ranges from about
50 to about 85 percent and preferably from about 60 to about
83 percent by weight. Although such a product may be used
directly in the treatment of water and the like, it is subject
to loss of available chlorine when the moisture content is
in excess of about 10 percent by weight and the product is
stored at elevated
-36-
B
-
868
temperatures for extended periods. Therefore, it is desir-
able to further dry products having a moisture content in
excess of about 10 percent by weight in a dryer such as
rotary dryer 68.
Calcium hypochlorite particles produced in spray grainers
18 or 89, or fluidized bed apparatus 130 which have the de-
sired moisture content and available chlorine content must
be cooled before storage. Generally, cooling can be effected
in a rotary drum wherein the particles are lifted in a manner
similar to the moving bed of spray grainers 18 or 89, or
fluidized bed 130 and subjected to an atmosphere of cool
ambient air maintained, for example, at a temperature from
about 20 to about 40C. Generally, storage of the thus
produced calcium hypochlorite particles may be effected when
the temperature is below about 40C.
As indicated in Figure 1, it is preferred to screen or
otherwise classify the product of spray grainer 18 or fluidized
bed 130 to obtain a product fraction of the desired particle
size. However, if particle size of the product is not im-
portant, sizing of the product of spray grainer 18 can beeliminated. In that case, seed particles of finely divided
calcium hypochlorite from another source is fed to spray
grainer 18 for coating with calcium hypochlorite. Generally,
the product fraction ranges from about 4 to about 40 mesh
and preferably from about 10 to about 30 mesh.
In a preferred embodiment of the invention, the pro-
duct of spray grainer 18 or fluidized bed 130 is screened to
obtain a product fraction within the above defined particle
size range. The product fraction as well as the product of
second spray grainer 89, is then further dried to a water
content in the range from about 0.5 percent to about 10 percent
and preferably from about 1.0 percent to about 8.0 percent by
-37-
, ' ' . ~ . '~: . ' '
368
weight of water. Drying to remove water of hydration i8
generally effected at a temperature higher than necessary
to effect evaporation of free water from the slurry on the
particles of calcium hypochlorite in spray grainers 18 and
89, or fluidized bed 130. Generally, the temperature in
the heating end of rotary dryer 68, of the type shown in
Figures 1 and 3, is maintained in the range from about 65C.
to about 100C. and preferably from about 70C. to about 80C.
In order to maintain this drying bed temperature, heated air
or other suitable gas is fed to the dryer con-currently with
the feed at a temperature in the range from about 85C. to
about 250C., and preferably from about 100C. to about 200C.
Simultaneously, ambient cooling air having a ~emperature from
about 0 to about 40C., for example, is fed counter-currently
at the discharge end of dryer 68 in order to reduce the
temperature of the dried particles to within a range where
decomposition of the available chlorine component of the
calcium hypochlorite particles does not occur to a substan-
tial degree. This technique reduces decomposition and also
avoids problems of aggregation and sticking of the finished
calcium hypochlorite product. The hot dry product can also -
be conveyed to a separate air-cooled cooling drum to conveyor
coolers with water cooled jackets, to fluidized bed air coolers
or the like.
Drying of the calcium hypochlorite in dryer 68 is gen-
erally a dehydration step as well as a drying step. Solid
calcium hypochlorite particles in the aqueous slurry fed
to spray grainer 18 are primarily in the form of calcium
hypochlorite dihydrate which contains about 16.6 percent by
weight of hydrated water. Thus, when the product fraction
discharged from product conduit 48 contains more than about
16.6 percent water by weight, the water in excess of this
-38-
,
.
68
amount is free water. When the product from product conduit
48 or the dry product from rotary dryer 68 contains less than
about 16.6 percent water, the bulk of the water is present
as hydrated calcium hypochlorite rather than as free water.
The dried calcium hypochlorite particles from rotary
dryer 68 contains from about 50 to about 85 percent by weight
of calcium hypochlorite (dry basis) and from about 0.5 to
about 10 percent b~ weight of water. The calcium hypochlorite
particles maintain their integrity during the drying stage
since the layered structure formed in spray grainers 18 or
89, or fluidized bed apparatus 130 imparts a unique degree
of strength to these particles which assists in resisting
degradation when subjected to rather severe handling con-
ditions in the dryer. The rounded grains are smooth and devoid
of sharp fragile edges and corners which easily forms dust under
abrasive conditions of movement. As a result, an additional
screening step is not necessary to improve the utility of
the calcium hypochlorite product of this invention.
The particle size of the dried calcium hypochlorite
granules which have not been coated with an additional
inorganic salt is substantially the same as the particle
size of the product fraction of spray grainer 18 or fluidized
bed apparatus 130 that is fed to rotary dryer 68.
The calcium hypochlorite particles produced by this
novel process are ready for packaging, storage, shipping
and use in the purification of water and the like.
In addition to producing calcium hypochlorite particles
of improved strength, the novel process of this invention
also results in improved yield of calcium hypochlorite based
upon initial lime and chlorine reactants since there is a
substantial reduction in the amount of available chlorine
lost during the processing of the filter cake to produce
-39-
~''' "
104~868 4Q
a dry granular product.
Improvement of the chemical and thermal stability of
the novel calcium hypochlorite particles of this invention or
conventional calcium hypochlorite particles is achieved by
encapsulating the particles in a protective coating of an
inorganic salt. Typical examples of suitable inorganic
salts include calcium hypochlorite, as well as chlorides,
chlorates, nitrates, carbonates, silicates, phosphates,
sulfates, pyrophosphates, tripolyphosphates, hexametaphos-
phates and tetraphosphates of an alkali metal such as sodium,
potassium and lithium and mixtures thereof. In addition,
certain hydrated salts which melt at relatively low temper-
atures, i.e. below about 150C., but which are solid at
ambient temperatures may also be used to form a protective
coating on the inorganic salts. Typical examples of suitable
low melting hydrated salts are aluminium sulfate hydrate, (from
about 12 to 18 moles of water), magnesium sulfate hydrate, (from
about 4 to 7 moles of water), eutectic mixtures of tetra- and
meta-borates of alkali metals and the like.
The protective coating may be applied in either second
spray grainer 89 or rotary dryer 68, depending upon the
properties of the coating composition. For example, inorganic
compounds which are applied as an aqueous solution or slurry
and require evaporation of the aqueous component in order to
obtain a thin protective coating on the calcium hypochlorite
particles, are fed to second spray grainer 89 through coating
feed line 96.
Pumpable and sprayable aqueous solutions or slurries of
calcium hypochlorite, as well as chlorides, chlorates,
nitrates, carbonates, silicates, phosphates, sulfates, pyro-
phosphates, tripolyphosphates, hexametaphosphates, and tetra-
metaphosphates of alkali metals such as sodium and potassium
are applied in spray grainer~89. The concentration of the
iV~B~8
coating composition in the aqueous solution or slurry will
vary with the inorganic compound, but should be generally
in the range from about 40 to about 90 percent water. Too
much water requires excessive exposure of the calcium
hypochlorite to hot gases, which cause~ loss of available
chlorine. Too little water in the coating composition may
cause spraying problems.
In the case where an aqueous solution or slurry of
calcium hypochlorite is employed as the protective coating,
it is preferred to employ aslurry of calcium hypochlorite
which forms a protective coating containing less than about
65 percent by weight of available chlorine, and preferably
from about 10 to about 50 percent available chlorine. A
suitable coating composition is the filtrate from calcium
hypochlorite filter 10, which contains from about 8 to about
12 percent by weight of calcium hypochlorite and from about
18 to about 25 percent by weight of sodium chloride. -
An aqueous solution of sodium chloride is also a pre-
ferred coating composition, particularly when admixed with
lime in a proportion of up to about a 4:1 weight ratio.
The salt coating, par~icularly when admixed with lime, provides
an alkaline barrier which permits the application of a
second coating from second coating feed line 119 or spray
feed line 88. In this case, the second coating may be slightly
acidic, such as aluminium sulfate without reaction with cal-
cium hypochlorite because of the protective salt barrier.
In another embodiment of the invention, coating of the
dried calcium hypochlorite particles, either those prepared
in spray grainer 18, fluidized bed apparatus 130, second
spray grainer 89 or calcium hypochlorite particles prepared
by conventional techniques can be coated in rotary dryer 68
by spraying a concentrated solution, a slurry or a melt of
4l-
., - . .,
.
1048B68
of the inorganic salt through spray nozzle 87 in the cooling
end of rotary dryer 68. The water applied to the product in
this case should be equal or less than that to be retained
in the final product (usually 0.5 percent to about 10 percent)
since subsequent drying is not desirable. Where the amount
of water is in excess of about 10 percent by weight, the
coating solutions, slurries, or melts are applied before final
drying as descrlbed above in second spray grainer 89. Never-
theless, calcium hypochlorite particles discharged from rotary
dryer 68 through product line 86 may be conveyed to an
additional dryer such as rotary dryer 68 or a conventional
shelf dryer, if it is desired to reduce the moisture content
of the resulting coated calcium hypochlorite product. Coating
of calcium hypochlorite in the cooling end of rotary dryer 68
is preferred when hydrated low melting salts which are molten
at temperatures below about 150C., and which are solid at
temperatures below about 40C., of the type listed above, are
employed as the coating composition. It is preferred to employ
molten salts such as sodium tetraborate, aluminum sulfate,
magnesium sulfate and various hydrates thereof as a coating
material. When molten salts of this type are employed, it
is only necessary to heat the hydrated salts until they are in
molten condition and then spray droplets of the molten
composition onto the calcium hypochlorite particles at the
lower temperatures in the cooling end of the dryer. Solidifica-
tion of an encapsulating layer of the hydrated salt on the ;
surface of the calcium hypochlorite is effected without the
need for evaporation of water. Moisture transfer from the
hydrated molten salt to the underlying dehydrated hypochlorite
is thereby minimized or prevented. The resulting solid layerof inorganic salt forms a protective coating on the calcium
hypochlorite and not only provides stability
~B -42-
B~3
for the available chlorine content during extended storage
and contact with elevated temperature conditions, but also
provides improved thermal stability when contacted with
burning matches, burning cigarettes, or reactive chemicals
such as isopropanol, glycerine, and products containing them.
Generally, the coated calcium hypochlorite particles
produced by spraying in either spray grainer 89 or rotary
dryer 68, after drying, have a particle size which ranges
from about -4 mesh to about ~40 mesh, and preferably from
about -lC mesh to about ~30 mesh. The coated calcium
hypochlorite particles thus produced generally contain a
protective layer or layers, as the case may be, of inorganic
salt which cGmprises from about 5 to about 40 percent by
weight, and preferably from about 5 to about 15 percent by
weight of the granule. The average available chlorine content
of the entire granule generally ranges from about 50 to ~-
about 85 percent by weight (dry basis) and the average water
content ranges from about 0.5 to about 10, and preferably
from about 1 to about 8. However, because of the heterogeneous
nature of the exterior layer, the coated calcium hypochlorite
particles are more stable to thermal decomposition and loss
of available chlorine.
The term "rounded" used to characterize the novel cal-
cium hypochlorite particles of this invention is intended to
cover particles which are substantially spherical in shape,
but which may exhibit "egg-shape" distortion also. Irregular
particles have a maximum diameter and a minimum diameter.
The ratio of the maximum diameter to the minimum diameter of
irregular particles of calcium hypochlorite produced by
crushing in conventional commercial processes is generally
-43-
,
,
8868
greater than about 2:1. In contrast, the novel rounded
calcium hypochlorite particles of this invention approach a
spherical shape and generally have a ratio of maximum diameter
to minimum diameter of about 1.5:1 or less.
A further difference between the novel rounded particles
of this invention and the irregular shaped conventional
particles is that the outer surfaces of the rounded particles
of this invention are substantially smooth undisturbed layers
of calcium hypochlorite or inorganic salt which are formed by
depositing the slurry and drying it under constant agitation to
remove the water component of the slurry. In contrast, the
irregular shaped calcium hypochlorite particles of commerce
have been formed be compressing wet filter cake between com-
pression rollers to form a sheet-like material, and then
fracturing the sheet into irregular shaped plateletswhich are
subsequently dried under quiescient conditions. Because of
the unique procedure for preparing the novel rounded compositions
of this invention, there is a markedly improved resistance to
dusting and physical breakdown.
Figure 5 shows the irregular shaped rough surfaced
calcium hypochlorite particles produced by fracturing compressed ;
calcium hypochlorite cake in a conventional commercial process.
Figure 6 shows the rounded smooth surfaced calcium
hypochlorite particles of this invention produced by the paint-
like effect of coating in spray grainer 18.
The following examples are presented to define Applicant's
invention more clearly without any intention of being limited
thereby. All parts and percentages are by weight unless
otherwise specified.
,''' . . .
:
1~}8136~3 ~
EXAMPLE 1
A rotary spray grainer was constructed of a drum 10" in
diameter and 12" long turning at 30 to ~0 rpm. Access to the
interior of the drum was through a 4" opening at one end.
Attached to the walls were 4 radial flights 1" high. Drum axis
was horizontal. Drum speed was set to produce cascading of the
bed over about 50 percen~ of the cross-sectional area of the
drum. Operation of the drum was batchwise.
The starting bed was 1.3 pounds of -20 +30 mesh calcium
hypochlorite, a commercial product having the composition shown
in Table I, column (1). Heat was supplied by an external gas ~ -
burner impinging on the drum walls to maintain the bed temperature
at about 60C. (140F.).
Feed was made up by diluting a calcium hypochlorite fil-
ter cake (from Eimco filter) having the composition shown in Table
I, column (2). Water was added to make a slurry of creamy,
pumpable consistency containing 50 percent water and the analysis
shown at Table I, column (3). The slurry was sprayed onto the
cascading bed in the heated rotary spray grainer for a period of
about 15 hours. A total bed weight of 4 to 5 pounds was required
to develop the maximum heat transfer capability of the drum.
Particle size control of material in the bed was by periodic
screening of the bed. Over-size grain was crushed and returned
as required to keep the seeding rate in balance with the pro-
duction rate. After all the feed was introduced, the bed was -
heated with air at 90C. (194F.) for 10 minutes to dry the
calcium hypochlorite particles and the product was removed and
analyzed. Total production was 8.9 pounds of product containing
Trade Mark -
-45-
- - .
- ~ ... .
3868
C-6429
62.5 percent available chlorine and water content of about 5
percent. The production rate was 0.5 lb./hr. Bed retention time
was about 300 minutes due to the low rate of heat transfer from
the external heater source through the drum walls. The excessive
loss of available chlorine is attributed to excessive retention
time at too high a bed temperature.
Table I
ComPosition of Materials in Percent by Wei~ht
(1) (2) (3)
Component Starting Filter Slurry
Bed Cake Feed
Calcium hypochlorite 72.0 45.43 41.50
Calcium chloride 0.5 0.44 0.42
Calcium chlorate 0.1 0.02 0.02
Calcium hydroxide 1.5 0.24 0.23
Calcium carbonate 1.0 0.44 0.42
- Sodium chloride 24.0 7.75 7.41
Water (Difference) 0.9 45.68 50.00
100 . O 100 . 00 100 . 00
_ 46 -
386~3
EXAMPLR II
In another run in the same equipment as used in Exam-
ple I, using an initial bed of 3,pounds of commercial -16 mesh
calcium hypochlorite, heat was introduced by means of an air ~ -
stream at a temperature 150C. (302F.). The air volume maintained
the bed at 45 to 50C. (113 to 122F.). '
Slurry feed was prepared as before from a filter cake
containing 37 percent calcium hypochlorite and 53 percent '
water. The resulting slurry was sprayed onto the cascading bed
in the heated rotary spray grainer for 4 hours. Production rate
was 1.3 lb./hr. The available chlorine content of the product
was 70.4 percent and the loss of available chlorine in the pro-
cess was acceptable. The lower loss of available chlorine is
attributed to a shorter bed retention time and a lower bed
operating temperature.
For purposes of comparison, the spray grainer of Example
II was charged with a bed of 4 pounds of commercial -16 mesh
calcium hypochlorite containing 69 percent available chlorine.
The feed slurry of the same composition as used in Example I
was sprayed on the cascading bed in the heated rotary spray
grainer for 4 hours, Bed temperature was 70 to 75C. (158 to ~ '
167F.). Production rate was 2 lb./hr. for 4 hours. The pro-
duct contained 55 percent available chlorine (dry basis). This -~
batch operation for 4 hours at 70 to 75C. (158 to 167F.)
resulted in a lower available chlorine product due to excessive
retention time at too high a temperature.
-47-
~8868
C-6429
EXAMPLE III
In another run in the same equipment as used in Example I,
7 pounds of calcium hypochlorite were grained at 43C. (109.4F.)
from slurry feed containing 55 percent water, 35 percent calcium
hypochlorite and 10 percent of inert salts. Production rate
was 1.5 lbs./hr. The starting bed was 4 pounds of commercial
granular hypochlorite containing 70 percent available chlorine. - -
The product as grained contained 20 percent of moisture in-
cluding water of hydration. Five pounds of the hydrated grain
was dehydrated in the same drum in 50 minutes by exposure to a
150C. (302F.) air stream. Heat input to the drum was electri-
cally heated hot air from an 800 watt source. The weight of
anhydrous product recovered was 4 pounds. Calcium hypochlorite
content of the product was 72 percent with 2 percent moisture.
Loss of product by dusting was negligible. Approximate bed
retention time of the starting bed was 120 minutes.
EXAMPLE IV
In another run in the same equipment as used in Example I,
11 pounds of calcium hypochlorite was grained at 50C. (122F.)
from slurry feed containing 55 percent water, 35 percent cal-
cium hypochlorite and 10 percent inert salts. Production rate
was 3.0 lbs./hr. The starting bed was 4 pounds of commercial
granular hypochlorite containing 70 percent available chlorine.
The product as grained contained 20 percent of moisture including
water of hydration. Five pounds of the hydrated grain was de-
hydrated in the same drum in 35 minutes by exposure to a 200C.
_ 48 -
-
1~488~3
(392F.) air stream. Heat input to the drum was electrically
heated hot air from a 1500 watt source. The weight of anhydrous
product recovered was four pounds. Loss of product by dusting
was negligible. Calcium hypochlorite content of the product
was 72.4 percent with 1.4 percent moisture. Approximate bed
retention time of the starting bed was 100 minutes.
EXAMPLES V-VI
Grained and dehydrated products from Examples III and IV
were stored for 2 hours at 100C. (212F.) equivalent to 1 year
at ambient temperatures. The available chlorine loss was 0.27
percent in each instance.
Under humid conditions at 35C. (95F.) and 95 percent
relative humidity for 16 weeks, the loss of available chlorine
content was 6.4 percent, comparing favorably with a 6.22 percent
loss for commercial, granular calcium hypochlorite under the
same eonditions.
EXAMPLE VII
Calcium hypochlorite was grained continuously in a drum ~-
3 feet in diameter and 6 feet long rotated at 18 to 20 rpm
provided with 16 radial flights 1" high positioned equidistant
from each other around the interior of the drum. Steam heated
air at 150C. (302F.) was injected at 800 cubic feet per minute.
Feed slurry containing 35 percent calcium hypochlorite, 55 per-
cent water and 10 percent inert salts was sprayed onto the cas-
cading bed in the rotating drum at a rate equivalent to 100
lbs./hr. of dry anhydrous product. Moisture in the bed was
104t~868
C-6429
15 to 22 percent during graining. The bed was continuously
recycled over a screen at a rate of 50 lbs./min. to isolate
particles from the bed in excess of 20 mesh screen size. Grained
product recovered contained 50 percent calcium hypochlorite and
21 percent water and was recovered at a rate of 127 lbs./hr.
The bed retention time was 75 minutes. The hydrated grain was
charged at a rate of 500 lb./hr. to a 3-foot diameter drying drum
supplied with 800 CFM of air at 177C. (350F.). Anhydrous
product containing 1 percent of residual moisture and about 70
percent calcium hypochlorite (dry basis) was recovered at a rate
of 400 lb./hr. The bed temperature at the dryer discharge end
was 74C. (165F.). The bed retention time in the dryer was
20 minutes.
EXAMPLE VIII
In a spray grainer of Example VII with a drum diameter of
3 feet and a drum length of 6 feet, the bed charge was 140
pounds of -30 +70 mesh particles commercial calcium hypochlorite.
Drum speed was 18 to 22 rpm. Initial drum slope from the feed
end was about 0.1 inch/ft. Operation was continuous.
The air stream produced some dusting of the originally
charged particles which subsided quickly as the feed spray
started and began to hydrate the bed. The air pressure was
adjusted to produce uniform droplets of spray.
When the bed weight built up to 160 pounds, the drum slope
was increased to 0.2 inch/ft. At this slope, the recycle was
adequate to accept the maximum feed rate from the spray head
- 50 -
1~34~868
which was equivalent to about 50 pounds of dry granular calcium
hypochlorite per hour. A batch of feecl from about 320 pounds
of wet cake was sprayed onto the warm bed at a rate equivalent
to 50 pounds per hour of dry product for about 3 hours. Bed -
temperature was maintained at 55 to 60C. (131 to 140F.) to
maintain a water evaporation rate in balance with the slurry
feed rate. Available chlorine in the bed and product was 73 to
74 percent (dry basis). With an increased recycle rate, and a
S0-pound per hour feed rate the bed temperature declined to
50C. (122F.) which resulted in an available chlorine content
of the bed and product in excess of 75 percent (dry basis).
EXAMRLE IX
. . .
In apparatus as shown in FIGURE 1, a diluted slurry of
calcium hypochlorite filter cake from an Eimco filter containing
40 percent of calcium hypochlorite, 10 percent sodium chloride
and normal impurities and 50 percent water was charged at a
temperature of 25C. (77F.) to a 10 x 30-foot spray grainer at
a rate of 4,000 lb./hr. The interior was fitted with 24 radial
; flights 6" high positioned equidistant from each other around
the interior of the spray grainer. Air was introduced into spray
heads on branches in the slurry line at intervals to distribute
the feed in the spray grainer. A recycle stream of partially
dried calcium hypochlorite pellets amounting to 60,0001b./hr.
(53 percent calcium hypochlorite, 22 percent solid diluents and
25 percent water) was also charged to the spray grainer.
The spray grainer and contents were heated to a temperature
--51--
1~48868
C-6429
of 50C. (122F.) by a stream of 20,000 cu. ft./min. of steam
heated air at 149C. (300F.). The spray grainer rotated at
10 rpm. Approximately one half of the recycle stream was
screened. A stream of pelletized product of de~ired size
(-16+ 30) was removed from the screens and charged to the de-
hydrator (rotary dryer) at the rate of 2670 lbs./hr. Retention
time of the bed in the grainer was about 40 minutes. The charged
pellets had the same composition as the recycle stream. The
dehydrator and contents were heated to 80C. (176F.) by hot
air in the heating part of the dehydrator by introducing a
stream of 7,000 cu. ft./min. at a temperature of 175C. (347F.).
Retention time in the rotary dryer was 15 minutes. Cooling air
at a temperature of 30C. (86F.) was drawn into the cooling
part (discharge end) of the dehydrator at a rate of about
2,000 cu. ft./min. The combined air streams withdrawn from the
spray grainer and from the dehydrator amounting to 29,000
cu. ft./min. were drawn through a dry cyclone dust collector.
Dust collected at the rate of 200 lb./hr. was pulverized and
recycled to the feed end of the spray graining drum. Residual
dust was trapped in a water scrubber. The air was discharged
and water contining dissolved calcium hypochlorite was purged
from the scrubber and used in making up fresh çalcium hypo-
chlorite slurry.
The product was-pelletized calcium hypochlorite containing
70 percent available chlorine and having mesh sizes of -16
+30 mesh, U.S. standard screens. It was dust free and dissolved
readily in water.
- 52 -
1C~48868
EXAMPLE X
Calcium hypochlorite filter cake produced by the
direct paste procedure described in U.S. Patent No. 3,895,099,
issued July 19, 1975, containing 83 percent available chlorine
(dry basis) was slurried with water to make a paste consisting
of 45 percent total solids and 55 percent water. This was
dispersed by spraying onto a cascading seed bed in a rotary
drum 3 feet in diameter and 6 feet long having 16 radial
lifters 1" high positioned equidistant from each other on the
interior of the drum, turning at 20 rpm. The seed bed was
calcium hypochlorite with a size range of -24 +40 mesh. The
slurry was sprayed onto the cascading seed bed at the rate of
222 lb./hr. Air heated to 121C. (250F) was admitted to
the rotating drum at the rate of 800 standard cubic feet per
minute. The bed temperature was maintained at 52C. (125F).
Water was evaporated at the rate of 100 lb./hr. to produce
spray-grained calcium hypochlorite with 2 moles of water of
hydration in the size range -20 +30 mesh at a rate of 1221b./hr.
The available chlorine content of the recovered grain was
81 percent. Retention time of the bed in the drum was 60
minutes.
The recovered grain in the size range -20+30 mesh was
used to form a seed bed of 160 lbs. in the drum described
above. Filtrate from the calcium hypochlorite filter,
containing 30 percent total solids and 70 percent water, with
35 percent available chlorine in the solids, was sprayed onto
the seed bed at a rate of 130 lb./hr. until the bed weight
was 200 lbs. The average available chlorine content of the
resulting two-layer product was 68 percent.
B -53-
` - -
1(~48B6~
The 200 pound bed was then exposed to 177C. (350F.)
air for 15 minutes in the same 3 foot diameter drum to volatize
the water of hydration. The bed temperature remained at 74C.
(165F.) until the residual moisture in the grain was reduced
to 1 percent.
EXAMPLE XI
:
A bed of 200 lbs. of the undried two-layer product pre-
pared a~ described in Example X was exposed to 177C. (350F.) air
for 10 minutes in the 3 foot diameter drum to volatilize water of
hydration. The bed temperature remained at 74C. (165F.).
Residual moisture remaining after 10 minutes of dehydration was
6 percent.
EXAMPLE XII
The procedure of Example X was repeated to form a bed
of dried two-layer product containing 1 percent of residual mois-
ture. It was cooled from 74C. to 38C. (165F. to 100F.) by
the passage of air at 27C. (80F.) for 5 minutes. The cooled
anhydrous product was treated by spraying onto the cascading bed
in the rotating drum a solution of 1 lb. of a polyacrylic acid
sold commercially under the trademark "Calnox" in 5 lbs. of
water. Moisture in the final product without further drying
was 4 percent and polyacrylic acid content was 0.6 percent.
Other products coated with polyacrylic acid or its
alkali metal salts were similarly prepared containing 0.6, 2.2,
2.7, 3.5, 4.9 and 6.1 percent water. Available chlorine contents
were 62.1 to 67.8 percent.
-54-
~ ~ ,
88~3
EXAMPLE XIII
A fluidized bed was maintained in a cylindrical tower
12 inches in diameter and 24 inches high. At the bottom of the
tower, the cross-section was reduced to a 6-inch circular ~ -
opening by a frustoconical transition section 16 inches high.
Heated air at 93C. (200F.) was injected at a rate of 60 cubic
feet per minute through a diffuser grid located in the 6-inch
opening to prevent the flow of solids back into the gas line.
Seed was fed into the tower to sustain a level 8 inches from
the top of the 12-inch section. Calcium hypochlorite slurry
containing 45 percent solids and 55 percent water was sprayed
onto the upper surface at a rate of 8 pounds per hour. The
upper surface was in active motion by virtue of its support on
the fluidized bed of seed contained in the tower. Seed was
added at the rate of 1.2 lb./hr. Product was withdrawn at the
rate of 4.8 lb./hr. to maintain a fixed upper level in the
fluidization tower~ The solid in the feed added through the -
sprays contained 82 percent available chlorine. The calcium
hypochlorite product recovered contained 74 percent available
chlorine. Grained calcium hypochlorite was withdrawn from the
tower at 74C. (165F.). It contained 10 percent moisture.
EXAMPLE XIV
The graining drum as described in Example I was loaded
with 4 pounds of spray grained calcium hypochlorite with granule
sizes ranging from 16- to 24-mesh. The material contained 25 -
percent moisture and 60 percent available chlorine. A NaCl
slurry of pulverized NaCl suspended in saturated NaCl solution
1~4~868 C-6429
was sprayed onto the cascading bed in the drum until the bed
weight had increased to 5 pounds. Simultaneously heated air
at 200C. was injected. The bed temperature remained at 45 C.
while the slurry was being sprayed. Slurry spray was then dis-
continued while additional hot air flow was sustained. The bed
temperature increased to 73C. and remained at this temperature
level until the bed moisture had declined to 1 percent. There-
after an increase in the bed temperature occurred. Drying was
discontinued when the bed temperature reached 80C. Bed moisture
at this time was 0.7 percent. m e recovered bed weighed 3.8
pounds. Weight loss was exclusively due to volatilization of
bed moisture. The weight of NaCl used to encapsulate the cal-
cium hypochlorite was 0.8 pounds. Particle size of the grain
after coating ranged from -12 to +20 mesh. Available chlorine
in the dried product was 63 percent. Encapsulated grain con-
tacted with lighted matches and cigarettes failed to undergo
thermal decomposition whereas uncoated grains decomposed
completely under similar exposure. The loss rate of available
chlorine from the encapsulated materiaI was equivalent to that
from unencapsulated material with the same moisture content.
EXAMPLE XV
The graining drum as described in Example I was loaded
with 4 pounds of dehydrated spray grained calcium hypochlorite
with an available chlorine content of 79 percent and a moisture
content of 1 percent. A hot concentrated slurry of basic
A12(S04)3 solution at 110Co containing 45 percent water was
sprayed onto the cool cascading bed in the drum until the weight
- 56 -
.
,
i~48868
of the bed had increased to 4.5 pounds. The alum encapsulatedcalcium hypochlorite contained 70 percent available chlorine and
6 percent water the bulk of which was retained in the outer alum
coating. Loss rates of available chlorine during 2 months in-
dicated equivalent storage stability for the dehydrated calcium
hypochlorite and the alum encapsulated grain. The alum encap-
sulated hypochlorite was also completely stable on exposure to
lighted cigarettes and chemical contaminants such as glycerine
which sufficed to decompose the untreated hypochlorite.
EXAMPLE XVI
Four pounds of dehydrated spray grained calcium hypoch-
lorite was coated with 0.5 pounds of a hot concentrated slurry of
alkalized magnesium sulfate as described in Example XV for the
alum coating. Available chlorine after coating was also 70 -
percent with 6 percent water. The 2-month storage stability
was equivalent to that of the uncoated anhydrous calcium hypo-
chlorite and the encapsulated product was also insensitive to
decomposition by exposure to localized heat or chemical contam-
inants. After cooling the hot alkalized magnesium sulfate
slurry froze onto the hypochlorite as the crystalline hydrate
of the salt.
EXAMPLE XVII
The graining drum of Example VII which was 3 feet in
diameter and 6 feet long turning at 20 RPM was loaded with 160
pounds of spray grained calcium hypochlorite containing 79 per-
cent available chlorine and 1 percent water. This bed was
-57-
.
', .' . ' : : ~ ' '
- ~ :'
. ~ t
:
1~48868
C- 642g ,
coated simultaneously from two feed sprays making applications
in approximately equal amouats of an acidic eutectic of molten
borates containing 12 percent Na20; 45 percent B20s; and 43
percent water, and an alkaline eutectic of molten borates con-
taining 26 percent Na20; 35 percent B203; and 39 percent water.
Neutralization of these ~wo molten eutectics on the surface on
the dehydrated ar.d cool hypochlorite resulted in crystallization
of the neutralJ hydrated sodium tetraborate. Total coating
weight applied was 20 pounds. The hypochlorite encapsulated in
~ the hydrated borate was insensitive to decomposition by
standard tests for thermal initiation or chemical contamination.
This material exhibited storage stability equivalent to that of
the dehydrated calcium hypochlorite.
,., .
~ ~ EXAMPLE XVIII
:'~ . .
The coating d~monstration as described in Example XVII
was repeated using an eutectic melt of sodium borate containing
22 percent Na20; 30 percent B203; and 48 percent water in one
spray and a 50 percent solution of NaOH in a second spray.
Both sprays were directed into the same position of the cascade
;20 and were operated simultaneously to form a hydrated metaborate
crystal shell on the surface of the hypochlorite containing 25
percent Na20; 28 percent B203; and 47 percent water. Total
coating applied to the 160 pound bed was 15 pounds. The en-
capsulated product contained 72 percent of available chlorine
and 5 percent of water. The encapsulated product was insensi-
tive to decomposition by standard tests for thermal initiation
- 58 -
.
~:
.
1~8868 C-6429
or chemical contamination and also exhibited long term storage
stability equivalent to the uncoated dehydrated calcium hypo-
chlorite.
EXAMPLE XIX
Four pounds of rounded spray grained calcium hypochlorite
containing 25 percent moisture prepared as in Example VII in the
spray grainer was dehydrated in the equipment described in
Example I by contact with heated air at 180C. for 15 minutes.
The dehydration temperature remained at 73C. until the bed
moisture was 1 percent. The recovered product weighed 3.0
pounds which includes 0.03 pounds of moisture. Dust loss during
drying was only 1 percent of the weight of the product recovered.
.
For purposes of comparison, the drying test of this
example was repeated with 4 pounds of irregular sharp-edged
flaky grain taken from the conventional calcium hypochlorite
- manufacturing operations. Dehydration was continued to 1 per-
cent moisture. The recovered product was only 2.5 pounds.
Dust loss during drying was 20 percent of the weight of the
recovered product.
This comparison shows the high degree of integrity and
resistance to dusting that is inherent in the novel rounded
calcium hypochlorite particles of the invention which are not
characteristic of prior art calcium hypochlorite product.
- 59 -
-
: ' ' ' . ' . ., ' ' '. ,
'' , ~ ' ~" "; ',', ,"::
