CA1048868A - Granular calcium hypochlorite by spray graining - Google Patents

Granular calcium hypochlorite by spray graining

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Publication number
CA1048868A
CA1048868A CA74215289A CA215289A CA1048868A CA 1048868 A CA1048868 A CA 1048868A CA 74215289 A CA74215289 A CA 74215289A CA 215289 A CA215289 A CA 215289A CA 1048868 A CA1048868 A CA 1048868A
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Canada
Prior art keywords
particles
calcium hypochlorite
percent
slurry
water
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
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CA74215289A
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French (fr)
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CA215289S (en
Inventor
Walter C. Saeman
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Olin Corp
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Olin Corp
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    • CCHEMISTRY; METALLURGY
    • C01INORGANIC CHEMISTRY
    • C01BNON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B11/00Oxides or oxyacids of halogens; Salts thereof
    • C01B11/04Hypochlorous acid
    • C01B11/06Hypochlorites
    • C01B11/068Stabilisation by additives other than oxides, hydroxides, carbonates of alkali or alkaline-earth metals; Coating of particles; Shaping; Granulation
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01JCHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2/00Processes or devices for granulating materials, e.g. fertilisers in general; Rendering particulate materials free flowing in general, e.g. making them hydrophobic
    • B01J2/16Processes or devices for granulating materials, e.g. fertilisers in general; Rendering particulate materials free flowing in general, e.g. making them hydrophobic by suspending the powder material in a gas, e.g. in fluidised beds or as a falling curtain

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • Geology (AREA)
  • Inorganic Chemistry (AREA)
  • Glanulating (AREA)
  • Treatment Of Water By Oxidation Or Reduction (AREA)
  • Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
  • Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

Abstract

ABSTRACT OF THE DISCLOSURE
Granular calcium hypochlorite particles having a core of calcium hypochlorite encapsulated in a plurality of layers of calcium hypochlorite are produced from an aqueous slurry of calcium hypochlorite by spraying a pumpable and spray-able slurry of calcium hypochlorite particles onto suspended particles of solid calcium hypochlorite above a moving bed of said particles. The solid particles coated with the slurry are heated to simultaneously evaporate and remove water from the slurry whereby said particles are coated with a layer of solid calcium hypochlorite.
A portion of the moving bed of coated particles is removed from the spraying zone and further processed, if desired. In one embodiment the coated particles, with or without sizing, are dried to produce granular particles having the desired moisture content. In another embodiments, the withdrawn portion is conveyed to another spraying zone where the particles are coated with a slurry of calcium hypochlorite having a lower available chlorine content than the particles which form the core material. In another embodiment, the withdrawn portion of calcium hypochlorite particles is conveyed to another spraying zone where the particles are coated with a plurality of layers of an inorganic salt.
The resulting coated or layered granular particles of calcium hypochlorite have a high level of integrity and resist degradation and dusting when subjected to rather severe handling conditions. In addition, the novel granular calcium hypochlorite particles of this invention are highly stable when contacted with lighted cigarettes, organic materials and the like.

Description

~ ~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 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 , 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.

, : , 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.

:: ~
.' ~ ' ' , ~ .

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 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.

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 - : . - .
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,.
.

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, . . .

.

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 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 ;. . ' ' . : :, ': ' ' ' ' ' : :

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.

~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.

.

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:

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 -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 ~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 .

~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 B

-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 , ' ' . ~ . '~: . ' ' 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 , .

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 ~''' "

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-., - . ., .

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 , , 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 ~

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 -- - .
- ~ ... .

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.

~8868 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 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 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 1~48868 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.

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.

` - -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.

~ ~ , 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 .
, 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 .
', .' . ' : : ~ ' ' - ~ :' . ~ 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 .
~:
.

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.

-: ' ' ' . ' . ., ' ' '. , '' , ~ ' ~" "; ',', ,"::

Claims (10)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
1. Granular calcium hypochlorite particles (a) each of said particles having a smooth, rounded, surface of substantially spherical shape, having a ratio of maximum diameter to minimum diameter of about 1.5:1 or less, said particles being comprised of (1) a core of calcium hypochlorite which ranges in diameter from about 200 to about 2,000 microns, (2) encapsulated with a plurality of individual layers of calcium hypochlorite, (a) wherein the outside diameter of said layers ranges from about 400 to about 5,000 microns, (b) each of said layers being substan-tially free of sharp fragile edges, (b) the calcium hypochlorite content of said particles ranges from about 50 to about 85 percent by weight, and (c) the water content of said particles ranges from about 0.5 to about 10 percent by weight, and (d) said particles of calcium hypochlorite being derived from calcium hypochlorite dihydrate.
2. The calcium hypochlorite particles of claim 1 wherein the particle size of said calcium hypochlorite particles ranges from about 600 to about 2,000 microns.
3. The calcium hypochlorite particles of claim 2 wherein the calcium hypochlorite content of said particles ranges from about 60 to about 83 percent by weight and the water content of said particles ranges from about 1 to about 8 percent by weight.
4. A method for preparing particulate solid calcium hypochlorite having a smooth rounded surface from a pumpable and sprayable aqueous slurry of calcium hypochlorite which comprises:
(a) maintaining a moving bed of particulate solid calcium hypochlorite having a diameter from about 200 to about 2,000 microns and containing from about 5 to about 30 percent by weight of water in the lower part of a distributing zone having an upper part and a lower part, (b) maintaining a temperature in said dis-tributing zone in the range from about 40 to about 70°C., wherein a stream of gas inert to calcium hypochlorite at a temperature of from about 85°C to about 250°C is passed through said distributing zone to remove water vapors therefrom, (c) lifting a portion of said moving bed to said upper part and releasing said particles to separately fall through said distributing zone to said bed, (d) spraying on said falling particles a pumpable and sprayable aqueous slurry of calcium hypochlorite containing from about 45 to about 90 percent by weight of water, (e) simultaneously evaporating and removing water from said slurry on said falling particles whereby said particles are coated with a layer of solid calcium hypochlorite, and the water content is from about 5 to about 30 percent by weight, (f) removing at least a portion of the resulting coated rounded solid calcium hypochlorite particles from said dis-tributing zone, and (g) heating said portion of coated rounded particles to a temperature in the range from about 65° to about 100°C. until the water content thereof ranges from about 0.5 to about 10 percent by weight of water, and recovering from the dried calcium hypochlorite particles rounded granules of calcium hypochlorite having an outside diameter in the range from about 400 to about 5000 microns.
5. The method of claim 4 wherein said slurry contains from about 50 to about 60 percent by weight of water.
6. The method of claim 5 wherein said particles contain from about 15 to about 27 percent by weight of water.
7. The method of claim 6 wherein said temperature in said distributing zone is from about 45 to about 60°C.
8. The method of claim 7 wherein heat is introduced into said distributing zone by maintaining a portion of said particles in contact with a heated surface.
9. The method of claim 7 wherein at least a portion of said particles removed from said distributing zone is classified into a product fraction, and over-size fraction and an under-size fraction, said under-size fraction is returned to said distributing zone, said over-size fraction is crushed and reclassified, and said product fraction is recovered.
10. The method of claim 4 wherein a plurality of said distributing zones are maintained in series, said solid calcium hypochlorite from each of said distributing zones except the last is charged to the next distributing zone, spraying an aqueous slurry of calcium hypochlorite onto said particles in each of said distributing zones, and removing from the last of said distributing zones said solid calcium hypochlorite particles, and charging said particles from the last of said distributing zones to said drying zone.
CA74215289A 1974-11-06 1974-12-05 Granular calcium hypochlorite by spray graining Expired CA1048868A (en)

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CA1048868A true CA1048868A (en) 1979-02-20

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CA74215289A Expired CA1048868A (en) 1974-11-06 1974-12-05 Granular calcium hypochlorite by spray graining

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JP (1) JPS5154097A (en)
BE (1) BE835001A (en)
CA (1) CA1048868A (en)
DE (1) DE2457144C2 (en)
ES (1) ES432621A1 (en)
FR (1) FR2290394A1 (en)
IT (1) IT1032154B (en)
NL (1) NL175513C (en)
YU (1) YU30075A (en)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CA1067763A (en) * 1975-01-30 1979-12-11 Walter C. Saeman Granular calcium hypochlorite coated with an alkaline earth metal hypochlorite by spray graining
US4321924A (en) * 1980-05-12 1982-03-30 The Procter & Gamble Company Bordered disposable absorbent article
JPS5742589A (en) * 1980-08-23 1982-03-10 Denpatsu Fly Ash Dry granulation for manufacture of potassium silicate fertilizer
US8252200B2 (en) * 2005-12-01 2012-08-28 Arch Chemicals, Inc. Coated calcium hypochlorite composition
JP5643962B2 (en) * 2009-12-07 2014-12-24 日本曹達株式会社 Tablet manufacturing method

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3036013A (en) * 1959-02-16 1962-05-22 Olin Mathieson Coated calcium hypochlorite and process for making same
CA975531A (en) * 1971-06-07 1975-10-07 John P. Faust High test calcium hypochlorite

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JPS5418999B2 (en) 1979-07-11
AU7583574A (en) 1976-06-03
NL7512952A (en) 1976-05-10
BE835001A (en) 1976-04-29
DE2457144A1 (en) 1976-05-13
NL175513C (en) 1984-11-16
FR2290394A1 (en) 1976-06-04
IT1032154B (en) 1979-05-30
FR2290394B1 (en) 1978-05-05
ES432621A1 (en) 1977-02-16
JPS5154097A (en) 1976-05-12
NL175513B (en) 1984-06-18
DE2457144C2 (en) 1981-12-10
YU30075A (en) 1982-02-28

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