WO1991017951A1 - Turbine agglomerated calcium hypochlorite particle - Google Patents

Abstract

A feed material is obtained from mixing hypochlorous acid and a lime slurry: 2HOC1 + Ca (OH)2 ----> Ca (OC1)2.2H2O. The feed material is used to produce a hydrated calcium hypochlorite agglomerated particle that is produced in a turbine agglomerator and has a plurality of connecting links of recrystallized material bridging the small particles forming the agglomerate which has therein a plurality of pores created by the substantial evaporation of the layer of surface liquid. The surface tension and adhesion forced of the layer of surface liquid at least partially hold the agglomerated particle together prior to drying.

Description

TURBINE AGGLOMERATED

CALCIUM HYPOCHLORITE PARTICLE

This invention relates generally to a process for the manufacture of hydrated calcium hypochlorite. More specifically it is directed to the product particle produced by the use of a turbine agglomerator in a process to produce a highly porous fast dissolving calcium hypochlorite product having the available

chlorine derived from hypochlorous acid.

Calcium hypochlorite compositions have been commercially utilized for a number of years as bleaching and sanitizing agents in water bodies, particularly in the sanitation and disinfection of swimming pool

waters. Calcium hypochlorite's commercial appeal lies in the fact that it is a relatively stable and inexpensive solid oxidizing agent that uses its available chlorine to remove impurities and kill pathogenic organisms in water.

Calcium hypochlorite has been manuf actured or proposed for manufacture from lime and sodium hydroxide by a number of processes. The different processes are either directed to reducing waste materials from the process or to produce the best quality product that is contaminate free in the most cost effective manner.

In most of the proposed methods for commercially manufacturing calcium hypochlorite, a slurry is obtained containing crystals of calcium hypochlorite dihydrate in a concentrated aqueous solution of calcium hypochlorite and sodium chloride, or other inorganic halide. The slurry is then filtered to produce a cake containing from about 42 to about 48% by weight of water. When this cake is dried, a very light , porous cake is obtained which breaks down to an undesirable fine, dusty powder. The crystals in the cake lack natural cohesiveness. The filter cake can then be compressed, but the compressed cake, although harder, fragments into flaky granules with fragile edges. These granules are easily abraded and form an unsatisfactory dusty

product. Alternately, the wet cake is partially dried, then compressed into a sheet between heavy rolls and further dried.

An alternate approach is the process of preparing calcium hypochlorite particles by admixing the wet cake of calcium hypochlorite in a cutting type mixer with dry fines in sufficient proportion to decrease the water content from the approximate 42 to about 48% by weight level down to a level of about 20 to about 30% by weight. Water is not evaporated during the mixing step, but rather the moist particles are dried in a separate step under carefully controlled conditions to avoid substantial crushing of the material. Compression pressures on the granules are less in this type of a mixer than with the aforementioned roll type of a mixer than with the aforementioned roll type of production. Therefore the mixer produced granules are softer. However, the granular particles so produced are not strong enough to resist dusting when subjected to severe handling conditions. In other techniques similar to this mixing technique, excessive dusting also has been a problem.

In all of the above-described calcium hypochlorite granulation techniques, drying is accomplished under generally gently handling conditions in devices such as a belt dryer or a tray type of dryer. A belt or tray type of dryer is used to minimize dust formation and dust entrainment in the drying atmosphere. Thermal degradation is a problem in these type of dryers, however, because the drying rates are relatively slow and calcium hypochlorite is thermally sensitive. An alternate approach has been developed through the use of a spray graining technique to produce product granules. Generally, the spray-graining technique employs the spraying and drying of calcium hypochlorite slurries to avoid filtration and drying problems. This technique also minimizes the loss of calcium hypochlorite due to thermal degradation by reducing the required drying time. A key consideration in this technique is the fact that calcium hypochlorite is susceptible to rapid chemical decomposition in the presence of moisture at temperatures only slightly above ambient room temperatures. The thermal stability of calcium hypochlorite improves as the water content is reduced. Spray graining techniques have been perfected to produce granular calcium hypochlorite particles with layers of calcium hypochlorite encapsulated in a smooth rounded granule. However, the apparatus necessary to produce these granules in a fluidized bed or rolling bed dryer, as well as the necessary careful control of conditions, have made this a costly technique. Also, the use of a rotary drum results in the buildup of moist materials on the inner drum walls that requires labor intensive scraping of the walls to remove.

Further, the techniques adopted to produce calcium hypochlorite have not necessarily led to the production of a durable granule of a particular size and shape that dissolves quickly in water. Dust produced from the recycling of particles during the manufacturing process normally must be compacted. These compacted particles are normally dense. These and other particles cannot dissolve completely when the granules are distributed on the surface of a swimming pool. Undissolved residue in pools is undesirable in calcium hypochlorite product, being aesthetically displeasing and possibly leading to the bleaching out of the color in pool liners when the residue settles on the bottoms of the pools. Further, the highly corrosive nature of calcium hypochlorite takes its toll on the apparatus employed in its production. Where pressure or preform rollers and granulators are employed, costly regular replacement or repair of the equipment must be accomplished every year or two since rapid oxidation of the exposed metallic parts occurs. The preform rollers press the partially dried and filtered cake into thick sheets at high pressures, for example up to 1000 pounds per square inch. The pressed sheets are then fed into the granulators where the sheets are broken up into small particles by rotary blades forcing the product through screens of predetermined size to create more surface area for drying. These screens and blades are

especially susceptible to corrosion.

Other costly handling equipment, such as elevators and conveyors, must be used to transport the filtered cake and crushed particles to, between, and away from the compressive and granulating apparatus.

These and other problems are solved in the application of the process to produce the agglomerated product particle comprising the present invention.

It is an object of the present invention to provide a fast dissolving calcium hypochlorite product.

It is another object of the present invention to provide a highly porous calcium hypochlorite product.

It is a feature of the product of the present invention that the product is produced by a process that utilizes a concentrated hypochlorous acid solution that is reacted with a lime slurry to produce a slurry of calcium dihydrate cake that is fed to a turbine agglomerator upstream of the final dryer and downstream of a separation device through which the slurry or paste used to manufacture the calcium hypochlorite passes.

It is another feature of the product of the present invention that feed material is centrifugally rotated and axially transported through the drum of a turbine agglomerator, being broken up and crushed by a shearing action and agglomerated into final product particles of desired size and moisture by the control of the layer of surface liquid such that the surface liquid comprises at least about 10 to about 26% of the particle weight before drying.

It is yet another feature of the product of the present invention that feed material is centrifugally rotated and axially transported through the drum of a turbine agglomerator, being crushed and broken into particles by a shearing action and agglomerated into final product particles of desired sizes, the final agglomerated product particles being formed from smaller particles or crystals that are interconnected by bridges or connecting links of calcium hypochlorite after drying.

It is another feature of the product of the present invention that fast dissolving, highly porous agglomerated product particles having a specific gravity of less than about 2.0 grams per milliliter as measured by displacement bulk density, and preferably less than about 1.95 grams per milliliter, are produced.

It is still another feature of the product of the present invention that the bulk density of the

agglomerated product particles as measured by mercury porosimetry is less than about 1.35 grams per milliliter.

It is an advantage of the present invention that a fast dissolving product with high porosity is obtained so that substantially no undissolved residue remains in pool water and no bleaching out of pool liners on the bottoms of pools occurs.

It is another advantage of the present invention that the apparatus employed to make the product by the instant process requires less maintenance than the

equipment traditionally employed in commercial processes. It is still another advantage of the present invention that the product is produced with lower power costs and a resulting lower evaporative load from the use of more energy efficient equipment in a more

efficient process.

It is yet another advantage of the present invention that more on-size final product particles are obtained from a dryer than in the traditionally employed prior commercial processes.

These and other objects, features and advantages are obtained in a porous agglomerated product particle of hydrated calcium hypochlorite produced from hypochlorous acid with a fast dissolving rate produced by employing a turbine agglomerator upstream of the final dryer.

The advantages of this invention will become apparent upon consideration of the following detailed disclosure of the invention, especially when it is taken in conjunction with the accompanying drawings wherein:

FIGURE 1 is a diagrammatic illustration of the process employed to make the product hydrated calcium hypochlorite;

FIGURE 2 is a diagrammatic illustration of an alternate process that may be used to make hydrated calcium hypochlorite;

FIGURE 3 is a diagrammatic illustration of a second alternate process that may be employed to produce hydrated calcium hypochlorite;

FIGURE 4 is a graphic illustration of the

dissolving rates of different size particles of calcium hypochlorite produced by different manufacturing processes;

FIGURE 5 is a graphic illustration of the dissolving rate of hydrated calcium hypochlorite

particles screened to a 25-30 mesh size compared to particle density; FIGURE 6 is a diagrammatic illustration of the location of the moisture addition with respect to the paddles in a turbine agglomerator;

FIGURE 7 is a sectional vie taken along the lines 7-7 of FIGURE 6 showing diagrammatically the positioning of the paddles and the moisture addition in a turbine agglomerator;

FIGURE 8 is a scanning electron photomicrograph with a magnification factor of 72 of hydrated calcium hypochlorite agglomerated particles produced by a representative process employing a turbine agglomerator;

FIGURE 9 is a scanning electron photomicrograph with a magnification factor of 2400 of hydrated calcium hypochlorite agglomerated particles produced by a

representative process employing a turbine agglomerator;

FIGURE 10 is a scanning electron photomicrograph with a magnification factor of 72 of hydrated calcium hypochlorite particles produced by a typical commercial process employing preform compression rollers, a

granulator and a tray dryer;

FIGURE 11 is a scanning electron photomicrograph with a magnification factor of 2400 of hydrated calcium hypochlorite particles produced by a typical commercial process employing preform compression rollers, a

granulator and a tray dryer;

FIGURE 12 is a scanning electron photomicrograph with a magnification factor of 72 of compacted dust or fines of hydrated calcium hypochlorite particles produced by a typical commercial process employing

preform compression rollers, a granulator and a tray dryer, where the dust or fines have been compacted, crushed and screened according to size;

FIGURE 13 is a scanning electron photomicrograph with a magnification factor of 2700 of compacted dust or fines of hydrated calcium hypochlorite particles produced by a typical commercial process employing preform compression rollers, a granulator and a tray dryer, where the dust or fines have been compacted, crushed and screened according to size;

FIGURE 14 is a scanning electron photomicrograph with a magnification factor of 77 of hydrated calcium hypochlorite particles produced by a spray graining process in a rolling bed agglomerator;

FIGURE 15 is a scanning electron photomicrograph with a magnification factor of 2700 of hydrated calcium hypochlorite particles produced by a spray graining process in a rolling bed agglomerator;

FIGURE 16 is a diagrammatical illustration of an agglomerated particle of calcium hypochlorite produced by a turbine agglomerator showing individual particles bound together by the liquid film layer;

FIGURE 17 is an enlarged diagrammatical illustration of the junction of two individual particles in the agglomerated particle of calcium hypochlorite shown in FIGURE 16 where the individual particles are bound together by a layer of liquid film; and

FIGURE 18 is an enlarged diagrammatical illustration of the junction shown in FIGURE 17 after the particle has been dried and the liquid film layer has recrystallized, showing the connecting bridges or links of calcium hypochlorite joining together the individual particles.

Hydrated calcium hypochlorite comprises calcium hypochlorite, Ca(OCl)₂, compositions having a water content in the range of from about 0.1 to about 15% by weight, and an available chlorine concentration of at least about 55%. The novel process of the present invention produces high purity agglomerated hydrated calcium hypochlorite granules by reacting a lime slurry with a hypochlorous acid solution containing from about 35 to about 60 percent by weight of HOCl to produce a slurry of calcium hypochlorite dihydrate crystals substantially free of alkali metal ions and having a calcium chloride concentration of less than about 4 percent by weight and then feeding that slurry to a turbine agglomerator.

The agglomerated hydrated calcium hypochlorite granules are produced by agglomeration in which agitation is employed. The agitation employed in this specific process is obtained by the use of a turbine agglomerator. This is apparatus that has a plurality of paddles mounted about a rotating shaft that extends axially through the turbine to mechanically blend moist feed particles and dry feed particles or feed particles and an agglomerating fluid. The paddles are arrayed in sets of generally four about the shaft, as seen in FIGURE 7. The paddles 11 engage the feed material as they turn with the shaft 12 to centrifugally rotate the feed material and axially transport it through the drum 14 while achieving a shearing action which breaks up large clumps of the feed material. These paddles 11 also can compact the feed material.

The feed material derived from hypochlorous acid as the starting material for the chlorine used in the

process to produce hydrated calcium hypochlorite can generally be stated to consist of calcium hypochlorite, water, sodium chloride and calcium salts selected from the group consisting of calcium chloride, calcium chlorate, calcium carbonate, and calcium hydroxide. A typical preferred analysis range for the dry calcium hypochlorite feed to the turbine agglomerator consists of about 73-90% calcium hypochlorite, about 1.3% calcium chloride, about 1.5-4% calcium chlorate, about 3.0-7.0% calcium hydroxide, about 1.0-2.0% calcium carbonate, less than 1% sodium chloride and about 3-20% water. More specifically the process to produce the calcium hypochlorite feed for the turbine agglomerator in the process of the present invention employs as one reactant a concentrated hypochlorous acid solution containing at least 35 percent by weight of HOCl. One method of producing these high purity concentrated HOCl solutions is that in which gaseous mixtures, having high concentrations of hypochlorous acid vapors and dichlorine monoxide gas and controlled amounts of water vapor, are condensed at temperatures in the range of from about -5°C to about +20°C and preferably from about 0°C to about +10°C to produce the concentrated hypochlorous acid solutions. These solutions are substantially free of ionic impurities such as chloride ions, chlorate ions, and alkali metal ions and have low concentrations of dissolved chlorine. For example, concentrations of the chloride ion are less than about 50 parts per million; the alkali metal ion concentration is less than about 50 parts per million; and the

chlorate ion concentration is no more than about 100 parts per million. The dissolved chlorine concentration in the hypochlorous acid solution is less than about 2 percent, and preferably less than about 1 percent by weight.

The gaseous mixtures having high concentrations of hypochlorous acid vapors and dichlorine monoxide gas and controlled amounts of water vapor may also contain varying amounts of chlorine gas. The gaseous impurities can be produced, for example, by the process described by J. P. Brennan et al in the U.S. Patent No. 4,147,761. Prior to condensing the gaseous mixtures, the gaseous mixture may be passed through a separation means to remove any solid particles, such as alkali metal chloride particles, which may be entrained. The condensation of the gaseous mixture is operated at autogenous pressures for the temperatures employed. The concentrated hypochlorous acid is initially reacted with lime. The lime employed can be any suitable lime having an active lime content of from about 85 to about 99, and preferably from about 90 to about 98 percent, where active lime is defined as the weight percent of Ca(OH)₂ in the lime. The lime employed usually contains impurities such as iron compounds, silica, aluminum salts, magnesium salts, manganese, unburned limestone (calcium carbonate and magnesium carbonate) and other compounds in trace quantities. These impurities represent from about 1 to about 15, and preferably from about 2 to about 8 percent by weight of the lime. More preferred are limes having low concentrations of heavy metal compounds such as those of iron and manganese.

A slurry of neutral calcium hypochlorite dihydrate crystals is produced in the reaction which is expressed by the equation:

2HOCl+Ca(OH)₂ --------> Ca(OCl)₂ • 2H₂O The slurry of calcium hypochlorite dihydrate solids is suspended in an aqueous solution of calcium hypochlorite.

The reaction between the concentrated hypochlorous acid solution and the lime slurry is carried out at a temperature in the range of from about 15° to about

40°C and preferably from about 25° to about 35°C. As the hypochlorous acid solution is produced at a temperature below about 10°C its use provides a portion of the cooling required for this exothermic reaction.

While the process of the present invention may be conducted batchwise, it is preferably operated with the hypochlorous acid solution and a slurry of lime, dibasic calcium hypochlorite or mixtures thereof, being charged continuously to the reactor. The rate of addition of reactants provides the reaction mixture with a slurry having a suspended solids concentration in the range of from about 5 to about 30 percent. A slurry of neutral calcium dihydrate crystals is continuously recovered from the reaction mixture. The slurry may be fed directly to a dryer; however, in a preferred embodiment, it is concentrated by removal of a mother liquor. Any suitable solid-liquid separation method may be used including filtration and centrifugation.

The moist cake formed during the separation is generally dried and fed to the turbine agglomerator as the feed material. The moist cake, or the slurry in the case of the use of a spray dryer, is dried by known means, for example, using a spray dryer, turbo dryer, louver dryer or vacuum dryer where the appropriate temperature ranges are employed to reduce the water content to the desired level.

The moist cake contains, on a dry basis, an available chlorine concentration of at least 55 percent by weight, is substantially free of alkali metal ions, and has a calcium chloride concentration of less than about 4 percent, preferably less than about 3 percent, and more preferably less than about 2.5 percent by weight.

Following drying, the hydrated granular calcium hypochlorite product contains on a dry basis, preferably at least 80, and more preferably from about 85 to about 95 percent by weight of Ca(OCl)₂. The hydrated calcium hypochlorite has a water content in the range of about 1 to about 12, preferably about 4 to about 12, and more preferably from about 5 to about 10 percent by weight. Anhydrous product will have a water content of about 1 to about 4 and, more preferably, about 1 to about 2 percent by weight water. The high purity calcium hypochlorite product produced by this process is substantially free of alkali metal chlorides and

contains less than about 4 percent, preferably less than about 3 percent, and more preferably less than about 2.5 percent by weight of calcium chloride. The mother liquor recovered from the separation of the calcium hypochlorite dihydrate crystals is a concentrated solution containing at least 15 percent, and normally from about 20 to about 25 percent by weight of Ca(OCl)₂. This concentrated calcium hypochlorite solution having very low concentrations of impurities may be used or sold as a bleach solution. In a preferred embodiment it is used in the preparation of the lime slurry to minimize the amount of water added to the process. Admixing the calcium hypochlorite mother liquor with fresh lime produces dibasic calcium hypochlorite in a reaction represented by the following equation:

Ca(OCl)₂+2Ca(OH)₂ ---> Ca(OCl)₂ • 2Ca(OH)₂ The reaction is carried out in a reactor equipped with an agitator at ambient temperatures.

The slurry form comprised of dibasic calcium hypochlorite crystals is fed to the hypochlorinator for reaction with the concentrated hypochlorous acid

solution to produce neutral calcium hypochlorite crystals as discussed above.

An agglomerated hydrated calcium hypochlorite granule of the instant process is produced from this above described feed material by the agglomeration of small crystals or particles into an aggregate or larger particle of much greater porosity and much larger pores, or interstitial spacing, and surface deformation than is achieved with previous commercial processes. These fine particles, which typically are less than 40 mesh (less than 425 microns), are agglomerated in the turbine agglomerator or mixer 10 of FIGURE 6. The turbine agglomerator 10 rotates at a fast enough rate to crush oversized feed particles to the proper or desired feed size of less than 40 mesh before the agglomeration zone, which is defined generally as the area in the drum 14 that is downstream of the point of water or liquid addition. The intense agitation caused by the rotation of the paddles in the agglomerator 10 also prevents overly large agglomerates from being formed. The final agglomerated product gives the appearance of an

aggregate of smaller rounded particles or in some instances displays layering on the individual particle. This lack of excessively oversized particles is significant for the ease and efficiency of the operation by minimizing the number of separate operational steps required in the process and, therefore, reducing the physical space, size and resulting cost of the apparatus necessary to employ the subject process.

Agglomeration by the instant process is achieved by providing the proper amount of binder to, in essence, glue the small, individual particles together in a manner that will be described in further detail hereafter. One method successfully employed to provide the proper amount of binder is to feed an overly wet mass of particles, such as particles of greater than 31% water by weight, to the turbine agglomerator while simultaneously blending dust or fines particles of less than 28% water by weight to achieve a final agglomerated particle with a discharge moisture of between about 19% to about 32%, preferably of between about 25% to about 31% and optimally of between about 28% and about 31% water by weight.

Another agglomeration method is to feed dry material with less than about 28% water by weight and blend in moisture in the form of water or other suitable solution or slurry into the turbine agglomerator to achieve the final desired agglomerated product having a moisture content of between about 19% to about 32%, preferably of between about 25% to about 31% and optimally of between about 28 to about 31% by weight. Still another method is to mill a material with about 28 to about 31% moisture by weight in the turbine agglomerator until an agglomerated particle of proper size and porosity is obtained.

Where the feed material is obtained from the

aforedescribed mixing of lime and hypochlorous acid, the feed material after drying contains from about 1 to about 12 percent by weight water, more preferably about 1 to about 8 percent, and optimally about 1 to about 5 percent. The feed material contains from about 75 to about 90 percent calcium hypochlorite and more preferably from about 85 to about 90 percent. The remainder of the feed material includes some very small amount of sodium chloride up to about 1 percent and calcium salts selected from the group consisting of calcium chloride calcium chlorate, calcium carbonate and calcium hydroxide. Once passed through the turbine agglomerator, the agglomerated particles will have a moisture content of about 5 to about 31 percent by weight, more preferably about 5 to about 15 percent, and optimally about 10 to about 15 percent before drying. After drying in a fluid bed dryer, the agglomerated particle has a moisture content of from about 1 to about 12 percent by weight, more preferably from about 5.5 to about 10.5 percent and optimally about 8.5 to about 10.5 percent.

The discharge products of turbine agglomerator 10 are dried to the desired moisture in an appropriate dryer, such as a tray dryer, a belt dryer, a fluid bed dryer or an energy efficient type of dryer. The dried agglomerated particles are then classified to the proper product size. Undersized and/or oversized material can be recycled into the turbine agglomerator for re-agglomeration to minimize additional compacting and crushing steps. Suitable particle sizes include those in the range from about 800 microns (20 mesh) to about 150 microns (100 mesh) and, preferably from about 800 microns (20 mesh) to about 300 microns (50 mesh). The final product particles have a displaced bulk density which is at least about 1.0 grams per milliliter and, preferably, in the range from about 1.0 to about 2.0 grams per milliliter. An alternate way of expressing the density is in terms of loose packed bulk density which includes the void spaces with air in the bulk density measurement. The loose packed bulk density of this product derived from the hypochlorous acid and lime slurry mixture is about 0.45 to about 1.0 grams per milliliter and preferably about 0.6 to about 0.8 grams per milliliter.

Particles produced in a turbine agglomerator in the instant process dissolve considerably faster than those produced from other conventional processes, as reflected in FIGURE 4. This faster dissolvability is the result of several factors.

This graph reflects the fact that agglomerated product particles with an available chlorine content obtained from hypochlorous acid at the larger particle mesh sizes or sieve cuts of 20-25 and 25-30, dissolve significantly faster at each size than product formed from a process employing preforming rolls and a

granulator. The graph in FIGURE 4 represents the percentage of product particles that dissolve in a tank that is filled with four feet of water and maintained at a water temperature at about 76°F. The predetermined quantity of the calcium hypochlorite particles, such as a 5 gram sample, is poured or scattered on the surface of the water. After one minute, testing is done by sampling to determine from top to bottom the undissolved particles. This graph reflects that the turbine agglomerated product between about 25-30 mesh size dissolved in one minute or less greater than 75% of the time when placed on the surface of the water. The particle bulk density measured by volume displacement in a suitable inert liquid, as described hereafter, correlates with the dissolving rate, regardless of the process used to produce the

particles. It was determined during testing that this dissolving rate is a direct function of the particle size, the degree of compaction of the material forming each particle, and the shape of the product particles. To achieve a rapidly dissolving product, it has been determined that the density of 25-30 mesh size particles should be about 2.0 grams per milliliter and preferably less than about 1.95 grams milliliter using saturated aqueous solutions of calcium hypochlorite as the inert liquid in determining the particle displacement bulk density. Turbine agglomerated particles produced, for example, in an 8 inch diameter turbine agglomerator appear to consistently dissolve faster than product produced by other processes, such as preform rolled and granulated, crushed preform rolled and granulated, or dust compacted processes.

Although final particle size and dissolving rates may vary, it appears that adhesion and surface tension of the liquid film formed on the individual hydrated calcium hypochlorite particles may be the key to

achieving agglomeration. The adhesion of the liquid film holds the individual particles of crystals together in a moist agglomerate. The thickness of the liquid film or surface moisture layer between the individual particles or crystals before exposing the agglomerated calcium hypochlorite particles to drying is determined by surface tension. It appears that surface moisture, or the thickness of the liquid film between the individual particles forming the agglomerate, rather than the composite moisture of the total agglomerate, is instrumental in forming a fast dissolving product. It is theorized that a relatively thick surface moisture layer is needed to properly agglomerate dust and other small particles on the surface of the agglomerated particle to achieve a fast dissolving particle with a lower density. The dust and other small particles are held together in spaced relationship by the adhesion and surface tension forces, respectively, which are created by the layer of surface liquid present. It is the distance between the spaced apart small particles in the agglomerated particle and the distances between the larger individual particles or crystals that are part of the agglomerates which have a substantial impact on the final particle density and dissolving rate after drying.

The layer of surface liquid should be at least about 10 to about 26% of the particle weight of the agglomerate before drying to minimize density, while still maintaining small particle sizes. Surface liquid layers above 26% of the particle weight can produce agglomerates that are fast dissolving, but there will be oversized agglomerates. This surface liquid layer results from liquid that is either already present in the material to be agglomerated or from liquid that is added to the material through an appropriate liquid inlet in the turbine agglomerator.

A process employing preform pressure rolls squeezes more moisture from between the crystals and thereby causes a much denser particle, which sinks more rapidly and dissolves more slowly in a body of water. Particles formed by rotary drum agglomeration appear to be

moderately denser, therefore sinking more rapidly and dissolving more slowly than turbine agglomerated particles. In contrast, a turbine agglomeration process produces faster dissolving particles than either preform pressure roll or rotary drum agglomeration processes.

The thickness of the surface layer of liquid or the liquid film also appears to determine the final porosity of the agglomerate product. This final porosity is also directly correlated to the final dissolving rate of the product. The faster dissolving rate appears to result from the fact that the higher surface moisture found in turbine agglomerated particles spaces the dust and small particles farther apart during agglomeration and subsequent drying. This greater space reduces the amount of compaction or force applied to the particles and leaves the pores essentially intact and large after drying, since the moisture evaporates from within the particle. This same mechanism appears also to produce particles with greater surface deformation and, hence, greater exposed external particle surface area.

FIGURES 16-18 diagrammatically show the theory behind the functioning of this surface layer of liquid on the agglomerated particle. FIGURE 16 shows a turbine agglomerated particle 23 with the individual particles or crystals 24 of calcium hypochlorite held together by liquid film or surface layer 25. FIGURE 17 shows in enlarged fashion how this liquid film 25 serves as a binder between portions of two other particles. The adhesion and surface tension forces of this liquid film 25 holds dust and small particles 26 of calcium hypochlorite, as well as the larger individual particles 24, together in a moist agglomerated particle 23 seen in FIGURE 16 and, as explained above, increases its dissolving rate. FIGURE 18 diagrammatically illustrates how bridges or connecting links 27 remain between the individual particles 24 of calcium hypochlorite after the moist agglomerated particle 23 of FIGURE 16 is

dried, having substantially evaporated the surface layer of liquid film 25 of FIGURE 17 and having had recrystallization occur. The spaces between these connecting links 27 and the individual particles 24 form the pores 28 that promote faster dissolving.

FIGURE 5 shows the relationship of particle density after drying measured by bulk displacement versus the percentage of dissolved particles in a tank filled with four feet of water and tested for one particular particle size ranging from 25-30 mesh or about 710 to about 600 microns. In this test the particles' specific gravity or displacement bulk density was maintained less than about 2.0 grams per milliliter and preferably less than about 1.95 grams per milliliter to give the significant dissolving rate improvements achieved. It was found that the particles' density also increases gradually as particle size decreases because the smaller agglomerates approach the size of simple crystals which have a density of about 2.35 grams per milliliter for hydrated calcium hypochlorite.

The thick surface moisture or liquor layer before drying, as previously stated, is the key to forming a fast dissolving particle. Crystallization of the calcium hypochlorite and NaCl within the surface liquor forms the final bridges or connecting links between the individual particles that form the agglomerated product. The length of these bridges help determine the dried agglomerated particle density and dissolving rate.

As presented earlier, adhesion and surface tension forces between the individual particles are the key mechanisms in the agglomeration process before drying the particles. The individual particles are held

together in the agglomerated particle by these adhesion forces. Spacing between the small particles in the larger agglomerated particle is determined by the surface tension in the surface moisture layer. When sufficient surface tension is present between the

particles being agglomerated, the instant process permits dried dust to be agglomerated onto the particles with a water or appropriate solution mist. Too thin of a layer of surface liquid will result in more dense particles and also the creation of more dust because of lower particle integrity due to less binder, that is the layer of surface liquid, between the small individual particles of calcium hypochlorite. The dust particles hydrate gradually, sometimes sticking to the walls of the turbine agglomerator 10 of FIGURE 6. As the agglomeration process continues, the particles

agglomerate into beads large enough to resist sticking to the walls and the particles are easily then agglomerated into the final agglomerate product. These beads of agglomerated particles occur when the total water content is about 28% by weight for both water agglomeration and solution agglomeration, such as filter cake mother liquor, techniques. It is estimated that the surface liquid layer comprises at least about 10% by weight of this total water content.

Good agglomeration of fines or dust and good

dissolvability appears to be directly influenced by the water addition rate and the moisture of the feed particles sent into the turbine agglomerator. Moisture control also determines the size of the product particles. More on-size or particles of the proper or desired size range are obtained when moisture control is maintained at the desired level. The revolutions per minute (rpm) of the paddles on the rotatable shaft axially extending through the drum of the turbine agglomerator 10 of FIGURE 6 can affect the final

product's dissolvability performance. The production of a greater percentage of on-size product minimizes product handling loads and minimizes fines generation and compaction, as well as reducing the recycle, crushing, and compaction load during product

classification.

At 800 rpm paddle rotation in a 30 inch diameter turbine agglomerator, most of the feed, at about 26 to about 28% moisture by weight, into the turbine agglomerator 10 of FIGURE 6 becomes a moist powder

within the size range of about 70-100 mesh. A water addition rate of about 0.5 to about 0.8 gallons per minute ensures agglomeration of the powder into particles that are predominantly in the 20 to 50 mesh size range particles, where nonpowders are agglomerated, flow rates of up to about 1.6 gallons per minute at up to 2000 rpm have provided good final product particles. Final product particles of good dissolvability and density were also achieved at 400 and 600 rpm.

The turbine agglomerator 10 of FIGURE 6 functions both as a disintegrator and an agglomerator, even permitting control of agglomeration of particles of very small size. A shearing action exists within the agglomerator 10 from its inlet end to its outlet end which is controlled primarily by the rotational speed and angular orientation of the paddles 11 as they rotate about the shaft 12, best seen in FIGURE 7. The agglomerator 10 has a generally circularly shaped drum 14 inside of which paddles 11 rotate. A liquid inlet 15 protrudes through the drum 14 into the interior of the agglomerator 10. Progressive growth of product particles past the maximum size is controlled by the angle of the paddles 11, speed of rotation of the paddles 11, and the clearance between the sidewall of the drum 14 and the individual paddles 11. Agglomerated particles achieve the required shape and sufficient surface strength to remain a particle within a very short period of time, as short as about one second holdup or residence within the turbine agglomerator 10. The turbine agglomerated particles, therefore, are much smaller than standardly produced commercial particles and resist dusting because of sufficient surface strength and integrity.

The angle of paddles 19, 20 and 21 from the inlet end 16 to the outlet end 18 is shown in FIGURE 6. The inlet and outlet ports, 13 and 17, respectively are shown with arrows to diagrammatically illustrate the flow of material into and out of the turbine agglomerator 10. Shaft 12 has about eighteen sets of paddles mounted in four rows about the shaft 12. Approximately the first seven paddles 19 are angled forwardly at the angle seen in FIGURE 6 to axially convey or transport feed material, representatively of the composition shown in Table I earlier, into the drum 14 of the agglomerator 10. Thereafter a desired number of paddles 20 are positioned or oriented generally axially within the agglomerator 10 to breakup large clumps of calcium hypochlorite and compact the particles.

In a horizontally positioned agglomerator 10, paddles 20 would be angled so that their flat surfaces are generally horizontally positioned with respect to the ground. Similarly, in a vertically positioned agglomerator with the long axis of the drum 14 of the agglomerator positioned generally vertically, the paddles 20 would be angled so they have their flat surface oriented generally vertically with respect to the ground. The greater the number of axially oriented paddles 20, the greater will be the breaking up or crushing, agglomeration and compaction. More axially oriented paddles 20 also increase powder generation and re-agglomeration. At higher speeds or revolutions per minute, the greatest effect on the product particles appear to be the reduction of oversized particles and powder generation. Higher speed has a lesser effect on increasing or decreasing the dissolvability of particles.

Rather, the dissolvability of particles appears to be affected directly by the number of axially oriented paddles 20 employed. For example, in a 30 inch diameter turbine agglomerator at 600 rpm, four such paddles 20 in each row of paddles were the maximum employed where good crushing and agglomeration was achieved with minimal compaction. In contrast, at 800 rpm only two axially oriented paddles 20 in each row of paddles were required to achieve both good crushing and agglomeration with minimal compaction.

Downstream of the axially oriented paddles 20 are a second series of forwardly angled paddles 19', only one of which is shown, to convey the particles toward the outlet end 18 of the drum of the agglomerator, as illustrated in FIGURE 6. At least a single axially oriented paddle (not shown) may be employed over the outlet 17 of the agglomerator 10, depending upon the size of the outlet, to facilitate directing the particles out of the outlet.

The last paddle 21 can be angled toward the front or inlet end 16 of the agglomerator 10 to prevent the build up of material along the back wall adjacent outlet end 18. The use of the turbine agglomerator 10 in the process to produce hydrated calcium hypochlorite accomplishes substantial shearing action at the inlet end 16 to de-lump or otherwise breakup feed material and then maintains sufficient shear through the agglomerator 10 as the feed material is centrifugally rotated and axially transported to produce only small agglomerates of the desired size, porosity and density.

It has been found that the water addition through the liquid inlet 15 should be accomplished at a point downstream of the axially oriented paddles 20 to minimize the compression or compaction of the product particles that adversely affects the dissolvability of the final product. This positioning of the liquid inlet 15 is best illustrated in FIGURE 6. The water addition rate generally depends on the feed particle moisture level, but should be about 0.8 to about 0.6 gallons per minute at about 27% to about 28% water by weight feed particle moisture, respectively for a 30 inch turbine agglomerator 10. At this rate of water addition the feed moisture content of the particles going into the final dryer in the process will be raised by about two percentage points.

Water addition is instrumental in permitting

product dust or fines to be circulated into the agglomerator 10 and be successfully agglomerated into on-size particles. Prior processes typically have employed dust that has been generated by the disintegration of particles with insufficient surface liquid for agglomeration. The dust is typically compacted and recrushed. Product particles coming from a dust compactor are denser and dissolve more slowly than other hydrated calcium hypochlorite particles in a tank test with four feet of water. The use of the agglomerator 10 with a controlled water addition rate removes the need for fines compaction and, therefore, substantially increases the rapid dissolvability of the product particles.

The use of the turbine agglomerator 10 in existing hydrated calcium hypochlorite production processes can obviate the need to preform the filtered cake feed by the use of high pressure rolls. The removal of the need for the high pressure preform rolls and the granulators that are necessary to break up the filter cake can

greatly simplify the process.

Maintenance problems are also reduced substantially. Further, and perhaps most significantly, the removal of the need for preform rolls and granulators produces a product that is faster dissolving within the desired particle size range. As reflected in FIGURES 4 and 5, it is clearly seen that the product produced by turbine agglomeration is faster dissolving in a tank that is filled with four feet of water.

FIGURE 5 reflects the effect of density determined by displacement bulk density on the dissolving rate of the turbine agglomerated particles one minute after the particles were scattered on the surface of the water in the tank. The desired density is between about 1.0 grams per milliliter to less than about 2.0 grams per milliliter and preferably less than about 1.95 grams per milliliter. The portion of the graph in Area A represents turbine agglomerated particles. The second data point at about 1.91 g/ml represents turbine agglomerated product which was formed from a feed material with an inlet moisture of about 6%, which is too low. The portion of the graph in Area B represents particles formed by rolling bed agglomeration in which feed material which was either dry or premoistened was fed to an unflighted 12 inch rotary drum into which moisture was added. The portion of the graph in Area C represents particles formed by use of preforms rolls to compress the feed material and a granulator to break it up into smaller particles in the typical prior commercial processes.

The displacement bulk density of hydrated calcium hypochlorite particles is measured by a standard method, such as ASTM Method C493-70 (Standard Test Method for Bulk Density and Porosity of Granular Refractory Materials by Mercury Displacement), in which a liquid inert to calcium hypochlorite is substituted for mercury and the heating step to remove water of hydration is eliminated. Suitable inert liquids include saturated aqueous solutions of calcium hypochlorite and orthodichlorobenzene.

The measurement of displacement bulk density is generally described as follows:

A graduate is filled to an initial level with the inert liquid and the volume recorded. A sample of hydrated calcium hypochlorite particles is weighed and the weight recorded. The particles are gradually added to the graduate while gently stirring the slurry. After addition of the particle sample, the final volume is recorded. The displacement bulk density is calculated from the following formula:

Displacement

Bulk Density = Weight of Crushed particles (grams)

(g/Ml) Final Vol. (ml) - Initial Vol. (ml)

Particle porosity has a marked effect on the dissolving rate of product particles. This is related to the increased surface area of each particle and the exposure of more of each particle to water. The surface area is increased from two sources; increased surface deformation and internal gaps or pores within each agglomerated particle are also characterized by the aforementioned bridges or links that develop when the surface liquor is evaporated during drying. The porosity of the product particles and the sizes of the pores can be measured in a mercury intrusion porosimeter, such as a Model 9200 Autopore manufactured by Micromeritics. Hydrated calcium hypochlorite

particles produced by the compressive techniques of preformed or pressure roll processes currently commercially employed, as well as particles produced by rolling bed or spray graining and turbine agglomeration techniques, can be measured by this device.

Mercury intrusion porosimetry functions by first evacuating a particulate sample and then back filling the particle with mercury under pressures up to 60,000 pounds per square inch. This high pressure must be used to squeeze mercury into the pores since the mercury has a negative contact angle and will resist intrusion into such pores in the hydrated calcium hypochlorite particles.

The amount of pressure and accurate measurements of the volume of mercury utilized give the number of pores of each size in the particulate sample. Bulk densities measured by mercury intrusion porosimetry tend to be lower than that measured by the displacement bulk density method because of the relative resistance of the mercury to intrusion. It has generally been observed that the filter cake mother liquor used in the hydrated calcium hypochlorite production processes described herein in a displacement bulk density test fills about 50 to about 95% of the volume of the surface deformities and pores which are not filled by mercury in a mercury intrusion porosimetry test method to determine bulk density.

The following table shows the effect of increased surface deformation and porosity measured by mercury intrusion porosimetry on the dissolving rate of four hydrated calcium hypochlorite samples produced from feed pastes of the same composition as previously described by a conventional pressure or preform roll/granulation commercial process, a pressure or preform roll/ granulation process with the product crushed prior to dissolving, a rolling bed agglomeration process and a process of the instant invention employing turbine agglomeration. Samples between 25-30 mesh sizing were scattered on the surface of a tank filled with four feet of water and the amount dissolved after one minute was recorded. Reflecting the porosity of the particles, the desired surface deformation of turbine agglomerates measured by mercury intrusion porosimetry is greater than about 26% to about 32%. The bulk density of turbine agglomerates measured by the same method is preferably less than about 1.39 grams per milliliter and greater than about 1.0 grams per milliliter. t

I

Agglomerated particles produced by the novel process of the present invention rapidly dissolve in water bodies, such as swimming pools, while leaving a minimal amount of undissolved residue materials on the pool bottom or walls. The agglomerated particles dissolve significantly faster than irregularly shaped non-agglomerated calcium hypochlorite particles produced by known commercial processes employing particle formation by compressive techniques, such as pressure or preform rolling.

The process shown in FIGURE 1 is exemplary of the type of process that can employ a turbine agglomerator in lieu of pressure or preform rollers and granulators. In this process a calcium hypochlorite cake of the alternate composition discussed earlier for an expression filter is made from paste and fed through a suitable separation device, such as a centrifuge or expression filter to reduce the water content to about 30 to about 40% by weight. The filtered cake is then fed to an appropriate crusher, if needed, which breaks up the cake to a size and texture suitable for feeding into a turbine agglomerator. A turbine agglomerator in many cases can accomplish the needed crushing of the feed material, obviating the need for a crusher

depending upon the size, moisture and hardness of the feed material.

Water or an aqueous solution is fed into a turbine agglomerator, for example, 30 inch diameter at a desired rate, normally from about 0.0 gallons per minute where no liquid is added because of the excessive moisture of the feed material to about 0.8 gallons per minute for a feed material comprised of both dust and crushed cake, the mixture discharged from the agglomerator having about a 28 to 31% by weight water content and a feed rate of the dust and crushed cake of about 8500 pounds wet basis per hour. The feed of the crushed cake per unit of time up to the capacity of the turbine agglomerator is primarily limited by the drying capacity of the final dryer. The agglomerated particles are then fed to a mechanically gentle dryer, such as a tray dryer, for final drying to a water content of less than about 10% by weight, but preferably from about 8.5% to about 5.5% by weight. The dryer temperature is maintained from about 280°F to about 320°F and can be as high as about 350°F, employing a residence time of about 2 hours. Screens are employed to size the product particles to the desired size, normally 20-50 mesh. Oversized and undersized product particles are fed back into the process immediately upstream of the size

reducer or crusher. Dust and fines from other areas in the production process are also recycled into the process at this point.

The process outlined according to FIGURE 1 produces a faster dissolving product from a cake of hydrated calcium hypochlorite that has been treated by high expression filters than do prior commercial processes, whether employing high expression filters or not.

FIGURE 2 shows an alternate process where a normal filter can be used to receive a hydrated calcium

hypochlorite paste of the type used to form the cake of the composition discussed earlier. The paste is sent through a suitable separation device, such as a filter to produce a cake with about a 43 to a 47% moisture content. The filtered cake may be blended with recycled dust and then is sent to a louvered dryer with a temperature of about 280°F to about 320°F or as high as about 350°F at the inlet and a residence time of about 50 minutes. The dried discharge, with about 25% to about 30% water, is fed directly into the inlet 13 in a turbine agglomerator 10 where water via the inlet 15 is added at a predetermined rate immediately before the second set of angled paddles 19' and after the last of the generally axially oriented paddles 20 of FIGURE 6. This predried product encounters the rotating paddles of the turbine agglomerator which is operated at about 800 rpm per minute in a 30 inch diameter drum. If an eight inch turbine agglomerator is utilized, the paddles are rotated at 1800 rpm. The agglomerated product is then sent to a mechanically gentle dryer, such as a tray dryer, where it is dried for two hours with an inlet temperature of about 280°F to about 320°F or as high as 350°F. The product exits the dryer with a moisture content of less than about 10% by weight and preferably of about 6.5% moisture by weight. The dried product is then classified according to size and off-size product is recycled through a crusher and then reclassified. Fines are sent through a compactor and crusher and then recycled through product classification.

A second alternate process employing high pressure expression filters is shown in FIGURE 3 wherein a calcium hypochlorite paste used to form a cake of an alternate composition discussed earlier is fed into the expression filter to reduce the moisture of the paste down to the level described in the process of FIGURE 1. The paste or cake is fed directly to turbine agglomerator 10 of FIGURE 6 with or without mixing of dry dust material. The turbine agglomerated product exits the agglomerator with a moisture of about 28 to about 31% by weight and is fed to an energy efficient dryer, such as a fluid bed dryer with a uniform temperature ranging from about 235°F to about 265°F and a residence time of about 30 minutes. This type of a fluid bed dryer is characterized by a good heat transfer coefficient between the product particles and the air because of the higher velocity of the air with respect to the particles. The final dried particles have a water content of less than about 10% by weight and preferably from about 8.5% to about 5.5% by weight. The dried particles are then fed to a product classifier, such as screens, where on-size product is removed and off-size product is recycled back through a crusher and reclassified or returned to the agglomerator. Fines are recycled back into the turbine agglomerator.

The following examples are presented to illustrate the novel process of the present invention without any intention of being limited thereby. All parts and percentages are by weight unless otherwise specified.

EXAMPLE 1

A gaseous mixture containing an average concentration of about 27.5 parts by weight of dichlorine monoxide, about 61.3 parts by weight of

Cl₂, about 6.5 parts by weight of oxygen and about 4.7 parts by weight of water vapor was passed through a baghouse separator to remove any entrained particles of alkali metal chloride. The solid-free gaseous mixture at a temperature of about 85-90°C was passed through a vertical shell and tube heat exchanger maintained at a temperature of about 0°C and a pressure of about 3-4 torr gauge to condense a portion of the dichlorine monoxide and substantially all of the water vapor to produce an aqueous hypochlorous acid solution containing about 40 to about 55 percent by weight of HOCl. The hypochlorous acid solution had a pH of about 1 and the dissolved chlorine concentration was determined to be about 1 pprcent by weight.

The concentrated hypochlorous acid solution was continuously added to a hypochlorinator reactor at a rate of about 113 parts per hour. Also added to the reactor was a slurry of dibasic calcium hypochlorite at a rate of 373 parts per hour. The reaction mixture was agitated and maintained at a temperature of about 30°C. A slurry of calcium hypochlorite dihydrate having about 40 percent by weight Ca(OCl)₂ and about 57 percent by weight water was produced and was conveyed to a spray dryer to produce a granular product having a Ca(OCl)₂ content of about 8.6 percent by weight and a water content of about 4 percent by weight. The balance of the granular product consisted of calcium salts selected from the group consisting of CaCl₂, Ca(ClO₃)₂, Ca(OH)₂, and CaCO₃, and less than about 1 percent by weight NaCl.

The dry granular calcium hypochlorite was fed into a turbine agglomerator which had 19 flat-faced paddles arranged in a helix pattern which were rotated at about 2000 rpm. The paddles were alternately arranged in a forward conveying position for the first three paddles, a flat-faced non-conveying position for the next seven, a forward conveying position for the next five and a flat-faced non-conveying position for the last four paddles to discharge the material. Water was added to the agglomerator adjacent the first of the first set of flat non-conveying paddles at a rate of about 1.1 pounds per minute.

Well formed agglomerates of about 13 percent moisture were produced and then dried in a fluid bed dryer that was operated with about 190°C drying air blown into the fluid bed. The bed depth was about 15 inches. The dried material was screened to the desired mesh sizes of to determine onsize and offsize particles. The onsized material was removed as desired product and the offsized material was recycled back to the turbine agglomerator. The particles were dried to about 8.9 percent water content and about 81.8 percent Ca(OCl)₂. The dry particle size distribution was about 2.6 percent greater than 20 mesh, about 91.5 percent between 20 and 70 mesh, and about 0.3 percent smaller than 70 mesh. The loose packed bulk density of the dried particles was about 0.70 grams per cubic centimeter.

The turbine agglomerator produced product dissolved significantly faster than the preform/granulator product between mesh sizes of 20 to about 35. A 5 gram sample of the product was scattered on the surface of a 55 liter tank filled with four feet of water maintained at a temperature of 76° C and was found to dissolve about 92 percent of the available chlorine in one minute, via the use of a volumetric titration analysis procedure.

After one minute a small amount of liquid up to 2 percent of the liquid volume and the undissolved calcium hypochlorite particles left on the cone-shaped bottom of the tank, was withdrawn and discarded. The remaining liquid was circulated to achieve uniform distribution of the dissolved available chlorine. A representative 1 liter sample was taken for volumetric analysis to determine the amount of dissolved available chlorine present in the water.

The dried calcium hypochlorite particles between about 20 to about 35 mesh appeared to dissolve significantly faster than similarly sized particles produced by other processes.

EXAMPLE 2

The same basic experiment as was done in Example 1 was repeated, except for use of a dry granular powder of about 5 percent moisture and about 85 percent available chlorine that was fed at a rate of about 14 pounds per minute to an eight inch diameter turbine agglomerator. All other operating conditions were the same, except that a solution of about 19 percent available chlorine and about 79 percent water, with the rest being the aforementioned calcium salts and sodium hydroxide, was fed into the turbine agglomerator at about paddle 5 in the 20 paddle, single helix agglomerator, at a rate of about 1.6 pounds per minute. Well formed aggregates were produced that had about 13% moisture by weight. The aggregates were dried in a fluid bed dryer at about 190° C air temperature. The depth of the bed was about 15 inches.

The particles were dried to about a 8.2% water content and about 84 percent available chlorine. The granular particles were sieved and found to have a particle size distribution of about 1.8 percent greater than 20 mesh, about 97.1 percent between about 20 to about 70 mesh, and about 1.1 percent smaller than 70 mesh. The loose packed bulk density of the dried product was 0.70 grams per cubic centimeter.

A sample of 5 grams was scattered on the surface of a tank of water that is four feet deep and is maintained at about 76° C. The analysis was conducted as explained in Example 1, with about 95 percent of the available chlorine being dissolved in one minute.

EXAMPLE 3

The same basic experiment as was done in Example 1 was repeated, except for use of a dry granular powder of about 5 percent moisture and about 85 percent available chlorine that was fed at a rate of about 12 pounds per minute to an eight inch diameter turbine agglomerator. All other operating conditions were the same, except that a solution of about 22 percent available chlorine and about 79 percent water, with the rest being the aforementioned calcium salts and sodium chloride, was fed into the turbine agglomerator at about paddle 5 in the 19 paddle, single helix agglomerator, at a rate of about 1.2 pounds per minute. Well formed aggregates were produced that had about 13% moisture by weight. The aggregates were dried in a fluid bed dryer at about 192° C air temperature. The depth of the bed was about 15 inches.

The particles were dried to about a 8.2% water content and about 82.6 percent available chlorine. The granular particles were sieved and found to have a particle size distribution of about 2.4 percent greater than 20 mesh, about 97.2 percent between about 20 to about 70 mesh, and about 0.4 percent smaller than 70 mesh. The loose packed bulk density of the dried product was 0.74 grams per cubic centimeter.

A sample of 5 grams was scattered on the surface of a tank of water that was four feet deep and was

maintained at about 76° C. The analysis was conducted as explained in Example 1, with about 85 percent of the available chlorine being dissolved in one minute. A second sample of the product was sieved to discrete size ranges of 20-25 mesh, 25-30 mesh, 30-35 mesh and 35-40 mesh. A sample of each size range was scattered on the surface of the four foot deep tank of water and was found to dissolve the available chlorine in the form of the Ca(OCl)₂ significantly faster in one minute than particles of Ca(OCl)₂ produced by the conventional commercial processes employing preform rollers and a granulator or a compactor. These results are graphically illustrated in Figure 4.

COMPARATIVE EXAMPLE A

A calcium hypochlorite filter cake of the

composition shown in Table I earlier was processed in a conventional, commercial process which included preforming by high pressure roll compaction, granulating into flakes and drying on tray dryers. The irregularly shaped, non-agglomerated flakes had an available

chlorine content of about 74%, a moisture content of about 7.3% water, and a displacement buuk density of about 2.33 grams per milliliter. These particles had an average pore size of about 0.034 microns and a mercury porosimeter bulk density of about 1.77 grams per

milliliter. Only about 13 percent of the pore volume of these particles was located on the surface. The product flakes were screened to 20 to 50 mesh. When scattered on the surface of a tank filled with four feet of water using the procedure employed in Examples 1-3, only about 75% of the flakes dissolved in one minute, whereas the turbine agglomerated product dissolved significantly faster at all mesh sizes, as seen in the graphical illustration in FIGURE 4. COMPARATIVE EXAMPLE B

Commercially produced hydrated calcium hypochlorite granules used in Comparative Example A were screened to provide three different granule size ranges of about 1000 microns (18 mesh), about 710 microns (25 mesh) and about 500 microns (35 mesh). A sample of each of these sizes of commercially produced Ca(OCl)₂ particles were scattered on the surface of a tank filled with four feet of water using the procedure of Examples 1-3. After one minute, the percent of dissolved particles at about 1000 microns was determined to be only about 34% of the granules. At about 710 microns only about 54% of the granules were dissolved after one minute. At about 500 microns only about 77% of the granules were dissolved after one minute. Turbine agglomerated product particles at comparable sizes dissolved significantly faster, as illustrated by the turbine agglomerated product plot in FIGURE 4.

FIGURES 8-15 show scanning electron

photomicrographs of hydrated calcium hypochlorite particles produced by four different processes, the photomicrographs being sequentially paired by the type of process. Specifically, FIGURES 8 and 9 are turbine agglomerated particles, FIGURES 10 and 11 are preform roll/granulated particles, FIGURES 12 and 13 are particles produced from compacted dust or fines, and FIGURES 14 and 15 are spray grained particles produced in a rotary drum agglomerator. Each type of particle was electron photomicrographed at two separate

magnification levels.

FIGURE 8 shows at a magnification level of 72 turbine agglomerated particles which have been dried to a final product form. The agglomeration effect of small individual particles being held together to build a larger agglomerate is clearly shown. The relative smoothness of the individual particles of the surface comprising the agglomerates is also clearly shown.

FIGURE 9 shows a portion of one of the agglomerated particles of FIGURE 8 at a magnification level of 2400. The bridges or connecting links contributing to the highly porous structure of the turbine agglomerated product are clearly visible in the upper left hand corner.

The product shown in FIGURES 8 and 9 was produced from a feed material which had about 29.2% moisture as it entered the turbine agglomerator, experienced about a 0.6 gallons per minute water feed rate in the turbine agglomerator, and was discharged with a moisture level of about 31%. The agglomerated particles were then fed to a tray dryer with an inlet air temperature of about 310°F. The particles exited the tray dryer with a discharge moisture of about 7.88% after a residence of about 90 minutes. The electron photomicrographed particles in FIGURES 8 and 9 were screened to a 25-30 mesh size.

A solubility test in a four foot deep tank with particles ranging in size from 25-30 mesh resulted in 78% of the particles scattered on the surface of the water dissolving within one minute. A five gram sample was scattered on the water, which was maintained at about 76°F.

FIGURES 10 and 11 show scanned electron photomicrographs of hydrated calcium hypochlorite particles produced by a standard commercial process employing preform compression rollers, a granulator and a tray type of final dryer. FIGURE 10 shows dried product particles at a magnification level of about 72. FIGURE 11 shows a portion of one of the particles of FIGURE 10 at a magnification level of about 2400.

Protruding platelets of what are probably calcium hypochlorite crystals are clearly visible in FIGURE 11. The platelets appear to form a relatively rough surface that is susceptible to fracture and subsequent dusting.

The product shown in FIGURES 10 and 11 was produced from a feed material with about 29.2% moisture and was discharged from the tray dryer with a discharge moisture of about 8.8% in irregularly shaped, non-agglomerated flakes. The electron photomicrographed particles were screened to a 20-25 mesh size.

A solubility test in a four foot deep tank with particles of the type shown in FIGURES 10 and 11 ranging in size from 25-30 mesh resulted in about 63.8% of the particles scattered on the water dissolving within one minute. A five gram sample was scattered on the water, which was maintained at about 76°F.

FIGURES 12 and 13 show scanned electron photomicrographs of compacted hydrated calcium hypochlorite particles produced from the fines or dust generated by a standard commercial process which employs preform compression rollers and granulators. The dust is recycled to a compactor and then recrushed, thereby forming product particles which were classified according to size.

The compacted product particles shown in FIGURES 12 and 13 come from dust or fines with a moisture content of about 6% to about 7%. The electron photomicrographed particles were screened to a 20-25 mesh size.

FIGURE 12 shows a representative sample of compacted commercial product particles at a magnification level of about 72. FIGURE 13 shows a representative sample of compacted commercial product particles at a magnification level of about 2700. Both figures show how the compacted product's surface consists of small, tightly packed grains with little evidence of porosity. FIGURES 14 and 15 show a representative sample of particles produced by spray graining particles in a rolling bed agglomerator. FIGURE 14 shows spray grained particles at a magnification level of about 77 and

FIGURE 15 shows a portion of the same type of particle at a magnification level of about 2700. The scanned electron photomicrographs in FIGURES 14 and 15 were screened to a 20-30 mesh size.

The product in FIGURES 14 and 15 were produced in a rotary drum agglomerator with a starting or seed bed of calcium hypochlorite particles. A slurry was sprayed into the rotating drum comprised of from about 45% to about 90% by weight of water, preferably from about 50% to about 60% by weight of water. The slurry was

obtained from a calcium hypochlorite filter cake produced by a conventional commercial calcium hypochlorite process. The filter cake typically has the analysis and preferred analysis range of the components shown in Table I earlier, expressed as percent by weight.

Forced drying air was inletted into the rotary drum at temperatures ranging from about 260°F to about 310°F. Bed temperatures of the spray grained particles ranged from about 125°F to about 140°F.

The particles shown in FIGURES 14 and 15 appear generally rounded and regular in shape, but with a different porous appearance than the particles produced by turbine agglomeration.

Having thus described the invention, what is claimed is:

Claims

WHAT IS CLAIMED IS:

1. A process for producing a hydrated calcium hypochlorite agglomerated particle produced in a turbine agglomerator comprising the steps of:

(a) reacting a concentrated solution of

hypochlorous acid with a lime slurry to form a feed material containing calcium hypochlorite dihydrate crystals using hypochlorous acid as the source of available chlorine, the fee material consisting of from about 73 to about 90 percent by weight calcium

hypochlorite, from about 1 to about 12 percent by weight water, sodium chloride and calcium salts selected from the group consisting of calcium chloride, calcium chlorate, calcium carbonate and calcium hydroxide;

(b) feeding the feed material into a turbine agglomerator where it is centrifugally rotated and axially transported while being subjected to a shearing action;

(c) agglomerating the particles of the centrifugally roatted and axially transported feed material within the turbine agglomerator into product particles by adding moisture at a controlled rate to form an agglomerated particle prior to drying that is formed from small particles held together at least partially by the surface tension and adhesion forces of a layer of surface liquid, at least a portion of the surface liquid which is provided by moisture in the feed material and the remaining surface liquid being introduced into the turbine agglomerator while the particles are centrifugally rotated and axially

transported to form a particle having a moisture content of from about 5 to about 31 percent by weight before drying; (d) drying the agglomerated particle to a moisture content of from about 1.0 to about 12.0 percent by weight to substantially evaporate the layer of surface liquid and to promote recrystallization of the feed material and calcium hypochlorite to form an agglomerated product particle having a plurality of connecting links of recrystallized material bridging the small particles and connected thereto with a plurality of pores formed by the evaporation of the layer of surface liquid between the small particles that is highly porous, fast dissolving of between about 20 to less than about 35 mesh size.

2. The process according to claim 1 wherein the percent by weight calcium hypochlorite in the feed material comprises from about 85 to about 90.

3. The process according to claim 2 wherein the percent by weight water in the feed material comprises from about 1 to about 5.

4. The process according to claim 3 wherein the percent by weight moisture content in the dried particle comprises about 5.5 to about 10.5.

5. The process according to claim 4 wherein the percent by weight moisture content in the dried particle comprises about 8.5 to about 10.5.

6. The process according to claim 4 wherein the percent by weight moisture content in the particle before drying comprises about 5 to about 15.

7. The process according to claim 6 wherein the percent by weight moisture content in the particle before drying comprises about 10 to about 15.

8. The process according to claim 1 wherein the percent by weight sodium chloride is less than about 4.0.