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IntroductionIntroduction

What is Granulation? Granulation may be considered as a size enlargement

processduring which primary particles are formed into larger,

physicallystrong agglomerates wherein the primary particles can still beidentified.

Objectives of granulation: To improve the flow properties Densification To improve compression characteristics Prevention of segregation of the constituents

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In a more broader way , Granulation methods can be classified as follows :

Granulation Process Methodology

Wet processes Pan granulation

Spray drying

High shear granulation

(wet massing)

Fluid bed spray granulation

Dry processes Slugging

Roller compaction

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In wet granulation process, a granulating In wet granulation process, a granulating liquid is used to facilitate the agglomeration liquid is used to facilitate the agglomeration process.process.

In dry granulation process, dry powder In dry granulation process, dry powder particles may be brought mechanically by particles may be brought mechanically by compression into slugs or, more frequently compression into slugs or, more frequently these days, by roller compaction.these days, by roller compaction.

Wet and Dry Granulation

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What is Spray Granulation?Spray Granulation occurs when a liquid solution is rapidly dried over an active ingredient. This newly encapsulated particle structure is harder and denser, yielding particle properties that are desirable in many applications. The newly formed particle can be sprayed again and again creating larger and larger spherical pellets that form in successive onion like layers.

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In the granulation process, the particles are conveyed through the inner partition into the expansion chamber by the hot fluidizing air. Gravity overcomes the force of the fluidized air and the particles fall back into the outer partition. The pneumatic atomizing nozzle in the bottom center of the chamber introduces the coating solution. This nozzle sprays upward providing successive applications of coating to the product.

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MechanismMechanism

Stages in Spray Granulation:Stages in Spray Granulation:

1.Atomization of granulation liquid1.Atomization of granulation liquid

2.Agglomeration of particles2.Agglomeration of particles

3.Drying3.Drying

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AtomizationAtomization

It is the process by which a liquid is disintegrated into many It is the process by which a liquid is disintegrated into many fine droplets, thereby yielding a high surface/mass ratio. fine droplets, thereby yielding a high surface/mass ratio.

This is achieved by supplying energy to the liquid in the form This is achieved by supplying energy to the liquid in the form of kinetic energy, pressure energy, centrifugal energy etc.of kinetic energy, pressure energy, centrifugal energy etc.

The most common form of atomization is hydraulic pressure The most common form of atomization is hydraulic pressure nozzle atomization.nozzle atomization.

The differential pressure drop across the orifice determines The differential pressure drop across the orifice determines the mean droplet diameter.the mean droplet diameter.

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AgglomerationAgglomeration

In this stage, the atomized granulating liquid is sprayed over In this stage, the atomized granulating liquid is sprayed over the particles to facilitate the agglomeration.the particles to facilitate the agglomeration.

At low moisture contents, particles contact each other and At low moisture contents, particles contact each other and adhere due to the formation of liquid bridges.adhere due to the formation of liquid bridges.

Finally, droplets are formed when the liquid completely Finally, droplets are formed when the liquid completely surrounds the granule.surrounds the granule.

The strength of the droplet is dependent on the surface The strength of the droplet is dependent on the surface tension of the liquid phase.tension of the liquid phase.

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Agglomeration (contd..)Agglomeration (contd..) The basic wet-granulated unit may be visualized as two The basic wet-granulated unit may be visualized as two

particles and a liquid bridge that serves to hold the particles particles and a liquid bridge that serves to hold the particles together by surface tension at air-liquid interface and by together by surface tension at air-liquid interface and by hydrostatic suction.hydrostatic suction.

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DryingDrying

In this stage, the agglomerated droplets are brought into In this stage, the agglomerated droplets are brought into contact with heated gas for the evaporation to take place contact with heated gas for the evaporation to take place equally from the surface of all droplets.equally from the surface of all droplets.

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Why Spray Granulation? AdvantagesMost spray granulation systems spray a liquid solution over a hot fluidized bed of active material. This process works by suspending the particles in a high velocity gas flow while applying the coating as a fine mist. Both liquid and solid powder coatings may be applied in this type of process.

Some of the desirable product properties of the spray granulation process are:

Dust-free granules Spherical pellets Free flowing properties Good solubility Compact structure Less hygroscopic Less abrasive

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Different types of granulators

Spray Granulator

The powder to be granulated is suspended in the heated air of a fluid bed, and a liquid binder sprayed from nozzles positioned above

High-shear Granulator

The high-shear granulation process combines the active powder with a binder solution using a high-speed mixing blade and chopper.

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Typical Applications

Spray granulators are widely used for forming materials in industries like chemicals, food products and pharmaceuticals. Its main purpose is to convert light, small powders into high-density free-flowing granulates.

Some of its applications are given below:

Soup powder Sweeteners Tea Coffee Cocoa Organic acids Enzymes

Soya Sauce

Gelatin

Animal Drugs

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Fluid Bed Spray GranulatorNowadays, spray granulation wherever used is mostly done in a fluid bed.

Fluid bed granules are very homogeneous. All particles in the powder mix are sprayed evenly with liquid starting materials. The type of granulate (size, density, porosity) can be influenced over a wide range by the adjustment of various parameters.

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The particle formation in fluidized bed granulation is influenced by numerous parameters

1. Moisture content in solids2. Liquid spray flow rate 3. Airflow rates 4. Atomization pressure

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Batch fluid bed

For Granulation in batch mode, the dry starting product is placed in the product container. Here it is mixed vigorously in the heated gas stream, held in suspension and agglomerated/granulated by spraying with a suitable bonding material. The product is then dried to the required end moisture content with high heat and material transition coefficients.

Principle:Batch fluid bed granulation, Top Spray

Principle:Batch fluid bed granulation, Bottom Spray

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Continuous fluid bed

Continuous granulators are sub-divided into several granulation zones, which are operated at different speeds and temperatures, e.g. Granulation in the first and second sections, drying in the third and cooling at the end of the process chamber.

Principle: Principle: Continuous fluid bed granulation, Continuous fluid bed granulation, Top Spray Bottom Spray

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Case Study I Port Kembla Steelworks

Problem – A significant amount of material is stored in theplant’s stockpile areas at any given time. In the Raw Materials area, approximately 1.2million tonnes of iron ore and other material is stored in the primary and secondary yards.

These stockpiles have the potential to create dustemissions as fine particles of material are blownfrom the stockpiles into the air and out into thecommunity.

Analysis – Dust emissions can be avoided if the particles that reside on the surface were somehow made heavy or large. This was achieved by granulation.

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Solution -The granulation process can be achieved by installing sprayers that spray water thereby increasing the size of fine particles (dust). The installed water spray granulator system effectively suppresses dust emissions from the stockpiles under most weather conditions. The spray system includes regular dampening of stockpiles and spraying.

Conclusion –The problem of dust emission was solved to a great extent by the installation of the sprayers in the stockpile area of Port Kembla Steelworks

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Bibliographyhttp://www.glatt.com

http://www.malvern.co.uk/ProcessEng/processes/granulation

http://www.pro-c-ept.com

http://www.google.com