SIZE ENLARGEMENT


The primary step in size enlargement is agglomeration, the formation of a ball or sphere by clumping particles together. Each type of equipment uses one of five agglomeration methods: pressure, spray, tumbling, thermal, or mixing.


BRIQUETTING MACHINES


Briquetting machines are used to create briquettes of material by compacting smaller pieces together.



(Copyright K.R. Komarek, Inc., Wood Dale, IL)

GENERAL INFORMATION

In briquetting machines, a feed stream of solid material is compacted into larger solids called briquettes through pressure agglomeration of the feed. The consistency of the feed stream has to be carefully controlled by wetting or drying the feed or by adding binders to the raw material. The movie below shows how a typical briquetting machine works. Smaller pieces of feed can be collected and then compacted with a series of counter rotating rollers. The rotation of the rollers squeezes and compacts the material into a fine briquette, which then falls out the bottom.



EQUIPMENT DESIGN

All briquetting machines have a similar design. They all have a hopper that collects the feed. The hopper settles the feed before it enters the counter rotating rollers. These rollers compact the feed stream into solid briquettes. Briquetting machines typically have a conveyor or other such device to collect the briquettes.



(Copyright PRAB, Inc., Kalamazoo, MI)

Materials that can be briquetted range from cardboard and hay to metals, such as aluminum, brass and zinc. The picture below shows metallic shavings before entering the briquetter, and the briquette product. Along with forming the shavings into solid bricks, the machine also claims almost all of the liquid found in the material.



(Copyright PRAB, Inc., Kalamazoo, MI)

USAGE EXAMPLES

Briquetting machines are used frequently in the mining industry, as well as in paper and pulp applications. A variety of briquettes are shown below. Click on the picture to see the briquette labels.



(Copyright K.R. Komarek, Inc., Wood Dale, IL)


Briquetting is also used to create fuel briquettes. Conventional fuels are briquetted to improve burning characteristics. One of the most common examples of briquettes used as fuel are the charcoal briquettes shown here. Other examples of fuel briquettes include wood and coal.



(Copyright Chemical Engineering Department, University of Michigan Ann Arbor, MI)

ADVANTAGES

DISADVANTAGES

  • Briquette formation is predictable and consistent.
  • Briquettes are easy to transport.
  • Wet and dry materials can be briquetted with the help of binders.
  • Low operating costs.
  • Rollers can wear down quickly.
  • Often the strength of the briquette can be affected by weathering or exposure to water.

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FLUID BEDS


Fluid beds are often used when small tablets are required.



(Copyright GEA Process Engineering Inc., Columbia, MD)

GENERAL INFORMATION

Fluid beds are based on spray agglomeration. In spray agglomeration, the feed is in a liquid or semi-liquid phase. The liquid stream is sprayed into a gas, usually air. The liquid is then dried and forms a solid due to heat and mass transfer.



(Copyright Vector Corporation, Marion, IA)

EQUIPMENT DESIGN

In a fluid bed system, the liquid feed is sprayed into the heated air. The air dries the particles, which eventually merge to product with a diameter no greater than 5 mm. Before the air is fed into the chamber, it is filtered and heated. The solid particles are discharged at the bottom and the exhaust air is released through a vent at the top.



(Copyright GEA Process Engineering Inc., Columbia, MD)

  1. Air preparation unit
  2. Product container
  3. Exhaust filter
  4. Exhaust blower
  5. Control panel
  1. Air distribution plate
  2. Product
  3. Spray nozzle
  4. Solution deliver

USAGE EXAMPLES

Fluid beds are used in the food processing, powdered metal, ceramics, mineral, and biotechnology chemical industries. They also are used to prepare the feed in tableting. Shown below are beads used in the pharmaceutical industry that were coated using a fluid bed and powder layering process.



(Copyright Vector Corporation, Marion, IA)


ADVANTAGES

DISADVANTAGES

  • Process usually continuous.
  • Normally a large-scale operation.
  • Product can only reach a diameter of 5 mm.
  • Liquid feed must be able to be pumped.

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PELLET MILLS


GENERAL INFORMATION

Pellet mills compact powder in a confined space via a process called pressure agglomeration. The first step in pressure agglomeration is the application of a small force to rearrange the particles in order to fill any large voids. Next, the pressure is increased in the compression step, causing brittle particles to break and malleable particles to deform. This step decreases the amount of air surrounding each particle.



(Copyright Feeco International, Inc., Green Bay, WI)



EQUIPMENT DESIGN

Pellet mills commonly use a roll- type extrusion press. Powder is fed into the pelleting chamber by the rollers. The pressure increases as the roller and the circular wall come closer together. The powder is then fed into the die, creating pellets. Adjustable knives cut the pellets to the desired size.



(Copyright California Pellet Mills, Crawfordsville, IN)


USAGE EXAMPLES

Pellet mills are used in a variety of applications, such as the pharmaceutical industry, and the manufacture of pet foods and agricultural feeds. They are also used to form fuel pellets. Pellet mills receive a blend of ingredients from a mixer, and then convert the feed into pellets.


ADVANTAGES

DISADVANTAGES

  • Low cost.
  • Relatively simple procedure.
  • Possibility of breakage during storage and transportation.
  • Relatively low yield.

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DISC GRANULATORS


GENERAL INFORMATION/EQUIPMENT DESIGN

Disc granulators, or pelletizing discs as they are known in the ore industry, work based on the tumbling technique of agglomeration. In tumbling agglomeration, inclined discs, such as the one shown on the left, are typically used. The feed is usually a fine powder mixed with a liquid, most commonly water. The particles collide with each other in the spinning disc. If the bonding forces are stronger than the repulsion forces, the particles coalesce. The agglomerate grows further either by coalescence or by layering.


Van der Waals, magnetic, and electrostatic forces bind the agglomerates together. The strongest force against agglomeration is the weight of the solid.



(Copyright W. S. Tyler, St. Catharines, ON)

The pelletizing disc with re-rolling ring shown below rotates the particles on an incline. The solid gradually grows in size. When the solid becomes the desired size, it is projected over the main rim into the re-rolling ring located on the outside of the apparatus. Here, the pellet surface is smoothed.



(Copyright Mars Mineral, Mars, PA)

USAGE EXAMPLES

The agglomerates formed by disc granulators are typically spherical, and used for fertilizers. They are also used to agglomerate ores and dusts in the minerals processing industry. The disc pelletizer below is being used to turn limestone powder into limestone pellets that are used in soil as a fertilizer.



(Copyright Mars Mineral, Mars, PA)

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MIXER GRANULATORS


GENERAL INFORMATION


In mixer granulators first the powder is chopped and mixed to produce a fine, free-flowing powder. Then a liquid binder is blended with the powder to produce granules.


EQUIPMENT DESIGN


A typical mixer granulator has a hemispherical bottom and flat sides. After the powder is added it is mixed by a flat impeller that runs along the bottom of the vessel. On one side is a rotating chopper that helps break up the clumps of powder. After the powder is flowing freely a nozzle on the top of the vessel begins to spray the liquid binder onto the powder. Then the powder is mixed at a lower speed to produce the granules. There are a variety of different impellers, choppers, and mixing speeds that can be used to produce granules of different sizes and densities. The main type types of mixers are high-shear and low-shear which refer to their respective mixing speeds. High shear mixer granulators are used for impeller speeds between 60 and 600 rpm or for chopper speeds of 500 to 3500 rpm. These granulators can range in volume from 10 liters to 1200 liters and have an average processing time of five minutes.



(Copyright Mendel Company, East Hanover, NJ)

USAGE EXAMPLES


Mixer granulators are used for pharmaceutical, ceramics, detergents, and agricultural chemical manufacturing. High-shear mixer granulators are almost exclusively used in the pharmaceutical industry.


ADVANTAGES

DISADVANTAGES

  • Can process cohesive powders.
  • Produces small granules.
  • More durable product.
  • High capital, maintenance, and operating costs.
  • Less spherical granules.
  • Difficult to scale.
  • Complex design.

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POWDER BLENDERS


GENERAL INFORMATION/EQUIPMENT DESIGN

Powder blenders use mixer agglomeration to enlarge the size of powders. In a powder blender, powder is gently sprayed with liquid as it is fed into a rotating drum. The spinning action of the shaft agitates the damp feed, causing the particles of the powder to clump together. The placement of the pins creates three different zones, mixing, pelletizing, and densifying, within the blender. In the pelletizing zone, the agglomerates are loosely formed and in the densifying zone the particles are compacted. The image below to the left is an example of a powder blender, and the animation below to the right shows the powder blender in action.


(Copyright Glen Mills, Inc., Clifton, NJ)

USAGE EXAMPLES

Powder blenders are mainly used in the food industry to instantize food. They are also used to make pills in the pharmaceutical industry.


ADVANTAGES

DISADVANTAGES

  • Product results in good uniformity.
  • Usually high maintenance.
  • Product may need further shaping.

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PUGMILLS


GENERAL INFORMATION/EQUIPMENT DESIGN

Pugmills are an example of mixer agglomeration. Pugmills are also referred to as blungers, pug mixers, and paddle mixers. They have two shafts aligned horizontally, as shown below.



As the twin blades move in opposite directions, material is thrown into the center and the agglomerates are formed. The feed can be added either through a single inlet or along the whole length of the apparatus. The video below shows an example of a paddle mixer in use, taking raw material from a conveyor and forming agglomerates.





USAGE EXAMPLES

Pugmills are used in minerals processing, and the formation of fertilizers, ceramics, and tablets. The picture on the left is an example of a paddle mixer and to the right are pictures of the end products of mixer agglomeration in the pharmaceutical industry.


(Copyright Feeco International, Inc., Green Bay, WI)




ADVANTAGES

DISADVANTAGES

  • Produce hard, strong agglomerates.
  • Yield very compact product.
  • Product may need further shaping.
  • Small agglomerates.

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ROTATING DRUMS


GENERAL INFORMATION/EQUIPMENT DESIGN

A rotating drum is a common piece of thermal agglomeration equipment. Other thermal agglomeration equipment include traveling grate machines, furnaces, and kilns


In thermal agglomeration, molten input is picked up by a rotating drum and moves toward the outer surface of the drum. Cool liquid is sprayed at the inner wall and the molten feed is cooled and solidifies. The solid product is then cut to the proper size with a knife. During the process, the coolant tumbles down the drum walls and is recycled back into the nozzle.



USAGE EXAMPLES

Rotating drums can be used in the formation of slates, drying of liquid feeds to coarse powders, and flaking of resins, hot melt adhesives, and other chemicals. The photo on the left is an example of a rotating drum and the picture on the right is an example of agglomerated powders.



(Copyright Feeco International, Inc.,
Green Bay, WI)



(Copyright GEA Process Engineering Inc., Columbia, MD)

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ACKNOWLEDGEMENTS


California Pellet Mills, Crawfordsville, IN

Feeco International, Inc., Green Bay, WI

GEA Process Engineering Inc., Columbia, MD

K.R. Komarek, Inc., Wood Dale, IL

Mars Mineral, Mars, PA

Mendel Company, East Hanover, NJ

Pioneer Sawdust, Salt Lake City, UT

PRAB, Inc., Kalamzoo, MI

RUF UK Ltd., Tutbury, Staffordshire

Vector Corporation, Marion, IA

W. S. Tyler, St. Catharines, ON


REFERENCES


Capes, C.E. Particle Size Enlargement. New York: Elsevier Scientific Publishing Company,      1980. Print.

Komarek, Richard. "Roll press briqueters improve handling and use of powdery granular or      shredded materials." Powder Handling and Processing Apr-Jun 1998: 143-146. Print.

Litster, Jim, and Bryan Ennis. The Science And Engineering of Granulation Processes.      Dordrecht: Springer Netherlands, 2004.

Peitsch, Wolfgang. "Successfully Use Agglomeration for Size Enlargement." Chemical      Engineering Progress April 1996: 29-45. Print.

Perry, Robert H., and Don W. Green. Perry's Chemical Engineers' Handbook. 7th ed. New      York: McGraw-Hill, 1997: 20-56 - 20-85. Print.


DEVELOPERS


Julie Messacar

Chris Seadeek

Steve Wesorick

Joseph Palazzolo

Matthew Robertson

Kelsey Kaplan

Keith Minbiole

Steve Cotton

Thomas Plegue


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