ENCYCLOPEDIA OF CHEMICAL ENGINEERING EQUIPMENT
SIZE REDUCTION Raw materials undergo size reduction through different mechanisms: impact, compression, and attrition. One way to classify size reduction equipment is into crushers and grinders, where grinders produce finer particles than crushers.
CRUSHERS COMPRESSION CRUSHERS In compression crushers particles disintegrate due to opposing rigid forces. Compression crushers are mainly used in processing brittle materials.
GENERAL INFORMATION Compression crushers are used to break rocks and coarse particles larger than cm in diameter. diameter. !here are three main types of compression crushers: "aw crushers, gyratory crushers, and rolls.
EQUIPMENT DESIGN Jaw Crushers #aw crushers consist of a rectangular frame with a fi$ed "aw plate and a "aw stock carrying the mo%ing "aw. !he mo%ing "aw swings toward the fi$ed "aw in the forward stroke, material is crushed, and discharge takes place during the backward or freeing stroke. !he "aw crusher pictured below can be used to crush items from large ob"ects such as demolition debris or broken concrete to smaller ob"ects such as asphalt or ri%er rock. Gyratry Crushers &aterial is fed through a feed plate that distributes the particles e%enly into the chamber between the mantle and the conca%e casing. !he mantle oscillates, causing a decrease in the %olume between the mantle and the conca%e casing and crushing the material. !he crushed material then e$its freely from the apparatus. R!!s 'uring the crushing operation, the two rolls rotate toward each other, resulting in crushing. !he feed particle size determines the type of rollers used. Rollers with teeth are able to grip large particles, making it possible to crush blocks of considerable size in rolls of moderate diameter. (owe%er, depending on what is being crushed and how fine it will be crushed, therollers can be selected for best performance.
USAGE E"AMPLES #aw crushers and gyratory crushers are commonly used in mines and in quarries. Rolls are used to reduce crystalline or fibrous materials that fracture on compression, such as in the production of sponge metal, asbestos, bituminous coal and certain plastics.
AD#ANTAGES • • •
)nergy efficient. 'oes not o%er*reduce materials. +ariable capacity.
DISAD#ANTAGES • •
imited size reduction. -urther classification needed.
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IMPACT CRUSHERS GENERAL INFORMATION$EQUIPMENT DESIGN ize reduction in impact crushers occurs through particle concussion by a single r igid force. !he swing hammer crusher is an e$ample of an impact crusher. !he hammers pi%ot freely on a disc mounted on the main shaft. /s the disc rotates, the material is struck and shattered by the descending hammers until it is fine enough to pass through the openings and e$it.
USAGE E"AMPLES
/ size reduction system, equipped with a swing*hammer is usually used to break down materials such as limestone, shale, phosphates, gypsum, barytes or asbestos rock. Return to Top
GRINDERS PUL#ERIZERS 0ul%erizers, also know as fluid energy mills, are used for fine grinding and close particle size control. !hey are primarily used when contamination*free products are desired.
GENERAL INFORMATION !here are two main classes of pul%erizers: air swept pul%erizers and air impact pul%erizers. /ir swept pul%erizers use air to transport particles to the pul%erizing section of the apparatus. /ir impact pul%erizers use high speed air to accomplish pul%erization. !he products from both air swept and air impact pul%erizers will be free of o%ersize particles and will need no further sie%ing or classifying.
EQUIPMENT DESIGN A%r Swe&t Pu!'er%(er !he particle feed is mi$ed with air as it is fed into the mill inlet 123. !he beater plates 143 support the hammers 13, and distribute the particles around the periphery of the grinding chamber. !he hammers grind the solid against the liner 153 of the grinding chamber. !he beater plates rotate between 2677 and 8777 rpm 1re%olutions per minute3 to reduce the size of the incoming particles. !he classifier plate 193 separates the finely ground product for e$it through the discharge outlet 163 while returning o%ersize material back to the mill inlet through the recycle housing 183.
A%r I)&a*t Pu!'er%(er In air impact pul%erizers, superheated steam or compressed air produces the force that reduces the size of large particles. !he "ets accelerate the inlet material, causing the particles to smash into one another, resulting in smaller particles. !he 0*"et fires the feed particles into the impact chamber, where they collide head* on with recycled particles mo%ing in the opposite direction fired by the O*"et. /fter the collision, all the particles tra%el to the classification chamber. !he larger particles are forced to the outer perimeter by centrifugal force, tra%el down the downstack to the O*"et and are recycled. -ine particles mo%e towards the center of the classification chamber and are discharged.
USAGE E"AMPLES 0ul%erizers are commonly used for chemicals, pigments and food processing. !he microscale air impact pul%erizer is used in laboratories, where small samples are needed.
AD#ANTAGES • • •
/ir needed is free. arge range of sizes a%ailable. (omogeneous blend.
DISAD#ANTAGES •
)nergy consuming.
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ATTRITION MILLS ize reduction in attrition mills occurs through the scraping of one surface against another. 0articles scrape against each other or against a rigid face.
GENERAL INFORMATION !he most commonly used attrition mills are sand mills and tower mills. In both of these a rotating rodscrew induces attrition between the feed particles. Other types of attrition mills include buhrstone, planetary, and ;<& attrition mills.
EQUIPMENT DESIGN Sa+, M%!! !he feed particles are suspended in a liquid to form a slurry which enters the chamber. (ere, rotating paddles help induce attrition between the particles. maller reduced particles mo%e up the chamber with the flow, pass through a screen and e$it. arger particles remain at the bottom.
1Copyright ;nion 0rocess Inc., /kron, O(3
Twer M%!! Syste) -eed enters the grinding chamber through the rotary feeder. !he particles fall down a chute into the grinding chamber. In the grinding chamber a double heli$ screw rotates on a shaft, inducing the particles to grind against each other. !he double heli$ screw and the grinding chamber are coated with rubber to make them wear resistant. !he ground product is then channeled through a series of two cyclone separators. !he fine ground product e$its through the discharge outlet, while any o%ersized material is recycled.
10rasher, C. . Crushing and =rinding 0rocess (andbook. >ew ?ork: #ohn @iley A ons, 2B8. Copyright #ohn @iley A ons imited, Reproduced with permission3
USAGE E"AMPLES /ttrition mills are used for fine grinding operations in the production of spices 1pepper, cinnamon, paprika3, food 1peanuts, grain, cereal3, fibers 1chips, cork, cellulose3 and blendings 1face powders, insecticides3. !he pictures below show pepper and cinnamon, finished products from attrition milling.
DEFF tdEFF styleEFmargin: 7p$GFH 10ictures Copyright Chemical )ngineering 'epartment, ;ni%ersity of &ichigan, /nn /rbor, &I3
AD#ANTAGES • •
-inely ground products. arge range of sizes a%ailable.
DISAD#ANTAGES • •
)nergy consuming. >eeds specific input size.
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CONE MILLS GENERAL INFORMATION ;nlike most types of mills, cone mills can be used for hard to grind products while using less energy than other types of mills. Cone mills are preferred in some industries because they produce less noise, dust, and heat than traditional milling equipment.
EQUIPMENT DESIGN &aterial is fed into the conical chamber by gra%ity or con%eying it. Inside the chamber is a rotor that spins at a low %elocity and forces the material against the wall. !he rotor has two paddles that pass o%er the material on the wall, inducing a shear force on it. !his shear force breaks apart the material and when the particles are small enough they pass through the holes in the wall and fall into a collection container. ince the rotor is spinning at a low %elocity the particles th at pass through the wall tend to ha%e a uniform size and the rotor generates little heat. !his system is completely enclosed so that little noise and dust are generated.
DEFF tdEFF styleEFmargin: 7p$GFH 1Copyright &endel Company, )ast (ano%er, >#3
1Copyright /ad%anced &achinery Inc., Clinton !ownship, &I3
USAGE E"AMPLES Cone milling is used in the pharmaceutical, food, and chemical industries. It is widely used in pharmaceuticals for wet and dry granulation. In the food industry it is many used for grinding of foods such as sugar, candy, and chocolate.
AD#ANTAGES • • • • •
(igh efficiency ow heat generation ow noise and dust emissions Can mill sticky materials )asy to clean
DISAD#ANTAGES •
mall %olume
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TUM-LING MILLS GENERAL INFORMATION !ypes of tumbling mills include rod mills, ball mills, and tube mills. 0ronounced preferential breakage of the coarser particles is responsible for the Fscreening effectsF that occur in rod mills.
1Copyright 0atterson Industries 1Canada3 td, carborough, Ontario3
EQUIPMENT DESIGN / rod mill may be regarded as containing a series of grinding zones in which both breakage and screening occur, such that the coarse size ranges are progressi%ely eliminated. !he main breakage mechanism is shatter breakage, resulting from particles striking against each other. Return to Top
#ERTICAL SPINDLE MILLS / popular type of %ertical spindle mill is the ring*roller mill.
GENERAL INFORMATION In ring*roller mills rollers feed solid coarse particles against a stationary grinding ring. !he particles are broken apart by the resulting compression forces.
EQUIPMENT DESIGN In a ring*roller mill, the material to be milled is fed into the grinding section. !he mo%ing roller forces the coarse material against the stationary grinding ring. !he particles emerge from the machine slightly finer than they entered.
USAGE E"AMPLES +ertical spindle mills are used in the mineral industry to grind materials such as phosphate, limestone, magnesite, and bau$ite.
AD#ANTAGES • • • •
)asily cleaned. 'ust*free operation. (igh capacity. /utomatic operation.
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DISAD#ANTAGES •
Rings and rollers wear easily.
MECHANICAL IMPACT MILLS !wo of the most common mechanical impact mills are the colloid mill and the pin mill. !he colloid mill shown here disperses a liquid feed into droplets.
1Copyright Chemicolloid aboritories Inc., >ew (yde 0ark, >?3
GENERAL INFORMATION !here are four different types of colloid mills: the hammer or turbine, smooth surface disk, rough surface disk, and %al%e or orifice type. Colloid mills are designed to break upagglomerates, particles that ha%e bonded together, into droplets about 2 micrometer in diameter.
1Copyright Chemineer, Inc., 'ayton, O(3 0in mills are used to reduce the size of medium* to low*density materials such as talc and clay. 0in mills use centrifugal forces to smash large particles against pins.
EQUIPMENT DESIGN / colloid mill rotor is an intermeshing rotor used for the size reduction of materials by multiple impacts with the maze of pins. (igh speed rotation applies fluid shear stress, inducing the breakdown of agglomerates. !he speed of the rotation can also be reduced during mi$ing to induce a smoother impact and a%oid material degradation while still producing enough turbulence to create a homogeneous blend. !he semi*liquid feed enters a groo%ed conical rotor that rotates with speeds of about 677 rpm. !he rotation produces currents inside each of the groo%es, producing hydraulic shear, centrifugal action, and particle impact. /fter the agglomerates are broken apart, the liquid rises through the groo%es until it reaches the outlet. !he colloid mill is wrapped in a cooling "acket to counteract the high heat generated by the process. In pin mills, solid material is fed through a hopper onto the rotor. !he rotor rotates either clockwise or counterclockwise. !his rotation causes the material to be broken apart into uniform*sized particles between the stationary upper pins and the lower rotating pins. !he standard*duty rotor has more pins than the hea%y*duty rotor, resulting in smaller particles.
USAGE E"AMPLES Colloid mills are used largely in asphalt production and grease manufacturing. !hey are also used in a wide %ariety of industries, such as paints, pigments, food and cosmetics, such as in the production of the lipstick. In the food processing industry, colloid mills are used in the production of mayonnaise, peanut butter, salad dressings, buttered syrups, and chocolate toppings. 0in mills are commonly used to produce talc, clays, resins, flour and starch.
AD#ANTAGES • • •
elf*cleaning. Rugged and durable. @ide %ariety of uses.
DISAD#ANTAGES •
•
In colloid mills, the feed must be in a pumpable slurry. 0ins in pin mills wear easily.
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ROLLER COMPACTORS GENERAL INFORMATION / roller compactor is used in dry processing to compact material into sheets or to reduce the particle size.
EQUIPMENT DESIGN
0owdered material is fed into a feed chute and is dri%en down to the rolls by a feed screw. It passes through the rolls and is compacted as the pressure increases till it reaches a ma$imum at the minimal distance between the rolls. !he rolls come in different sizes and types depending on the desired granule or flake size. !he pressure can also be controlled by %arying the gap between the rolls and their speeds.
1Copyright &endel Company, )ast (ano%er, >#3
USAGE E"AMPLES Roller compactors are used in the chemical, pharmaceutical, and food industry to increase the density of powders and for granulation.
AD#ANTAGES • • •
>o additional binders needed. mall size. 'ust free.
DISAD#ANTAGES •
'oes not work for all powders.
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AC.NO/LEDGEMENTS Aadvanced Machinery Inc., Clinton !ownship, &I Mendel Company , )ast (ano%er, ># Union Process Inc. , /kron, O( Patterson Industries (Canada) Ltd , carborough, Ontario
REFERENCES
Cone &ills. ew ?ork: )lse%ier cientific 0ublishing Company, 2B88. &iller, @illiam !. @. Crushers for tone and Ore. ondon: &ining 0ublications, td, 2B9. 0erry, Robert (., and 'on @. =reen. 0erryJs Chemical )ngineersJ (andbook. 8th ed. >ew ?ork: &c=raw*(ill, 2BB8: 47*27 * 47*8. 0rasher, C. . Crushing and =rinding 0rocess (andbook. >ew ?ork: #ohn @iley A ons, 2B8. FRoll Compactor.F Prism. 0rism, @eb. www.drygranulationrollercompactor.com.
DE#ELOPERS #ulie &essacar Chuan (uey ?ap #oseph 0alazzolo te%e @esorick (enry Chen !homas 0legue Return to Top
