I. Methods, Process and Equipments involved in handling of solids

A. FEEDERS & STORAGE SILOS

. FEEDERS are machineries used in assembly and manufacturing applications to move or “transport” materials or products to a designated storage or to other processing equipment.

Types of Feeders

Rotary feeders, also known as rotary airlocks or rotary valves, are commonly used in industrial and agricultural applications as a component in a bulk or specialty material handling system. Rotary feeders are primarily used for discharge of bulk solid material from hoppers/bins, receivers, and cyclones into a pressure or vacuum-driven pneumatic conveying system. Components of a rotary feeder include a rotor shaft, housing, head plates, and packing seals and bearings. Rotors have large vanes cast or welded on and are typically driven by small internal combustion engines or electric motors.

Rotary airlock feeders have wide application in industry wherever dry free-flowing powders, granules, crystals, or pellets are used. Typical materials include: cement, ore, sugar, minerals, grains, plastics, dust, fly ash, flour, gypsum, lime, coffee, cereals, pharmaceuticals, etc.

Industries requiring this type include cement, asphalt, chemical, mining, plastics, food, etc.

Rotary feeders are ideal for pollution control applications in wood, grain, food, textile, paper, tobacco, rubber, and paint industries, the Standard Series works beneath dust collectors and cyclone separators even with high temperatures and different pressure differentials.

Rotary valves are available with square or round inlet and outlet flanges. Housing can be fabricated out of sheet material or cast. Common materials are cast iron, carbon steel, 304 SS, 316 SS, and other materials. Rotary airlock feeders are often available in standard and heavy duty models, the difference being the head plate and bearing configuration. Heavy duty models use an outboard bearing in which the bearings are moved out away from the head plate. Housing inlet and discharge configurations are termed drop-thru or side entry. Different wear protections are available such as hard chrome or ceramic plating on the inner housing surfaces. Grease and air purge fittings are often provided to prevent contaminants from entering the packing seals.

Rotary airlock

The basic use of the rotary airlock feeder is as an airlock transition point, sealing pressurized systems against loss of air or gas while maintaining a flow of material between components with different pressure and suitable for air lock applications ranging from gravity discharge of filters, rotary valves, cyclone dust collectors, and rotary airlock storage devices to precision feeders for dilute phase and continuous dense phase pneumatic convey systems.

Rotary valve

Rotary airlock feeders/ rotary airlock valves are used in pneumatic conveying systems, dust control equipment, and as volumetric feed-controls.

Volumetric feeder

Rotary airlock valves are also widely used as volumetric feeders for metering materials at precise flow rates from bins, hoppers, or silos onto conveying or processing systems.

Types of rotary feeder

Rotary airlock feeders

Drop through rotary airlock feeders are designed for rugged applications that require an outboard bearing style unit where contamination and /or an abrasive product cannot be handled with an inboard bearing style. The outboard bearing feeders is engineered for use in high pressure pneumatic conveying systems, with high temperatures where more of an effective seal is required due to high or excessive wear that is experienced with a simple dust collector.

Blow-thru rotary airlock feeder

The blow-thru rotary airlock feeder is ideal for pneumatic conveying applications in food, grain, chemical, milling, baking, plastics and pharmaceutical industries. The blow-thru airlocks feature a low profile with large capacity. High pressure differentials integral mounting feet, and retrofit competitive units. The blow-thru valves are available with 10-vane open-end rotor; outboard bearings and replaceable shaft seals.

Easy clean rotary feeder

The easy-clean series rotary feeders can be fast and simply disassembled, thoroughly quick cleaned, sanitized and inspected or maintenance in a minimum amount of time without the use of tools or removal from service, thereby reducing downtime and increasing system production. Reassembly without tools is accomplished in minutes. Internal clearances are automatically re-established every time.

The Clean-in-place rotary feeder is a special purpose valve designed for where cross-contamination is a major concern and lengthy shut-downs for clean-out are cost-prohibitive, suited for Dairy, Pharmaceutical industries, Food, Baking, Chemical, Plastics, Paint, and Powder Coating plants.

It is ideal for batch mixing systems such as those handling different colored resins which demand regular cleaning between cycles.

Filter valve

The filter valve is a low-cost solution designed for light duty dust collector applications.

Knife rotary feeder

This type of feeder is used for discharge of secondary fuel as for example: plastics or wood. The knife is cutting the oversize material and is preventing the rotor from blockage.

Vibratory Feeders-use both vibration and gravity to move material used to transport a large number of smaller object suncontrolled recovery of the material from top of feeder controlled delivery of the material from bottom of feeder

How It Works

Example: PILL BOTTLING SYSTEM a large batch of pills is dumped into the top of the vibratory feeder gravity will pull the pills toward the bottom of the feeder where they can exit one at a time so that they can be counted once the correct number is in the container, the feed is stopped until a new bottle is placed in position

Screw Feeders-used for handling bulk materials, in which a rotating helicoid screw moves the material forward, toward and into a process unit, very similar to screw conveyors in their basic structure, both of which are based on the principles of the Archimedean screwcapable of delivering dense slurries and dry granular products with great accuracy at a range of operational speedsdrive is controlled by servo motors capable of precise stop-start and speed control

Volumetric Screw Feeders- amount of material transported is carefully calculated and controlled by adjusting the speed at which the screw turns. very accurate feed values to be maintained rotational speed may be preset or constantly adjusted GRAVIMETRIC SCREW FEEDER delivery rate is controlled by adjusting the rate at which the material is introduced into the machine

Apron Feeders- a limited-length version of apron conveyor also known as plate-belt feeder; plate feeder, allows automatic control the volume of materials that are added to a process construct is from heavy, durable materials like steel .The belt portion of the apron feeder is made from thick steel trays or pans can be found in mining operations, factories, and concrete plants cannot be used in applications where precise feeding and measuring is required

How It Works

Materials that will be carried by the apron feeder are held in a large hopper above one end of the belt. The amount of material that reaches the feeder is determined by the distance between this hopper and the top of the feeder. As the hopper deposits materials onto the apron feeder, the metal pans that make up the belt travel horizontally like a conveyor belt. When the trays reach the end of the belt, they dump, or feed the materials into another vessel.

Bowl Feeders-used to feed parts to an assembly line or piece of manufacturing equipment individual components exit the feeder at specific intervals and enter the next step in the assembly process. Each

bowl feeder uses special sensors to spot jams or parts that may be misaligned, one drawback is its precise operation.

How It Works

In a standard application: the bowl feeder sits below a hopper or binworkers fill the hopper with bulk material, and these objects fall into the feeder below

Types of Bowl Feeders

Cylindrical Material Aluminum/Steel/Stainless Steel Suitable for:Continuous transport of components and for handling small parts

ConicalMaterialAluminum/Stainless SteelSuitable for:Heavy sharp-edged componentsLarger LoadsAutomatic pre-separating

SteppedMaterialAluminum/Stainless SteelSuitable for:Larger loads and larger componentsSimilar to conical bowls

Polyamide bowl (conical or stepped)Suitable for:Small components with simple geometry and where mass production of feeders is required

STORAGE SILOS

A silo is a structure for storing bulk materials. Silos are used in agriculture to store grain (see grain elevators) or fermented feed known as silage. Silos are more commonly used for bulk storage of grain, coal, cement, carbon black, woodchips, food products and sawdust. Three types of silos are in widespread use today - tower silos, bunker silos and bag silos. Missile silos are used for the storage and launching of ballistic missiles.

Types of Silos

Cement storage silos

There are different types of cement silos such as the low-level mobile silo and the static upright cement silo, which are used to hold and discharge cement and other powder materials such as PFA (Pulverised Fuel Ash). The low-level silos are fully mobile with capacities from 10 to 75 tons. They are simple to transport and are easy to set up on site. These mobile silos generally come equipped with an electronic weighing system with digital display and printer. This allows any quantity of cement or powder discharged from the silo to be controlled and also provides an accurate indication of what remains inside the silo. The static upright silos have capacities from 20 to 80 tons. These are considered a low-maintenance option for the storage of cement or other powders. Cement silos can be used in conjunction with bin-fed batching plants.

Tower silo

Storage silos are cylindrical structures, typically 10 to 90 ft (4 to 30 m) in diameter and 30 to 275 ft (10 to 84 m) in height with the slipform and Jumpform concrete silos being the larger diameter and taller silos. They can be made of many materials. Wood staves, concrete staves, cast concrete, and steel panels have all been used, and have varying cost, durability, and airtightness tradeoffs. Silos storing grain, cement and woodchips are typically unloaded with air slides or augers. Silos can be unloaded into rail cars, trucks or conveyors.

Tower silos containing silage are usually unloaded from the top of the pile, originally by hand using a silage fork, which has many more tines than the common pitchfork, 12 vs 4, in modern times using mechanical unloaders. Bottom silo unloaders are utilized at times but have problems with difficulty of repair.

An advantage of tower silos is that the silage tends to pack well due to its own weight, except in the top few feet. However, this may be a disadvantage for items like chopped wood. The tower silo was invented by Franklin Hiram King.

In Canada, Australia and the United States, many country towns or the larger farmers in grain-growing areas have groups of wooden or concrete tower silos, known as grain elevators, to collect grain from the surrounding towns and store and protect the grain for transport by train, truck or barge to a processor or to an export port. In bumper crop times, the excess grain is stored in piles without silos or bins, causing considerable losses.

Concrete stave silos

Concrete stave silos are constructed from small precast concrete blocks with ridged grooves along each edge that lock them together into a high strength shell. Much of concrete's strength comes from its high incompressibility, so the silo is held together by steel hoops encircling the tower and compressing the staves into a tight ring. The vertical stacks are held together by intermeshing of the ends of the staves by a short distance around the perimeter of each layer, and hoops which are tightened directly across the stave edges.

The static pressure of the material inside the silo pressing outward on the staves increases towards the bottom of the silo, so the hoops can be spaced wide apart near the top but become progressively more closely spaced towards the bottom to prevent seams from opening and the contents leaking out.

Concrete stave silos are built from common components designed with high strength and long life. They have the flexibility to have their height increased according to the needs of the farm and purchasing power of the farmer, or to be completely disassembled and reinstalled somewhere else if no longer needed.

Low-oxygen tower silos

Low-oxygen silos are designed to keep the contents in a low-oxygen atmosphere at all times, to keep the fermented contents in a high quality state, and to prevent mold and decay, as may occur in the top

layers of a stave silo or bunker. Low-oxygen silos are only opened directly to the atmosphere during the initial forage loading, and even the unloader chute is sealed against air infiltration.

It would be expensive to design a such a large structure that is immune to atmospheric pressure changes over time. Instead, the silo structure is open to the atmosphere but outside air is separated from internal air by large impermeable bags sealed to the silo breather openings. In the warmth of the day when the silo is heated by the sun, the gas trapped inside the silo expands and the bags "breathe out" and collapse. At night the silo cools, the air inside contracts and the bags "breathe in" and expand again.

While the iconic blue Harvestore low-oxygen silos were once very common, the speed of its unloader mechanism was not able to match the output rates of modern bunker silos, and this type of silo went into decline. Unloader repair expenses also severely hurt the Harvestore reputation, because the unloader feed mechanism is located in the bottom of the silo under tons of silage. In the event of cutter chain breakage, it can cost up to US$10,000 to perform repairs. The silo may need to be partially or completely emptied by alternate means, to unbury the broken unloader retrieve broken components lost in the silage at the bottom of the structure.

In 2005 the Harvestore company recognized these issues and worked to develop new unloaders with double the flow rate of previous models to stay competitive with bunkers, and with far greater unloader chain strength. They are now also using load sensing soft-start variable frequency drive motor controllers to reduce the likelihood of mechanism breakage, and to control the feeder sweep arm movement.

While the sight of multiple tall silos may look impressive, many have been abandoned for silage use, or converted to hold grain. Ground-level bunker silos carry none of the hazards outlined above, and need only a standard tractor/loader to feed out with, and no specialized machinery.

Bunker silos

Bunker silos are trenches, usually with concrete walls, that are filled and packed with tractors and loaders. The filled trench is covered with a plastic tarp to make it airtight. These silos are usually unloaded with a tractor and loader. They are inexpensive and especially well suited to very large operations.

Bag silos

Bag silos are heavy plastic tubes, usually around 8 to 12 ft in diameter, and of variable length as required for the amount of material to be stored. They are packed using a machine made for the purpose, and sealed on both ends. They are unloaded using a tractor and loader or skid-steer loader. The bag is discarded in sections as it is torn off. Bag silos require little capital investment. They can be used as a temporary measure when growth or harvest conditions require more space, though some farms use them every year.

Bins

A bin is typically much shorter than a silo, and is typically used for holding dry matter such as concrete or grain. Bins may be round or square, but round bins tend to empty more easily due to a lack of corners for the stored material to become wedged and encrusted.

The stored material may be powdered, as seed kernels, or as cob corn. Due to the dry nature of the stored material, it tends to be lighter than silage and can be more easily handled by under-floor grain unloaders. To facilitate drying after harvesting, some grain bins contain a hollow perforated or screened central shaft to permit easier air infiltration into the stored grain.

Sand and salt silos

Sand and salt for winter road maintenance are stored in conical dome-shaped silos. These are more common in North America, namely in Canada and the United States.

B. Conveyors and Conveying System

A conveyor system is a common piece of mechanical handling equipment that moves materials from one location to another. Conveyors are especially useful in applications involving the transportation of heavy or bulky materials. Conveyor systems allow quick and efficient transportation for a wide variety of materials, which make them very popular in the material handling and packaging industries. Many kinds of conveying systems are available, and are used according to the various needs of different industries. There are chain conveyors (floor and overhead) as well. Chain conveyors consist of enclosed tracks, I-Beam, towline, power & free, and hand pushed trolleys.

Industries that use conveyor systems

Conveyor systems are used widespread across a range of industries due to the numerous benefits they provide.Conveyors are able to safely transport materials from one level to another, which when done by human labor would be strenuous and expensive.They can be installed almost anywhere, and are much safer than using a forklift or other machine to move materials. They can move loads of all shapes, sizes and weights. Also, many have advanced safety features that help prevent accidents. There are a variety of options available for running conveying systems, including the hydraulic, mechanical and fully automated systems, which are equipped to fit individual needs.

Conveyor systems are commonly used in many industries, including the automotive, agricultural, computer, electronic, food processing, aerospace, pharmaceutical, chemical, bottling and canning, print finishing and packaging. Although a wide variety of materials can be conveyed, some of

the most common include food items such as beans and nuts, bottles and cans, automotive components, scrap metal, pills and powders, wood and furniture and grain and animal feed. Many factors are important in the accurate selection of a conveyor system. It is important to know how the conveyor system will be used beforehand. Some individual areas that are helpful to consider are the required conveyor operations, such as transportation, accumulation and sorting, the material sizes, weights and shapes and where the loading and pickup points need to be.

Types of conveyor systems

Gravity roller conveyor Gravity skatewheel conveyor Belt conveyor Wire mesh conveyors Plastic belt conveyors Bucket conveyors Flexible conveyors Vertical conveyors Spiral conveyors Vibrating conveyors Pneumatic conveyors Electric Track Vehicle Systems Belt driven live roller conveyors Lineshaft roller conveyor Chain conveyor Screw conveyor aka Auger conveyor Chain driven live roller conveyor Overhead conveyors Dust proof conveyors Pharmaceutical conveyors Automotive conveyors Overland conveyor Drag Conveyor

Pneumatic conveyor systems

Every pneumatic system, would makes use of pipes or ducts called transportation lines that carry mixture of materials and a stream of air. These materials are such as dry pulverized or free flowing or light powdery materials like cement, fly ash etc. These materials can be transported conveniently to various destinations by means of a stream of high velocity air through pipe lines. Products are moved through various tubes via air pressure, allowing for extra vertical versatility. Pneumatic conveyors are either carrier systems or dilute-phase systems; carrier systems simply push items from one entry point to one exit point, such as the money-exchanging tubes used at a bank drive-through window. Dilute-phase systems use push-pull pressure to guide materials through various entry and/or exit points. It is

important to note that either air compressors, vacuums, or blowers can be used to generate the air. This will all depend on what the engineers think will be the most efficient and economical way of developing the system.[5] Three basic systems that are used to generate high velocity air stream:

Suction or vacuum systems, utilizing a vacuum created in the pipeline to draw the material with the surrounding air. The system operated at a low pressure, which is practically 0.4–0.5 atm below atmosphere, and is utilized mainly in conveying light free flowing materials.

Pressure-type systems, in which a positive pressure is used to push material from one point to the next. The system is ideal for conveying material from one loading point to a number of unloading points. It operates at a pressure of 6 atm and upwards.

Combination systems, in which a suction system is used to convey material from a number of loading points and a pressure system is employed to deliver it to a number of unloading points.

Vibrating conveyor systems

A Vibrating Conveyor is a machine with a solid conveying surface which is turned up on the side to form a trough. They are used extensively in food grade applications where sanitation, washdown, and low maintenance are essential. Vibrating conveyors are also suitable for harsh, very hot, dirty, or corrosive environments. They can be used to convey newly cast metal parts which may reach upwards of 1,500 °F (820 °C). Due to the fixed nature of the conveying pans vibrating conveyors can also perform tasks such as sorting, screening, classifying and orienting parts. Vibrating conveyors have been built to convey material at angles exceeding 45° from horizontal using special pan shapes. Flat pans will convey most materials at a 5° Incline from horizontal line.

Flexible conveyor systems

The flexible conveyor is based on a conveyor beam in aluminum or stainless steel, with low friction slide rails guiding a plastic multi-flexing chain. Products to be conveyed travel directly on the conveyor, or on pallets/carriers. These conveyors can be worked around obstacles and keep production lines flowing. They are made at varying levels and can work in multiple environments. They are used in food packaging, case packing, and pharmaceutical industries but also in retail stores such as Wal-Mart and Kmart.[6]

Vertical conveyor systems and spiral conveyors

Vertical conveyor - also commonly referred to as freight lifts and material lifts - are conveyor systems used to raise or lower materials to different levels of a facility during the handling process. Examples of these conveyors applied in the industrial assembly process include transporting materials to different floors. While similar in look to freight elevators, vertical conveyors are not equipped to transport people, only materials.

Vertical lift conveyors contain two adjacent, parallel conveyors for simultaneous upward movement of adjacent surfaces of the parallel conveyors. One of the conveyors normally has spaced apart flites for

transporting bulk food items. The dual conveyors rotate in opposite directions, but are operated from one gear box to insure equal belt speed. One of the conveyors is pivotally hinged to the other conveyor for swinging the pivotally attached conveyor away from the remaining conveyor for access to the facing surfaces of the parallel conveyors.[7] Vertical lift conveyors can be manually or automatically loaded and controlled.[8] Almost all vertical conveyors can be systematically integrated with horizontal conveyors, since both of these conveyor systems work in tandem to create a cohesive material handling assembly line.

In similarity to vertical conveyors, spiral conveyors raise and lower materials to different levels of a facility. In contrast, spiral conveyors are able to transport material loads in a continuous flow. Industries that require a higher output of materials - food and beverage, retail case packaging, pharmaceuticals - typically incorporate these conveyors into their systems over standard vertical conveyors due to their ability to facilitate high throughput. Most spiral conveyors also have a lower angle of incline or decline (11 degrees or less) to prevent sliding and tumbling during operation.

Heavy duty roller conveyors

Heavy Duty roller conveyors are used for moving items that are at least 500 lbs. This type of conveyor makes the handling of such heavy equipment/products easier and more time effective. Many of the heavy duty roller conveyors can move as fast as 75 feet/minute.

Other types of heavy duty roller conveyors are gravity roller conveyor, chain driven live roller conveyor, pallet accumulation conveyor, multi-strand chain conveyor, and chain & roller transfers.

Gravity roller conveyors are extremely easy to use and are used in many different types of industries such as automotive and retail.

Chain driven live roller conveyors are used for single or bi-directional material handling. Large heavy loads are moved by chain driven live roller conveyors.

Pallet accumulation conveyors are powered through a mechanical clutch. This is used instead of individually powered and controlled sections of conveyors.

Multi-strand chain conveyors are used for double pitch roller chains. Products that can not be moved on traditional roller conveyors can be moved by a multi-strand chain conveyor.

Chain & roller conveyors are short runs of two or more strands of double pitch chain conveyor built into a chain driven line roller conveyor. These pop up under the load and move the load off of the conveyor.

C. Size Reduction of solids

Four commonly used methods for size reduction:

1). Compression; 2). Impact; 3). Attrition; 4). Cutting.

Principle of size reduction

Criteria for size reduction

An ideal crusher would (1) have a large capacity; (2) require a small power input per unit of product; and (3) yield a product of the single size distribution desired.

Energy and power requirements in size reduction

The cost of power is a major expense in crushing and grinding, so the factors that control this cost are important.

Crushing efficiency

Empirical relationships: Rittinger’s and Kick’s law

The work required in crushing is proportional to the new surface created. This is equivalent to the statement that the crushing efficiency is constant and, for a giving machine and material, is independent

of the sizes of feed and product. If the sphericities a (before size reduction) and b (after size reduction) are equal and the machine efficiency is constant, the Rittinger’s law can be written as

where P is the power required, is the feed rate to crusher, is the average particle diameter

before crushing, is the average particle diameter after crushing, and Kr is Rittinger’s coefficient.

Kick’s law: the work required for crushing a given mass of material is constant for the same reduction ratio, that is the ratio of the initial particle size to the finial particle size

where Kk is Kick’s coefficient.

Bond crushing law and work index

The work required to form particles of size Dp from very large feed is proportional to the square root of

the surface-to-volume ratio of the product,sp/vp. Since s = 6/Dp, it follows that

where Kb is a constant that depends on the type of machine and on the material being crushed.

The work index, wi, is defined as the gross energy required in KWH per ton of feed to reduce a very large

feed to such a size that 80% of the product passes a 100 m screen. If Dp is in millimetres, P in KW,

and in tons per hour, then

If 80% of the feed passes a mesh size of Dpa millimetres and 80% of the product a mesh of Dpb millimetres, it follows that

Example: What is the power required to crush 100 ton/h of limestone if 80% of the feed pass a 2-in screen and 80% of the product a 1/8 in screen? The work index for limestone is 12.74.

Solution:  =100 ton/h, wi =12.74, Dpa =2 25.4=50.8 mm, Dpb =25.4/8=3.175 mm

Size reduction equipment

Size reduction equipment is divided into crushers, grinders, ultrafine grinders, and cutting machines. Crusher do the heavy work of breaking large pieces of solid material into small lumps. A primary crusher operates on run-of -mine material accepting anything that comes from mine face and breaking it into 150 to 250 mm lumps. A secondary crusher reduces these lumps into particles perhaps 6mm in size. Grinders reduce crushed feed to powder. The product from an intermediate grinder might pass a 40-mesh screen; most of the product from a fine grinder would pass a 200-mesh screen with a 74 m opening. An ultrafine grinder accepts feed particles no larger than 6mm and the product size is typically 1 to 5 m. Cutters give particles of definite size and shape, 2 to 10mm in length.

The principal types of size-reduction machines are as follows:

A. Crushers (coarse and fine)

A crusher is a machine designed to reduce large rocks into smaller rocks, gravel, or rock dust.

Crushers may be used to reduce the size, or change the form, of waste materials so they can be more easily disposed of orrecycled, or to reduce the size of a solid mix of raw materials (as in rock ore), so that pieces of different composition can be differentiated. Crushing is the process of transferring a force amplified by mechanical advantage through a material made of molecules that bond together more strongly, and resist deformation more, than those in the material being crushed do. Crushing devices hold material between two parallel or tangent solid surfaces, and apply sufficient force to bring the surfaces together to generate enough energy within the material being crushed so that its molecules separate from (fracturing), or change alignment in relation to (deformation), each other. The earliest crushers were hand-held stones, where the weight of the stone provided a boost to muscle power, used against a stone anvil. Querns and mortars are types of these crushing devices.

1. Jaw crushers

A jaw crusher uses compressive force for breaking of particle. This mechanical pressure is achieved by the two jaws of the crusher of which one is fixed while the other reciprocates. A jaw or toggle crusher consists of a set of vertical jaws, one jaw is kept stationary and is called a fixed jaw while the other jaw, called a swing jaw, moves back and forth relative to it, by a cam or pitman mechanism, acting like a class II lever or a nutcracker. The volume or cavity between the two jaws is called the crushing chamber. The movement of the swing jaw can be quite small, since complete crushing is not performed in one stroke. The inertia required to crush the material is provided by a weighted flywheel that moves a shaft creating an eccentric motion that causes the closing of the gap.

2. Gyratory crushers

A gyratory crusher is similar in basic concept to a jaw crusher, consisting of a concave surface and a conical head; both surfaces are typically lined with manganese steel surfaces. The inner cone has a slight circular movement, but does not rotate; the movement is generated by an eccentric arrangement. As with the jaw crusher, material travels downward between the two surfaces being progressively crushed until it is small enough to fall out through the gap between the two surfaces.

A gyratory crusher is one of the main types of primary crushers in a mine or ore processing plant. Gyratory crushers are designated in size either by the gape and mantle diameter or by the size of the receiving opening. Gyratory crushers can be used for primary or secondary crushing. The crushing action is caused by the closing of the gap between the mantle line (movable) mounted on the central vertical spindle and the concave liners (fixed) mounted on the main frame of the crusher. The gap is opened and

closed by an eccentric on the bottom of the spindle that causes the central vertical spindle to gyrate. The vertical spindle is free to rotate around its own axis. The crusher illustrated is a short-shaft suspended spindle type, meaning that the main shaft is suspended at the top and that the eccentric is mounted above the gear. The short-shaft design has superseded the long-shaft design in which the eccentric is mounted below the gear.

3. Cone crusher

With the rapid development of mining technology, the cone crusher can be divided into four types: compound cone crusher, spring cone crusher, hydraulic cone crusher and gyratory crusher. According to different models, the cone crusher is divided into VSC series cone crusher(compound cone crusher), Symons cone crusher, PY cone crusher, single cylinder hydraulic cone crusher, multi-cylinder hydraulic cone crusher ， gyratory crusher, etc.

A cone crusher is similar in operation to a gyratory crusher, with less steepness in the crushing chamber and more of a parallel zone between crushing zones. A cone crusher breaks rock by squeezing the rock between an eccentrically gyrating spindle, which is covered by a wear resistant mantle, and the enclosing concave hopper, covered by a manganese concave or a bowl liner. As rock enters the top of the cone crusher, it becomes wedged and squeezed between the mantle and the bowl liner or concave. Large pieces of ore are broken once, and then fall to a lower position (because they are now smaller) where they are broken again. This process continues until the pieces are small enough to fall through the narrow opening at the bottom of the crusher.

A cone crusher is suitable for crushing a variety of mid-hard and above mid-hard ores and rocks. It has the advantage of reliable construction, high productivity, easy adjustment and lower operational costs. The spring release system of a cone crusher acts an overload protection that allows tramp to pass through the crushing chamber without damage to the crusher.

B. Grinders (intermediate and fine)

1. Hammer mills; impactors2. Rolling-compression mills3. Attrition mills4. Tumbling mills

C. Ultrafine grinders

1. Hammer mills with internal classification2. Fluid-energy mills3. Agitated mills

D. Cutting machines

1. Knife cutters; dicers; slitters

D. Separation and Classification of Solids

Mechanical separations are performed based on the physical difference between particles such as size, shape, or density. Mechanical separations are applicable to heterogeneous mixtures, not to homogeneous solutions.

Screening

Screening is a method of separating particles according to size alone.

Undersize: fines, pass through the screen openings

Oversize: tails, do not pass

A single screen can make but a single separation into two fractions. These are called unsized fractions, because although either the upper or lower limit of the particle sizes they contain is known, the other limit is unknown. Material passed through a series of screens of different sizes is separated into sized fractions, i.e. fractions in which both the maximum and minimum particle sizes are known.

Screening equipment

Stationary screens and grizzlies; Gyrating screens; Vibrating screens; Centrifugal sitter.

Cutting diameter Dpc: marks the point of separation, usually Dpc is chosen to be the mesh opening of the screen.

Actual screens do not give a perfect separation about the cutting diameter. The undersize can contain certain amount of material coarser than Dpc, and the oversize can contain certain amount of material that is smaller than Dpc.

Material balances over a screen

Let F, D, and B be the mass flow rates of feed, overflow, and underflow, respectively, and xF, xD, and xB be the mass fractions of material A in the streams. The mass fractions of material B in the feed, overflow, and underflow are 1- xF, 1- xD, and 1- xB.

F = D + B

FxF = DxD + BxB

Elimination of B from the above equations gives

Elimination of D gives

Screen effectiveness

A common measure of screen effectiveness is the ratio of oversize material A that is actually in the overflow to the amount of A entering with the feed. These quantities are DxD and FxF respectively. Thus

where EA is the screen effectiveness based on the oversize. Similarly, an effectiveness EB based on the undersize materials is given by

A combined overall effectiveness can be defined as the product of the two individual ratios.

Filtration

Filtration is the removal of solid particles from a fluid by passing the fluid through a filtering medium, or septum, on which the solids are deposited. The fluid may be liquid or gas, the valuable stream from the filter may be fluid, or the solid, or both. Sometimes it is neither, as when waste solid must be separated from waste liquid prior to disposal.

Filters are divided into three main groups: cake filters, clarifying filters, and crossflow filters. Cake filters separate relatively large amount of solids as a cake of crystals or sludge. Often they include provisions for washing the cake and for removing some of the liquid from the solids before discharge. At the start of filtration in a cake filter, some solid particles enter the pores of the medium and are immobilised, but soon others begin to collect on the septum surface. After this brief period the cake of solids does the filtration, not the septum; a visible cake of appreciable thickness builds up on the surface and must be periodically removed. Clarifying filters remove small amount of solids to produce a clean gas or a

sparkling clear liquid such as beverage. The solid particles are trapped inside the filter medium or on its external surfaces. Clarifying filters differ from screens in that the pores of the filter medium are much larger in diameter than the particles to be removed. In a crossflow filter, the feed suspension flows under pressure at a fairly high velocity across the filter medium. A thin layer of solids may form on the surface of the medium, but the high liquid velocity keeps the layer from building up. The filter medium is a ceramic, metal, or polymer membrane with pores small enough to exclude most of suspended particles. Some of the liquid passes through the medium as clear filtrate, leaving a more concentrated suspension behind.

The theory of filtration

In cake filters, the particles forming the cake are small and the flow through the bed is slow. Streamline conditions are invariably obtained. From Kozeny equation,

(1)

where u is the velocity of the filtrate, L is the cake thickness, S is the specific surface of the particles, e is the porosity of cake, m is the viscosity of the filtrate, and D P is the applied pressure difference. The filtrate velocity can also be written as

(2)

where V is the volume of filtrate which has passed in time t and A is the total cross-sectional area of the filter cake.

For incompressible cakes e can be taken as constant and the quantity e 3/[5(1-e )2S2] is then a property of the particles forming the cake and should be constant for a given material. Therefore

(3)

where

(4)

Eq(3) is the basic filtration equation and r is termed the specific resistance. It is seen to depend on e and S. For incompressible cakes it is taken as constant, but it will depend on the rate of deposition, nature of particles, and on forces between the particles.

In Eq(3), the variables V and L are connected, and the relation between them can be obtained by making a material balance between the solids in the slurry and in the cake.

Mass in the filter cake is (1-e )ALr s, where r s is the density of the solids.

Mass of liquid retained in the filter cake is e ALr , where r is the density of the filtrate.

If J is the mass fractions of solids in the original suspension

(5)

That is

(6)

Therefore

(7)

and

(8)

If v is the volume of cake deposited by unit volume of filtrate then:

or (9)

and from Eq(8):

(10)

Substituting for L in Eq(3)

or

(11)

Eq(11) can be regarded as the basic relation between D P, V, and t. Two important types of operation will be considered: 1). where the pressure difference is maintained constant and, 2). where the rate of filtration is maintained constant.

Constant pressure difference

Eq(11) can be re-written as

(12)

Integrating Eq(12) gives

or (13)

Thus for a constant pressure filtration, there is a linear relation between V2 and t. Filtration at constant pressure is more frequently adopted in practical conditions.

Constant rate filtration

constant (14)

Therefore

or (15)

In this case, D P is directly proportional to V.

Flow of filtrate through the septum and cake combined

Suppose that the filter septum to be equivalent to a thickness Ls of cake, then if D P is the pressure drop across the cake and septum combined Eq(3) can be written as:

(16)

i.e.

(17)

For constant rate filtration we have

(18)

For constant pressure filtration we have

(19)

Separations based on the motion of particles through fluids

Devices that separate particles of differing densities are known as sorting classifiers. They use one of the two principal separation methods: sink-and-float and differential settling.

Sink-and-float methods

A sink-and-float method uses a liquid sorting medium, the density of which is intermediate between that of the light material and that of the heavy material. Then the heavy particles settle through the medium, and the lighter ones float, and a separation is thus obtained. This method has the advantage that, in principle, the separation depends only on the difference in the densities of the two substances and is independent of the particle size. This method is also known as the heavy-fluid separation.

Heavy fluid processes are used to treat relatively coarse particles, usually greater than 10-mesh. A comment choice of medium is a pseudoliquid consisting of a suspension in water of fine particles

Differential settling methods

Differential settling methods utilise the difference in terminal velocities that exist between substances of different density. The density of the medium is less than that of either substance.

Consider particles of two materials A and B settling through a medium of density p . Let A be the heavier. If the smallest particle of A settles faster than the largest particle of B, then complete separation of A and B can be achieved.

For settling in the Stokes’ law region, the terminal velocity can be calculated as

For equal-settling particles, utA = utB, therefore

For settling in the Newton’s law range

If the ratio of diameters of the smallest particle of A and the largest particle of B is larger than the equal-settling ratio, then perfect separation of A and B can be achieved.

II. Dryers and Drying processes

Drying is a mass transfer process consisting of the removal of water or another solvent by evaporation from a solid, semi-solid or liquid. This process is often used as a final production step before selling or packaging products. To be considered "dried", the final product must be solid, in the form of a continuous sheet (e.g., paper), long pieces (e.g., wood), particles (e.g., cereal grains or corn flakes) or powder (e.g., sand, salt, washing powder, milk powder). A source of heat and an agent to remove the vapor produced by the process are often involved. In bio products like food, grains, and pharmaceuticals like vaccines, the solvent to be removed is almost invariably water.

In the most common case, a gas stream, e.g., air, applies the heat by convection and carries away the vapor as humidity. Other possibilities are vacuum drying, where heat is supplied by conduction or radiation (or microwaves), while the vapor thus produced is removed by the vacuum system. Another indirect technique is drum drying (used, for instance, for manufacturing potato flakes), where a heated surface is used to provide the energy, and aspirators draw the vapor outside the room. In contrast, the mechanical extraction of the solvent, e.g., water, by centrifugation, is not considered "drying" but rather "draining".

Drying mechanism

In some products having a relatively high initial moisture content, an initial linear reduction of the average product moisture content as a function of time may be observed for a limited time, often known as a "constant drying rate period". Usually, in this period, it is surface moisture outside individual particles that is being removed. The drying rate during this period is mostly dependent on the rate of heat transfer to the material being dried. Therefore, the maximum achievable drying rate is considered to be heat-transfer limited. If drying is continued, the slope of the curve, the drying rate, becomes less steep (falling rate period) and eventually tends to nearly horizontal at very long times. The product moisture content is then constant at the "equilibrium moisture content", where it is, in practice, in equilibrium with the dehydrating medium. In the falling-rate period, water migration from the product interior to the surface is mostly by molecular diffusion, i,e. the water flux is proportional to the moisture content gradient. This means that water moves from zones with higher moisture content to zones with lower values, a phenomenon explained by the second law of thermodynamics. If water removal is considerable, the products usually undergo shrinkage and deformation, except in a well-designed freeze-drying process. The drying rate in the falling-rate period is controlled by the rate of removal of moisture or solvent from the interior of the solid being dried and is referred to as being "mass-transfer limited".

Methods of drying

The following are some general methods of drying:

Application of hot air (convective or direct drying). Air heating increases the driving force for heat transfer and accelerates drying. It also reduces air relative humidity, further increasing the driving force for drying. In the falling rate period, as moisture content falls, the solids heat up and the higher temperatures speed up diffusion of water from the interior of the solid to the surface. However, product quality considerations limit the applicable rise to air temperature. Excessively hot air can almost completely dehydrate the solid surface, so that its pores shrink and almost close, leading to crust formation or "case hardening", which is usually undesirable. For instance in wood (timber) drying, air is heated (which speeds up drying) though some steam is also added to it (which hinders drying rate to a certain extent) in order to avoid excessive surface dehydration and product deformation owing to high moisture gradients across timber thickness. Spray drying belongs in this category.

Indirect or contact drying (heating through a hot wall), as drum drying, vacuum drying. Again, higher wall temperatures will speed up drying but this is limited by product degradation or case-hardening. Drum drying belongs in this category.

Dielectric drying (radiofrequency or microwaves being absorbed inside the material) is the focus of intense research nowadays. It may be used to assist air drying or vacuum drying. Researchers have found that microwave finish drying speeds up the otherwise very low drying rate at the end of the classical drying methods.

Freeze drying or lyophilization is a drying method where the solvent is frozen prior to drying and is then sublimed, i.e., passed to the gas phase directly from the solid phase, below the melting point of the solvent. It is increasingly applied to dry foods, beyond its already classical pharmaceutical or medical applications. It keeps biological properties of proteins, and retains vitamins and bioactive compounds. Pressure can be reduced by a high vacuum pump (though freeze drying at atmospheric pressure is possible in dry air). If using a vacuum pump, the vapor produced by sublimation is removed from the system by converting it into ice in a condenser, operating at very low temperatures, outside the freeze drying chamber.

Supercritical drying (superheated steam drying) involves steam drying of products containing water. This process is feasible because water in the product is boiled off, and joined with the drying medium, increasing its flow. It is usually employed in closed circuit and allows a proportion of latent heat to be recovered by recompression, a feature which is not possible with conventional air drying, for instance. The process has potential for use in foods if carried out at reduced pressure, to lower the boiling point.

Natural air drying takes place when materials are dried with unheated forced air, taking advantage of its natural drying potential. The process is slow and weather-dependent, so a wise strategy "fan off-fan on" must be devised considering the following conditions: Air temperature, relative humidity and moisture content and temperature of the material being dried. Grains are increasingly dried with this technique,

and the total time (including fan off and on periods) may last from one week to various months, if a winter rest can be tolerated in cold areas.

Applications of drying

Foods are dried to inhibit microbial development and quality decay. However, the extent of drying depends on product end-use. Cereals and oilseeds are dried after harvest to the moisture content that allows microbial stability during storage. Vegetables are blanched before drying to avoid rapid darkening, and drying is not only carried out to inhibit microbial growth, but also to avoid browning during storage. Concerning dried fruits, the reduction of moisture acts in combination with its acid and sugar contents to provide protection against microbial growth. Products such as milk powder must be dried to very low moisture contents in order to ensure flowability and avoid caking. This moisture is lower than that required to ensure inhibition to microbial development. Other products as crackers are dried beyond the microbial growth threshold to confer a crispy texture, which is liked by consumers.

Classification of dryers

Adiabatic or direct: Solid directly exposed to hot gas (usually air). Nonadiabatic or indirect: Heat transfer from an external medium, usually through a contact with

a metal surface. Dryers heated by dielectric, radiant, or microwave energy.

Handling of solids

a) Crosscirculation

b) Throughcirculation

c) Rotary dryer

d) Fluidized bed

e) Entrained in high-velocity gas stream

f) Spray drying

PRINCIPLES OF DRYING

Temperature pattern

Temperature patterns

The particular way temperature varies depends on many factors OTOH, there exist typical patterns of variation

Batch dryer with heating medium at constant temperatureo Rapid rise to initial vaporization temperature Tv where a considerable part of drying time is

spento As a dry solids zone forms near the surface, the temperature of wet solids gradually riseso In the final stages, the solids temperature once again increases rapidly to a higher value Tsb

Heat transfer in dryers

Heat is needed to:

Heat the feed (solids + liquid) to the vaporization temperature Tv Vaporize the liquid Heat the solids to their final temperature Tsb Heat the vapor to its final temperature Tva Heat the air to its final temperature.

Phase equilibria

Equilibrium data provided for most solids: relationship between relative humidity of the gas and the liquid content of the solid. Almost independent of the temperature. Wet solid brought into contact with air of humidity differing from the equilibrium one tends to either lose or absorb moisture and come to the equlibrium with the air.