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Material Handling Systems

 


Syllabus:
Liquid handling – different types of pumps.
Gas handling – various types of fans, blowers and compressors.
Solid handling – conveyors.
 


PUMPS

Pump is a device that moves the fluid through a pipe.
Minimum configuration of a pump:                            Cylinder,
                                                                           piston or plunger,
                                                                           power to drive the piston and
                                                                           valves.

1. Classification of pumps according to mode of operation

A.     Reciprocating pumps: The piston or plunger moves in to-and-fro movement. Examples are piston pump, plunger pump and diaphragm pump.
B.     Rotary pumps: The liquid moves in one direction by rotating a part inside the pump. Examples are centrifugal pumps and gear pumps.
C.     Miscellaneous pumps: Example is peristaltic pump.


Few terms:
1.      Water cylinder: The pumping element moves in forward and backward direction inside a cylinder. This cylinder is called water cylinder because it is usually used for pumping water. A pump may be known as simplex, duplex, or triplex when there is one, two, or, three water cylinders respectively.
2.      Positive displacement pump: This type of pump creates a pressure and lifts the liquid by the displacement of moving member (i.e. piston or plunger).
3.      Steam cylinder: Some reciprocating pumps are driven by steam. In those cases the piston or plunger moves inside the water cylinder and the piston or plunger is driven by a shaft connected to the pistons of cylinders in which steam creates the pressure.
4.      Power reciprocating pumps: In this case the piston is driven by electrical motors.
5.      Piston: It is a rod one end of which is fixed with a packing material.
6.      Plunger: It is a complete cylinder without any packing material.
7.      Single-acting pump: When the piston moves towards one side



RECIPROCATING PUMP PISTON TYPE
(SIMPLEX, DOUBLE ACTING, DECK VALVE, PISTON TYPE PUMP)

Construction
The pump in the figure has single water cylinder – hence called simplex pump. The pump consists:
(i)     A piston consisting essentially of two discs A1 and A2 with rings of packing B between them. The piston operates within a removable bornze liner, C.
(ii)   The lower row of valves, E1 and E2 are suction valves, in the upper row F1 and F2 are discharge valves.
(iii) The overall assembly is packed within an air-tight casing.
Operation
(i)     If the piston is moving from left to right, it will create a suction on the left hand side which will open the left hand suction valves E1 and close the left hand discharge valves F1.
(ii)   At the same time a pressure is develop on the right hand side which will close the E2 suction valves and open F2 discharge valves.
This pump is double acting , because it displaces water on both halves of the cycle.
               The pump requires minimum 4 valves.
Uses
·        This type of pump is suitable for pressure heads upto 150 to 200 ft and for any liquids that are not viscous, corrosive or abrasive.
·        The valve type is deck valves, hence it cannot withstand very high pressure.
RECIPROCATING DUPLEX PUMP
(Reciprocating, Duplex, Plunger Type Pump)


Construction
               The pump in the figure consists of two water cylinders, hence called duplex pump. The pump consists:
(i)     Two plungers are packed inside the cylinders. Two stationary packing ring in between the plungers and the cylinders.
(ii)   Two suction valves, C1,C2 and two discharge valves D1, D2 are provided.
(iii) the cylinder is divided into two parts by a partition F.
Operation
(i)     Both the plungers act synchronously. When left plunger A1, is producing suction, right plunger A2 increases the pressure.
(ii)   When plunger A1 produce suction pressure, suction valve C1 opens and discharge valve D1 remains closed. At the same time plunger A2 produce pressure so discharge valve D2 opens while suction valve C2 remains closed.
Use
(i)     When pump liquids contains suspended matter that may abrade the packing so that replacement are more frequent then this type of pump is useful.
Since the valves are of pot-valve type hence can be used under high pressure.

RECIPROCATING DIAPHRAGM PUMP
Construction
               In the figure of diaphragm pump instead of a piston or plunger it employs a flexible diaphragm with a discharge valve attached to the shaft the discharge valve is flap type]. it also has a suction valve.
Operation
               When the shaft is moved upward the chamber C experiences partial vacuum and suction valve is opened and liquid comes in. When the shaft goes down the discharge valve opens and suction valve closes – the liquid comes out of the pump.
Uses / Advantages
(i)     Since it has  no moving parts except the flexible diaphragm and the valve, since its construction is rugged and simple and repairs are easily made, it is suited for the most severe services.
(ii)   It is the most satisfactory pump available for handling liquids with large amounts of solids in suspension under low pressure.
By adjusting the diaphragm the stroke may be varied and the discharge  controlled within accurate limits.
ROTARY PUMP
(i)     Rotary positive displacement pump
(ii)   Centrifugal pump

ROTARY POSITIVE DISPLACEMENT PUMP (GEAR PUMP)

Construction
               The pump consists of essential two gears, which match with each other and which run in close contact with the casing. The number of teeth of the gears varies from two or more in each wheel.
Operation
Slugs of liquids are cut between the gear teeth and the casing, carried around next to the casing and forced out through the discharge pipe.
Use
(i)     Such a pump handles viscous or heavy liquids.
(ii)   Since the performance of positive displacement rotary pump depends on maintaining a running fit between the rotating member and the casing it is not desirable to use this pumps on liquids that carry solids in suspension.
(iii) They are used to handle quite stiff pastes, semifluid waxes and similar material can be handled with those pumps when the speed is not too high.

CENTRIFUGAL PUMP

The main principle of these pumps is that the liquid is sucked from the centre of an impeller and thrown centrifugally upwards to the periphery from where liquid is discharged.
Centrifugal pumps are of two distinct types, Volute type and Turbine type.
Construction
The simplest form of the centrifugal pump is the single-stage single suction, open runner volute. The most important member of the centrifugal pump is the impeller or runner. This consist essentially of a series of curved vanes extending from a hub. This is maintained in the casing of the pumps in such a way that the two halves of the casing are as near by as possible in contact with the surface of these vanes.
Operations
Water entering at the suction connection is thrown outward by the rotation of the vanes. As the liquid leaves the vanes and enters the volute of the casing , the velocity is increased according to Bernoulli’s theorem therefore, its pressure must be correspondingly increased and this increase in pressure is the source of the head developed by the pump.
Disadvantages
In case of open impeller system there are two main power losses:
(i)     The water which was thrown out radically by the vanes must suddenly change its direction as it enters the volute. Any such sudden change in direction involves turbulence which consumes power in the form of friction.
(ii)   These are cheap pumps and therefore not accurately finished. This fit between the impeller and the casing is usually poor and therefore there is leakage from the discharge side back to the suction side.
To prevent this loss by leakage from the discharge side to the suction side, the closed impeller system has bee developed. In this case the vanes of the impeller are enclosed between two rings.
TURBINE CENTRIFUGAL PUMP
Construction
               Turbine pumps consists of an impeller with vanes, a diffusion ring – they are fitted in a casing. The diffusion ring is stationary. The liquid is discharged in a volute.
Operation
               In case of volute pumps the principal energy loss was due to turbulence that occurs at the point where the liquid changes its path from radial flow (due to the action of the impeller) to tangential flow in the discharge volute. The diffusion ring in a turbine pump cause the liquid to make this change in direction smoothly and without shocks or eddies. The liquid issuing from the tip of the impeller is caught in these passages and turned gradually and smoothly into the discharge volute.
Use
Turbine pumps is reserved for clear, non-viscous and non-corrosive liquids.

GAS HANDLING


The devices for transportation of gases are called blowers or compressors. The devices available are Ejectors, Fans, Blowers and Compressors.

FANS

Fans consists a set of blades placed on a shaft. This blade assembly is placed inside a casing. When the blades rotates the air inside the casing is thrown forward and a partial vacuum is created inside the casing. Gas enters inside the casing through the center and passes out through the volute.
Classification of fans:      (i) Propeller type,                             (ii) Plate fan        and (iii) Multiblade type.

 

 

 

 

 

 

 

 



Propeller type:

These fans are similar to electric fan and are not of much use in industrial plants. They propels the gas from one end to other.

Plate fan

They consist of steel-plate blades on radial arms inside a casing. Each fan may have 8 to 12 plates. The blades may be flat or curved (like vanes in centrifugal pumps). When the blades rotates the air inside the casing is thrown forward and a partial vacuum is created inside the casing. Gas enters inside the casing through the center and passes out through the volute. These fans can draw gas from an area having pressure of 0 to 5 inches water.

Multiblade fan

In these types of fans a large number of blades are fitted in the form of a circle. When the blades rotates the air inside the casing is thrown forward and a partial vacuum is created inside the casing. Gas enters inside the casing through the center and passes out through the volute. These fans can draw gas from an area having pressure of 0 to 5 inches water. These fans can deliver much larger volume of gas for a given size of drum (casing) than steel plate fans (due to multiple blades).

BLOWERS

 

CYCLOIDAL BLOWER

This type of blower has two moving parts. Either they may be cycloidal or gear type. In the figure the moving parts are cycloidal type or lobe shape. The lobes move in opposite direction. When they move tightly against the casing the air is displaced and a suction is produced. The gas is expelled out.
Advantages:
1.      These fans can draw gas from an area having pressure of 0.5 to 12 psi.
2.      Very simple construction.
3.      Very large capacity. They can expel gas against very high pressure where normal fans cannot.

NASH HYTOR


It has a central cylindrical rotor, carrying vanes around its circumference. This rotor is placed inside a casing that is nearly elliptical in shape. A sufficient amount of liquid is placed inside the casing to seal the impeller (rotor and vanes) at its minor axis of the ellipse. When the impeller rotates it causes the liquid to rotate, but centrifugal force keeps the liquid pressed against the casing. The liquid therefore, moves in to-and-fro motion along the major axis of the elliptical casing. As the liquid moves away from inlet a suction is produced, gas is drawn inside and as they move towards outlet a compression is produced and gas is expelled out.
Advantages:
1.      This blower can work at 8 to 20 psi.
2.      Impeller and casing do not have any contact with each other, hence the rotor may be made of any non-corrosive material.
3.      The liquid should be inert to the gas handled. E.g. Concentrated H2SO4 may be used to compress chlorine gas.

CENTRIFUGAL BLOWER


It acts just like a centrifugal pump. The impeller is turbine type.
Construction:
·        Gases have relatively low density, so the centrifugal force that can be developed by an impeller is very small, and therefore the pressure that can be developed in one stage is also small. So instead of one stage multistage constructions are used where three or more impellers are used in separate casings.
·        The rotating parts (impellers) are very light.
·        The impellers are fitted on one shaft and rotates at a speed of 4000 to 6000 rpm.  The pressure developed due to this rotation is approximately 40 to 100psi.
Working
·        Low pressure gas is admitted by the inlet volute, pumped by the impellers through stationary diffusion channels and discharged from the outlet volute. Replaceable wearing rings are provided at all points where moving surface must be sealed to a stationary one.
Advantages: They are the most efficient blowers.
Disadvantages: High cost of initial installation.

RECIPROCATING COMPRESSOR

Use: This compressor can deliver gas against a pressure of more than 5 psi.
Principle:
The design is similar to piston pump. For higher pressures usually two or more compressors are joined in series. The diagram shows the scheme of a two stage compressor.
Two air-cylinders are there. Second cylinder is smaller than the first one because when the gas is compressed in the first stage the volume of the gas is reduced.
Gases are compressible. When the gas is compressed heat is generated. To cool the cylinder water jackets are provided around the cylinders and when the high temperature compressed gas is transferred to second stage it is passed through an intercooler.

Working:
The gas is drawn through the inlet of Stage-I during suction cycle. The gas is compressed and passed to intercooler for cooling during compression cycle of Stage-I. During the suction cycle of Stage-II the compressed gas is drawn inside the cylinder of Stage-II. The gas is compressed and released through the outlet of Stage-II.

SOLID HANDLING (CONVEYORS)


The term conveying is applied to the transportation to solids.

Classification of conveyors:

1. Belt conveyors                             2. Screw conveyors           3. Pneumatic conveyors
4. Chain conveyors           5. Bucket conveyors

BELT CONVEYORS


 
Construction
·        The belt conveyor consists of a belt which is made of several layers of cotton pasted with rubber. Both ends of the belt is joined, so that the belt can revolve continuously. The belts move from the feed end to discharge end.
·        For support the belt is placed over steel rollers called idlers. After feeding the material may spill over the belt so the belt is placed over inclined (200) idlers and thus a trough shape is formed.
·        The belt moves on two steel pulleys – one at the feed end and the other at the discharge end. Usually the pulley at the discharge end is driven by a motor.
·        The bottom part of the belt is supported by a few non-toughing idlers. At the feed end and discharge end two snubber idlers keep the belt pressing with the feed and discharge pulleys.
·        Some times the belt is increased due to temperature, humidity or other factors. To tight the belts again tightners are installed to maintain an even tension on the belt.
·        Hopper is provided at the feed end to guide the feed material at the center of the belt.
·        Revolving brushes and rubber scrappers are installed on the path of the belt to clean it.
Working:
When power is applied to the motor the pulley at the discharge end starts revolving. The belt begins to travel from feed to discharge end.
The material to be transported are loaded at the center of the belt from the hopper. The belt moves forward on the troughing idlers. The material is unloaded at the discharge end.
Once the material is unloaded the belt returns to the feed end.
Advantages:
1.      Belts can be made of asbestos fibers, neoprene, teflon and vinyl polymer.
2.      Belt conveyors can be of any size even several kilometers (e.g. in coal mines).
3.      Routine maintenance of belt conveyors are easy.
4.      It is economical in terms of cost per unit tonne that it can handle.
Disadvantage: Initial installation is expensive.
Pharmaceutical applications:
1.      Used in transporting containers for filling, capping,  sealing, labeling, pasting, visual inspection in the filling and packing line.
2.      In blister and strip packing of tablets or capsules strips are conveyed on moving belts.

SCREW CONVEYORS

Principle
A screw-shaped flight is set in a trough either horizontally or in a slightly inclined position. As the flight rotates the material moves within the trough from feed point to discharge point.
Construction
·        The trough is a U-shaped vessel in which the material is placed for conveying. The trough is usually made of steel. If more length is required several troughs (units) are joined in series.
·        The flight is a spiral blade. It is made of a single long ribbon that is twisted and wrapped into a spiral shape. These ribbons are welded to the central shaft.
·        The shaft is driven by a motor. This end is called drive-end. Material is fed in a hopper placed over the drive end.
·        Material is collected from the other end. At this end the trough may be totally open pr bottom of the trough may be opened.
Working
When poured is applied, motor drives the shaft of the flight. The material is fed through a hopper. The material will be trapped between the gaps  of the spiral blades. As flight moves, the material also moves forward along the trough. The material is received at the discharge end.
Use
1.      Conveys fine powder and pasty solids.
2.      Materials of any density (heavy or light) can be conveyed.
3.      They can be used for mixing, heating, cooling and drying of solid powders by specially designed jacketed trough.
4.      It has a capacity to handle 280 cubic meter of material per hour.
Advantages
1.      Materials can be conveyed horizontally, vertically, and in inclined position.
2.      Easy to operate, occupies less space.
3.      Can be operated under high pressure or vacuum.
4.      High or low temperature can be maintained by jacketing the trough.
Disadvantages: High power consumption.

PNEUMATIC CONVEYOR

Principle
When a high velocity air is passed through a bed of solid powder, the individual particles are dragged by the air. Finally they are suspended in air. Such a system is called fluidized bed. In this condition the fluidized bed can be transported from one place to another. At the discharge end the gas is separated and the solids are recovered.
Construction
An air pump draws air and the air is blown by a cycloidal blower. The air is carried through a pipe. Powders are taken in silo (container) which is connected to air path through a rotary feeder valve. The other end of the pipeline is connected to a cyclone separator (for separation of bigger particles) and a bag filter (for separation of finer particles).
Working
The cycloidal blower (or fans) produces high pressure air. This air passes through the pipe at a rate of 1.5 meter / min. During this process, the rotary feeder valve rotates and allows the feed to enter the pipeline. This solids are suspended into a stream of air in a fluidized state until it reaches the discharge end. The material is then admitted to cyclone separator to remove large particles and the finer particles are separated by bag filters. The larger and finer particles are collected in bins.
Uses
1.      Used to convey light and fluffy materials.
2.      Since the over all process is a closed system hence pneumatic conveyors are used to convey unpleasant and toxic materials.
Advantages
1.      The materials can be conveyed horizontally, vertically and through any type of turns.
2.      Economical.
3.      Frictional losses are small.
Disadvantages
1.      Needs more power than other types of conveyor systems.
2.      Erosion of internal surface of the pipe may take place.
3.      Side reduction of solid may take place due to attrition in between particles.

BUCKET CONVEYOR

Construction
Buckets are used for loading the materials. The buckets are made of cast iron and are available in various forms. The buckets are attached to belts or chains. The chains are endless and buckets are fixed between two chains. The buckets are spaced to prevent interference in loading and unloading. At the foot of the elevator, a structure known as ‘boot’ is used for feeding the buckets. The bucket and chains are enclosed within a casing. The casing may be made of wood or steel sheet.
Working
The elevators are generally by motors and the upper end. The materials are filled in the bucket in the boot region. Buckets are discharged at the upper end with the help of a tripping device, causing each bucket to turn 900.
Uses: Are used to convey coal, stone ad grains etc.









DOWN LOAD-----ORIGINAL----MATERIAL HANDLING SYSTEM




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