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.
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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.
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RECIPROCATING DUPLEX PUMP
(Reciprocating, Duplex,
Plunger Type Pump)
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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.
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.
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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.
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.