Pneumatic Transfer – A Natural Phenomenon
Transfer of Seeds and Pollens by Wind
AIR KINETICS
The Basic Scheme of Pneumatic
Conveying
• Generate the airflow into a closed pipe or duct
• Introduction of bulk solid from source into air
stream
• Convey this material to the desired
destination
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Saltation Velocity
• When powder or granular material is
introduced in the pipe
• Particles will be either carried away by air
current.
Or
• They will settle down at the bottom of the
pipe.
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Saltation Velocity
• For different materials value of "Vc" is
different.
• Even for same material (Same Particle Density)
"Vc" will depend on particle size and shape.
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Pneumatic
Conveying Systems
Dense Phase
Dilute Phase
Positive
Pressure
Negative
Pressure
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Positive Pressure & Negative Pressure
System
• Positive Pressure System
• Negative Pressure System
• Higher Efficiency
• Lower Efficiency
• To generate given pick up
velocity lesser of air volume
is required and hence
blower size is smaller
• To generate given pick up
velocity higher volume of
air is required and hence
blower size is bigger.
• In case of leakage in the
conveying line this is easily
detected.
• In case of leakage in the
conveying line this is not
easily detected.
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Positive Pressure & Negative Pressure
System Contd.
• Preferred for conveying
hygroscopic products
• Rotary Air Locks should
be of superior quality
with smaller clearance
between rotor blades
and casing to limit
leakage air or else loss
of air can choke the
conveying lines.
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• To be avoided for
hygroscopic products.
• Rotary air lock quality
need not matter.
Dilute Phase Conveying Systems
• If conveying velocity is sufficient to carry away
the particles in suspended state in air stream
this is called dilute phase system.
AIR KINETICS
AIR KINETICS
Common Sources of Bulk Solids in the
Industry.
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1)Blenders
2)Storage Silos
3)Intermediate Silos
4)SFD Bag house
5)Blenders
6)Pulverizes
7)Jumbo Bags
AIR KINETICS
Common Destinations for Bulk Solids
in the Industry.
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1)Blenders
2)Storage silos
3)Packing Silos
4)Mixing Tanks
5)Reactors
AIR KINETICS
Properties of the Bulk Solids
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1. Fluidizing Property
2. Bulk Density
3. particle Size Distribution
4. Wall Friction Angle
5. Moisture Content
6. Air Permeability
These properties matter in selection of
pneumatic conveying system and storage silos
AIR KINETICS
Review of Dilute Phase & Dense Phase
System
Advantages and Disadvantages
of Dilute Phase System
Advantages and Disadvantages
of Dense Phase System
• Almost All Materials
irrespective of fluidizing
property can be conveyed.
•
Only good fluidizing property bulk
solids or good air permeability solids
can be conveyed.
•
Any System of comparable conveying
distance requires higher pressure
drop and hence air mover required is
expensive like screw compressor.
•
Energy efficiency is high but generally
these systems are batch conveying
processes and any continuous
process dense phase system requires
special rotary feeders.
• Any System where conveying
distance is maximum 200 mtrs
can be operated by
inexpensive air movers like fan
blowers and roots blowers as
conveying pressure drop can
be maintained less than 1 bar
AIR KINETICS
Review of Dilute Phase & Dense Phase
System Contd.
Advantages and Disadvantages of Dilute Phase System
Advantages and Disadvantages of Dense Phase System
• Though Initial capital cost is
low, energy efficiency is less
than dense phase conveying
• Pipe line sizes for the given
conveying rate are smaller but
the conveying lines are prone to
heavy vibrations and hence
requires stronger supports and
the distribution equipment like
diverter valves need special
strong holding locking system.
• For Abrasive Materials higher
conveying velocities cause
excessive wear to the pipes,
bends and feeding devices.
• Excessive Conveying Velocities
cause particle degradation of
friable materials.
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• Because of Low conveying
velocities wear and tear can be
limited.
• The particle degradation is least
in dense phase conveying
Building Blocks of
Pneumatic Conveying
Systems
Air Blower
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Feeding
Devices
Conveying
Lines
Diverter
Valves
Air Separation
Unit or Bag
Filter
Air Mover
• For dilute phase pneumatic conveying systems
roots blowers or fan blower is used. If
conveying distance is short and solid loading
ratio is small fan can be used as maximum
pressure drop can be limited to values less
than
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Feeding Devices
• Many different feeding devices are used but in
general rotary air locks and ventury feeders
are used in dilute phase systems and blow
tanks are the most common feeding device in
dense phase system.
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Conveying Lines
• Conveying lines are of normal pipes with a
good internal surface finish. As these lines
carry solid particles mixed with air the bends
used are long radius bends these can be 7D or
10D bends using shorter radius bends cause
excessive pressure drop across bend hence
long radius bends are used.
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Diverter Valves
• When conveying Line is intended to carry the
material to different destinations diverter valves are
used. There can be different types of diverters with
different diversion angle. Also there are three main
construction variants in diverters.
Types of Diverter Valves
Flap type
diverter
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Pipe
Diverters
Plug
Diverters
Pipe
Diverter
Plug
Diverter
Flap
Diverter
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Air Separation Unit or Bag Filter
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Safety Devices on Pneumatic Conveying
System
Pressure Safety
Valve
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Pressure Switch
Differential
Pressure Switch
Trouble Shooting
• Tripping of Overload Relay of roots
blower motor
• Insufficient conveying Rate
• Insufficient conveying Rate in case of
negative pressure system
• Choking of conveying line
• Frequent deposition of powder
layers inside the pipe line