pneumatic transfer – a natural phenomenon transfer of seeds and pollens by wind air kinetics
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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
AIR KINETICS
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.
AIR KINETICS
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.
AIR KINETICS
Pneumatic Conveying Systems
Dense Phase Dilute Phase
Positive Pressure
Negative Pressure
AIR KINETICS
Positive Pressure & Negative Pressure System
• Positive Pressure System
• Higher Efficiency
• To generate given pick up velocity lesser of air volume is required and hence blower size is smaller
• In case of leakage in the conveying line this is easily detected.
• Negative Pressure System
• Lower Efficiency
• 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 not easily detected.
AIR KINETICS
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.
• To be avoided for hygroscopic products.
• Rotary air lock quality need not matter.
AIR KINETICS
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.
• 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.
• 1)Blenders• 2)Storage silos• 3)Packing Silos• 4)Mixing Tanks• 5)Reactors
AIR KINETICS
Properties of the Bulk Solids
• 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
• Almost All Materials irrespective of fluidizing property can be conveyed.
• 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
Advantages and Disadvantages of Dense Phase System
• 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.
AIR KINETICS
Review of Dilute Phase & Dense Phase System Contd.
Advantages and Disadvantages of Dilute Phase System
• Though Initial capital cost is low, energy efficiency is less than dense phase conveying
• 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.
Advantages and Disadvantages of Dense Phase System
• 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.
• Because of Low conveying velocities wear and tear can be limited.
• The particle degradation is least in dense phase conveying
AIR KINETICS
Building Blocks of Pneumatic Conveying Systems
Air Blower Feeding Devices
Conveying Lines
Diverter Valves
Air Separation Unit or Bag Filter
AIR KINETICS
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
AIR KINETICS
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.
AIR KINETICS
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.
AIR KINETICS
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 Pipe Diverters Plug Diverters
AIR KINETICS
Pipe Diverter Plug
Diverter
Flap Diverter
AIR KINETICS
Air Separation Unit or Bag Filter
AIR KINETICS
Safety Devices on Pneumatic Conveying System
Pressure Safety Valve Pressure Switch Differential
Pressure Switch
AIR KINETICS
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
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