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