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Pneumatic Conveying System

vacuum transfer systemPneumatic conveying system uses an air stream to move dry bulk powders through horizontal or vertical pipelines in a powder processing system. Traditionally, pneumatic conveying systems include an air source, an infeed device, a conveying line, a receiver and dust filtration. At Prochem we work with our customers to design pneumatic conveying systems that are not only efficient and sanitary, but are also tailored to their unique requirements of the application and the type of powder being processed.

Advantages of Pneumatic Conveying

Pneumatic conveying systems offer greater advantages over mechanical conveying systemswhich include

  • Added flexibility. A pneumatic conveying system can be designed to fit around existing equipment, taking up less space and providing more flexibility than mechanical conveying systems. Longer conveying distances can be achieved.
  • Low maintenance. Pneumatic conveying systems also have less moving parts than mechanical systems and typically require less maintenance.
  • Elevated safety. With less moving parts and less required maintenance, pneumatic conveying systems present less operator dangers. They also make less noise, which improves workplace conditions for employees.
  • Less spillage and dust. A pneumatic conveying system features an enclosed pipeline and contains dust better than mechanical conveying systems.
  • Improved sanitation. Because pneumatic conveying systems have an enclosed pipeline, the risk of product contamination is greatly reduced and the workplace remains cleaner as well.

While pneumatic conveying systems are often a great choice for many powder processing systems, they’re not recommended for materials with large particle sizes or extremely sticky materials like high fat powders, as they are more difficult to convey or cause buildup in the system.

Pneumatic Conveying Types and Applications

Pneumatic conveying systems are characterized by pressure or vacuum systems, and use either a dilute phase or dense phase technology to transport material.

Dilute phase conveying systems use high volume, low pressure air to keep the product suspended in the air all the way through to its destination. For dense phase conveying systems, the opposite is true. In dense phase systems, material is not suspended and low volume, high pressure air is used to move material through the pipeline.

Below are four types of pneumatic conveying systems that Prochem designs for its customers

 

Dense Phase Vacuum  Conveying Systems

vacuum dense phase2Dense Phase Vacuum Conveying Systems use high capacity vacuum pumps (up to 99% Vacuum) to convey materials from a feed hopper or silo to a Receiving Vessel (also known as a Vacuum Hopper) where the air and product are separated by a filter. When this vessel is full, the vacuum is isolated and the conveyed product discharged into the destination silo. The product conveys through the pipeline at a controlled low velocity, usually in a fluidised state to reduce friction and pressure drop.

Systems generally operate on a batch basis as follows: (simplified)

  1. The vacuum pump sucks powder to the Vacuum Hopper until full.
  2. The vacuum isolation valve closes and the discharge valve opens.
  3. Conveyed powder is emptied from the Vacuum Hopper.
  4. The discharge valve is closed and the cycle repeats.

Valves and sensors are used throughout the system to control the applied vacuum and product fluidisation settings and velocities at all parts of the system to ensure smooth reliable conveying of the product.

 Specifications

Convey Rates: Medium, up to 5 tonnes/hr (higher with multiple vessels)
Convey Velocities: Low, 0.5-8 m/s
Convey Distances: Medium, up to 100m (longer with push-pull systems)
Air Mover: Vacuum Pump (Dry Vane, Oil or Water Sealed)
Operating Pressure: Up to 99% Vacuum
Material/Air Ratios: Medium, up to 50 kg/kg
Note All values approximate, revert for details on how to convey your product.

Applications

Dense Phase Vacuum Conveying Systems are particularly suitable for systems, which convey materials at high capacities over short to medium distances, from multiple sources to a single or multiple destinations.

The low convey velocities and vacuum method make it particularly suitable for Food, Dairy and Pharmaceutical applications with friable or fragile agglomerated powders.

Options

To optimise the system various techniques are used to enhance operation, and additional options for specialised applications are available:

  • Feedback Velocity control systems to minimise product degradation
  • Pulsed air injection to break up the product flow into discrete slugs
  • In-Line sifting, sampling, delumping, metal detection and magnetic separation systems
  • Line Boosters to assist conveying along convey route
  • Automatic unblocking systems using compressed air injection
  • Vibration to loosen cohesive powders prior to conveying
  • Twin vessels to provide continuous conveying
  • Stainless Steel construction for sanitation or corrosion resistance
  • Demountable and polished designs to USDA 3A standards for ease of cleaning
  • Multiple inlet / multiple outlet convey networks for maximum flexibility

 

 

Dense Phase Pressure Conveying Systems

pressure dense phase2Pressure dense phase conveying systems are most often used to transport fragile or abrasive materials over long distances.

  • Utilizing compressed air, this method conveys material at low velocities to reduce product degradation.
  • Operates in a “batch-like” manner, filling an ASME vessel, pressurizing the vessel, conveying, and starting over.
  • Powder can remain in the convey line while the vessel refills with powder.
  • Velocities can range from 200 to 1000 feet/minute, and are regulated by monitoring the convey pressures.
  • Boosters may be required for longer distances. 

Features

Some of the features of Dense Phase Pressure Conveying Sysytem are

  • Gentle conveying
  • Mild steel and stainless steel construction
  • Control system utilizes sensors to control dense phase convey rate
  • Air-to-product ratio is maintained for reliable conveying, no plugging
  • Compressed air is used as conveying medium
  • Batch sequence operation
  • Opptional - continuous dense phase.

pressure dense phaseBenefits

  • Reduced wear on pipelines
  • Low conveying velocity
  • Suited to gentle convying of agglomerated and abrasive powders
  • low air-to product ratio
  • Reduced filter area
  • Minimum product breakage and degradation
  • Minimum degradation of blended powders
  • Compressed air as conveying medium eliminates the need of seperate dehumidification

 

Lean Phase Vacuum Conveying Systems

vacuum dilute phaseLean Phase Vacuum Conveying Systems (also known as Dilute Phase) generally use positive displacement (Roots type) exhausters providing up to 50% vacuum to convey materials through a pipeline to the destination where the air and product are separated at a receiving vessel with a filter, or a cyclone. Lower capacity systems are also available which use fans as the prime mover.

The product enters the convey line directly, or if metering is required, via a special feeding device such as a rotary valve or screwfeeder. The product is frequently suspended in the airflow, moving at relatively high velocities depending on the particle sizes and densities.

The conveyed product is discharged from the receiving vessel either on a continuous basis by a rotary airlock or intermittently by valves.

vacuumdilutephaseSpecifications

Convey Rates: Low to Medium, typically <10 tonnes/hr
Convey Velocities: Typically 15-30 m/s
Convey Distances: Up to 100m or longer
Air Mover: Positive displacement (Roots Type) Exhauster, or Fan
Operating Pressure: Up to 50% Vacuum
Material/Air Ratios: Low to medium, typically 3-15 kg/kg
Note All values approximate, revert for details on how to convey your product.

Applications

Lean Phase Vacuum Conveying Systems are particularly suitable for systems which convey materials at low to moderate capacities over medium distances, from multiple points to a single destination. These systems are versatile and adaptable for different materials and the low operating pressures allow lower cost pipelines and fittings. This method is frequently used for Central Vacuum Cleaning Systems and other applications, which require a reticulated network of vacuum pipes to convey product to a single collection point.

Options

A wide variety of options for system and component design are available to suit particular system requirements, including the following:

  • Weighing and dosing equipment
  • Specialised feeding systems for cohesive, sticky or lumpy products, and other special properties
  • Air Filtration, dehumidification and cooling systems
  • Noise attenuation systems
  • In-Line sifting, sampling, delumping, metal detection and magnetic separation systems
  • Sanitary systems for food, dairy and pharmaceutical products
  • Stainless Steel construction for sanitation or corrosion resistance
  • Demountable and polished designs to USDA 3A standards for ease of cleaning
  • Stepped convey lines to reduce terminal velocities, abrasion and degradation

Lean Phase Pressure Conveying Systems

pressure dilute phasePressure dilute phase conveying systems are one of the most common and practical conveying types for powder processing.

  • Used when product degradation and segregation are not a concern
  • Materials that have light bulk density such as flour, sugar or plastic granules.
  • Multiple infeed points and destinations are possible.
  • Higher capacities and longer distances.
  • Conveying is continuous.
  • Velocities can range from 3000 to 7000 feet/minute.

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