S. Howes

What is a Powder Conveying System?

Thermal screw powder testing

Powder conveying systems are used for handling various types of bulk powders. Conveyors designed specifically for transporting powdered materials are used in chemical processing, food processing, mining, mineral processing, pharmaceuticals, and many other industries to move materials consisting of finer particles. These finer particles tend to become airborne, which, with some materials, can lead to conflagrations and even explosions. Additionally, their fineness causes them to cling to equipment, often leading to clogging, so powder conveyors are designed to deal with such issues. For those in industries that utilize powder conveying systems, understanding how they work will help manufacturers optimize their operations to achieve greater efficiency and profitability.

Understanding Powder Conveying Systems

Powder conveying systems comprise multiple equipment, including control systems, feeders, exhaust devices, and piping. Bulk powders are fed into the system through a pipeline, after which they are transported mechanically or pneumatically, with both types of powder conveying systems having their advantages and disadvantages. Some powder conveyors even use both mechanical and pneumatic means for transferring material. Exhaust devices, in turn, control dust as it’s transported, limiting the number of airborne particles that can lead to explosions and clog equipment with dust collectors and filtering systems. Control systems for powder conveyors regulate this equipment to ensure safe and stable bulk powder processing and monitor many other processing aspects.

Considerations for Powder Conveyors 

The design of a powder conveying system depends greatly on the application for which it’s to be used. Manufacturers of powder conveyors generally have a good idea of the specifications needed to deal with materials consisting of finer particles. While equipment suppliers often provide good advice about the best means for conveying their products, it’s important that manufacturers also understand the basic factors involved in putting together an efficient powder conveying system for their specific application.

Considerations when putting together a powder conveying system include: 

  • Controls: Most modern control systems for powder conveyors use software to manage every part of a powder conveying system; additionally, advances in software give manufacturers working with bulk powders much greater control over their handling.
  • Distance: The distance powdered material must travel during processing affects the whole system’s efficiency; as an example, pneumatic powder conveying systems allow manufacturers to move product over considerably longer distances than mechanical systems.
  • Piping: The design of a pneumatic piping system will also need to consider the distance over which material must be conveyed and the density of the powder; pneumatic powder conveyers must also be designed to handle the rate at which product is fed.

Mechanical powder conveyors, belts, troughs, tubing, or other means for guiding products into and through the system are used instead of piping. Though enclosed piping is most often used for handling pneumatically conveyed powders, conveying systems also often feature filters to protect the rest of the system and the facility’s workers, especially if the bulk powder is potentially explosive or toxic. Poor filtration can also lead to damage to certain sections within the powder conveying system, which in turn leads to unnecessary maintenance costs, along with the need to replace certain parts more frequently. Ventilation, too, is a safety concern, with some powder conveyors featuring fans and vents to reduce hazards to both equipment and personnel.

An equipment manufacturer or supplier can advise on the best design for a particular application. Before purchasing equipment for powder conveying, system design should be carefully considered. Manufacturers should look at the features of an ideal powder conveyor for their specific application and then consider the most important aspects based on cost and throughput. Equipment manufacturers may even be able to help customize a powder conveying system so that it optimally performs the tasks for which it was designed.

Different Types of Powder Conveying Systems

The type of powder conveyor used for bulk material handling operations depends ultimately on the application. Primarily, powders are either moved via pneumatic or mechanical means, though specific systems use both methods. Pneumatic powder conveyors are generally the safer option, as they help prevent dust buildup in enclosed spaces that can lead to dust-related conflagrations. Pneumatic powder conveying systems also provide better hygiene as they keep material moving, limiting contamination. Additionally, wastage of material during processing is considerably lower, as air keeps product moving through the system.

As a powder handling technology, powder conveyors that instead use mechanical rather than pneumatic force to transport bulk powders offer certain advantages for certain applications. Mechanical powder conveying systems transfer product at an angle, horizontally or vertically, depending on the exact type of design arrangement. These mechanical systems consist of belts, buckets, chains, trays, and other moving components that transfer bulk powders from one process to another.

Pneumatic Powder Conveying Systems

With equipment that utilizes pneumatic methods for conveying, powder systems essentially fall into two categories. One involves pulling powders through the system via a vacuum, while the other method involves pushing them through the system through the use of air pressure. Within these two methods of using air to transport bulk powder, conveying systems also include various other features that depend on the exact application.

Basic elements of a pneumatic powder conveying system include: 

  • Point at which material is introduced.
  • Device to feed bulk powders, such as feeders or feed hoppers.
  • Source for air or other gas used for conveying.
  • Line for conveying.
  • System for separating air from material.
  • Pneumatic conveying elbows.
  • Piping systems
  • Gaskets and other components.
  • Device for controlling airflow.
  • Point for collecting product once processed.

Both vacuum and pressure powder conveying systems help prevent product contamination, due to the enclosed design of pneumatic equipment for powder conveying. Systems that use pneumatic forces to move materials are also more efficient and easier to maintain. Maintenance is also less of an issue with fewer moving parts, while continuous airflow tends to keep material from clinging to equipment.

Vacuum powder conveyors suck material toward its desired destination through a piping system, which then transfers the product to hoppers or storage containers for packaging or further processing. Powder conveying systems use compressed air – or other gas – to push bulk powder through the piping. These pressurized powder conveying systems are generally used for shorter distances or to push product upwards to a higher elevation.

Various types of pneumatic powder conveying systems include:

  • Closed-loop powder conveying system: These powder conveyors minimize contamination within the surrounding processing environment, incorporating dust collectors that can be used in either dense-phase or dilute-phase conditions. These closed systems transfer bulk powders without human intervention, sometimes using a heat exchanger to dissipate heat during conveying. 
  • Dense-phase pneumatic powder conveying systems: Used in numerous industries, this process moves material through enclosed pipelines between different silos or storage containers. Often used for denser bulk powders, this powder conveying method uses low volumes of gas along with higher pressures, which often is. Though it uses more energy, it tends to be gentle on the material, minimizing separation and degradation of a product’s particles.
  • Dilute-phase powder conveying system: Also known as lean-phase systems, these powder conveyors use either vacuum pumps, side channel blowers, or positive displacement blowers. These systems are generally simple and tend to be used in processing applications with lighter material with higher airflow rates, resulting in less material within the airstream. They tend to be used when quality degradation or lost material properties aren’t an issue while additionally creating less equipment wear and higher energy efficiency.
  • Two-phase powder conveying systems: The principle behind these powder conveyors is based on material being conveyed in its solid phase, with a conveying gas as the second phase. It’s used to optimally transport bulk powders based on the density, flow properties and particle size of the material.

Pneumatic powder conveyors can additionally be customized to better serve an application. They’re used in the manufacture of sugar, flour, cement, and other bulk powders. Pneumatic conveying systems also have a smaller footprint, so can fit better in areas where space is an issue. As they also have more points from which materials are fed and contained, pneumatic systems can convey bulk powders over longer distances.

Mechanical Powder Conveying Systems

While pneumatic systems have their benefits for certain applications, mechanical powder conveying systems also have certain advantages over pneumatic powder conveyors. They’re far more energy efficient, for example, often requiring only a tenth of the horsepower than that used in pneumatic powder conveying. Systems additionally aren’t required to separate material from the conveying air, meaning smaller dust collecting systems are necessary. As a result, mechanical powder conveying systems also tends to be less expensive to design and fit into a production facility.

Mechanical powder conveying systems consist of: 

  • Rollers or sprockets
  • Motors
  • Chains
  • Buckets
  • Belts

When it comes to conveying powder, systems that transport high moisture bulk material, or that with high oil or fat content, tend to use mechanical means to transport product. Mechanical conveying is preferred for materials such as brown sugar, cake mix and titanium dioxide.

Various types of mechanical powder conveying systems include:

  • Belt powder conveying systems: These systems use a continuously moving belt to transfer bulk powders from one point to another. Within an endless loop, these are the traditional conveyor belts common in production facilities, which consist of at least two powered pulleys that carry material on top of the belt as it moves.
  • Bucket elevators: Consisting of buckets that are spaced at an equal distance to each other, they use a chain or belt to vertically transport material. With the buckets acting as scoops, they pass through a pile of bulk powder, carrying the bulk powder upwards before centrifugal force causes the material to fly out once the chain or belt reaches its apex. These powder conveyors are commonly used in the agriculture, mining and other industries.
  • Differential motion powder conveyor: Also known as a horizontal-motion conveyor, horizontal differential-motion conveyor or differential conveyor, these powder conveyors move bulk material along a plane, operating on a dual cycle that advances slowly and returns quickly into place. The machine consists of a seamless unit with either a fully enclosed conduit or open pan. The relatively gentle manner in which this powder conveyor transports material greatly reduces the chance of damage to product, while it’s also capable of moving bulk powders at distances up to 200 feet (61 m).
  • Drag powder conveyors: Operating similarly to bucket elevators but horizontally rather than vertically, these powder conveying systems feature either flights or paddles that are attached to looped chains. Often used for abrasive or heated bulk material, it feeds bulk powders into the system at one end of the conveyor and a channel or trough, pulling material to a chute at the other end of the system. The empty flights or paddles then return to the pickup point to gather more material.
  • Screw conveyors: These systems consist of a tube or trough with a rotating screw contained within. The screw’s rotation causes its flights to push bulk powders along the trough’s bed. Screw powder conveying systems are one of the most cost-effective means to mechanically convey bulk powders. Able to be positioned at an incline or horizontally, these powder conveyors are used for adding small amounts of powder, discharging into small hoppers and unloading a wide array of bulk materials.
  • Screw feeders: Placed under a container like a hopper or silo, these powder conveyors are used as feeding systems, with bulk powders discharged from the feeder and fed into other equipment. Screw feeders typically are used to control flowrates of powdered material into processing equipment downstream.
  • Vibrating powder conveyors: This type of powder conveying system provides controlled transport of bulk material. Conveying product horizontally within either an enclosed or open process, it works at low speeds to move bulk material without any moving components contacting the bulk powder. Conveying systems of this type operate quietly, while also ensuring very little degradation to the product, especially with models that are enclosed.

As with pneumatic systems, processing companies should consider a number of aspects regarding powder conveying. Systems should be designed to optimize the processing of the material for its specific application, while also considering available space, flowrates, travel distance and other processing constraints.

Aero-Mechanical Powder Conveyors

Certain powder conveying systems use both pneumatic and mechanical means to transport material during processing. With a tubular construction, these powder conveyors consist of wire ropes under tension that feature equally spaced discs for transporting materials, which are flanked by terminal sprockets. These discs fit loosely within the tubes, moving straight through the tubing at a relatively high speed to displace both material and air. Once fed into the system, this displaced air fluidizes the materials, transporting them to the outlet.

For powder conveying, these systems enable high throughputs while consuming only moderate amounts of energy. They’re used for loading product into tanks or silos, conveying it upwards, and for applications that require the piping to be emptied. Aero-mechanical powder conveyors are often used in the production of materials like bath salts, ceramic powders, coffee, diatomaceous earth, pharmaceuticals, polymers, powdered soap products, rice, sugars, talcum powder, and titanium dioxide. Aero-mechanical powder conveying systems are capable of handling high production rates without damaging products while also preventing particle separation.

To learn more about powder conveying systems and which one best suits your application, contact the powder conveyor experts at S. Howes.