Two main methods for the transfer of bulk materials are by means of pneumatic conveyors and mechanical ones. When making bulk material handling decisions, there are a number of considerations to address in order to select an optimal conveying method for handling a specific material for a unique application.

Pneumatic and Mechanical Conveyors: General Information

Conveyor systems are used to transfer powders, granular material, and many other types of dry bulk materials from one process area to another, through negative (vacuum) or positive (pressure) conditions. ). These systems are made up of four basic elements: an air source, a material feeding device, a transport line and a material receiving filter. The main difference between pneumatic and mechanical conveyors is that pneumatic systems convey material within a completely enclosed line, which greatly reduces the chance of material loss.

The basic components of a mechanical conveying system include a motor driven through a reduction gear and/or chain, connected to a drive device, such as a roller or sprocket. Power from the motor is transferred directly to the conveyor, which is in direct contact with the material. Mechanical conveyors can be open or closed to the atmosphere, with hundreds of moving parts working.

Pneumatic and Mechanical Conveyors: Which is Right for You?

The most important factor when selecting a type of conveyor is the shape of the material to be conveyed. Identifying the key characteristics of your material will help determine the best transportation method for you. These features include:

The ideal materials for pneumatic conveying systems are fine, fluidizable and dry powders. These particular characteristics allow the material to be successfully aerated (fluidized) and pumped through a conveying line. Some types of bulk materials are also good candidates for pneumatic conveying. Some of the materials commonly transferred with the use of pneumatic conveyors include wheat flour, cement dust, carbon black, starch, sugar, plastic pellets and resins, food products, coal dust, sands and metal powders, among many others. .

Mechanical conveyors are well-suited for heavy, bulk materials that can be wet, pasty, and caking. Mechanical systems are most practical for materials with widely varying particle distributions; materials with both small and large particles combined. Materials commonly transported by mechanical systems include whole grains, crushed stone, gravel, wet sand, and large-particle foods, among others.

Another important factor when selecting a type of conveyor is the application. The app has several key areas to consider, including:

Transportation capacity: both pneumatic and mechanical systems can transport kilos or hundreds of tons per hour; however, the type of materials and transportation conditions will determine the system.

Distance – Pneumatic systems are generally not used for short distance transportation, as it requires the same amount of equipment to transport 6 meters as it does to transport 200. Transfer of bulk materials over short distances can be accomplished with the equipment. Mechanical, even at the cost of some material damage or equipment wear. Both types of systems can be used for distances of more than 1,000 feet if required, but the cost of installing the single conveying line against the frame of a belt conveyor is an important consideration. Long distances with multiple direction and elevation changes are easily accomplished with a pneumatic system.

Installation environment: indoor or outdoor installations; certainly the closed pneumatic system offers some advantages for most outdoor installations.

Altitude; air is less dense at altitude and in some circumstances can have enough of an effect in a pneumatic type of system design to create a disadvantage in the form of larger equipment, especially the air source, when handling difficult material.

The clean-out and clean-up system can be problematic for mechanical systems, such as a screw conveyor or bucket elevator. In contrast, purging material from a rotary valve or pressurized tank and conveying piping are easily accomplished with pneumatic conveying systems.

Simple routing

Compared to mechanical conveyors, pneumatic systems have an easier time transporting material through the plant and diverting it to different destinations. For example, screw conveyors only run in a straight line and are limited to the amount of incline (based on the type of materials).

Additionally, helical systems require precise installation to keep alignment intact and take up a large amount of floor space. On the other hand, pneumatic conveyors are much easier to route. Because the transmission line consists of a single pipe, they usually require minimal surface area and the line can flow in both horizontal and vertical directions. Often the transmission line can be supported on existing structures, columns or beams, thus eliminating the need for special foundations and support frames. In fact, most pneumatic systems free up floor space by replacing a mechanical system, allowing for a high level of flexibility in material routing design. Conveyor lines can be easily retrofitted to existing equipment, and can be built to bypass or go around obstructions. Due to the straight path required by mechanical conveyors, any equipment in their path must be relocated during construction, adding cost.

A Cleaner Method

Pneumatic conveyors eliminate many spill opportunities that occur with mechanical conveying systems. Because mechanical conveyors primarily work in straight lines, there may be many transfer points for bulk materials along the way, such as changing direction or changing feed from one conveyor to another. Whenever transfer occurs, spillage of material is possible. Spillage can also occur when materials are stopped in the transfer process, which is especially important to consider when transporting hazardous materials.

It is not unusual to combine different types of mechanical conveyors to create a unique transportation system, for example; a screw conveyor feeding a bucket elevator. However, when this is done, it is vital that the design types are compatible to avoid overfilling or underutilizing the next conveyor in the series. Taking into account the aforementioned, the possibility of spills at each transfer point increases. In addition, a complex dust system is often required to mitigate dust escape at the intersection of each conveyor.

A pneumatic conveyor is a closed system, so it will further protect a company's workforce and the environment at large from potentially dangerous spills. The closed design also prevents product contamination, which is especially important when dealing with sensitive products such as sugar. Contaminated food can cause serious health problems and financial loss. Closed piping systems create a seal during transfer that helps keep contaminants out as well as hazardous materials in. This protects the material and also the workers and the environment from the hazardous materials being transported.

Pneumatic conveyors also protect against dust, which can become a significant hazard when transporting certain materials such as starch or activated carbon. Exposed dust can increase the risk of explosions, as well as endanger the health of employees. A pneumatic system, simply by concept, will contain particles and eliminate dust from escaping during the transport of materials, negating these risks.

Less Maintenance

One thing all mechanical conveyors have in common is the large number of moving parts. A large number of belts, rollers, and bearings are used in its construction, and all of these parts need to be maintained. Failure to complete proper maintenance could result in failure, which can lead to catastrophic results to the conveying system and the bulk material being conveyed. Mechanical systems such as bucket elevators can fail if a single belt or chain in the system breaks. Even despite the possibility of part failure, individual maintenance and inspection of all working components of mechanical conveyors add to the cost of operation.

Pneumatic conveyors are made up of a few key working parts: an air compressor or vacuum pump, a feeding device, feeding pipes or transfer pipes, and a separating device. Each part of this system can be repaired at the component level, with the equipment still in place, so the entire system will not need to be removed or replaced; only the faulty part. Pneumatic systems rely on the airflow created by a fan or blower, rather than the multiple parts that make up mechanical systems. The overall result of having fewer moving parts is that there is less susceptibility to mechanical failure, which keeps productivity and work efficiency at the highest level.

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