Identify_the_Correct_Phase_for_Pneumatic_Conveying

Identify the correct phase for your pneumatic conveying system:
Dense, Semi-dense or Dilute

2922 North Division Avenue, P.O. Box 366, York, NE 68467
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Identify the correct phase for your pneumatic conveying system:
Dense, Semi-dense or Dilute
For dry bulk material transfer, pneumatic conveying is simply one of the most efficient, effective solutions. It is used to handle
a wide range of materials for countless industries, and offers value as high as its effectiveness.
For those considering the use of pneumatic conveying, there can be many questions – the most common being which
conveying phase is the best option, based on specific materials, applications, and industry. In order to make the best choice,
it’s also important to first understand what conveyors are and how they are used. Next will be an explanation of the various
types and how to choose the appropriate phase.
TABLE OF CONTENTS
Overview
How They Work....................................................................2
Industries and Applications...................................................3
Three Different Pneumatic Conveying Phases...............................4
Identifying the Correct Phase for Your Material/Application
Characteristics......................................................................5
Location/Plant Environment..................................................6
Final Selection (Phase Selection and Testing)................................7
About Cyclonaire............................................................................8

Overview: What are pneumatic conveyors? How are they used?
How They Work:
Pneumatic conveying systems are one of the most common methods for transferring dry bulk materials. These materials can include,
but are not limited to, powders, flakes, granules and pellets. The materials are transferred within an enclosed pipeline through the use
of air. At its most basic, a pneumatic conveying system is made up of the air source, i.e. a compressor or blower, a material-introduction
device, a conveying line, and an air-material receiver with a dust collector.
The airflow, created by a pressure differential, provides the energy needed to move the materials through the pipeline. The air source
changes the air pressure, creating either pressure or a vacuum.
In the case of systems moving material while under pressure, the air source produces a higher pressure at the start of the system,
pushing the air and the material through. However, when the air source is at the end of the system, the material is pulled with the air
through the convey line toward the destination.

Overview: What are pneumatic conveyors? How are they used? (cont.)
Industries & Applications:
Due to the long and varied list of dry materials for which pneumatic conveying is used, there are a myriad of industries that can take
advantage of this technology. These include railroads, rubber, energy, transportation, building materials, battery, foundries, government,
utilities, environmental and manufacturing companies.
More specifically, below is a small sample of applications within these industries:
• Batteries: Lead oxide, soda ash, plastics, etc.
• Building Materials: Blended cements, brick, concrete blocks and pavers, cement kiln dust (CKD), roofing granules, wall
board, joint compounds, grouts and mortars, etc.
• Energy: Electrical/coal gasification, filtration, fracking, etc.
• Environmental: Ash handling, activated carbon, air filtering, water treatment, etc.
• Foundries: Sand.
• Government: Department of Defense, rocket fuel, etc.
• Manufacturing: Food and grains, pulp and paper, plastics, pharma/bio products, inorganic and
organic chemicals, steel, glass, etc.
• Railroads: Traction control, railcar loading and unloading, etc.
• Rubber: Tires, compounders, carbon black, silicas, etc.
• Transportation: Bulk truck loading and discharge, bulk containers, trans-loading, etc.
• Utilities: Fly ash collection, ESP discharge, carbon injection, etc.
Union Pacific Railroad in Houston, Texas uses
a Cyclonaire sanding system to fill locomotive
sandboxes.

While there are many complexities and subcategories that fall under the umbrella of pneumatic
conveying, the technology can be broken down into three categories: dilute phase, dense phase and
semi-dense phase. Understanding each of these not only helps one decide which is the best choice,
but also helps a potential user to realize that it’s not as confusing as it might sound at first.
The most basic way to look at it is this: If the conveyed material is suspended in the air within the
pipeline at a high velocity, it is considered dilute phase conveying. This phase is used when degradation
and abrasive wear are not an issue.
If a material is conveyed at a low velocity and not suspended in the airstream, it is dense phase
conveying. This can be used for low or high-rate transfer of abrasive or friable materials.
If a material is conveyed at medium velocity, with not all of the material being suspended, it is
considered semi-dense conveying. This is used for transfer of aeratable abrasive or friable materials.
A bit more specifically, dilute phase conveying utilizes conveying air volume and velocity that are high enough to keep the material
suspended continuously, so as not to accumulate on the bottom of the convey line. Therefore a relatively high air velocity must be
maintained, often between 5,000 ft./ min. and 8,000 ft./min.
While there are several different forms of dense phase conveying, they will typically feature low material velocity with high pressure,
ranging from 400 ft./min to 1,000 ft./min.
Semi-dense phase conveying offers material velocities higher than dense phase, but lower than dilute phase. These velocities range
from 1,500 ft./min to 3,500 ft./min.
Three different pneumatic conveying phases
Dense
Semi-dense
Dilute

Identifying the correct phase for your material or application
Because each convey phase varies based on factors such as velocity and pressure, the correct phase choice is based on the material
characteristics being transferred and the purpose.
Characteristics:
Due to the fact that there are so many materials that can employ the use of pneumatic conveying, there are many factors or
characteristics to consider in order to determine the correct phase. These factors include:
• Particle size and shape: The particle size and shape has the most influence on the selected phase of conveying. An analysis of
the distribution of sizes, as well as the aerodynamic form defining the shape, is necessary to determine how well a given material will
perform in each phase. Abrasive and large or heavy particles are poor candidates for dilute phase as it requires high airflow (velocity)
to keep the particle suspended. Widely mixed particles are not ideal for dense phase as they tend to nest and pack in a convey line.
Semi-dense requires materials that are somewhat fluidizable and it is best suited for products in a powdery state.
• Bulk density: A material’s bulk density is a minor factor in phase consideration. Since dilute phase conveying suspends particles in
the air, it’s usually better suited for materials with a light bulk density.
• Moisture content: Moisture has two elements as related to the conveyed particle; surface moisture and entrained moisture. If the
material with entrained moisture is formed into a ball and stays in that shape, it will more likely pack in a convey line in dense phase,
but maintain particle separation in dilute. In most cases, material with high moisture that allows it to pack is not a good candidate for
pneumatic conveying in any phase.
• Abrasiveness: The low velocity of dense phase conveying makes it suitable for high-rate transfer of abrasive materials, while
the medium velocity of semi-dense conveying makes it best for aeratable abrasive materials. Dilute phase can be considered when
abrasiveness is not a factor.
• Friability: Similarly, the nature of dense phase and semi-dense phase conveying make them best suited for materials where
particles are easily crumbed or pulverized. The lower velocity of these modes aids in reducing material degradatation.
• Cohesiveness: For materials that adhere to themselves or interlock under pressure and tend to agglomerate can often create
convey problems. These types of materials can be difficult in all phases of pressure conveying. For these materials a vacuum system,
dilute or dense phase, may be the best or only choice.

Identifying the correct phase for your material or application (cont.)
Other aspects to keep in mind when selecting a phase of conveying include:
The fact that there are so many materials that can employ the use of pneumatic conveying, there are many factors or characteristics to
consider in order to determine the correct phase. These factors include:
• Hygroscopicity: If the material is subject to absorbing moisture from its surroundings either from the ambient air or the air used for
conveying the material, then the air may need to be dried. Dense phase is usually served by a compressor. It is common to have a
dryer on a compressed air system and less air is used in dense phase conveying making it the choice for hygroscopic material. Other
modes can be used but it is much more difficult to dry the air.
• Static charge: Conveying materials can cause a build-up of static charge, regardless of the mode of conveying. Common practice
is to reduce any hazard by grounding the convey line and system equipment
• Explosivity: In certain conditions, some materials can form potentially explosive mixtures when combined with air. Generally, explosive
materials are conveyed in an inert environment to avoid this condition, often using nitrogen as the convey gas. Since it is common to reuse
the gas in a closed loop system, dilute phase is more adaptable to the introduction and recirculation of the gas. In systems where the gas
is not captured and reused, any mode can be employed based on other material characteristics and application parameters.
• Toxicity: Good practice demands that toxic materials be conveyed with caution. A pressure convey mode can be used but
consideration should be given to vacuum systems. Since any leakage that might occur the vacuum will prevent the material from
escaping into the environment.
• Melt point: Certain materials, such as plastics or sugars, can be affected by heat. In these conditions, any mode can be selected
but cooling air should be incorporated into the system design. Another question to ask: will your system include long conveying line
runs? If so, a dense phase system might be best due to its low energy use for the same rate of conveyance, as compared to dilute or
even semi-dense.
Location/Plant Environment:
Beyond the characteristics of the material being transferred, another important factor that must be considered is how the system will
fit and where the equipment will be located in your plant. For example, is headroom an issue? What other physical limitations and/or
constraints exist within the area for installing the equipment? Will there be other equipment nearby? Are there aisles that must be kept
open or bridged?
Installation must also allow for easy access to the system for operation and for maintenance. When planning for the installation, it’s
important to consider the system’s convey length and line routing.

Final Selection
Testing and Phase Selection:
Once you are aware of these factors and considerations, you should have a good sense of the right choice for your material handling
requirements. However, when working with an experienced, knowledgeable company for your pneumatic conveying selection, you will
have ample guidance, and you will be assured of the right choice.
The company you work with should ask questions and guide you based on your requirements, and then should perform extensive
testing with your material, followed by a full-scale convey test. This test should be done utilizing the same equipment, convey line size,
airflow and distance as the proposed system, in order to ensure the pneumatic conveyor’s ability to successfully convey your material.
Team members will have expertise on all phases, materials, applications, and industries, as well as the equipment itself, making certain
the right phase is chosen, and the system suits all of your needs.
At Cyclonaire, we have a comprehensive knowledge of, and experience in, all aspects of pneumatic conveying technology. We utilize
our state-of-the-art CycloTech Technology Demonstration and System Proving Facility to verify the conveying selection. Here, we
provide full-scale testing of dry bulk materials for semi-dense, dense, and dilute phases, in vacuum, pressure, and combined vacuum-
pressure modes.
Cyclonaire’s all-inclusive testing facility performs transfer simulations (i.e. to/from rail cars, bulk storage/transfer, in-plant processing) in
the exact equipment to be used. The facility has convey line lengths up to 1,137 feet with line diameters of 2 1/2, 3, 4, 5, 6, and 8 inches,
and conveyor units ranging from one to 75 cubic feet. Testing also includes computerized analyses and data capture and reporting.
In the end, the results are complete assurance that the equipment will handle the target rate, air usage, pressure, degradation
requirements, and more.
Cyclonaire’s state-of-the-art Technology
Demonstration and System Proving Facility
allows full-scale testing of dry bulk materials.

About Cyclonaire
Founded in 1973, today Cyclonaire is a world leader in material handling. The company was originally built on technology invented and
patented in the early 1960s, which changed the way American construction materials were transported.
Cyclonaire moved from a focus on railcar unloading systems to all types of pneumatic transfer applications, and now provides solutions
from the very basic to the highly complex and customized, working with hundreds of materials across an extremely wide range of
industries. In addition to world-class equipment, Cyclonaire offers in-house automation capabilities, from a basic system to full-plant
automation. Cyclonaire’s capabilities, including the engineering, manufacturing and servicing of pneumatic conveying systems, has
brought the company worldwide recognition.
Continuing the mission that began over 40 years ago, the company aggressively strives to enhance its position as a leader in
technology and service, while consistently building long, meaningful relationships with customers, suppliers, sales organizations, and
its dedicated employees.
For more information, visit www.cyclonaire.com.

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