As the name suggests, Conveyor Systems efficiently transfers materials from one location to another. These systems come in various configurations, but they all feature a motive force (which can be either mechanical force or pneumatic force) used to move the product. Examples are screw conveyors, vibrating conveyors & Pneumatic conveyors.
Manual movement by lifting and carrying or transport by forklift are other options. The main point to note is that we will be covering conveying systems dealing with bulk materials such as powders, pellets, grains, etc., and not liquids or cargo material handling large size products.
Pneumatic Conveying may be defined as the art of transporting dry bulk materials through a pipeline by either a negative or a positive pressure air stream. It is also described as harnessing air movement to accomplish the conveying task. The air (pneumatic) movement is nothing more than air in motion.
Pneumatic Conveying Requires:
- The pressure differential causes air movement.
- Air mass at velocity moves material mass at a velocity that overcomes frictional forces.
- Kinetic energy transfers from gas to solid.
Knowledge of how pneumatic conveying systems function is essential. A conveyor manufacturer must consider several factors regarding the process and the materials used to develop a plan with the appropriate components to give a solution according to the customer’s needs. Here are factors you need to consider for a Pneumatic Conveying Systems Design.
Considerations for Pneumatic Conveying Systems Design
1. Bulk Density of the Material
Bulk density refers to the weight/volume of the product. In other words, it tells us how much 1 cuft volume of the product will weigh and is generally expressed in Pounds/Cubic Feet.
It tells us how light or how heavy the material is. E.g., Fumed silica or Polystyrene bead is very light (1-8 lb./cuft. is very light, and Iron Oxide, or 250lb/cuft, and very heavy.
For any pneumatic conveying application, loose bulk density is the critical indicator for size selection (higher the bulk density, difficult to convey).
Note: We should not confuse the bulk density with the particle density of the product. Particle density (or specific gravity) is a material characteristic and assumes that there is no air present between the particles (which is not possible in real-world)
The distance that material must travel is another essential factor when designing and defining the bulk solids transportation system. When the product moves with the air inside the conveying pipe, it requires specific energy to move forward to overcome frictional losses. Hence longer the conveying distance, the more significant is the energy required.
As the conveying pipe routing consists of horizontal piping, vertical piping, and bends, each configuration has a specific energy requirement. Hence, we need to know the conveying distances (horizontal, vertical, and number of bends) as a first step.
A general guideline is that pressure conveying is recommended if the total conveying distance exceeds 300FT. Mainly because we can only generate a vacuum of less than 28.9 Inch HG (or 14.5 PSIG), whereas in pressure conveying, the air can deliver pressures exceeding 14.5 PSIG.
3. Pick-up Location and Material Container
In most cases, bulk materials are stored in silos, totes (or bulk bags), 55 lb kraft bags, Gaylord bins, or drums. The conveying system should pick up products from these pick-up points and transport them to the destination.
Each pick-up station and product will have a feature specific to the design that will affect the conveying process. E.g., a flour storage silo discharging into a conveying line requires an airlock, whereas a plastic pellet storage silo may not require an airlock (for vacuum conveying).
Similarly, whether it is a bulk bag discharger, bag dump station, gaylord bin, or drum, it’s interfacing with a conveying system for a specific product is the most crucial consideration for a system designer.
4. Headroom Requirements
It’s not always about the materials for customizing equipment, and facility limits sometimes necessitate equipment adjustments. The compact footprint of pneumatic conveying systems relative to other material handling technologies is their advantage.
Any pneumatic transport system will have an air material separator (AMS) at the end of the convey line to separate and discharge the product and exhaust the clean conveying air. AMS should have filters in powder conveying applications, and there is some minimum headroom space is required to attend to and maintain the filters and instruments and generally above a minimum of 4 – 5 FT for many conveying applications.
5. Product Characteristics
It is vital to know the product characteristics before selecting the SC Vacuum Conveying unit.
Food/Dairy/Chemical products have different requirements and selection processes.
Food and Dairy products may require unique product contact materials and special regulatory approvals, such as FDA/USDA, etc. regulatory bodies, and GMP practices.
Chemical derivatives may require unique corrosion-resistant product contact materials.
High moisture products must be treated with caution, and testing is mandatory before selection. Hygroscopic products (where the products may pick up moisture from conveying air) also require special attention and testing and may require an air-conditioned room or dehumidification of conveying air.
These would cause wear and tear on the convey lines, and sometimes special wear-resistant convey lines/elbows are recommended.
It is also essential to know any environmental and emission requirements from statutory bodies such as OSHA or local authorities.
Generally, powders are those less than 1000 microns or 1mm in size. Granules are products usually larger than 1mm, and pellets/Grains are much more significant. A larger particle size greater than 10 mm (<1/2″ size) requires special attention or testing. In some cases, particle size is expressed in mesh size (10 mesh, 100 mesh, etc.)
6. Know the Construction Materials
A pneumatic conveying system’s design and functionality are heavily influenced by the materials used in its construction. The emphasis is on product-contact surfaces. Usually, all metallic surfaces are used. Plastics are avoided for static control and contamination reasons. Will your process materials come into touch with carbon steel, stainless steel, or aluminum that has been coated?
Carbon steel comes with various coatings, but these can corrode or degrade over time. 304 or 316L stainless steel with a specific level of polish for ease of cleaning and contamination prevention is the choice for food- and dairy products. FDA-approved plastics are mandatory for food products.
7. Are You Using a Batch or Continuous Process?
You must specify whether you’re feeding a batch or a continuous process. Small conveyors discharging into a surge bin are examples of a batch process. Determine if a batch of material will enter the process through a feeder or an intermediate hopper and whether your conveying system can handle a batch’s influx of material.
8. Be Aware of Your Upstream Process
To successfully design a vacuum conveying system, you must first understand the material supply process upstream. Determine whether the material came from a volumetric feeder, mixer, reactor, or other material-handling equipment. All of these factors have an impact on the conveying process.
9. Process Equipment
Upstream equipment impacts downstream equipment, and the more a pneumatic conveyor manufacturer understands the process, the more equipped it is to provide a system that fulfills a customer’s needs. Conveyor design can be affected by the process equipment, such as loss-in-weight feeders and mixers, such as loss-in-weight feeders, extruders, packers, volumetric feeders, and other equipment. Feeders that have lost weight, for example, must be replaced as soon as possible.
10. Know Your Conveying Rate
It’s crucial to know how many pounds or kilos will be transported per hour when calculating conveying rates. Define whether the procedure is batch or continuous as well. For example, if a process calls for 2000 lb/hr of product transport, the batch process calls for 2000 lb every 5 minutes for 1 hour, 24,000 lb/hr. This is the difference between lifting 2000 pounds in 5 minutes versus lifting 2000 pounds over 60 minutes.
11. Plant Site and Industry Environment
When developing a system, consider the plant’s geographic location and the industrial environment where you will use the equipment.
Vacuum source sizing is affected by altitude, much as it is by cooking at higher elevations. For example, a plant on the Jersey shore (sea level) might utilize a 5-HP vacuum pump for an application. In contrast, the same application in Denver (one mile above sea level) will require a 7.5-HP vacuum pump.
12. Product Dust Explosion Hazard & Hazardous Area Classification
After the Georgia Sugar explosion incident, OSHA released National Emphasis Program Directive NEP and declared that most powders that can be dispersed in the air could cause dust explosion risk, and preventative measures/protection measures should be taken for end-users.
Any product, regardless of particle size, can cause a dust explosion. However, finer particles pose more explosion risk. Hence, a risk analysis (or Dust Hazard Analysis) must confirm that the residual explosion risk is acceptable: the protection measures to be taken should conform to the available knowledge and technology.
As per OSHA and NFPA 70 (section 500), in some instances, the equipment location area needs to be classified under various hazardous zones, especially appropriate electrical equipment such as electric enclosures, motors, solenoids, etc.
How We Can Help: Pneumatic Conveying Systems Designed to Your Specifications
At Pneu-Con Pneumatic Conveying, Inc, we offer superior and specialized pneumatic conveying systems solutions tailored to meet your exact needs. Regardless of the complexity of your project, or the nature of the material you are moving, we can assess your company’s needs and determine the best solution for you and solve your dry bulk and powder handling problems.
Pneu-Con’s experience spans four decades of unrivaled expertise in pneumatic conveying systems, which allows us to build high-quality custom conveying solutions for your needs. And what’s more, we are with you every step of the way. We can help you scale your systems anytime you need to, according to your business’s dynamic and growing needs.
From, Food to Cosmetics, and every Dry Bulk Material in between, let’s move it. Our Mantra is short and straightforward, Designed, Engineered, Customized for you. For more information on Pneumatic Conveyor Systems and how we can help, feel free to Contact Us today, and we will be more than willing to assist.