Vacuum conveying systems for powders and difficult-to-transport materials involve a starting point and an end point, and hazards need to be avoided along the way.Here are 10 tips for designing your system to maximize movement and minimize dust exposure.
Vacuum conveying technology is a clean, efficient, safe and worker-friendly way to move materials around a factory.Combined with vacuum conveying to handle powders and difficult-to-convey materials, manual lifting, climbing stairs with heavy bags and messy dumping are eliminated, while avoiding many hazards along the way.Learn more about the top 10 tips to consider when designing a vacuum conveying system for your powders and granules.Automating bulk material handling processes maximizes material movement and minimizes dust exposure and other hazards.
Vacuum conveying controls dust by eliminating manual scooping and dumping, conveying powder in a closed process with no fugitive dust.If a leak occurs, the leak is inward, unlike a positive pressure system that leaks outward.In dilute phase vacuum conveying, the material is entrained in the air flow with complementary ratios of air and product.
System control allows material to be conveyed and discharged on demand, ideal for large applications requiring the movement of bulk materials from large containers such as bulk bags, totes, rail cars and silos.This is done with little human intervention, reducing frequent container changes.
Typical delivery rates in the dilute phase may be as high as 25,000 lbs/hr.Typical delivery distances are less than 300 feet and line sizes up to 6″ diameter.
In order to properly design a pneumatic conveying system, it is important to define the following criteria in your process.
As a first step, it is important to learn more about the powder being conveyed, especially its bulk density.This is usually described in pounds per cubic foot (PCF) or grams per cubic centimeter (g/cc).This is a key factor in calculating the size of the vacuum receiver.
For example, lighter weight powders require larger receivers to keep the material out of the airflow.The bulk density of the material is also a factor in calculating the size of the conveyor line, which in turn determines the vacuum generator and conveyor speed.Higher bulk density materials require faster shipping.
The conveying distance includes horizontal and vertical factors.A typical “Up-and-In” system provides vertical lift from ground level, delivered to a receiver via an extruder or loss-in-weight feeder.
It is important to know the number of 45° or 90° swept elbows required.”Sweep” usually refers to a large centerline radius, usually 8-10 times the diameter of the tube itself.It is important to remember that one sweep elbow is equivalent to 20 feet of 45° or 90° linear pipe.For example, 20 feet vertically plus 20 feet horizontally and two 90 degree elbows equals at least 80 feet of conveying distance.
When calculating conveying rates, it is important to consider how many pounds or kilograms are conveyed per hour.Also, define whether the process is batch or continuous.
For example, if a process needs to deliver 2,000 lbs/hr.product, but the batch needs to deliver 2,000 pounds every 5 minutes.1 hour, which is actually equivalent to 24,000 lb/hr.That’s the difference of 2,000 pounds in 5 minutes.With 2,000 pounds over 60 minutes.period.It is important to understand the needs of the process in order to properly size the system to determine the delivery rate.
In the plastics industry, there are many different bulk material properties, particle shapes and sizes.
When sizing receiver and filter assemblies, whether mass flow or funnel flow distribution, it is important to understand particle size and distribution.
Other considerations include determining whether the material is free-flowing, abrasive, or flammable; whether it is hygroscopic; and whether there may be chemical compatibility issues with transfer hoses, gaskets, filters, or process equipment.Other properties include “smoky” materials such as talc, which have a high “fine” content and require a larger filter area.For non-free-flowing materials with large angles of repose, special considerations for receiver design and discharge valve are required.
When designing a vacuum delivery system, it is important to clearly define how material will be received and introduced into the process.There are many ways to introduce material into a vacuum conveying system, some are more manual, while others are more suitable for automation – all requiring attention to dust control.
For maximum dust control, the bulk bag unloader uses an enclosed vacuum conveyor line and the bag dump station integrates a dust collector.Material is transported from these sources through filter receivers and then into the process.
To properly design a vacuum conveying system, you must define the upstream process for supplying materials.Find out if the material is coming from a loss-in-weight feeder, volumetric feeder, mixer, reactor, extruder hopper, or any other equipment used to move the material.These all affect the conveying process.
Additionally, the frequency of material coming out of these containers—whether batch or continuous—affects the conveying process and how the material behaves when it comes out of the process.Simply put, upstream equipment affects downstream equipment.It is important to know all about the source.
This is an especially important consideration when installing equipment into existing plants.Something that might be designed for manual operation might not provide enough room for an automated process.Even the smallest conveying system for powder handling requires at least 30 inches of headroom, given the maintenance requirements for filter access, drain valve inspection, and equipment access below the conveyor.
Applications requiring high throughput and large headroom can use filterless vacuum receivers.This method allows some of the entrained dust to pass through the receiver, which is collected in another ground filter container.A scaling valve or positive pressure system may also be a consideration for headroom requirements.
It is important to define the type of operation you are feeding/refilling – batch or continuous.For example, a small conveyor that discharges into a buffer bin is a batch process.Find out if a batch of material will be received in the process through a feeder or intermediate hopper, and if your conveying process can handle a surge of material.
Alternatively, a vacuum receiver can use a feeder or rotary valve to meter material directly into the process—that is, continuous delivery.Alternatively, the material can be conveyed into a receiver and metered out at the end of the conveying cycle.Extrusion applications typically utilize batch and continuous operations, feeding material directly into the mouth of the extruder.
Geographical and atmospheric factors are important design considerations, especially where altitude plays an important role in sizing the system.The higher the altitude, the more air is required to transport the material.Also, consider plant environmental conditions and temperature/humidity control.Certain hygroscopic powders may have expulsion problems on wet days.
Materials of construction are critical to the design and function of a vacuum conveying system.The focus is on product contact surfaces, which are often metal – no plastic is used for static control and contamination reasons.Will your process material come in contact with coated carbon steel, stainless steel or aluminum?
Carbon steel is available in various coatings, but these coatings deteriorate or degrade with use.For food-grade and medical-grade plastic processing, 304 or 316L stainless steel is the first choice – no coating required – with a specified level of finish to ease cleaning and avoid contamination.Maintenance and quality control personnel are very concerned about the materials of construction of their equipment.
VAC-U-MAX is the world’s leading designer and manufacturer of vacuum conveying systems and support equipment for conveying, weighing and dosing more than 10,000 powders and bulk materials.
VAC-U-MAX boasts a number of firsts, including the development of the first pneumatic venturi, the first to develop direct-charge loading technology for vacuum-resistant process equipment, and the first to develop a vertical wall “tube hopper” material receiver.Additionally, VAC-U-MAX developed the world’s first air-powered industrial vacuum in 1954, which was manufactured in 55 gallon drums for combustible dust applications.
Want to learn more about how to transport bulk powders in your plant?Visit VAC-U-MAX.com or call (800) VAC-U-MAX.