Particulate matter in the air is a major health risk in both personal and industrial contexts. Additionally, in some industrial processes, the presence of particulate matter can represent a significant source of waste and lead to lost profits. Such realizations are what motivated German mill builder Wilhelm Beth a century ago. Beck realized that eliminating the so-called “dust sickness” could greatly improve his operations, and he ended up patenting multiple filters for dust collectors. His technology created the dedusting industry and was quickly employed in the lumber, grain, and cement sectors.
From industrial dust collectors to portable dust collectors, Beth’s invention remains relevant even today. This Dust Collectors Buying Guide will detail how these machines work, the most popular types, and what you should know when looking for secondhand dust collectors for sale.
Popular Types of Dust Collectors
While air purifiers use disposable filters to improve air quality, dust collectors employ more robust components. At their most fundamental level, basically all dust collectors for woodworking, manufacturing, recycling, food processing, and industries with similar processes contain similar elements, such as a filter, a blower, a system to clean the filter, and a place where the dust gets deposited.
Naturally, current-generation dust collectors come in many different designs and models. In this section, we will detail the most popular types and describe how they function.
Inertial separators employ multiple forces in order to clean particulate matter from the air. Larger applications may see the installation of multiple inertial separators in either series or parallel to ensure the desired level of cleanliness.
Inertial separators are all comprised of a body and an inlet that allows “dirty” (i.e., particle laden) air to enter. Centrifugal collectors (known as cyclone dust collectors) also include a cone, and in their case, as air comes into the separator’s body, it begins to spin in a cyclone-like pattern. The inertia of heavier particles sends them spiraling downward, while lighter particles begin to move upward. Gravity draws heavier particles through an exit port at the bottom of the separator. Cleaned air exits the separator through a separate outlet.
There are two other main types of inertial separators, which are classed according to their dust-collection method. Settling dust collectors include a chamber or chambers at the bottom of the separator into which the collected material falls. Baffle separators install a stationary plate that causes the air to change direction and the heavier particulate matter to remain on the bottom.
Inertial separators only filter out the heaviest particulate matter, and the shape of the particles can cause some to escape from the system. For this reason, they are often used as a kind of prefiltering system. Because they don’t include a physical filter that “catches” the particles, they are also used for easy industrial recycling. Though simple in design, inertial separators have several significant drawbacks, such as a susceptibility to erosion, an inability to process sticky material, and relatively low efficiency.
Fabric-filter dust collectors are the oldest type of dust collectors, and they are the type that Wilhelm Beth patented about 100 years ago. They’re also the most common dust collector for home and business uses. Dubbed baghouse filters, they force air through a bag of multiple layers.
The bag will become clogged over time, which will necessitate its cleaning. Common cleaning systems include the following:
- Shaking: A sheet placed beneath the fabric bag and connected by a tube collects the dust by shaking the bag.
- Reverse Air: A sheet placed beneath the fabric bag and connected by a tube collects the dust by forcing air in a reverse direction into the bag.
- Pulse Jet: Similar in design to a reverse-air system, pulse-jet dust collectors dislodge the collected dust by running quick bursts of air into the bag.
- Cartridge Collectors: Prefab cartridges with pleated filters can be manually changed or cleaned using the pulse-jet method.
- Sonic Collectors: Instead of relying on mechanical motion or air propulsion, sonic collectors use bursts of sound to dislodge dust from fabric filters.
Fabric-filter dust collectors have the advantage of being highly efficient and easy to operate. However, they typically require frequent cleaning and numerous replacement bags. Also, they typically will not work well (or at all) in high-temperature environments.
Wet scrubbers are the best dust collectors for end-use scenarios that involve a lot of heat. Instead of using physical barriers or gravity to filter out particles, wet scrubbers employ a liquid (typically water, although some applications call for oil). These types of systems perform three main tasks. They cause particulate matter to swell, making it easier to collect (gas-dehumidification). They directly touch the liquid and get enveloped by it (gas-liquid contact). And they get removed from the flow of air before it is cycled back into its operating context (gas-liquid separation). In order to perform that final step, the liquid must flow through a mist eliminator (also known as demister pads). The liquid gets funneled into a collection receptacle where gravity draws the solid matter to the bottom. It can then be collected or recycled.
Classifications for wet scrubbers vary based on the energy that they use to purify the air. Low-energy scrubbers may use a tank studded with misters (gravity tower scrubbers) or a fan that’s being constantly kept wet (wet-fan scrubbers). Medium-energy scrubbers impart a twisting motion to the water so that particulate matter settles, which is decidedly similar to that of some inertial separators (wet cyclone scrubbers). Medium-to-high-energy scrubbers force air through wet packing material that’s arranged in either a vertically ascending pattern (packed bed scrubbers) or that travels horizontally (cross-flow scrubbers).
Advantages of wet scrubbers include a relatively low purchase price and installation cost, as well as a smaller physical footprint. But these dust collectors are very expensive to operate and typically need some sort of pre-cleaner if the particulate matter is too large.
Electrostatic Precipitators (ESP)
These power-reliant dust collectors employ static electricity to scrub particulate matter from the environment. Electrostatic precipitators (ESPs) employ a pair of metallic, pass-through gates (i.e., plates, tubes), each connected to a separate electrode. The first electrode will charge the initial gate, typically giving it a negative charge. The second electrode imparts a positive charge, which causes a static-electricity attraction, making the negatively charged stick to its surface. ESPs can either be high-voltage or low-voltage.
ESPs have the advantage of costing little to operate and running in a highly efficient manner. They also function well in extremely hot environments. Still, upfront expenses tend to be high, and they can be rather expensive to maintain. There are no automatic cleaning options, and the system can become compromised if the dust isn’t regularly emptied. Also, failure to do so may pose an explosion risk when dealing with flammable materials.
Unit collectors function as a kind of subset of the already described dust collectors. These types of dust collectors get installed right at the source of the particulate-matter generation and can be portable. They return the particulate matter into a hopper or right back to the area from whence it came. Unit collectors are typically either fabric collectors or cyclone collectors.
Inertial Separators vs Fabric Filters vs Wet Scrubber vs Electrostatic Precipitators [ESP] vs Unit Collectors
As the previous section has hopefully shown, there is no such thing as the best dust collector. Though there are large and small dust collectors with mechanisms relying on elements as diverse as water, physical barriers, electricity, and physical motion in order to achieve their designed purpose, the ideal dust collector is one that works most efficiently in its required context. In this section, we will describe the end-use applications where each of the most popular types of dust collectors excels.
Because inertial separators are relatively inexpensive, easy to operate, and require little maintenance, they excel in contexts where near continuous running, high temperatures, and large particles are expected. Some industries that employ these kinds of dust collectors include blasting, foundries, and food production. They can also serve as a prefilter for some of the other kinds of collectors that focus on removing finer particles.
Though they are the oldest kind of collector, fabric filters find regular usage today in woodworking and mineral production due to their flexibility, ease of use, and high efficiency. While they can function in hot environments if constructed of the proper, heat-resistant material, other choices will function better.
Wet scrubbers have the advantage of being able to process both solid material and gasses. That’s why they are used in electricity production and to filter exhaust from diesel engines. Unfortunately, when dealing with dry particulate matter, they often require a prefilter. Wet scrubbers are also very expensive to operate.
Electrostatic precipitators are specialized by their very nature, and despite the fact that they can handle significantly smaller particulate loads than their counterparts, require highly knowledgeable personnel to keep them operational, and are expensive to purchase and install, they perform admirably in very specific end uses. Some of these include chemical plants, health care, metallurgy, and steam plants.
What to look for when buying Dust Collectors
Before you buy a dust collection, you should consider a number of factors, such as:
- Where the dust is coming from. The specific use case that is producing your dust will determine what size dust collector you need and how exactly it should be positioned in your work space.
- The properties of your dust. The size, flammability, shape, and quantity of your dust will all contribute to what kind of dust collector you need.
- The available space you have. Virtually all dust collectors have different configurations, some of which allow you to maximize smaller spaces. Others require an expansively large area in order to operate at all.
- Your local climate. Excess moisture or heat can render some dust collection methods untenable. Make sure that your purchase will work in the surrounding environment.
- The available power supply. Some dust collectors (e.g., inertial separators) don’t require power at all. Others need substantial amounts (e.g., wet scrubbers, electrostatic precipitators). Consider your business’ infrastructure before buying.
- Maintenance & Repairs. Older units may require more upkeep, but so do certain specific kinds of collectors. You’ll need to factor those expenses in to your operating costs.
- Downtime. Some collectors can run virtually continually. Others require frequent cleaning. Failing to match downtime with your operating schedule can lead to costly delays.
- Airflow. Certain collectors can tolerate changes in airflow, but some will cease to function effectively should variance occur.
- Noise. Electrostatic precipitators are completely silent. Fabric filters combined with sonic collectors are most definitely not. Louder collectors may require you to purchase hearing protection for employees or may lead to issues with local authorities due to noise ordinances.
Real-Life Applications for Dust Collectors
We have already listed a number of real-life applications for dust collectors in previous sections but allow us to restate the fact that these devices are used in a wide array of industries. Some of these include:
- Steel Production
- General Manufacturing
- Food Processing
- Metal Fabrication
- Fume Collection
- Pharmaceutical Production
- Paper Production
- Wastewater Treatment
- Powder Coating
- Power Production
Accessories for Dust Collectors
Though dust collectors have numerous configurations, most of their accessories fall into the category of spare parts, replacement filters, and required adapters for specific uses. To find more information about dust collector accessories and the units themselves, check what we have available at Surplus Record. Head to our Machinery & Equipment page, enter in the phrase “Dust Collectors,” click on the category, and see what we have in stock.