In recent years, cartridge-style dust collectors have become the go-to technology for industrial dust collection in the manufacturing and processing industries. These dust collectors offer a combination of high efficiency filtration, compact size and reduced pressure drop. As a result, a high efficiency cartridge dust collector is used for most industrial applications, including pharmaceutical, chemical, food processing, woodworking and metalworking.

Figure 1: Specifying a dust collection system for a new or expanded facility involves research and attention to detail. Source: Camfil

These dust collectors are a safe and cost-effective way to improve indoor air quality by removing dangerous dusts and fumes. However, selecting the best cartridge collection system for a particular application requires thorough research and attention to detail. This paper will outline six key factors that need to be considered when choosing a cartridge collection system.

Compliance with emission requirements

Engineering and operations departments are faced with increasingly complex regulations from organizations like the EPA and OSHA, as they continue to tighten air quality and safety requirements. Compliance with these regulations should be the top priority in any dust collection strategy. Failure to comply can result in fines, production shutdowns or costly litigation. In fact, in one well-publicized case, a federal jury awarded $20.5 million to the plaintiffs in a lawsuit involving inhalation of welding fumes.

OSHA has established permissible exposure limits (PELs) for hundreds of dusts, ranging from nonspecific or “nuisance” dust to highly toxic substances. These limits are based on eight-hour time-weighted average (TWA) exposure. More information on PELs can be found on OSHA’s website.

One area of concern is stricter limits on exposure to hexavalent chromium, a known carcinogen generated by processes like welding and cutting stainless steel, thermal spraying and application of anticorrosion paints. OSHA has set thresholds as low as 5 micrograms (0.005 milligram) per cubic meter TWA. This is 10 times stricter than the limits for some other toxic dusts. Dust collectors must be equipped with very high efficiency filtration media to meet such requirements.

It is crucial to specify a dust collector that complies with emission thresholds. Reputable equipment suppliers will provide a written guarantee stating the maximum emissions rate for the equipment over an eight-hour TWA. Filter efficiency stated as a percentage is not an acceptable substitute, even if the supplier promises 99.9% efficiency. OSHA only cares that the quantified amount of dust in the air is below established limits.

Combustible dust issues

Explosive dusts can be organic or metallic in nature and are present in a wide range of manufacturing industries, including agricultural, chemical, food, paper, pharmaceutical, textile and woodworking. Combustible dust explosions can happen suddenly in many manufacturing areas, but the dust collection system is one of the most common locations. This is because dust collectors can hold a large amount of suspended combustible dust in a confined space.

Therefore, dust collection systems must meet the National Fire Protection Association (NFPA) standards and codes that protect buildings against fire and explosion risks if a hazard exists. Nowadays, the OccupationalFigure 3. Kst values of common dusts. Source: Camfil Safety & Health Administration (OSHA) is enforcing these standards with increasing vigilance.

Figure 2 compares the Kst values of various common dusts. For a more comprehensive list, visit this website. This website contains a European database called “GESTIS-DUST-EX,” which provides information on the combustion and explosion characteristics of over 4,000 dusts. Although this database is useful as a reference, it cannot replace required dust testing.

Dusts other than common ones must be tested by a private lab or OSHA, and the facility must keep the test data on file. Many commercial test labs offer a low-cost test to determine whether a dust sample is combustible. If the test is positive, then the explosive index (Kst) and the maximum pressure rise (Pmax) of the dust should be determined by ASTM E 1226-10, Standard Test Method for Explosibility of Dust Clouds. In fact, any dust above 0 Kst is now considered explosive, and most dusts fall into this category.

If tests show that a dust has a Kst value greater than zero, it is combustible dust, and NFPA 652 requires a dust hazard analysis (DHA). A DHA is needed to assess risk and determine the required level of fire and explosion protection for dusts produced or handled in the facility. The analysis can be conducted internally or by an independent consultant, but in either case, the authority having jurisdiction will ultimately review and approve the findings.

Engineering firms should also have a good understanding of NFPA 654 Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids. This set of guidelines is designed to prevent and mitigate fire and explosion hazards that involve combustible particulate solids or hybrid mixtures. It applies to various industries and covers every aspect of the manufacturing, processing, blending, conveying, repackaging and handling of these materials.

The facility owner or operator is responsible for implementing these guidelines. The latest edition of the standard, published in 2020, has been reorganized to align with NFPA 652, which introduces the concept of dust hazard analysis. This standard is referred to by OSHA’s Combustible Dust National Emphasis Program to identify dust hazards and define mitigation strategies.

Depending on the nature and severity of the hazard, refer to NFPA 654 to guide you to the appropriate standard(s) for explosion venting or explosion prevention, as follows:

NFPA 68: Standard on Explosion Protection by Deflagration Venting: This document deals with explosion venting — which is a system that vents combustion gases and pressures from an enclosure to reduce damage caused by deflagration. The 2007 edition of the standard has more stringent requirements than previous editions and is now considered a standard rather than just a guideline.

NFPA 69: Standard on Explosion Prevention Systems: This standard covers explosion protection of dust collectors when venting is not possible. It covers several methods for preventing deflagration explosions, including control of oxidant and combustible concentration, explosion suppression, deflagration pressure containment and spark extinguishing systems.

Additionally, other NFPA standards may be relevant to your situation, such as 664 for wood processing facilities, 484 for combustible metals, 61 for agricultural and food processing facilities, 91 for air conveying of vapors, gases, mists and particulate solids, 655 for sulfur fires and explosions, 13 for sprinkler systems and 17 for static electricity.

NFPA 652: Standard on the Fundamentals of Combustible Dust: This standard introduces the requirement for conducting DHA to assess potential combustion risks for dusts produced or handled in a facility. If tests show that a dust has a Kst value greater than zero, it is considered combustible dust and a DHA is required to determine the necessary level of fire and explosion protection. The analysis can be conducted internally or by an independent consultant, but the authority having jurisdiction will ultimately review and approve the findings.

Dust collector functionality

While emissions compliance and combustible dust are important considerations, they are not the only factors to keep in mind when selecting a dust collector. Other functions that the dust collector may need to perform include reclaiming valuable product, maintaining a higher level of cleanliness in manufacturing areas, accommodating changes or expansions in the plant, or addressing performance issues with an older system.

Conducting a site survey can help identify specific objectives, and reliable equipment suppliers will typically provide a survey form to gather important information such as:

· The process

· The material to be collected

· Operating hours and conditions

· Electrical requirements

· Airflow and pressure ratings

· The physical properties of the dust

Even if the dust is a common type, such as wood dust, it can behave differently depending on the specific process it’s involved in. Therefore, it’s always important to test the dust, preferably using a sample collected from used filters.

Dust testing can identify important characteristics such as the median size and particle distribution of the dust, as well as its shape (such as long fibers, uniform spheres or jagged crystals), combustibility, and stickiness or hygroscopicity. Independent laboratories and equipment suppliers offer a range of bench tests to determine these characteristics.

Conducting a site survey and lab testing is the best approach for determining the filtration efficiency and pressure drop across the filter media required for the dust collector, and to identify the most effective collector design and media for the application.

Factors that impact performance and reliability

It’s crucial to choose dust collection equipment that minimizes maintenance issues, as reliability problems can arise from misunderstandings during the initial selection process or changes made in the plant that affect the unit’s performance.

While a site survey and lab analysis can typically provide enough data, full-scale dust collection testing may be necessary for applications involving hard-to-handle dusts or stringent emissions control requirements. Figure 6: The open-pleated design of this filter results in significantly lower pressure drop as well as improved dust release characteristics during pulse cleaning. Source: Camfil Full-scale testing involves running a large (55 gallon) dust sample through a full-size dust collector on a test rig to simulate real-life operating conditions. Dust particle size, pressure drop and other parameters can be precisely monitored, and real-time emissions monitoring can be performed.

In addition to selecting the right equipment, it’s helpful to be aware of design and technological improvements that can enhance reliability and performance. For instance, vertically mounted cartridges with a high, side entry inlet and staggered baffles can distribute air and separate out larger particles, reducing the load on the filters.

Filter media pleating technology: Premium cartridges are designed to maximize the amount of usable filter media in each cartridge, but not by simply squeezing in more square meters of media using tightly packed pleats. Instead, they use pleating technology that maximizes efficiency.

Safety options

The primary function of a dust collector is to maintain worker and workplace safety, but not all collectors are equally safe. As noted above, vertically mounted cartridge systems offer inherent safety advantages for heavy dust loading applications.

When working with your equipment supplier, consider these additional safety features:

OSHA-compliant railed safety platforms and caged ladders can prevent slips and falls when workers access the collector for service.

Where highly toxic dust is being handled, a bag-in/bag-out (BIBO) containment system may be required to isolate workers from used filters during change-out.

Ease of filter change-out should also be explored. Are the filter cartridges positioned for easy access? Do they slide in and out of the housing easily? Pulling out a dirty overhead filter that weighs 100 lb can result in neck, back and foot injuries, so make sure the collector you choose is service-friendly.

Fire and explosion prevention must also be optimized using features and technologies such as flame-retardant filter media, spark arrestors, sprinkler systems and approved explosion vents or other componentsFigure 8: Cartridge dust collector equipped with an OSHA-compliant safety platform. Source: Camfil for controlled deflagration.

The collector can also be equipped with a safety monitoring filter, which is a secondary bank of high-efficiency air filters that prevent collected dust from re-entering the workspace in case of a leak in the dust collector’s primary filtering system.

Recirculating dust collection systems require a safety monitoring filter to prevent the re-entry of collected dust back into the workspace. Using a recirculating system is a cost-effective way to maximize return on investment.

This system recycles air downstream of the collector, which eliminates the need to replace heated or cooled air, resulting in significant annual energy savings for many plants. Additionally, dust collectors installed in shops with high ceilings can improve heating system efficiency by taking hot air from the ceiling and distributing it at ground level.

Impact on ROI

When considering the cost of operating cartridge-style dust collectors, it’s important to look at the total cost of ownership (TCO) rather than just the initial purchase price. There are four main cost factors to consider: energy consumption, the price of filter cartridges and other consumables, and maintenance time.

Lowering energy consumption

Dust collectors consume electricity while running, with the largest portion going to the fan motor that moves air through the system. This air is replaced with heated or cooled air, which can be expensive. The amount of energy used is directly proportional to the volume of air the motor is moving through the system (measured in cubic feet per minute or CFM).

Dust collectors are variable systems and when started up, there is less pressure drop across the filters. This can lead to higher-than-designed air to cloth ratios if the fan isn’t dampened back. To improve the system’s efficiency, a variable frequency drive (VFD) with a static pressure controller can be used.

At start-up, the controller is set to the designed CFM and the fan motor’s HZ is reduced to maintain the design CFM. As the resistance increases on the filters, the controller will increase the HZ of the motor to compensate for the extra static pressure and maintain the designed CFM.

Lowering compressed air costs

Pulse cleaning is an essential technology to maintain the steady airflow (CFM) of dust collectors and increase their efficiency. Pulse cleaning systems blast accumulated dust off the filters with quick bursts of compressed air when the pressure drop reaches a certain level, increasing filter life and maintaining a lower average pressure drop.

However, compressed air production is expensive, and pulse cleaning is often one of the highest operating costs associated with dust collection. Therefore, it has the most potential for cost savings.

Today’s most advanced dust collectors can reduce compressed air consumption by as much as 50% versus competitive dust collectors. They use less compressed air because they are able to pulse clean far less often. When properly designed, the cleaning system will remove the built-up material from the filter cartridges, reduce the pressure drop across them, reduce the fan energy consumption, and in turn, reduce associated energy costs. Properly designed dust collection systems that take this into consideration will provide more airflow while maintaining a low pressure drop. Among other design features, they use high-efficiency filter cartridges that can handle higher airflows while maintaining a high level of filtration efficiency.

Reducing filter cartridge costs

As shown in Figure 10, properly designed premium filter cartridges generally last 50% longer than standard filters because they pulse-clean more effectively. This is because premium filters are able to maintain a consistent airflow and low pressure drop longer than standard filters. The vertical lines in the graph represent the times that filter cartridges are changed out.

As a hypothetical example, consider a side-by-side comparison of two identical dust collection systems — one outfitted with standard filter cartridges and the other with premium cartridges. Here is what would likely play out during the course of a year:

At around four months, the collector with standard cartridges would be using twice as much compressed air as the collector with premium filter cartridges.

At six months, the standard cartridges would need to be changed out because they would be too clogged with dust for the pulse cleaning system to maintain low differential pressure. If not changed at this point, they will put undue stress on the fan motor and use unnecessary energy. However, the premium filters would still be working effectively because they have more usable media and the media is pleated in a way that releases more dust with each pulse.

At 12 months, the premium filters would also need to be changed out because they would be fully loaded and unable to maintain a low pressure drop and prevent excess energy from being consumed.

After one year, the dust collector with standard filter cartridges would have used 5,037 cubic feet of compressed air and $14,600 of energy. The dust collector with premium filter cartridges would have used 2,518 cubic feet of compressed air and $7,300 of energy. The cost of six additional filter cartridges and the additional $7,300 energy savings far exceed the cost of a year's worth of premium filter cartridges.

Selecting the right filter media for a cartridge-style dust collector is important for efficiency and longevity. Premium cartridges are made with filter media that is appropriate for the specific application and dust being collected. Coatings may be necessary for dust release, flame retardance or conductivity. Incorrect media can cause unsafe conditions, high pressure drop and excessive energy use. The correct media promotes a safer, cleaner work environment with less maintenance. Filter media selection is a vital component of the effectiveness of a dust collector.

Reducing waste disposal

Making dust collection systems more environmentally friendly and cost-effective involves reducing waste disposal costs and minimizing CO₂ emissions. Depending on the type of material being filtered, there are costs associated with properly disposing of filters that are laden with process dust.

A comprehensive cost analysis should be conducted to determine the operating and maintenance costs and expenses associated with filter replacement. Dust collectors that utilize “green” features like variable frequency drives and energy-efficient fan motors can help to reduce energy costs and may be eligible for utility rebates or incentives.

Additionally, these systems can help save on maintenance costs for electrical components like motors and control panels that are exposed to dust. A reputable equipment supplier can provide a cost projection analysis and offer advice on ways to improve return on investment and enhance dust collector performance.