Arresting Fugitive Dusts

The use of vacuum conveyors to transfer materials between processes improves indoor air quality while increasing efficiency and the bottom line.  

• By Doan Pendleton
• Oct 01, 2021

Most often when hearing the term fugitive dust, one thinks of combustible fugitive dust. However, fugitive dust is simply a particulate matter that becomes entrained in ambient air (usually by wind or human interaction). Respirable dust particles are invisible to the naked eye and universally considered to be 10 microns or less in size. Of all the harmful respirable dusts, silica gets the most attention, perhaps because it is present in so many products and nearly all industries, and it can lead to incurable lung disease and death. Silica is an anti-caking agent in food, pharmaceutical and supplement products in metal powders, paint and coatings formulations and in a host of other materials.

Respirable dust hazards in these industries are not limited to silica exposure. Food flavorings, fine metal powders and active pharmaceutical ingredients contain other substances that are toxic to the human body when inhaled. Even some inert respirable dusts have the ability to cause irritation or sensitivity. Across the board, regulatory agencies favor closed systems as an engineering control to mitigate respirable dust exposure that occurs during manual dumping or transfer of materials. Vacuum conveying systems contain respirable dust from source to destination in a closed system preventing respirable dusts from escaping into the plant environment in the first place.

Vacuum conveyors are inherently safer and more efficient than manual transfer of materials and some of the most common reasons facilities implement them is to meet increased demand, mitigate ergonomic, fall and fugitive dust hazards, reclamation of expensive materials and improving product quality through precision ingredient delivery.

Whatever the objective, the outcome of implementing vacuum conveyors to transfer powder and bulk solids is increased safety, improved indoor air quality and a better bottom line with proper design. Although vacuum conveyors are relatively simple systems consisting of five basic components, working with an expert manufacturer that deals exclusively with vacuum technology and how that technology interacts with materials ensures that potential challenges are anticipated and addressed prior to equipment delivery. Every customer likes to do things a little bit differently, so there is no one size fits all approach to vacuum conveying. Specific components of each system are selected based on a customer’s objectives and material requirements.

Experienced vacuum technology experts engineer systems from their storied knowledge base without having to reinvent the wheel. As a result, they are able to present customers with different options that allow them to determine the level of automation they want and calculate ROI accordingly. More automation costs more upfront, but it costs less in the long run due to reduced labor costs or an increased ability to run more batches in an hour if the system is automated, or it is eliminating an ergonomic or safety issue and the costs associated with an accident. Product quality can also be a factor with less waste and better customer satisfaction.

The following are several examples of how vacuum conveyors solved common industry challenges specific to customers’ needs.

It is important to note that when working with pharmaceutical powders, silica, lead, asbestos, beryllium, hexavalent chrome and other potentially hazardous respirable dusts, a HEPA secondary filter cartridge, rated 99.97 percent efficient at 0.3 micron is utilized with vacuum conveying systems. When a noodle manufacturer made the switch from handling 50-pound bags of flour to handling 2000-pound bulk bags, an older pressure-based conveyor system, which transported 20 tons of very fine flour per week from a hopper through a volumetric feeder to a mixer, no longer satisfied the company’s needs.

In pressure-based systems material is pushed through the conveying line, and if there are any leaks in the system dust escapes outwardly into the environment making a mess and exposing workers to potential dust hazards. With vacuum conveyors material is pulled through the conveying line, and in the event of a leak, the leak is inward, containing dust within the closed system. The primary objective of the noodle producer was to accommodate new super sacs and eliminate the need for workers to climb up to a large hopper to fill it manually, preventing slip and fall hazards as well as exposure to respirable dust.

The new system, a compressed-air powered vacuum conveying system, utilizes a bulk bag unloader, adapted to accommodate the oddly shaped super sacs, to feed the fine flour into the system directly without manual exertion, and without dust. Although the system did reduce housekeeping labor, the customer said the bulk of the gain came through safety and efficiency. Additional safety and cost benefits of the new system that the customer noted were its small footprint, the reduction of noise by eliminating electric motors to run the system and reduced energy costs as a result of eliminating the motors.

Compressed-air-powered vacuum conveyors are the most economical and energy efficient method to convey materials. Operating on the Venturi principle, these systems create their own vacuum without motors or moving parts, making them intrinsically safe. No moving parts or motors also means that units generate no heat and last longer because there are no parts to fail. The vacuum conveying system supplied to the noodle producer is fairly simple, delivering flour from super sacs to a mixer; however, delivery of minor and micro ingredients to process vessels requires a bit more engineering.

Adding minor and micro ingredients into process vessels has traditionally been done by hand-scooping and measuring, especially within the pharmaceutical industry. Hand-scooping of active pharmaceutical ingredients exposes workers to dust from harmful drugs that can produce adverse health effects beyond occupational lung diseases (OLDs). Batch weighing, or multi-ingredient handling, has been around for more than 40 years, but the pharmaceutical industry has been slow to adopt it, due to confusing regulatory language. As the FDA continues to clarify regulations, more and more pharmaceutical processors utilize this technology to protect workers health and achieve accurate formulation control.

Utilizing state-of-the art controls technology, sophisticated vacuum conveying systems employ loss-in-weight or gain-in-weight methods to meter multiple minor and micro ingredients into the conveying line. In one instance, five minor ingredients metered into the conveying line simultaneously by piping the entire conveying line together and metering ingredients from bulk bags to feeders and then into the conveying line to a mixer.

Another application metered is micro ingredients by loss-in-weight into a common weigh hopper. With this method, the weigh hopper is suspended directly above a mixer where a valve opens and discharges ingredients directly into the customer’s process. Manual loading of powders and bulk solids into mixers is a recognized hazard across all industries and although materials used in food, pharmaceutical or chemical applications may be vastly different, basic vacuum conveying technology is relatively the same across industries.

While it is not feasible for some manufacturers to completely eliminate manual handling of materials, inventive design and application of vacuum conveyors provide innovative solutions that minimize exposure. In an ongoing effort to amplify safety and get ahead of rising raw materials costs, a major paint manufacturer purchased a vacuum conveying system with the primary goal of returning captured materials from a dust collector back into the process to reclaim expensive ingredients and preserve product quality by ensuring all formulation weights made it into the process.

The paint producer was handling approximately 3,000 pounds of powder per batch through a combination of super sacs and 50-pound bags. The dust collector captured dust created by manual dumping of materials into a mixer. Typically, material captured from dust discharge will go into a drum or container. There are several fine powders included in a paint’s formulation. One of the most challenging is Titanium Dioxide which has a reputation of sticking, bridging, plugging, clogging and ratholing. Without an optimized system, the dust collection system could experience a backup.

While a mechanical conveyor could have been used to deliver the captured material into the mixer at a lower upfront cost than a vacuum conveyor, the smaller footprint and minimal maintenance requirements offset any savings due to existing equipment that created obstacles to maintenance and installation of a mechanical conveyor. The combination of the dust collector and the vacuum conveying system produced a zero-waste system and eliminated the need for operators to wear respirators.

Engineering out a respirable dust hazard with a closed processing system is especially important when dealing with metal powders that are toxic to the human body. Additive manufacturing (AM) is quickly becoming a focus within the occupational health and safety world due to its combustible, respirable and skin contact hazards (and the usual musculoskeletal injuries associated with heavy materials).

Recently, an OEM of hybrid additive manufacturing technology focused on automating the messy, daunting and potentially hazardous sieving process to improve the work environment at its own facility and to be able to offer that same technology as ancillary equipment to its clients. Metal recovery systems are fairly simple systems in terms of design, but because metal powders used in AM are fine, heavy, dusty and sometimes reactive, special knowledge of material characteristics is required for a safe, effective vacuum conveying system.

What made this particular application unique was the customer’s desire to weigh small amounts of the recovered powder back into its original containers for inventory control purposes and ergonomics, and that required a little more engineering. With this system the customer achieved his/her safety goals and experienced greater than anticipated labor cost savings. What used to take an hour and a half, and require two operators, now only takes four minutes and one operator. In addition, the use of respirators is no longer necessary for the task, although operators can still choose to wear one. The inherent nature of fully enclosed vacuum conveying systems improves indoor air quality and routinely increases efficiency and the bottom line.

This article originally appeared in the October 2021 issue of Occupational Health & Safety.