Airborne particulates: Dealing with dust

Airborne dust in the industrial environment can be a serious problem unless tackled correctly and efficiently. Filtration+Separation reports on ways to assess the risks and what measures can be taken.

An installed DFC Dust Collector from Clean Air America.
An installed DFC Dust Collector from Clean Air America.
Air flow in a Smart Collector.
Air flow in a Smart Collector.

Modern industrial processes produce significant quantities of airborne dust made up of a variety of particulates, which can be harmful to workers who breathe in the dust. Industrial processes such as welding, laser and plasma cutting, abrasive blasting, metalworking, mixing, and grinding handle dry materials which release minute dust particles in the air where they float freely or settle on surfaces.

Indoor air is often two-to-five times more polluted than outdoor air and can be up to 1,000 times as dirty. The EPA estimates that most workers are exposed every day to indoor air contaminants than can lead to serious health problems, respiratory ailments, and fatigue, along with causing cancer and headaches.

Industrial environments require dust control systems that are designed to protect plant personnel from exposure to these hazardous airborne dust particulates.

Risks of dust

Dust particles have hazardous effects on a person's respiratory passages, especially people with allergies. Several factors contribute to the hazardousness of dust, such as the size of the dust particle, the type of dust, and the type of substances that accompany the dust particulates, such as smoke or oil.

Most inhaled particles are captured in the cilia inside the nose and do not reach the lungs. However, smaller dust particles get trapped in the upper respiratory tract where they can cause or aggravate asthma, pneumonia and bronchitis. Studies show a correlation between increased dust particle content in the air and an increased frequency of diseases of the respiratory tract, cancer and cardiovascular diseases. Dust particles can also contain toxic poisons and heavy metal dust, which are extremely hazardous to health.

Plus, dust emissions have an impact on the environment by settling on the soil or in water.

How to remove dust

Air purification involves the separation of particles from the air. Dust extraction hoods or direct dust extraction on enclosed machines are commonly used and this involves conveying air containing impurities to a dust filter where the air is purified. The air is then discharged into the premises or to the open air outside. Because, in most cases, this involves large airflows, heat exchangers are generally used for recovering heat from the purified air as a means of reducing power consumption.

Textile filters, such as pleated cartridge filters, have a high dust collecting efficiency, as much as 99% or more in many cases and their efficiency for collecting small particles is also high. The performance of filters depends on a combination of several factors: filtering capacity, diffusion and forces of inertia, for example. Textile filters are well suited for arresting particles of 1–100 μm in size.

Welding equipment is notorious for generating excess dust and smoke. Plants should utilise self-contained weld booths with downdraft capabilities that draw the smoke away from the welder's face and vent it elsewhere. Welding booths protect operators through maximum containment of airborne particulates.

Dust collectors are devices that filter dust from polluted air generated by industrial processes and discharge clean air into the environment. Efficient dust collectors protect employees from dry particulates and pollution in the air.

There are a variety of dust collectors on the market today ranging from cartridge dust collectors to baghouse designs. Power plants, steel mills, pharmaceutical producers, food manufactures, chemical producers and other industrial companies often use baghouses to control emission of air pollutants. Baghouses came into widespread use in the late 1970s after the invention of high-temperature fabrics (for use in the filter media) capable of withstanding temperatures over 177°C/350°F. Baghouses typically have a particulate collection efficiency of 99% or better, even when particle size is very small. Baghouses are characterised by their cleaning methods, which include shaking, reverse air and pulse jet.

Reverse air baghouses are cleaned by blowing clean air in a reverse flow that causes the dust collected on the inside of the bag to crumble and release into a hopper. Pulse jet baghouses are cleaned via a high-pressure blast of air that enters the top of the bag, temporarily ceasing the flow of dirty air. The air blast causes the baghouse fabric to expand which discharges the dust cake. The blast of compressed air must be powerful enough to ensure that the shock wave will travel the entire length of the bag and fracture the dust cake.

Portable dust collectors work well for temporary worksites. They can be used for grinding, stone, and dry dust, powders and welding fumes. Most feature a flexible extraction arm that offers a high level of filtration.

Cartridge collectors are highly efficient and utilise vertical or horizontal filters. Filters positioned vertically with pulsing from the bottom utilise an enhanced Down-Flow technology that provides crystal clean air even in high production environments. Vertical filter cartridges provide more efficient pulsing of dust, thus eliminating uneven dust loading associated with horizontally mounted cartridges. Cartridge collectors use perforated metal cartridges that contain a pleated, nonwoven filtering media, as opposed to woven or felt bags used in baghouses. The pleated design allows for a greater total filtering surface area which results in a reduced air to media ratio, pressure drop, and overall collector size. Cartridge collectors are available in single use or continuous duty designs. In single-use collectors, the dirty cartridges are changed and collected dirt is removed while the collector is off. In the continuous duty design, the cartridges are cleaned by the conventional pulse-jet cleaning system.

Bottom line, adequate ventilation is a key to controlling exposure to smoke and dust particulates in the production area. Using top quality air filtration solutions keeps the production and welding areas free from harmful smoke, dust, and oil mist. Workers breathe crystal clean air, which leads to them protecting their health.

Case study: Removing silica dust

A privately-held, quality cast iron cookware manufacturer needed a way to remove silica dust from the manufacturing environment. The company was utilising a baghouse dust collector, but found it hard and costly to maintain. A Clean Air America (CAA) self-cleaning cartridge dust collector, the DFC 48 Dust Collector, was installed. These collectors come in a variety of sizes, require a ducted system, and are suitable for a variety of applications including; welding, grinding, plasma and laser cutting, buffing, polishing, sanding, mixing operations and blasting. Additionally, CAA's SmartControl panel was utilised, which contains a 6 inch colour Human Machine Interface (HMI) and variable frequency drive (VFD) to capture the immense potential energy savings available over the life of the system. The data on the HMI confirmed that after more than a year in almost 100% continuous operation, the manufacturer has yet to perform a single filter change. The automated pulse feature of the collector, combined with the extremely dry silica dust, has resulted in a current static loading of less than half of what the system is designed to handle while remaining operational and effective. Clean Air America's dust collector provided a cleaner manufacturing environment and better air quality for all of the company's employees.