Where dust comes from
Dust is generated when materials are transported, handled, processed, polished, ground, and shaped. It can be created by sanding, cutting, mixing, screening, or welding. The deposition of dry residues from the processing of wet materials can also generate dust.
In a factory or warehouse, dust accumulates quickly and can cause many problems, such as increased equipment maintenance, replacement costs, high employee absenteeism and turnover, and increased cleaning costs.
Maintaining air quality is vital in any work environment. Dust extraction systems does that by removing particulate matter from the air and the environment. Dust is captured through devices such as capture hoods, duct systems and finally filtered by a dust collector through filters.
Industrial Dust Collectors
A dust collector is the essential type of equipment for controlling air pollution in industrial environments such as woodworking, agriculture, food processing, pharmaceuticals, metal manufacturing, mining, and chemical processing. A dust collector improves air quality in the workplace and meets environmental safety requirements. A dust collection system is designed to filter and remove hazardous dusts, and potentially harmful fumes.
There are several types of pollutants in the industry that vary in concentration and particle size. In addition, some types of dust are flammable or explosive. It is essential to know the properties of the dust to be treated. Therefore, the selection of a dust collector requires an in-depth analysis of the various factors to be considered and requires the intervention of an expert in the field.
Factors to consider when selecting an effective dust collector
1. Type of dust
The moisture level, texture, size, and concentration of the dust will be directly considered to determine the type of industrial dust collector capable of collecting the dust efficiently.
- Class L (Low Risk) represents a low degree of risk: These dusts are the least toxic. These are simple house dusts, soil, general construction dust, soft woods, and solid surface materials.
- Class M (Medium Risk) represents a medium degree of risk: These are hardwood, synthetic wood (MDF), cement, brick, mortar (silica), concrete dust, quartz, sand.
- Class H (High Risk) represents a high degree of risk: These dusts are highly toxic and contain pathogenic or carcinogenic particles: These are asbestos, mold spores, bitumen, mineral fibers.
- Light: 01 to 5.0 grams/ft3
- Medium: 6.0 to 15.0 grams/ft3
- Large: 16.0 to 30.0 grams/ft3
2. Determine if the type of dust in the application is combustible or explosiveCombustible dust is a substance in the form of finely divided solid particles that, upon ignition, are likely to ignite or explode when dispersed in the air.
Many materials can become combustible in specific situations. Workplaces can either purchase these materials for use or generate dust as part of their processes.
- Agricultural products such as egg whites, powdered milk, cornstarch, sugar, flour, grain, potatoes, rice, etc.
- Metals such as aluminum, bronze, magnesium, zinc, etc.
- Chemical dusts such as coal, sulfur, etc..
There are many other types of materials that can produce combustible dust. See more examples.
Explosions can occur whenever combustible substances are in contact with reaction products.
Explosions in industry are a hazard whenever explosive substances and mixtures are used. These substances and mixtures can be solid, liquid, or gaseous. The conditions that must be met for an explosion to occur are illustrated in the hazard pentagon.
Industries and production areas with an increased probability of explosion must take protective measures in accordance with legal requirements.
Reactive dusts are classified according to the Kst value. The Kst value and Pmax are explosive properties measured in the laboratory to quantify the severity of a dust explosion. The deflagration index Kst is a constant defined for dusts of a given particle size while the Pmax defines the maximum pressure of the explosion. The ST class is based on the Kst value as follows: ST class 1 : KST value below 200 bar m/sec (very low explosive) ST class 2 – KST value between 200 and 300 bar m/sec (medium explosive) ST class 3 – KST value higher than 300 bar m/sec (very explosive) Exemple
|Grain dust||89bar.m/sec||9,3 bar eff.||ST1|
|Coal dust||85bar.m/sec||6,4 bars eff.||ST1|
|Flour||63bar.m/sec||9,7 bars eff.||ST1|
|Sugar||138bar.m/sec||8,5 bars eff.||ST1|
|Wood dust||224bar.m/sec||10,3 bars eff.||ST2|
|Aluminium dust||515bar.m/sec||11,2 bars eff.||ST3|
However, one should not rely exclusively on the ST classification, as the concentration of dust, humidity and the presence of turbulence are also important variables to consider.
3. Determine toxicity
The effects of dust depend on a number of factors. The dust itself, for example, can be a problem simply because of the amount of dust present. The human body, especially the respiratory tract, has various protective systems to counteract dust as long as the amount remains within limits. To determine the hazard potential, the size of the particles as well as their composition are important. Depending on the content of the material, even larger particles that only reach the upper respiratory tract may present a hazard. For this reason, the toxicological properties must be taken into account:
- Sensitizing dusts These dusts can trigger allergies. Example: Organic plant and animal dusts
- Fibrogenic dusts Fibrogenic dusts can cause scarring of lung tissue and have permanent effects on lung function. Example: Quartz dust
- Caustic dusts Caustic dust particles can destroy human tissue by forming acids or bases. Example: Bird droppings
- Toxic dusts Inhaling toxic dusts can damage internal organs, such as the lungs. Example: lead, cadmium, etc.
- Carcinogenic dusts These dusts can cause cancer. Example: Oak dust, asbestos
- Radioactive dusts Radioactive dusts can attack genetic material, cause tumors, be deposited in mucous membranes or bronchial tubes. Example: Tritium
4. Identify the source of dust generation
Depending on the type of equipment used, certain arrangements will be necessary for dust collection at the source.
5. Determine the type of exhaust hood needed to capture dust or fumes
Contaminant capture and control will be achieved by the inward airflow created by the fume hood. The airflow to the hood opening must be high enough to maintain control of the contaminant until it reaches the hood. External air movement can disrupt the airflow induced by the fume hood and requires higher airflow rates to overcome the disruptive effects. Eliminating sources of external air movement is an important factor in achieving effective control without the need for excessive airflow and associated costs. Important sources of air movement are:
- Thermal air currents, especially from hot processes or heat-generating operations.
- Movement of machinery, such as grinding wheels, conveyor belts, etc.
- Movement of materials, such as when dumping or filling containers.
- Operator movement.
- Room air currents (which are usually taken at 50 fpm minimum and can be much higher).
- Rapid air movement caused by spot cooling and heating equipment.
6. Determine the transport velocity of the dust in the ventilation duct
Typically 1000 ppm to 4500 fpm.
Capture Velocity: The minimum air velocity induced by the fume hood, necessary to capture and transport the contaminant into the fume hood, is called the capture velocity. This velocity will be a result of the fume hood’s airflow rate and configuration.
Fume hoods with exceptionally high airflow (for example, large foundry side-draft hoods) may require less airflow than indicated by the recommended capture velocity values for small hoods. This can be attributed to:
- The presence of a large mass of air moving through the hood.
- The fact that the contaminant is under the influence of the fume hood for a much longer time than in the case of small fume hoods.
- The fact that the large air flow allows considerable dilution
7. Select the type of dust collector
After determining the size of the dust particles and the concentration of the dust, we must select the dust collector with the filtration area and the type of filter, cartridge or bag that will best suit the application needs. If the dust being processed represents an explosion hazard, we must select the appropriate safety devices.
8. Select the Air/Fabric ratio
It is important to get the right air to fabric ratio. The air to fabric ratio of a filter is the rate of airflow through each square foot of filter media. To calculate the air to fabric ratio of the dust collector, divide the air flow in cubic feet per minute by the total square footage of the filter media. Also check the NFPA safety codes that apply to the application.
AQC has designed 5 types of dust collectors in order to adapt to the needs of different industries. These 5 types of products will allow an appropriate air treatment by taking into account the particularities of the environment. There will be dust collectors designed for light dust concentration, dust collectors for light to medium concentration, dust collectors that will allow to treat a large concentration of dust while operating without stopping, others that will treat a medium concentration with several stopping times within a day and finally, those that will be used to treat the reactive metals with water
Light concentration: MAXIFLO
When the application needs are of a light concentration, it is that the place treats fine particles such as produced by smoke, welding, sanding or polishing. These types of particles will be treated with a cartridge system that will also allow for the recirculation of clean air into the environment and thus save energy. When the system will treat solid particles, the top row of cartridges is equipped with a series of baffles that will protect the cartridges and prevent them from clogging.
Light to medium concentration: MAXIFLO-VC
When the application needs are of light to medium concentration, the vertical cartridge system will handle different types of dusts such as those produced by welding fumes, metal sanding, polishing, etc. The fact that the cartridges are placed vertically, the cleaning of the system will be more efficient since larger particles will be filtered out.
High concentration with non-stop operation: MAXITUBE
Baghouses allow the treatment of large concentrations of particles. By using alternative filter bags or pleated bags, this type of system is capable of handling all types of special dusts. It can handle huge air volumes and dust loads by drawing them into a velocity reduction chamber adjacent to the filter section. The particles separate from the air stream and settle directly into the hopper. Subsequently, the smaller particles are drawn into the filter section for filtration.
Average dust concentration with several downtimes per day: MAXIVIBE
Pleated bag dust collectors are used for medium dust concentrations. They have been designed for the business in question to handle several types of dust, such as in training centers or professional schools. These dust collectors can filter solid particles such as wood chips that will fall, due to gravity, into the machine’s hopper to finally settle in the cartridge that traps the dust. On the other hand, the finer particles are sucked to the top of the machine and into the filter housing.
Reactive metal applications where a waterborne dust collector is indicated: MAXIHYDRO
Where there is a risk of explosion due to reactive metals, a waterborne dust collector is required. It does not contain any mechanism that could fail, clog or wear out. Some media can be found with explosive particles such as magnesium, aluminum, titanium and many other materials. Wet scrubber treatment ensures safety within the work environment.
AQC quickly came to the conclusion that a complete line of dust collectors was needed to handle the multitude of particles that can be found in our work environments. The five categories of dust collectors that have been developed make it possible to meet the divergent application needs of the different industries and the different projects that they undertake. All you have to do is choose the appropriate dust collector model for the environment in question, taking into account the points developed in this article.