Follow these four key steps to get the best dust collection system
When the dust removal equipment is handling different working conditions, it is necessary to select suitable treatment equipment according to different dust characteristics, especially the combustible dust or dust-intensive working conditions. If the equipment design is unreasonable or the consideration is not enough, the risk of the explosion will be caused.
As materials containing explosive dust, most of them are organic materials and metal materials, and the use of properly designed dust removal equipment helps to reduce the risk of flammable dust.
This article describes the four key steps to follow when choosing the best dust collection system for your application.
Understand the difference between the two devices.
Wet scrubbers and dry scrubbers are two different techniques for capturing dust generated during production, both of which have inherent advantages and disadvantages.
1. Dry dust collection
Dry scrubbers are generally defined as cyclones, such as baghouses and filter cartridges. Dry dust collectors are widely used for fine particle dust generated in processing applications. The dust-laden air enters the dust collector and collects the dust on the filter media. A periodic array of compressed air exhausts the dust from the filter and into the hopper. Dust is then drained from the funnel into a separate storage bin or another container that must be emptied periodically to ensure that dust does not pour into the hopper.
Filter cartridges are available in a variety of primary filter media for high removal efficiency on very fine particulates, including nanofiber media. Nanofiber media combines high performance with long life. Choose the appropriate filter material according to different dust characteristics, such as flame retardancy, electrostatic conductivity, and anti-adhesive materials.
2. Wet dust collection
Wet dust collectors include Venturi dust collectors, self-exciting wet scrubbers, cyclone wet scrubbers, and gravity spray wet scrubbers, etc., which work differently than dry scrubbers. The wet scrubber captures dust by colliding with water droplets. The smaller the droplets, the higher the efficiency of the dust collector.
Equipment design may include one or more of the following techniques to capture dust: nozzles, atomization, cyclonic action, Venturi dispersion, wet impact configurations.
Once captured, water and dust fall into the sedimentation tank where they are separated by gravity or dust are removed from the surface. The dust-laden air enters the dust collector in a tangential direction, and the centrifugal force pushes the particles to the outer wall like a cyclone. The airflow is specifically directed to create intense vortex water mixed with dust, causing the particles to impinge on the droplets. The captured particles then settle to the bottom of the sludge tank.
The dust collector must be kept clean or recycled. The concentration of dust particles in the washing liquid must be kept below 5% to maintain the operating efficiency, and in the case of combustible metals, the amount allowed to accumulate in the discharge tank is regulated by NFPA.
The filtration efficiency of the wet scrubber depends on the dust particle size. For particles smaller than 10 microns, a venturi dust collector is recommended because it is more suitable for capturing smaller particles. For particles above 10 microns, the centrifugal dust collector will save a lot of energy.
View application standards.
In general, dry scrubbers are best suited for large airflow systems, heavy dust load applications, especially those requiring high particle removal efficiency, dust with a dust deflagration index value below 150, but sometimes treated with a dry dust collector. Higher Kst dust (Kst is a dust property that measures dust explosion characteristics).
Dry scrubbers have many operational advantages over wet scrubbers. A single precipitator can handle very large airflows and heavy dust loads in applications where the wet scrubber requires multiple systems. Dry scrubbers provide higher particle removal efficiency and use less energy to capture fine dust particles, and dust maintenance and handling are simplified, especially when hazardous dust is involved.
Due to these benefits, dry scrubbers are often the system of choice, except for wet scrubbers that have performance advantages: light-duty applications such as grinding large particles; very sticky dust; high Kst dust, usually above 150 Kst.
Dry scrubbers may not meet standard metal dust such as aluminum, tantalum, magnesium, niobium, tantalum, titanium and zirconium. The wet scrubber inherently controls the flammability of the dust. When combustible dust particles are combined with the washing liquid, they are not exposed to oxygen and the hazard is controlled.
In contrast, dry dust collectors have a higher risk of flammable dust explosions and require more auxiliary explosion-proof equipment to meet standards and control hazards.
Sometimes it is difficult to determine which technology is best for the application. Two types of tests are recommended in these cases:
1. Laboratory testing
Laboratory testing of dust samples involves a series of tests that provide valuable data that can be used to determine the optimal filter and other dust collection system components.
Among other things, these tests reveal:
(1) The particle size distribution of the dust is reduced to the sub-micron range to determine the filtration efficiency required to meet the emission standards.
(2) Visual analysis of dust shape and elemental composition
(3) Analysis of the weight percentage of dust and the rate at which dust absorbs moisture
2. Explosive test
To determine if the dust is flammable, a separate explosive test should be performed as specified in the explosion standard.
Ventilation through deflagration. If there is no dust sample, it is allowed to use equivalent dust with the same particle size and other parameters in the same application to determine flammability. Once the dust sample becomes available, it is recommended to test the actual equipment dust.
Using dust samples, the laboratory will conduct a screening test to determine if the dust is flammable. If the dust is not flammable, the test stops there. If it is flammable, the laboratory further tests the dust cloud parameters to determine the maximum pressure value in the explosion.
Explosive testing is critical to help analyze the best dust collection system (wet or dry) in the application, as well as the explosion-proof or explosion-proof equipment required for the precipitator and related components.
Apply the correct NFPA standard.
The types of precipitators, explosion protection and pipe isolation required for each application are different and DHA should be used to determine system requirements. Engineers who are familiar with the process should evaluate with the support of the dust collector supplier and protection controls.
Hazard analysis helps optimize safety by identifying hazards such as flammable dust deflagration, fire and explosion hazards. The analysis should begin with the design phase of the project and track the end of the process through regular reviews and updates.
When selecting flammable metal dust application equipment, the flammable metal standard is a standard for dry and wet dust collection of metal dust. It covers all metals and alloys that can burn or explode and explains how to determine whether the metal is flammable or non-flammable. It also covers the processing or finishing operations for the production of combustible metal powders or dust.