Central Dust or Fume Collection System Triad
Curt Corum, Contributor
The proper three are the key. Hooding, piping, and dust or fume collector. It is our objective to effectively capture the contaminant at the source and relay it to the collection device.
Number one is the hooding. It is critical that a hood encompasses the area where the contaminant is being discharged, without interfering with the operation. The hood should be created as small as possible. The larger the hood, the more air volume that will be required.
Once the size of the hood opening is determined, the necessary face/capture velocity is then applied, which will designate the amount of airflow in cubic feet per minute (CFM). Please refer to chapter three of the Industrial Ventilation Manual (www.acgih.org ), which will give you all of the information pertaining to proper hood design.
Cardboard prototypes can be fabricated, which then can be duplicated in the correct material. When purchasing a machine with a factory-made hood, pay special attention to the hood design. A machine may have good production capability, but if the hooding is lacking, look for another piece of equipment. We must have a proper hood first and foremost.
This is our starting point, as we pursue a safe and operational system.
Number two is the piping. Dust and fume control piping is available in many different materials and thicknesses. Stainless steel, galvanized, black iron, aluminum, PVC and poly-coated are just some examples.
The contaminant being collected will determine the piping design, material and thickness. Is it abrasive, corrosive, hot, cold, sticky, light, heavy, volatile, explosive or stringy?
Once the type of piping is determined, it is now time to pursue proper piping design. Some common questions include:
- What is the angle of entry at a junction?
- What is the required radius of elbows?
- What is the transport velocity in feet per minute (FPM)?
- What is the branch and main pipe sizing?
- What type of connections are necessary?
- Do we need angle-ring flanges or rolled ends with clamps to provide a smooth interior and aid in withstanding the vacuum pressure?
- Do we need all laps in direction of flow, such as for systems conveying oil mist?
All of these questions and more must be answered as we pursue proper piping design.
No matter what type of connection is required, it is imperative that they are air-tight or, in some cases, liquid-tight. Please refer to chapter five of the Industrial Ventilation Manual (www.acgih.org), Exhaust System Design Procedures. For pipe material and thickness, please refer to SMACNA (smacna.org). Most central systems are percentage use, which means not all of the branches are under simultaneous suction. Correct use of dampers is required for airflow balancing in this scenario.
Number three is the collection device. Below are the most important questions to ask:
- Do I need a dust collector?
- What type of dust collector?
- What should the filter material consist of?
- Do I need a fume scrubber?
- Do I need an electrostatic precipitator air purifier?
- Can I just use a blower and emit to atmosphere?
Collection equipment is available in many different types and sizes. Each device is designed for a specific amount of airflow and the contaminant being collected. Commonly used dust collectors are the cyclone separator with after-filter and cartridge-filter collector. A cyclone separator with after-filter is applied to primarily coarse material. The cyclone vessel separates a majority of the coarse particles prior to filter section.
The GyroAir axial centrifugation dust processors are a new and unique patented technology. Dust-laden air is relayed into a series of turbine vanes which results in the dust spinning at 4,000RPM. The particles are forced to the outer edges of airflow, where they drop into internal bins. Only 0.3% of the dust gets to the pleated cartridge filters chamber, resulting in an optimum level of final filtration.
Cartridge filter-only type dust collectors are used for mostly fine dust applications. They have predominantly replaced bag house collectors, as the surface area of a pleated cartridge is substantial, relative to a filter bag. This main factor results in a much smaller unit capable of sub-micron filtration. Please refer to chapter four of the Industrial Ventilation Manual, Air Cleaning Devices.
In addition, consult with a dust- or fume-control equipment manufacturer. A representative will help you determine the proper piece of equipment. It is extremely important to address safety devices, such as spark-detection and suppression, explosion vents and return-air abort gates. Always refer to the National Fire Protection Association (nfpa.org) for pertinent codes, standards, recommended practices and guides. If exhaust air is emitted to atmosphere, a makeup air unit will be necessary to avoid negative pressure in the facility.
A makeup air unit will pull in outside air and replace the amount that is exhausted. In cold weather climates, the makeup air can be heated.
Remember: One weak link, and the chain breaks. IHW
Curt Corum is National Sales Manager for Gyro Air Dust Solutions.
American Conference of Governmental Industrial Hygienists, Industrial Ventilation Manual of Recommended Practice: www.acgih.org (http://www.acgih.org/ )
SMACNA Round Duct Construction Standards: smacna.org (http://smacna.org/)
National Fire Protection Association: nfpa.org (http://nfpa.org/)
Air Handling Systems (Specifically, stainless steel, galvanized): airhand.com (http://airhand.com/)