Many wonder about airflow when looking to add or change pickup points on an existing dust collector system. Dust collector systems consist of the hoods, ductwork, dust collectors and exhaust fans; when properly designed, a dust collection system can deliver outstanding performance. If one of these parts fails or is poorly sized the whole system will fail. Today, we will take a closer look at individual parts of system beyond the collector.
Hoods / pickup points
Hoods mark the start of dust collection. Hoods are designed for providing a specific airflow at a minimum velocity while picking up particulate in the air. The hood type, location and number are usually specific for your application. The Industrial Ventilation Manual, the standard for ventilation put out by the American Conference of Industrial Governmental Hygienists, provides guidelines for velocity ranges to provide the proper ventilation. A velocity lower than suggested could cause dust to escape the hood. Adding additional hoods to an existing system could cause the airflow (thereby pickup velocity) to drop below the minimum suggested, thereby making a notable reduction of performance.
If dust and airflow are blood, ductwork is the circulatory system. The ductwork of a properly designed ventilation system should be sized so that it has the lowest possible pressure drop and have a minimum velocity. Best ductwork practices for avoiding a pressure drop include keeping the ductwork as straight as possible, minimizing turns, and keeping the duct size larger. Since the ducts are carrying dust, a minimum velocity is required lest the dust settle in straight sections. These accumulations will cause increased resistance and are a fire and explosive hazard. Usually, a velocity of the air over 4,000 FPM prevents dust from accumulating. Keeping ductwork in a standard size keeps costs down and assures availability if additional or replacement ductwork must be added.
Some dust collectors are less sensitive to added airflow than others. A cyclone’s pressure drop will increase as airflow increases through the system, but a baghouse or cartridge collector’s removal efficiency will decrease if airflow is increased too much. Many of these are very particulate specific; a cartridge collector for an airstream containing wood dust could handle higher airflows than one for silica dust. Contacting the dust collector manufacturers is the best way to understand the capabilities of a collector.
The exhaust fan is the most important equipment in a dust collection system, providing the motive force to collect the air-dust mixture. In many cases, companies will add additional pickup points and not change the fan, causing less air to be pulled from each of the existing pickup point. When looking at the airflow in a dust collection system, make sure to calculate the total airflow and static pressure required, then check to see if the existing fan can handle it under different conditions, such as open dampers or increased speeds. If not, a new fan will be required.
For more information on how Aerodyne's GPC line of compact, efficient dust collectors can fit into your existing dust collection system and be tailored to your airflow, click on the button below, call us at (440) 543-7400 or e-mail us at email@example.com.