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30 / June 2020 powderbulk.com TESTING MATERIALS TO ACHIEVE OPTIMAL AIR FILTRATION Almost every business in the powder and bulk solids industry uses dust collectors and other particulate air pollution control equipment to ensure a safe and orderly workplace as well as comply with governmental regulations. No matter the material type used in your process, there's no question that a filter will most likely be necessary. However, the material does matter when it comes to choosing the right type of separation equipment. This article describes the necessary material testing that should be performed when choosing a gas (or air)-material separator as well as how to use the test data to ensure the separator's optimal performance. Todd Smith, K-State Bulk Solids Innovation Center operates in the same manner as a silo, barge, or other large container. When large, dust-free particles are loaded or blown into the container, the solid material falls to the container's bottom due to gravity while relatively clean air is vented out of the top. In a grav- ity settling chamber, the air-material stream enters the chamber through a small duct or pipe. As the air spreads across a larger cross-section of the cham- ber, the air velocity is reduced to the point where the solids drop out of the airstream. The point at which the air flowing upward carries the particles with it is called the material's terminal velocity, and the enlarged chamber serves to reduce the air velocity to below terminal velocity, causing the particles to settle at the chamber's bottom. Terminal velocity is also used to describe the max- imum velocity attained when something is dropped from a very high point. A skydiver, for example, accelerates and falls faster and faster until reaching a maximum terminal velocity due to air resistance. The skydiver will have greater air resistance and, thus, a W hether you're dealing with minerals, pharmaceuticals, dry dog food, or other powder and bulk materials, chances are likely that you're going to need an air filtration or par- ticulate air pollution control system. Two of the most common separator types are cyclones and baghouse filters, which include dust collectors and filter-receiv- ers. There are many variations of each. Selecting this type of equipment, however, isn't as straightforward as you might think. There are various factors to consider depending on the type of separator you're interested in, factors including the material's terminal velocity, particle size, precise velocity calculations, and accurate material samples. You want the air-material separation process to be as efficient as possible to abide by federal regula- tions, reduce environmental pollution, achieve optimal production, and maintain a safe workspace. This efficiency can be achieved by testing your material's properties in relation to the separators. There are many types of particulate separators and filter media and also many types of material that need to be filtered. Your separator choices will require you to balance filter life and filtration efficiency against system cost. To optimize this tradeoff, be sure to take into account the different separator types, how each separator interacts with your material's properties, and the precise calculations needed to make your process and separator operate as efficiently as possible. Terminal velocity testing for gravity settling chambers The most basic type of air-material separator is a gravity settling chamber, which works best for big, heavy particles such as clean pellets, grain, and rock. A gravity settling chamber, as shown in Figure 1, FIGURE 1 Gravity settling chamber for larger particles Air-material in Air out Material out