Miller Magazine Issue 107 / November 2018

61 MILLER / NOVEMBER 2018 COVER STORY A bulk trailer equipped with a motor-driven blower acts as a self-contained pneumatic conveying system.The type of air mover is determined by the flow rate and pres- sure.The environments of dry bulk trailer are extremely diverse and can contribute to contamination of plastics or food grade products. Dust concentration, particle size distribution, and the chemical composition of particulates are affected local factors and environmental conditions. Ambient particulates are a mixture of particles from na- tural processes and anthropogenic sources. Pollutant concentration, size, and Chemical compositi- on. All depend on the location of the dry bulk trailer, the industrial activities in the surrounding area, and weather conditions. For example, air contaminants may contain a high percentage of soot particles in areas with diesel engines. However, the primary sources of particles (direct emis- sion) are windblown, metal shavings from the blower, industrial processes, motor vehicle emissions, and fuel combustion.Coal and oil combustion contribute to most particulate emissions in industrial areas.Coal combusti- on particles consist primarily of carbon, silica, alumina, and iron oxide.Particles generated during oil combustion consist of carbon, cadmium, copper, cobalt, and nickel. Secondary particles are formed by the atmospheric trans- formation of gases to particles. Sulfur-derived particulates are a major component of secondary particles. Most of the atmospheric aerosol is distributed in a fine mode of 0.1-1.0 microns and a coarse mode, which is greater than five microns. These two modes generally have different physical and chemi- cal characteristics and are produced by different sources. Combustion particles, including motor vehicle emissions, typically are fine mode. Particles generated by crushing, grinding, loading and similar processes usually are larger than 15 microns. Par- ticles ranging from 1-10 microns are suspended in air for appreciable periods by air currents and are not captured by an intake filter.An intake filter generally houses either a polyester or paper filter medium, which captured con- taminants 10 microns and larger. The filter is positioned before the positive displacement (P/D) blower and protects it from airborne. Particles lar- ger than 10 microns settle fairly quickly and can be found only in near their sources or under strong wind condi- tions. These particles typically will be captured by the intake filter. In addition to airborne particulate matter, the P/D blower can be a source of contaminants. Wear and cor- rosion of a blower can cause particulate generation. Age and lob wear, improper use and cool down, high tem- perature, moisture, and corrosive gases can promote corrosion and other undesirable chemical reactions, such as scaling. Another source of contamination is the oil re- leased during a catastrophic blower failure. Oil from a blower injected into the conveying line contaminates the product. Which contaminants enter the blower of a pneuma- tic conveying system depend on the performance of the intake filter and the presence of an inline, high-pressu- re (24 psi rating) filter. An inline, high-pressure filter is mounted after the P/D blower and filter the pneumatic air before it mixes with the product. By installing an inline, high-pressure filter, 99,998% of particulates four microns and larger, and any hot oil or oil mist are removed from the airstream, leaving the load virtually free of contaminations. Conclusion material conveyed with a positive displa- cement blower can be contaminated in various ways. The intake filter allows small particles from ambient sources to pass into the conveyed material. In some cases, the filter element can break down and pass into the load. In the event of a catastrophic failure, lubricating oil will be injected from the P/D blower into the conveyed material. Most importantly, the deterioration of blower components produces very small particles that pass un- detected into the conveyed material.