Dust Control Handbook for Industrial Minerals Mining and Processing

CHAPTER 7: BULK LOADINGDuring the bulk loading of product, dust contained within the product can be liberated andemitted into the ambient air as the product falls from the loadout area to the transport container(truck, rail car, barge, or ship). This dust-laden air can expose workers to respirable dust, as wellas create nuisance dust problems.A number of factors impact the severity of dust liberation during bulk loading, including:the type of product and its size distribution,moisture content of the product,volume of the product being loaded and the loading rate,the falling distance,environmental factors such as wind velocity and rain, andphysical characteristics of the receiving vessel.The first three factors represent the characteristics of the product being loaded and may bedefined by the process or by the customer. Past research has shown that larger size distributionsand higher moisture contents typically result in less respirable dust liberation. As a general rule,a moisture content of 1 percent by weight is recommended as a starting point for adding moistureto a crushed product [NIOSH 2003]. Chapter 2—Wet Spray Systems provides a detaileddiscussion on using water to reduce dust liberation.The last three factors represent the characteristics of the loading process. Engineering controlscan be implemented to minimize the impact of these factors. For example, the falling distancecan be reduced and physical barriers can be installed to protect against high winds.The following dust controls, which have been implemented in the industry, will be discussed inthis chapter:loading spouts,the Dust Suppression Hopper, andenclosures.LOADING SPOUTSThe loading spout is designed to transfer product from a plant/storage container into the vehiclethat will be used to transport the product. Typically, these spouts have the capability to extenddown to the vehicle being loaded and then be retracted to allow the vehicle to move away fromthe loading station. A review of several loading spout manufacturer specifications shows thatthis spout travel can be as little as a few feet and can extend up to 100 feet. As shown inFigure 7.1, these loading spouts are equipped with a series of telescoping cups or pipes thatextend and retract. This figure also shows that the spout typically has an outer shroud whichBulk Loading 189