In addition to ventilation solutions, other dust control approaches have been used in a variety of industries and should be applicable for nanomaterial production. For example, an inflatable seal can be used to create a dust-tight seal on the discharge outlet of a spray dryer during the product discharge/bag filling process (Figure 15). The seal inflates during the product transfer from the process to the packaging bag (providing the seal) and deflates once the transfer is completed to allow removal of the bags. These systems are available on many commercially available bulk bag filling systems [Hirst et al. 2002].
Another system that can be used to contain powders during process off-loading/emptying is the continuous liner system (Figure 16). Polypropylene liners are often used when products are discharged from the industrial processes into the intermediate or final product containers. In this operation, a sleeve of polypropylene liners is stowed around the circumference of the discharge outlet. The first liner, the bottom having been sealed, is pulled down into the overpack (usually a drum or a cardboard box). Product is discharged into the liner through a butterfly valve on the process outlet. Once full, the top of the first liner sleeve is closed using tape or a fastener, or it is heat sealed and cut. The product is sealed within the poly-lined container, and a new sealed poly liner is pulled down to start discharge into the next container. This continuous process seals off the primary leak paths for dust during unloading of an industrial blender or other equipment. These systems are commonly used in the pharmaceutical industry and may provide cost-effective alternatives to traditional local exhaust ventilation control systems for nanotechnology facilities.
Figure 15. An inflatable seal used to contain nanopowders/dusts as they are discharged from a process such as spray drying
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Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes
