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Show its lower flammability limit in air is over 12% by volume; this will go even higher as the oxygen is consumed.) Therefore, the coal in the bin consumes all the oxygen and becomes self-inerting and remains so when left undisturbed. Similarly, it has been shown that when significant air infiltration and agitation is permitted, silo fires will almost invariably result. Bin Feeding: The reliable feeding of material from pulverized coal bins has often had problems, ranging from bin flushing to bin hang-ups, which can easily be encountered within minutes of each other in the same bin with the same material. Bins that are improperly designed operate in what is often referred to as "funnel flow." In this situation much of the bin volume is inactive, as shown in Figure 3, and only a central funnel shaped portion of the bin is actually in active use. When this type of bin flow is encountered, extremely erratic performance can result. To avoid this problem, C-E has used what is called a "mass flow" bin. A mass flow bin is designed such that the entire bin volume is active and all of the material is moving. It is necessary to determine what is known as the critical arch dimension and to ensure that the bin outlet is not narrower than this critical minimum dimension. It is also necessary to ensure that the material on the inner surfaces of the bin is moving at all times that the bin is in use; therefore, special surfaces may also be required on the inside of the bin. Because many of the problems discussed above do not lend themselves to modeling or scaling, a decision was made to construct a mass flow bin in thp laboratory that simulated, full size, one of the actual mass flow bins that would be used in our first commercial application. Figure 4 shows the height, outlet dimensions, and wall angles employed in this bin. The "mass flow" bin bottom is also lined with 2-B finish 304 stainless steel to prevent material hang-up on the walls of the bin. Figures 5 and 6 show a schematic layout of the Pneumatic Transport Facility and 11-8 |