Dust feed mechanisms

Type of dust Treatment No. of rats Exposure [h] Date 

---

Semiclosed systems for handling solids often involve the use of big bags or tote bins. In these systems the solid is shipped in alarge (>1 t) container which is then lifted into place over a closed hopper or feed mechanism and a sealed connection is made. It is sometimes necessary to rap or agitate the big container to keep the solid moving and this action can result in deterioration or damage to the container or seals with consequent leaks. Also, there is some release of solids when containers are connected or disconnected as well as opportunities for dust generation. 

Fig. 10.—Rotary microtome. The feed mechanism is covered to protect the wearing parts from dust.

Explosion test data, such as the dust explosibility characteristic Kjt (bar m s ), LEL, etc, are obtained under controlled laboratory conditions using standard 20 litre or 1 m explosion vessels [2,3]. Special feeding mechanisms are employed in these vessels to ensure homogenous dust-air mixtures and minimal turbulence levels at the point of ignition. However, the chances for such conditions occurring in industry are quite low. 

In this process EAF dust, other zinc-bearing wastes, recycled materials, coke or coal, lime, and silica are mixed and fed to a rotary furnace. The zinc and other volatile nonferrous metals in the feed are entrained in the furnace off-gas and are carried from the furnace to an external dust collection system. The resulting oxide (zinc calcine) is a crude zinc-bearing product that is further refined at zinc smelters. A byproduct of the process is a nonhazardous, iron-rich slag that can be used in road construction. Solidification technologies change the physical form of the waste to produce a solid structure in which the contaminant is mechanically trapped. 

Dust will cling to the walls of the grading chamber until the collection is so heavy it faUs off in mass. These dust falls seriously contaminate the gradings. It is very difficult to feed the granulated mass evenly to the blower. The most satisfactory feeding devices are those which mechanically put the grains in motion in the same direction as the air blast and with the same velocity. 

---