99/02824 Role of anthropogenic NO x and VOC as ozone precursors: a case study from the SOS Nashville/middle Tennessee Ozone study

Abstract

The advanced coal cleaning technologies, which also include flotation, involve finer sizes of coal than previously tested. The U.S. Bureau of Mines developed a procedure in which a centrifuge is used to increase gravimetric force for improving the separation. It is well known that fine particles tend to form larger aggregates when suspended in water. This is especially true in the case of particles such as coal, which are hydrophobic to some extent. To separate such particles into various density fractions, they first must be dispersed. Moisture causes agglomeration of fine fractions in an organic liquid (as oil does in agglomeration of fine coal particles suspended in water). Therefore, fine coal fractions must be dried very well before carrying out the float-sink tests in organic heavy liquids and, in addition, dispersing agents should also be used. The shape of the primary washability curve and M-curve is an indication of the ease or difficulty of cleaning the coal. This chapter illustrates four different cases: ideal separation, easy cleanability, difficult cleanability, and impossible separation. The primary washability curve for the difficult-to-clean coal exhibits only a gradual change in slope revealing a large proportion of middlings. The separation produced by a washability analysis is based on the bulk property of the material (density), while the separation resulting from a flotation process is based on surface properties. The differences between these two types of separation processes can be substantial.