In the oil agglomeration process, the effect of ground coal partile size on the deashing of coal was experimentally investigated by adding various amounts of bridging liquid. Ash particle size was hardly affectedby the grinding of coal. The decreasing size of coal particles could promote the separation of combustibles and ash in coal, but the deashing efficiency is not always increased by oil agglomeration. The deashing efficiency for each coal species attained its highest value at a specific size of ground coal particles. It is considered that the low deashing efficiency of the slurry including fine coal particles was given by the deterioration of the selective agglomeration of combustibles. The deterioration was caused by the formation of coal particle aggregates in the slurry before the addition of the bridging liquid and by the incorporation of a number of high-ash particles into the agglomerates with water.

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In the same way as mentioned in my third repot (part 3), evaluations of the particle cut size, d_c, from the author's formula and the equilibrium particle size d_R=E, from the collection efficiency are also done with cyclones for the separation of various dusts. Considering the effects of the re-entrainment of dust near the discharge port on the collection efficiency, the values of the ratios of d_R=E to d_c are expressed by correlation with the particle Froude number based upon inlet velocity u_o and the height of imaginary cone defined as Fr=u_o/√gH, in stead of correlating the diameter ratio with particle Reynolds' number Re which was obtained in my previous paper (part 3).
When there is no re-entrainment in cyclones on the whole, the values of the grain diameter ratio (d_R=E/d_c) become on average equal to 0.6 (constant) so far as the investigations are concerned, which embodies the availability of the au hor's equation for particle cut size.
When dust re-entrainment into the gas stream at the base of the vortex core is followed, the following expression holds on the whole: d_R=E/d_c=K u_o/√gH in which the proportional constant K depends on the particle properties and the inlet leading as shown in Fig. 5.

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