Impact attrition

Pulverization occurs by impact, attrition, or crushing. The capacity of a pulverizer depends on the grindability of the coal and the fineness desired, as shown by Fig. 27-19. Capacity can also be seriously reduced by excessive moisture in the coal, but it can be restored by increasing the temperature of the primary air. Figure 27-20 indicates the temperatures needed. For PC boilers, the coal size usually is 65 to... 

The maximum contribution of turbulent attrition rate varies in the range 30-40 per cent of total fine numbers with the assumption that impact attrition fragments are not generated by the rubber coated turbine (i.e. similar to the 25 per cent estimate of Evans etal., 1974). 

Cleaver, J. A. S., and Ghadiri, M., Impact Attrition of Sodium Carbonate Monohydrate Crystals, Powder Tech., 76 15 (1993)... 

Yuregir, K. R., Ghadiri, M., and Clift, R., Observation of Impact Attrition of Granular Solids, Powder Tech., 49 53 (1986)... 

ATTRITION MILLS. Equipment of this type is used in the process industries to reduce the size of various feeds. Attrition connotes a rubbing action, although this action usually is combined with other forces, including shear and impact. Attrition mills also are referred to as disk mills and normally comprise two vertical disks mounted on horizontal shafts, with adjustable clearance between the vertical disks. In some designs, one vertical disk may be stationary. In other designs, the two vertical disks... 

J.A.S. Cleaver, M. Ghadiri, Impact attrition of sodium carbonate monohydrate crystals, Powder Technol. 76 (1993) 15-22. 

Ghadiri, M. Zhang, Z. 2002 Impact attrition of particulate solids part 1. A theoretical model of chipping. Chemical Engineering Science 57, 3659-3669. 

Forces commonly used in food processes for particle size reduction are compressive, impact, attrition (or shear), and cutting forces. More than one force usually participates in the comminution operation in industrial size-reduction equipment. In particular, crushing rolls use mainly compressive forces, hammer mills are based on impact, disc mills cause particle attrition through shear force application, and rotary knife cutters use cutting forces. 

Particles in fluidized beds undergo collisions and frictional contacts with each other and with fixed surfaces, sometimes causing the particles to break [40, 41]. The most important mechanisms of attrition are impact attrition (also called fragmentation) and abrasion. Impacts can be especially energetic, and therefore likely to cause attrition, when particles are accelerated in distributor jets, feed jets, or cyclone entrances and then collide with fixed surfaces or stationary particles. 

Yuregir KR, Ghadiri M, Clift R. Observation of impact attrition of granular solids. Powder Technol 49 53-57, 1986. 

Types of Pulverizers. AU pulverizing machinery operates to grind by impact, attrition, compression, or a combination of two or more of these. 

Then the crystal-impeller impact attrition rate may be described by Synowiec etal. (1993)... 

In the analysis of Synowiec etal. (1993), while the turbulent attrition rate is predicted to be constant with increasing scale of operation at constant power input, the impact attrition rate is predicted to decline with the square of vessel size. In combination... 

Ghadiri M, Zhang Z Impact attrition of particulate sohds. Part 1 a theoretical model of chipping, Chem Eng Sci 57 3659—3669, 2002. 

Zhang Z, GhadiriM Impact attrition of particulate solids. Part 2 experimental work, Chem Eng Sci 57 3671-3686, 2002. 

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