Coal, sizing

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 performance of spreader stokers is affected by changes in coal sizing. The equipment can distribute a wide range of fuel sizes, but it distributes each particle on the basis of size ana weight. Normal size specifications call for 19-mm (H-in) nut and slack with not more than 30 percent less than 6.4 mm i U in). 

The effect of feed rate upon the conversion of the 802 coal (size group 1, —72 B.S. mesh) to acetylene is shown in Figure 6 both for reactions carried out in an argon plasma and in a 90% argon plus 10% hydrogen plasma. The rectilinear portions of the graph, represented by the unbroken lines, corre-... 

ASTM D-4749. Standard Test Method for Performing the Sieve Analysis of Coal and Designating Coal Size. 

Coal sizes in the coal industry, the term 5 inches to inch means all coal pieces between 5 inches and inch at their widest point. Plus 5 inches means coal pieces over 5 inches in size 1 to 0 or 1 means coal pieces 1 inches and under. 

For flotation to be most effective, reagents such as oil (collector) and surfactant (frother) must be added to the aqueous coal slurry. The collector adsorbs on the coal surface and makes it more hydrophobic, while the surfactant facilitates production of a stable froth. According to Leonard (26), the optimum coal sizes for froth flotation are between 50 and 140 mesh (0.3 and 0.106 mm). While conventional froth flotation will successfully remove minerals from coal, it has limited effect on the pyrite content, as pyrite tends to float almost as well as coal. Because of this, researchers have been looking for better ways to remove pyrite from coal. In addition, as previously mentioned, it is necessary to grind coal to very fine sizes in order to sufficiently liberate the mineral matter and pyritic sulfur. But, at these very fine sizes,... 

The 12 mesh x 0 IL6 coal, sized as 80% plus 60 mesh, was used in run 6. When the sample was ground to 85% minus 70 mesh and used in run 10, the final ash content of 0.56% and final sulfur content of 0.57% achieved represent significant improvements in removal, to 96% and 86%, respectively. The lower recovery of 65% can again be attributed in part to mechanical losses of the finer coal through the mesh of the basket. 

While friability is a property that may be attributed to crystals and many chemical compounds, tests devised thus far pertain only to coals however, the same tests may be used on other materials having the same relative degree of friability. Several methods have been used to determine friability, and are based on two procedures (a) Measurement of work done in reducing coal of a given size to a smaller size, or (b) subjecting the coal to a definite amount of work and measuring the reduction in coal size due to such work. 

Fig. 19.7. Coal-cleaning equipment in common use in the coal industry with respect to the coal size processed.

Process Type Description Extent of Coal Use In U.S. (% of Total Used) Commercial Use Scale Size (TPDf Coal Types Coal Size... 

The load characteristic of circulating fluidized bed boilers is closely related to the gas-solid flux through the combustor. Thus, choice of coal size and the proper gas-solid separator deserves attention. Generally, the fraction of particles below 0.1 mm is smaller than 10%, which could be removed only by a cyclone separator, while the major fraction of coarser particles could be easily separated by inertia or gravity (Li and Kwauk, 1981). The diagram of ash balance for a circulating fluidized bed boiler, shown in Fig. 22, can... 

Coal, sized wet or dry Coconut, shredded Coffee, ground Corn flakes Flour, wheat... 

The product size distribution after short grinding times is also very revealing. This allows better evaluation of the effect of feed coal size. The results for the 1" x 3/4" feed are shown in Table V. Comparison of the 10 minute grinding time results for treated and untreated results show that, as in our previously reported results, there is a significant improvement in grindability. This is particularly prominent at the minus-1/2" size which essentially means that the feed coal has been weakened. The difference is less significant, however, with a 200 mesh product. 

Using this short grinding time approach comparisons of wet and dry grinding were also studied. Table VI shows that the diminishing improvement from CO2/water treatment with finer coal sizes occurs for both wet and dry grinding. 

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