FUELS AND COMBUSTION 221
Analysis Bituminous
mass percent Anthractive medium velocity Subiluminous LagniteUltimate
C 83.9 80.7 58.8 42.4
H 2 2.9 4.5 3.8 2.8
S 0.7 1.8 0.3 0.7
O 2 0.7 2.4 12.2 12.4
N 2 1.3 1.1 1.3 0.7
H 2 O 2.5 3.3 19.6 34.8HHV
Btu/lbm 13.320 14.310 10.130 7.2107.4 Coal Firing
Since the old days of feeding coal into a furnace by hand, several major advances have been
made that permit increasingly higher rates of combustion.
The earliest in the history of steam boilers were mechanical stokers, and several types are still
being used for small and medium-sized boilers. All such stokers are designed to continuously feed coal
into the furnace by moving it on a grate within the furnace and also to remove ash from the furnace.
99.99
99.90
99.5099.00
98.00
95.00
90.00
80.00
70.00
60.00
50.00
40.00
30
20105
0.05 0.1 0.2 0.5 1 2 5 10 20 50 100270 140 60 50 4030 20 14 10 6 4200100US standard sieve designationSieve aperture nmFineness present passingFig. 7.1. Coal Sieve Analysis.
Fig. 7.1 Coal sieve analysis. (A) pulverized-coal sample; (B) coal range for cyclone firing; (C)
coal as fired.