Solid Fuels. 朱信 Hsin Chu Professor Dept. of Environmental Engineering National Cheng Kung University. 1. Introduction.
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The same consideration apply to coal-fired installations as to oil-fired combustion equipment namely that condensation inside the plant must be avoided and that the design of the flue must ensure that ground concentration of sulfur oxides are controlled within acceptable limits.
Fluidized Bed Combustors (FBC)The basic principle of operation is that the coal is mixed with an inert material (e.g. sand) and the bed is “fluidized” by an upwards flow of air (Fig. 9.1, next slide).
Although the fluidization requires more fan power than the conventional grate combustions (Figs. 9.3 & 9.4), there are a number of advantages in FBC:(1) The bed temperature can be kept cooler than in the case of grate combustion-fluidized bed temperatures are generally within the range 750-950℃. This means that ash fushion does not occur and the low temperatures produce less NOX.
(2) High rates of heat transfer can be attained between the bed and heat exchanger tubes immersed in it.(3) A wide range of fuel types can be burned efficiently.(4) additives (such as limestone) can be used which react with oxides of sulfur retaining the sulfur in the bed with consequent reduction in SOX emission.