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Pulverized Coal Combustion System
Combustion and conversion systems can generally be
categorized into either of the following two categories: 1) current commercial
technologies or 2) emerging technologies. The CCBs currently produced
and used primarily result from current commercial technologies, and of
these, the most common are pulverized coal (pc) combustion, cyclone firing,
and stoker firing.
The illustration shows a simple schematic diagram for a typical pc combustion
system. In this type of system, the coal is prepared by grinding to a
very fine consistency for combustion. Typically, 70% of the coal is ground
to pass through a mesh screen.
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Ash is formed in the combustion chamber while coal combusts. There are several configurations for commonly used pc furnaces, which can impact ash formation, but the primary advantage of pc combustion is the very fine nature of the fly ash produced. In general, pc combustion results in approximately 65%–85% fly ash, and the remainder is coarser bottom ash or boiler slag. Bottom ash is a coarse material and falls to the bottom of the combustion system. Fly ash is finer than bottom ash and is carried along the combustion process with flue gas. Particulate collection devices generally capture fly ash before being discharged into the atmosphere.
Emerging technologies are being developed to improve cost, efficiency, and environmental compliance. Advanced clean coal technologies, including atmospheric fluidized-bed combustors (AFBCs), circulating or pressurized fluidized-bed combustors (CFBCs or PFBCs), slagging combustors, and gasification systems, produce ash characteristics that differ significantly from conventional coal-firing technologies.