coal selection criteria for industrial pfbc firing project 3.2 - CCSD

“Coal Selection Criteria for Industrial PFBC Firing”
oxidation and erosion (Tsumita, Namba et al. 1997). In preventing such a phenomenon, at
low temperature it is important to apply thermal spray coatings. For high temperature, the
tube materials should have sufficient erosion and corrosion resistance due to the
formation of hard oxide scale on the surfaces (Tsumita, Namba et al. 1997). Abrasion and
leakage was found in Osaki’s boiler tube. The cause of this problem was believed to be
solidified fluid deposits which remained on tubes in the furnace. When high velocity fluid
flowed, abrasion progressed ten times faster. Modifications in the shutdown procedure
were proved to prevent such occurrence (Matsumoto and Kawahara ).
3.6.4 In-bed Heat Exchanger Tubes Corrosion
Some researchers found that the presence of ash in the bed accommodated the
competition between gaseous halide carrier and solid alumino-silicate for corrosion. The
kinetics of this competition were controlled by the location of chlorine and alkali release
from the coal, re-trapping of alkali may occur if the bed is relatively high (~ 10 ft)
(Keairns, Alvin et al. 1977). The same researchers discovered that more alkali will be
released at lower pressure (Keairns, Alvin et al. 1977). Decreasing the bed temperature
will reduce the alkali emission, but at the expense of reduced efficiency.
When alumino-silicate was present, in sufficient concentration, it would reduce the alkali
emissions from the bed by forming feldspars (Keairns, Alvin et al. 1977). Aluminosilicate,
as a getter, is cheap and effective over a wide range of temperature. It is an
attractive option in reducing alkali emissions, however neither its capacity nor
concentrations were known in order to design an effective alkali suppression stage
(Keairns, Alvin et al. 1977). In addition, its presence could cause plant deterioration
through erosion.
3.7 Environmental Performances
Most PFBC plants do not encounter any environmental problems since PFBC is already
an environmentalal friendly technology. Nevertheless, the local Environmental Protection
Agency (EPA) sets the pollutant emission regulation to achieve sustainable environment
control.
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