Flue gas temperature close to the hotter probe (500 -C) is
lower in the large than in the small CFB (640 -C vs. 850 -C).
Higher gas velocity in the 4 MW CFB and differences in the
constructions of the return cyclones allow larger fly ash
particles to pass this probe in the 4 MW CFB than in the
100 kW CFB. The lower flue gas temperature in the 4 MW
CFB, in turn, enhances deposition of alkali chlorides on those
particles. Larger particles tend to deposit by impaction mechanism to the wind-side increasing Cl concentration at this
location. In the smaller reactor, where flue gas temperature is
higher close to 500 -C probe, condensation of alkali chlorides
on larger particles presumably is much less. In addition, smaller
fly ash particles promote capture of alkali chlorides by
aluminosilicates in the flue gas, increasing the overall ratio of
particle surface to particle volume. Chlorine deposition to the
lee-side was not as dependent on reactor size as it was at
windside. Al and Si concentrations were higher in the deposits
of 100 kW than in the 4 MW CFB reactor whereas the trend in
sulfur concentration was the reverse.