Figure 8. The failure mechanism of PPS-based bag filters in coal-fired
power plants.
The SO2 in the flue gas would turn into
H2SO4vapor under high temperature assisting with oxygen and water. Generally,
the Ta is higher than T, but the Taincreases with the addition of SO2 content in the flue
gas (Fig. 7). When the T is lower than Ta, the vapor
converts into liquid for H2SO4, which
combines with fly ashes and transports to the fiber surface in the
three-dimensional network of PPS-based bag filter. Then, the strong
oxidant of SO3 produced in the fiber surface through
dehydration reaction. The SO3 would absorb on the
surface of fiber and attack the C-S bond in the PPS chains inducing by
high temperature (route (1)), which transforms into sulfoxide (-SO-) and
sulfone (-SO2-). As the consumption of C-S bond reaches
to a critical point, the hydrogen in the benzene ring of PPS could
initiate and substitute by sulfonic acid group (-SO3H,
route (2)). Moreover, the above reactions get intensified as the
SO2 content increases. Therefore, the higher
SO2 content is, the deeper oxidation is, the worse
damage of fiber is, and thus the shorter lifetime of PPS-based bag
filter in coal-fired power plants is.