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.