Research On Failure Mechanism Of Polyphenylene Sulfide Filter Media

Polyphenylene Sulfide (PPS) filter media is now the first choice for fine particles (PM10, PM2.5) control in coal-fired power plants. However, the complicated operating conditions usually cause frequent earlier failure of filter media, which affects the normal operation of the power plant and results in economic losses and environmental pollution. Therefore, to study on the failure mechanism of PPS filter media and perfect the basic theory of filter media failure has profound theoretical and practical significance for improving filter media performance, extending filter media service life and controlling fine particulate emissions as well as construction of conservation-oriented society.Failure of filter media is the phenomenon that the pressure drop of filter media is greater than the designed requirements or its efficiency is lower than the designed requirements caused by some reason during its operation. The two main failure modes are breakage and blocking, in which breakage is the most common failure mode. This paper focuses on the breakage failure.By means of thermal analysis, the thermal stability of PPS filter media is studied, the kinetic parameters of thermal decomposition and the thermal lifetime are calculated. By means of TG-DSC and FTIR coupling technique, the thermal decomposition process and product of PPS filter media are studied; the thermal decomposition mechanism of PPS filter media is discussed. The results show that, from the perspective of the thermal stability, TG data and the thermal decomposition activation energy can characterize high temperature performance of different PPS filter media more accurately; the thermal decomposition of PPS filter media begins from cleavage of a relatively weaker C-S bond on the molecular chain. In an inert atmosphere, the thermal decomposition reaction of PPS filter media is first-order reaction, the thermal weight loss is done in one step. The thermal decomposition in air presents a second phase characteristics, which is caused by the crosslinked network formed by oxidative crosslinking or thermal crosslinking. The weight loss rate decreases, so step appears in weight loss curves. According to this, the performance of PPS filter media can be optimized by adjusting the temperature and oxygen content in its processing and post-processing.A self-designed and developed real work environment simulation system is adopted to carry out the experimental research on the influence of O2, O3, SO2, NO, NO2 and other gases, which may exist in the flue gas, on the performance of PPS filter media. The performance changes under the different gas concentration, temperature and time are studied. The appearance, fracture and mechanical properties testing results are analyzed. It shows that high temperature, O2, O3, SO2, NO, NO2 can all affect the mechanical properties of PPS filter media. With the increases of temperature, concentration and time, the mechanical strength decrease of PPS filter media will be ultimately resulted. The stronger the ambient flue gas oxidations, the faster the strength of PPS filter media decreases. So it is strongly recommended that exposure to O3 has better be avoided in the usage of the PPS filter media.The crystallinity and molecular weight of PPS filter media under the different conditions are tested and analyzed, the influence of test temperature on the mechanical performance of the filter media is also analyzed, and the influence mechanism of flue gas on the PPS filter media is discussed. By means of reaction kinetics theory, a filter media residual strength model is built, and it is validated by the experimental data. The results show that along with the increase of processing temperature, the melting point and crystallinity of PPS filter media decreases. The branching, crosslinking and degradation reaction of PPS filter media in high temperature flue gas destroy original linear crystalline structure, and the molecular weight changes with it. The effect of flue gas on the PPS filter media performance is the result of cooperation and competition between oxidative crosslinking and oxidative degradation. In the cross-linking dominated stage, the strength of filter media slightly increases the elongation at break decreases. In the degradation dominated stage, the strength decrease caused by degradation is greater than the strength increase caused by crosslinking, the mechanical strength of the filter media gradually decreases. Under the action of external force, the filter media ultimately become breakage and failure. Validated by the measured data, the deviation of the predicted residual strength values is small, so it can be concluded that the model has high prediction accuracy. The strength of filter media at high temperatures is far below that under room temperature, and the mechanical properties of filter media show great differences under different temperatures, which should be emphasized not only for the choice of filter media but also for the establishment of standards.