1. Introduction
Recently, release standards of the atmospheric particulate pollution became more and more strict [1-5]. As a main source of particulate pollution, flue gas containing NOx, SOxfrom coal-fired power plants needs to be handled carefully. As a feasible and cost-effective dust removal technology, bag-filter or electrostatic-bag composite precipitators with polyphenylene sulfide (PPS)-based bag-filter material have attracted numerous attentions from researchers and relative industrial engineers because of its high rejection rate, low resistance and easy cleanout [6-11]. A critical and limited parameter of precipitators is the lifetime, which is closely related to the operating cost of factories. Besides, the lifetime of PPS with high resistance to aggressive chemicals and high temperature is dominate in the durability of precipitators [12-16]. The designed life of a PPS-based filter bag could reach to 5 years under ideal conditions. In practice, the lifetime can range from 8 months to several years in coal-fired power plants owing to its complicated environments [1, 17].
Compared with PTFE, PET or other polymer materials [18-20], the C-S bond in the PPS chains is easily oxidized into sulfoxide and sulfone groups, and even broken under the high temperature and acid corrosion[21-23]. Consequently, the reduced mechanical properties, shorter service life can be observed. Extensive researches [24-27] have been conducted to illustrate the degradation mechanisms of PPS under the simulated environments. Tanthapanichakoon [8] examined the resistance of a PPS-based filter to several chemicals, concluding that HNO3 caused severe degradation of the PPS filter while remaining highly resistant to HCl and H2SO4. Besides, they also discovered that the mechanical properties of PPS material become poor at the atmosphere [28]. Cai [29] investigated that oxidation degradation of PPS can be aggravated with the increase in H2SO4 dew point. Moreover, the effect of mixtures of NO and O2 [30], NO2 and SO3 [9] on the degradation of PPS have also been put forward. Although the effects of several chemical species on the degradation of PPS have been interpreted to a certain degree, the influence or substantial effect of SO2 and O2 gases at high temperature has not been well understood. Moreover, it is worth mentioning that the previous works about the degradation of PPS are executed under the normal environments, but the intricate environment with flue gas from coal-fired power plants containing multiple corrosive gases such as NO, NO2, SO2, SO3, O2 and so on has never been explored. The effects of corrosive gases and corresponding rules in actual engineering projects are lacking and need to be further explored.
In this work, scanning electron microscope (SEM), differential thermal analysis (DTA), fourier transform infrared spectroscopy (FT-IR) and electronic fabrics strength tester (CRE) are employed to analyze the structural transformation of PPS-based bag filter materials collected from the coal-fired power plants. The effects of SO2 and O2 gases at high temperature were also investigated. The work would explain the actual structural evolution of PPS and mechanisms under the complicated corrosive gases with high temperatures, which will provide a guidance for prolonging the service life of PPS-based bag filters during the usage of coal-fired power plants.