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.