2.1. Reagents and vaporization of E

2.1. Reagents and vaporization of EF solution
30% (w/w) of H2O2, 16% (w/w) of PAA, and 99–101% (w/w) of
FeSO4·7H2O [26–28] were used to prepare EF solution. Ca (OH)2 and
anhydrous CaCl2 were used as the absorbent and the dryer respectively.
The EF solution pH was adjusted by 1 mol/l of H2SO4 and 1 mol/l of
NaOH. The preparation order of EF solution was that the fresh solutions
of FeSO4, PAA, and H2O2 were added in beaker in turn by using pipettes
(10–1000 μl and 1–5 ml) and then shaken mildly. For the vaporization
of EF solution (17), which was pumped by a peristaltic pump (16) and
carried simultaneously by the simulated flue gas into a vaporization
device (10), where it was vaporized immediately. During the process
of vaporization, some of FeSO4 were residual in the bottom of the vaporization device and oxidized to Fe3+ with yellow color by oxidants;
whereas the other Fe2+ or Fe3+ were carried together with the oxidants
such as H2O2, PAA, and radicals to the reactor, then absorbed by
Ca(OH)2.
2.2. Experimental apparatus and procedure
The bench scale experiments were conducted on a fix-bed, which
mainly consists of the simulated flue gas generation, the vaporization
of EF solution, the integration of oxidation and absorption, and the tail
gas detection. As shown in Fig. 1, the compressed gas cylinders (1–5)
provided N2, SO2, NO, O2, and CO2 to generate the simulated flue gas
that was preheated by a thermostat water bath (9). A peristaltic pump
(16) (BT100-1F, Longerpump, Baoding) was used to pump the EF
solution in a vaporization device (10), which was heated by a thermal
control electric heater (11). The reactor is a cylindrical quartz tube
(13) with a length of 30 cm and an inner diameter of 3.2 cm, heated
by a tube type resistance furnace (14). The tail gas was detected on
line by a flue gas analyzer (19) (ECOM-J2KN, RBR Company, Germany).
Of note, the temperatures of vaporization device (10) were consistent
with those of reactor (13) and both of them were detected over time
by three thermal couples (12) (XMTD, Baoding).
During the experiments, SO2, NO, and N2, or other gases were
metered through the mass flow controller (6) and mixed in a buffer
bottle (7), in which SO2, NO, and other coexistence gases were diluted
by N2 to the desired concentrations, from which the simulated flue gas
was formed. The oxidation of SO2 and NO were carried out when the
mixture of vaporized EF, SO2, and NO entered into the reactor (13),
and then the oxidation products as well as the unreacted vaporized oxidants was absorbed by Ca(OH)2 powders (15) supported on the glass
wool in the latter part of the reactor. The removal efficiencies were
calculated based on the D-value of inlet and outlet concentrations of
SO2 and NO. The detail experimental conditions are shown in Table 1.
2.3. Analytical methods
The EF solution pH was tested by a pH meter (PHS-3C, Youke,
Shanghai). The surface patterns of the fresh and spent Ca(OH)2 powders were observed by using a scanning electron microscope (SEM, JEOL
JSM-7500F, Japan). An energy dispersive X-ray spectrometer (EDS,
Vantage DIS type, Thermo NORAN Company) and an X-ray diffraction
(XRD, D8 ADVANCE type, BRUKER-AXS in Germany) (40 kV and
20 mA) were used to determine the elements and compounds in the
fresh and spent Ca(OH)2 powders, the scanning range of XRD was
from 20° to 70° with a scanning velocity of 7°min−1. The XRD phases
presented in the samples were identified with the help of JCPDS data
files