Abstract
Considering the practical requirements for continuous operation under part load condition, the commercial honeycomb selective catalytic reduction (SCR) catalyst was modified with Sb addition. Experiments were performed to investigate the effect of modification on long-time SCR performance under part load condition. Characterizations for the original and modified catalysts were also conducted to analyze the changes of the catalysts. The results indicated that the activity of modified catalyst was obviously enhanced in the temperature range of 275–325 °C and it achieved about 64.5% removal efficiency during the 30 h stability test at 275 °C. The characterization results indicated that the ammonium sulfate was chemically adsorbed on the catalyst surface at low temperatures, which led to the decrease of the specific surface area, pore volume, and V4+/V5+ ratio of the catalysts. These are the reasons for the decrease of the catalyst activity at low temperatures, while the deposition amount of ammonium sulfate was relatively small over the modified catalyst. In addition, the decomposition temperature of the ammonium sulfate was reduced in the modified catalyst compared with the original one. NH4+ ions decomposed at 275 °C by reacting with the NOx in the flue gas, and the dynamic equilibrium of this reaction was achieved on the modified catalyst after a short period of time. Therefore the modified catalyst can be continuously and stably operated at this temperature, and the part load operation of the SCR system in the coal-fired power plant can be realized.
Highlights
Among the techniques for removing nitrogen oxide, selective catalytic reduction (SCR) that usesNH3 as a reducing agent has become the top choice internationally for the efficient control of NOx emissions
The main commercial catalyst used for SCR is the V2 O5 –WO3 (MoO3 )/TiO2 catalyst, which is available in honeycomb, plate, and corrugated forms
The V2 O5 –WO3 (MoO3 )/TiO2 catalyst has been widely used in flue denitrification in power plants, with an active temperature window of 300 ◦ C–400 ◦ C, namely, a medium-temperature SCR catalyst [1,2]
Summary
Among the techniques for removing nitrogen oxide, selective catalytic reduction (SCR) that uses. The SO2 , SO3 , and H2 O in the flue gas react with NH3 to produce ammonium bisulfate (ABS), which adsorbs into the micropores of the catalyst, and blocks the micropores of the catalyst, or bonds with fly ash to form large particles that cover the surface of the catalyst [3,4]. These phenomena cause catalyst deactivation, which decreases the efficiency of the SCR system; the system fails to meet its standard, or excess ammonia slip occurs [5,6]. Characterization methods such as N2 physisorption, scanning electron microscope (SEM) mapping, X-ray fluorescence (XRF), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, and thermogravimetry were employed to analyze the experimental results, and an optimized SCR catalyst suitable for use at 275 ◦ C–400 ◦ C was obtained
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