Status and development for detection and control of ammonium bisulfate as a by-product of SCR denitrification

Abstract

When denitrification technology using NH3 or urea as the reducing agent is applied to remove NOx from the flue gas, ammonium bisulfate (ABS) by-product will also be generated in the flue gas. ABS has an impact on catalyst life span, denitrification efficiency etc., air preheater and its downstream thermal equipment also have a significant negative impact due to its plugging and corrosion. The requirement for NOx removal efficiency is improved by ultra-low emissions in China. However, wide-load denitrification makes the flue gas composition and temperature changing more complicated. Increasing ammonia injection can improve the NOx removal effect, but too much ammonia injection will lead to the formation of ABS and the increase of deposition risk, the contradiction between these two aspects is amplified by ultra-low emissions and wide-load denitrification in many plants. Coordinating NOx control and reducing the impact of ABS on equipment are issues that the industry needs to solve urgently. In recent years, extensive research on ABS had been carried out deeply, consequently, there has been a relatively in-deepth knowledge foundation for ABS formation, formation temperature, deposition temperature, dew point temperature, decomposition behavior, etc., but the existing researches are insufficient to support the problem of ABS under full load denitrification completely resolved. Therefore, some analysis and detection methods related to ABS are reviewed in this paper, and the impact of ABS on SCR, air preheater and other equipment and the existing research results on reducing the impact of ABS are summarized also. It is hoped that this review will provide a reference for the industry to solve the problems of ABS that hinder wide-load denitrification and affect ultra-low emissions.

Study on the equilibrium constants and initial formation temperature of NH4HSO4 and (NH4)2SO4 in coal‐fired flue gas

“…In the context of this study, at lower temperatures, gaseous H 2 SO 4 dominates the experimental system, indicating that ABS is primarily formed through a binary reaction. As the temperature rises, the contribution of the ternary reaction to ABS formation gradually becomes more significant 19 …”

“…As the temperature rises, the contribution of the ternary reaction to ABS formation gradually becomes more significant. 19 Based on the input of dilute sulfuric acid quantity, the partial pressures of SO 3 and H 2 SO 4 at different temperatures are calculated, as depicted in Figure 11. Subsequently, the molar equivalent partial pressures of ABS and AS are computed based on the measured amounts of these products, as illustrated in Figure 12.…”

“…Maintaining flue gas temperature in the air preheater at 350 C achieves a balance: it achieves a certain level of ABS volatilization, mitigates air preheater fouling, and prevents potential corrosion from subsequent volatilization and condensation products. Jiao K et al 19 summarized previous works, indicating that ABS formation temperatures range from 250 to 350 C. Within the SCR system, ABS primarily forms through gas-phase ternary reactions, while within the air preheater, gasphase binary reactions predominantly lead to AS formation. The dew point temperature of ABS is approximately 250-290 C, and the deposition temperature within the air preheater lies around 150-190 C. There remains ongoing debate regarding the decomposition process and products of ABS.…”

Progress of selective catalytic reduction denitrification catalysts at wide temperature in carbon neutralization

“…Among them, compared with nanorods (W-NR) and nanorod self-assembled microspheres (W-MP), WO 3 nanoparticles (W-NP) have the best redox ability, and its W 5+ /(W 5+ +W 6+ ) The molar ratio of α is the largest, and the concentration of Ce 4+ on the surface of Ce/W-NPs is the highest, which exhibits the best redox performance, thereby promoting the SCR performance. When CeO 2 is used as the active component of SCR catalyst, it is easy to deactivate due to the instability of pure CeO 2 at high temperature (Ma S. et al, 2021). Therefore, many researchers tried to add different transition metals into CeO 2 to improve its stability and SCR activity.…”

“…The unit deviates from the original design conditions during low-load operation, and the flue gas parameters are quite different from those during normal high-load operation, which adversely affects the operation of various equipment in coal-fired power plants. For example, increasing the actual operating coal consumption of the unit, affecting the cooling of the boiler, reducing the NO X control ability of the denitrification system, and increasing the amount of ammonia injection and the generation of ammonium hydrogen sulfate ( Zhang Y. et al, 2019 ; Shen and Zhang, 2020 ; Jiao et al, 2021 ). This not only significantly increases the operating cost of the unit, but also poses a greater safety risk to the operation of the boiler, catalyst, air preheater and electrostatic precipitator system.…”