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.
Highlights
Coal-fired flue gas contains sulfur oxides and nitrogen oxides, which cause a direct negative impact on the environment, and cause serious environmental problems, such as acid precipitation, photochemical smog and haze, etc.[1]
As the flue gas temperature decreases along the flue gas flow, ammonium bisulfate (ABS) is initially generated in the temperature range of the selective catalytic reduction (SCR)
Part of the ABS reacts with fly ash, which changes the properties of fly ash and affects the efficiency of the dust collector; the generation of ABS will increase the emission of fine particles from coal-fired power p lants[11,12,13,14]
Summary
Choosing an appropriate method of ABS collection and analysis is a necessary basis for in-depth research on ABS characteristics. Due to the different focus of research on ABS by related scholars, their collection, analysis and detection methods are different. When studying ABS-related issues in SCR, the most common detection method is FT-IR(Fourier transform infrared spectroscopy) to observe the characteristic absorption peak of ABS. This method can only be qualitative but not quantitative. There is still room for improvement in the collection and detection and analysis of substances in the study of ABS characteristics. This article summarizes some of the collection and analysis methods of ABS-related species. Sampling method Controlled condensation[24] Spiral tube method 80% isopropanol absorption method NaOH absorption method Direct spectroscopy Power Plant CEMS(Continuous emission monitoring system) Ammonia infrared analyzer Lye absorption Quartz wool glass bead Electric scale low voltage impactor[25]
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