Ammonium Bisulfate Deposition Research Articles

Mechanism of ammonium bisulfate deposition on V1M5/Ti catalysts with synergistic effects of V and M (M = Ce, Co, Fe, and Mn) in low-temperature NH3-SCR

Two pathways of ammonium sulfate deposition on V1M5/Ti are elucidated in detail. The synergistic effect of V sites and transitional metal sites reflects in the selective adsorption and competitive oxidation of SO2.

Laboratory Study on Adhesive Ash Deposition Characteristics of Ammonium Bisulfate in Conditions Simulating an Air Preheater for Hard Coal Combustion

The ash blockage of the rotary air preheater is a serious problem of the coal-fired boiler that urgently needs to be solved, which is caused by the adhesive deposition of ammonium bisulfate (ABS) and the fly ash. A comprehensive experimental study was performed to investigate the adhesive ash deposition characteristics based on an experimental platform established. The influences of the gas temperature, the gas velocity, the mass ratio of the ABS to the fly ash (R), and the ash particle size on the ash deposition characteristics were mainly analyzed and discussed under different conditions. The experimental results indicate that the liquid ABS is the root cause of the ash particles adhering to the heat transfer elements of the air preheater. The experimental results indicate that when the gas temperature is in the range of 420–493 K, the ABS ash deposition intensity and the ABS adhesion rate both increase with the increase in the gas temperature. When it is 493 K, the ABS adhesion rates of the corrugated plate and the positioning plate both reach maximum values, which are 31.7% and 27.9%, respectively. With the decrease in gas velocity, the total ash deposition intensity, the ABS ash deposition intensity, the ABS adhesion rate, and the growth rate of the ABS adhesion all increase. The content of ABS in the fly ash is also an important factor. When R rises, the ash deposition intensity and the ABS adhesion rate increase significantly. The particle size of the fly ash has little influence on the total ash deposition intensity, but has a great influence on the ABS ash deposition intensity and the ABS adhesion rate. With the increase in the particle size in the range of 30.8–100 μm, the ABS ash deposition intensity decreases by nearly 50%, and the ABS adhesion rates of plates A and B decrease by about 43.9% and 49.6%, respectively. According to the study results, some effective measures can be taken to solve the ash blocking problem of the rotary air preheater, including using the steam air heater, optimizing the operation parameters of the soot blower, and inhibiting ABS formation.

Analysis of ammonium bisulfate/sulfate generation and deposition characteristics as the by-product of SCR in coal-fired flue gas

The generation and deposition of ammonium bisulfate (ABS) in flue gas caused serious blockage and corrosion to the air preheater, which seriously affect the safe and economic operation of coal-fired power plants. The generation and deposition of ABS/ammonium sulfate (AS) under non-catalytic conditions were studied on a simulated air preheater test bench, and FT-IR and XRD tests were performed to characterize the products under different conditions. Experimental results show that the generation of ABS/AS is complicated and controlled by the concentration of SO3 and NH3, the ratio of SO3 to NH3 (SO3/NH3) and deposition temperature. Under the same SO3 conditions, ABS/AS generation rate under different SO3/NH3 conditions is 1:2 > 2:1 > 1:1. The initial deposition temperature of ABS/AS will increase with the corresponding increase of SO3 and NH3 concentration, and is exponentially correlated with the product of SO3 and NH3 concentration in flue gas. In the temperature range 390–223 °C, ABS generated and deposited under all conditions, and in the temperature range 223–131 °C, the mixture of H2O, H2SO4, and ABS generated and deposited when SO3/NH3 is 2:1, and AS with a small amount of (NH4)3H(SO4)2 generated and deposited when SO3/NH3 is 1:1 and 1:2.

Unraveling SO2-tolerant mechanism over Fe2(SO4)3/TiO2 catalysts for NOx reduction

Developing low-temperature SO2-tolerant catalysts for the selective catalytic reduction of NOx is still a challenging task. The sulfation of active metal oxides and deposition of ammonium bisulfate deactivate catalysts, due to the difficult decomposition of the as-formed sulfate species at low temperatures (<300 °C). In recent years, metal sulfate catalysts have attracted increasing attention owing to their good catalytic activity and strong SO2 tolerance at higher temperatures (>300°C); however, the SO2-tolerant mechanism of metal sulfate catalysts is still ambiguous. In this study, Fe2(SO4)3/TiO2 and Ce2(SO4)3/TiO2 catalysts were prepared using the corresponding metal sulfate salt as the precursor. These catalysts were tested for their low-temperature activity and SO2 tolerance activity. Compared to Ce2(SO4)3/TiO2, Fe2(SO4)3/TiO2 showed significantly better low-temperature activity and SO2 tolerance. It was demonstrated that less surface sulfate species formed on Fe2(SO4)3/TiO2 and Ce2(SO4)3/TiO2. However, the presence of NO and O2 could assist the decomposition of NH4HSO4 over Fe2(SO4)3/TiO2 at a lower temperature, endowing Fe2(SO4)3/TiO2 with better low-temperature SO2 tolerance than Ce2(SO4)3/TiO2. This study unraveled the SO2-tolerant mechanism of Fe2(SO4)3/TiO2 at lower temperatures (<300 °C), and a potential strategy is proposed for improving the low-temperature SO2-tolerance of catalysts with Fe2(SO4)3 as the main active component or functional promoter.

Investigation on optimal active layer thickness and pore size in dual-layer NH3-SCR monolith for low SO2 oxidation by numerical simulation

Nitrogen oxides (NOx) and sulfur dioxide (SO2) are common gaseous pollutants in the flue gas of stationary resources, such as thermal power plants. The undesired oxidation of SO2 on the catalytic monolith for Selective Catalytic Reduction (SCR) with ammonia will cause deposition of ammonium bisulfate, corrosion and extra pressure drop to downstream devices. A dual-layer model of catalytic monolith was established in this work to thoroughly investigate the effects of active layer thickness on SCR reaction and SO2 oxidation under various operating parameters. Besides, the influences of different sizes of nanopore in catalyst on both reactions are discussed. Thus, optimal parameters and suggestions were given for the design of SCR catalytic monolith with low SO2 oxidation.

Influence of operating conditions on ammonium bisulfate deposition in the rotary air preheater of coal-fired power plants

Influence of operating conditions on ammonium bisulfate deposition in the rotary air preheater of coal-fired power plants

Single and multi-objective optimizations of rotary regenerative air preheater for coal-fired power plant considering the ammonium bisulfate deposition

Although much work has been done on the optimization of the recuperative heat exchangers, little attention has been paid to the optimization of rotary regenerative air preheater (RAPH) in coal-fired power plants. It is known that the ammonium bisulfate deposition (ABS) can adversely affect the safe operation of RAPH, so an improved Radian number was proposed to estimate the impact of ABS in the optimization of RAPH. The thermal hydraulic calculation program integrated with genetic algorithms was developed to conduct optimizations of RAPH. The design parameters included rotor radius, each fluid sector angle and each matrix layer height. The multi-objective optimization was carried out to maximize the effectiveness and to minimize the pressure drop from the perspective of users, while the single-objective optimization was performed to minimize the weight of the heat transfer elements from the perspective of manufacturers. The improved Radian number is more reasonable to reflect the ABS deposition compared with the original Radian number. The designer can estimate the ABS deposition status using the improved Radian number not only in the operating process but also in the design process of RAPH. The range of optimal solution becomes smaller but the rank of the Pareto solution stays unchanged with the decrease in the restriction of improved Radian number. The optimization with larger rotor radius restriction could obtain better Pareto results. The total weight of heat transfer elements could be reduced by at least 26.5% compared with that of the original design by using genetic algorithm.

Corrosion and viscous ash deposition of a rotary air preheater in a coal-fired power plant

The corrosion and viscous ash deposition characteristics of a rotary air preheater were investigated. Deposit samples and corroded heat transfer elements were taken from the air preheater of a 300MW coal-fired power plant in China and analyzed by X-ray fluorescence, X-ray diffraction and scanning electron microscope equipped with energy dispersive X-ray spectroscopy. The results show that the serious corrosion and viscous ash deposition were both caused by sulphuric acid condensation rather than ammonium bisulfate deposition. The mechanisms of corrosion and viscous ash deposition were discussed and the coupling formation model of corrosion and viscous ash deposition was proposed.

Optimization of coal-fired boiler SCRs based on modified support vector machine models and genetic algorithms

An integrated combustion optimization approach is presented for the combined considering the trade offs in optimization of coal-fired boiler and selective catalyst reaction (SCR) system, to balance the unit thermal efficiency, SCR reagent consumption and NO x emissions. Field tests were performed at a 160 MW coal-fired unit to investigate the relationships between process controllable variables, and optimization targets and constraints. Based on the test data, a modified on-line support vector regression model was proposed for characteristic function approximation, in which the model parameters can be continuously adapted for changes in coal quality and other conditions of plant equipment. The optimization scheme was implemented by a genetic algorithm in two stages. Firstly, the multi-objective combustion optimization problem was solved to achieve an optimal Pareto front, which contains optimal solutions for lowest unit heat rate and lowest NO x emissions. Secondly, best operating settings for the boiler, and SCR system and air preheater were obtained for lowest operating cost under the constraints of NO x emissions limit and air preheater ammonium bisulfate deposition depth.

Deposition of ammonium bisulfate in the selective catalytic reduction of nitrogen oxides with ammonia

Deposition of ammonium bisulfate in the selective catalytic reduction of nitrogen oxides with ammonia