Yuqun Zhuo

DRIFTS study of ammonia activation over CaO and sulfated CaO for NO reduction by NH3.

CaO catalyzes NH(3) oxidation, while sulfated CaO catalyzes NO reduction by NH(3) in the presence of O(2), and the adsorption and transformation of ammonia over CaO and sulfated CaO has been investigated by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to understand their catalytic mechanism. It has been found that ammonia is first adsorbed over Lewis or Brönsted acid sites, and later undergoes hydrogen abstraction giving rise to either NH(2) amide or NH imide intermediates. The intermediates react with NO or lattice O to produce N(2) or NO. Comparing the DRIFTS of NH(3) adsorption over CaO and sulfated CaO, it is obvious that ammonia adsorbed over CaO is activated mainly in NH form apt to react with surface oxygen to produce NO, while ammonia adsorbed over sulfated CaO is activated mainly in NH(2) form apt to reduce NO. The DRIFTS results agree with experimental data and explain the catalytic mechanisms of CaO and sulfated CaO.

Fate of mercury in flue gas desulfurization gypsum determined by Temperature Programmed Decomposition and Sequential Chemical Extraction

A considerable amount of Hg is retained in flue gas desulfurization (FGD) gypsum from Wet Flue Gas Desulfurization (WFGD) systems. For this reason, it is important to determine the species of Hg in FGD gypsum not only to understand the mechanism of Hg removal by WFGD systems but also to determine the final fate of Hg when FGD gypsum is disposed. In this study, Temperature Programmed Decomposition (TPD) and Sequential Chemical Extraction (SCE) were applied to FGD gypsum to identify the Hg species in it. The FGD gypsum samples were collected from seven coal-fired power plants in China, with Hg concentrations ranging from 0.19 to 3.27μg/g. A series of pure Hg compounds were used as reference materials in TPD experiments and the results revealed that the decomposition temperatures of different Hg compounds increase in the order of Hg2Cl2<HgCl2<black HgS<Hg2SO4<red HgS<HgO<HgSO4. The Hg compounds existing in FGD gypsums identified by TPD included HgCl2, Hg2Cl2, Hg2SO4, black HgS and red HgS, of which mercury sulfides were the primary compounds. The results of SCE indicated that Hg was mainly distributed in the strongly complexed phase. The low Hg content in FGD gypsum increases the ambiguity of assigning extraction fractions to certain Hg species by SCE. The fact that the primary compounds in FGD gypsum are HgS phases leads the leaching of Hg in the natural environment to be quite low, but a considerable amount of Hg may be released during the industrial heating process.

Impact of Flue Gas Species and Temperature on Mercury Oxidation

Abstract Systematic experimental research has been conducted in a fix-bed reactor system to determine the impact of coal-fired flue gas species and temperature on mercury oxidation. This work focuses on the temperatures range of 200°C to 800°C to demonstrate that temperature is a critical factor for the effect of the gas components on the mercury oxidation process. Among the investigated gases, hydrogen chloride is essential for oxidizing the elemental mercury. Nitrogen oxide was also found to have a positive correlation with the mercury oxidation when hydrogen chloride was present. Sulfur dioxide can either promote or inhibit the oxidation depending on the conditions; however, when nitrogen oxide is also present, sulfur dioxide has a negative impact. Ammonia exhibits an strong inhibitory effect. Several plausible mercury oxidation pathways are suggested in this paper.

Density functional theory study on Hg removal mechanisms of Cu-impregnated activated carbon prepared by simplified method

The preparation of activated carbon sorbent for Hg removal was simplified by combining activation and functionalization processes into one step. Jujube-based carbon material was first mixed with CuCl2 solution and then activated for the preparation of Cu-impregnated activated carbon. Physical and chemical properties of prepared activated carbon were investigated by means of N2 adsorption, SEM-EDS, XRD. A fixed-bed reactor with CEMS (Continuous emission monitoring system) was used to test the Hg adsorption ability of prepared activated carbon. DFT (Density functional theory) method of computational chemistry calculation was applied to identify the Hg adsorption mechanisms on sorbent surface.

Mercury Emission and Removal of a 135MW CFB Utility Boiler

To evaluate characteristic of the mercury emission and removal from a circulating fluidized bed (CFB) boiler, a representative 135 MW CFB utility boiler was selected to take the onsite measurement of mercury concentrations in feeding coal, bottom ash, fly ash and flue gas using the US EPA recommended Ontario Hydro Method (OHM). The results show that particulate mercury is of majority in flue gas of the CFB boiler. Mercury removal rate of the electrostatic precipitator (ESP) reaches 98%. Mercury emission concentration in stack is only 0.062μg/Nm3, and the mass proportion of mercury in bottom ash is less than 1%. It was found that the fly ashes were highly adsorptive to flue gas mercury because of its higher unburned carbon content. Adsorption effect is related to carbon pore structural properties of fly ash and temperature of flue gas. However mercury adsorption capacity by fly ash can not be improved any more when unburned carbon content in fly ash increases further.

The Promotion by Steam on CaO Adsorbing SeO2 at Medium Temperature

This study investigated the promotion of steam for CaO adsorbing SeO2 gas at the medium temperature interval (240°C-800°C), based on the previous studies on CaO adsorbing SeO2 gas. The experiments revealed both the influences of temperature and steam concentration. The mechanism of the promotion is similar to those of steam in carbonation and is confirmed by a series of designed experiments and characterization of the products of gaseous SeO2 adsorption.

Catalytic Mechanism of NaY Zeolite Supported FeSO4 Catalyst for Selective Catalytic Reduction of NOx

The experimental results suggested that FeSO4-NaY and FeSO4-ZSM-5 prepared by impregnation method performed well in NOx removal. The NOx removal rates of the prepared catalyst were 20–35% higher than those of pure FeSO4, The effective temperature window was largely expanded with the best performance temperature shifted from 440 to 340°C. SO2 and H2O in flue gas had no obvious effect on catalyst performance. Mossbauer spectrometry, XPS and in-situ infrared spectra analysis had been employed to investigate the catalytic mechanism of catalysts. It had been found that FeSO4, Fe(OH)SO4 and Fe2O(SO4) were the major components existing in the prepared catalyst, with their portions related to carrier type and preparing condition. FeSO4 combined tighter with carriers after de-NOx reaction. Fe2O3 and the chemical bond between Fe and Al had been found. Fe(OH)SO4 was better in terms of NOx removal than that of Fe2O(SO4). NH3 absorbed on FeSO4-NaY catalyst generated the spectra of NH 4 + and NH3, suggesting the Eley-Rideal mechanism. FeSO4-ZSM-5 absorbed both NH3 and NO and the carrier (ZSM-5) itself demonstrated some catalytic effect, indicating a different reaction mechanism. \( {\text{SO}}_4^{{2 - }} \) from FeSO4 and hydroxyl from carrier jointly enhanced the adsorption of reaction gas. Fe provided the active sites for the reaction between NH3 and NO.

Leaching Characteristics of Trace Elements in Desulfurization Gypsum from a Coal-Fired Power Plant

The contents and leaching characteristics of Cr, Cd, As, Pb and Se in FGD gypsum from a 200 MW coal-fired power plant were investigated in this study. Experimental results revealed that: the leaching characteristics of As and Se were similar, both leaching rates were not obviously affected by pH but increased with increase of the liquid-solid ratio. Pb and Cr had similar leaching characteristics, their leaching rates were closely related with the pH of leaching solution and increased with the lowering of pH and both increased with the increasing of solid-liquid ratio. Along with the increase of the liquid-solid ratio, the leaching gradually achieved balance, and the balanced liquid-solid ratio was bigger when pH of leaching solution was lower. Cd content of leaching solution was below detect limit, and thus failed to get its leaching characteristics. The order of trace element content in leaching solution is Pb < Cr < As < Se, and the order of leaching rates is Cr < As < Pb < Se. BCR extraction procedure revealed that trace elements in FGD gypsum were mainly existed as available fraction and migration ability was stronger than that of trace elements in fly ash from coal-fired power plants.