Fe2O3 and CeO2 modified activated coke (AC) synthesized by the equivalent-volume impregnation were employed to remove elemental mercury (Hg0) from simulated flue gas at a low temperature. Effects of the mass ratio of Fe2O3 and CeO2, reaction temperature, and individual flue gas components including O2, NO, SO2, and H2O (g) on Hg0 removal efficiency of impregnated AC were investigated. The samples were characterized by Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Results showed that with optimal mass percentage of 3 % Fe2O3 and 3 % CeO2 on Fe3Ce3/AC, the Hg0 removal efficiency could reach an average of 88.29 % at 110 °C. Besides, it was observed that O2 and NO exhibited a promotional effect on Hg0 removal, H2O (g) exerted a suppressive effect, and SO2 showed an insignificant inhibition without O2 to some extent. The analysis of XPS indicated that the main species of mercury on used Fe3Ce3/AC was HgO, which implied that adsorption and catalytic oxidation were both included in Hg0 removal. Furthermore, the lattice oxygen, chemisorbed oxygen, and/or weakly bonded oxygen species made a contribution to Hg0 oxidation. 相似文献
Abstract Selective catalytic reduction (SCR) technology increasingly is being applied for controlling emissions of nitrogen oxides (NOx) from coal-fired boilers. Some recent field and pilot studies suggest that the operation of SCR could affect the chemical form of mercury (Hg) in coal combustion flue gases. The speciation of Hg is an important factor influencing the control and environmental fate of Hg emissions from coal combustion. The vanadium and titanium oxides, used commonly in the vanadia-titania SCR catalyst for catalytic NOx reduction, promote the formation of oxidized mercury (Hg2+). The work reported in this paper focuses on the impact of SCR on elemental mercury (Hg0) oxidation. Bench-scale experiments were conducted to investigate Hg0 oxidation in the presence of simulated coal combustion flue gases and under SCR reaction conditions. Flue gas mixtures with different concentrations of hydrogen chloride (HCl) and sulfur dioxide (SO2) for simulating the combustion of bituminous coals and subbituminous coals were tested in these experiments. The effects of HCl and SO2 in the flue gases on Hg0 oxidation under SCR reaction conditions were studied. It was observed that HCl is the most critical flue gas component that causes conversion of Hg0 to Hg2+ under SCR reaction conditions. The importance of HCl for Hg0 oxidation found in the present study provides the scientific basis for the apparent coal-type dependence observed for Hg0 oxidation occurring across the SCR reactors in the field. 相似文献
Abstract This paper is particularly related to elemental mercury (Hg0) oxidation and divalent mercury (Hg2+) reduction under simulated flue gas conditions in the presence of nitric oxide (NO) and sulfur dioxide (SO2). As a powerful oxidant and chlorinating reagent, Cl2 has the potential for Hg oxidation. However, the detailed mechanism for the interactions, especially among chlorine (Cl)-containing species, SO2, NO, as well as H2O, remains ambiguous. Research described in this paper therefore focused on the impacts of SO2 and NO on Hg0 oxidation and Hg2+ reduction with the intent of unraveling unrecognized interactions among Cl species, SO2, and NO most importantly in the presence of H2O. The experimental results demonstrated that SO2 and NO had pronounced inhibitory effects on Hg0 oxidation at high temperatures when H2O was also present in the gas blend. Such a demonstration was further confirmed by the reduction of Hg2+ back into its elemental form. Data revealed that SO2 and NO were capable of promoting homogeneous reduction of Hg2+ to Hg0 with H2O being present. However, the above inhibition or promotion disappeared under homogeneous conditions when H2O was removed from the gas blend. 相似文献
Activated carbon was one of the main adsorptions utilized in elemental mercury (Hg0) removal from coal combustion flue gas. However, the high cost and low physical adsorption efficiency of activated carbon injection (ACI) limited its application. In this study, an ultra-high efficiency (nearly 100%) catalyst sorbent-Sex/Activated carbon (Sex/AC) was synthesized and applied to remove Hg0 in the simulated flue gas, which exhibited 120 times outstanding adsorption performance versus the conventional activated carbon. The Sex/AC reached 17.98 mg/g Hg0 adsorption capacity at 160 °C under the pure nitrogen atmosphere. Moreover, it maintained an excellent mercury adsorption tolerance, reaching the efficiency of Hg0 removal above 85% at the NO and SO2 conditions in a bench-scale fixed-bed reactor. Characterized by the multiple methods, including BET, XRD, XPS, kinetic and thermodynamic analysis, and the DFT calculation, we demonstrated that the ultrahigh mercury removal performance originated from the activated Se species in Sex/AC. Chemical adsorption plays a dominant role in Hg0 removal: Selenium anchored on the surface of AC would capture Hg0 in the flue gas to form an extremely stable substance-HgSe, avoiding subsequent Hg0 released. Additionally, the oxygen-containing functional groups in AC and the higher BET areas promote the conversion of Hg0 to HgO. This work provided a novel and highly efficient carbon-based sorbent -Sex/AC to capture the mercury in coal combustion flue gas.
Due to its adverse impact on health, as well as its global distribution, long atmospheric lifetime and propensity for deposition in the aquatic environment and in living tissue, the US Environmental Protection Agency (US EPA) has classified mercury and its compounds as a severe air quality threat. Such widespread presence of mercury in the environment originates from both natural and anthropogenic sources. Global anthropogenic emission of mercury is evaluated at 2000 Mg year−1. According to the National Centre for Emissions Management (Pol. KOBiZE) report for 2014, Polish annual mercury emissions amount to approximately 10 Mg. Over 90% of mercury emissions in Poland originate from combustion of coal.
The purpose of this paper was to understand mercury behaviour during sub-bituminous coal and lignite combustion for flue gas purification in terms of reduction of emissions by active methods. The average mercury content in Polish sub-bituminous coal and lignite was 103.7 and 443.5 μg kg−1. The concentration of mercury in flue gases emitted into the atmosphere was 5.3 μg m−3 for sub-bituminous coal and 17.5 μg m−3 for lignite. The study analysed six low-cost sorbents with the average achieved efficiency of mercury removal from 30.6 to 92.9% for sub-bituminous coal and 22.8 to 80.3% for lignite combustion. Also, the effect of coke dust grain size was examined for mercury sorptive properties. The fine fraction of coke dust (CD) adsorbed within 243–277 μg Hg kg−1, while the largest fraction at only 95 μg Hg kg−1. The CD fraction < 0.063 mm removed almost 92% of mercury during coal combustion, so the concentration of mercury in flue gas decreased from 5.3 to 0.4 μg Hg m−3. The same fraction of CD had removed 93% of mercury from lignite flue gas by reducing the concentration of mercury in the flow from 17.6 to 1.2 μg Hg m−3. The publication also presents the impact of photochemical oxidation of mercury on the effectiveness of Hg vapour removal during combustion of lignite. After physical oxidation of Hg in the flue gas, its effectiveness has increased twofold.
A previously proposed technology incorporating TiO2 into common household fluorescent lighting was further tested for its Hg0 removal capability in a simulated flue-gas system. The flue gas is simulated by the addition of O2, SO2, HCl, NO, H2O, and Hg0, which are frequently found in combustion facilities such as waste incinerators and coal-fired power plants. In the O2 + N2 + Hg0 environment, a Hg0 removal efficiency (ηHg) greater than 95% was achieved. Despite the tendency for ηHg to decrease with increasing SO2 and HCl, no significant drop was observed at the tested level (SO2: 5–300 ppmv, HCl: 30–120 ppmv). In terms of NO and moisture, a significant negative effect on ηHg was observed for both factors. NO eliminated the OH radical on the TiO2 surface, whereas water vapor caused either the occupation of active sites available to Hg0 or the reduction of Hg0 by free electron. However, the negative effect of NO was minimized (ηHg > 90%) by increasing the residence time in the photochemical reactor. The moisture effect can be avoided by installing a water trap before the flue gas enters the Hg0 removal system.
Implications: This paper reports a novel technology for a removal of gas-phase elemental mercury (Hg0) from a simulated flue gas using TiO2-coated glass beads under a low-cost, easily maintainable household fluorescent light instead of ultraviolet (UV) light. In this study, the effects of individual chemical species (O2, SO2, HCl, NO, and water vapor) on the performance of the proposed technology for Hg0 removal are investigated. The result suggests that the proposed technology can be highly effective, even in real combustion environments such as waste incinerators and coal-fired power plants. 相似文献
A laboratory size spray dry scrubbing unit consisting of a spray dryer and a pulse Jet baghouse was used to study the effect of grinding recycle waste on SO2 removal across the spray dryer and on sorbent utilization. The equipment treats simulated flue gas with a dry flow rate of 1.5 m3 h?1 (stp) and utilizes an ultrasonic nozzle for atomization. The apparatus was initially tested over a broad range of operating conditions; a close agreement in SO2 removal was found with data from much larger units. The effect of grinding the FGD recycle material on the SO2 removal across the spray dryer was found to be great. Grinding the recycle material can enhance the SO2 removal efficiency to a level comparable to operation with a large excess of fresh lime. 相似文献
This article presents the results of an industrial-scale study (on 400 MWe lignite fired unit) of simultaneous NOx, SO2, and HgT removal in FGD absorber with oxidant injection (NaClO2) into flue gas. It was confirmed that the injection of sodium chlorite upstream the FGD (Flue Gas Desulfurization) absorber oxidize NO to NO2, Hg0 to Hg2+, and enhancing NOx and HgT removal efficiency from exhaust gas in FGD absorber. Mercury removal efficiency grows with the rise of degree of oxidation NO to NO2 and was limited by the phenomenon of re-emission. For NOx removal the most critical parameters is slurry pH and temperature. There was no negative effect on sulfur dioxide removal efficiency caused by oxidant injection in tested FGD absorber. Based on the data provided, NOx and HgT emissions can be reduced by adjusting the FGD absorber operating parameters combined with oxidant injection. 相似文献