Study on the removal of NO_x from simulated flue gas using acidic NaClO_2 solution

The study on the removal of NOx from simulated flue gas has been carded out in a lab-scale bubbling reactor using acidic solutions of sodium chlorite. Experiments were performed at various pH values and inlet NO concentrations in the absence or presence of SO2 gas at 45℃. The effect of SO2 on NO oxidation and NO2 absorption was critically examined. The oxidative ability of sodium chlorite was investigated at different pH values and it was found to be a better oxidant at a pH less than 4. In acidic medium, sodium chlorite decomposed into C102 gas, which is believed to participate in NO oxidation as well as in NO2 absorption. A plausible NOx removal mechanism using acidic sodium chlorite solution has been postulated. A maximum NOx removal efficiency of about 81% has been achieved.

Analysis of solid sorbents for control and removal processes for elemental mercury from gas streams:a review

Due to the restriction such as the Minamata Convention as well as the IED of the European Commission,mercury removal from flue gases of coal-fired power plants(CPP)is an increasingly important environmental issue.This makes this topic very crucial for both the energy industry and scientists.This paper shows how mercury arises from natural resources,i.e.,coals,through their combustion processes in CPP and considers the issue of mercury content in flue gases and solid-state coal combustion by-products.The main part of this paper presents a review of the solid sorbents available for elemental mercury control and removal processes,tested on a laboratory scale.The described solutions have a potential for wider usage in exhaust gas treatment processes in the energy production sector.These solutions represent the latest developments in the field of elemental mercury removal from gases.The authors present an overview of the wide range of solid sorbents and their modifications intended to increase affinity for Hg^(0).Among the presented sorbents are the wellknown activated carbon solutions but also novel modifications to these and other innovative sorbent proposals based on,e.g.,zeolites,biochars,other carbon-based materials,metal-organic frameworks.The paper presents a wide range of characteristics of the described sorbents,as well as the conditions for the Hg^(0) removal experiments summarizing the compendium of novel solid sorbent solutions dedicated to the removal of elemental mercury from gases.

Study on the removal of Hg^0 from flue gas by coal dry powder gasification coarse slag

The prevention and treatment of mercury in coal-fired power plants has always been the focus and difficulty.How to control the pollution of mercury to human body and ecological environment quickly and effectively is a hot research topic nowadays.As a low cost and potential adsorbent,there is a huge space for the development of coal dry powder gasification coarse slag.In this paper,Mercury osmotic tubes are heated by water bath tank as mercury source,and the scavenging effect of adsorbent on Mercury monomer under different influence conditions is explored.The adsorbent plays an important role in adsorption of mercury monomer because of its special active sites on the surface.The reason is that the adsorbent surface is rich in carboxyl group,hydroxyl functional group,combined with mercury to form complexes.This shows that chemical adsorption facilitates the adsorption process.

In-situ measurement and distribution of flue gas mercury for a utility PC boiler system

The in-situ instrumentation technique for measuring mercury and itsspeciation downstream a utility 100 MW pulverized coal (PC) fired boiler system was developed andconducted by the use of the Ontario hydro method (OHM) consistent with American standard test methodtogether with the semi-continuous emissions monitoring (SCEM) system as well as a mobile laboratoryfor mercury monitoring. The mercury and its speciation concentrations including participate mercuryat three locations of before air preheater, before electrostatic precipitator (ESP) and after ESPwere measured using the OHM and SCEM methods under normal operation conditions of the boiler systemas a result of firing a bituminous coal. The vapor-phase total mercury Hg(VT) concentration declinedwith the decrease of flue gas temperature because of mercury species transformation from oxidizedmercury to particulate mercury as the flue gas moved downstream from the air preheater to the ESPand after the ESP. A good agreement for Hg°, Hg^(2+) and Hg( VT) was obtained between the twomethods in the ash-free area. But in the dense particle-laden flue gas area, there appeared to be abig bias for mercury speciation owing to dust cake formed in the filter of OHM sampling probe. Theparticulateaffinity to the flue gas mercury and the impacts of sampling condition to accuracy ofmeasure were discussed.

Mercury Speciation of Flue Gas Desulphurization By-Products in Coal-Fired Power Plants in China

The aim of this study was to develop and examine the morphology and distribution of mercury (Hg) in flue gas desulfurization (FGD) by-product. Mercury in the coal of coal-fired power plants is concentrated in the by-products of desulfurization process, and it is widely used as an additive in cement, building materials and other industries. Due to the different stability of various forms of mercury in the environment, subsequent use of products containing desulfurization by-product additives will continue to be released into the environment, endangering human health. Therefore, it is very necessary to study the form and distribution of mercury in the by-products of desulfurization in coal-fired power plants to provide a theoretical basis for subsequent harmless treatment. For content and morphology of mercury analysis, 1 sample of dry FGD ash and 6 samples of wet FGD gypsum were analyzed. The total 7 samples were extracted using a modification of sequential chemical extractions (SCE) method, which was employed for the partitioning Hg into four fractions: water soluble, acid soluble, H2O2 soluble, and residual. The Hg analysis was done with United States Environmental Protection Agency (USEPA) method 7471B. Comparing with the wet FGD gypsums of coal-fired boilers, the total Hg content in the dry FGD by-product was as high as 1.22 mg/kg, while the total Hg content in the FGD gypsum is 0.23 - 0.74 mg/kg, which was 2 times over the wet FGD gypsum. The concentration of water soluble Hg in the dry FGD by-product was the highest amount (0.72 mg/kg), accounting for 59.02% of the total mercury. While residual Hg content was 0.16 mg/kg, only about 13.11% of the total mercury. Mercury content in FGD gypsum was expressed in the form of ρ (residual Hg) > ρ (H2O2 soluble Hg) > ρ (water soluble Hg) > ρ (acid soluble Hg). The morphology and distribution of mercury in FGD by-products is supposed to be analyzed before utilization, and the impact of mercury on the environment should be considered.

A novel carbon trap sampling system for coal-fired flue gas mercury measurement

A novel carbon trap sampling system for gas-phase mercury measurement in flue gas is developed, including the high efficient sorbents made of modified biomass cokes and high precision sorbent traps for measuring particle-bound and total vapor-phase mercury in flue gas. A dedusting device is installed to collect fine fly ash for reducing the measurement errors. The thorough comparison test of mercury concentration in flue gas is conducted between the novel sampling system and the Ontario hydro method （OHM） in a 6 kW circulating fluidized bed combustor. Mercury mass balance rates of the OHM range from 95.47% to 104.72%. The mercury breakthrough rates for the second section of the sorbent trap are all below 2%. The relative deviations in the two test cases are in the range of 15. 96% to 17. 56% under different conditions. The verified data suggest that this novel carbon trap sampling system can meet the standards of quality assurance and quality control required by EPA Method 30B and can be applied to the coal-fired flue gas mercury sampling system.

Heteroatoms doped iron oxide-based catalyst prepared from zinc slag for efficient selective catalytic reduction of NO_(x) with NH_(3)

Excessive emissions of nitrogen oxides from flue gas have imposed various detrimental impacts on environment,and the development of deNO_(x) catalysts with low-cost and high performance is an urgent requirement.Iron oxide-based material has been explored for promising deNO_(x) catalysts.However,the unsatisfactory low-temperature activity limits their practical applications.In this study,a series of excellent low-temperature denitrification catalysts(Ha-FeO_(x)/yZS)were prepared by acid treatment of zinc slag,and the mass ratios of Fe to impure ions was regulated by adjusting the acid concentrations.Ha-FeO_(x)/yZS showed high denitrification performance(>90%)in the range of 180–300℃,and the optimal NO conversion and N2 selectivity were higher than 95%at 250℃.Among them,the Ha-FeO_(x)/2ZS synthesized with 2 mol/L HNO3 exhibited the widest temperature window(175–350℃).The excellent denitrification performance of Ha-FeO_(x)/yZS was mainly attributed to the strong interaction between Fe and impurity ions to inhibit the growth of crystals,making Ha-FeO_(x)/yZS with amorphous structure,nice fine particles,large specific surface area,more surface acid sites and high chemisorbed oxygen.The in-situ DRIFT experiments confirmed that the SCR reaction on the Ha-FeO_(x)/yZS followed both Langmuir-Hinshelwood(L-H)mechanism and Eley-Rideal(E-R)mechanism.The present work proposed a high value-added method for the preparation of cost-effective catalysts from zinc slag,which showed a promising application prospect in NO_(x) removal by selective catalytic reduction with ammonia.

Study on Flue Gas Desulfurization Process with Selective SO2 Removal by N-formylmorpholine

Absorptive separation for resource utilization by selective SO2 removal from flue gas is a potential method applicable in practice. A flue gas desulfurization process for SO2 utilization by selective absorption in a lab-scale absorption tower at atmospheric pressure using N-formylmorpholine (NFM) as the absorbent is developed to capture and concentrate the SO2 from flue gas, in which the CO2 content is several orders higher than that of SO2. The investigation of the effects of different operating conditions on the SO2 removal efficiency shows that the SO2 removal efficiency can be obviously enhanced by increasing NFM concentration, or decreasing the absorption temperature, the superficial gas velocity, the gas-liquid ratio, or the SO2 concentration in absorption solution. Under the optimum operating conditions (covering a temperature of 40 °C, a superficial gas velocity of <0.0165 m/s, a gas-liquid ratio of 200—250, a SO2 concentration in lean NFM solution of 0—10 mg/L, and a NFM concentration of 3 mol/L), the SO2 removal rate reaches over 99.5% while the absorption of CO2 is negligible. Similarly, the SO2 removal rate is as high as 99.5% obtained in consecutive absorption-desorption cycles. Desorption experiment results indicate that the absorption of sulfur dioxide is completely reversible and the release of SO2 from NFM is very easy and rapid at 104 °C. The absorption simulation result for desulfurization of flue gas vented from the industrial catalytic cracking regenerator shows that 98.0% of SO2 can be absorbed in the absorber and most of them are released in the desorber. The experimental and simulated results show that the desulfurization ability and regenerability of NFM solution is encouraging for the development of FGD process to capture the SO2 from flue gas.

Evaluation of flue gas desulfurization gypsum as a low-cost precipitant for phosphorus removal from anaerobic digestion effluent filtrate

Land application of anaerobic digestion(AD)effluent as a fertilizer is desirable for nutrient recycling,but often supplies excess phosphorus(P),which contributes to surface water eutrophication.Reducing the P content in AD effluent filtrate using calcium(Ca)treatment prior to land application is a potential strategy for improving effluent disposal and meeting the discharge standard.This study took flue gas desulphurization(FGD)gypsum,a by-product of coal-fired power plants,as a low-cost Ca source,and combined with traditional phosphorus removal agents to achieve high phosphorus removal efficiency with less chemical cost.As the results showed,FGD gypsum dosages of 20 mmol/L Ca(3.44 g/L)and 40 mmol/L Ca(6.89 g/L)removed up to 97.1%of soluble P(initially 102.8 mg/L)within 60-90 minutes.Combining FGD gypsum treatment with traditional chemical treatments using calcium hydroxide[Ca(OH)2]or ferric chloride(FeCl3)could achieve>99%P removal with reduced chemical costs.This study demonstrated that FGD gypsum is an efficient calcium-based precipitant for phosphorus removal,offering a cost-effective and sustainable approach to enhance wastewater treatment practices and meet discharge standards in wastewater management.

Study on influencing factors of Baosteel’s swirl-jet sintering FGD technology

This paper introduced the research background and technical features of Baosteel＇ s sintering flue gas desulfurization （FGD）. It was also named swirl-jet-absorbing wet limestone-gypsum sintering FGD technology. By means of industrial online pilot plants, through continuous running and orthogonal tests, the effects of various influencing factors on SO2 removal efficiency of Baosteel sintering flue gas desulgurization （BSFGD） were studied carefully. The results indicate that the slurry pH value,temperature （T） and flow rate （Q） of inlet flue gas,liquid level （H） in the absorber and flue gas jet velocity （V） are the main influencing factors. Furthermore, when pH is between 5.0 and 5.5, H is between 4.2 m and 4.3 m, Q is 43 000 m3/h, T is below 65℃ and V is between 20 m/s and 28 m/s, the best desulfurization efficiency can be available.

Distribution and Accumulation of Major and Trace Elements in Gypsum Samples from Lignite Combustion Power Plant

Flue gas containing volatile elements, fine fly ash particulates not retained by particle control devices, and limestone are the most important sources of trace and major elements (TMEs) in wet flue gas desulphurization (WFGD) gypsum. In this study, samples of gypsum slurry were separated into fine and coarse fractions. Multi-elemental analysis of 45 elements in the different size fractions of gypsum, slurry waters and lignite were performed by k0-INAA (k0-instrumental neutron activation analyses). The study found that the volatile elements (Hg, Se and halogens) in the flue gas accumulate in the fine fractions of gypsum. Moreover, the concentrations of most TMEs are considerably higher in the fine fractions compared to the coarse fractions. The exceptions are Ca and Sr that primarily originate from the limestone. Variations of TMEs in the finer fractions are dependent on the presence of CaSO4·2H2O that is the main constituent of the coarse fraction. Consequently, the content of TMEs in the fine fraction is highly dependent on the efficiency of separating the fine fraction from the coarse fraction. Separation of the finer fraction, representing about 10% of the total gypsum, offers the possibility to remove effectively TMEs from WFGD slurry.

Experimental research on influencing factors of wet removal of NO from coal-fired flue gas by UV/H_2O_2 advanced oxidation process

Wet removal of NO from coal-fired flue gas by UV/H2O2 Advanced Oxidation Process (AOP) were investigated in a self-designed UV-bubble reactor. Several main influencing factors (UV intensity, H2O2 initial concentration, initial pH value, solution temperature, NO initial concentration, liquid-gas ratio and O2 percentage content) on the NO removal efficiency were studied. The results showed that UV intensity, H2O2 initial concentration, NO initial concentration and liquid-gas ratio are the main influencing factors. In the best conditions, the highest NO removal efficiency by UV/H2O2 advanced oxidation process could reach 82.9%. Based on the experimental study, the influencing mechanism of the relevant influencing factors were discussed in depth.

Hierarchical Ag-SiO_2@Fe_3O_4magnetic composites for elemental mercury removal from non-ferrous metal smelting flue gas

Hierarchical Ag-SiO_2@Fe_3O_4 magnetic composites were selected for elemental mercury(Hg^0) removal from non-ferrous metal smelting flue gas in this study. Results showed that the hierarchical Ag-SiO_2@Fe_3O_4 magnetic composites had favorable Hg^0 removal ability at low temperature. Moreover, the adsorption capacity of hierarchical magnetic composite is much larger than that of pure Fe_3O_4 and SiO_2@Fe_3O_4. The Hg^0 removal efficiency reached the highest value as approximately 92% under the reaction temperature of 150°C, while the removal efficiency sharply reduced in the absence of O_2. The characterization results indicated that Ag nanoparticles grew on the surface of SiO_2@Fe_3O_4 support. The large surface area of SiO_2 supplied efficient reaction room for Hg and Ag atoms. Ag–Hg amalgam is generated on the surface of the composites. In addition, this magnetic material could be easily separated from fly ashes when adopted for treating real flue gas, and the spent materials could be regenerated using a simple thermal-desorption method.

Mercury removal from coal combustion flue gas by modified fly ash

Fly ash is a potential alternative to activated carbon for mercury adsorption. The effects of physicochemical properties on the mercury adsorption performance of three fly ash samples were investigated. X-ray fluorescence spectroscopy, X-ray photoelectron spectroscopy, and other methods were used to characterize the samples. Results indicate that mercury adsorption on fly ash is primarily physisorption and chemisorption. High specific surface areas and small pore diameters are beneficial to efficient mercury removal. Incompletely burned carbon is also an important factor for the improvement of mercury removal efficiency, in particular. The C-M bond, which is formed by the reaction of C and Ti, Si and other elements, may improve mercury oxidation. The samples modified with CuBr2 , CuCl 2 and FeCl3 showed excellent performance for Hg removal, because the chlorine in metal chlorides acts as an oxidant that promotes the conversion of elemental mercury （Hg0） into its oxidized form （Hg2＋）. Cu2＋ and Fe3＋ can also promote Hg 0 oxidation as catalysts. HCl and O2 promote the adsorption of Hg by modified fly ash, whereas SO2 inhibits the Hg adsorption because of competitive adsorption for active sites. Fly ash samples modified with CuBr2 , CuCl2 and FeCl3 are therefore promising materials for controlling mercury emissions.

Experimental Study of the Removal of Fine Particulate Matter and Moisture from Flue Gas

Liquid desiccant systems are promising methods to recover water and waste heat simultaneously from flue gas.Prior research found that the reduction of particulate matter could occur during the absorption processes.In the present paper,experiments were carried out to explore the effect of removing fine particulate matter(PM_(2.5))in a liquid desiccant dehumidifier.Aqueous calcium chloride(CaCl_(2))was used as the desiccant in the experiments.The discrepancies in mass and energy conservation were within±10%and±15%,respectively,which showed the good reliability of the experimental results.Additionally,23.5%–46.0%of the PM_(2.5)and 23.9%–45.1%of the moisture in the flue gas were removed.By comparing the desiccant solution and water,it was found that they could minimally remove PM_(2.5)through washing the flue gas.Regardless of whether the flue gas was dehumidified by water or the solution,the removal fractions of PM_(2.5)of these two methods could be very close if they achieve the same fraction of moisture removal.From the results of a parameter analysis,it was found that the removal fraction of PM_(2.5)was nearly proportional to the removal fraction of moisture within the experimental range.

Mercury transportation in soil via using gypsum from flue gas desulfurization unit in coal-fired power plant

The mercury flux in soils was investigated, which were amended by gypsums from flue gas desulphurization （FGD） units of coal- fired power plants. Studies have been carried out in confined greenhouses using FGD gypsum treated soils. Major research focus is uptakes of mercury by plants, and emission of mercury into the atmosphere under varying application rates of FGD gypsum, simulating rainfall irrigations, soils, and plants types. Higher FGD gypsum application rates generally led to higher mercury concentrations in the soils, the increased mercury emissions into the atmosphere, and the increased mercury contents in plants （especially in roots and leaves）. Soil properties and plant species can play important roles in mercury transports. Some plants, such as tall fescue, were able to prevent mercury from atmospheric emission and infiltration in the soil. Mercury concentration in the stem of plants was found to be increased and then leveled off upon increasing FGD gypsum application. However, mercury in roots and leaves was generally increased upon increasing FGD gypsum application rates. Some mercury was likely absorbed by leaves of plants from emitted mercury in the atmosphere.

Hg^0 removal from flue gas over different zeolites modified by Fe Cl_3

The elemental mercury removal abilities of three different zeolites（Na A, Na X, HZSM-5）impregnated with iron（Ⅲ） chloride were studied on a lab-scale fixed-bed reactor. X-ray diffraction, nitrogen adsorption porosimetry, Fourier transform infrared spectroscopy,X-ray photoelectron spectroscopy, and temperature programmed desorption（TPD） analyses were used to investigate the physicochemical properties. Results indicated that the pore structure and active chloride species on the surface of the samples are the key factors for physisorption and oxidation of Hg0, respectively. Relatively high surface area and micropore volume are beneficial to efficient mercury adsorption. The active Cl species generated on the surface of the samples were effective oxidants able to convert elemental mercury（Hg0）into oxidized mercury（Hg2＋）. The crystallization of Na Cl due to the ion exchange effect during the impregnation of Na A and Na X reduced the number of active Cl species on the surface, and restricted the physisorption of Hg0. Therefore, the Hg0 removal efficiencies of the samples were inhibited. The TPD analysis revealed that the species of mercury on the surface of Fe Cl3–HZSM-5 was mainly in the form of mercuric chloride（Hg Cl2）, while on Fe Cl3–Na X and Fe Cl3–Na A it was mainly mercuric oxide（HgO）.

Elemental mercury removal from coal gas by CeMnTi sorbents and their regeneration performance

Ce and Mn modified TiO_(2) sorbents(CeMnTi) were prepared by a co-precipitation method,and their ability to remove elemental mercury from coal gas in a fixed bed reactor was studied.Based on results of Brunauer-Emmett-Teller(BET),X-ray diffraction(XRD),scanning electron microscope(SEM),and X-ray photoelectron spectroscopy(XPS) studies,the modification mechanisms of the CeMnTi sorbents are discussed.Mn doping improved the specific surface area and dispersion of cerium oxides on the sorbent surface,while Ce doping increased the proportion of Mn^(4+)in manganese oxides by a synergetic effect between manganese oxides and cerium oxides.The effects of the active component,temperature,and coal gas components on the mercury removal performance of the sorbents were investigated.The results showed that the CeMnTi sorbents exhibited high mercury removal efficiency.Ce_(0.2)Mn_(0.1)Ti adsorbed 91.55% elemental mercury from coal gas at 160℃.H2 S and O2 significantly improved the ability of sorbents to remove mercury.Part of the H2_(S) formed stable sulfates or sulfites through a series of oxidation reaction chains on the sorbent surface.HCl also improved the mercury removal performance,but reduced the promotion effect of H2_(S) for mercury removal when coexisting with H2_(S).CO and H2 had a minor inhibitory effect on mercury adsorption.The recycling performance of the sorbents was investigated by thermal regeneration.The thermal decomposition of the used sorbents indicated that mercury compounds were present mainly in the form of HgO and HgS,and higher temperature was beneficial for regeneration.The formation of sulfates and sulfites in the presence of H2_(S) led to a decrease in mercury removal efficiency.

An Experimental Study on Oxidized Mercury Adsorption by Bromide Blended Coal Combustion Fly Ash

The application of forced mercury oxidation technology would lead to an increase of Hg^(2+)concentration in the flue gas.Although Hg^(2+)can be easily removed in the WFGD,the mercury re-emission in the WFGD can decrease the total removal of mercury from coal-fired power plants.Hence,it is necessary to control Hg^(2+)concentration in the devices before the WFGD.Fly ash adsorbent is considered as a potential alternative for commercial activated carbon adsorbent.However,the adsorption efficiency of the original fly ash is low.Modification procedure is needed to enhance the adsorption performance.In this study,the adsorption of Hg^(2+)by brominated fly ash was studied.The fly ash was collected from the full-scale power plant utilizing bromide-blended coal combustion technology.The brominated fly ash exhibited excellent performance for Hg^(2+)removal.The flue gas component HBr and SO_(2)could improve adsorbent’s performance,while HCl would hinder its adsorption process.Also,it was demonstrated by Hg-TPD experiments that the adsorbed Hg^(2+)mainly existed on the fly ash surface in the form of HgBr_(2).In summary,the brominated fly ash has a broad application prospect for mercury control.

Mechanism Research of Hg^0 Oxidation by Pulse Corona Induced Plasma Chemical Process

The oxidation of Hg^0 by Pulse Corona Induced Plasma Chemical Process （PPCP） was investigated through changing discharge voltage, pulse frequency and gas compositions. Experimental results indicate that active radicals including O, O3 and OH can contribute to the oxidation of elemental mercury. 10 kV is the onset voltage, and the higher voltage the better removal efficiency. While with the increase of pulse frequency, the Hg^0 concentration falls rapidly at first but then rises rapidly. The best oxidation condition is at 12 kV and 600-800 PPS. Adding O2 can significantly promote oxidation. With NO and SO2 existed, there is an inhibition of mercury oxidation, and NO has a greater influence. Addition of HCl can promote oxidation slightly but affect the initial concentration of mercury significantly. Little moisture content can promote oxidation, while too much H2O can not only resist the oxidation, but also affect the initial concentration of mercury. The mercury oxidation rate can increase to 97.95% at 12 kV/800 PPS with the system of 10% 02/3% H2O/50 ppm HCI. However, mercury oxidation efficiency can reduce down to 20% with 100 ppm NO added.