Removal Of Flue Gas Research Articles

Removal of Hg0, NO, and SO2 by the surface dielectric barrier discharge coupled with Mn/Ce/Ti-based catalyst.

In this study, power parameters (power, frequency, and voltage), initial Hg0 concentration, and residence time are investigated for the removal of the increased Hg0 concentration via surface dielectric barrier discharge (SDBD). The synergistic effect of a Mn/Ce/Ti catalyst with SDBD is verified with a mixture of flue gas (Hg0, NO, and SO2). Results show that Hg0 oxidation efficiency has an optimal frequency, which declines as the input voltage increases. The amplification of the Hg0 removal efficiency decreases as voltage increases. The effect of the initial Hg0 concentration gradually decreases as the peak voltage increases. The residence time slightly affects the Hg0 removal efficiency at a high peak voltage. The cooling water temperature behaves differently on Hg0 oxidation under high and low voltages. X-ray photoelectron spectroscopy (XPS) reveals the relative atomic concentrations of Mn2+ and Mn3+ in the Mn-TiO2 and Mn-Ce-TiO2 catalysts are 66.84% and 65.80%, respectively, which indicate that Ce addition will not affect surface Mn. Mn has a limited catalytic action on the removal of flue gas with and without SDBD. Nevertheless, SDBD can stimulate the oxygen storage capacity of Mn to increase the NO2 conversion rate. Mn-Ce-TiO2 greatly improves the removal efficiencies of NO and SO2 because of the existence of the redox pairs of Mn4+/Mn3+, Ce4+/Ce3+, and Ti4+/Ti3+. However, the three catalysts slightly differ on Hg0 removal when combined with SDBD, indicating that the effect of the catalyst was weakened after SDBD was added.

Synergistic effects of Fe-Mn binary oxide for gaseous arsenic removal in flue gas

High-efficient and economic sorbents are highly desired for arsenic (As) emission control in flue gas from coal-fired power plant. A series of Fe-Mn binary oxides were prepared by a facile method, and their behaviors for gaseous arsenic removal in flue gas were investigated. The binary oxide exhibited a remarkable synergistic effect for arsenic removal compared with Mn or Fe monometallic oxide. The possible effects of CO2, NO, SO2, and O2 on the removal performance were also studied. The adsorption ability was excellent and stable in simulated flue gas conditions. X-ray photoelectron spectroscopy (XPS) and high-performance liquid chromatography atomic fluorescence spectroscopy (HPLC−AFS) coupling system were applied to analyze the species of surface-adsorbed arsenicals and soluble arsenicals. It was confirmed that the good sorption performance resulted from oxidation of As2O3 (As(III)) to As2O5 (As(V)) by Mn oxide and followed by efficient adsorption of As(V) on Fe oxide. Considering the toxicity of pentavalent arsenicals is lower than trivalent arsenicals, the oxidation of arsenic compounds can not only enhance its removal capacity but also decrease the toxicity of arsenicals after capture.

The coupling use of electro-chemical and advanced oxidation to enhance the gaseous elemental mercury removal in flue gas

A novel diffusion electro-chemical combined advanced oxidation reactor offers potential for elemental mercury (Hg0) removal in flue gas and shown excellent performance. This study introduced an ultraviolet light into the electric catalytic system to form an UV-electric oxidation system to strengthen Hg0 removal. Hg0 removal efficiency in the combined UV-electric oxidation system reached up to 65%. Hg0 is excited by UV lamp with a wavelength of 253.7 nm, and a very small amount of oxygen contained in high-purity nitrogen can still participate in Hg0 oxidation reaction. In addition, the Fenton method has also been introduced into the simple electrolysis system. Both the above combined system can improve the efficiency of Hg0 removal. The electro-chemical GDE was characterized by SEM, BET, and contact angle and gas permeability. The electro-chemical and advanced oxidation process (Fenton method and UV illumination) combined within a system or individually in series were explored the different influencing factors. The gaseous elemental mercury removal mechanism of the combined electro-chemical and advanced oxidation was investigated via combining the experimental data and theoretical reasoning. Electrochemical coupling with other advanced oxidation technologies is a promising technology.

Investigation of Droplets Distribution and Reaction Kinetics on SO2 Removal in Flue Gas via Venturi Scrubber

This paper investigates the problem of gas-liquid flow SO2 removal in nonquiescent flue gas. Using venturi scrubber as the prototype, the population balance model (PBM) combined with the CFD is implemented to characterize the droplets behaviors. Discrete methods as class model (CM) and various quadrature-based moment models (QBMMs) are applied to numerically solve the population balance equations (PBEs). Taking NaOH solution as the reaction kinetics, the sulfur removal efficiency simulation with CM and different QBMMs methods is validated through the operation measurements. The comparison results show that the CM can achieve better accuracy with more bins, which showed the minimal error 3.6%, consisting 30 bins. However, the computational time of the CM is approximately 19.3 times as long as QBMMS. Among the QBMMs, the ECQMOM approach enjoys the best balance between the simulation efficiency and accuracy, while EQMOM shows the least computational load and CQMOM wins the minimal calculation precision. This result will provide sufficient reference for engineers working in the field of the droplets distribution in the venturi scrubber design.

Numerical modelling of sulfur dioxide absorption for spray scrubbing

An increased concern for the environment and the stricter regulations necessitate the development of new technologies that curtail the harmful emissions from industry, energy and power sectors. Wet flue gas desulfurisation in scrubbers is a common approach for reducing the emissions of sulfur oxides, which have a detrimental effect on human health and nature. Although the idea of using seawater as a scrubbing liquid is not a novel one, recent studies on the advantages of seawater absorption and requests from the maritime sector prompted new investigations of its usage and the development of advanced modelling tools. Absorption of sulfur dioxide in the spray is a complex process consisting of two main phenomena. The first one is the interphase mass transfer of pollutants due to concentration differences, with mass transfer coefficient being the crucial factor determining the absorption dynamics. Another essential part is the chemical reactions of the absorbed pollutants in the aqueous phase, which enhance the absorption capabilities. In this work, a novel model for the absorption of sulfur dioxide in spray scrubbers is presented. It is based on a single droplet, concentrated-parameter approach that takes into account mass transfer coefficients and the in-droplet chemistry of the absorbed pollutants for pure water and seawater. The model was implemented in the computational fluid dynamics framework and validated against the available experimental data, with the relative error for removal efficiency within the ±10% for most of the operating points—a satisfactory result considering the uncertainties in the experimental setup. Therefore, with the results showing that the model is capable of correctly predicting the sulfur dioxide removal from flue gases, it presents a useful tool for designing more sustainable flue gas removal equipment.

CFD simulation of fine particle removal in flue gas condensing heat exchanger

Considering the obvious difference between dry and wet deposition, an original simplified model suitable for the particle removal process in the condensing heat exchanger was developed. With the help of user-defined functions, the proposed model was implemented into ANSYS FLUENT. The laboratory-scale experiments were performed to verify this simplified model. The numerical results were in good agreement with the experimental measurements, and the maximum error was within 8%. Using the CFD simulations, the effects of particle size and particle wettability on the removal of particles were analyzed. The results showed that the removal efficiency, growth rate of mean diameter and the proportion of grown particles increased with the decrease of contact angle. And they first decreased then increased with the increase of particle size. But the enhancement of removal efficiency was limited when the contact angle was small enough. The condensation growth transformed the particle system from monodisperse to polydisperse. The outlet particle size distribution could become bimodal distribution, which implied the potential for integrating acoustic agglomeration and condensing heat exchanger. However, the combined system should be well designed; otherwise, the bimodal distribution would degenerate.

Experimental Study on the Influence of Surface Characteristics of Activated Carbon on Mercury Removal in Flue Gas

The influences of the physical features and chemical properties of activated carbon on Hg0 adsorption were investigated. The textural characteristics of the samples were studied by Brunauer–Emmett–...

Enhanced activity and SO2 resistance of Co‐modified CeO2‐TiO2 catalyst prepared by facile co‐precipitation for elemental mercury removal in flue gas

The Co‐modified CeO2‐TiO2 catalyst prepared by facile co‐precipitation was used for efficient elemental mercury oxidation in flue gas. Results indicated that Co doping greatly enhanced the activity and SO2 resistance of the CeO2‐TiO2 catalyst. In the presence of 5% O2, 500 ppm NO, 800 ppm SO2 and 3% H2O at 200 °C, the Hg0 removal efficiency of CeCo3/Ti could maintain at about 87% for a relatively long time. Characterizations of catalysts (BET, XRD, Raman spectroscopy, TEM, H2‐TPR, O2‐TPD, XPS, TG‐MS and SO2‐DRIFTS) were carried out to reveal the mechanism of Co modification on the redox ability, SO2 resistance and resultant mercury oxidation removal performance of catalyst. It was found that an interaction of Ce with Co promoted the dispersion of CeO2, increased chemisorbed oxygen concentration, and improved the oxygen storage capacity and the reducibility of catalyst, which was beneficial to the improvement of Hg0 oxidation removal. Hg0 would adsorb onto the catalyst and react with surface active oxygen species replenished by gas‐phase O2 to be oxidized via Mars‐Maessen mechanism. SO2 consumed the surface active oxygen species and resulted in the reduction of Ce4+ to Ce3+, which induced the deactivation of catalyst. The introduced Co in CeO2‐TiO2 catalyst exerted the function of protecting Ce4+ from being poisoned by SO2 and thus promoted the sulfur resistance and Hg0 removal performance of the catalyst in the presence of SO2.

Industrial Application of Non-thermal Plasma (NTP) for Mercury and Dioxin Removal in Flue Gas

At present, there is an urgent demand for mercury and dioxin pollution control technology, internationally. It is necessary to find a solution other than the activated carbon adsorption process. In recent years, our self-developed low temperature plasma coupling system has been applied for mercury and dioxin removal in the flue gas, the system is composed of corona discharge plasma reactor and ceramic nano-material adsorption tank. The parameters of the plasma are 35-40kV, 400-450A, 1000Hz. The saturated adsorption capacity of ceramic nano-materials for Hg2+ is more than 5156μ g(Hg2+)/g. Pilot plant testes have been conducted in several industries, including collaborative disposal of cement kiln, medical waste incineration, recovery of waste mercury catalyst, recycling of waste fluorescent tubes, and achieved ideal result (Hg removal efficiency > 95%). It is expected to be an economical and efficient technology for mercury and dioxin removal, with great promotion value and social significance.

Isolation and characterization of Chlorella sp. mutants with enhanced thermo- and CO2 tolerances for CO2 sequestration and utilization of flue gases

BackgroundThe increasing emission of flue gas from industrial plants contributes to environmental pollution, global warming, and climate change. Microalgae have been considered excellent biological materials for flue gas removal, particularly CO2 mitigation. However, tolerance to high temperatures is also critical for outdoor microalgal mass cultivation. Therefore, flue gas- and thermo-tolerant mutants of Chlorella vulgaris ESP-31 were generated and characterized for their ability to grow under various conditions.ResultsIn this study, we obtained two CO2- and thermo-tolerant mutants of Chlorella vulgaris ESP-31, namely, 283 and 359, with enhanced CO2 tolerance and thermo-tolerance by using N-methyl-N-nitro-N-nitrosoguanidine (NTG) mutagenesis followed by screening at high temperature and under high CO2 conditions with the w-zipper pouch selection method. The two mutants exhibited higher photosynthetic activity and biomass productivity than that of the ESP-31 wild type. More importantly, the mutants were able to grow at high temperature (40 °C) and a high concentration of simulated flue gas (25% CO2, 80–90 ppm SO2, 90–100 ppm NO) and showed higher carbohydrate and lipid contents than did the ESP-31 wild type.ConclusionsThe two thermo- and flue gas-tolerant mutants of Chlorella vulgaris ESP-31 were useful for CO2 mitigation from flue gas under heated conditions and for the production of carbohydrates and biodiesel directly using CO2 from flue gas.

Bio-oxidation of Elemental Mercury into Mercury Sulfide and Humic Acid-Bound Mercury by Sulfate Reduction for Hg0 Removal in Flue Gas.

Bioconversion of elemental mercury (Hg0) into immobile, nontoxic, and less bioavailable species is of vital environmental significance. Here, we investigated bioconversion of Hg0 in a sulfate-reducing membrane biofilm reactor (MBfR). The MBfR achieved effective Hg0 removal by sulfate bioreduction. 16 S rDNA sequencing and metagenomic sequencing revealed that diverse groups of mercury-oxidizing/sulfate-reducing bacteria (Desulfobulbus, Desulfuromonas, Desulfomicrobium, etc.) utilized Hg0 as the initial electron donor and sulfate as the terminal electron acceptor to form the overall redox. These microorganisms coupled Hg0 bio-oxidation to sulfate bioreduction. Analysis on mercury speciation in biofilm by sequential extraction processes (SEPs) and inductively coupled mass spectrometry (ICP-MS) and by mercury temperature programmed desorption (Hg-TPD) showed that mercury sulfide (HgS) and humic acid-bound mercury (HA-Hg) were two major products of Hg0 bio-oxidation. With HgS and HA-Hg comprehensively characterized by X-ray diffraction (XRD), excitation-emission matrix spectra (EEM), scanning electron microscopy-energy disperse spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR), it was proposed that biologically oxidized mercury (Hg2+) further reacted with biogenic sulfides to form cubically crystallized metacinnabar (β-HgS) extracellular particles. Hg2+ was also complexed with functional groups -SH, -OH, -NH-, and -COO- in humic acids from extracellular polymeric substances (EPS) to form HA-Hg. HA-Hg may further react with biogenic sulfides to form HgS. Bioconversion of Hg0 into HgS was therefore achieved and can be a feasible biotechnique for flue gas demercuration.

Investigation of mass and heat transfer transitional processes of water droplets in wet gas flow in the framework of energy recovery technologies for biofuel combustion and flue gas removal

In this paper, complex processes of water droplet heat and mass transfer are analyzed in a cycle of condensing, transitional evaporation and equilibrium evaporation regimes during phase change which occurs on a droplet's surface. The dynamics of a heated droplet's surface temperature is directly related to the change in the regimes. The definition of the dynamics is based on a numerical iterative scheme which depends on the balance of a droplet surface's heat flux. In this scheme, the energy of phase change and external heat transfer are combined as well as the internal heat transfer occurring in droplets. The numerical investigation results of the water droplets' phase change were used as a basis while defining the inputs provided by the droplet slipping and the radiation absorbed in the flue gas within the interactions between the processes of complex transitional transfers. For this investigation, the conditions have been set to be typical for heat utilization technologies and biofuel furnaces used in flue gas removal.

Mechanism of Mercury Adsorption and Oxidation by Oxygen over the CeO₂ (111) Surface: A DFT Study.

CeO2 is a promising catalytic oxidation material for flue gas mercury removal. Density functional theory (DFT) calculations and periodic slab models are employed to investigate mercury adsorption and oxidation by oxygen over the CeO2 (111) surface. DFT calculations indicate that Hg0 is physically adsorbed on the CeO2 (111) surface and the Hg atom interacts strongly with the surface Ce atom according to the partial density of states (PDOS) analysis, whereas, HgO is adsorbed on the CeO2 (111) surface in a chemisorption manner, with its adsorption energy in the range of 69.9–198.37 kJ/mol. Depending on the adsorption methods of Hg0 and HgO, three reaction pathways (pathways I, II, and III) of Hg0 oxidation by oxygen are proposed. Pathway I is the most likely oxidation route on the CeO2 (111) surface due to it having the lowest energy barrier of 20.7 kJ/mol. The formation of the HgO molecule is the rate-determining step, which is also the only energy barrier of the entire process. Compared with energy barriers of Hg0 oxidation on the other catalytic materials, CeO2 is more efficient at mercury removal in flue gas owing to its low energy barrier.

The Behaviors and Relationships of PCDD/Fs and Chlorobenzenes in the Whole Process of one Municipal Solid Waste Incinerator

We examined the characteristics of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) and chlorobenzenes (CBzs) in the flue gas and fly ash of a municipal solid-waste incinerator in four locations: the outlet of the furnace, the outlet of the high-temperature superheater, the inlet of the semi-dry scrubber and the stack after air pollution control device (APCD) processing. Both PCDD/Fs and CBzs were mostly formed at low temperatures. The dominant PCDD/Fs generated in the gaseous phase were 23478-PeCDF and TCDF, and 124-TrCBz was the major CBz in both the gaseous and solid phase. More PCDD/Fs were found in the solid phase with the decrease of temperature, while CBzs exhibited the opposite trend. Furthermore, activated carbon with a low surface area and mesoporous volume showed low flue gas removal efficiencies for PCDD/Fs and CBzs in the flue gas. The fraction of PCDD/Fs in the solid phase largely decreased when the flue gas passed through the fabric filter. Additionally, the memory effects of the aged filters increased the fractions of 234678-HxCDF, 1234678-HpCDF and 1234678-HxCDD. Most important, the relationships between PCDD/Fs and CBzs in the flue gas and fly ash were analyzed, respectively. In the gaseous phase, most of the CBzs displayed high correlation coefficients with PCDD/Fs, especially 123-TrCBz (R2 > 0.8). In the solid phase, low correlation coefficients were found between CBzs and PCDD/Fs except for 135-TrCBz and 123-TrCBz (R2 = 0.8). A remarkable correlation was also found between 124-TrCBz in the flue gas and PCDD/Fs in the fly ash. We conclude that TrCBzs may be regarded as the best indicator for PCDD/Fs in both flue gas and fly ash.

A Green Desulfurization Technique: Utilization of Flue Gas SO2 to Produce H2 via a Photoelectrochemical Process Based on Mo-Doped BiVO4.

A green photoelectrochemical (PEC) process with simultaneous SO2 removal and H2 production has attracted an increasing attention. The proposed process uses flue gas SO2 to improve H2 production. The improvement of the efficiency of this process is necessary before it can become industrial viable. Herein, we reported a Mo modified BiVO4 photocatalysts for a simultaneous SO2 removal and H2 production. And the PEC performance could be significantly improved with doping and flue gas removal. The evolution rate of H2 and removal of SO2 could be enhanced by almost three times after Mo doping as compared with pristine BiVO4. The enhanced H2 production and SO2 removal is attributed to the improved bulk charge carrier transportation after Mo doping, and greatly enhanced oxidation reaction kinetics on the photoanode due to the formation of after SO2 absorption by the electrolyte. Due to the utilization of SO2 to improve the production of H2, the proposed PEC process may become a profitable desulfurization technique.

Combined membrane photocatalytic ozonation and wet absorption of elemental mercury

Membrane photocatalytic ozonization coupled with wet absorption offers potential for elemental mercury (Hg0) removal. This study reports on a novel FeTiO2-coated polyvinylidene fluoride (PVDF) wet photocatalytic membrane reactor (WPCMR) for mercury removal in flue gas. Hg0 removal efficiency in the WPCMR reached up to 93.3%. Ozone could enhance mercury oxidation in WPCMR. Wet absorption helps to increases mercury removal efficiency. FeTiO2 catalyst was synthesized by sol-gel method and characterized by XRD, FTIR, UV–Vis, XPS and SEM. XPS analysis confirmed Hg0 oxidation to divalent mercury (Hg (II)). Elemental mercury was oxidized to mercuric oxide followed by wet absorption in the presence of OH free radical and ozone. Wet photocatalytic membrane reactor and photocatalytic membrane reactor (PCMR) of elemental mercury reaction with the FeTiO2/PVDF catalyst all follow Langmuir-Hinshelwood kinetics.

A numerical investigation of the effect of flue gas recirculation on the evolution of ultra-fine ash particles during pulverized coal char combustion

Flue gas recirculation (FGR) has been widely employed for NOx reduction. However, because PM removal in flue gas is never 100% efficient, a gradually accumulated particle concentration (particularly the ultra-fine particles, smaller than 1.0μm in aerodynamic diameter) may occur in the furnace, affecting PM emission and power plant operation. Experimental measurements cannot provide detailed information on the evolution of ultra-fine particle (including formation, and time-dependent growth and number size distribution). In this work, an improvement over our previous effort to model ultrafine particle formation during coal char combustion is developed and applied to elucidate the effects of various FGR parameters on ultrafine particle formation, including FGR ratio, dust removal efficiency, and particle size distribution in FGR. Model results show that FGR without recirculated particles results in the nucleation of fewer but larger particles. However, the presence of diluting FGR gases results in a low particle collision frequency and consequently yields small particle size and high number density after coalescence. The recirculated particles not only provide available surface area for condensable mineral vapors but also take part in coalescence via collision; consequently, larger particles are formed at a lower overall number density. The ultra-fine particle size first increases slowly with an increase in dust removal efficiency, but then drops rapidly after reaching a peak; An increase in recirculated particle size and a decrease in FGR results in increased particle size. For all cases, the particle number density shows opposite trends to particle size. Overall, the results derived here provide meaningful guidelines for practical application.

A review on the applications of coal combustion products in China

ABSTRACTOwing to the continuous high demand for energy, huge amounts of coals are consumed every year in China, giving rise to large volumes of coal combustion products (CCPs) from coal-fired power plants. Fly ash (FA), bottom ash (BA), boiler slag (BS), and flue gas desulphurization (FGD) gypsum are the primary CCPs generated. The disposal of these CCPs may occupy large areas of useful cultivated land, and cause serious environmental problems. However, these products might be also utilized as recoverable resources. Therefore, it is of economic and environmental significance to carry out research on the utilization of these CCPs. The present review first describes the physicochemical, mineralogical, and environmental geochemical properties of FA, slag, and FGD gypsum. Then the authors focus on the current and potential high value-added applications for these products in China. The utilization of FA for concrete and cement, soil amendment and fertilizer, in the ceramic industry, for catalysis, as adsorbents for the removal of flue gas, heavy metals, dyes and organic compounds, for zeolite and geopolymer synthesis, for recovery of valuable metals, and for recovery of unburned carbon and cenospheres, is discussed. The utilization of slag, such as reclamation of the burnable carbon, use in concrete, cement, and building materials, for roadway pavement and waste-water treatment, and for the production of acoustic barriers is reviewed as well. The current utilization of FGD gypsum includes use as a cement retarder, for the production of building plaster (β-hemihydrated gypsum) and calcium sulphate whiskers (α-hemihydrated gypsum), the production of fire-resistant panels, and use as a fertilizer and soil amendment agent. Furthermore, the possible influence of CCP properties on their utilization, and the advantages and disadvantages of various applications are discussed in this review. Finally, new directions for the future utilization prospects of CCPs in China are proposed.

Elemental mercury removal by CeO2/TiO2-PILCs under simulated coal-fired flue gas

CeO2/TiO2-PILCs with different Ce loading were synthesized by an impregnation method for Hg0 removal in flue gas considering the effect of various flue gas compositions. Nitrogen adsorption–desorption, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Fourier transform infrared spectrometer were employed for material characterization. The mechanisms of the effect of gas compositions on Hg0 oxidation were discovered in detail in this paper. The results demonstrated that 15% Ce/Ti-PILC has the best Hg0 oxidation efficiency at 300°C under N2+O2 due to the redox switch of Ce4+/Ce3+. The presence of SO2 in flue gas could restrain the oxidation activity by generating SO42− on 15% Ce/Ti-PILC surface. Hg0 oxidation was enhanced by HCl in flue gas because of the Deacon mechanism. NO2 was detected on the catalyst surface when NO was introduced into the in flue gas, which was responsible for the promotional effect of NO on Hg0 oxidation. The prohibitive influence of NH3 and H2O on Hg0 oxidation was obvious, which was due to the competitive adsorption. CeO2/TiO2-PILCs was demonstrated to be a potential catalysts for Hg0 oxidation in flue gas.

Numerical Simulation of Heat Transport from the Electric Arc Furnace to the Heat Recovery System

The paper presents a numerical model of heat transport from melting charge of the electric arc furnace designed for ferroalloy production, into a cooled roof of the electric arc furnace from which waste heat is led to the heating system of a company. The model considers the influence of an asymmetric flue gas removal and geometry of electrode arrangement. The model was developed implementing CFD - the finite volume method in ANSYS - Fluent program code. Outputs of the simulation model served as a basis for dimensioning heat exchanger circuits designed for waste heat recovery to provide a company heating.