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To effectively reduce SO2 emissions, flue gas desulfurization methods are widely used in coal‐fired power plants. In desulfurization, the dry sorbent injection (DSI) technology has the advantages of high desulfurization efficiency, simple operation, convenient adjustment, and low initial investment. Here, a pilot‐scale experimental system was designed and built to investigate the desulfurization characteristics of the DSI technology. The influence of the residence time of the desulfurizer, the reaction temperature, the stoichiometric ratio of the desulfurization reaction, the particle size of the desulfurizer, the inlet SO2 concentration, the dust concentration, and the water vapor content in the flue gas on the desulfurization efficiency at low SO2 concentrations was studied by injecting NaHCO3 into the pipeline. The desulfurization efficiency can be significantly improved by reducing the desulfurizer particle size or increasing the water vapor content in the flue gas at low SO2 concentration. An empirical formula describing the dependence of the desulfurization efficiency on experimental parameters is given. [ABSTRACT FROM AUTHOR]

This study focuses primarily on sulfur dioxide (SO2) emissions control problem in a wet flue gas desulfurization (WFGD) process, and our objective is to design an intelligent control system so that the outlet SO2 concentration satisfies the SO2 emission standard. In our approach, a multimodel control framework, which is made up of a linear robust controller and a neural controller, is integrated with the invasive weed optimization (IWO) algorithm in an elegant fashion and used for SO2 emissions control purposes. A case study is carried out based on operation data from a 600 MW coal-fired unit, and simulation results show that IWO-based automatic clustering can identify different operating modes in the WFGD process with high accuracy. Further, the established multimodel control system can remove SO2 emissions effectively. Experimental results show that SO2 emissions can be removed effectively with the proposed method, and this could provide engineering guidance to design a WFGD control system. [ABSTRACT FROM AUTHOR]

Flue gas desulfurization is crucial for both human health and ecological environments. However, developing efficient SO2 adsorbents that can break the trade‐off between adsorption capacity and selectivity is still challenging. In this work, a new type of fluorinated anion‐pillared metal–organic frameworks (APMOFs) with a pillar‐cage structure is fabricated through pillar‐embedding into a highly porous and robust framework. This type of APMOFs comprises smaller tetrahedral cages and larger icosahedral cages interconnected by embedded [NbOF5]2− and [TaOF5]2− anions acting as pillars. The APMOFs exhibits high porosity and density of fluorinated anions, ensuring exceptional SO2 adsorption capacity and ultrahigh selectivity for SO2/CO2 and SO2/N2 gas mixtures. Furthermore, these two structures demonstrate excellent stability towards water, acid/alkali, and SO2 adsorption. Cycle dynamic breakthrough experiments confirm the excellent separation performance of SO2/CO2 gas mixtures and their cyclic stability. SO2‐loaded single‐crystal X‐ray diffraction, Grand canonical Monte Carlo (GCMC) simulations combined with density functional theory (DFT) calculations reveal the preferred adsorption domains for SO2 molecules. The multiple‐site host–guest and guest‐guest interactions facilitate selective recognition and dense packing of SO2 in this hybrid porous material. This work will be instructive for designing porous materials for flue gas desulfurization and other gas‐purification processes. [ABSTRACT FROM AUTHOR]

Flue gas desulfurization is crucial for both human health and ecological environments. However, developing efficient SO2 adsorbents that can break the trade‐off between adsorption capacity and selectivity is still challenging. In this work, a new type of fluorinated anion‐pillared metal–organic frameworks (APMOFs) with a pillar‐cage structure is fabricated through pillar‐embedding into a highly porous and robust framework. This type of APMOFs comprises smaller tetrahedral cages and larger icosahedral cages interconnected by embedded [NbOF5]2− and [TaOF5]2− anions acting as pillars. The APMOFs exhibits high porosity and density of fluorinated anions, ensuring exceptional SO2 adsorption capacity and ultrahigh selectivity for SO2/CO2 and SO2/N2 gas mixtures. Furthermore, these two structures demonstrate excellent stability towards water, acid/alkali, and SO2 adsorption. Cycle dynamic breakthrough experiments confirm the excellent separation performance of SO2/CO2 gas mixtures and their cyclic stability. SO2‐loaded single‐crystal X‐ray diffraction, Grand canonical Monte Carlo (GCMC) simulations combined with density functional theory (DFT) calculations reveal the preferred adsorption domains for SO2 molecules. The multiple‐site host–guest and guest‐guest interactions facilitate selective recognition and dense packing of SO2 in this hybrid porous material. This work will be instructive for designing porous materials for flue gas desulfurization and other gas‐purification processes. [ABSTRACT FROM AUTHOR]

The circulating fluidized bed flue gas desulfurization (CFB-FGD) process is a promising semi-dry flue gas desulfurization technology. The gas-droplet flow characteristics and droplets evaporation characteristics are critical to improving the desulfurization efficiency of the FGD tower. The effects of droplet parameters, including spray droplet diameter, spray droplet velocity, spray droplet mass flow rate and spray angle are investigated. Two evaluation indices, the coefficient of variation of droplet concentration (CV) and droplet mass-weighted life, are adopted to evaluate mixing degree of gas-droplet and droplet evaporation time, respectively. Results show that as the spray droplet diameter increases from 40 µm to 80 µm, the amount of water droplets trapped by tower wall increases from 3% to 21%. Increasing the spray droplet velocity and spray droplet mass flow rate could effectively increase the turbulent kinetic energy, which could improve the turbulent mixing ability. Moreover, droplet with smaller diameter and high velocity are beneficial to improving the temperature distribution uniformity. When the spray droplet mass flow rate exceeds 2.7 kg/s, the temperature in the tower would be lower than the dew point temperature, resulting in corrosion of the tower wall. Furthermore, the evaporation rate of droplets decreases with the increase of droplet diameter, spray droplet velocity and spray mass flow rate, while increases with the increase in the spray angle. This study would provide a better reference for the optimum operating scheme in practical applications. [Display omitted] • A 3D model was established to simulate droplet evaporation process in CFB-FGD tower. • Gas-droplet mixing and droplet evaporation time are analyzed with evaluation indices. • Smaller droplets are beneficial to improving the temperature distribution uniformity. • Lower droplet velocity and smaller droplet mass increase the droplet evaporation rate. • Appropriate spray angle improves the two-phase mixing and prolongs droplet lifetime. [ABSTRACT FROM AUTHOR]

Efficient capture of sulfur dioxide (SO 2) in the preheater of the cement production system is the key to achieving process compatible flue gas desulfurization (FGD). Herein, the rapid oxidation of trace SO 2 over V 2 O 5 -based catalysts in the preheater environment was realized to enhance the SO 2 capture capacity of limestone in raw meal, and the catalytic efficiency was further improved by 45.2%, 56.1% and 61.9% after introducing TiO 2 /MnO 2 /CeO 2 as cocatalysts, respectively. The V 2 O 5 -based catalysts had superior catalytic behavior only when the flue gas temperature exceeded 500 °C, while the composition variation of flue gas had a minor influence on SO 2 oxidation. Finally, a maximum SO 2 oxidation efficiency of 68.1% was achieved in the presence of 4.0% O 2 , 25.0% CO 2 and 15.0% H 2 O at 600 °C. Furthermore, the mechanism of SO 2 catalytic oxidation over V 2 O 5 -based catalysts was deduced based on the results of XRD, BET, XPS and Raman, and V5+ was identified as the primary vanadium species for SO 2 oxidation. The results provide a deeper insight into the catalytic oxidation of SO 2 in the preheater environment, and then facilitate the improvement of process compatible FGD and available dry FGD technologies for cement industry. [Display omitted] • V 2 O 5 co-catalyzed by TiO 2 /MnO 2 /CeO 2 were prepared for rapid oxidation of trace SO 2. • Catalytic efficiency of V 2 O 5 -based catalysts was investigated. • Factors influencing the oxidation efficiency of trace SO 2 were studied. • 68.1% of SO 2 was oxidized in preheater environment within 1.0 s • Catalytic mechanism and pathways of SO 2 oxidation were proposed. [ABSTRACT FROM AUTHOR]

Air pollution sourced from untreated sulfur dioxide-rich flue gas is one of the major environmental and human health issues. Throughout the years, many sulfur dioxide removal technologies have been invented and implemented on a wide scale. Despite the high sulfur dioxide removal efficiency of conventional treatment methods, such as limestone-gypsum desulfurization and spray dry absorption, they generate a large number of secondary sulfur-containing by-products. Thus, sulfur dioxide catalytic reduction, with the help of suitable reducing agents, is sustainable with acceptable desulfurizing efficiency while recovering valuable solid sulfur. Herein, we review advances in sulfur dioxide catalytic reduction with critical insights contributed by internal and external factors. Sulfur dioxide catalytic reduction is a regenerative desulfurization treatment with lower space requirement and water consumption, simultaneously transforming waste sulfur dioxide to elemental sulfur. Catalytic sulfur dioxide reduction to sulfur via transition metal-based catalysts (copper-alumina and nickel-alumina) and sulfided metal-based catalysts (cobalt-molybdenum/ γ -alumina) appeared to be highly promising for complete sulfur dioxide conversion (100%) while maintaining high sulfur selectivity (more than 99.5%). High industrial and market demands for solid sulfur have also imposed great opportunities to advance this technology. However, the critical weaknesses of sulfur dioxide catalytic reduction are low process maturity and relatively energy-intensive, which is threatened by the high performance of conventional flue gas desulfurization and energy-efficient emerging desulfurization methods. Hence, several strategic directions through threat, opportunity, weakness, and strength analysis (TOWS) are discussed in-depth based on the strength, weakness, opportunity, and threats (SWOT) findings. In realizing environmental sustainability and a circular economy, sulfur dioxide catalytic reduction is a promising method to mitigate sulfur dioxide pollution while transforming waste-to-product, and this study serves as a guide to making sulfur dioxide catalytic reduction a mainstream desulfurization technology. [Display omitted] [ABSTRACT FROM AUTHOR]

The kinetics of oxidation of ammonium sulfite from flue gas desulfurization by ammonia process was studied by changing initial ammonium sulfite concentration, pH, air flow rate, temperature, and concentration of ammonium sulfate in a bubble reactor. The experimental results show that the oxidation rate of ammonium sulfite decreased with the increase of pH but increased with the increase of temperature and airflow rate when the concentration of ammonium sulfate is 0.15 mol/L, temperature of 25–60°C, and an airflow rate of 150–400 L/h. When the concentration of ammonium sulfate increases from 0.2 to 1.0 mol/L, the oxidation rate of ammonium sulfite decreases. At pH 5.0, the activation energy of the apparent oxidation is 26.40 kJ/mol. A kinetics model containing SO32−, SO4, and O2 is used to simulate the oxidation of ammonium sulfate. The results can provide a theoretical basis for the uncatalyzed oxidation of ammonium sulfite in the process of wet ammonia desulfurization process. [ABSTRACT FROM AUTHOR]

[Display omitted] • A promising route for resource utilization of semi-dry FGD ash was proposed. • Subcritical hydrothermal technology was employed for the oxidation of CaSO 3. • The subcritical hydrothermal oxidation macroscopic kinetics was investigated. • The oxidation ratio of CaSO 3 was 89.83% with the optimized parameters. • The reaction was co-controlled by the oxygen diffusion and CaSO 4 precipitation. Realization of low temperature and high efficiency oxidation of CaSO 3 is the key to solve the issue of ecological hazards caused by semi-dry sintering flue gas desulfurization ash. The subcritical hydrothermal technology was employed for the oxidation of CaSO 3 , achieving 89.83% of CaSO 3 at 180 °C, 2 MPa for 120 min with a solid-to-liquid ratio of 1:20. The macroscopic oxidation kinetics of CaSO 3 in the subcritical hydrothermal reaction system was investigated. A mathematical model was established, incorporating the intrinsic reaction, CaSO 3 dissolution, oxygen diffusion and CaSO 4 precipitation. It was concluded that the macroscopic oxidation of CaSO 3 was co-controlled by the oxygen diffusion and CaSO 4 precipitation. Subcritical hydrothermal technology promises not only higher efficiency, but more importantly, potentially "one-step" preparation of CaSO 4 whiskers, enabling cost-effective and high value-added resource utilization of the semi-dry FGD ash. [ABSTRACT FROM AUTHOR]

Removal of hydrogen sulfide (H2S) from coke oven gas has attracted increasing attention due to economic and environmental concerns. In this study, tannin extract (TE) absorption combined with binuclear sulfonated phthalocyanine cobalt organic polymer (OTS) and binuclear sulfonated phthalocyanine cobalt (PDS) with a fixed bed reactor is used for removal of H2S. The effect of gas flow rate, concentration of H2S, co-existence of organic sulfide compounds and O2 were investigated. Then, the effect of total alkalinity content of TE, NaVO3, OTS and PDS was studied in detail. The experimental results demonstrated that 100% H2S conversion could maintain for 13 h at a total alkalinity of 5.0 g/L, TE concentration of 4.0 g/L, NaVO3 concentration of 5 g/L, and OTS and PDS concentration of 0.2 g/L and 0.2 g/L, respectively. The OTS and PDS showed synergistic effect on boosting TE desulfurization efficiency. The results provide a new route for the investigation of liquid catalyzed oxidation desulfurization in an efficient and low-cost way. [ABSTRACT FROM AUTHOR]

The effect of carbon dioxide (CO2) on the desulfurization of sintering flue gas with hydrate (Ca(OH)2) as an absorbent was investigated, and the formation of calcium carbonate (CaCO3) and its effect on the desulfurization was discussed. The competitive relationship between carbon dioxide (CO2) and sulfur dioxide (SO2) with the deacidification agent in sintering flue gas is discussed thermodynamically, showing that sulfates are more likely to be generated under high oxygen potential conditions and that SO2 reacts more preferentially than CO2 under a thermodynamic standard state. The amount of produced CaCO3 increases under the condition that the CO2 concentration is absolutely dominant to SO2 in the sintering flue gas atmosphere. The effect of temperature, humidity and CO2 concentration on the desulfurization of Ca(OH)2 are discussed experimentally. The increasing temperature is not conducive to desulfurization, and the humidity can promote desulfurization, while excessive humidity could inhibit desulfurization. The suitable relative humidity is 20%. In situ generated calcium carbonate has a certain desulfurization effect, but the desulfurization effect is not as good as Ca(OH)2. However, a large proportion of CaCO3 was produced in the desulfurization ash under the condition that CO2 concentration was absolutely dominant to SO2 in the sintering flue gas atmosphere. [ABSTRACT FROM AUTHOR]

Sulfur and nitrogen oxides (SOX/NOX) are the primary air toxic gas pollutants emitted during fuel combustion, causing health and environmental concerns. Therefore, their emission in flue gases is strictly regulated. The existing technologies used to decrease SOX/NOX content are flue gas desulfurization, which necessitates high capital and operating costs, and selective catalytic reduction, which, in addition to these costs, requires expensive catalysts and high operating temperatures (350–400 °C). New wet scrubbing processes use O3 or H2O2 oxidants to produce (NH4)2SO4 and NH4NO3 fertilizers upon ammonia injection. However, these oxidants are expensive, corrosive, and hazardous. SiO2/Co(OH)2 nanocomposites are presented here as potential catalysts for SOX/NOX oxidation in wet scrubber reactors to scrub these toxic gases using atmospheric oxygen as the oxidant at relatively low temperatures of 60–90 °C. Several silica-cobalt-oxide-based nanocomposites were synthesized as potential catalysts at different concentrations and temperatures. The nanocomposite catalysts were characterized and exhibited excellent catalytic properties for SOX/NOX oxidation using atmospheric oxygen as the oxidant, replacing the problematic H2O2/O3. We thus propose SiO2-supported Co(OH)2 nanoparticles (NPs) as excellent catalysts for the simultaneous scrubbing of polluting SOX/NOX gases in flue gases using atmospheric O2 as the oxidation reagent at a relatively low-temperature range. [ABSTRACT FROM AUTHOR]

Summary: The wet flue gas desulfurization (WFGD) process is a complex controlled system with nonlinear and time‐varying characteristics. There are a variety of external disturbances in the desulfurization process, which can easily cause a jump in system parameters and even structure. In response to this problem, a model‐free adaptive control scheme based on a switching mechanism is proposed, and the convergence analysis is given. In the scheme, firstly, the operating conditions of the WFGD system are divided into n kinds based on multiple external disturbances, and the mathematical models of the multi‐input multi‐output WFGD system under different operating conditions are established. Then the MFA controllers of the WFGD system under multiple operating conditions are established, respectively. Finally, a switching index function is designed to switch the controller of the WFGD system according to different operating conditions, so that the desulfurization system is always controlled by the most appropriate controller. In the simulation experiment, according to the actual data of the WFGD system of a 1000 MW coal‐fired power station in Beijing, the modeling test and algorithm simulation of the WFGD system under three operating conditions are carried out. The simulation results show that this method can effectively reduce the transient error of the WFGD system output and improve the desulfurization effect. [ABSTRACT FROM AUTHOR]

Ca(OH)2, a widely available and low-cost calcium-based desulfurizer, needs further improvement in calcium utilization in flue gas desulfurization. In this experiment, Ca(OH)2 crystals with different morphologies were prepared by doping impurity ions including SO42− and SiO32− by precipitation method, which played directing role in the process of crystal growth. The prepared Ca(OH)2 crystals were applied to cement kiln flue gas desulfurization environment to investigate the effect of crystal morphology on flue gas desulfurization. The observed results illustrated that Ca(OH)2 prepared by SO42− as impurity ion in hexagonal plate shape presents the best desulfurization performance with desulfurization efficiency up to 93%. The structural characterization of Ca(OH)2 crystals by XRD and SEM, and the investigation of the reasons for desulfurization by BET, EDS, and XPS showed that the hexagonal plate-shaped Ca(OH)2 crystals increased the specific surface area and had the highest elemental sulfur content of 5.04% on the (100) crystal plane, and the high surface energy on the (100) plane led to the high reactivity. This confirms the guiding significance of hexagonal plate-like morphology for improving the desulfurization performance of Ca(OH)2. [ABSTRACT FROM AUTHOR]

Manganese ore slurry flue gas desulfurization will produce the by-product manganese dithionate（MnS2O6）, and the presence of dithionate greatly affects the resource utilization of manganese in the desulfurization solution. A new process for iron-enhanced MnS2O6 elimination by MnO2 is proposed based on the composition of most manganese ore. The results show that the addition of Fe（Ⅲ）has a good promotion effect on the elimination of dithionite by MnO2. The degradation efficiency gradually increases with the increase of Fe（Ⅲ）, and the best degradation efficiency can reach 55.1% at 5 g·L-1 of H2SO4. The optimum operation conditions obtained are 90 ℃ reaction temperature, 5 g·L-1 of H2SO4, 15 g·L-1 of Fe（Ⅲ）addition, n(S2O62-) ∶ n（MnO2）=1∶20 and 3 h duration time. [ABSTRACT FROM AUTHOR]

Flue gas with high SO 2 content presents a series of human health and environmental problems, which prompted Flue Gas Desulfurization (FGD) technologies widely utilised in industries. However, the conventional FGD using absorbents or adsorbents could generate secondary sulfur-containing pollutants. Thus, a regenerative FGD reaction system that eliminates secondary pollutants while recovering valuable S has been researched. Ba-based materials, viz. Ba(OH) 2 , BaCO 3 and BaO as the precursors, are involved in a regenerative BaS/BaSO 4 reaction system of this research. Current thermodynamic study via minimization of Gibbs free energy explored the feasibility of BaS production from these Ba-based materials and reviewed its potential in SO 2 reduction to S. Formation of BaS from Ba-based materials was feasible but the yield depends strongly on the temperature and sulfidizing agent used. Compared to BaCO 3 -systems, Ba(OH) 2 - and BaO-systems showed better performance in BaS synthesis due to their high equilibrium conversion, even at temperatures< 773 K. Besides, H 2 S is a better sulfidizing agent for BaS synthesis due to higher BaS yield (maximum 99%). Synthesis routes of different Ba-systems were confirmed by their respective K eq profiles. The feasibility of BaS catalyst in SO 2 reduction to S was proven by the excellent SO 2 reducing activity and high S yield (100%) at 273 – 1173 K with S 8 and S 2 as major products. BaS regeneration via H 2 was also validated by high BaS yield (100%) at 473 – 1273 K. [Display omitted] • Barium-based materials involve in a regenerative BaS/BaSO4 reaction system. • Gibbs free energy minimization method analyzes the feasibility of reaction system. • High yield of barium sulfide catalyst is generated from the barium-based materials. • High feasibility of barium sulfide in reducing sulfur dioxide to sulfur. • Waste-to-material concept could preserve environmental sustainability. [ABSTRACT FROM AUTHOR]

MIL-53(Fe) was prepared and modified with benzoic acid to prepare MIL-53(Fe)-BA additive, which was used to improve the catalytic oxidation rate of sulfite, prevent the scaling of the desulfurization tower, and improve the desulfurization efficiency during the wet flue gas desulfurization (WFGD) process of power plants. MIL-53(Fe)-BA exhibits abundant Lewis acid sites because of the appearance of coordination unsaturated Fe atoms. Due to the excellent sorption capacity, Ca(OH)2 was used as the main SO2 desulfurizer. The composite desulfurizers were prepared by mixing MIL-53(Fe)-based additives and Ca(OH)2, and were characterized by SEM, XRD, and FT-IR. A desulfurization unit was set up at laboratory scale to study the effect of catalytic oxidation additives on sulfite oxidation and desulfurization efficiency. The results showed that the addition of MIL-53(Fe)-BA can increase the oxidation capacity of sulfite by 159%, and greatly improve the desulfurization efficiency. These composite desulfurizers broaden the adaptability of the desulfurizing system to high-sulfur coals, and provide support for improving the desulfurizing efficiency of power plants. [ABSTRACT FROM AUTHOR]

Air pollution by sulfur dioxide (SO 2) remains a pressing concern for both the environment and human health. Desulfurization enhanced by persulfate based advanced oxidation processes (PS-AOPs) has been proven to be a feasible method. However, the inherent contradiction between the rapid diffusion mass transfer of SO 2 in the "gas-liquid-gas" phase and the limited lifespan of reactive oxygen species (ROS) can not be ignored. Excessive investment in PS is required to sustainably generate ROS to achieve continuous desulfurization performance, which may lead to excessive PS consumption. To address this issue, whether PS can achieve the oxidation absorption of SO 2 via a non-reactive oxygen species pathway was investigated. Experimental and computational results demonstrated that peroxymonosulfate (PMS) instead of peroxydisulfate (PDS) had a great SO 2 removal performance, the utilization of PS could be effectively achieved by maintaining a 1:1 molar ratio of PMS and removed SO 2. The presence of H O O bonds in the PMS introduced a partial positive charge to the oxygen atom, making the PMS polar and more susceptible to be attacked by the nucleophile HSO 3 -. So SO 2 underwent a series of processes including dissolution, dissociation, one-oxygen atom transfer, and ionization before ultimately being converted into SO 4 2- ions, effectively achieving its removal from flue gas. This study may presents a novel approach for achieving high-efficiency flue gas desulfurization. [Display omitted] • The direct removed of SO 2 by PMS with non-activated was systematically studied. • The stoichiometric ratio between SO 2 removed and PMS was close to 1:1. • The polar of PMS made O-O bond more susceptible to nucleophilic attacked by HSO 3-. • PMS and H 2 O 2 had completely different SO 2 absorption pathways. [ABSTRACT FROM AUTHOR]

• A novel reduction–oxidation dual-zone method for treating desulfurization ash is proposed. The lowest S content in the sample obtained after the desulfurization ash treatment was 0.03%. The f-CaO content of the decomposed product can reach 88%, which meets the requirements for the use of actual industrial lime. • The principle of minimum free energy was used to construct new thermodynamic models to predict the reaction parameters of the new process. • The reduction–oxidation dual-zone method was successfully practiced in semi-industrial experiments. Not only stable and efficient desulfurization, but also has a higher economic value. The recovery of CaO from flue gas desulfurization ash provides a new avenue for desulfurization ash recycling, but the conventional high-temperature reduction treatment of desulfurization ash often generates CaS as a byproduct, which reduces the desulfurization rate and lowers the purity of CaO. In this study, a novel strategy using a dual-region reduction–oxidation decomposition process was proposed to prepare highly active CaO products by decomposing the desulfurization ash in two steps via low-temperature reduction and high-temperature oxidation with CaS as an intermediate product to yield active and high-purity CaO. The minimum free energy principle was used to construct a thermodynamic model for optimizing parameters in conjunction with laboratory experimental results. First, the desulfurization ash was reduced to CaS in the low-temperature reduction region at a temperature of 1027 °C and a C/S molar ratio greater than 2. Thereafter, CaO was produced from CaS in the high-temperature oxidation region, which had a temperature greater than 1250 °C, an oxygen concentration of 3 % and an oxidation time greater than 90 min. The laboratory experimental results showed that desulfurization ash can be effectively decomposed; the lowest S content in the decomposition products was 0.03 %. The f-CaO content of the product was 88 %, and the particle size was small enough to meet requirements for practical industrial uses. In addition, this strategy was successfully applied in semi-industrial experiments, and with more than 95 % desulfurization rate and even lower theoretical energy consumption. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sludge porous carbon created rough surface and exposed flake structure for mayenite. • The removal efficiencies of Cl− and SO 4 2− reached 68 % and 77 %, respectively. • A high Cl− adsorption capacity of 97 mg/g was achieved from FGD wastewater. • Mayenite has a negative Cl embedding energy and is favorable for the embedding of Cl. • The Cl− removal product possessed high degradation efficiency of carbonyl sulfide. The high concentration of chloride ions (Cl−) in flue gas desulfurization (FGD) wastewater not only corrodes equipment but also reduces the quality of desulfurization gypsum. The mayenite (Ca 12 Al 14 O 33) has a notable capacity for adsorbing Cl−, but its efficacy is hindered by its inherently low specific surface area and long reaction time. To improve the effectiveness of mayenite in Cl− removal, the porous carbon derived from sewage sludge (SSC) was employed to modify the mayenite-based Ca/Al oxides (CAO). The resultant SSC/CAO composites featured a predominant mayenite phase with rough surface and exposed flake structure, leading to an increase in surface area from 2 m2/g for CAO to 54 m2/g for SSC/CAO-1 (mass ratio of sewage sludge: CAO = 1: 1). Within 2 h of reaction, SSC/CAO-1 achieved a Cl− removal efficiency of 68 % and a high Cl− adsorption capacity of 97 mg/g. The Cl− removal mechanism is related to the presence of a higher percentage of AlO 4 5-, more oxygen vacancies, and larger surface area in SSC/CAO-1 compared to that in CAO, which facilitated the dissolution and reconstruction of the [Ca − Al − O] framework, resulting in the formation of Ca 2 Al(OH) 6 Cl·2H 2 O with high crystallinity. The negative Cl embedding energy indicates that Ca 12 Al 14 O 33 is favorable for the embedding of Cl, and its transformation into Ca 2 Al(OH) 6 Cl·2H 2 O occurs spontaneously. The final product after Cl− removal consisted of efficient components to obtain high catalytic hydrolysis efficiency of carbonyl sulfide, which holds great importance to address the issue of handling the Cl– removal product during backend treatment. [ABSTRACT FROM AUTHOR]

Spraying flue gas desulfurization wastewater into flue ducts is an emerging technology that is receiving extensive attention in thermal power plants. In order to study the evaporative performance of wastewater-atomizing droplets under variable working conditions, a combined Euler–Lagrange model was developed to demonstrate the thermal behavior of FGD wastewater spray evaporation in flue gas. The effects of several control factors under various operating conditions were numerically determined and validated against experimental data. Due to the complicated parameters and various other conditions, a least-square support vector machine (LSSVM) model relying on numerical results was used to anticipate the evaporation rate of the droplets. We prove that the LSSVM model has high prediction accuracy for the evaporation rate at different cross-sections of flue under a different operating situation. The conclusion is that for the sake of improving the quality of evaporation, the spacing between two adjacent nozzles should be increased while increasing the flow rate. However, using a higher flue gas temperature, higher initial temperature and smaller diameter of droplets can shorten the time and distance of complete evaporation. In summary, this research analysis can be used effectively to determine the design of the FGD wastewater flue gas evaporative process in thermal power plants. [ABSTRACT FROM AUTHOR]

This article summarizes the source and water quality characteristics of desulfurization wastewater, and introduces the main treatment technologies for heavy metals, COD, chloride ions and other pollutants in desulfurization wastewater at this stage・ The basic reviews and analyzsis the principles, applicability and problems of different processing technologies in actual operation, lists cases of zero discharge of desulfurization wastewater that are already in operation. In view of the shortcomings of different technologies, the future direction of zero discharge treatment technology for desulfurization wastewater of coal-fired power plants is expected to be expanded, that is - the implementation of pre treatment integration to reduce operating costs; the development of new membrane materials to improve the efficiency of the advanced treatment stage of desulfurization wastewater. In order to provide idea for the selection and design of desulfurization wastewater removal technology for coal-fired power plants. [ABSTRACT FROM AUTHOR]

The flue evaporation of desulfurization wastewater can solve the problem that it is difficult to remove some heavy metal ions and chloride ions by conventional methods. A large amount of chloride ions in desulfurization wastewater can also promote the catalytic oxidation removal of Hg in the flue gas. The migration character of chloride ions in the flue evaporation process of desulfurization wastewater was studied by using the coal-fired thermal state experimental platform. The concentrations of Hg0 and Hg2+ in the flue gas at the inlet and outlet of selective catalytic reduction denitration (SCR), electrostatic precipitator (ESP), and wet desulfurization (WFGD) devices were tested, and the synergistic removal of traditional pollutant removal equipment by flue evaporation of desulfurization wastewater was analyzed. The influence of Hg and the effect of the evaporation of desulfurization wastewater at different positions on the removal of Hg in the flue gas were compared and analyzed, and the catalytic mechanism of Hg on the SCR surface was further revealed. The results show that 10% chloride ions enter the flue gas after the desulfurization wastewater evaporates. The content of chlorine elements and evaporation temperature influence the evaporation of desulfurization wastewater. The mechanism of SCR catalytic oxidation of Hg0 was explored; oxygen atoms have catalytic oxidation effects on Hg0 at different positions in the V2O5 molecule in SCR; and chloride ions can enhance the catalytic oxidation of Hg0 by V2O5. The intermediate product HgCl is generated, which is finally converted into HgCl2. The oxidation efficiency of Hg0 in electrostatic precipitation (ESP) is increased from 3% to 18%, and the removal efficiency of Hg is increased from 5% to 10%. The removal efficiency of Hg2+ in WFGD is basically maintained at approximately 85%. In addition, a small amount of Hg2+ was restored to Hg0 in WFGD. The removal efficiency of Hg0 in the flue gas of evaporative desulfurization wastewater before SCR is 65%, and the removal efficiency of gaseous Hg is 62%. When the evaporative desulfurization wastewater before ESP, the synergistic removal efficiency of Hg0 is 39%, and the gaseous Hg removal efficiency is 39%, and the removal efficiency of Hg is 40%. Evaporation of the desulfurization wastewater before SCR was more conducive to the coordinated removal of Hg by the device. [ABSTRACT FROM AUTHOR]

The desulfurization performances of semi-cokes (XR and ZR) produced by different pyrolysis processes were analyzed. It was found that the breakthrough sulfur dioxide capacity of both XR and ZR were less than 2. 5 mg/g. Therefore, the raw semi-cokes are not suitable for flue gas desulfurization direct. ly. Two kinds of activated semi-coke XC and ZC were prepared by CO2 activation method, and their desulfurization performances and pore structures were investigated. The result shows that activated semi-coke ZC has the best comprehensive performance. The optimized preparation process conditions are activation temperature of 950 °C, activation time of 2 h, CO2 flow rate of 150 mL/min. The comprehensive sulfur dioxide capacity of ZC reaches 70. 9 mg/g. Both XC and ZC have rich microporous structures, and the pore size distribution is mainly concentrated at 1.20 nm and 1. 84 nni. [ABSTRACT FROM AUTHOR]

SO2 and NOx in flue gas are serious environmental pollutants. As an excellent adsorbent, activated coke has good application potential in flue gas desulfurization and denitrification. In this study, different concentrations of NH3 and K2CO3 solutions were used to modify the activated coke made from biomass and coal, and then separate and coordinated desulfurization and denitrification experiments were carried out. The adsorption efficiency of activated coke and the adsorption capacity of SO2 and NO were compared, and the adsorption relationship between SO2 and NO was clarified. The changes of the surface functional groups of activated coke before and after adsorption and the forms of SO2 and NO after adsorption were analyzed by Fourier transform infrared spectrometer and X-ray diffractometer patterns. Results show that K2CO3 and NH3 modification can promote the adsorption of SO2 and NO in activated coke, and K2CO3 modification is more significant for improving the denitrification and desulfurization capacity. When the unmodified activated coke synergistically adsorbs SO2 and NO, there is a competitive adsorption between NO and SO2. However, when the activated coke modified with K2CO3 solution and NH3 synergistically adsorbs SO2 and NO, both have a promoting effect. After the adsorption of NH3-modified activated coke, CaSO4 and Na2SO4 crystals will appear. K2SO4 will exist after the adsorption of activated coke modified with K2CO3 solution. [ABSTRACT FROM AUTHOR]

Safe and efficient operation of the forced -oxidation system is of importance to the wet flue gas desulfurization (WFGD). However, equipment and system failures are commonly found due to the long-time running, frequent blower switching, and heavy workload etc., especially after the ultra-low emission (ULE) renovation to meet strict emission standard in China. This work develops a fault early detection method to improve the predictive maintenance of the forced-oxidation system including blowers, pipes, and the slurry tank. A model based on long shortterm memory (LSTM) network and attention mechanism (AM) is constructed to predict real-time operation parameters and compare with the measured values. Then the sequence probability ratio test (SPRT) is utilized to analyze the prediction-measurement residual and provide automatic and dynamic warning. All the data for model training and prediction are from the build-in distributed control system (DCS) without additional sensors. The LSTM-AM model proves to accurately predict time-dependent and highly relevant parameters. SPRT can sensitively perceive the fault-caused residual deviation while alleviating the noises. industrial application to the cases iii a 50 MW combined heat and power generation plant is then carried out. Results show that the bearing failure of the oxidation blower and branch pipes (immersed in the slurry tank) blockage can be forecast in advance when the incipient degradation occurs. [ABSTRACT FROM AUTHOR]

For the purpose of the gradual decrease of calcium carbonate resources and reduction of carbon emissions in wet flue gas desulfurization process, the utilization process of carbide slag to replace limestone is systematically analyzed. The properties of carbide slag and limestone have been analyzed, and the mass transfer and reaction behaviors in desulfurization process have been calculated and comprehensively evaluated. Desulfurization performances have been also compared through response surface analysis method. The results show that the calcium content and specific surface area of carbide slag are higher than limestone, which is conducive to the dissolution and mass transfer rate. Therefore, carbide slag is suitable for the treatment of flue gas with high SO2 concentration. Desulfurization efficiencies of the two desulfurization agents of carbide slag and limestone under the optimal process are 99.15% and 96.53%, respectively. In conclusion, carbide slag can be used in desulfurization process to replace limestone. The consumption of carbide slag slurry in the desulfurization process is about half of limestone slurry at the same conditions, and the higher desulfurization efficiency of carbide slag is attributed to the higher mass transfer and dissolution rate. Utilization of carbide slag also reduces the carbon emission in desulfurization process and economic cost. The reduction amount of CO2 emission can reach to about 0.76 t /1 carbide slag. This work provides a basis for the industrial application and desulfurization efficiency improvement of carbide slag as the desulfurizer. [ABSTRACT FROM AUTHOR]

A dynamic model for the flue gas desulfurization tower in coal-fired power plants is proposed. The model is validated with the data from a 350 MW unit. The penetration theory is adopted in modeling. The movement and the size of the slurry droplets, the temperature and the flow rate of the flue gas, as well as the chemical reactions have been taken into account. Three parameters in the model are found to have a critical impact on the model accuracy, i.e., the droplets' initial velocity, the number of droplets leaving all nozzles in a single spray layer per unit time, and the liquid side mass transfer coefficient of sulfur dioxide. These parameters need to be identified periodically in real applications. The quantitative relationship between pH and liquid side mass transfer coefficient is given. The main hypotheses and parameters of the model were discussed in order to quantify their respective influence. The model may be used to simulate the desulfurization process across the entire load range. Specifically, it may be used to predict the desulfurization efficiency online, so that applied potentially for the operational optimization. [ABSTRACT FROM AUTHOR]

NOx removal performance accompanying with SO2 is investigated in a two-step process containing O3 pre-oxidation of NO and NOx post-absorption in the scrubber of wet flue gas desulfurization (WFGD) unit. Based on Eulerian-Lagrangian framework, a comprehensive CFD model is established to describe the reactions of NO2 and N2O5 with S(IV) in droplets coupled with NOx transfer process and hydrodynamics in the scrubber. Taking the WFGD scrubber of 330 MW coal-fired power unit as case study, the results indicate NOx absorption efficiency in scrubber is increased by increasing O3/NO molar ratio from 1.0 to 2.2 and decreasing reaction temperature from 423 1< to 363 K in O3 pre-oxidation process. The obtained highest removal efficiency is 85.79% for pH of 5.5 or 96.32% for pH of 9.0 in droplets. NO2 absorption is much slower than N2O5 and more sensitive to chemical compositions in droplets or hydrodynamics in scrubber. The overall mass transfer coefficient (KG) for NO2 is mainly determined by pH and S(IV) concentration in droplets, while the specific interfacial area (α) is largely influenced by gas-droplet hydrodynamics in scrubber. Finally, a correlation is proposed to predict the volumetric mass transfer coefficient (KGα) for NO2 absorption accompanying with SO2 in WFGD scrubber. [ABSTRACT FROM AUTHOR]

NO x removal performance accompanying with SO 2 is investigated in a two-step process containing O 3 pre-oxidation of NO and NO x post-absorption in the scrubber of wet flue gas desulfurization (WFGD) unit. Based on Eulerian Lagrangian framework, a comprehensive CFD model is established to describe the reactions of NO 2 and N 2 O 5 with S(IV) in droplets coupled with NO x transfer process and hydrodynamics in the scrubber. Taking the WFGD scrubber of 330 MW coal-fired power unit as case study, the results indicate NO x absorption efficiency in scrubber is increased by increasing O 3 /NO molar ratio from 1.0 to 2.2 and decreasing reaction temperature from 423 K to 363 K in O 3 pre-oxidation process. The obtained highest removal efficiency is 85.79% for pH of 5.5 or 96.32% for pH of 9.0 in droplets. NO 2 absorption is much slower than N 2 O 5 and more sensitive to chemical compositions in droplets or hydrodynamics in scrubber. The overall mass transfer coefficient (K G) for NO 2 is mainly determined by pH and S(IV) concentration in droplets, while the specific interfacial area (a) is largely influenced by gas droplet hydrodynamics in scrubber. Finally, a correlation is proposed to predict the volumetric mass transfer coefficient (K G a) for NO 2 absorption accompanying with SO 2 in WFGD scrubber. [Display omitted] [ABSTRACT FROM AUTHOR]

For the purpose of the gradual decrease of calcium carbonate resources and reduction of carbon emissions in wet flue gas desulfurization process, the utilization process of carbide slag to replace limestone is systematically analyzed. The properties of carbide slag and limestone have been analyzed, and the mass transfer and reaction behaviors in desulfurization process have been calculated and comprehensively evaluated. Desulfurization performances have been also compared through response surface analysis method. The results show that the calcium content and specific surface area of carbide slag are higher than limestone, which is conducive to the dissolution and mass transfer rate. Therefore, carbide slag is suitable for the treatment of flue gas with high SO 2 concentration. Desulfurization efficiencies of the two desulfurization agents of carbide slag and limestone under the optimal process are 99.15% and 96.53%, respectively. In conclusion, carbide slag can be used in desulfurization process to replace limestone. The consumption of carbide slag slurry in the desulfurization process is about half of limestone slurry at the same conditions, and the higher desulfurization efficiency of carbide slag is attributed to the higher mass transfer and dissolution rate. Utilization of carbide slag also reduces the carbon emission in desulfurization process and economic cost. The reduction amount of CO 2 emission can reach to about 0.76 t /t carbide slag. This work provides a basis for the industrial application and desulfurization efficiency improvement of carbide slag as the desulfurizer. [ABSTRACT FROM AUTHOR]

A dynamic model for the flue gas desulfurization tower in coal-fired power plants is proposed. The model is validated with the data from a 350 MW unit. The penetration theory is adopted in modeling. The movement and the size of the slurry droplets, the temperature and the flow rate of the flue gas, as well as the chemical reactions have been taken into account. Three parameters in the model are found to have a critical impact on the model accuracy, i.e. , the droplets' initial velocity, the number of droplets leaving all nozzles in a single spray layer per unit time, and the liquid side mass transfer coefficient of sulfur dioxide. These parameters need to be identified periodically in real applications. The quantitative relationship between pH and liquid side mass transfer coefficient is given. The main hypotheses and parameters of the model were discussed in order to quantify their respective influence. The model may be used to simulate the desulfurization process across the entire load range. Specifically, it may be used to predict the desulfurization efficiency online, so that applied potentially for the operational optimization. [ABSTRACT FROM AUTHOR]

This study develops an elemental sulfur recovery (ESR) process from sulfur dioxide (SO2) as a hazardous material removed from flue gas emitted at thermal coal-fired power plants with a carbonate melt flue gas desulfurization (CMFGD) process. The carbonyl sulfide (COS) generated as a byproduct after removing SO2 from flue gas using carbonate melt in the CMFDG is utilized as a resource to produce elemental sulfur by applying the hydrolysis and Claus processes in the ESR process. In addition, to increase energy independence in the integrated CMFGD-ESR process, heat integration was applied by introducing new heat exchanger networks that utilize the waste heat in the proposed process. The levelized cost of the integrated CMFGD-ESR process was determined to be US$ 811 per ton SO2 removed; from this result, the proposed process to remove hazardous material from flue gas emitted at thermal coal-fired power plants is economically benign compared to conventional SO2 removal processes (US$ 500 ~ US$ 1200 per ton SO2 removed), which use limestone as the raw material. [ABSTRACT FROM AUTHOR]

[Display omitted] This study develops an elemental sulfur recovery (ESR) process from sulfur dioxide (SO 2) as a hazardous material removed from flue gas emitted at thermal coal-fired power plants with a carbonate melt flue gas desulfurization (CMFGD) process. The carbonyl sulfide (COS) generated as a byproduct after removing SO 2 from flue gas using carbonate melt in the CMFDG is utilized as a resource to produce elemental sulfur by applying the hydrolysis and Claus processes in the ESR process. In addition, to increase energy independence in the integrated CMFGD-ESR process, heat integration was applied by introducing new heat exchanger networks that utilize the waste heat in the proposed process. The levelized cost of the integrated CMFGD-ESR process was determined to be US$ 811 per ton SO 2 removed; from this result, the proposed process to remove hazardous material from flue gas emitted at thermal coal-fired power plants is economically benign compared to conventional SO 2 removal processes (US$ 500 ~ US$ 1200 per ton SO 2 removed), which use limestone as the raw material. [ABSTRACT FROM AUTHOR]

[Display omitted] • Dopants are screened via DFT calculation for γ -Al 2 O 3 catalyst over COS hydrolysis. • Lanthanum has been identified as the most promising dopant in preventing poisoning. • The S resistance of γ -Al 2 O 3 under aerobic conditions has been significantly improved. • La-doped γ -Al 2 O 3 exhibits the highest activity and stability. Catalytic hydrolysis of carbonyl sulfide (COS) is an efficient way of desulfurization for industrial flue gas, while the frequently used Al 2 O 3 -based catalysts always suffer from sulfur poisoning leading to poor stability, especially in the presence of O 2. With this regard, an analysis of the reaction pathway has been conducted, and the tri-coordinated Al in γ -Al 2 O 3 is identified as the responsible site for poisoning, on which produced H 2 S is over-oxidized resulting in active sites covering. Density functional theory (DFT) has been adopted for dopant screening to eliminate tri-coordinated Al on γ -Al 2 O 3 , inhibit H 2 S over-oxidation, and prevent sulfur poisoning. Results show La, Fe, Ni, and Cu all can eliminate tri-coordinated Al, while only La-doped γ -Al 2 O 3 exhibits inhibition to H 2 S oxidation, thus, improving activity and stability for γ -Al 2 O 3. Experiments show COS conversion of 99 % over 30 h can be attained in the presence of O 2 , which agrees well with the DFT calculation. [ABSTRACT FROM AUTHOR]

The new flue gas desulfurization system of 108m2 sintering machine is reformed, combined with the applicable scope of common desulfurization and dust removal process and the basic principles of desulfurization and dust removal process selection, the advanced and reliable rotary spray dryer absorber(SDA) technology is selected for flue gas desulfurization. Taking the process equipment of desulfurization system as the carrier, the process flow of desulfurization and dust removal system is designed. [ABSTRACT FROM AUTHOR]

[Display omitted] • A nanofibrous membrane with water contact angle around 145° is synthetized. • The SO 2 absorption flux of membrane is higher than that reported in literature. • The surface roughness of prepared nanofibrous membrane is increased to 6.597 μm. • PS-5 nanofiber membrane owns the highest SO 2 absorption flux and stability. It is essential to design a stable membrane material to solve the pollution produced by SO 2 emissions. This study aims to fabricate polystyrene (PS) nanofiber membranes, which are applied for flue gas desulfurization. PS nanofiber membranes are fabricated via electrospinning with porous polypropylene (PP) membrane as the support and high hydrophobic PS as the main membrane material. The modified membranes are characterized by scanning electron microscopy, true color confocal microscopy and other analytical methods, and the effects of mixed solvent ratio and polymer concentration on the desulfurization performance and on the stability of PS nanofiber membranes are investigated. The results suggest that an optimum hydrophobicity of PS nanofiber membrane is obtained with a water contact angle of 145°, when the polymer concentration is 5 %. The average pore size of PS nanofiber membrane is 1.56 μm, and the liquid entry pressure of water (LEPw) is 0.26 bar and the roughness of membrane is 5.674 μm. The desulfurization performance of the PS nanofiber membrane is better than that of the PP membrane. The SO 2 absorption flux of the modified membranes keeps at 7.2 × 10−4 to 7.6 × 10−4 mol·m−2·s−1 during 5 h operating, and SO 2 removal efficiency is up to 50 %, which potentially makes contributions to air pollution reduction. [ABSTRACT FROM AUTHOR]

With massive impurities, desulphurization wastewater is difficult to achieve zero liquid discharge (ZLD). The present paper proposes a novel ZLD technology based on solvent extraction desalination (SED) to avoid the intensive use of high-grade electrical energy and steam. Three amines are compared for the water extraction and salt precipitation performance from desulphurization wastewater simulated by NaCl and Na 2 SO 4 solution. Results show that with the same volume ratio, diisopropylamine exhibits the optimized extraction performance, while N,N-dimethylcyclohexylamine has the highest ions removal efficiency of over 98 %. Diisopropylamine is selected as the target solvent for further evaluation regarding its feasibility. The detailed analysis indicates that for 100 mL of wastewater, the corresponding solvent volume to achieve ZLD is 300 mL, 400 mL and 600 mL when the extraction temperature is 5°C, 10°C and 15°C, respectively. High water recovery efficiencies and salt removal efficiencies within five repeated ZLD tests highlights the reusability performance of SED. In addition, a novel SED-ZLD system with the flue gas before desulphurization as heat source is proposed. Thermodynamic calculation results show that for 5 t/h of wastewater, less than 50,000 m3/h of flue gas is sufficient for heating. Energy evaluation suggests that although SED-ZLD system consumes more energy, the exergy values of the heat source is much lower than that of multiple effect distillation or reverse osmosis, highlighting the superiority in waste heat utilization. [ABSTRACT FROM AUTHOR]

Wet flue gas desulfurization is widely used for its high efficiency, however, the low absorption capacity, high viscosity and poor thermal stability of absorbents remains an open question. Herein, a low viscosity and high thermal stability SO 2 absorbent with dual interacting sites was synthesized by introducing phenyl into organic silicon. The thermal stability of 1,5-bis (diethylamino)− 1,1,5,5-tetramethyl-3,3-diphenyltrisiloxane (BADPS) is comparable to ILs, while its viscosity is much lower than that of ILs. For the first time, we use a variant of the pseudo-first-order reaction rate equation obtained the reaction rate constant and the saturation absorption capacity. In addition, the optimal absorption and desorption temperatures were obtained based on an objective function. Mostly importantly, the absorption enthalpy change (ΔH) and entropy change (ΔS) of BADPS absorption reaction show the highest absolute values of SO 2 absorbents reported so far. These results indicated that the prepared amine alkyl organosilicon could serve as a promising desulfurizing agent with low-energy consumption. [Display omitted] • Synthesis of dual interacting sites amine alkyl organosilicon for SO 2 absorption. • High thermal stability with relatively low viscosity absorbent. • The great absolute value of enthalpy change and entropy change. • The small optimal absorption-desorption temperature difference. • Thermogravimetric absorption curves at very low SO 2 partial pressures are obtained. [ABSTRACT FROM AUTHOR]

• O 3 oxidation combined with semi-dry process is proposed for simultaneous desulfurization and denitrification of sintering/pelletizing flue gas. • Some factors affecting the efficiency of denitrification and desulfurization are introduced. • The reaction mechanism of desulfurization and denitrification is expounded explicitly. With the vigorous development of China's iron and steel industry and the introduction of ultra-low emission policies, the emission of pollutants such as SO 2 and NO x has received unprecedented attention. Considering the increase of the proportion of semi-dry desulfurization technology in the desulfurization process, several semi-dry desulphurization technologies such as flue gas circulating fluidized bed (CFB), dense flow absorber (DFA) and spray drying absorption (SDA) are briefly summarized. Moreover, a method for simultaneous treatment of SO 2 and NO x in sintering/pelletizing flue gas by O 3 oxidation combined with semi-dry method is introduced. Meantime, the effects of key parameters such as O 3 /NO molar ratio, CaSO 3 , SO 2 , reaction temperature, Ca/(S+2N) molar ratio, droplet size and approach to adiabatic saturation temperature (AAST) on denitrification and desulfurization are analyzed. Furthermore, the reaction mechanism of denitrification and desulfurization is further elucidated. Finally, the advantages and development prospects of the new technology are proposed. [Display omitted] [ABSTRACT FROM AUTHOR]

Summary: Limestone method is widely used in FGD process because of high desulfurization efficiency and low cost. However, it is easy to precipitate and block the equipment because of large particle size. Thus, micron CaCO3 slurry and CaCO3 (30‐ and 100‐nm diameter) nanofluids of the same concentrations were prepared to investigate the influence of the particle size on suspension of absorbent and the desulfurization effect. Settlement experiment and zeta potential (ζ) measurements depicted that the stability of CaCO3 nanofluids were much better than that of micron CaCO3 slurry, which could avoid the blocking of equipment. Moreover, the viscosity of CaCO3 nanofluids was directly proportional to concentration and inversely proportional to temperature. Dynamic viscosity of two types of CaCO3 nanofluids decreased first and then remained unchanged with the shear rate varying from 0 to 1000 s−1 while the viscosity of CaCO3 (30‐nm‐diameter) nanofluids was higher than that of CaCO3 (100‐nm‐diameter) nanofluids. Dynamic absorption experiments indicated that the desulfurization effect of two kinds CaCO3 nanofluids were better than that of micron CaCO3 slurry. While the maximum saturated sulfur content of CaCO3 (100‐nm‐diameter) nanofluids could be 54.38 mg/mL and the maximum breakthrough time was 300 minutes, which was higher than CaCO3 (30‐nm‐diameter) nanofluids. The maximum mass transfer rate of CaCO3 (100‐nm‐diameter) nanofluids could be 2.523 m/s, which was consistent with the desulfurization experiment. Hence, properly reducing the particle size of CaCO3 particles can improve the desulfurizing effect on the premise of not increasing the viscosity of desulfurizing solvent. Novelty Statement: The manuscript "An investigation into the influence mechanism of particle size of CaCO3 on FGD process by limestone method" reduced the particle size of CaCO3 in limestone method from micron to nanometer for the first time. The stability and rheology of high concentration CaCO3 (30‐ and 100‐nm in diameter) nanofluid were studied. It also found that properly reducing the particle size of CaCO3 particles could improve the desulfurizing effect on the premise of not increasing the viscosity of desulfurizing solvent. [ABSTRACT FROM AUTHOR]

• Sulfite removal from high-sulfur coal fly ash is rapid and selective in acidic pH. • Acid generated from oxidation of dissolved sulfite can be gainfully recycled. • Sulfuric acid as an acid source is promising for using treated ash in concrete. • Carbonic acid use is feasible and allows integrated capture CO 2 from flue gas. • Water demand of semi-dry FGD with proposed sulfur removal is less than wet FGD. High-sulfur mixed fly ash residues from semi-dry flue gas desulfurization units in coal-fired power plants are unsuitable for use as supplementary cementitious material (SCM) for concrete production or carbon dioxide utilization. In this work, we explore the potential for upcycling a representative spray dry absorber ash (10.44 wt% SO 3) into concrete-SCM by selective sulfur removal via weak acid dissolution while simultaneously exploring the possibility for CO 2 capture. Towards this effort, parametric studies varying liquid-to-solid ratio, acidity, and CO 2 pressure were conducted in a batch reactor to establish the sulfur removal characteristics in de-ionized water, nitric acid, and carbonic acid, respectively. The dissolution studies show that the leaching of sulfur from calcium sulfite hemihydrate, which is the predominant S phase, is rapid and achieves a concentration plateau within 5 min, and subsequently, appears to be controlled by the primary mineral solubility. Preferential S removal was sufficient to meet SCM standards (e.g., 5.0 wt% as per ASTM C618) using all three washing solutions with 0.62–0.72 selectivity (S ^), defined as the molar ratio of S to Ca in the leachate, for a raw fly ash with bulk S ^ = 0.3. Acid dissolution with 1.43 meq/g of ash or under 5 atm CO 2 retained > 18 wt% CaO and other Si-, Al-rich phases in the fly ash. Based on the experimental findings, two sulfur removal schemes were suggested for either integration with CO 2 capture and utilization processes using flue gas or to produce fly ash for use as a SCM. [ABSTRACT FROM AUTHOR]

The zinc oxide method is one of the most popular flue gas desulfurization processes, especially for the control of low-content sulfur dioxide. In this process, zinc sulfite can be oxidized to form a soluble zinc sulfate, which can solve the problems of scale formation and pipe plugging. This paper aims to study the oxidation kinetics of zinc sulfite in the zinc-based wet flue gas desulfurization (FGD) process by varying the zinc sulfite concentration, initial pH, oxygen partial pressure, temperature, stirring speed, gas flow rate, and particle size. The oxidation results indicate that there is a critical sulfite concentration of 7.5%, below which the reaction rate is 0.32 order dependence from sulfite, while above which the order turns to −0.78. Meanwhile, the reaction rate is 1.0 order in the oxygen partial pressure. The initial pH and particle size have little effect on the oxidation rate, while the oxidation rate increases with the stirring speed, gas flow rate, and temperature. Moreover, the apparent activation energy is calculated to be 15.85 kJ·mol−1. Integrated with the kinetic model, it is concluded that the oxidation rate of zinc sulfite is controlled by the mass transfer of oxygen in the liquid phase. [ABSTRACT FROM AUTHOR]

This study aims to explore the feasibility of using dry flue gas desulphurization ash (DFGDA) as a filler in asphalt pavements. Two DFGDA materials were added into the base asphalt with different mineral powder proportions to prepare asphalt mastic and mixture, and the pure mineral powder asphalt mastic and mixture were used as the blank control group to evaluate the properties of DFGDA-doped asphalt mastic and mixture. The results show that the addition of DFGDA can improve the high-temperature rheological property and reduce the low-temperature rheological property of asphalt mastic; similarly, the high-temperature stability of asphalt mixture can be greatly improved, while its low-temperature performance and water stability are reduced; despite these decreases, all outcomes still meet the requirements of relevant specifications. No chemical reactions are observed between DFGDA and asphalt, indicating that the physicochemical properties of fillers are responsible for the change in the properties of DFGDA-doped slurry and mixture. Notably, the DFGDA-added asphalt mixture does not bring additional negative effects to the environment. Based on cost analysis, the high-quality use of DFGDA in asphalt mixture can save direct material costs of about $920,000 per 100 kilometers of asphalt road construction. In summary, the application of DFGDA in the asphalt mixture can not only meet the basic performance requirements of asphalt pavements but also greatly save material costs and protect the environment. • The feasibility of using DFGDA as an alternative filler in asphalt was examined. • DFGDA decreased the asphalt mastic strain and enhanced rutting resistance. • DFGDA reduced the low temperature performance and water stability of mixture. • Asphalt mastic performance depends on the physicochemical properties of fillers. • The application of DFGDA can save material costs and protect the environment. [ABSTRACT FROM AUTHOR]

To address the challenges of low waste heat utilization rates and high desulfurization costs, this study proposes a novel method for combined desulfurization and heat utilization of low-temperature flue gas. By utilizing the low-temperature flue gas from hot blast stoves to dry lump metallurgical coke, the method also achieves flue gas desulfurization during the lump coke drying process. During the drying process, the wet lump coke desulfurizes due to the reaction between water vapor in the lump coke and the SO 2 and oxygen in the flue gas, resulting in the formation of sulfuric acid. Additionally, the coke powder generated by friction during the drying process of lump coke has a large specific surface area, enabling it to adsorb additional quantities of SO 2 and enhance the desulfurization process. It's important to note that the lump coke itself does not exhibit adsorption properties towards SO 2 during the drying process, and the gas is not retained within the lump coke. Industrial applications indicate the outlet flue gas temperature is reduced from 175 °C to 60 °C, and the concentration of SO 2 in the outlet flue gas is reduced from 150 mg/m3 to 29 mg/m3. • Waste heat utilization of low-temperature flue gas (about 150 °C) of hot blast stove • Combined desulfurization and heat utilization of low-temperature flue gas • Desulfurization under the cooperation of chemical reaction and physical adsorption [ABSTRACT FROM AUTHOR]

• Activated carbons from petroleum coke have a high affinity for sulfur dioxide in both wet and dry experiments. • Sulfate formation on the active surface was not found to be significant. • Wet SO 2 experiments did not degrade the activated carbons through 10 thermal swing adsorption cycles. The removal of sulfur dioxide from flue gas is an important process for the mitigation of acid rain. Activated carbons have a low affinity for water and a high affinity for polarizable molecules, such as sulfur dioxide, making them good candidates for selective adsorbents for flue gases. This work presents results on the multicomponent adsorption of N 2 /CO 2 /SO 2 and N 2 /CO 2 /SO 2 /H 2 O flue gas mixtures on four activated carbons prepared from petroleum coke, and one carbon black. Multicomponent adsorption was measured at T = 30, 60, 90 °C. All five activated carbons had a high affinity and selectivity for SO 2 in both the presence and absence of water. The activated carbons prepared with KOH (P_K) and NaOH (P_Na) showed the highest capacity for SO 2 under wet conditions with thermal swing regeneration (P_K: n ads SO₂ = 0.148 ± 0.002 mmol g−1, P_Na: n ads SO₂ = 0.13 ± 0.01 mmol g−1). In pressure swing experiments of the wet flue gas mixture, the activated carbon prepared with a K 2 CO 3 and KOH (P_CK) (n ads SO₂ = 0.077 ± 0.002 mmol g−1) and P_K (n ads SO₂ = 0.064 ± 0.005 mmol g−1) activated carbons had the highest SO 2 capacities. Of the activated carbon, P_K had the greatest SO 2 /H 2 O selectivity for the thermal swing adsorption (T = 30 °C, S SO₂/H₂O = 3.0 ± 0.2) and pressure swing adsorption (T = 90 °C, S SO₂/H₂O = 3.9 ± 0.6) experiments. It was observed that activated carbons with higher carbon fraction were less likely to have a difference in SO 2 adsorption from dry versus wet conditions. After the wet SO 2 multicomponent adsorption, no change in the adsorption performance of any activated carbons was observed after 10 cycles. [ABSTRACT FROM AUTHOR]

A research on semi-dry FGD technology using CFD-DEM method is conducted to study the motion of wet particles and their performance on SO 2 remove. The liquid bridge force model proposed by Mikami (1998) et al. is introduced to estimate the interactionamong wet particles. The reaction rate of desulfurization is calculated depended on the two-film theory. The profiles of particle volume fractions, velocities and the main forces on particles are obtained. Simulation results indicate that liquid bridge force facilitates the formation of particle aggregation. Meanwhile, the distributions of particles are more inhomogeneous, which result in a decrease on SO 2 removal efficiency. Furthermore, the effect of humidity on the desulfurization is also investigated by adjusting the parameter of dimensionless liquid bridge volume. As the humidity increases, the agglomerate grows and the SO 2 removal efficiency increases first and gradually decreases. Simulation results of SO 2 removal efficiency are in a good agreement with the experimental data from Kunio Kato (1999) et al. Unlabelled Image • The semi-dry FGD process is simulated by CFD-DEM. • Liquid bridge force model is considered to simulate the motions of wet particles. • Two-film theory is used to calculate the reaction rate of desulfurization. • The influence of humidity on the distributions of forces on particles is studied. • The effects of humidity on the SO 2 removal efficiency are predicted. [ABSTRACT FROM AUTHOR]

MgO slurry become more and more important in wet desulfurization process because of high desulfurization activity and recyclable by-products. While the removal of SO 2 by micron-sized MgO slurry is limited due to particle size. Hence, micro-sized MgO slurry and MgO nanofluids of the same concentration were prepared. The stability of MgO nanofluids had been investigated. The density and viscosity of MgO nanofluids increased with the increase of concentration, but decreased as the temperature increase, and MgO nanofluids belong to Newtonian fluids. The evaluation of desulfurization effect and calculation of the mass transfer coefficient indicated that MgO nanofluids had better desulfurization effect compared with MgO slurry. The desulfurization efficiency increased with the increase of concentration, while the growth rate of desulfurization efficiency dropped sharply as the concentration exceed 4 wt%. Therefore, reducing the particle size properly can improve desulfurization efficiency of MgO absorbent in removal of SO 2 from flue gas. Unlabelled Image • MgO nanofluids were used in flue gas desulfurization. • Compared with MgO slurry, MgO nanofluid had better stability. • The removal efficiency of SO 2 increased as the particle size reduced to nanometer. • The mass transfer coefficient could be 2.302 mmol/(m2·s·kPa)−1 at 5 wt% nanofluids. [ABSTRACT FROM AUTHOR]

Due to wet desulfurization system lacks effective control indicators for the oxidation process, so the sulfite oxidation in the slurry and the quality of gypsum become unstable. In this paper actual desulfurization system operation data are used to improve the ORP semi-empirical formula obtained in the laboratory. It was concluded that the ORP was mainly affected by the concentration of sulfite and pH during the operation of the actual desulfurization system, the dissolved oxygen was less affected by the small concentration change during operation. It is verified that the model can correct the ORP measurement value by using other conventional measurement data from the power plant. The results can provide theoretical support for adding ORP as a control index to optimize the oxidation process. At present, the main control parameter of wet FGD is pH control, but wet FGD has two main reactions at the same time, one is acid-base reaction, the other is redox, single pH control can not reflect the degree of redox, so it is necessary to introduce another control index to evaluate redox, which is the ORP control proposed in this paper, ORP can reflect the degree of slurry oxidation, avoid the occurrence of excessive oxidation and inadequate oxidation, so that the operation of desulfurization system can be more healthy and stable. [ABSTRACT FROM AUTHOR]

The purification of industrial sulfur‐containing tail gas mainly adopts the wet flue gas desulfurization of gas–liquid mass transfer, and a new separator utilizes the gas–liquid coupling field to rapidly update the effective phase boundary area in the reaction process to enhance the mass transfer effect. This study used NaOH solution as the reaction liquid phase to determine the effects of the selection of overflow port of gas cyclone–liquid jet absorption separator on gas desulfurization efficiency under the changing rates of gas and absorption liquid flow. Results showed that desulfurization efficiency decreased as the diameter of the overflow port increased but increased as the depth of the overflow port increased. The optimal design ratio Dx/D1 of overflow tube diameter Dx and separator tube diameter D1 is 0.35, and the optimal design ratio S/H1 of overflow tube insertion depth S and separator tube length H1 is 0.62. At constant operating conditions, overflow port selection can increase desulfurization efficiency by up to 20%, which provides optimization guidance for the structural design of a gas cyclone–liquid jet absorption separator. [ABSTRACT FROM AUTHOR]