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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]

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]

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]

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]

An experimental investigation of low-temperature SO2 removal reaction by porous sodium carbonate was carried out via thermogravimetry. Further, mathematical modeling was employed based on the random pore model to study the kinetics of this reaction. The experiments were performed at various temperatures (100–250 °C) and different SO2 concentrations (0.13–1.12 vol%). The initial slope method was used to determine dependency of the reaction rate constants versus temperature. First-order kinetics with respect to gaseous reactant was observed and the activation energy was determined as 22.5 kJ mol−1. Furthermore, product layer diffusivities were evaluated by comparison of experimental data with the model predictions. The mechanism was determined as competition between pore diffusion and surface reaction (mixed control regime) at initial stages, and product layer diffusion at later steps of the reaction. These random pore model predictions indicated good agreement with experimental conversion-time data under various conditions. The resulting kinetic parameters are essential for engineering calculations of SO2 removal from the coal-based power plants through low-temperature flue gas desulfurization. [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]

Increasing the utilization of copper tailing and flue gas desulfurization is significant for copper smelters. Copper tailing, derived from the copper production, was applied to flue gas desulfurization and increasing utilization of copper tailing and smelting gas with low concentrations of SO 2 by preparing slurries composed of copper tailing and water. The effects of different factors, including the inlet SO 2 concentration, the ratio of solid to liquid, the absorption temperature, the O 2 concentration, the gas flow rate, the initial copper tailing slurry pH, and the presence of a coexisting gas were investigated systematically. The resulting products and the mechanism driving the flue gas desulfurization were also studied. The results indicated that desulfurization efficiency was primarily influenced by the inlet SO 2 concentration, the ratio of solid to liquid, the absorption temperature, and the gas flow rate. An appropriate amount of NO facilitated the desulfurization. The desulfurization efficiency was maintained at or above 80% for 60 h under optimal conditions. The total weight of the copper tailing was reduced by approximately 8%. Ferric sulfate and magnetite could be recycled through evaporation and magnetic separation. Liquid phase catalytic oxidation by metal ions, including ferric and manganese, played a vital role in the flue gas desulfurization. Copper tailing is the solid waste produced by pyrometallurgical process for copper production. Approximately 2 tons of copper tailings are produced in the process of 1 ton of copper. Traditional approaches of reuse have significant disadvantages, including high capital costs for installation and complicated construction and operating costs, including massive acid consumption. We firstly use the copper tailing and water as desulfurization agents to removal SO 2 -containing gas, which provides a practical reference to flue gas desulfurization from the copper industry, thus promoting the flue gas desulfurization at a lower cost and meanwhile realizing the goal of effective copper tailing recycling. Unlabelled Image • A novel, inexpensive wet desulfurization method with copper tailing is proposed. • Formed metal ions, including Fe2+ and Mn2+, play a vital role in removing SO 2. • Up to 75% copper is leached with high efficient desulfurization simultaneously. • Copper tailing was reduced 8% when solid waste is used to remove SO 2. [ABSTRACT FROM AUTHOR]

Tunable chelate-based ionic liquids were synthesized through a one-step method, which exhibited excellent desulfurization performance in flue gas. [Display omitted] • Novel and tunable chelate-based ionic liquids were prepared conveniently by one-step method. • Highly efficient separation of SO 2 in flue gas was achieved through tuning the effect of the anion, ligand and metal ion. • Absorption mechanism was explained via the combination of experimental absorption, spectroscopic investigation and DFT calculation. A strategy for facile preparation of chelate-based ionic liquids (ILs) by simple chelation was developed, where a series of chelate-based ILs with tunable functionalized anions (azole), cheap ligands (PEG400), and simple metal ions (Li+, Na+, and K+) were designed for SO 2 capture under 2000 ppm in flue gas. Both the anion-tunable strategy and the fine-tuned strategy were used to explore the effect of anions, ligands, and metal ions. The experimental absorptions, spectroscopic investigations, and DFT calculations indicated that the process of SO 2 capture was mostly based on the nucleophilic effect of electronegative N site toward SO 2. Furthermore, the tuning of alkali metal ions was proved to have little influence on SO 2 absorption. The ideal IL, [Na(PEG400)][Tetz], exhibited splendid available absorption capacity of SO 2 (0.57 mol/mol), excellent selectivity (63 under 2000 ppm SO 2 /15% CO 2), and outstanding reversibility, indicating good potential for industrial application. [ABSTRACT FROM AUTHOR]

Cement industry contributes to more and more SO 2 emission due to utilization of alternative raw materials and fuels, whereas the available calcium-based dry flue gas desulfurization (FGD) technologies present low efficiency due to slow reversible de-SO 2 reactions and short gas-solid contact time in the preheater. In the present study, the SO 2 capture potentials of CaCO 3 , CaO, and Ca(OH) 2 in the preheater environment were maximized by introducing V 2 O 5 -based catalyst and selecting optimal reaction temperature, and the de-SO 2 mechanism was extensively discussed. The results showed that the de-SO 2 efficiency of calcium-based adsorbents increased by 10–57 times as SO 2 was effectively oxidized to SO 3 in the presence of V 2 O 5 -based catalyst, then maximum de-SO 2 efficiency of 75.5% was achieved using Ca(OH) 2 and V 2 O 5 -CeO 2 at 600 °C. Furthermore, CaCO 3 assisted by V 2 O 5 -CeO 2 also had a de-SO 2 efficiency of 65.6%. Subsequently, a novel process compatible FGD technology was designed to maximize the de-SO 2 ability of raw meal in the preheater by adding V 2 O 5 -based catalyst and humidification, the SO 2 concentration of flue gas reduced from 1000 mg/Nm3 to less than 100 mg/Nm3 in the industrial-scale trial, as more sulfur was solidified into clinker in the form of alkali sulfate without reducing its properties. This novel process compatible de-SO 2 strategy is of real significance for reducing SO 2 emission of cement industry at low economic cost. [Display omitted] • SO 2 capture by calcium-based adsorbents in the preheater environment was studied. • Higher SO 2 capture efficiency was obtained after introducing V 2 O 5 -based catalysts. • Catalyst-assisted SO 2 capture with de-SO 2 efficiency of 75.5% was first reported. • A novel process compatible FGD technology was proposed and designed. • SO 2 in flue gas reduced from 1080 mg/Nm3 to <100 mg/Nm3 during industrial trial. [ABSTRACT FROM AUTHOR]

Stricter emission regulations require the improvement of SO 2 scrubbing efficiency and energy usage. In this work, the dissolution of two very pure limestone samples under the effect of ultrasound (US) was compared to their dissolution in silent conditions. The aim of this work was to assess experimentally whether this method could be adopted as a process intensification technique for Wet Flue Gas Desulfurization (WFGD) applications. A pH-stat method with vigorous agitation, coupled with in situ particle size distribution measurements was developed for evaluating the effect of US in limestone dissolution. The samples were characterized in detail, the experiments were modeled mathematically and, a chemical reaction constant was determined and used to compare quantitatively the use of US and the silent case. The results indicate that US does enhance limestone dissolution, and that the degree of enhancement depends largely on the type of sample, i.e. the geological origin and the particle size. The developed mathematical model was implemented satisfactorily; the model was able to fit the data with high degrees of accuracy (>94%). The degree of enhancement, quantified in terms of the increase in the estimated chemical reaction constant, ranged from 18% to 150%. [ABSTRACT FROM AUTHOR]

A novel wet flue gas desulfurization method based on the Bunsen reaction of sulfur-iodine (SI) thermochemical cycle was investigated in this paper. I 2 and HI absorption system was utilized to remove SO 2 from simulated coal-fired flue gas. The SO 2 removal efficiency was about 98.8% when the I 2 concentration was 25.6 mmol/L. The influences of reaction temperature, initial SO 2 concentration and the other flue gas components on SO 2 removal were investigated, respectively. The absorption products were H 2 SO 4 and HI, which could be easily separated by distillation. Compared with the traditional wet flue gas desulfurization (FGD) byproducts, such as gypsum or magnesium sulfate, H 2 SO 4 has better commercial value and application prospect. Moreover, HI could be used as the raw material for the hydrogen production in the SI thermochemical cycle. In short, it is a promising technology for the SO 2 removal and recycling from coal-fired flue gas. [ABSTRACT FROM AUTHOR]

Clean fuel technologies have been widely developed in current society because fuel combustion can directly bring about the emission of hazardous gasses such as SO2. Flue gas desulfurization by polyethyleneimine (PEI)-phosphoric acid solution is an efficient desulfurization method. In this research, the PEI and the additive H3PO4were used as absorption solution. SO2was absorbed by the system and desorbed from the loaded solution. The cycle operation was also analyzed. Some technology conditions such as the concentration of PEI, the temperature, the gas flow rate, the concentration of SO2and the pH value were experimentally researched. With the optimized process, the absorption efficiency of this system could reach 98% and the desorption efficiency was over 60%, showing good absorption/desorption capability. With this efficient approach, the present study may open a new window for developing high-performance absorbents which can make SO2be well desorbed from the loaded solution and better reused in the flue gas desulfurization. [ABSTRACT FROM PUBLISHER]

A pilot-scale study of flue gas desulfurization based on an amine-based solvent using applicable industrial values was carried out for sulfur dioxide (SO2) removal. The plant consisting of absorption and desorption columns was operated with different working parameters such as solvent flow rate, inlet concentration of SO2, temperature of desorption column, and pH of absorption agent. The Taguchi method was utilized to obtain the best combination of working parameters for the most efficient reduction of SO2 outlet concentration. The industrial gas-to-liquid ratio could be optimized by applying a defined SO2 concentration, stripper temperature, and solvent pH value. The achieved efficiency is much better compared to our previous study while the gas-to-liquid ratio is higher in this work. [ABSTRACT FROM AUTHOR]

Wet flue gas desulfurization (WFGD) has been widely used to reduce the harmful effects of sulfur dioxide during coal combustion, of which sulfite is a byproduct. Recycling this desulfurization byproduct requires the oxidation of sulfite, and transition metals might considerably promote the sulfite oxidation rate. We compared the oxidation rates of four sulfites—sodium sulfite, ammonium sulfite, magnesium sulfite, and calcium sulfite—and found that transition metals have selective catalytic performance. Although each transition metal was confined to specific sulfites, Co 2+ and Mn 2+ were the most effective catalysts. In addition, the sensitivity levels of the sulfite oxidation rates to various transition metals were classified. The orders of the reactions of the four sulfites catalyzed by Co 2+ and Mn 2+ were calculated. Although both magnesium sulfite and calcium sulfite exist as solids, the oxidation rate of magnesium sulfite was considerably sensitive to Co 2+ . The same results were observed for sodium sulfite and ammonium sulfite. However, the oxidation rate of calcium sulfite was sensitive only to Mn 2+ . The properties of the two prepared solid samples, magnesium sulfite and calcium sulfite, were compared using X-ray diffraction, scanning electron microscopy, and particle size analysis. The position-occupying hypothesis was applied to determine the selective catalytic behaviors of transition metals for the oxidation of various sulfites by comparing the ionic potentials of the metals. The results provide an effective theoretical basis for catalyzing the sulfite oxidation in WFGD. [ABSTRACT FROM AUTHOR]

• A dynamic model for in-situ desulphurization of CFB boilers was established. • The model was validated against measured data from a 300 MW CFB boiler. • In-situ SO 2 emission can be predicted based on the model about 120 s in advance. • A novel control strategy used for operation optimization of CDS was developed. • The limestone consumption of CDS was reduced by 15.14% after operation optimization. As the emission regulation becomes more stringent, in-situ desulfurization and wet flue gas desulfurization have been widely used for circulating fluidized bed (CFB) boilers. However, few studies focus on real-time operation optimization of combined desulfurization system (CDS) in wide-load range based on in-situ SO 2 emission prediction. In this work, according to mechanism analysis, a dynamic prediction model of in-situ SO 2 emission was developed. Then, closed-loop and step response experiments were conducted to validate the established model, combined with measured data from a 300 MW CFB boiler. Validation results show that the model has satisfactory prediction accuracy in different load conditions and it can capture special dynamic characteristics of in-situ SO 2 desulfurization. More importantly, the model can be feasible for building an economical operation strategy of CDS. Thus, a novel control strategy based on dynamic prediction model was designed, which contributes to decrease the SO 2 emission fluctuation and operation costs by correcting the limestone-feed rate in advance. The proposed control strategy was applied to actual operation of the 300 MW CFB boiler. In the long-term operation of CDS after optimization, it was easier to reach ultra-low SO 2 emission standard and limestone consumption reduces 15.14% compared with before the operation optimization. [ABSTRACT FROM AUTHOR]

Coal-fired power plants are amongst the largest sources of air pollution in India. These power plants emit a number of gaseous pollutants, including sulphur dioxide (SO), nitrogen oxides (NO) and also particulate matter. Recent international as well as national studies show a rapid increase in SO and NO emissions. Both these gases have harmful impact on human health and hence need to be controlled. Typically, these pollutants are controlled using the wet flue gas desulphurization (FGD) units (for SO) and hot-side selective catalytic reduction (SCR) units (for NO)-mostly absent in the coal-fired power plants in India. This paper attempts to understand the plant level implications of using Wet FGD and hot-side SCR systems in Indian coal-fired power plants. The impacts on the technical (efficiency, energy penalty), environmental (emissions, fuel use) and economic (cost of electricity) aspects have been estimated through simulation of a power plant with and without the emission controls. Effect of increasing use of high-sulphur imported coal has also been discussed. [ABSTRACT FROM AUTHOR]

An environmentally friendly method for electrochemically regenerating alkali-sorbent (NaOH) and recovering sulfur in the flue gas as H2SO4, while producing H2 as a clean energy source from flue gas desulfurization (FGD) residuals in an electromembrane reactor, was proposed in this article. To optimize and improve the performance, the optimal operating conditions were deduced from the numerical simulation and validated using experimental data. Under the optimized conditions, the current efficiencies of alkali-sorbent regeneration and H2SO4 reached 84 and 87%, respectively, which is comparable to those obtained in the chlor-alkali industry. Therefore, this method has the potential to be scaled up. If this technology is integrated into an existing FGD facility, the money-consuming chemical process could be transferred into a renewable resource and clean energy conversion process. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2613-2624, 2014 [ABSTRACT FROM AUTHOR]

Both the processes of refining oil and gas processing and petroleum products and in phase storage and delivery of finished products, petro chemical plants generate emissions in the atmosphere, waters and along the ground. Therefore environmental management and pollutants has become a major activity in the development of refineries . The type and quantity of environmental emissions from refineries are usually cuantificate and so well known. The main pollutants generated by the petrochemical industry are oxides of carbon, nitrogen and sulfur, particulates (mainly generated from combustion processes) and volatile organic compounds. This paper aims to introduce the reader to the study of sulfur recovery technologies from flue gases and numerical modeling of the effect of pH on the absorption of sulfur dioxide. [ABSTRACT FROM AUTHOR]

In the coal slurry scrubbing process, SO2can be removed through both the coal pyrite leaching reaction and the oxidation reactions catalysed by Fe2+/Fe3+produced in situ. In the present study, experiments of SO2removal with coal slurry (particle size fraction 65–150 μm) were carried out using a double-stirred vessel to investigate the effects of temperature, coal particle size and pulp density on SO2absorption rate and on the proportion of SO2removed through the leaching reaction. Results show that the SO2absorption rate can be increased by decreasing particle size and increasing pulp density, but it is relatively less affected by temperature. Although decreasing coal particle size and pulp density can increase coal pyrite conversion, the effectiveness is limited and the proportion of SO2removed through the leaching reaction is little affected. Increasing temperature can evidently increase the proportion, but there also exists the problem of energy expenditure; satisfactory coal pyrite conversion during SO2removal could not be achieved economically by such measures. In addition, the apparent rate constant has a linear relationship with the reciprocal of the coal particle diameter. [ABSTRACT FROM PUBLISHER]

Abstract: Effects of humidification water parameters (ratio of humidification water to total water, location of humidification water) on semi-dry flue gas desulfurization removal efficiency has been experimentally investigated. The optimal values of the parameters were obtained under the experiment conditions, which were 30% for ratio of humidification water to total water and at 6 meters above the lime slurry nozzle. SO2 removal efficiency of the scrubber and the whole system can reach 72% and 87% respectively which are 14% and 6% higher than corresponding efficiency without humidification water. [Copyright &y& Elsevier]

Abstract: A model of wet limestone flue gas desulfurization (WLFGD) system has been developed based on the use of the number of transfer units (NTU) and height of transfer unit (HTU) focused to full-scale coal-fired power plants. The model describes the process occurring in the absorber as the most important step in the WLFGD system by establishing what increase in SO2 removal can be achieved as the higher levels of nozzles come progressively into service when initially the first spray header is operating alone, and keeping the other operating conditions under control. This relative improvement of the SO2 removal can be obtained from only one datum: the number of mass transfer units when only the first spray level is on service (N 1). The model computes the gains in both the volumetric overall mass transfer coefficient and the number of transfer units. The model can be used to evaluate data or changes in an existing full-scale system as well as to evaluate proposed system designs and even as a pre-design tool in relation to the number of spray levels on service under controlled operating conditions. The model is tested on the basis of some data taken from a power plant and from the literature. The model results agree well with the real and published data. [ABSTRACT FROM AUTHOR]

Abstract: Water-bath microwave method was used for hydroxyl ammonium ionic liquids (ILs) synthesis to study the removal of sulfur dioxide (SO2) from the flue gas. The results showed that the water-bath microwave method has some advantages of short reaction time and good yields. The synthesis of ethanolamine lactate ILs was fundamentally studied by an orthogonal experiment design (L9(34)). Based on statistic analysis, it is revealed that the molar ratio of ammonium/acid is the most significant variable, and the optimized preparation conditions are under 338K, wave power of 300W for 30min with the molar ratio 1:1.1 (ethanolamine vs. lactic acid). At the same condition, the yield of the other ILs was over 90% except dimethyl ethanolamine-based ILs. Results showed that the solubility of SO2 in ethanolamine lactate ILs was 0.51 (mole fraction), higher than others. Ethanolamine lactate ILs was a better absorbent for SO2. The optimal temperature for the absorption and desorption process were 298 and 363K, respectively. The optimal desorption time was 60min. It was also found that water-bath microwave can improve the release of the absorbed SO2 from ILs. [Copyright &y& Elsevier]

Dry regenerative flue gas desulfurization (FGD) is a promising method to tackle industrial issues regarding SO 2 emission into the atmosphere due to its sorbent being highly accessible, the lack of water dependency and reduction in waste management. This study examined the feasibility of using fibrous mesoporous silica KCC-1 which has been reported to possess better properties than several other predecessor mesoporous silica as alternative sorbents for dry FGD. Calcium metal was introduced to overcome the lack of active sites available on KCC-1 while simultaneously providing sufficient basicity to counter the increase in acidity brought by SO 2 adsorption. Three sorbent modification parameters were analyzed: metal loading (5–15 wt %), calcination temperature (823–973 K) and calcination time (5.5–7 h), and the prepared samples were characterized using BET surface area and pore analyzer, FESEM-EDX, XRD and H 2 -TPR. The breakthrough experiment was conducted using a lab scale fixed bed reactor system with 1500 ppm SO 2 /N 2 at 200 mL/min. SO 2 removal was optimized by sorbent prepared with calcium loading of 5 wt %, calcination temperature of 923 K and calcination time of 6.5 h with adsorption capacity of 3241.94 mg SO 2 /g KCC-1. The optimized sorbent demonstrated highest surface area, good pore development, high dispersion of calcium metal, appropriate impregnation of calcium oxide which caused only minor distortion to the silica framework of KCC-1. Subjecting the optimized sample to five consecutive regeneration cycles by heating at 773 K while simultaneously flowing N 2 gas for an hour shows good regeneration performance with a total final reduction of only 25% from the initial adsorption capacity obtained from a fresh sample. [Display omitted] • Dry desulfurization using calcium modified KCC-1 mesoporous silica as sorbent. • Optimized calcium metal loading, calcination temperature and calcination time. • Adsorption capacity of 3241.94 mg/g attained by optimized Ca/KCC-1. • SO 2 removal controlled by surface area, porosity, basicity and crystallite size. • Feasible for regeneration by simple heating at 773 K and nitrogen flow. [ABSTRACT FROM AUTHOR]

Abstract: Dry scrubbing processes, especially dry sorbent injection technology, offer a more economical technology for retrofitting than wet or semi-wet scrubbing processes. A simple realistic model for the in-duct desulfurization process has been developed. The model has been conceived as an approach useful for both analyzing results and aiding in design of an in-duct desulfurization process. The model of the process involved, which is the basis for the discussion in this paper, has been evaluated by comparing the model results and the experimental data, obtained in a pilot plant study. The predicted values agree reasonably well with the available experimental data, and the relationships in the model presented have been verified. The sensitivity analysis of variables is relevant for the design and operation of the in-duct process, allowing a parametric study that reveals the effect of the different operation and design factors. Although this model is specific to our in-duct pilot plant, it may be used with confidence in commercial DSI (dry sorbent injection) units as it was designed and implemented according to widely accepted engineering rules in this field. The model has been built in an open structure to allow for rearrangements of and extensions to the process. [Copyright &y& Elsevier]

This article introduces a predictive capability for Hg retention in any Ca-based wet flue gas desulfurization (FGD) scrubber, given mercury (Hg) speciation at the FGD inlet, the flue gas composition, and the sulphur dioxide (SO2) capture efficiency. A preliminary statistical analysis of data from 17 full-scale wet FGDs connects flue gas compositions, the extents of Hg oxidation at FGD inlets, and Hg retention efficiencies. These connections clearly signal that solution chemistry within the FGD determines Hg retention. A more thorough analysis based on thermo-chemical equilibrium yields highly accurate predictions for total Hg retention with no parameter adjustments. For the most reliable data, the predictions were within measurement uncertainties for both limestone and Mg/lime systems operating in both forced and natural oxidation mode. With the U.S. Environmental Protection Agency's (EPA) Information Collection Request (ICR) database, the quantitative performance was almost as good for the most modern FGDs, which probably conform to the very high SO2 absorption efficiencies assumed in the calculations. The large discrepancies for older FGDs are tentatively attributed to the unspecified SO2 capture efficiencies and operating temperatures and to the possible elimination of HCl in prescrubbers. The equilibrium calculations suggest that Hg retention is most sensitive to inlet HCl and O2 levels and the FGD temperature; weakly dependent on SO2 capture efficiency; and insensitive to HgCl2, NO, CA:S ratio, slurry dilution level in limestone FGDs, and MgSO3 levels in Mg/lime systems. Consequently, systems with prescrubbers to eliminate HCl probably retain less Hg than fully integrated FGDs. The analysis also predicts re-emission of Hg0 but only for inlet O2 levels that are much lower than those in full-scale FGDs. [ABSTRACT FROM AUTHOR]

• Mixed Na 2 SO 3 and (NH 4) 2 SO 3 are employed as absorbents to remove NO X and SO 2. • Effects of mass concentration ratio and pH are investigated. • High absorption efficiencies for SO 2 and NO X (over 93%) are obtained. • The initial pH of the absorbent affects the absorption performance. Wet flue gas desulfurization is considered as one of the most effective methods for the simultaneous removal of NO X and SO 2 in the flue gas. To investigate the absorption performance of NO X and SO 2 with the absorbents of Na 2 SO 3 and (NH 4) 2 SO 3 and study the controlling factors of the process, the sulfite-based mixed absorbents with different mass concentration ratios of Na 2 SO 3 to (NH 4) 2 SO 3 are employed for the gas removal in a bubble absorber. The results indicate that the absorbents have high absorption efficiency for SO 2 and NO 2 (all over 93%) with different mass ratios of Na 2 SO 3 to (NH 4) 2 SO 3 , and the absorbent with the proportion of 50%: 50% has the highest removal efficiency for NO (73.8%). The pH of the absorbent solution is a controlling factor affecting the absorption performance, and the alkaline condition is more conducive to absorption. The more the content of (NH 4) 2 SO 3 is, the lower the pH value and SO 2 absorption amounts are. Moreover, the absorbent with a ratio of 30%: 70% has the highest removal efficiency (99.6%) and also the highest absorption amount (2761 mg/100 g) of SO 2 (when the initial pH is the same). For the simultaneous absorption of NO X and SO 2 , the absorbent with a ratio of 30%: 70% has the highest removal efficiency (64.3% for NO X and 99.5% for SO 2). [ABSTRACT FROM AUTHOR]

• A novel process using red mud-limestone slurry as composite absorbent for flue gas desulfurization, which has better absorption ability to SO 2 in flue gas. • The process was applied in a pilot test of a demonstration project, which provided a theoretical basis for engineering application. • The possible mechanism of desulfurization is discussed through the simulation of thermodynamics and kinetics models. With the increasingly stringent emission standards of flue gas, a demonstration project of desulfurizing by "red mud-limestone process" was established to make the flue gas meet the Emission Standards of Pollutants for Aluminum Industry. As shown by the detection results, the emission concentration of Sulfur dioxide (SO 2) was less than 50 mg/m3, and the particulate pollutant was less than 10 mg/m3, which realized the ultra-low emission of flue gas pollutants in a cheap and efficient way. In addition, the desulfurization mechanism was analyzed by laboratory comparative experiments and characterization analysis of engineering samples. Furthermore, the advantages and disadvantages of the red mud-limestone process are analyzed. Compared with other desulfurization processes, the red mud-limestone process is a reliable process for desulfurization of flue gas from calcination. [ABSTRACT FROM AUTHOR]

• SO 2 absorption depending on spray conditions is identified in a commercial scrubber. • Optimal droplet diameter is the synergy between flow pattern and mass transfer. • Dual-direction spray balances flow uniformity and slurry holdup in three regions. • A unique combination of full- and hollow-cone sprays optimizes transfer condition. To intensify SO 2 absorption process in wet flue gas desulfurization (WFGD) spray scrubber, a comprehensive CFD model coupled transfer process with chemical reactions is established by Eulerian‒Lagrangian method and verified in a commercial-scale device of 330 MW coal-fired power unit. The desulfurization performance is significantly affected by both the property of each droplet and the dispersion of droplet swarm, which are determined by the spray behaviors. Three dominant factors, including droplet diameter, injection direction and spray morphology, are explored to optimize the spray conditions for intensifying SO 2 absorption process. Differing from the ideal plug flow, the optimal diameter of droplet in non-ideal flow is obtained by considering the synergistic effect of the uniformity of gas–slurry distribution and the dynamics of SO 2 mass transfer. Compared with the single-direction spray with downward or upward injection, the dual-direction spray reaches a great balance between the competitive effects of the uniformity of gas‒slurry flow and the interfacial area for mass transfer. The influence of spray morphology on mass transfer process is essentially the difference of dispersion characteristics of droplets in the middle part of scrubber. A design scheme combining full-cone and hollow-cone nozzles is suggested for improving the overall SO 2 removal efficiency. [Display omitted] [ABSTRACT FROM AUTHOR]

A method was proposed for simultaneously regenerating magnesia from the Mg-based flue gas desulfurization byproducts in the power plant and generating the high concentration of sulfur dioxide. Elemental sulfur particles were evaporated to sulfur vapor and the latter one was used as the reductive agent to regenerate magnesia from the magnesium gypsum. The experiments were carried out in a successive fixed-bed system to study the concentration of sulfur dioxide in the exhaust gas and the activity of the regenerated magnesia under different reaction conditions. Sulfur vapor effectively reduced the magnesia regeneration temperature from above 950 °C to merely 650 °C. The concentration of sulfur dioxide in the exhaust gas could achieve 20% by volume when the sulfur vapor partial pressure was 1674 Pa, the regeneration temperature was 750 °C, the gas hourly space velocity was 1200 h−1 and the loading of the reaction materials in the regeneration reactor was 16 g, respectively. The activity of the regenerated magnesia after the decomposition of the magnesium gypsum at 750 °C was satisfactory. Both the magnesium gypsum and the regenerated magnesia were characterized using X-ray fluorescence spectroscopy, thermogravimetric analyzer, X-ray diffraction spectroscopy, BET surface area analyzer, scanning electron microscopy, high resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. The kinetics of the magnesia regeneration from the magnesium gypsum in the presence of the sulfur vapor was analyzed and the nucleation model was determined to be the most appropriate kinetic model. The activation energy and the pre-exponential factor were determined to be 76.51 kJ/mol and 228.66 min−1, respectively. All the results demonstrate that there is considerable potential for the application of this proposed method in flue gas desulfurization process. Image 1 • Sulfur vapor can regenerate MgO from magnesium gypsum at low temperature. • Highly active MgO and high concentration of SO 2 were generated. • A nucleation mechanism was uncovered for the regeneration of MgO. • The activation energy between sulfur vapor and MgSO 4 was 76.51 kJ/mol. [ABSTRACT FROM AUTHOR]

Given the positive effects of jet bubble reactors as particulate matter (PM) traps, a new integrated technology was investigated, termed here the spray-and-scattered-bubble process. The main goal was to demonstrate that it can satisfy ultra-low emission limits for the ammonia-based desulfurization process, where the aerosol generated by the spraying droplets is further removed by the bubbling step in one device. Compared with the conventional spray-only method, this new technology generates a lower particulate level based on the same desulfurization efficiency, and the particulate size has an effectively unimodal distribution with a main size range from 0.156 μm to 1.64 μm. The removal mechanism under the new technology is further explored by density functional theory (DFT) and a large adsorption energy between was found to exist between the sulfites and (NH 4) 2 SO 4 particles. The process parameters that affect the particulate emission were studied using lab-scale tests, by changing the SO 2 concentration, the immersion depth and the liquid/gas ratio. The results indicated that the amount of particulate matter significantly increases in the presence of SO 2 in the flue gas and was positively correlated with the SO 2 concentration. The liquid/gas ratio showed a positive correlation with the particulate matter emissions, while the immersion depth is closely tied to the inhibition effect. To further verify its potential, long-term experiments with actual flue gas were performed in a 5000 Nm3/h pilot platform. The "daily mean results" showed that the PM emission concentration was 5 mg/m3, which is far below the ultra-low limits now proposed in China. • An integrated technology was studied to meet the PM ultra-low emission limit. • The removal mechanism is explored by quantum chemistry calculation. • The field test of pilot-scale spray-and-scattered-bubble facility is built. [ABSTRACT FROM AUTHOR]

• Simultaneous NO and SO 2 removals was effectively achieved by Recycling Process based on MNBOS. • The oxidation of OH generated by MNBs chiefly contributed to NO removal. • HA-Na reacted with H+ formed by the oxidation-absorption of NO and SO 2 , thus promoting NO removal. • The recycling oxidation-absorption of NO and SO 2 was realized because the system ran in a loop. • Byproducts were mainly HA, sulfate and nitrate, which can be recycled as a compound fertilizer. Wet oxidation-absorption is a promising process for flue gas desulfurization and denitration due to its simple system and high removal efficiency. In comparison to the ordinary bubbles, micro-nano bubbles have some special properties such as spontaneous generation of hydroxyl free radicals and self-pressurized solution. Sodium humate (HA-Na), which is a cheap, easily accessible and recyclable reagent, can react with H + to produce humic acid sediment so that it may promote the solution of NO 2 and SO 2 in the water. In this study, a new wet recycling micro-nano bubble oxidation-absorption process based on HA-Na was developed for the simultaneous removal of NO and SO 2. A micro-nano bubble generator (MNBG) was utilized to generate the micro-nano bubble oxidation-absorption system (MNBOS) from HA-Na aqueous solution and the mixed gases, composed of N 2 , NO, SO 2 and/or other gases including O 2 and CO 2. The MNBOS was recycled continuously from the MNBG to the reactor. The critical operation parameters, including operation time, initial pH and temperature of the absorbent, HA-Na concentration, NO concentration, SO 2 concentration, presence of O 2 and/or CO 2 , were investigated to explore the simultaneous removal of NO and SO 2 with the MNBOS. The results showed that hydroxyl free radicals generated by micro-nano bubbles played a critical role in the removal of NO and HA-Na promoted the removal of NO. All the investigated parameters affected NO removal. Only initial pH and temperature of the solution and concentrations of NO and SO 2 affected SO 2 removal, whereas the presence of O 2 and CO 2 or HA-Na concentration had no significant effect on SO 2 removal. This new process could achieve high removal efficiency which was respectively above 91.1% for NO and 99.7% for SO 2 under the conditions of 0.5 g/L HA-Na, initial solution pH 7.47, initial solution temperature 298 K, 1250 ppm NO and 1650 ppm SO 2. Moreover, according to the analysis of FTIR and XPS, the removal products were mainly HA, sulfate and nitrate, which are the components of fertilizer and can be recycled as compound fertilizer which has higher activity compared with the traditional HA fertilizer because HA from this system is subjected to oxygenolysis by nitric acid and sulfuric acid in solution. [ABSTRACT FROM AUTHOR]

Electrochemical oxidation of sulfite ions offers an efficient and profitable approach to the conversion of sulfur dioxide, a harmful air pollutant, into valuable by-products via flue gas desulfurization. Here, the electrochemical oxidation of sulfite in near-neutral pH electrolytes is studied in order to determine kinetic parameters and a reaction mechanism. Sulfite electrooxidation on palladium is demonstrated at pH 7.5 and 8.5, the latter being comparable to platinum. Anodic charge transfer coefficients and non-linear reaction orders are linked to a mechanism which involves sulfite adsorption at low potentials. This study proves that sulfite electrooxidation on palladium at near-neutral pH is a useful approach for sulfur dioxide exploitation. Unlabelled Image • Kinetic parameters from sulfite electrooxidation at near-neutral pH are obtained. • Electrooxidation of sulfite on Pd proved to be similar to that on Pt at pH 8.5. • Sodium sulfite electrooxidation on Pd exhibited higher current densities. • A reaction mechanism based on adsorption of sulfite occurs at low potentials. • Catalytic activity of Pd offers a useful approach for ammonia-based FGD. [ABSTRACT FROM AUTHOR]