SO2 Removal Efficiency Research Articles

Modular manganese/diatomite-Santa Barbara Amorphous-15 sorbent for moderate-temperature flue gas desulfurization

As two typical silicon source carrier, the features of diatomite and Santa Barbara Amorphous-15 (SBA-15) supported Mn-based sorbents for moderate-temperature flue gas desulfurization are investigated in this paper. The framework structure, high mechanical strength and large density of diatomite make great contributions to the high desulfurization efficiency (96%) of diatomite supported Mn-based sorbents (MxDy). Nevertheless, the excessive Mn doping (50 wt%) exhibits the decline in desulfurization efficiency, resulting from the self-seeding nucleation and the bareness of micro-pores. Compared to M4D6, the dispersion of active component on the surface of SBA-15 is much more uniform and the sulfur capacity of SBA-15 supported Mn-based sorbent (M4S6) is sharply increased from 186 mg/g to 494 mg/g. On the other hand, the small density of SBA-15 and formation of some bare micro-regions of Mn2O3 in M4S6 lead to the weak contact between SO2 molecule and the active component on the surface of sorbent, as well as the decrease of desulfurization efficiency of M4S6 (88%). Further, the desulfurization mechanism of M4D6 and M4S6 is explored through analyzing the chemical reaction, external mass transfer and internal diffusion. The modular Mn/diatomite-SBA sorbents are developed by combining the advantages of M4D6 and M4S6. When the weight ratio of M4D6 and M4S6 reaches 3:2, the SO2 removal efficiency of modular sorbent and sulfur capacity can reach 96% and 366 mg/g, respectively.

Simultaneous NO/SO2 removal by coconut shell char/CaO from calcium looping in a fluidized bed reactor

A simultaneous NOx/SO2 removal system using bio-char and CaO combined with calcium looping process for CO2 capture was proposed. The simultaneous NO/SO2 removal performance of coconut shell char/CaO experienced CO2 capture cycles was investigated in a fluidized bed reactor. The effects of reaction temperature, mass ratio of CaO to coconut shell coke, CaO particle size and number of CO2 capture cycles from calcium looping process were discussed. The NO removal efficiency of char is improved under the catalysis of CaO. The reaction temperature plays an important role in the simultaneous NO/SO2 removal. Coconut shell char/CaO achieve the highest NO and SO2 removal efficiencies at 825 oC, which are 98% and 100%, respectively. The mass ratio of CaO to coconut shell char of 60: 100 is a good choice for the simultaneous NO/SO2 removal. Smaller CaO particle size contributes to higher NO and SO2 removal efficiencies of coconut shell char/CaO. The NO and SO2 removal efficiencies of coconut shell char and cycled CaO from calcium looping declined slightly with the number of CO2 capture cycles. In addition, the Ca-based materials balance in process of simultaneous NOx/SO2 removal combined with calcium looping is given. The novel simultaneous NO/SO2 removal method using bio-char and cycled CaO from calcium looping process appears promising.

Simultaneous Removal of SO2 and NO by O3 Oxidation Combined with Wet Absorption.

The effects of ozone concentration, NaOH concentration, type and concentration of additives, initial pH, temperature, and NO and SO2 concentration on simultaneous removal of NO and SO2 were studied through ozone oxidation combined with wet absorption. Results indicated that ozone concentration and the type and concentration of additives had the most significant effect on NO removal. The optimal ozone concentration was 250 ppm (NO/NO2 = 1), and the best additive was KMnO4. The removal efficiency of NOx was as high as 97.86% when NO/NO2 = 1, and the concentration of KMnO4 was 0.025 mol/L. Considering economic and other factors, the KMnO4 concentration was selected to be 0.006 mol/L. At this time, the removal efficiencies of NOx and SO2 were 81.35 and 100%, respectively. This method has potential application prospects for simultaneous removal of SO2 and NO in the industrial flue gas.

SO3 removal efficiency and ash particle flowability of low-low-temperature flue gas systems (LLTSs)

SO3 removal efficiency and ash particle flowability of low-low-temperature flue gas systems (LLTSs) were studied. The results indicate that when the temperature is approximately 40 °C lower than acid dew point (Td), the SO3 removal efficiency reaches a maximum. This optimum temperature is affected by particle physical characteristics and elemental composition. The SO3 removal efficiency increases as ash/sulfur ratio (D/S) increases. However, when temperature is low, the effect of D/S is weak. Particle size is also an important factor for the removal efficiency. The adsorption process is a synergistic effect of physical and chemical reactions. Chemical adsorption, which depends on the metal elements, especially Al elements, helps fix the sulfur element on particle surface and increase the stickiness of it. The agglomeration of ash particles mainly happens between smaller particles or between small particles and large particles. However, when temperature drops too much, large particles will agglomerate with each other due to the effect of H2O vapor. The particle flowability is greatly reduced after the adsorption process. When temperature is 20 °C lower than Td, the repose angle increased greatly. Hence, the temperature should be properly lowered in pursuit of high sulfur oxide removal efficiency and dust removal efficiency.

A novel semi‐dry method for the simultaneous removal of Hg and SO2 using spray drying absorption method

AbstractBACKGROUNDA novel semi‐dry method called SDA (spray drying absorption) for the simultaneous removal of mercury (Hg0) and sulfur dioxide (SO2) have been proposed in this article, in which Hg0 was initially oxidized by gaseous oxidant (O3) and liquid oxidant (K2S2O8, H2O2, and NaClO2), after which SO2 and Hg2+ were absorbed by Ca(OH)2.RESULTSThe effects on different process conditions and additives on Hg0 removal were explored at first, and the results indicated that the Hg removal efficiency could be improved by oxidizing or extending the residence time of the liquid phase reaction. When SO2 and Hg coexist in the atmosphere, additives including oxidants or composite additives were added into the mixed system, and the results indicated that the best removal efficiency of SO2 and Hg was about 99.5% and 51% respectively.CONCLUSIONSince SO2 has good water solubility, it would affect the oxidation of Hg and the removal of Hg. When there was nitric oxide (NO) in the atmosphere, a new stable product was generated which contributed to the removal of Hg, and the removal efficiency of SO2 and Hg was about 99.5% and 57% respectively. © 2020 Society of Chemical Industry

Catalytic effect of Mn2+, Fe3+ and Mg2+ ions on desulfurization using phosphate rock slurry as absorbent

Wet phosphate rock flue gas desulfurization is a new and promising technology, which has drawn increasing attention in recent years. The effect of Mn2+, Fe3+ and Mg2+ dissolved from phosphate rock on removal efficiency of SO2 were systematically investigated in this paper. The XRD, FT-IR, SEM, XPS, IC and ICP were used to characterize the reacted products, demonstrating that these metal ions have promotive effect on the purification of SO2. Especially, trace Mn2+ and Fe3+ ions can rose up about 19%–31.5% SO2 absorption capacity compared to the system without metal ions. Furthermore, the catalytic effect of these metal ions on the oxidation of S(IV) were compared, by adding them to the sodium bisulfite aqueous solution system. The order of catalytic capability of metal ions to S(IV) is: Mn2+ > Fe3+ > Mg2+. Interestingly, in the simultaneous presence of Mn2+ and Fe3+, the catalytic synergism between them toward S(IV) oxidation is exhibited. And only 16.56 kJ/mol of activation energy is needed, which is reduced by 74.1% compared to systems without catalyst. Consequently, a satisfactory result for absorption of SO2 can be obtained although the concentrations of Mn2+ and Fe3+ in phosphate rock slurry is low. Additionally, the catalytic mechanism of Mn2+ and Fe3+ towards S(IV) was investigated by reaction barrier and free energy calculation.

Prediction of SO2 removal efficiency for ammonia-based wet flue gas desulfurization in a packed tower

Wet flue gas desulfurization is widely used in power plants because of its high desulfurization efficiency. The reason why it is difficult to predict sulfur dioxide removal efficiency in flue gas is that it is related to many factors. In this paper, the SO2 was removed by absorbing with ammonia solution in a packed tower. Experimental studies have shown that the operating conditions affecting the removal of sulfur dioxide include pH, liquid-to-gas, the concentration of SO2 and inlet velocity. Based on the two-film theory, the mass transfer rate equation of SO2 in the ammonia desulphurization process was studied, and the prediction of SO2 removal efficiency based on certain assumptions was developed. In order to prove the responsibility of the model, significant factors such as pH, liquid-to-gas, the concentration of SO2, and inlet velocity were studied in a packed tower. The experimental results show that it is possible to improve desulphurization efficiency by increasing the liquid-to-gas ratio and pH value, lowering the concentration of SO2 and inlet velocity. Experimental results show that the experimental value is consistent with the predicted value.

Simultaneous removal of NO and SO2 from flue gas by FeIIEDTA/sodium dithionite solutions

AbstractBACKGROUNDThe SO2 and NO emitted from coal‐fired power plants have caused serious air pollution in China. FeIIEDTA complexation technology is one of the most promising processes to realize the simultaneous removal of SO2 and NO. However, FeIIEDTA is easily oxidized to FeIIIEDTA, causing loss of activity, which limits its further application. To solve this problem, sodium dithionite (SD) combined with FeIIEDTA was used for the simultaneous removal of SO2 and NO.RESULTSResults showed that the SO2 removal efficiencies were ≈92–99% in all experiments, whereas the NO removal fluctuated substantially under different operating conditions. Specifically, SD can markedly improve NO removal efficiency, and the optimal FeIIEDTA:SD ratio was 3 mmol L–1:0.026 mol L–1. With increasing temperature, pH value, SO2 concentration or O2 concentration, the NO removal efficiency increased first and then decreased. As the NO concentration increased, the NO removal efficiency continually decreased. Finally, based on the analysis of different ion concentrations, the main products were identified as sulfite, sulfate, ammonium, nitrite and nitrate.CONCLUSIONThe synergistic mechanism of SD and FeIIEDTA on SO2 and NO was investigated. SD can regenerate FeIIEDTA solution by reducing FeIIIEDTA and FeIIEDTA‐NO. These fundamental findings can offer valuable guidance for industrial denitrification and desulfurization by mixed FeIIEDTA and SD systems. © 2019 Society of Chemical Industry

A preliminary study on effect of additive in the removal of NOx and SO2 by electron beam irradiation

In this study, an electron beam (EB) was used to remove target compounds (NOx and SO2), which exist in flue gas that is emitted from fossil fuel combustion. In order to improve the removal efficiency of NOx and SO2, we investigated various influencing factors such as type (H2O, NH4OH, NaCl, NaOH, Ca(OH)2, CaCl2, NaClO2, and HA–Na (C9H8Na2O4)) and injection amount of additive, and absorbed dose (5, 10, and 20 kGy). When NaOH solution was added to EB treatment process, the removal efficiencies of all target gases (NOx and SO2) were the highest. When NaOH was used as additive, the removal efficiencies of NOx and SO2 were additionally increased up to 60 and 18.5%, respectively, compared to electron beam only process. As the amount of injected additive increased, the removal efficiency also increased. The removal efficiencies of SO2, NO, and NO2 at 10 kGy were 100, 79.8, and 83.9%, respectively, when the stoichiometric ratio (reaction ratio) between target compounds and NaOH was 1:2. Also, the removal efficiencies of SO2, NO, and NO2 increased gradually as absorbed dose increased.

An experimental study on the simultaneous removal of NO and SO2 with a new wet recycling process based on the micro-nano bubble water system.

The micronano bubble water system (MNBW) generated by a micronano bubble generator (MNBG) has the superior oxidation properties and can improve gas solubility. In the study, a new wet recycling process based on MNBW is proposed to simultaneously remove nitric oxide (NO) and sulfur dioxide (SO2). The important experimental parameters such as initial water pH, initial water temperature, NO and SO2 concentrations, and the presence of oxygen (O2) were investigated to explore the feasibility of desulfurization and denitration with MNBW. The experimental results showed that decreasing initial water pH or increasing initial water temperature and NO and SO2 concentrations were not conducive to the removal of NO or SO2. O2 could promote the removal of NO, but it had no effect on SO2 removal. In addition, SO2 removal efficiency always remained high and did not change obviously during the experimental period. However, NO removal efficiency gradually decreased in the first 50min and then became stable.

Selective removal of SO2 from coal-fired flue gas by alkaline solvents using a membrane contactor

The presence of SO2 in coal-fired flue gas has adverse effects on the amine solutions used for CO2 capture. In addition, SO2 emissions in the atmosphere are also a primary source of pollution. In this study, the SO2 removal efficiency of three aqueous alkaline absorbents NaOH, Na2SO3, and CaO was studied using a membrane contactor. The morphology of the used membrane was examined using SEM and contact angle characterization techniques. Gas removal efficiency was studied within a feed gas flow rate of 0.5–5 m3/h, absorbent flow rate of 5–100 mL/min, and absorbent concentration of 0–0.01 mol/L. The gathered results showed that aqueous CaO has superior gas removal performance. It achieved a SO2 removal efficiency of 99.99 % at a concentration of 0.0025 mol/L, while the aqueous NaOH and Na2SO3 absorbents achieved 99.99 % removal efficiency at concentrations of 0.001 mol/L. Through comprehensive experimental work, the optimum operating parameters needed to achieve maximum SO2 removal efficiency were also determined. Furthermore, the durability of the membrane was tested in a four week continuous gas removal test and SEM images were recorded weekly to observe module morphology. The obtained results indicated that the membrane was quite durable and did not deteriorate noticeably.

Simultaneous removal of NO and SO2 through a new wet recycling oxidation–reduction process utilizing micro-nano bubble gas–liquid dispersion system based on Na2SO3

Wet desulfurization and denitrification technologies are one of the main research directions in the future air pollution control. Compared with the traditional macro-bubbles, the MNBs can spontaneously generate ·OH with high oxidizing ability, and also improve the gas solubility. Na2SO3 is a strong reducing agent and can react with NO, NO2, NO2– and NO3– to convert ionic N to non-toxic and harmless N2. In the study, based on the principle of wet desulfurization and denitrification, a new recycling oxidation–reduction process was firstly proposed for simultaneous removal of NO and SO2 by using the MNBGLS which was generated with a MNBG through recycling Na2SO3 aqueous solution at a given concentration from a column reactor and the simulated flue gas composed of NO, SO2, N2 and/or other gases such as O2 and CO2. The MNBGLS was recycled continuously from the MNBG to the reactor. The effects of various experimental parameters, such as operation time, initial pH and temperature of absorbent, Na2SO3 concentration, NO concentration, SO2 concentration, the presence of O2 and CO2, on the removal of NO and SO2, were investigated. All the investigated parameters affected the removal of NO, whereas only initial solution pH influenced the removal of SO2. This new process can not only achieve high NO and SO2 removal efficiencies but also treat NO2– and NO3– so as to reduce the cost of subsequent wastewater treatment. Moreover, the main removal product, SO42−, can be recycled. Thus it is an economical, environmentally friendly and efficient desulfurization and denitrification process.

Desulfurization performance of sulfur dioxide and product characteristics in semi-batch bubble column and foam-bed contactor

Two calcium-based absorbents, hydrated lime and calcium carbonate slurries, were employed for studies on absorption of SO2 from simulated flue gases in semi-batch bubble column and foam-bed slurry reactors. The concentration of SO2 at the inlet to, and exit from, the reactor was measured using a ZRJFAY36, Fuji, Japan make infrared SO2 analyzer. Different surface-active agents were used for studies of performance of the foam-bed reactor for the desulfurization operation. With the bubble column reactor, the maximum value of the transient SO2 removal efficiency obtained was 99.4% with hydrated lime slurry, while with the use of calcium carbonate slurry this value was 97.7%. In the foam-bed reactor, the maximum removal efficiencies were found to reduce, more with lime slurry: 91% with each of Triton X-100 and Tween 80, but to 95.2% and 96%, respectively, when calcium carbonate was used as the absorbent. The products obtained from the desulfurization operation were characterized using FT-IR and TGA analyses. Calcium sulfate hemihydrate was obtained for all the combinations of absorbents without and with the surfactant additives, except in the case where Teepol was added to the hydrated lime slurry and gypsum was obtained as the FGD product.

Flue Gas Desulphurization in Circulating Fluidized Beds

Sulphur dioxide (SO2) is mostly emitted from coal-fueled power plants, from waste incineration, from sulphuric acid manufacturing, from clay brick plants and from treating nonferrous metals. The emission of SO2 needs to be abated. Both wet scrubbing (absorption) and dry or semi-dry (reaction) systems are used. In the dry process, both bubbling and circulating fluidized beds (BFB, CFB) can be used as contactor. Experimental results demonstrate a SO2-removal efficiency in excess of 94% in a CFB application. A general model of the heterogeneous reaction is proposed, combining the external diffusion of SO2 across the gas film, the internal diffusion of SO2 in the porous particles and the reaction as such (irreversible, 1st order). For the reaction of SO2 with a fine particulate reactant, the reaction rate constant and the relevant contact time are the dominant parameters. Application of the model equations reveals that the circulating fluidized bed is the most appropriate technique, where the high solid to gas ratio guarantees a high conversion in a short reaction time. For the CFB operation, the required gas contact time in a CFB at given superficial gas velocities and solids circulation rates will determine the SO2 removal rate.

Interaction among the simultaneous removal of SO2, NO and Hg0 by electrochemical catalysis in K2S2O8

Sulfur dioxide (SO2), nitrogen oxides (NOx) and mercury (Hg0) produced by coal combustion are still the main sources of atmospheric pollutants. To find out the interaction among the simultaneous removal of SO2, NO and Hg0, the method of electrochemical catalysis in K2S2O8 was used to oxidize and remove these three pollutants from the simulated flue gas. Results indicated that the presence of SO2 promoted the oxidative absorption of NO under the condition of sufficient oxidant, while NO showed a weak competitive oxidation relationship to SO2. SO2 promoted the oxidative absorption of Hg0 through the generated SO32−, and Hg0 had no obvious effect on the desulfurization process due to its low concentration. NO promoted the oxidative absorption of Hg0 by its oxidation product NO2, and Hg0 also had no significant effect on the denitrification process due to the low concentration. During the removal of SO2, NO and Hg0 by electrochemical catalysis in K2S2O8, the electrochemical method could not only promote the rapid decomposition of S2O82− to produce a large amount of SO4−, but also help the electrolysis of H2O into HO. The oxidation of the solution was enhanced by oxidative free radicals such as SO4− and HO. Thus, the removal efficiency of SO2 oxidized by electrochemically catalyzed K2S2O8 was as high as 96%, the removal efficiency of NO could reach 90%, and the Hg0 removal efficiency was up to 92%.

Simultaneous removal of sulphur dioxide and nitric oxide at different oxygen concentrations in a thermophilic biotrickling filter (BTF): Evaluation of removal efficiency, intermediates interaction and characterisation of microbial communities

Simultaneous flue gas desulphurisation and denitrification in biotrickling filter was investigated under different O2 concentrations (0%, 3%, 5%, 8% and 10%) at 45 °C. NO and SO2 removal efficiency, intermediates (NO3−, NO2−, NO2, SO42− and S2−) interaction and accumulation, S0 recovery and microbial community structure were investigated. Results indicated the highest NO removal efficiency was 96.5% at 5% O2. Maximum SO2 removal efficiency was 95.6% at 3% O2. Moreover, N intermediates accumulation increased when O2 concentration increased from 0% to 10%. The lowest S2− concentration of 61 mg/L and the maximum S0 recovery of 76.9% were achieved at 5% O2. The bioreactor at 10% O2 contained less bacterial OTUs richness and evenness compared with other conditions. Illumina analysis indicated Proteobacteria, Firmicutes and Bacteroidetes were the dominant members. Overall, microbial community structure differs significantly under different O2 concentrations.

Simultaneous Removal of NO and SO2 via an Integrated System of Nonthermal Plasma Combined with Catalytic Oxidation and Wet Electrostatic Precipitator

An integrated system of dielectric barrier discharge (DBD) combined with MnCu/Ti catalyst and wet electrostatic precipitator (DBD–catalyst–WESP) was constructed for simultaneous removal of SO2 and NO. The removal mechanism and the effects of special energy density (SED) and initial concentrations of NO and SO2 on oxidation efficiency were investigated. Experimental results showed that compared with Mn/Ti and Cu/Ti, the MnCu/Ti catalyst exhibited a higher dispersion of active constituents and has more catalytic oxidation active substances. The removal efficiencies of NO and SO2 in the DBD-catalyst system increased with increasing SED (15–275 J/L), and the lower the initial concentration was, the higher were the simultaneous removal efficiencies of NO and SO2. The competitive relationship between the removal of NO and SO2 was clarified. Compared with the DBD–catalyst system, the DBD–catalyst–WESP system significantly improved the simultaneous removal efficiencies of NO and SO2. With low initial concentratio...

Flue Gas Desulfurization by Using Calcined Dolomite

SO2 emissions has begun to cause serious problems in industrialized countries. Today, various methods are used for removal of SO2 gas. SO2 gas is an important raw material for production of sulfuric acid. However, SO2 content of flue gas must be over 6% to produce sulfuric acid commercially. Flue gases, which don’t have enough amount of SO2 to produce sulfuric acid commercially are harmful to the environment and human health and they must be filtered. In this study, calcined dolomite was used to remove SO2 in flue gas which doesn’t have enough SO2 to produce sulfuric acid but have high emission values. Pyrite was used as SO2 source and SO2 removal efficiency of dolomite was determined for different experimental parameters. SO2 capturing system was thermodynamically modeled and SO2 capturing efficiency was determined as 77.81% in the experiments.

Simultaneous removal of gaseous NOx and SO2 by gas-phase oxidation with ozone and wet scrubbing with sodium hydroxide

In conventional coal-fired power plants, selective catalytic reduction (SCR) is used for NOx removal and wet scrubbing is used for SO2 removal. Because of the high operational cost of SCR, researchers have applied wet scrubbing for De-NOX, without SCR. Herein, NO was injected in a lab-scale reactor and oxidized to NO2 by reacting with ozone. Subsequently, wet scrubbing with NaOH solution was conducted in a lab-scale packed-bed scrubber. By varying the concentrations of ozone and SO2, which was also injected in the oxidation reactor, the NO and NO2 concentrations were measured using a gas analyzer. Ion chromatography, X-ray diffraction, and Fourier-transform infrared spectroscopy were used to characterize the scrubbing products. The effects of temperature and pH of NaOH on the NOx and SO2 removal efficiencies are discussed.In the absence of SO2, the injection of ozone at 60% with respect to the NO concentration resulted in the maximum NOx removal efficiency. This was attributed to the formation of trivalent N species (N2O3 and HNO2) and their fast absorption in NaOH. In the presence of 1000 ppm SO2, the ozone concentration needed to be increased to 90% of the NO concentration to maximize the NOx removal efficiency. Higher SO2 concentration led to greater NOx removal efficiency because the SO2 scrubbing product, Na2SO3, enhanced NO2 scrubbing. Higher pH and lower temperature increased the NOx removal efficiency, whereas SO2 was not as sensitive to temperature and pH.

Comprehensive understanding of SO3 effects on synergies among air pollution control devices in ultra-low emission power plants burning high-sulfur coal

Abstract The environmental issue of SO3 pollution caused by coal-fired power plants attracts increasing attention. This work focused on the synergies between air pollution control devices in a 660 MW power plant burning high-sulfur coal. Parameters such as gas temperature and flow rate were varied within wide ranges under actual conditions. Both continuously tested SO3 concentration and on-line operational data were combined to establish a correlation between device performance and operational parameter. Results indicated that the gas temperature acted as a bridge of synergies between the electrostatic precipitator (ESP) and wet electrostatic precipitator (WESP). The SO3 removal efficiency across the ESP increased from 60.3% to 91.1% with the gas temperature decreasing from 136.7 to 114.8 °C, leading to the increase in corona current and the decrease in spark-over frequency of WESP. Moreover, additional electric field stages are also effective to enhance the corona current and reduce spark-over frequency. Furthermore, deviations between the design and operational data within 0–100% loading provided a correction to appropriately choose the gas velocity. With the proposed countermeasures, the SO3 emission can achieve a favorable level less than 5 mg/m3. The research findings provide a valuable technical pathway to eliminate the SO3 emission from power plants burning high-sulfur coal.