Formation Of Sulfur Trioxide Research Articles

Direct Electro-oxidation of H2S gas in a membrane electrode assembly cell (MEA): A proof of concept

This work focuses on the treatment in gas phase of air polluted with hydrogen sulphide in an electrochemical cell equipped with a MEA and demonstrates that it is a feasible option, in which this pollutant can be efficiently transformed into solid sulphur and sulfuric oxide. This later species can be successfully retained by reactive absorption into a sodium hydroxide solution producing a sodium sulphate solution, while the elemental sulphur obtained is dragged from the electrochemical reactor to a solid trap. This product has a pale-yellow colour and the XRD diffraction analysis shows that it has a S8 crystallization type. An increase in the current density applied produces an increase in the percentages of hydrogen sulphide removal (37.47, 50.67 and 65.33 % at 20, 50 and 100 mA cm−2) from the gas fed and influences on the speciation, favouring the formation of sulphur and the oxidation of water to oxygen over the formation of sulphur trioxide. The gas flowrate increment gives lower H2S elimination percentages (72.73, 50.67 and 51.69 % at 4, 7 and 10 mL min−1) and favours the dragging of sulphur which seems to be very positive to avoid its further oxidation to sulfuric oxide. Electrochemical characterization indicates that direct electro-oxidation of H2S gas takes place in the anode surface and that MEA does not undergo any relevant deterioration during performance of continuous operation tests. The maximum Coulombic efficiency for SO3 production was 60 % at 7 mL min−1 and 20 mA cm−2, while for the S0 production was 9.5 % at 10 mL min−1 at 50 mA cm−2. Energy consumption for H2S removal ranges from 18 to 87 Wh gS-1.

Experimental and density functional study of sulfur trioxide formation catalyzed by hematite in pressure oxy-combustion

Pressurized oxy-combustion is one of the most promising carbon capture technologies which could reduce global CO2 emission. SO3 is one of the main conventional pollutants and might be produced in large concentration in pressurized oxy-combustion than air combustion, posing risks to the environment and safe operation of boiler. However, no research has been conducted on SO3 catalytic formation in pressurized oxy-combustion, despite the fact that SO3 heterogeneous formation accelerated by hematite is more significant than homogeneous formation. Consequently, it is critical to understand SO3 catalytic formation in pressurized oxy-combustion. In this study, SO3 homogeneous and heterogeneous formation catalyzed by hematite were explored at 1 bar and 4 bar in a pressured fixed bed reactor. Temperature, pressure, and the addition of NO were discussed in this study. Density functional study method was employed to further elucidate the hematite catalysis mechanism. The findings show that hematite can catalyze the SO3 formation, but the catalytic effect weakens at high pressure. The inclusion of NO could enhance SO3 catalytic formation. Density functional study indicated that changing the main gas from N2 to CO2 has little impact on SO2 and O2 adsorption and subsequent SO3 production. SO3 adsorption becomes more stable with increasing O atom coverage, making SO3 desorption more difficult. Since NO has a lower adsorption energy than SO2 and O2, it has less effect on catalysis, however, NO2 formation could act as a strong catalyst and can enhance SO3 formation. This study could provide a better understanding of how the atmosphere and pressure influence SO3 heterogenous formation in pressured oxy-combustion.

Effect of Metal Oxides and Smelting Dust on SO2 Conversion to SO3

The purpose of this study was to investigate the effects of metal oxides and smelting dust on the formation of sulfur trioxide during copper, lead, zinc smelting process and flue. Focusing on the effects of SO2 concentration, O2 concentration, and temperature on SO2 oxidation conversion rate under homogeneous test conditions, and under various metal oxide oxidation conditions, further in dust (mainly electric dust removal ash in copper, lead, zinc smelting process), which were studied by single factor experiment test. The results showed that the effect of heterogeneous catalytic oxidation on SO2 conversion rate is much greater than that of pure gas phase oxidation. The addition of five pure metal oxides such as Fe2O3, CuO, Al2O3, ZnO, and CaO obviously promoted the SO2 conversion rate under different conditions. At different temperatures, the ability of metal oxides to promote SO2 conversion is ranked: Fe2O3 > CuO > CaO > ZnO > Al2O3. The catalytic oxidation of copper, lead, and zinc smelting dust to SO2 conversion rate was studied, and the conclusion was drawn that the metal oxides that promoted SO2 conversion rate in copper smelting dust were Fe2O3, Al2O3, ZnO, CaO, and the main substance was Fe2O3; the metal oxides that promoted SO2 conversion in zinc smelting dust were Fe2O3, Al2O3, ZnO, CaO, CuO, and the main substances were Fe2O3 and ZnO; the metal oxides that promoted SO2 conversion rate in lead smelting dust were Fe2O3. Whether metal oxides or copper, zinc, lead smelting dust in the experiment, Fe2O3 displayed the strongest catalytic oxidation capacity.

Assessment of sulfur trioxide formation due to enhanced interaction of nitrogen oxides and sulfur oxides in pressurized oxy-combustion

Pressurized oxy-combustion is emerging to be one of the best technologies for significantly decreasing the energy penalty for CO2 capture in coal-fired power plants. However, the higher pressure boosts the formation of acid gases, including SO3 and NO2, which could increase the risk of corrosion. The synergistic promotion of SO3 and NO2 formation in pressurized oxy-combustion is kinetically evaluated under representative conditions (1 ~ 30 atm, 600 ~ 1200 °C, NO/SO2 = 0.1 ~ 5). We begin with a comprehensive mechanism (72 species and 428 reactions), covering nitrogen and sulfur chemistry, relying on GRI-Mech 3.0. This analysis shows that the interaction of SOX and NOX enhances the conversion rates of SO2 → SO3, and this effect is more apparent at elevated pressures and lower temperatures. Mechanism analyses indicate that at elevated pressures, the formation pathways of SO3 through HOSO2 + O2 = SO3 + HO2, and NO2 through HO2 + NO = NO2 + OH, are promoted due to the strong interaction between SOX and NOX. The intermediate between these two reactions is SO2 + OH + M = HOSO2 + M, resulting in a strong cycle, that can be expressed by the global reaction NO + SO2 + O2 = NO2 + SO3. Finally, a nine-step reduced chemistry is developed and validated to accurately predict the formation of SO3 in the post-flame region at elevated pressures.

Monitoring and Control of Cooler Tank Level Measurement In Gas Cleaning Plant (GCP)

The Cooler Tank Level plays a major role in Gas Cleaning Plants (GCP) and it is a very important parameter to be measured and controlled. If the tank level is not maintained in nominal range, the dust particles will accumulate on the Cooler Tank and affect the process. The production of copper metal at Vedanta, Thoothukudi include Blending of various grades of copper concentrates, Smelting and Refining. Sulphur dioxide is generated from during the smelting of copper and is converted to Sulphuric acid as a byproduct. This process involves three steps such as cleaning of sulphur dioxide gas from Furnace, Catalytic conversion of S02 to SO3 and amalgamation of SO3 with sulphuric acid. The conversion process is exothermic, reversible and adiabatic reaction and hence if the temperature increases it destroys the formation of sulphur trioxide. Hence in order to achieve high conversion efficiency, the converter gases need to be cooled. The SO2 gas from smelter contains metallic dust, fume, acid mist, water vapour and other impurities like halides which will contaminate the product. Therefore the gases are to be cooled and cleaned in Gas Cleaning Plant (GCP). Cooler tank used to remove water vapour from the gas and dust settle at the bottom of cooler. Cooler tank level needs to be maintained in order to avoid overflow of water into scrubber which will block the inlet gas. The level of cooler tank is to be continuously monitored and controlled to achieve the optimum results. The limitations of using Differential Pressure Transmitter for level measurement are overcome by ultrasonic based level sensor and automated using Distributed Control System and Human Machine Interface (HMI).

Catalytic function of ferric oxide and effect of water on the formation of sulfur trioxide

Sulfur trioxide (SO3) is not only environmentally harmful but also highly corrosive, taking a great threat to the safe operation of coal-fired power plants. A dominant pathway of SO3 formation in coal-fired power plant is through the catalytic oxidation of SO2 (SO2+1/2O2→SO3) on the surfaces of ash particles containing Fe2O3. The catalytic formation of SO3 could be affected by complex atmosphere, where the effect from H2O is still debatable. In this paper, density functional theory (DFT) is employed to explore the reaction pathway of SO3 formation catalyzed by α-Fe2O3 in complex atmosphere containing O, O2, SO2 and H2O. In order to get the stable adsorption sites of these species, the adsorption energy of potential adsorption configurations on the α-Fe2O3 (001) surface is calculated. The dissociations of O2 molecule on complete and defect α-Fe2O3 (001) surfaces with O vacancy are calculated, and the Langmuir-Hinshelwood and Eley-Rideal mechanisms for the O(ads) reaction with SO2(ads) or SO2 are compared. The effect of H2O besides of SO2 and O2 on the formation of SO3 is especially discussed. The DFT calculation results show that for the formation of SO3 in gas phase, the energy barrier of ‘SO2+1/2O2→SO3’ is 436.75 kJ mol−1, in contrast, for the catalytic formation of SO3 on α-Fe2O3 surfaces, this energy barrier becomes an order of magnitude smaller, 24.82 kJ mol−1. O2 molecules can dissociate on the defect α-Fe2O3 (001) surface with O vacancy spontaneously, indicating that the defect α-Fe2O3 is favorable for the dissociation of O2, thereby promotes the formation of SO3. The energy barrier of ‘SO2(ads)+O(ads)→SO3(ads)’ through Langmuir-Hinshelwood mechanism is much higher than that of ‘SO2+O(ads)→SO3(ads)’ through Eley-Rideal mechanism. The adsorption energy on the α-Fe2O3 (001) surface of H2O is much smaller than that of SO2 and O2, indicating that H2O has little effect on the adsorption of O, O2, SO2 and eventually the heterogeneous formation of SO3. The DFT analysis results in this study provide a deep understanding on the reaction pathway of SO3 catalytic formation by Fe2O3.

Enhanced effects of ash and slag on SO3 formation in the post-flame region.

The effects of slag, fly ash (formed in boiler above 1500 °C), and experimental ash (formed in muffle furnace at 815 °C) on the formation of sulfur trioxide (SO3) were studied in a fixed bed rector. The results showed that the slag had the best catalytic effect on SO3 formation, the effect of fly ash was second, and the effect of experimental ash was the worst. The reason may be that the forms of iron in different samples were different. Iron in the experimental ash all existed in the form of Fe2O3. Iron in the fly ash mainly existed in the form of composite iron oxides, such as Fe0.3Mg0.7SiO3, Ca3Fe2(SiO4)3, and MgFe2O4. Iron in the slag also mainly existed in the form of composite iron oxides, such as CaFe2O4, MgFe2O4, and CaMgO0.88Fe0.12SiO4. The different forms of iron had different effects on SO3 formation. Composite iron oxides could produce more oxygen vacancies owing to lattice defects. This likely promoted the migration and regeneration of lattice oxygen and thus better promoted the formation of SO3 than Fe2O3. Moreover, MgFe2O4 and Ca3Fe2(SiO4)3 could better promote SO3 formation than CaMgO0.88Fe0.12SiO4 and Fe0.3Mg0.7SiO3. In addition, increasing the SO2 concentration and O2 concentration increased the SO3 concentration but increasing the SO2 concentration decreased the SO3 formation ratio.

Formation of sulfur trioxide during the SCR of NO with NH3 over a V2O5/TiO2 catalyst.

The oxidation of sulfur dioxide (SO2) to sulfur trioxide (SO3) is an undesirable reaction that occurs during the selective catalytic reduction (SCR) of nitrogen oxides (NOx) with ammonia (NH3), which is a process applied to purify flue gas from coal-fired power plants. The objectives of this work were to establish the fundamental kinetics of SO3 formation over a V2O5/TiO2 catalyst and to illustrate the formation mechanism of SO3 in the presence of NOx, H2O and NH3. A fixed-bed reactor was combined with a Fourier transform infrared (FTIR) spectrometer and a Pentol SO3 analyser to test the outlet concentrations of the multiple components. The results showed that the rate of SO2 oxidation was zero-order in O2, 0.77-order in SO2 and -0.19-order in SO3 and that the apparent activation energy for SO2 oxidation was 74.3 kJ mol−1 over the range of studied conditions. Based on in situ diffuse reflectance infrared Fourier transform (in situ DRIFT) spectroscopy, X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD) tests, the SO3 formation process is described here in detail. The adsorbed SO2 was oxidized by V2O5 to produce adsorbed SO3 in the form of bridge tridentate sulfate, and the adsorbed SO3 was desorbed to the gas phase. NOx promoted the oxidation of the adsorbed SO2 due to the promotion of the conversion of low-valent vanadium to high-valent vanadium. In addition, the desorption of the adsorbed SO3 was inhibited by H2O or NH3 due to the conversion of tridentate sulfate to the more stable bidentate sulfate or ammonium bisulfate. Finally, the mechanism of the influence of NOx, H2O and NH3 on the formation of gaseous SO3 was proposed.

Effect of Sodium Sulfate in Ash on Sulfur Trioxide Formation in the Postflame Region

To investigate the effects of different factors, including sodium sulfate (Na2SO4), etc., on the formation of sulfur trioxide (SO3) during oxy-fuel circulating combustion, the experiment was perfor...

Sulfur trioxide formation/emissions in coal‐fired air‐ and oxy‐fuel combustion processes: a review

AbstractIn oxy‐fuel combustion, fuel is burned using oxygen together with recycled flue gas, which is needed to control the combustion temperature. This leads to higher concentrations of sulfur dioxide and sulfur trioxide in the recycled gas, which can result in the formation of sulfuric acid and enhanced corrosion. Current experimental data on SO3 formation, reaction mechanisms, and mathematical modelling have indicated significant differences in SO3 formation between air‐ and oxy‐fuel combustion for both the wet and dry flue gas recycle options. This paper provides an extensive review of sulfur trioxide formation in air‐ and oxy‐fuel combustion environments, with an emphasis on coal‐fired systems. The first part summarizes recent findings on oxy‐fuel combustion experiments, as they affect sulfur trioxide formation. In the second part, the review focuses on sulfur trioxide formation mechanisms, and the influence of catalysis on sulfur trioxide formation. Finally, the current methods for measuring sulfur trioxide concentration are also reviewed along with the major difficulties associated with those measurements using data available from both bench‐ and pilot‐scale units. © 2018 Society of Chemical Industry and John Wiley & Sons, Ltd.

Effect of HCl and CO on sulfur trioxide formation mechanisms during oxy-fuel combustion

The concentration of SOX, HCl, CO, NOX etc. in the flue gas during oxy-fuel combustion is all relatively higher compared with air combustion. Higher SO3 concentration increases the risk of low-temperature corrosion. The higher concentration of HCl and CO can also cause corrosion, and they may play roles on SO3 formation. Thus homogeneous experiment and pulverized coal experiment were done on different furnace system to clarify the effects of HCl and CO on SO3 formation during oxy-fuel combustion. Different inlet concentration of HCl, CO, SO2, H2O, O2 and CO2 were used to simulate the flue gas of the combustion. The results indicated that HCl inhibited SO3 formation but CO promoted SO3 formation at the experimental temperature. HCl richens the radical pool and might generate HO2 radical which was negative to SO3 formation. CO could react with O2 to generate more O radical which was vital to SO3 formation and consume HO2 radical when steam existed. The pulverized coal experiment presented a different SO3 concentration at the same input sulfur and steam level, meaning the fly ash and other gas phase components in the flue gas could also influence SO3 formation.

A comprehensive experimental and modeling study of sulfur trioxide formation in oxy-fuel combustion

This study focuses on the sulfur chemistry occurring within an oxy-combustion system by adopting a combined approach of detailed kinetic modeling and experiments. Influences of variable combustion parameters on SO3 generation have been investigated computationally by implementing different combustion mechanisms. Results indicated significant influences of the equivalence ratio, inlet SO2 concentration and presence of NO on SO3 formation while the inlet O2 concentration exhibited minimal effect. Presence of NO demonstrated different degrees of direct and indirect interactions between NOx and SOx species for different reaction sets. Sensitivity analysis indicated radicals to be playing a dominant role in SO3 formation. Collected temporal profiles of SO3 from the lab-scale combustion setup showed evidence of significant SO3 formation at temperatures as low as 650K under realistic boiler temperature conditions. The equivalence ratio and the concentrations of SO2, O2 and NO were found to influence the SO3 formation. Predictions of final SO3 concentration from different mechanisms were comparable with the experimental data; however, the trend of the temporal profiles could not be anticipated by the models. Experiments conducted in the presence of NO indicated the existence of interactions between NOx and SOx species and also the requirement of modifications to the existing oxy-combustion models.

Effect of steam and sulfur dioxide on sulfur trioxide formation during oxy-fuel combustion

The purpose of the present study is to clarify the effects of temperature, initial SO2 concentration and steam addition on SO3 formation under oxy-fuel combustion. The experiments consisted of two parts. The first part was the homogeneous experiment conducted with the simulated flue gas in a horizontal tube furnace. In order to further study the formation characteristics of SO3 in the heterogeneous gas atmosphere, the other part of the experiments was carried out by using a high-sulfur coal and a low-sulfur coal respectively in a drop tube furnace. The experiment results indicated that SO3 concentration increased first but then decreased with the temperature increasing, and the maximum SO3 concentration appeared at around 950°C. The increase of initial SO2 concentration could significantly enhance SO3 formation. But the injected steam inhibited SO3 formation in all test cases obviously, as the injection of steam could increase the kinds of the radical pool compositions in the flue gas, which might involve more complex interactions with the formed SO3 during wet recycling. Moreover, compared to the former homogeneous experiment, the latter presented a more intense inhibiting behavior, which was probably attributed to the more diversification of the radical pool compositions in pulverized-coal combustion.

Consequences of Acid Rain

2SO2+O2→2SO3 SO3+H2O→H2SO4 The second reaction occurs rapidly, and therefore formation of sulphur trioxide in a humidified atmosphere leads to formation of sulphuric acid. However, first reaction is very slow in absence of a catalyst, although it does not have a significant contribution. There are several other potential reactions that prove insignificant but for different reasons. Although each of these reactions can make a minor contribution to oxidation of sulphur dioxide, there is only one response significant. The reaction is as follows:

Measurement and modeling of sulfur trioxide formation in a flow reactor under post-flame conditions

The present work focuses on the impacts of different combustion parameters on the formation of sulfur trioxide (SO3). The outlet SO3 concentrations from a quartz reactor operated within the temperature range of 800K to 1673K were measured using the controlled condensation method. Post-flame conditions were examined with and without combustibles, and the effects of SO2, O2, NO, H2O, and CO2 on SO3 formation were investigated. The formation of SO3 along the quartz reactor was modeled with a detailed chemical reaction mechanism by assuming plug-flow and using measured temperature profiles. Only reactions that occurred in the gas phase were considered.In the absence of combustibles, the outlet SO3 concentration increased as the experimental temperature and O2 concentration increased. When reactive gases (e.g., NO, CO, and CH4) were introduced, the formation of SO3 was increased, mainly as the result of increased concentrations of radicals. In addition, the combustion atmosphere (comprising N2, CO2, and H2O) influenced the amount of SO3 formed. A higher concentration of H2O clearly increased SO3 formation in the absence of combustibles.

Sulfur trioxide formation during oxy-coal combustion

The purpose of this study was to investigate the effects of increased oxygen and carbon dioxide concentration on the formation of sulfur trioxide during oxy-coal combustion in two different types of pilot-scale furnaces: a pulverized-coal and a circulating-fluidized-bed-fired system. For pulverized-coal (PC) testing, concentrations of SO 3 and SO 2 were significantly higher for oxy-fired conditions as compared to air-fired conditions. For a high-sulfur Illinois bituminous coal, SO 3 concentrations were 4–6 times greater on average. When firing a low-sulfur Utah Bituminous coal, SO 3 concentrations were similar for oxy-firing vs. air-firing, and the overall levels were very low compared to the Illinois coal, consistent with differences in the fuel sulfur contents. PC-fired emissions on a normalized mass basis (mass SO 3 per unit energy input) indicated higher SO 3 emissions under air-fired conditions vs. oxy-firing, for both the Illinois and Utah coals. Circulating fluidized bed testing was also carried out using the low-sulfur Utah coal, and SO 3 concentrations were notably higher for oxy-firing vs. air-firing, in contrast to the similar concentration levels observed for PC-firing. When compared on a normalized mass basis, the emissions were similar for both air- and oxy-firing, which is also in contrast to the PC-fired results for this coal.

Theoretical study on the atmospheric formation of sulfur trioxide as the primary agent for acid rain

The reaction mechanism of SO2 with O3 on the singlet potential energy surface has been investigated theoretically at the G3MP2B3//B3LYP/6-311+G(3df) level of theory. The reactants are initially associated with adducts IN1(O2S–OOO) and IN2(OS-cyclic O4) in a barrier-less process. Subsequently, these adducts undergo isomerization and dissociation processes to produce cis-OSOO + 3O2, SO3(C s ) + 3O2 and SO3(D 3h ) + 3O2 products. The SO3(D 3h ) + 3O2 is major product and the cis-OSOO + 3O2 and SO3(C s ) + 3O2 are minor products. No stable pathway has been found for the formation of trans-OSOO and cyclic-SOOO isomers in the reaction of SO2 + O3. For major product, the rate constant of SO2 + O3 reaction is 2.30 × 10−23 cm3 molecule−1 s−1, at room temperature and atmospheric pressure.

Studies of the Fate of Sulfur Trioxide in Coal-Fired Utility Boilers Based on Modified Selected Condensation Methods

The formation of sulfur trioxide (SO(3)) in coal-fired utility boilers can have negative effects on boiler performance and operation, such as fouling and corrosion of equipment, efficiency loss in the air preheater (APH), increase in stack opacity, and the formation of PM(2.5). Sulfur trioxide can also compete with mercury when bonding with injected activated carbons. Tests in a lab-scale reactor confirmed there are major interferences between fly ash and SO(3) during SO(3) sampling. A modified SO(3) procedure to maximize the elimination of measurement biases, based on the inertial-filter-sampling and the selective-condensation-collecting of SO(3), was applied in SO(3) tests in three full-scale utility boilers. For the two units burning bituminous coal, SO(3) levels starting at 20 to 25 ppmv at the inlet to the selective catalytic reduction (SCR), increased slightly across the SCR, owing to catalytic conversion of SO(2) to SO(3,) and then declined in other air pollutant control device (APCD) modules downstream to approximately 5 ppmv and 15 ppmv at the two sites, respectively. In the unit burning sub-bituminous coal, the much lower initial concentration of SO(3) estimated to be approximately 1.5 ppmv at the inlet to the SCR was reduced to about 0.8 ppmv across the SCR and to about 0.3 ppmv at the exit of the wet flue gas desulfurization (WFGD). The SO(3) removal efficiency across the WFGD scrubbers at the three sites was generally 35% or less. Reductions in SO(3) across either the APH or the dry electrostatic precipitator (ESP) in units burning high-sulfur bituminous coal were attributed to operating temperatures being below the dew point of SO(3).

Kinetics and stoichiometry in the Karl Fischer solution.

The mechanisms of the Karl Fischer (K.F.) reaction are reviewed and further investigated. Both kinetic measurements of the iodine concentration and chromatographic determinations of the reaction products were performed. In alcoholic solutions mainly alkyl sulfite is oxidized, and a reaction via partial formation of sulfur trioxide is proposed. In methanol an exact 1:1 stoichiometry (H2O:I2) has been verified. In the aprotic, dipolar solvents acetonitrile, DMF and propylene carbonate HSO3- is oxidized by iodine. Based on formation and subsequent hydrolysis of base - SO3 adducts the stoichiometric factor for water is determined by type and concentration of the base, by the concentration of water and by the solvent itself. - In K.F. reagents the oxidation of SO2 by aerial oxygen to sulfate and alkyl sulfate takes place as a side reaction.

Emission Control for Gas Turbines

Johnson Matthey are reporting successful commercialisation of oxidation catalysts for the clean-up of gas turbine exhaust. The reduction of carbon monoxide and hydrocarbons is achieved with a platinum-rhodium catalyst which minimises the formation of sulphur trioxide. The catalyst system, supported on an energy saving, low pressure drop metal monolith, has been used continuously for five years on large industrial gas turbines.