SO2-containing Gas Research Articles

Mathematical modelling of a semi-dry SO2 scrubber based on a Lagrangian-Eulerian approach

Semi-dry desulfurization is an efficient means of SO2 removal from the effluent gases from electrolysis cells in aluminum smelters. These gases are at low temperature and contain low concentrations of SO2, as opposed to thermal power plants. The removal is carried out by injecting powdered alkaline sorbent, hydrated lime (solid particles), into the SO2-containing gas (gas phase) in the presence of humidity. The reaction is controlled by the adsorption of SO2 onto the surface of lime. This study involves the mathematical modelling of a lab-scale scrubber using a Lagrangian-Eulerian approach in order to analyze the desulfurization efficiency. The model was validated based on experimental data. A parametric study was carried out to investigate the effects of particle size, sorbent amount, and relative humidity (RH) on the desulfurization efficiency. The results show that the particle size is the most important parameter; as the particle size decreases, the desulfurization efficiency increases. However, using finer particles may increase the process cost. The loss in SO2 capture efficiency due to the use of coarser particle size could be compensated by increasing the relative humidity (RH) of the gas, another key parameter of the process.

Evaluation of packing materials for thermophilic biofilter by refined evaluation scheme and application in the treatment of SO2 with high temperature

The selection of packing materials is essential to maintaining biofilter performance in waste gas treatment. In this study, 12 types of packing materials were evaluated to determine the most suitable for the SO2 removal by a thermophilic biofilter. Scanning electron microscopy and the Baunauer–Emmett–Teller equation were utilized to identify the texture of the tested packing materials, while Fourier transform infrared spectroscopy and X-ray diffraction were applied to analyze the surface functional groups and crystal structures, respectively. Characteristics were accompanied by economic considerations. Results showed that the polyurethane sponge had better porous structure and water retention than other packing materials. In terms of microbial growth and carrier economy, it was chosen for the biofilter used to treat SO2. The performance of a full-scale thermophilic biofilter with polyurethane sponge as the packing material was investigated for the purification of SO2-containing gases at an inlet temperature of 55 °C. The biofilter effectively removed SO2 at an average removal rate of 93.36%. Thermophilic bacteria and sulfur-oxidizing bacteria, e.g., Bacillus thermophilus, could attached growth on the surface of selected packing materials and exhibited degradation activity. This study provides an effective and feasible method of packing material selection for biological waste gas treatment.

Positive bias in particulate matter emissions data due to sulfur dioxide adsorption and oxidation on glass fiber filters

ABSTRACT Recent particulate matter emisssion tests at an ArcelorMittal sintering line in Vitoria, Brazil have indicated a change in particulate matter emissions that was not consistent with the steady and proper operation of the combined electrostatic precipitator and pulse jet fabric filter control system. ArcelorMittal Brazil, ERM Brasil, and Air Control Techniques, P.C. have evaulated the use of borosilicate glass fiber filters in the U.S. EPA Method 5 sampling train as a possible reason for the anomolous change. The scope of this study included (1) possible adsorption and oxidation of SO2 on borosilicate glass and quartz filter media, and (2) the possible loss of fibers from borosilicaate glass and quartz filter media at normal sampling train vacuums and temperatures. Air Control Techniques, P.C. conducted a series of laboratory tests replicating gas stream conditions using both borosilicate and quartz circular and thimble filters. The laboratory tests confirmed the formation of sulfate artifacts due to sulfur dioxide adsorption on the borosilicate filters. These tests also confirmed that neither the borosilicate glass-fiber filters or the quartz filter lost significant filter weight during sampling at normal Method 5 sampling train vacuum levels and filter temperatures. Tests conducted by ERM Brasil, SA on the ArcelorMittal sintering process stack using both quartz and borosilicate glass fibers also indicated significant adsorption and oxidation of sulfur dioxide on the borosilicate filters. These laboratory and field tests confirmed the positive bias associated with glass fiber filters in SO2 environments reported as early as 1970. The authors recommend that only quartz fiber filter be used for particulate matter testing in SO2-containing gas streams. Furthermore, EPA Method 5 Section 7.1.1 should be revised to explicitly approve the use of quartz fiber filters. Implications: Filterable particulate matter emission tests using EPA Method 5 in sulfur dioxide laden gas streams have had a large positive bias due to outdated sampling practices. Our manuscript provides bias quantification data from both laboratory tests and tests on a sintering process stack. We recommend that (1) particulate matter emission tests conducted in SO2-containing gas streams be conducted using only quartz filter and (2) The U.S. EPA change the definition of filter media to be used in EPA Method 5 and other particulate matter test methods based on Method 5 specifically allow the use of quartz filters.

Sulfur-Resistant Ceria-Based Low-Temperature SCR Catalysts with the Non-bulk Electronic States of Ceria.

Although ceria-based catalysts serve as an appealing alternative to traditional V2O5-based catalysts for selective catalytic reduction (SCR) of NOx with NH3, the inevitable deactivation caused by SO2 at low temperatures severely hampers the ceria-based catalysts to efficiently control NOx emissions from SO2-containing stack gases. Here, we rationally design a strong sulfur-resistant ceria-based catalyst by tuning the electronic structures of ceria highly dispersed on acidic MoO3 surfaces. By using Ce L3-edge X-ray absorption near edge structure spectra in conjunction with various surface and bulk structural characterizations, we report that the sulfur resistance of the catalysts is closely associated with the electronic states of ceria, particularly expressed by the Ce3+/Ce4+ ratio related to the size of the ceria particles. As the Ce3+/Ce4+ ratio increases up to or over 50%, corresponding to CeO2/MoO3(x %, x ≤ 2.1) with the particle size of approximately 4 nm or less, the non-bulk electronic states of ceria appear, where the catalysts start to show strong sulfur resistance. This work could provide a new strategy for designing sulfur-resistant ceria-based SCR catalysts for controlling NOx emissions at low temperatures.

Enhancing the catalytic oxidation of elemental mercury and suppressing sulfur-toxic adsorption sites from SO2-containing gas in Mn-SnS2

It is difficult to stabilize gaseous elemental mercury (Hg°) on a sorbent from SO2-containing industrial flue gas. Enhancing Hg° oxidation and activating surface-active sulfur (S*) can benefit the chemical mercury adsorption process. A Mn-SnS2 composite was prepared using the Mn modification of SnS2 nanosheets to expose more Mn oxidation and sulfur adsorption sites. The results indicate that Mn-Sn2 exhibits better Hg° removal performances at a wide temperature range of 100–250 °C. A sufficient amount of surface Mn with a valance state of Mn4+ is favorable for Hg° oxidation, while the electron transfer properties of Sn can accelerate this oxidation process. Oxidized mercury primary exists as HgS with surface S*. A larger surface area, stable crystal structure, and active valance state of each element are favorable for Hg° oxidation and adsorption. The Mn-SnS2 exhibits an excellent SO2 resistance when the SO2 concentration is lower than 1500 ppm. The effects of H2O and O2 were also evaluated. The results show that O2 has no influence, while H2O and SO2 coexisting in the flue gas have a toxic effect on the Hg° removal performance. The Mn-SnS2 has a great potential for the Hg° removal from SO2-containing flue gas such as non-ferrous smelting gas.

Cavity size dependent SO2 resistance for NH3-SCR of hollow structured CeO2-TiO2 catalysts

CeO2-TiO2 hollow spheres with distinct cavity sizes of ca. 500 nm and 5 μm were prepared from carbon spheres and hybrid Ce–C sphere templates, respectively. After 40 h of successive operation in SO2-containing gas stream for the NH3-SCR reaction, the catalyst with large cavity showed only 4.7% activity loss, while that with small cavity exhibited sharp decrease (ca. 72.6%) in its deNOx activity. Results of physicochemical characterizations manifested that accelerated decomposition of NH4HSO4 on the CeO2-TiO2 catalyst with larger cavity size is likely largely responsible for the improved SO2 resistance of catalyst activity loss.

Highly Selective and Reversible Sulfur Dioxide Adsorption on a Microporous Metal-Organic Framework via Polar Sites.

It is very challenging to achieve efficient and deep desulfurization, especially in flue gases with an extremely low SO2 concentration. Herein, we report a microporous metal-organic framework (ELM-12) with specific polar sites and proper pore size for the highly efficient SO2 removal from flue gas and other SO2-containing gases. A high SO2 capacity of 61.2 cm3·g-1 combined with exceptionally outstanding selectivity of SO2/CO2 (30), SO2/CH4 (871), and SO2/N2 (4064) under ambient conditions (i.e., 10:90 mixture at 298 K and 1 bar) was achieved. Notably, the SO2/N2 selectivity is unprecedented among ever reported values of porous materials. Moreover, the dispersion-corrected density functional theory calculations illustrated the superior SO2 capture ability and selectivity arise from the high-density SO2 binding sites of the CF3SO3- group in the pore cavity (Sδ+···Oδ- interactions) and aromatic linkers in the pore walls (Hδ+···Oδ- interactions). Dynamic breakthrough experiments confirm the regeneration stability and excellent separation performance. Furthermore, ELM-12 is also stable after exposure to SO2, water vapor, and organic solvents.

Selective catalytic reaction of NOx with NH3 over Ce–Fe/TiO2-loaded wire-mesh honeycomb: Resistance to SO2 poisoning

Ce–Fe/TiO2/Al2O3/wire-mesh honeycomb catalyst (Ce–Fe/WMH) exhibited a high activity for the selective catalytic reduction (SCR) of NOx in SO2-containing gases. Analysis of fresh and spent catalysts by XRD, BET, XPS, TG and FTIR indicated that Ce sites were sulfated preferentially over Ce–Fe/WMH during the SCR reaction in the presence of SO2, which could increase the amount of surface active oxygen species. On the other hand, the formation of surface hydroxyls due to the hydration of SO42− could supply more Brønsted acid sites to adsorb NH3 in the form of NH4+. These two factors played significant roles in the good SO2 durability of Ce–Fe/WMH. In addition, the sulfation of CeO2 on catalyst surface might approach a stable state upon certain amount of SO2 in reactant gas. The reaction mechanism study showed that only Eley–Rideal reaction pathway between ionic NH4+, coordinated NH3 and gaseous NO dominated in the reaction; the Langmuir–Hinshelwood reaction pathway was cut off by the sulfation, resulting in the rapid decrease of NOx conversion in the early period of SCR reaction in the presence of SO2.

Reverse-flow reactor concept for combined SO2 and co-oxidation in smelter off-gases

The study is dedicated to the problem of CO admixtures in the SO2-containing waste gases of non-ferrous smelters which may significantly complicate the operation of SO2 oxidation reverse-flow reactors, used for purification of such gases, due to catalyst overheating, decrease of SO2 conversion and worsening of operation stability. The concept of the reverse-flow reactor with additional catalyst beds for separate CO oxidation between the beds of vanadia catalyst and inert heat regenerative material was proposed. The catalyst with Pt supported in small amount (0.01–0.1% mass) at SiO2–ZrO2 glass fabric (Pt–GFC) was experimentally found to have the sufficient activity in CO oxidation at moderate temperatures combined with experimentally proven high resistance to deactivation by SOx. According to mathematical simulation data, the proposed approach provides efficient elimination of the reverse-flow reactor overheating and subsequent problems, caused by CO appearance in smelter waste gases.

Exergy analysis of hydrogen production from different sulfur-containing compounds based on H2S splitting cycle

There is a tremendous demand for hydrogen production worldwide but the current H2 production routes from natural gas and other carbon fuels lead to large greenhouse gas emissions. Intentionally coupled with nuclear power, the sulfur–iodine (S–I) thermochemical water splitting cycle is one of the most widely studied cycles for the large-scale hydrogen production that has environmental benignity. Based on the inspiration of the S–I cycle, a novel chemical cycle called hydrogen sulfide splitting cycle has been proposed for hydrogen production. In addition to the SO2 production from the reaction of H2S and sulfuric acid, SO2 can be produced from the burning (direct oxidation) of hydrogen sulfide or elemental sulfur. And it can also be provided by SO2 capture from flue gas or other SO2-containing waste gases. This paper performs exergy analysis on the various SO2 provisions to the Bunsen reaction that make different routes for hydrogen production from waste sulfur-containing compounds as feedstock. It has been found that the route including SO2 from direct H2S oxidation potentially makes the best energy-efficient process of H2 production. The heat that is generated from H2S oxidation can be recovered and used to support the energy requirements for other steps of the cycle, making the entire hydrogen production cycle more energy-efficient.

Interaction between (alumino)silicates and SO2-containing gas: experiment and thermodynamic model

Interaction between (alumino)silicates and SO2-containing gas: experiment and thermodynamic model

Protection behavior of SO 2-containing cover gases to molten magnesium alloy

Sulphur dioxide (SO 2) mixed with carrier gases was used as an alternative to SF 6 to protect molten magnesium alloys. The protection behavior of AZ91D alloy in a sealed melting furnace was investigated under the atmosphere containing SO 2 with different mixed gases. The morphology and composition of the surface film were studied. The melt was well protected in an atmosphere of SO 2 and a proper amount of air, and was not protected properly in the other atmospheres. Based on the understanding of the protective effects of SO 2 in the sealed furnace, the protection mechanism of SO 2-containing cover gases on molten AZ91D alloy was studied in an open melting furnace. The cover gas protected the melt by reacting with the melt to form a coherent protective film with a network structure on the melt surface. The film contains MgO and MgS. MgS increases the Pilling and Bedworth ratio of the surface film and enhances the protective capability of the films.

Sulfur poisoning resistant mesoporous Mn-base catalyst for low-temperature SCR of NO with NH3

Mesoporous MnO2-Fe2O3-CeO2-TiO2 was prepared with sol–gel method and demonstrated to have good low-temperature activity and sulfur-poisoning resistance for selective catalytic reduction (SCR) of NO with NH3 in SO2-containing gases. In comparison with this, the catalyst with the same composition but made according to the conventional impregnation method exhibited obviously lower SO2-poisoning resistance and selectivity to the formation of N2 in the SCR reactions. FTIR analysis of the spent catalysts after SCR reactions for 16h and 60h in a SO2-contaning gas demonstrated that there was little difference in the amount of deposited ammonium sulfate over the mesoporous catalyst between the two cases. The mesopore channels existing in the mesoporous catalyst enabled probably a dynamic balance between the formation and decomposition of ammonium sulfate in SCR reactions. This concern was justified through comparing the N2 adsorptions and XPS spectra for the catalysts made with the impregnation and sol–gel methods. The article clarified as well the facilitation effects of introducing Ce and Fe into the mesoporous catalyst on activity, selectivity and SO2-poisoning resistance.

SO2-induced stability of Ag-alumina catalysts in the SCR of NO with methane

We report on a stabilization effect on the structure and activity of Ag/Al2O3 for the selective catalytic reduction (SCR) of NOx with CH4 imparted by the presence of SO2 in the exhaust gas mixture. The reaction is carried out at temperature above 600°C to keep the surface partially free of sulfates. In SO2-free gases, catalyst deactivation is fast and measurable at these temperatures. Time-resolved TEM analyses of used samples have determined that deactivation is due to sintering of silver from well-dispersed clusters to nanoparticles to micrometer-size particles with time-on-stream at 625°C. However, sintering of silver was dramatically suppressed by the presence of SO2 in the reaction gas mixture. The structural stabilization by SO2 was accompanied by stable catalyst activity for the NO reduction to N2. The direct oxidation of methane was suppressed, thus the methane selectivity was improved in SO2-laden gas mixtures. In tests with high-content silver alumina with some of the silver present in metallic form, an increase in the SCR activity was found in SO2-containing gas mixtures. This is attributed to redispersion of the silver particles by SO2, an unexpected finding. The catalyst performance was reversible over many cycles of operation at 625°C with the SO2 switched on and off in the gas mixture.

Synthesis and SO2 Absorption/Desorption Properties of Poly(1,1,3,3-tetramethylguanidine acrylate)

A novel ionic polymer, poly(1,1,3,3-tetramethylguanidine acrylate) (PTMGA), was synthesized, and its SO2 absorption and desorption properties were studied for the first time. 1,1,3,3-Tetramethylguanidine acrylate, a polymerizable ionic liquid (IL), was first prepared via neutralization of 1,1,3,3-tetramethylguanidine and acrylic acid. PTMGA was then synthesized via free radical polymerization of TMGA. The polymer adsorbed SO2 with high selectivity, capacity, and rate. The absorption capacity and rate of PTMGA were significantly higher than the monomer. The SO2 absorbed at a relatively low temperature was effectively desorbed at higher temperatures and/or under vacuum. The absorption/desorption process could be repeatedly operated, and thus the polymer was reused. Under a typical operation condition, about 0.3 g of SO2 per gram of polymer was separated in each cycle. The PTMGA material showed a good potential as solid-state SO2 absorbent for applications in purification of SO2-containing gas such as fuel g...

Exergoecological analysis of processing of SO2-containing gases from zinc production

AbstractAn energy and technological study of processing SO2-containing metallurgical gases from zinc production to sulfuric acid production using the exergy method of thermodynamic analysis has bean carried out. A real operating installation since 2003 at the KCM-SA, Plovdiv, Bulgaria, has been used as the model scheme. The principal production stages have been analyzed. The absolute and the relative exergy characteristics of the separate stages as well as of the process as a whole have been calculated. The results have been used to evaluate the influence of sulfuric acid production on the environment. The results obtained have been compared with previous studies on similar processes both in zinc and in copper production. The studied installation of sulfuric acid production has good exergoecological indices, defining it as an effective process both in thermotechnical and in ecological aspects.

Optimisation of in-service performance of boiler steels by modelling high-temperature corrosion

The main objective of the EU OPTICORR project is the optimisation of in-service performance of boiler steels by modelling high-temperature corrosion, the development of a life-cycle approach (LCA) for the materials in energy production, particularly for the steels used in waste incinerators and co-fired boiler plants. The expected benefits of this approach for safe and cost effective energy production are: - control and optimisation of in-service performance of boiler materials, - understanding of high-temperature corrosion and oxidation mechanisms under service conditions, - improvement of reliability to prevent the failure of components and plant accidents and - expanding the limits of boiler plant materials by corrosion simulations for flexible plant operation conditions (steel, fuel, temperature etc.). The technical aim of the EU OPTICORR project is the development of modelling tools for high-temperature oxidation and corrosion specifically in boiler conditions with HCl- and SO2-containing combustion gases and Cl-containing salts. The work necessitates thermodynamic data collection and processing. For development and modelling, knowledge about the corrosion mechanisms and exact data are needed. The kinetics of high-temperature oxidation and corrosion are determined from laboratory thermo-gravimetric tests (TG) and multi-sample exposure tests. The materials studied are typical boiler tubes and fin-steels: ferritic alloys, the austenitic steel T347 and the Ni-based alloy Inconel 625. The exposure gases are dry air, air with 15 vol-% H2O, and with 2000 ppm HCl and 200 ppm SO2. The salt deposits used are based on KCl-ZnCl2 and Ca, Na, K, Pb, Zn-sulfates. The test temperatures for exposures with deposits are 320 and 420°C and, for gas exposures, 500 to 600°C. At present the tools being developed are ChemSheet based programmes with a kinetic module and easy-to-use interface and a more sophisticated numerical finite-difference-based diffusion calculation programme, InCorr, developed for prediction of inward corrosion and internal corrosion. The development of modelling tools for oxidation and high-temperature corrosion was started with thermodynamic data collection for relevant systems and thermodynamic mappings. Further, there are needs to develop the simulation model and tool for salt-induced hot corrosion based on the ChemSheet approach. Also, the work on modelling and simulating with the InCorr kinetic modelling tool will be continued to demonstrate the use of the tool for various steels and alloys in defined combustion environments.

Selective catalytic oxidation of ammonia to nitrogen at low temperature on Pt/CuO/Al 2O 3

Pt/CuO/Al 2O 3 catalysts with 20 wt% CuO and 0.5–4 wt% Pt were prepared and used for the selective catalytic oxidation of ammonia in wet and dry gases and in synthetic biogas with CO, hydrogen, and methane. Imaging of the catalysts with HREM and STEM, combined with elemental analysis, reveals that copper is well dispersed and occurs in the form of patches on the support. Platinum in the form of nanometer-sized particles are localised on copper-rich areas. The activity measurements show that Pt/CuO/Al 2O 3 is active and selective for the oxidation of ammonia to form nitrogen. Compared with dry feeds, the catalyst shows higher selectivity for nitrogen when the feed is wet. Pretreatment of the catalyst with SO 2-containing gas produces an improved catalyst with a selectivity for nitrogen of about 97–98% at complete ammonia conversion. Pt/CuO/Al 2O 3 shows good performance also for the oxidation of ammonia to nitrogen in the presence of biogas components including water. However, the performance is not as good under dry conditions, giving either low selectivity for nitrogen or low conversion of the ammonia, depending on the partial pressure of oxygen.

Sulfur deactivation of NO x storage catalysts: influence of exposure conditions and noble metal

In the present study, barium-based NO x storage catalysts containing platinum, rhodium, or both noble metals were investigated. The influence of SO 2 exposure conditions on the performance of NO x storage catalysts was studied using flow reactor measurements, FTIR, and XPS where the samples were exposed to lean and/or rich SO 2-containing gas mixtures, simulating the conditions in a mixed lean application. The main results show that all samples are sensitive to sulfur and that deactivation is faster when SO 2 is present in the feed under rich conditions than under lean or continuous SO 2 exposure. It was also found that SO 2 affects the performance of noble metals strongly and that noble metal deactivation most likely occurs during the rich period of a NO x storage cycle. Additionally, the influence of the noble metals present in the catalysts was investigated with respect to sulfur sensitivity and it was found that a combination of platinum and rhodium seems to be preferable for retaining high performance (high NO oxidation and reduction activity) of the catalyst under SO 2 exposure and subsequent regeneration.

A Qualitative Study on the Retention of Mercury From SO2-Containing Process Gases on Copper Smelter Dusts

Mercury present in process gases can to some extent be removed in dust filters such as textile bag house filters. The removal efficiency in such filters is dependent on gas composition, gas temperature and properties of dust particles collected in the filter. In the present study, laboratory scale experiments were conducted to study qualitatively the influence of different types of dusts on the retention of mercury in SO2-containing gases. A gas mixture composed of N2, SO2, O2 and Hg was passed through a textile filter covered with dust. Two different types of dust were used in the experiments: one dust containing mainly Cu- and Fe-sulphides and Fe-oxides and one containing mainly Cu-, Fe, and Zn-oxides and -sulphates. The dusts were studied using microprobe equipment after exposure to the mercury-containing gas. Thermodynamic calculations were carried out for comparison with the experimental results. The study shows that mercury is mainly associated with partially roasted chalcopyrite particles.Le mercure présent dans les gaz du procédé peut, jusqu'à un certain degré, être enlevé parles filtres à poussière tels que les filtres textiles de l'unité de filtration. L'efficacité d'enlèvement de ces filtres dépend, par exemple, de la composition et de la température du gaz ainsi que des propriétés des particules de poussière recueillies par le filtre. Dans l'étude présente, on a exécuté des expériences à l'échelle du laboratoire afin d'étudier qualitativement l'influence de différents types de poussière sur la rétention du mercure de gaz contenant du SO2. On a passé un mélange de gaz composé de N2, de SO2, d'O2 et de Hg à travers un filtre textile couvert de poussière. Dans les expériences, on a utilisé deux types différents de poussière; un type de poussière contenait principalement des sulfures de Cu et de Fe ainsi que des oxydes de Fe alors que l'autre type contenait principalement des oxydes et des sulfates de Cu, de Fe et de Zn. On a étudié les poussières à l'aide d'une microsonde après l'exposition au gaz contenant du mercure. On a comparé les calculs thermodynamiques avec les résultats expérimentaux. L'étude montre que le mercure est associé principalement avec des particules de chalcopyrite partiellement grillées.