Molten Sulfur Research Articles

Recovering element sulfur from sulfur-containing waste through a pressure induced melting-crystallization method: Optimization using response surface methodology

Metallurgical sulfur-containing wastes (MSCWs) is an important secondary resource for recovering element sulfur in chemical and metallurgical industries. However, it is challenging to simultaneously achieve high recovery rate and sulfur purity, due to the multiple impurities combining with sulfur in these wastes. In this paper, we developed a novel method of pressure induced melting-crystallization to efficiently recover sulfur from MSCWs. The effects of condition parameters on the sulfur recovery rate and purity were optimized through response surface methodology. The single objective optimization results showed that the interaction between melting temperature and slurry concentration had a great influence on sulfur purity. The slurry concentration and pressure had great influence on sulfur recovery rate. The results of multi-objective optimization showed that under the conditions of pressure 1.2 MPa, slurry concentration 14.9% and melting temperature 140.9℃, the highest sulfur purity and recovery rate could reach 93.0% and 89.1% respectively. Mechanism investigation revealed that the high efficiency of sulfur recovery was ascribed to recrystallization of molten sulfur under the combined action of pressure and water, forming dense sulfur blocks and separating hydrophilic impurities. This work provides a new way to recover sulfur resources from MSCWs with sulfur content higher than 50%.

Bringing the Submarine Mariana Arc and Backarc Basin to Life for Undergraduates and the Public

ABSTRACTThis paper aims to better teach about submarine arc and backarc basin volcanic and hydrothermal activity using the ~1400 km long Mariana convergent margin as an example. Four US National Oceanographic and Atmospheric Administration (NOAA) expeditions (2004–2016) equipped with a remotely operated vehicle (ROV) have discovered and explored many of submarine volcanoes and associated hydrothermal fields and generated many short (~1 min long) videos about them. Some of these videos would be very useful for teaching about these processes if they were organized and context provided, which is done here. Eighteen short videos about nine sites generated by NOAA are presented and discussed here. These are organized into three categories: volcanic eruptions, magmatic degassing, and hydrothermal activity. Volcanic eruption videos include two about glassy pillow lavas erupted in 2013–2015 and a rare example of a submarine eruption. Four videos about magmatic degassing include an example of sulfur produced by disproportionation of magmatic sulfur dioxide associated with a submarine eruption, two rare examples of molten sulfur lakes, and liquid carbon dioxide venting. Four videos about hydrothermal activity are provided. Suggestions for how this material might be used in the classroom are also given.

Sulphur attack on RCC wall of sulphur pit

Sulphur attack is not a very popular damage mechanism in Reinformed Cement Concrete (RCC) structures. For Sulphur Recovery Units (SRU) of Hydrocarbon Processing Industry, it is not so. Here concrete pits are used for storing molten sulphur and hence concrete is exposed to corrosive materials. In BPCL- Kochi Refinery, during an internal inspection of a sulphur pit, bulging was noticed on the acid resistant brick lining. After removal of brick lining, sulphur attack was observed on RCC walls of pit. Full repair and refurbishment of the wall was carried out accordingly. As a case study approach, this paper deals with various aspects of sulphur attack on concrete including symptoms, damage patterns etc. It also includes materials & methodology adopted in refurbishment jobs. The paper shall impart awareness about sulphur attack damages to industry/technical experts.

The predictive machine learning model of a hydrated inverse vulcanized copolymer for effective mercury sequestration from wastewater

Inverse vulcanized polysulfides (IVP) are promising sulfur-enriched copolymers with unconventional properties irresistible for diverse applications like Hg2+ remediation. Nevertheless, due to their inherent hydrophobic nature, these copolymers still offer low Hg2+ uptake capacity. Herein, we reported the synthesis of IVP by reacting molten sulfur with 4-vinyl benzyl chloride, followed by their functionalization using N-methyl D-glucamine (NMDG) to increase the hydration of the developed IVP. The chemical composition and structure of the functionalized IVP were proposed based on FTIR and XPS analysis. The functionalized IVP demonstrated a high mercury adsorption capacity of 608 mg/g (compared to <26 mg/g for common IVP) because of rich sulfur and hydrophilic regions. NMDG functionalized IVP removed 100 % Hg2+ from a low feed concentration (10–50 mg/l). A predictive machine learning model was also developed to predict the amount of mercury removed (%) using GPR, ANN, Decision Tree, and SVM algorithms. Hyperparameter and loss function optimization was also carried out to reduce the prediction error. The optimized GPR algorithm demonstrated high R2 (0.99 (training) and 0.98 (unseen)) and low RMSE (2.74 (training) and 2.53 (unseen)) values indicating its goodness in predicting the amount of mercury removed. The produced functionalized IVP can be regenerated and reused with constant Hg2+ uptake capacity. Sulfur is the waste of the petrochemical industry and is abundantly available, making the functionalized IVP a sustainable and cheap adsorbent that can be produced for high-volume Hg2+ remediation. Environmental implicationThis research effectively addresses the removal of the global top-priority neurotoxic pollutant mercury, which is toxic even at low concentrations. We attempted to remove the Hg2+ utilizing an inexpensive adsorbent developed by NMDG functionalized copolymer of molten sulfur and VBC. A predictive machine learning model was also formulated to predict the amount of mercury removal from wastewater with only a 0.05 % error which shows the goodness of the developed model. This work is critical in utilizing this low-cost adsorbent and demonstrates its potential for large-scale industrial application.

Longitudinal opening and Fe3C modifying of carbon nanotubes applied for high-performance lithium-sulfur batteries

Carbon nanotubes (CNTs) have shown great potential as host materials for sulfur in lithium‑sulfur batteries. However, during the melting-diffusion process, liquid sulfur faces difficulties in penetrating deeply into the inner cavities of CNTs, particularly those with a large length-diameter ratio, which results in a limited number of attachment sites for sulfur. Additionally, the weak physical adsorption nature of carbon and the shuttling effect of soluble lithium polysulfides have been intractable issues. In this paper, we report the use of the high-frequency induction method to longitudinally open multiwalled CNTs derived from polypyrrole nanotubes, resulting in single-edge slotted carbon nanotubes (SCNT). These SCNTs significantly enhance the filling ratio of molten sulfur within the CNTs. Furthermore, Fe3C nanoparticles are introduced to enhance the chemisorption capacity of SCNT, thus alleviating the shuttle effect and improving the cycling stability of lithium‑sulfur batteries. As a result, the SCNT@Fe3C-S electrodes exhibit an initial capacity of 968 mAh g−1 and a stable cycling performance with a negligible capacity fading of 0.043 % per cycle over 1000 cycles at 1.0C with a sulfur loading of 3.0 mg cm−2. Overall, this work offers a new strategy for synthesizing high-performance sulfur hosts based on CNTs by cutting and modifying them.

High sulfur-doped microporous carbon for high-rate potassium ion storage: Interspace design and solvent effect

Carbon materials as promising anode for potassium ion batteries (PIBs) suffer from low rate performance, which is attributed to sluggish K+ transport stemming from limited carbon interspace and elusive solvent effect. Herein, interspace design and solvent effect are investigated to resolve this issue. Through an innovative salt template assisted molten sulfur method, large hollow pores, massive micropores and expanded interlayer spacing are integrated in a high sulfur-doped porous carbon (S-PC), showing obviously higher rate capability (351.5 and 122.3 mA h g−1 at 0.1 and 20 A g−1, respectively) than pristine porous carbon (PC). Furthermore, the S-PC exhibits significantly-higher rate performance in ester-based electrolyte (1 M KFSI/EC + DEC) than in ether one (1 M KFSI/DME). Kinetic study demonstrates advantage of interspace design and ester-based electrolyte on promoting faster K+ transport. The explicit solvent effect on S-PC is further examined by XPS and HRTEM analyses, revealing a desirable inorganic KF-salt-dominated, thin solid electrolyte interface (SEI) layer in ester-based electrolyte. This work opens new avenues for precise design of advanced carbon materials for high-rate PIBs.

Physical and chemical characteristics of active sulfur flows observed at Lastarria volcano (northern Chile) in January 2019

Molten sulfur is found in various subaerial volcanoes. However, limited records of the pools and flows of molten sulfur have been reported: therefore, questions remain regarding the physicochemical processes behind this phenomenon. A suite of new sulfur flows, some of which active, was identified at the Lastarria volcano (northern Chile) and studied using satellite imagery, in situ probing, and temperature and video recording. This finding provides a unique opportunity to better understand the emplacement mechanisms and mineral and chemical compositions of molten sulfur, in addition to gaining insight into its origin. Molten sulfur presented temperatures of 124–158°C, with the most prolonged sulfur flow reaching 12 m from the source. Photogrammetric tools permitted the identification of levees and channel structures, with an estimated average flow speed of 0.069 m/s. Field measurements yielded a total volume of 1.45 ± 0.29 m3 of sulfur (equivalent to ∼2.07 tons) mobilized during the January 2019 event for at least 408 min. Solidified sulfur was composed of native sulfur with minor galena and arsenic- and iodine-bearing minerals. Trace element analysis indicated substantial enrichment of Bi, Sb, Sn, Cd, as well as a very high concentration of As (&amp;gt;40.000 ppm). The January 2019 molten sulfur manifestations in Lastarria appear to be more enriched in As compared to the worldwide known volcanoes with molten sulfur records, such as the Shiretoko-Iozan and Poás volcanoes. Furthermore, their rheological properties suggest that the “time of activity” in events such as this could be underestimated as flows in Lastarria have moved significantly slower than previously thought. The origin of molten sulfur is ascribed to the favorable S-rich chemistry of fumarolic gases and changes in host rock permeability (fracture opening). Molten sulfur in Lastarria correlates with a peak in activity characterized by high emissions of SO2 and other acid species, such as HF and HCl, in addition to ground deformation. Consequently, molten sulfur was framed within a period of volcanic unrest in Lastarria, triggered by changes in the magmatic-hydrothermal system. The appearance of molten sulfur is related to physicochemical perturbations inside the volcanic system and is perhaps a precursor of eruptive activity, as observed in the Poás and Turrialba volcanoes.

Study on the Effect of Calcium Alloy on Arsenic Removal from Scrap-Based Steel Production.

Scrap steel is a kind of resource that can be recycled indefinitely. However, the enrichment of arsenic in the recycling process will seriously affect the performance of the product, making the recycling process unsustainable. In this study, the removal of arsenic from molten steel using calcium alloys was investigated experimentally, and the underlying mechanism was explored based on thermodynamic principles. The results show that the addition of calcium alloy is an effective means of reducing the arsenic content in molten steel, with the highest removal percentage of 56.36% observed with calcium aluminum alloy. A thermodynamic analysis revealed that the critical calcium content required for arsenic removal reaction is 0.0037%. Moreover, ultra-low levels of oxygen and sulfur were found to be crucial in achieving a good arsenic removal effect. When the arsenic removal reaction occurs in molten steel, the oxygen and sulfur concentrations in equilibrium with calcium were wO=0.0012% and wS=0.00548%, respectively. After successful arsenic removal, the arsenic removal product of the calcium alloy is Ca3As2, which usually does not appear alone. Instead, it is prone to combining with alumina, calcium oxide, and other inclusions to form composite inclusions, which is beneficial for the floating removal of inclusions and the purification of scrap steel in molten steel.

Modeling of Interfacial Tension and Inclusion Motion Behavior in Steelmaking Continuous Casting Mold.

The current work is an expansion of our previous numerical model in which we investigated the motion behavior of mold inclusions in the presence of interfacial tension effects. In this paper, we used computational fluid dynamic simulations to examine the influence of interfacial tension on inclusion motion behavior near to the solid-liquid interface (solidifying shell). We have used a multiphase model in which molten steel (SPFH590), sulfur, and alumina inclusions have been considered as different phases. In addition, we assume minimal to negligible velocity at the solid-liquid interface, and we restrict the numerical simulation to only include critical phenomena like heat transport and interfacial tension distribution in two-dimensional space. The two-phase simulation of molten steel mixed with sulfur and alumina was modeled on volume of fluid (VOF) method. Furthermore, the concentration of the surfactant (sulfur) in molten steel was defined using a species model. The surfactant concentration and temperature affect the Marangoni forces, and subsequently affects the interfacial tension applied on inclusion particles. It was found that the alteration in interfacial tension causes the inclusion particles to be pushed and swallowed near the solidifying boundaries. In addition, we have compared the computational results of interfacial tension, and it was found to be in good agreement with experimental correlations.

A trip into molten sulfur

AbstractLakes of molten sulfur are features sometimes found in seafloor hydrothermal vent systems. Daikoku of the northern Mariana Arc is notable for being home to one of such features inside its summit caldera, the “Sulfur Cauldron” discovered in 2006. A number of oceanographic research cruises since then have revealed significant volcanic activities on Daikoku Seamount, including an eruption event in 2014 leading to the formation of a new basin‐like crater. How this event impacted the sulfur lake on Daikoku Seamount remained unclear. Here, we revisited Daikoku Seamount with a remotely operated vehicle to show that the new crater is currently home to a much larger molten sulfur lake than the Sulfur Cauldron, which we name the “Rengoku” sulfur lake. Our samples provided new insights on the structure of submarine sulfur lakes, and contribute to the time‐series observation of volcanic and hydrothermal activities on Daikoku Seamount.

Phase transition process of sulfur in bitumen and its effect on rheological properties of bitumen

Partial substitution of sulfur for bitumen helps reduce bitumen consumption while promoting recycling of the sulfur in waste residues. The properties of sulfur-extended bitumen (SEB) are closely related to the chemical reaction process and the phase transition process of sulfur in bitumen, and these two processes are influenced by sulfur dosage and curing time. Therefore, SEB samples with sulfur dosages of 1 %, 5 %, 10 %, 15 %, 20 %, 25 % and 30 % were prepared and cured for 0, 15, 30, or 60 days. Differential scanning calorimetry was conducted to understand the sulfur recrystallization process in bitumen, and a dynamic shear rheometer was used to analyze the rheological properties of SEB samples. Results show that molten sulfur can turn to monoclinic sulfur immediately after cooling; the monoclinic sulfur gradually turns to orthorhombic sulfur, and the ratio between the two forms stabilizes after curing for 15 days. The recrystallization of sulfur in bitumen needs sufficient curing time, and the sulfur states in bitumen vary depending on the sulfur dosage. When the sulfur dosage is lower than 15 %, sulfur dissolves into bitumen. The dissolved sulfur softens the bitumen and increases its low-temperature properties and resistance to fatigue cracking. When the sulfur dosage is 10 %, 15 %, 20 %, 25 %, or 30 %, surplus sulfur is recrystallized to orthorhombic sulfur. When the sulfur dosage is 35 % or more (the dosages evaluated in the former study), surplus sulfur is recrystallized to monoclinic sulfur. The chemically crosslinked sulfur and recrystallization sulfur help increase the elastic component in bitumen and improve the rutting resistance and fatigue life of bitumen. However, when the sulfur dosage exceeds 20 %, the effect of stress concentration stands out due to bulk gathering of recrystallized sulfur, and this effect stops further improvement in the fatigue life of SEB samples. The effects of recrystallization sulfur on bitumen are mainly concentrated in the first 15 days of curing time, even though much more recrystallized sulfur is detected after more curing time, even at 60 days (the longest curing time evaluated in this study). Therefore, a curing time of 15 days is sufficient for accurate evaluation of SEB properties.

Incorporating TiO2 nanoparticles into the multichannels of electrospun carbon fibers to increase the adsorption of polysulfides in room temperature sodium-sulfur batteries

With the rapid development of electric vehicles and large-scale power grids, lithium-ion batteries inevitably face the problem that their limited energy density and high cost cannot meet the growing demand. Room temperature sodium-sulfur (RT Na-S) batteries, which have the potential to replace lithium-ion batteries, have become a focus of attention. However, the challenging problem of their poor cycling performance cause by the “shuttle effect” of the reaction intermediates (sodium polysulfides) needs to be addressed. We report a method to incorporate TiO2 nano particles into the multichannels of electrospun carbon fibers (TiO2@MCCFs) to stabilize the sulfur compounds and produce high-performance RT Na-S batteries. The TiO2@MCCFs were prepared by electrospinning followed by heat treatment, and were infiltrated by molten sulfur to fabricate S/TiO2@MCCF cathode materials. The addition of the TiO2 nanoparticles increases the affinity of cathode materials for polysulfides and promotes the conversion of polysulfides to lower order products. This was verified by DFT calculations. A S/TiO2@MCCF cathode with a S content of 54% has improved electrochemical rate and cycling performance, with a specific capacity of 445.1 mAh g−1 after 100 cycles at 0.1 A g−1 and a nearly 100% Coulombic efficiency. Even at 2 A g−1, the cathode still has a capacity of 300.5 mAh g−1 after 500 cycles. This work provides a new way to construct high performance RT Na-S battery cathodes.

Martian and lunar sulfur concrete mechanical and chemical properties considering regolith ingredients and sublimation

• Sulfur sublimation rate at vacuum is 8000 times lower at −60 °C than at 20 °C. • Sulfur concrete permeability decreases strongly with higher sulfur content. • Sulfur concrete porosity does not change much with varying sulfur content. • The presence of alumina in sulphur concrete results in higher porosity. • Alumina and iron oxide together in sulphur concrete leads to lower porosity. Space constructions require unique materials suitable for the harsh conditions in space. Sulfur concrete (SC) is one of the most promising materials for such applications. However, the behavior of sulfur concrete in a vacuum, microgravity, and different temperature conditions and its chemical changes has not been well established yet. This study investigated the effect of vacuum, sulfur content, and compaction (trowel effect) on mechanical and hydro-mechanical properties. Moreover, this study assesses the impact of chemical reactions of aluminum and iron oxides with molten sulfur on the sulfur concrete’s mechanical properties via X-ray diffraction analysis (XRD), scanning electron microscopy (SEM-EDS), and Fourier-transform infrared spectroscopy (FTIR). The predictions from this research show that the sublimation rate under vacuum conditions at very low temperature (−60 °C) can be reduced nearly 8000 times compared with that at 20 °C according to the vapor pressure-sublimation rate relationship. In addition, mechanical experimental tests show that a slight increase in sulfur content dramatically reduces the permeability of sulfur concrete. On the other hand, the porosity is not much affected by the sulfur content. Moreover, sample compaction leads to a significant reduction and increment of the hydro-mechanical and mechanical strength, respectively, indicating the trowel's positive effect. Chemically, sulfur dioxide reacts with alumina and iron oxide via chemical adsorption, and then reaction with molecular oxygen produces S O 4 2 - confirmed by SEM-EDS, XRD, and FTIR results. The presence of alumina increases the sample porosity, although, together with iron oxide, another mineral, namely A l 2 F e 2 S O 4 6 ( H 2 O ) 12 . 6 H 2 O (Aluminocoquimbite), is formed resulting in a lower porosity. To conclude, we have shed light on sulfur concrete properties and preparation processes in unconventional environments and we have shown how different unknown parameters affect the mechanical and chemical properties of the sulfur binder.

Subsurface Archaea associated with rapid geobiological change in a model Yellowstone hot spring

Despite over a century of study, it is unknown if continental hydrothermal fields support high-temperature subsurface biospheres. Cinder Pool is among the deepest hot springs in Yellowstone and is widely studied due to unique sulfur geochemistry that is attributed to hydrolysis of molten elemental sulfur at ∼18 m depth that promotes several chemical reactions that maintain low sulfide, low oxygen, and a moderate pH of ∼4.0. Following ∼100 years of stability, Cinder Pool underwent extreme visual and chemical change (acidification) in 2018. Here, we show that depth-resolved geochemical and metagenomic-based microbial community analyses pre- (2016) and post-acidification (2020) indicate the changes are likely attributable to feedbacks between geological/geochemical processes, sulfur oxidation by subsurface Sulfolobales Archaea, and the disappearance of molten sulfur at depth. These findings underscore the dynamic and rapid feedback between the geosphere and biosphere in continental hydrothermal fields and suggest subsurface biospheres to be more prevalent in these systems than previously recognized.

Enhanced Production of Biogas Using Biochar-Sulfur Composite in the Methane Fermentation Process.

The methane fermentation of organic waste is one way to minimize organic waste, which accounts for 77% of the global municipal waste stream. The use of biochar as an additive for methane fermentation has been shown to increase the production potential of biogas. Sulfur waste has a potential application to synergistic recycling in a form of composites with other materials including biochar. A composite product in the form of a mixture of biochar and molten sulfur has been proposed. In this experiment, additions of the sulfur–biochar composite (SBC) were tested to improve the fermentation process. The biochar was produced from apple chips under the temperature of 500 °C. The ground biochar and sulfur (<1 mm particle size) were mixed in the proportion of 40% biochar and 60% sulfur and heated to 140 °C for sulfur melting. After cooling, the solidified composite was ground. The SBC was added in the dose rate of 10% by dry mass of prepared artificial kitchen waste. Wet anaerobic digestion was carried out in the batch reactors under a temperature of 37 °C for 21 days. As an inoculum, the digestate from Bio-Wat Sp. z. o. o., Świdnica, Poland, was used. The results showed that released biogas reached 672 mL × gvs−1, and the yield was 4% higher than in the variant without the SBC. Kinetics study indicated that the biogas production constant rate reached 0.214 d−1 and was 4.4% higher than in the variant without the SBC.

An Experimental Investigation on Properties of Concrete by Partial Replacement of Cement with Sulfur

Knowing how long Mars has been around A new planet has been designated as a "sulfur-rich planet." simulation-based building material The development of Martian soil and molten sulfur. in addition to the availability of raw materials for Creating sulfur concrete, while maintaining its strength achieves levels comparable to traditional cementations materials concrete, low temperature, quick curing resistance to acid and salt in the environment,100% recyclability is a desirable feature. The developed Martian Concrete's properties Different sulfur percentages are tested in this study. The best mixing proportions were investigated. To determine strength development, strength variability, and failure mechanisms, three-point bending, unconfined compression, and splitting tests were used 7days 28 days. The results are compared to sulfur concrete made with ordinary sand. The particle size distribution is found to have a significant impact on the final strength of the mixture. Furthermore, because Martian soil is metal-rich, high-temperature mixing produces sulphates and, possibly, polysulfates, which contribute to the high strength. Due to the difference in gravity between Mars and Earth, the optimal mix developed as Martian Concrete has an unconfined compressive strength of above 50 MPa, which corresponds to a roughly 150 MPa concrete on Mars.

Effect of temperature on hot corrosion of nickel-based alloys for 700 °C A-USC power plants

Nickel-based alloys were exposed to a synthetic flue gas at varying temperatures from 700 °C to 800 °C. Two main damage mechanisms were revealed, including general surface oxidation caused by eutectic melting of sulfates and internal cracking caused by sulfur diffusion. The damage level of the alloys did not monotonically increase with temperature. Significant weight losses due to molten sulfate corrosion were found at 700–760 °C, and the minimum damage was at 780 °C. Nimonic 263 with the highest cobalt, titanium contents and the lowest aluminum content exhibited the best resistance to both molten sulfate corrosion and sulfur invasion.

Highly sulfur-rich polymeric cathode materials via inverse vulcanization of sulfur for lithium–sulfur batteries

In the present study, a new polythiophene derivative bearing an acryloyloxy moiety in the side chain as a functional co-monomer, poly (3-[(2-acryloyloxy) methyl]) thiophene (PAMT), was synthesized to be used for the inverse vulcanization method with elemental sulfur (S8). Highly sulfur-rich graft materials, S- poly (3-[(2-acryloyloxy) methyl]) thiophenes (52 and 74%) (S-PAMT), were prepared by inverse vulcanization of PAMT with different feed ratios of molten sulfur. Their structural characterizations were carried out by using appropriate standard spectroscopic methods such as FT-IR, DSC, TGA, SEM as well as XPS. The electrochemical performance of S-PAMT (74%) as a Li–S battery cathode material was evaluated. It was found that the fabricated cells delivered around 400 mAh·g−1 stable capacity at a C/5 current density over 100 cycles. Electrochemical impedance spectroscopy (EIS) was also performed before and after cycling to further investigate the lithium storage mechanism of S-PAMT (74%).

Deposition of copper sulfide films on polyamide surface

In this paper, we present a novel and low - cost method for preparing copper sulfide films on polyamide. Non-treated as well as pre-treated PA6 films by 3 different methods (in boiled water; in NaOH solution; in boiled water and then in NaOH solution) were used for the formation of Cu2S layers by the sorption-diffusion method. Molten sulfur has been used as a sulfurization agent. The XRD, FTIR, and UV-VIS methods were used to characterize the structural, optical, and electrical properties of samples and to track changes in samples after each treatment stage. The sheet resistance of Cu2S layers depends on the pre-treatment method and varied from 7 k?/sq to 6 M?/sq. The optical band gaps (Eg) for direct and indirect transitions are determined to be 2.61-2.67 eV and 1.40-1.44 eV, respectively. Furthermore, the optical constants n, k, and ? are determined from UV-VIS measurements.

Hydrodynamics of an Airlift Column for Aeration in Molten Sulfur

The airlift column is a promising technology for the removal of volatile gas from high-viscosity molten sulfur. However, a detailed analysis is lacking on the hydrodynamic properties inside the column, due to the difficulty in flow behavior detection in the opaque molten sulfur. In this work, we adopted the computational fluid dynamics simulation to understand the hydrodynamic behaviors in an airlift column for molten sulfur aeration. In addition, we analyzed the impacts of the superficial gas velocity (UGr) and column height on the hydrodynamic characteristics, such as gas holdup, average bubble diameter, and liquid circulation velocity (ULr) in the column. The simulation shows that at a constant column height of 15 m, an increase on gas holdup can be obtained with the increase of the superficial gas velocity, while the bubble diameter remains almost constant. Once the superficial gas velocity exceeded 0.333 m/s, the liquid circulation velocity increased slowly. With a variation on the column height from 5 to 25 m, a negligible change on gas holdup, but an obvious increase on liquid circulation velocity and bubble diameter is observed at the given superficial gas velocity of 0.0389 m/s. Furthermore, the simulation shows a similar trend, but with considerably more detailed information, on the relationship between the gas holdup and liquid circulation velocity when compared to the predictions from the Chisti correlation (1988) and an optimized correlation proposed in this work.