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.

Hydrodynamics of an airlift reactor for aeration in molten sulfur

An industrial-scale internal loop airlift reactor is used to remove volatile gas from high-viscosity molten sulfur. The effects of the superficial gas velocity and reactor height on the hydrodynamic characteristics were studied. The gas holdup, average bubble diameter, and liquid circulation velocity in the reactor under different conditions were analyzed using computational fluid dynamics simulation. The superficial gas velocity was varied from 0.0056 m/s to 0.05 m/s at a constant reactor height of 15 m. The total reactor height was varied from 5 m to 25 m at a superficial gas velocity of 0.0389 m/s.Based on the correlation between the gas holdup and liquid circulation velocity proposed by Chisti (1988), an optimized correlation between the gas holdup and liquid circulation velocity was developed by considering the influence of the bubble diameter. The results obtained using the proposed correlation were compared with those obtained using the Chisti correlation and simulation.

Kinetic investigation of surfactants’ influence on pressure leaching of zinc sulfide concentrates

Pressure leaching is one of the most high-demanded and promising hydrometallurgical technology, which allows one to obtain high efficiency. Taking into account the shutdown of zinc plant in Vladikavkaz («Electrozinc, Lls.») searching the modern methods of zinc production is of current interest. In this work, the issue was observed on influence of temperature and sodium lignosulfonate (SL) onto the zinc and iron sulfides behavior during pressure leaching of zinc sulfide concentrate from the Uchalinsk deposit. Temperature increasing from 130 to 150oC led to decreasing of zinc extraction and sulfur-sulfide pellets formation; that indicated increasing the zinc sulfide wettability by the molten sulfur due to reduction of viscosity and surface tension of molten sulfur. Increasing the LSN dosage promoted running up of the absolute value of the zinc extraction. The highest growth of the zinc extraction (17.39 %) was obtained at 0.2 g/dm3 LSN. Further increasing of the LSN concentration on 0.2 g/dm3 (up to 0.4, 0.6, 0.8 g/dm3) led to double decrease of their effectiveness in reference to previous LSN concentration.

Features of structure state and magnetic properties of mono- and polycrystalline LiNiPO4 and LiNi0.9Co0.1PO4

Pressure leaching is one of the most high-demanded and promising hydrometallurgical technology, which allows one to obtain high efficiency. Taking into account the shutdown of zinc plant in Vladikavkaz («Electrozinc, Lls.») searching the modern methods of zinc production is of current interest. In this work, the issue was observed on influence of temperature and sodium lignosulfonate (SL) onto the zinc and iron sulfides behavior during pressure leaching of zinc sulfide concentrate from the Uchalinsk deposit. Temperature increasing from 130 to 150o C led to decreasing of zinc extraction and sulfur-sulfide pellets formation; that indicated increasing the zinc sulfide wettability by the molten sulfur due to reduction of viscosity and surface tension of molten sulfur. Increasing the LSN dosage promoted running up of the absolute value of the zinc extraction. The highest growth of the zinc extraction (17.39 %) was obtained at 0.2 g/dm3 LSN. Further increasing of the LSN concentration on 0.2 g/dm3 (up to 0.4, 0.6, 0.8 g/dm3 ) led to double decrease of their effectiveness in reference to previous LSN concentration.

An integrated fuzzy-AHP and TOPSIS approach for maintenance policy selection

Purpose The purpose of this paper is to select the best maintenance policy for different types of equipment of a manufacturer integrating the fuzzy analytic hierarchy process (FAHP) and the technique for order of preference by similarity to ideal solution (TOPSIS) models. Design/methodology/approach The decision hierarchy of this research includes three levels. The first level aims to choose the best maintenance policy for different types of equipment of an acid manufacturer. These equipment pieces include molten sulfur ponds, boiler, absorption tower, cooling towers, converter, heat exchanger and sulfur fuel furnace. The second level includes decision criteria of added-value, risk level and the cost. Lastly, the third level comprises time-based maintenance (TBM), corrective maintenance (CM), shutdown maintenance and condition-based maintenance (CBM) as four maintenance policies. Findings The best maintenance policy for different types of equipment of a manufacturer is the main finding of this research. Based on the obtained results, CBM policy is suggested for absorption tower, boiler, cooling tower and molten sulfur ponds, TBM policy is suggested for converters and heat exchanger and CM policy is suggested for a sulfur fuel furnace. Originality/value This research develops a novel model by integrating FAHP and an interval TOPSIS with concurrent consideration of added-value, risk level and cost to select the best maintenance policy. According to the highlights of the previous studies conducted on maintenance policy selection and related tools and techniques, an operative integrated approach to combine risk, added-value and cost with integrated fuzzy models is not developed yet. The majority of the previous studies have considered classic fuzzy approaches such as FAHP, FANP, Fuzzy TOPSIS, etc., which are not completely capable to reflect the decision makers’ viewpoints.