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.

Mechanical energy-induced CO2 conversion using liquid metals

We report a green carbon capture and conversion technology offering scalability and economic viability for mitigating CO2 emissions. The technology uses suspensions of gallium liquid metal to reduce CO2 into carbonaceous solid products and O2 at near room temperature. The nonpolar nature of the liquid gallium interface allows the solid products to instantaneously exfoliate, hence keeping active sites accessible. The solid co-contributor of silver-gallium rods ensures a cyclic sustainable process. The overall process relies on mechanical energy as the input, which drives nano dimensional triboelectrochemical reactions. By altering the secondary solvent and changing the reactor height, the dissolution and conversion efficiency can be tuned. The optimum reactor height is only 27 cm, when gallium/silver fluoride mix at 7:1 mass ratio is employed as the reaction material. At CO2 input of ~8 sccm, 92% efficiency was obtained at the record low input energy of 228.5 kW∙h for the capture and conversion of a tonne of CO2. The potential impact of this green technology is remarkable, likely benefiting a variety of industries and offering an economical solution for CO2 capture and conversion.

The effect of reactor height on coal gasification

A comprehensive 2-D numerical model has been developed to simulate the coal gasification and investigate the effect of reactor height on the coal gasification in fluidized bed. Gas-solid flow, homogeneous and heterogeneous chemical reactions were considered. An Eulerian model for fluid phase and discrete particle method (Lagrangian) for particle phase were used in this study. The reaction rates of homogeneous and heterogeneous reactions were determined by Arrhenius-eddy dissipation reaction rate and Arrhenius-diffusion rate, respectively. Simulations were performed in a fluidized bed coal gasifier with twelve different reactor heights and with a diameter of 0.22 m. The calculated values were compared with the experimental values for the reactor height of 2 m available in open literature. It shows that the predicted exit gas mole fractions are in a good agreement with the experimental data.

THE IMPACT OF REACTOR HEIGHT/DIAMETER (H/D) RATIO ON AEROBIC GRANULAR SLUDGE (AGS) FORMATION IN SEWAGE

Until now, the development of aerobic granules sludge (AGS) has been extensively reported using sequencing batch reactor (SBR) with reactor height/diameter (H/D) ratio of over 10. This is because the formation process of aerobic granules itself is depending upon the flowing trajectory inside reactor indulge by reactor height and superficial air velocity (SUAV). Thus, this study aims to determine effect of reactor H/D ratio on performance of AGS develop in two SBRS with equal working volume and organic loading rate (OLR). The two SBRs namely as SBR1 and SBR2 had a difference in reactor H/D ratio of 11.3 and 4.4, respectively. At an aeration rate of 4 L/min, SUAV for SBR1 was two time higher than in SBR2, which were 1.33 cm/s and 0.7 cm/s, respectively. Thus, the SBR2 configuration condition seems unfavorable for development of compact aerobic granules. However, it was found that aerobic granules can be developed in both SBRs at an OLR as low as 0.12 kg CODs/m3 d and up to 0.49 kg CODs/m3 d. Mature aerobic granules were successfully developed after 49 and 89 days of formation, for Batch1 AGS and Batch2 AGS, respectively. At stable conditions, the highest CODs removal and SS effluent for Batch1 AGS and Batch2 AGS were more than 80% and below 26 mg/L, respectively. While effluent performance in both reactors was high, analysis on SVI30 indicated that SBR1 produced more sludge than SBR2. Compare to SBR1, at similar settling time of 15 min, SBR2 provide a short settling distance for biomass which was preferable in case of system breakdown due to shock OLR.

Numerical Investigations to Quantify the Effect of Horizontal Membranes on the Performance of a Fluidized Bed Reactor

Reactive simulations of gas-solid flows occurring in fluidized beds with horizontal membrane insertion were carried out using computational fluid dynamics based on the kinetic theory of granular flows. The effect of altering the membrane arrangement on the overall reactor performance (degree of conversion achieved) was investigated by means of fractional factorial designs. When membranes served only as hydrodynamic modifiers to the flow, it was found that significant improvements could be obtained by optimising the membrane arrangement. A slightly larger improvement could be attained by injecting some of the reacting gas through the membranes. When compared to the improvements that can be attained by simply scaling up the reactor height and especially the reactor width, however, these improvements were of less significance. The use of membranes solely for altering reactor hydrodynamics by serving as obstructions and gas injection points can therefore not be merited. Further optimisation studies into membrane arrangement are therefore only recommended for specific processes in which the membranes play a central role by extracting some of the process gasses.