Loop Airlift Reactor Research Articles

An integrated airlift loop reactor for continuous production of calcium carbonate from phosphogypsum using a one-step method

Commercial exploitations of phosphogypsum and CO2 are the research hotspots and difficulties. A coupled reaction and separation airlift loop reactor, which integrates four consecutive processes (i.e., dissolution of slightly soluble raw material, impurity separation, product preparation, and product separation) for reactive crystallization, was proposed to continuously prepare high-value products (i.e., (NH4)2SO4 and nano-sized CaCO3) using waste to treat waste (i.e., phosphogypsum and CO2) at ambient conditions by a one-step method. The technical feasibilities of the coupled reactor were verified, and principal influencing factors on the CaCO3 product quality were systematically investigated and optimized. Additionally, the coupled fluid hydrodynamics dependent on the two individual airlift loop reactors were also inspected. This work shed some new light on the practical resource utilization of phosphogypsum and waste CO2 in tandem at a low cost, and a solid basis for the rational design, optimization, and scale-up of such promising reactors was provided.

Investigation of hydrodynamic performance in a staggered multistage internal airlift loop reactor

The multistage internal airlift loop reactor (MIALR) has shown promising application prospects in gas–liquid–solid reaction systems. However, traditional MIALRs have a global circulation with strong interstage liquid-phase exchange. This paper proposes a staggered multistage internal airlift loop reactor (SMIALR) that incorporates special guide elements to create a staggered flow. Both experiments and computational fluid dynamics-population balance model simulations were conducted to investigate the hydrodynamic performances of MIALR and SMIALR. The results demonstrate that SMIALR exhibits a local circulation at each stage. Bubbles have a longer residence time in SMIALR, resulting in a 28.35%–55.54% increase in gas holdup and a 7.27%–13.69% increase in volumetric mass transfer coefficient. The gas–liquid mass transfer coefficient of SMIALR was improved by increasing the gas–liquid interfacial area. Additionally, the radial distribution of solids was found to be more uniform. This study offers insights for optimizing MIALR and provides a theoretical foundation for the design and scale-up of SMIALR.

Hydrodynamics and Mass Transfer in an Airlift Loop Reactor: Comparison between Using Two Kinds of Spargers

The effects of different spargers on the hydrodynamics and mass transfer of an airlift loop reactor were investigated. The gas holdup, liquid loop velocity, and volumetric mass transfer coefficient of the reactor were tested using a ring orifice distributor and a jet nozzle. The study was conducted in a 6 m high airlift loop reactor at a superficial gas velocity of 0.01~0.04 m/s, and the superficial liquid velocity was maintained at 0.0154 m/s. The results showed that using the jet nozzle provided a higher gas holdup, liquid loop velocity, and mass transfer. When the superficial gas velocity was less than 0.0325 m/s, the liquid loop velocity generated by the jet nozzle was approximately 1.1-fold higher than that generated by the ring orifice distributor, and the disparity in gas holdup between the riser and downcomer enhanced the power of liquid circulation. When the superficial gas velocity was more than 0.0325 m/s, the jet kinetic power dominated the improvement in the liquid loop velocity, and the energy input from the nozzle to the airlift loop reactor was greater than 10.8 J/(s·m2). This indicated a threshold of energy input for overcoming the friction loss. In this situation, the liquid loop velocity in the jet form increased considerably, thus favoring the mixing performance and temperature uniformity of the reactor. It was also of significance for avoiding the formation of a flow dead zone in scale-up airlift loop reactors.

A gas distributor capable of multiple injection directions to improve the gas–liquid dispersion performance in the airlift loop reactor

As the gas supply equipment, the gas distributor is one of the core components in the airlift loop bioreactor. The gas injection direction and the dynamic behavior of the bubbles significantly affect the gas–liquid dispersion performance in the bioreactor. Therefore, based on the previously designed airlift loop reactor, a new type of tubular convex gas distributor (TCD) with multi-angle gas injection capability was developed. Under the conditions of different superficial gas velocities, the gas–liquid flow in the reactor was numerically simulated by computational fluid dynamics. The results showed that TCD had better gas–liquid dispersion and mass transfer performance in this reactor than several other traditional types of distributors. Under the experimental conditions, the optimal gas–liquid two-phase flow in the reactor was observed when the angle of the TCD vent tube was 15°, the number was 12, and the diameter was 1 mm. It was found that the error between the experimental results and the simulation results was controlled within 10 %, which verified the accuracy of the simulation. The application of TCD in the airlift loop bioreactor improved the wastewater treatment and biomass accumulation, significantly. The TCD can provide design ideas for gas distributors in other types of bioreactors, and is beneficial to improving the process of biological wastewater treatment for industrial application.

Impacts of solid physical properties on the performances of a slurry external airlift loop reactor integrating mixing and separation

Solid physical properties are vital for the design, optimization, and scale-up of gas–liquid–solid multiphase reactors. The complex and interactional effects of the solid physical properties, including particle diameter, density, wettability, and sphericity, on the hydrodynamic behaviors in a new external airlift loop reactor (EALR) integrating mixing and separation are decoupled in this work. Two semi-empirical equations are proposed and validated to predict the overall gas holdup and liquid circulating velocity satisfactorily, and then the individual influence of such solid physical properties is further investigated. The results demonstrate that both the overall gas holdup in the riser and the liquid circulating velocity in the downcomer increase with the contact angle, but decrease with particle size, density, and sphericity. Additionally, the impact of the particle size on the liquid circulating velocity is also profoundly revealed on a micro-level considering the particle size distribution. Moreover, the axial solid concentration distribution is discussed, and the uniformity of the slurry is described by the mixing index of the solid particles. The results show that a more homogeneous mixture can be achieved by adding finer particles other than attaining violent turbulence. Therefore, this work lays a foundation for the design, scale-up, and industrialization of the EALRs.

Removal of Phenol by Expanded Bed Airlift Loop Reactor

The exaggerated release of industrial wastes especially those containing phenol into the environment led to the contamination of both surface and groundwater supplies. In present work a synergistic and combined system technique between three operations, adsorption of phenol via (rice husk or granular activated carbon GAC as adsorbents) together with stripping by airflow and advance oxidation via hydrogen peroxide as the oxidation agent, to evaluate the possibility of using a proposed new design for internal airlift loop reactor for removing the phenol from wastewater. The experiments were set up in a cylindrical Perspex column consisted of a transparent outer column having a 15 cm inside diameter and 150 cm height that included an internal draught tube of 7.5 cm and extending vertically to 120 cm top contains a bed having a dimension (7.5 x 30 cm) filled with adsorbent materials (rice husk, granular activated carbon GAC) and a volume capacity 25 liters. The experiments were conducted under the influence of both of the following variables air flow rate(2-20) (L/min), treatment time(5-60 min), the molar ratio of hydrogen peroxide to phenol,(1:10, 1:15 and 1:20)). The results showed the success of the proposed design with obtaining a removal efficiency (83%),( 81%)when using GAC and the rice husk as adsorbent materials respectively, with minimum remediation time 60 minutes, airflow rate of 18 L/min, and molar ratio(20) hydrogen peroxide to phenol. This study demonstrated that the proposed synergistic system could be utilized for the remediation of contaminated aqueous systems.

The use of air-lift adsorber with a floating filling from a cross-linked chitosan hydrogels for Reactive Black 5 removal

This work substantially extends knowledge on the possibilities of treating colored industrial wastewater via sorption under flow conditions. The presented study aimed to determine the effectiveness of Reactive Black 5 (RB5) dye sorption from aqueous solutions under dynamic (flow) conditions in an unconventional air-lift type loop reactor with a filling made of hydrogel chitosan sorbents. The dye was removed from mono-component solutions (deionized water + RB5) and synthetic dyeing wastewater containing RB5 dye, NaCl (3 g/L), and an anti-creasing agent—UNICREASE JET (2 g/L). The sorbents tested in the study included: unmodified chitosan (CHs), chitosan ionically cross-linked with sodium citrate (CHs-CIT), and chitosan covalently cross-linked with epichlorohydrin (CHs-ECH). Each experimental series aimed to determine: the bed break-through time (CE = 0.1 C0), time of depletion of the sorbent’s sorption properties (CE = C0), and maximal sorption capacity of the sorbents (Qmax). The data obtained under dynamic conditions were described using Thomas, Yoon–Nelson, and Bohart–Adams models. The volume of the solution effectively treated in the air-lift reactor was significantly affected by chitosan sorbent type. At C0 = 50 mg RB5/L, the adsorber with the filling made of 1 g d.m. CHs allowed for the effective treatment of 4.6 L of synthetic wastewater (Qmax = 1504.7 mg/g), whereas CHs-ECH ensured 34.6 L of the treated solution (Qmax = 3212.9 mg/g).

Computational Fluid Dynamics Simulation of Hydrodynamics in a Two-Stage Internal Loop Airlift Reactor with Contraction-Expansion Guide Vane.

Global circulation and liquid back mixing adversely affect the continuous production of a multistage internal airlift loop reactor. A contraction-expansion guide vane (CEGV) is proposed and combined with a two-stage internal loop airlift reactor (TSILALR) to suppress the liquid back mixing between stages. A computational fluid dynamics (CFD) simulation is conducted to evaluate the performance of the CEGV in the TSILALR. The bubble size distribution and turbulent flow properties in the TSILALR are considered in the CFD simulation by using the population balance model and RNG k-ε turbulence model. The CFD model is validated against the experimental results. The deviations in the gas holdup and mean bubble diameter between the simulation and experimental results are less than 8% and 6%, respectively. The streamlines, flow pattern, bubble size distribution, and axial liquid velocity in the TSILALRs with and without the CEGV at superficial velocities of 0.04 and 0.08 m/s are obtained by CFD simulation. It has been shown that the CEGV generated local circulation flows at each stage instead of a global circulation flow in the TSILALR. The average global gas holdup in the TSILALR with a CEGV increased up to 1.98 times. The global gas holdup increased from 0.045 to 0.101 and the average axial velocity in the riser decreased from 0.314 to 0.241 m/s when the width of the CEGV increased from 50 to 75 mm at the superficial gas velocity of 0.08 m/s.

Process Intensification in Pneumatically Agitated Slurry Reactors

Abstract Pneumatically agitated slurry reactors, including bubble column reactors and airlift loop reactors (ALRs), are important gas–liquid–solid multiphase reactors. These reactors have been widely applied in many processes, especially in the biological fermentation and energy chemical industry, due to their low shear stress, good mixing, perfect mass-/heat-transfer properties, and relatively low costs. To further improve the performance of slurry reactors (i.e., mixing and mass/heat transfer) and to satisfy industrial requirements (e.g., temperature control, reduction of back-mixing, and product separation), the process intensification of slurry reactors is essential. This article starts by reviewing the latest advancements in the intensification of mixing and mass/heat transfer in these two types of reactors. It then summarizes process-intensification methods for mixing and separation that allow continuous production in these slurry reactors. Process-intensification technology that integrates directional flow in an ALR with simple solid–liquid separation in a hydrocyclone is recommended for its high efficiency and low costs. This article also systematically addresses vital considerations and challenges, including flow regime discrimination, gas spargers, solid particle effects, and other concerns in slurry reactors. It introduces the progress of numerical simulation using computational fluid dynamics (CFD) for the rational design of slurry reactors and discusses difficulties in modeling. Finally, it presents conclusions and perspectives on the design of industrial slurry reactors.

An Experimental Investigation of Synergistic Pulsation Bubble Column with Inverse Fluidized Loop Reactor for Removing Chloroform from Wastewater

In this study, the feasibility of using the developed design for the removal of organic pollutants from wastewater was examined. The design includes the integration of the work of both pulsation bubble column (PBC) and the inverse fluidization airlift loop reactor (IFALR). The experimental podium was fabricated and installed which that consists of a bubble column with a diameter of 5 cm and a height of 210 cm, contains at the top a solenoid valve which is electrically turned via at least two timers, and its connection with the loop reactor by a one-way valve. The loop reactor consists of an outer rectangular tube with dimensions (29 cm long x 15.5 cm wide x 150 cm high) and an internal draft tube with 9 cm diameter and 120 cm long as granular activated carbon is put as an adsorbent in the annulus region between the inner and outer tube. Experiments were conducted using one of the organic pollutants namely chloroform, with a work scenario that includes changing both the airflow rate (2-20) liters/minute, the total survival time of the treatment (5-60) minutes, the molar ratio of the chloroform pollutant to the oxidizing agent of hydrogen peroxide (1/10 - 1/20). The results showed removal efficiency near to 89%, and it gives an indication of the success of the proposed design, with the possibility of recycling the treated water and releasing it to the environment due to the low risk of the organic pollutant in it.

Phenol removal using pulsation bubble column with inverse fluidization airlift loop reactor

Phenol and phenolic compounds are omnipresent organic contaminants which are sent out to water bodies and wastewater systems produced from industrial processes, and they require specific attention due to their extraordinary features such as high toxicity, carcinogenic characteristics, and ability to accumulate, which affects the health of humans and the environment. In this practical study, the integrated system of a pulsation bubble column with an inverse fluidization air loop reactor was tested to remove phenol. The test platform was made and operated with a bubble column containing at its upper end an electrical solenoid valve engaged via at least two timers, and connected to the air loop reactor consisting of an outer rectangular tube and an internal draft tube by one-way valve, where the granular activated carbon is put as an adsorbent material in the annulus region between the inner and outer tube. The effects of various parameters [molar ratio of Phenol to H2O2 (1/10, 1/15 and 1/20), airflow rate (5-20 L/min), remediation time (5-60 min), initial phenol concentration (10- 150 mg L-1) have been studied. Removing 90% of the contaminated phenol as a result of this study may represent a partial solution to the ecological problem.

Development of a dynamic feeding strategy for continuous-flow aerobic granulation and nitrogen removal in a modified airlift loop reactor for municipal wastewater treatment

This study investigated the aerobic sludge granulation and nitrogen removal performance in a modified airlift loop reactor treating municipal wastewater under different operation conditions. Dynamic feeding and aeration control were applied to create feast/famine conditions to facilitate microbial aggregation. Experimental results demonstrated that aerobic granular sludge could be cultivated in continuous-flow reactors fed with an optimized dynamic feeding condition. Fresh granules sizing 0.4–0.6 mm were observed in the reactors after a 61-day operation, then turned to matured granules after another 33-day operation with a compact structure, a stable size of 2–4 mm, and a low SVI of ~35 mL/g. Extracellular polymeric substances (EPS) analysis results showed that both EPS contents and the ratio of protein to polysaccharides increased with the granulation process, leading to an increase of cell hydrophobicity. Granular sludge exhibited a good nitrogen removal ability with a comparable level of specific nitrification rate and denitrification rate with those measured in state-of-the-art sequential batch reactors. Microbial population analysis showed an increase in the relative abundance of functional microbes, including Zoogloea, Nitrospira, Dechloromonas, and Thauera in the cultivated granules, suggesting a potentially crucial role of these microbes in sludge granulation and nitrogen removal. The dynamic feeding strategy and the reactor configuration are considered as critical factors for aerobic granulation under continuous-flow conditions for creating feast/famine conditions and allow sludge backflow without structure damage.

Computational fluid dynamics and factor analysis of a novel swirling demulsified airlift loop reactor for the treatment of refined soybean oil wastewater

A swirling demulsified airlift loop reactor (SD-ALR) was developed for the treatment of oily wastewater with yeasts. Computational fluid dynamics simulations showed that the gas holdup and liquid velocity gradient in the SD-ALR were 2.9% and 0.37 m/s higher than those in the traditional airlift loop reactor. The optimization results of the swirling demulsifier showed that the optimal number and elevation angle of the blades were 8 and 45°, and the optimal installation position was 150 mm from the bottom of the draft tube. The results of treating refined soybean oil wastewater in the SD-ALR showed that the wastewater treatment time was decreased by 8 h, and the removals of chemical oxygen demand and oil content increased by 5.10% ± 0.02% and 9.55% ± 0.40%, respectively, compared with those in the traditional airlift loop reactor. A volumetric mass transfer coefficient model was established for SD-ALR and oily wastewater.

Hydrodynamics and mass transfer in a slurry external airlift loop reactor integrating mixing and separation

A pilot external airlift loop reactor (EALR) integrating mixing and separation was first proposed by combining directional flow in the EALR and liquid-solid separation in two parallel hydrocyclones. In this developed reactor, mixing, mass transfer, and liquid-solid separation can be simultaneously realized without extra energy input. Technical feasibility was firstly verified, and then hydrodynamics and mass transfer were measured. It was found that the minimum diameter of solid particles retained for circulation was 6.82 μm, and the treatment capacity of clean liquid was up to 3.0 m3/h. Additionally, global gas holdup, liquid circulating velocity, and volumetric mass transfer coefficient increased monotonously with increasing the superficial gas velocity while declined with the increase of solid concentration. Axial inhomogeneity of solid particles was decayed with increasing the superficial gas velocity and solid concentration. This new type of slurry EALR is promising to be applied in the gas-liquid-solid catalytic industries.

Experimental investigation of hydrodynamics and mass transfer in a slurry multistage internal airlift loop reactor

Hydrodynamics and mass transfer of gas-liquid-solid slurry flow in a simple pilot multistage internal airlift loop reactor with a classic stage clearance are investigated experimentally. The presence of a critical superficial gas velocity to keep the multistage internal airlift loop reactor operating normally without particle deposit was first observed at a certain solid concentration and a fixed height of stage clearance, and an empirical model related to solid concentrations for a constant stage gap is also put forward here to predict the minimum critical superficial gas velocity in the slurry multistage internal airlift loop reactor. The results showed that compared to hydrodynamics and mass transfer in the gas-liquid two-phase flow at the same conditions, the solid concentration and the superficial gas velocity have some distinct effects. The increment of superficial gas velocity can increase the gas holdup, circulating liquid velocity, and volumetric mass transfer coefficient and at the same time decrease the mixing time, while the addition of solid particles would get the opposite effects. Additionally, compared to the two-phase flow, reverse tendencies of the gas holdup and circulating liquid velocity in different stages in the three-phase slurry multistage internal airlift loop reactor are first observed due to axial non-uniform distribution of solid particles. Therefore, solid particles can change the nature of multiphase flow in the multistage internal airlift loop reactor, and some critical information for designing this type of reactor was provided in this work.

Elimination of Chloroform (CHCl3) from Drinking Water via a Synergistic Effect of Stripping, Oxidation and Adsorption Process in Air Lift Loop Reactor

In this work, a modified internal loop airlift reactor has been designed to remove the organic pollutants in synthetic wastewater at an efficient and inexpensive treatment technique by means of a synergistic effect combining of (oxidation, stripping and adsorption). The validation of the current style was experimentally examined in the treatment of synthetic Wastewater contained chloroform. The experimental testing rig was implemented at various air flow rates range (5-20) (L/min), with total variable residence period (5-60 min) with a different molar ratio of CHCl3 to H2O2 i.e. 1:10, 1:15 and 1:20. The results showed that the best molar ratio of chloroform to hydrogen peroxide was 1:20 for the air flow rate 18 L/min and extended retention period (60 min) having the uppermost results (83.3%) to remove chloroform from the contaminated effluent water. This design complements the research objectives with high efficiency through the synergy of stripping, oxidation and adsorption processes to remove contaminated chloroform from wastewater. This work contributes to a part of the solution of the environmental problems of the contaminated water before recycling, reuse or released to our safe environment.

Biodesulfurization of sulfide wastewater for elemental sulfur recovery by isolated Halothiobacillus neapolitanus in an internal airlift loop reactor

The biodesulfurization of sulfide wastewater for elemental sulfur recovery by isolated Halothiobacillus neapolitanus in an internal airlift loop reactor (IALR) was investigated. The flocculant producer Pseudomonas sp. strain N1-2 was used to deposit the produced elemental sulfur during biodesulfurization. The functional group analysis indicated that biofloculation was closely associated with NH and CO. The biodesulfurization system performed well under moderate water quality fluctuations (1.29–3.88 kg·m−3·d−1 COD; 1.54–3.08 kg·m−3·d−1·S2−) as it maintained stable S2− removal and sulfur flocculation rates. Meanwhile, the qRT-PCR analysis indicated that the transcriptional level of cbbL decreased in the presence of organic carbon, while the expressions of sqr, sat, and cytochrome C3 increased under higher sulfide stress. Moreover, the relative proportions of Halothiobacillus was strengthened via microbial intervention of the LJN1-3 strain. The S2− removal efficiency and elemental sulfur production was further improved by 32.5% and 28.2%, respectively, in an IALR.

Hydrodynamics and mass transfer in an internal airlift slurry reactor for process intensification

By combining the prominent advantage of directional fluid flow in an internal airlift loop reactor with the cheap cost of liquid-solid separation in a hydrocyclone, a new slurry reactor for process intensification integrating solid catalytic reactions with liquid-solid separation for clear liquid products is proposed and designed to cut down the capital and operating costs. The reactor can be operated properly when the superficial gas velocity is above 0.0108 m/s, and the solid particles of aluminum oxide are all retained in the slurry reactor if the particle diameter is larger than 57.9 μm. The influences of superficial gas velocity and top clearance on the performance of hydrodynamics and mass transfer in the gas-liquid two-phase and the gas-liquid-solid three-phase systems are measured and discussed systematically, and some data base for the rational design, optimization and scaling-up of this type of promising reactor is provided.

Analysis on the Spatial Difference of Bacterial Community Structure in Micro-pressure Air-lift Loop Reactor

In order to reveal the spatial difference of the bacterial community structure in the Micro-pressure Air-lift Loop Reactor, the activated sludge bacterial at five different representative sites in the reactor were studied by denaturing gradient gel electrophoresis (DGGE). The results of DGGE showed that the difference of environmental conditions (such as substrate concentration, dissolved oxygen and PH, etc.) resulted in different diversity and similarity of microbial flora in different spatial locations. The Shannon-Wiener diversity index of the total bacterial samples from five sludge samples varied from 0.92 to 1.28, the biodiversity index was the smallest at point 5, and the biodiversity index was the highest at point 2. The similarity of the flora between the point 2, 3 and 4 was 80% or more, respectively. The similarity of the flora between the point 5 and the other samples was below 70%, and the similarity of point 2 was only 59.2%. Due to the different contribution of different strains to the removal of pollutants, it can give full play to the synergistic effect of bacterial degradation of pollutants, and further improve the efficiency of sewage treatment.

Softening of wastewater from wet flue gas desulfurization process based on internal airlift loop reactor (IALR)

Softening of wastewater from wet flue gas desulfurization process based on internal airlift loop reactor (IALR)