Airlift pumps are commonly employed in oil and gas operations, utilising the upward motion of a gas-liquid mixture driven by buoyancy and density contrasts. While numerous investigations have focused on their behaviour in vertically aligned straight pipes, the influence of pipe curvature—particularly relevant in directional drilling—has not been extensively explored. This work provides a comprehensive experimental assessment of how bends affect the hydraulic performance and flow dynamics of airlift systems. Five bent riser configurations were tested and compared with a conventional straight riser, with emphasis on variations in bend height and horizontal spacing. The findings reveal that pump efficiency diminishes as the horizontal distance between bends increases or when bends are positioned higher along the riser. Specifically, a 15% reduction in water flow rate occurred when the bend’s horizontal span reached twice the pipe diameter. Additionally, a 6% drop was observed when a bend was introduced at three-quarters of the riser height. The minimum air flow rate required to initiate water lifting also increased when bends were placed above the submergence level. Visual flow analysis further identified cyclic flow behaviour within the bent sections. These insights offer practical guidance for enhancing airlift pump designs in non-vertical geometries, addressing notable gaps in two-phase flow system optimisation.

Abstract Currently, there is an increasing emphasis on energy conservation and nitrogenous pollutant emission reduction, and conventional wastewater treatment processes can no longer meet the demand. Enhancing the reflux ratio of the mixed liquor suspended solids (MLSS) is a promising option to improve nitrogen removal in wastewater treatment. However, a high reflux ratio can lead to a significant carryover of dissolved oxygen (DO), which can negatively impact the denitrification process. Currently, eliminating the effects of DO remains a challenging area with high DO concentration inhibiting denitrification process. The high MLSS system can significantly reduce the impact of DO. Therefore, this study compares it with the conventional internal recirculation method in terms of pollutant removal and DO recovery. It explores the feasibility of using high MLSS system to enhance nitrogen removal in wastewater treatment while achieving energy savings, and calculates the potential energy savings achieved. At the same time, the biological tank reflux pump used by the air-lift pump exhibited more energy-saving advantages than the traditional mixture of liquid reflux pumps. This study focuses on wastewater treatment plants with poor denitrification performance, aiming to enhance denitrification efficiency. The results show that when the MLSS concentration is 8.0 g L−1 with the DO concentration 2.5 mg L−1, the system removed 97% of biochemical oxygen demand at influent 200 mg L−1, 86% of chemical oxygen demand (Cr method) at 350 mg L−1, 94% of ammonia nitrogen at 35 mg L−1, and 72% of total nitrogen at 45 mg L−1. This study can significantly reduce operating costs. The air-lift pump facilitates the lifting of wastewater, it also supplies DO to the water, thereby reducing the need for aeration. Compared to traditional recirculation methods, this approach saves approximately 32% of DO, resulting in an effective recovery, which notably enhances energy savings. However, it is important to note that the small scale of the bioreactor used in this experiment does not fully capture the advantages in energy saving and management that come with the implementation of a high MLSS system.

Optimizing airlift pumps for efficient solid-liquid transport: Effect of particle properties, submergence ratio, and injector design

Airlift pumps (ALPs) are pump-based riser systems in which air is applied as a power source. They play an important role in the development of marine resources and the chemical industry. However, research detailing the frictional pressure drop gradient in ALPs is scarce. Therefore, this paper conducts experimental studies on the pressure characteristics within ALPs. The experiment was conducted in a vertical pipeline with a total length of 3.245 m and pipe diameter of 0.05 m. The experimental conditions included an air inlet, with a submergence ratio ranging from 0.6 to 0.815 and a gas superficial velocity ranging from 0 to 4 m/s. It was found that the frictional pressure drop gradient in ALPs exhibits a significant linear relationship with the gas void fraction. Additionally, the total pressure drop gradient has a linear relationship with the distance from the intake to the liquid surface. The frictional pressure drop gradient correlation established through these relationships can effectively predict experimental data for frictional pressure drop gradients under gas superficial velocities ranging from 0.5 to 4 m/s (where larger frictional pressure drop gradients are observed). The mean percentage error was 3.63%, while the mean absolute percentage error and root mean square percentage error were 8.92% and 11.05%, respectively. Finally, by analyzing pressure data from seven positions at different gas superficial velocities, it was discovered that in ALPs, pressure exhibits a significant linear relationship with height. Furthermore, this linear relationship remains remarkably consistent across various gas superficial velocities.

Polymetallic nodules and REE-rich mud under the seabed of 5500–5700 m water depth around Minamitorishima island are promising and attractive for exploration and development. Following our previous research, numerical analysis was used to investigate the unsteady flow characteristics and the lifting performance of a commercial production system using an air-lift pump for hybrid lifting, lifting both polymetallic nodules and REE-rich mud. Gas–liquid–solid three-phase flow and gas–liquid two-phase flow in the system were analyzed using the one-dimensional drift–flux model. First, the reliability of the schemes and program was verified by comparing the numerical results with the experimental ones. Next, numerical simulations were conducted, in which the model’s dimensions were related to a commercial production system operated in the deep sea around Minamitorishima island, and the conditions fit the expected production rate. The results revealed the unsteady flow characteristics under the operations, such as start-up, shut-down, feed of polymetallic nodules and REE-rich mud, and those associated with disturbances, such as feed rate fluctuations. We demonstrate that the program and the schemes can simulate the unsteady flow characteristics and the lifting performance of a commercial production system with an air-lift pump well, and they can derive useful information and know-how in advance for the safe and continuous operation of the system.

Mechanical behavior analysis of a marine riser considering mass and velocity changes of three-phase internal mixture in air-lift pump for seabed mining

Airlift pumps (ALPs) have the advantages of simple structure, easy operation, wide applicability, environmental friendliness, and safety reliability. It plays an important role in the chemical industry and the development of marine resources. The gas–liquid two-phase flow in such devices is similar yet different from those used in applications like nuclear reactor systems and heat pump systems. Research on the key parameter of gas void fraction (GVF) in ALPs is relatively scarce. Therefore, this paper establishes a GVF correlation through the drift-flux model. The experiment was conducted in a vertical pipeline with a total length of 3.245 m and pipe diameter of 0.05 m. The experimental operating conditions included three air inlets, with the submergence ratio ranging from 0.6 to 0.815 and a gas superficial velocity ranging from 0 to 2.5 m/s. A validation was conducted using 315 sets of data under the aforementioned conditions, resulting in a mean percentage error, mean absolute percentage error, and root-mean-square percentage error of 2.37%, 7.82%, and 9.62%, respectively. The comparison and analysis of a large amount of experimental data revealed that the abrupt changes in distribution parameter and drift velocity can accurately reflect and explain the transition and transformation of flow pattern. Furthermore, changing the submergence ratio and the inlet position within a certain range has a minimal effect on the distribution parameter and drift velocity, meaning it has little impact on the distribution of the phases and the relative velocity between the phases.

Hybrid Mining of Rare-Earth Elements-Rich Mud and Polymetallic Nodules by Air-Lift Pump in Deep Sea around Minamitorishima Island

Due to the increase of sediment carried by the upstream with years, sediment deposition and hardening gradually aggravated, which has severe impact on the waterway passage and agricultural irrigation. Therefore, to develop a highly efficient dredging device is urgently needed. An externally excited oscillating airlift pump is proposed to improve the dredging performance of the existing ring-jet airlift pump, and the influence of excitation methods and working conditions is analyzed. The findings show that under different excitation methods, both water and sand discharge show a reciprocal oscillating pattern as the duty cycle increases, and the overall trend is decreasing. When the duty cycle is 50% and 30% respectively, both water and sand discharge reach their maximums; the corresponding sand discharge in horizontal operation performs better than that in descent operation, and in either operation mode, the externally excited oscillating airlift pump exhibits better discharge performance of solids than the continuous air intake. In the untimed continuous suspended pumping, its sand discharge capacity and disturbance range on the silt layer are greater than the continuous airlift pump. At the duty cycle of 30% and the frequency of 0.4 Hz, its discharge performance and disturbance effect on the bottom silt layer work best.

Evaluate the performance of the vertically upward gas–liquid two-phase flow in an airlift pump system

Urban and storm water retention ponds eventually become eutrophic after years of receiving runoff water. In 2020, a novel biological and chemical treatment was initiated to remove accumulated nutrients from an urban retention pond that had severe algae and weed growth. Our approach installed two 6.1 m × 6.1 m floating treatment wetlands (FTWs) and two airlift pumps that contained slow-release lanthanum composites, which facilitated phosphate precipitation. Four years of treatment (2020–2023) resulted in median nitrate-N concentrations decreasing from 23 µg L−1 in 2020 to 1.3 µg L−1 in 2023, while PO4-P decreased from 42 µg L−1 to 19 µg L−1. The removal of N and P from the water column coincided with less algae, weeds, and pond muck (sediment), and greater dissolved oxygen (DO) concentrations and water clarity. To quantify the sustainability of this bio-chemical approach, we focused on quantifying nitrate removal rates beneath FTWs. By enclosing quarter sections (3.05 × 3.05 m) of the field-scale FTWs inside vinyl pool liners, nitrate removal rates were measured by spiking nitrate into the enclosed root zone. The first field experiment showed that DO concentrations inside the pool liners were well below the ambient values of the pond (<0.5 mg/L) and nitrate was quickly removed. The second field experiment quantified nitrate loss under a greater range of DO values (<0.5–7 mg/L) by including aeration as a treatment. Nitrate removal beneath FTWs was roughly one-third less when aerated versus unaerated. Extrapolating experimental removal rates to two full-sized FTWs installed in the pond, we estimate between 0.64 to 3.73 kg of nitrate-N could be removed over a growing season (May–September). Complementary laboratory mesocosm experiments using similar treatments to field experiments also exhibited varying nitrate removal rates that were dependent on DO concentrations. Using an average annual removal rate of 1.8 kg nitrate-N, we estimate the two full-size FTWs could counter 14 to 56% of the annual incoming nitrate load from the contributing watershed.

Airlift pumps (ALPs) are promising in the oil and chemical industry, owing to their advantages such as a simple structure, convenient operation, wide applicability, high cost-effectiveness, environmental friendliness, safety, and reliability. However, there are few studies on the frictional pressure drop of vertically upward gas–liquid two-phase flow in ALPs. Therefore, this study presents an experimental investigation of the frictional pressure drop in the vertically upward gas–liquid two-phase flow in ALPs. Experiments were conducted in a vertical pipe with a total length of 3.245 m and a two-phase section of 2.8 m; the working pressure of the air compressor was 0.4 MPa, pipe diameter was 0.05 m, submergence ratio ranged from 0.6 to 0.85, and gas superficial velocity ranged from 0 to 4 m/s. A total of 74 sets of experimental data were obtained, and the frictional pressure drop models of 36 classical gas–liquid two-phase flows were evaluated. The results indicated that classical gas–liquid two-phase flow models significantly underestimated the experimental results. By analyzing the experimental data, visualizing the internal flow field, and performing theoretical derivations, a new frictional pressure drop correlation was established for the vertically upward gas–liquid two-phase flow in ALPs. The results demonstrated that the new model could accurately predict the frictional pressure drop of ALPs with mean percentage error, mean absolute percentage error, and root mean square percentage error values of 7.8%, 12.18%, and 25.86%, respectively.

Abstract Airlift systems are widely used for mass, momentum, and energy transport, particularly in hydrothermal and oil extraction wells. Predicting the impact of nozzle design parameters, such as perforation diameters and air injection areas, remains challenging. This study experimentally investigates an annular airlift pump to understand the influence of various nozzle configurations on performance. Using radial and axial injection with different perforation counts, high-speed camera visualization categorized flow regimes (bubbly, slug, slug-churn) across different gas flow rates. Dimensional analysis assessed energy efficiency, revealing a strong dependence on submergence ratio and perforation-to-inlet pipe area ratio. A dimensionless number, analogous to a restriction coefficient, explained discrepancies with theoretical models at high Reynolds numbers. A specific dimensionless group unified the experimental results for large submergence ratios (greater than 0.8). This study provides insights into optimizing airlift pump performance by exploring the effects of nozzle configurations on transport phenomena.

The airlift pump is a key part of wastewater treatment and is employed as an innovative and feasible collection tool. However, as one of the key factors in the lifting capability of airlift pumps, film thickness in the gas–liquid two-phase flow operating in pumps is still an unknown topic because it is difficult to measure. This paper proposes a visualization method for measuring film thickness and investigates the film thickness when operating under gas flow with a high rate in airlift pumps using experiments. Firstly, a simulation experiment platform was built, and the images of the film structure were acquired by a high-speed camera. Then, image-processing technology and an image distortion correction were proposed to extract the gas–liquid interface for studying the thickness of the film. The experimental results demonstrated that a large film thickness ranging from 0.15 D to 0.24 D was found in airlift pumps and that its film thickness kept a constant value, even under a high gas superficial velocity, maintaining a large output liquid flow from airlift pumps. As wastewater was carried by wastewater treatment, a larger film thickness of the annular film will benefit the high lifting rate of wastewater. The works in this paper offer valuable insights for the higher performance of working airlift pumps and wastewater treatment efficiency.

Detailed 3D URANS analysis of two-phase flow in an airlift pump

Airlift pumps (ALPs) have a simple structure and significant application potential. However, previous studies on ALPs have generally assumed that the gas density remains constant. In this paper, the gas state equation (GSE) for ALP is established based on the van der Waals formula, which explicitly considers the density of gas. An electrical resistance tomography system is used to collect the gas void fractions at different heights under different gas flow rates, and an empirical formula for the gas void fraction is established. To verify the effectiveness of the proposed model, high-precision pressure sensors and a high-speed camera are used alongside an electrical resistance tomography system to determine the realistic ALP flow parameters. The results of 409 sets of experiments show that: (1) the gas in ALP cannot be regarded as ideal gas, because the ideal GSE cannot distinguish between different gas flow rates; (2) the state change of gas in ALP is a quasi-equilibrium process, whereby the GSE of ALP can be obtained from the pressures under several locations; (3) the axial pressures predicted by the proposed GSE for ALP are in good agreement with experimental data; and (4) a single parameter of the GSE uniquely determines the state process. The proposed model and the experimental data provide a new methodology and comprehensive references for studying the working mechanism and efficiency of ALPs.

An airlift pump can be used to move from one location to another. The pump lifts liquid or solid particles from air bubbles through a vertical pipe. In this experiment, the airlift pump system was modified using a microbubble generator installed on the injector to produce air bubbles. Two injectors were installed with a swirl model. This study aims to visualise the flow pattern that forms in a vertical pipe when air bubbles lift water toward the endpoint. The flow pattern was observed by varying airspeed and water column h in the vertical pipe. The method in this study was carried out using a two-phase flow (air-water). An acrylic pipe with an inner diameter of 50 mm and a height of 327 cm was used in this study. The immersion ratios were set to 0.44, 0.50, 0.56, 0.62, and 0.68. Air was injected into the system through a compressor injector, and air release was controlled by an airflow meter. m ³/h, 1.5 m ³/h, 2 m ³/hour, 2.5 m ³/h, and 3 m ³/h. The flow pattern in the thriller pipe is captured using a video camera. The research results show that bubble, slug, churn, and annular flow patterns are formed owing to variations in the airflow injected into the system. The slug flow changed to an annular flow as the slug flow speed increased. The slug and churn flows lifted the water, and the annular flow reversed the buoyancy force of the slug and churn flows. This study concludes that the ratio of the water column height in the vertical pipe affects the driving force for lifting water to the separator. The greater the immersion ratio, the better is the pump performance. In addition, the influence of the injected airflow forms a flow pattern that can move water from the bottom to a certain height.

In this study, the installation of an airlift pump with inner diameter of 102 mm and length of 5.64 m was utilized to consider the conveying process of non-spherical coal particles with density of 1340 kg/m3 and graining 25–44.5 mm. The test results revealed that the magnitude of increase in the solid transport rate due to the changes in the three tested parameters between compressed air velocity, submergence ratio, and feeding coal possibility was not the same, which are stand in range of 20%, 75%, and 40%, respectively. Hence, creating the optimal airlift pump performance is highly dependent on submergence ratio. More importantly, we measured the solid volume fraction using the method of one-way valves in order to minimize the disadvantages of conventional devices, such as fast speed camera and conductivity ring sensor. The results confirmed that the volume fraction of the solid phase in the transfer process was always less than 12%. To validate present experimental data, the existing empirical correlations together with the theoretical equations related to the multiphase flow was used. The overall agreement between the theory and experimental solid delivery results was particularly good instead of the first stage of conveying process. This drawback can be corrected by omitting the role of friction and shear stress at low air income velocity. It was also found that the model developed by Kalenik failed to predict the performance of our airlift operation in terms of the mass flow rate of the coal particles.

This paper presents two case studies dealing with undesirable impacts of overburden drilling of casings for end-bearing piles to bedrock. Monitored pore-water pressures and ground settlements are used to document and assess the influence from rotary percussive drilling with “down-the-hole” (DTH) hammers. The studies show that drilling with high-pressure air-driven DTH hammers may cause considerable erosion and soil volume loss adjacent to the drill bit and along the casing, resulting in settlements of the surrounding ground. The risk of soil volume loss increases when the drilling is carried out in erodible soils such as silt and fine sands. The volume loss is found to be caused by a combined air-lift pump effect and a Venturi suction effect. Monitoring pore pressures in the vicinity of the drilling may be used to reduce soil volume loss and prevent damaging settlements. Results from drilling with water-driven DTH hammer showed significantly less ground settlements and influence on pore pressures compared to using an air-driven hammer. The study suggests that the drilling parameters flow rate and penetration rate, and the cross-sectional area of the pile casing can be combined in a non-dimensional methodology to assess the mass balance of drill cuttings when drilling with water flushing. A design framework is suggested to guide overburden drilling in urban settings to reduce potential impact on the surroundings.

Numerical analysis of air–water two-phase upflow in artificial upwelling of deep ocean water by airlift pump