Hydraulic Cleaning Research Articles

Mathematical Modeling of Hydraulic Fracture Formation and Cleaning Processes

The effectiveness of the hydraulic fracturing procedure is crucially dependent on the stage of fracture planning and design. Forecasting fracture behavior in rock formations characterized by non-uniform toughness is a serious challenge. In the present paper, a planar-3D model considering the rock’s non-uniform fracture toughness has been developed for the uneven propagation of a hydraulic fracture. The series of numerical experiments were designed to study the effect of inhomogenous fracture toughness. The results show that the fracture toughness contract significantly controls the overall direction of fracture propagation, and a combination of toughness contrast and the proportion between the pay zone and barrier zone determine the fracture profile: from almost circular with or without a pair of narrow wedges when the proportion is small to almost rectangular otherwise. This paper also discusses the process of cleaning a fracture from hydraulic fracturing fluid by oil. Using numerical modeling on the basis of the constructed mathematical model, a relationship is established between the quality of hydraulic fracture cleaning and the geometrical parameters of the fracture and the region filled with the hydraulic fracturing fluid. The results of numerical experiments show that while fracturing fluid is more viscous than oil, the length of the fracture has a greater influence on the cleaning process than the viscosity of the fracturing fluid.

Optimization of ultrafiltration as pre-treatment for seawater RO desalination

Ultrafiltration (UF) is increasingly used as pretreatment for reverse osmosis (RO) desalination, as an alternative to granular filtration. To ensure a sustainable and cost-effective operation of UF, key operational parameters must be optimized. In the present study we used a pilot UF system to optimize filtration flux, length of filtration cycle, coagulant dosing, and membrane cleaning procedure. Filtration flux of 82 LMH resulted in reversible fouling, which could be completely removed during chemically enhanced backwash, and did not affect filtration performance. Increasing the flux to 85 LMH on the other hand, resulted in the formation of irreversible fouling, which rapidly deteriorated UF operation. Filtration time of 35 min between backwashes did not affect filtration, whereas, at longer filtration time of 45 min, (hydraulically) irreversible fouling was formed. Addition of Ferric chloride coagulation prior to UF (up to 0.6 mg/L-Fe) improved the removal of reversible fouling during backwash (BW), through the formation of pinflocs. In parallel, high ferric chloride concentrations generated ferric-based irreversible fouling, which could only be removed by chemical cleaning. Finally, the study proposes a unique analysis of the trans membrane pressure (TMP) curve shape, for the optimization of coagulation and hydraulic cleaning during UF.

Advances and Applications of Hollow Fiber Nanofiltration Membranes: A Review.

Hollow fiber nanofiltration (NF) membranes have gained increased attention in recent years, partly driven by the availability of alternatives to polyamide-based dense separation layers. Moreover, the global market for NF has been growing steadily in recent years and is expected to grow even faster. Compared to the traditional spiral-wound configuration, the hollow fiber geometry provides advantages such as low fouling tendencies and effective hydraulic cleaning possibilities. The alternatives to polyamide layers are typically chemically more stable and thus allow operation and cleaning at more extreme conditions. Therefore, these new NF membranes are of interest for use in a variety of applications. In this review, we provide an overview of the applications and emerging opportunities for these membranes. Next to municipal wastewater and drinking water processes, we have put special focus on industrial applications where hollow fiber NF membranes are employed under more strenuous conditions or used to recover specific resources or solutes.

Facile fabrication of covalent organic framework composite membranes via interfacial polymerization for enhanced separation and anti-fouling performance

Covalent organic frameworks (COFs) have the advantages of high porosity, uniform and adjustable pore size, as well as superior compatibility with polymer, which are favorable for the production of defect-free films with high flux and excellent separation performance. In this work, TAPB-PDA COF thin films were synthesized by interfacial polymerization of benzaldehyde (PDA) and 1,3,5-tris (4-aminophenyl) benzene (TAPB) on polyethersulfone (PES) substrates with the aid of a catalyst. Different thicknesses of the COF films could be achieved by varying the concentration of the monomers. The TAPB-PDA COF/PES composite membranes exhibited enhanced removal capacities for organic matters compared to the pristine PES membrane, e.g., with the rejections of calcon (molecular weight of 416 g mol-1) and humic acid at 92.3% and 98.0%, respectively. Moreover, after the fouling of model organic pollutants or the filtration of natural surface water, the recovery coefficient of water permeability by hydraulic cleaning was 22–35% higher for the TAPB-PDA COF/PES composite membrane than that of the PES membrane. The improved anti-fouling performance was mainly attributed to the increased membrane surface hydrophilicity benefiting from the hydrophilic nature of the TAPB-PDA COF materials.

A new model considering the morphological changes of cake and gel for the in-situ membrane cleaning process

Understanding the hydraulic cleaning mechanism of the membrane fouled with activated sludge (AS) and establishment of the flux predictive model can effectively improve the cleaning efficiency of the membrane in MBR. In this study, an instantaneous flux prediction model was established by considering the cascade mechanisms (irreversible swelling, reversible dissolution and re-deposition) for the gel and dynamic equilibrium mechanisms (direct reversible dissolution and re-deposition) for the cake in the hydraulic cleaning process. In addition, the XDLVO theory was used to calculate the variation of interaction energy between AS and membrane surface in the swelling process of AS. The result showed that the proposed model was fully adequate for the 200 kDa PAN membrane fouled with AS suspension (R2=0.9987) or yeast suspension (R2=0.9958) in the hydraulic cleaning process. The swelling of AS can significantly reduce the attractive interaction energy and improve the membrane cleaning efficiency. Moreover, the predictive model showed better accuracy (σ = 0.39%) than other models (Kong’s model (σ = 0.71%) and Cabero’s model (σ = 0.88%)). In addition, the proposed model also exhibited excellent performance for the multiple fouling and cleaning processes (R2>0.9860) and for other membranes (100 kDa PES membrane (R2=0.9995), 200 kDa PVDF membrane (R2=0.9976) and 0.1 µm PAN membrane (R2=0.9999)) fouled with AS suspension.

Optimization Rate Of Penetration In Directional Drilling With Adjustable Bit Rotating and Hydraulic Hole Cleaning

Optimization Rate Of Penetration In Directional Drilling With Adjustable Bit Rotating and Hydraulic Hole Cleaning

Response surface methodology to investigate the effects of operational parameters on membrane fouling and organic matter rejection in hard-shell encased hollow-fiber membrane

The response surface methodology (RSM) was found useful statistical tool for understanding combined effect of filtration, backwashing time and dosage of sodium hypochlorite (NaOCl) added into backwash water as three operational parameters on transient behavior of transmembrane pressure (TMP) and organic rejection efficiency. Here, encased, hollow-fiber ultrafiltration (UF) system was developed for treating synthetic humic acid (HA) solution. To carry out RSM analysis, experimental matrix was designed by Box-Behnken model. Results showed that the NaOCl dosage for the chemical enhanced backwashing (CEB) as single parameter played most dominant role in fouling mitigation. Effect of hydraulic cleaning by applying the permeate backwashing only without performing the CEB was almost negligible to flush the fouling layer from membrane. Considering two correlated parameters, backwashing time combined with NaOCl dosage was found much more important than combination of other parameter such as filtration time to reduce fouling rate. Regardless of the operational parameters, the organic rejection efficiency was maintained 30% only. The RSM analysis also found that 40.1 min of filtration, 1.1 min of backwashing and 834 mg/L of NaOCl were optimum operating parameters to enhance both permeate recovery and fouling mitigation.

An Experimental Study of Clogging Recovery Measures for Ceramic Permeable Bricks.

To explore the best clogging restoration measures for ceramic permeable bricks, ceramic permeable bricks were accurately clogged using a self-designed device by controlling the permeability, and different technical measures were adopted to restore the permeability. Then, the recovery effect, operating parameters and pore change inside the bricks using pressure washing were further discussed. The results showed that pressure washing was the best recovery measure, the joint methods was not recommended due to performance to price ratio. It was necessary to conduct pressure washing in relatively moist conditions, increase the cleaning frequency or prolong the cleaning time in the case of no serious blockage. Hydraulic cleaning can not only increase isolated pores but also remove the trapped solid particles, and increase the proportion of connected pores and dredges through water channels. This research offers some reference for the daily maintenance of permeable bricks.

Effects of pollutants in alkali/surfactant/polymer (ASP) flooding oilfield wastewater on membrane fouling in direct contact membrane distillation by response surface methodology

The characteristic pollutants in alkali/surfactant/polymer (ASP) flooding oilfield wastewater are complex [e.g., NaCl, sodium dodecyl sulfate (SDS), petroleum, and polyacrylamide (PAM)]; thus, membrane distillation (MD) applied to treat this wastewater will be fouled and wetted easily. In this study, response surface methodology (RSM) was used to analyze the effects of pollutant interactions in ASP flooding oilfield wastewater on membrane fouling. The response model showed quantitative relationships between the membrane flux and the pollutant concentrations. The analysis of variance (p-value of the model < 0.0001, p-value of lack of fit > 0.05, R2 = 0.9750 and R2adj = 0.9500) showed that the regression equation fit the empirical data well. The results also indicated that the interactions of pollutants (NaCl and SDS; petroleum and PAM) had significant influence on the flux decline in the simulated ASP flooding oilfield wastewater. The characterization of Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) revealed that the MD membrane was fouled by simulated ASP flooding oilfield wastewater to a certain degree. Moreover, the membrane flux was restored to 86.9% after hydraulic cleaning.

Green Combined Resource Recycling System for the Recycling of Waste Glass

As a major part of municipal waste, the amount of waste glass has greatly increased. Due to its stable physical and chemical properties, glass can be effectively recycled with very little loss of quality. Meanwhile, recovery of waste glass is considered to be meaningful for saving resources and energy for sustainable development. However, remanufacturing processes always need a higher level of cleaning of waste glass. Traditionally, the combination technology of hydraulic cleaning and semimanual sorting is used to clean the organic and metallic impurities of waste glass. This combination technology has the disadvantages of low efficiency and producing lots of organic wastewater, which causes heavy environmental pollution. This study proposed an environmental-friendly combined recycling system of waste glass. Waterless cleaning, iron removing, eddy current separation, and optical separation were combined to realize the cleaning and sorting of waste glass. The operation parameters of each process of this new system were discussed and optimized. This system contributed to a high-efficiency and environmental-friendly way for the recovering of waste glass in municipal wastes, and it is an engineering practice to upgrade the urban solid waste recycling technology.

Identifying the fouling behavior of forward osmosis membranes exposed to different inorganic components with high ionic strength.

Functionalized multiwalled carbon nanotube (f-MWCNT) mixed matrix forward osmosis (FO) membranes were fabricated by phase inversion, and the mechanism of sodium alginate (SA) membrane fouling in the presence of various inorganic components with high ionic strength was thoroughly investigated. The membrane incorporated with 0.5% f-MWCNTs (M-0.5) exhibited enhanced performance, which was attributed to the hydrophilicity of the modified nanoparticles and their good compatibility with the cellulose acetate (CA) substrate. Moreover, it was found that the initial permeate flux decline rate for all FO membranes investigated followed the order Na+ + Ca2+ + Mg2+ > Na+ + Ca2+ > Na+ + Mg2+ > Na+, which was attributed to the particle size of SA macromolecules in the corresponding solutions. However, the gradual change in attenuation was consistent with adhesion force observations made for the SA-fouled FO membrane in the later steady-state stage, and there was little difference among M-0 (without f-MWCNTs), M-0.5, and M-1 (with 1% f-MWCNTs). Furthermore, the SA adsorption layer was most compact in the presence of Ca2+, and the flux recovery rate (FRR) was the lowest after simple hydraulic cleaning, but the overall FRRs for FO membranes were greater than 85%. This implies that although a decrease in electrostatic repulsion leads to the formation of a compact fouling layer, an increase in hydration repulsion of hydrated salt ions plays a major role in membrane fouling under high ionic strength conditions.

Effect of minimal pre-treatment on reverse osmosis using surface water as a source

Reverse osmosis is increasingly used in drinking water supply for treatment of fresh water sources which can directly result in high quality water. In practice reverse osmosis is never applied directly on fresh water sources, predominantly because of the occurrence of membrane fouling. Strategies to control membrane fouling in reverse osmosis without expensive and extensive pre-treatment include low flux operation, increase cross-flow velocities and improved (periodic) hydraulic cleaning. The objective of this research is to technically and economically compare minimal pre-treated reverse osmosis to state-of-the art ultrafiltration pre-treated reverse osmosis in surface water treatment to obtain high quality water. A parallel reverse osmosis system with six parallel 2540-type spiral wound membrane elements has been systematically operated during several months with only screens pre-treatment before reverse osmosis. A minimal pre-treated reverse osmosis system using only screens on surface water did not result in stable reverse osmosis operation, however, the ultrafiltration pre-treated reverse osmosis system also failed in the longer run. Lowering the membrane flux from 25 L/m2.h to 10 L/m2.h in minimal pre-treated RO resulted in an approximately 10-fold decrease of the membrane fouling rate, while not influencing the pressure drop increase. Periodical air water cleaning in minimal pre-treated RO resulted in an approximately 4-fold reduction of the spacer clogging rate, while not affecting the membrane fouling rate. The total cost of a minimal pre-treated low flux (10 L/m2.h) operated RO was significantly lower (0.46 €/m3) compared to state-of-the-art UF pre-treated RO at normal flux (25 L/m2.h) (1.21 €/m3). The cost difference in financial space provides an opportunity to develop minimal pre-treated RO systems with improved control of membrane fouling and spacer clogging.

A porous carbon-based electro-Fenton hollow fiber membrane with good antifouling property for microalgae harvesting

Electro-Fenton enhanced porous carbon (PC) - carbon nanotubes (CNT) hollow fiber membranes loaded with Fe2+ were firstly used to alleviate the membrane fouling caused by microalgal cells and extracellular organic matter (EOM) in microalgae harvesting. Electrical repulsion effect could reduce the deposition of oppositely charged algal cells and EOM on the membrane surface. The generation of •OH in-situ in electro-Fenton process could degrade EOM on the membrane surface and even inside the pores. Continuous mode results illustrated that the electro-Fenton enhanced microalgae harvesting process could significantly retard transmembrane pressure increasing and strengthen microalgae concentration capacity by 2.5 times at the optimally applied voltage (−1.0 V). The pure water permeance after operation was 16 times higher compared to the control (without electro-Fenton), and recovered to 98% of the initial value after the hydraulic cleaning, while the control group only recovered to 88%. In intermittent mode, the membrane permeance could recover to 100% after operation by electro-Fenton regeneration for 30 min with microalgae concentrating from 1.05 g/L to 7.45 g/L. The electro-Fenton-enhanced membrane could not only mitigate the reversible fouling, but also effectively inhibit the irreversible fouling, and presented prominent separation abilities without obvious damage to membranes and microalgae cells.

An experimental study on the use of a sequencing-batch membrane bioreactor (SBMBR) for the treatment of mixed municipal wastewater.

Several water treatment techniques have been combined using the sequencing batch reactor with the membrane bioreactor for addressing water pollution. However, cleaning of the membrane is dependent on the approach involved as well as the operating conditions. In the present study, the sequencing-batch membrane bioreactor was used to treat real mixed municipal wastewater. The pollutant removal and membrane filtration performances were examined. The results show that the average removal rates of chemical oxygen demand (COD), total nitrogen, NH3-N, total phosphorus, and turbidity were 90.75, 63.52, 92.85, 87.58, and 99.48%, respectively, when the system was in continuous operation for 95 days. The membrane had a significant effect on COD and turbidity removal and provided stable performances for nitrogen and phosphorus removal. By observing the appearance of the membrane modules before and after the cleaning operation, it was concluded that the deposited sludge and granular sediment on the membrane surface can be effectively removed by hydraulic cleaning. In addition, recovery of membrane filtration performance to 60% of that of a new membrane can be achieved. Furthermore, we found that different sequences and duration of cleaning have different effects on the recovery of membrane filtration performance.

ПРОЦЕДУРЫ И ИНСТРУМЕНТАРИЙ МОНИТОРИНГА ПРОЦЕССОВ И МЕХАНИЗМОВ ТРАНСПОРТА ШЛАМА ПРИ ГИДРАВЛИЧЕСКОЙ ОЧИСТКЕ ГОРИЗОНТАЛЬНЫХ СКВАЖИН

Актуальность работывызвана необходимостью идентифицировать, понять, прогнозировать и контролировать физические механизмы, сопровождающие процесс очистки скважин от бурового шлама. Риск некачественной очистки создает условия, обостряющие процессы заклинивания трубы, управления скважиной, снижения скорости бурения, износа бурового специального оборудования, особенно при увеличении количества отверстий, пробуренных под большими углами. Такие экстремальные ситуации характерны для протяженных горизонтальных скважинах. В настоящее время они получили широкое распространение в силу своей повышенной производительности и исключительной эффективности в способах достижения определенных продуктивных пластов. Все это характеризует проблему поиска и разработки эффективных методов очистки скважин как одну из важнейших задач современного бурения. Цель: глубже понять явления в масштабе модели и фактически разработать методы прогнозирования процессов при гидравлической очистке горизонтальных скважин от шлама для определения приоритетов будущих научных и практических разработок процессов очистки. Методы: современные методы теоретического и экспериментального моделирования течений твердых частиц с потоком вязкой среды в ограниченных областях, характерных для задач нефтегазовой отрасли; практические методы исследования таких вопросов, как седиментация, коагуляции, течение реологически сложных вязких сред в затрубном пространстве скважин с произвольной образующей ее ствола. Результаты. Представлен обзор и анализ современных экспериментальных и теоретических результатов моделирования процесса засорения продуктами выработки горизонтальных скважин. Численно исследованы процессы и механизмы транспорта шлама на базе оригинальных редко используемых в практике приложений математических моделей. По результатам мониторинга процессов сформулировано множество критериальных связей и эмпирических правил, которыми руководствуются при техническом проектировании элементов оборудования и прогнозах оптимальных режимов гидравлической очистки. Критически оценены возможности моделей, методов, инструментария опытного оборудования для регистрации, прогноза и управления режимами поступательно-вращательного движения смесей в скважинах с криволинейной образующей стенки. Даны объяснения противоречивости наблюдаемых и рассчитанных процессов при гидравлической очистке в рамках используемого оборудования.

Enhanced hydraulic cleanability of biofilms developed under a low phosphorus concentration in reverse osmosis membrane systems

A critical problem in seawater reverse osmosis (RO) filtration processes is biofilm accumulation, which reduces system performance and increases energy requirements. As a result, membrane systems need to be periodically cleaned by combining chemical and physical protocols. Nutrient limitation in the feed water is a strategy to control biofilm formation, lengthening stable membrane system performance. However, the cleanability of biofilms developed under various feed water nutrient conditions is not well understood.This study analyzes the removal efficiency of biofilms grown in membrane fouling simulators (MFSs) supplied with water varying in phosphorus concentrations (3 and 6 μg P·L-1 and with constant biodegradable carbon concentration) by applying hydraulic cleaning after a defined 140% increase in the feed channel pressure drop, through increasing the cross-flow velocity from 0.18 m s-1 to 0.35 m s-1 for 1 h. The two phosphorus concentrations (3 and 6 μg P·L-1) simulate the RO feed water without and with the addition of a phosphorus-based antiscalant, respectively, and were chosen based on measurements at a full-scale seawater RO desalination plant. Biomass quantification parameters performed after membrane autopsies such as total cell count, adenosine triphosphate, total organic carbon, and extracellular polymeric substances were used along with feed channel pressure drop measurements to evaluate biofilm removal efficiency. The outlet water during hydraulic cleaning (1 h) was collected and characterized as well. Optical coherence tomography images were taken before and after hydraulic cleaning for visualization of biofilm morphology.Biofilms grown at 3 μg P·L-1 had an enhanced hydraulic cleanability compared to biofilms grown at 6 μg P·L-1. The higher detachment for biofilms grown at a lower phosphorus concentration was explained by more soluble polymers in the EPS, resulting in a lower biofilm cohesive and adhesive strength. This study confirms that manipulating the feed water nutrient composition can engineer a biofilm that is easier to remove, shifting research focus towards biofilm engineering and more sustainable cleaning strategies.

Prediction of the Optimum Conditions for Hydraulic Cleaning Process of Typical Organic Foulants on the Membrane Surface

In order to systematically analyse the impacts of stirring speed, temperature and cleaning duration on the membrane flux during hydraulic cleaning, a series of experiments were carried out with the PAN MF membrane and SA solution. Through comparative analysis, it is found that the membrane flux increases with the increase of temperature and stirring speed, but there is a critical value for cleaning duration. Considering the swelling, dissolution and redeposition of foulants, a formula to predict the instantaneous membrane flux during hydraulic cleaning is proposed. This method was used to successfully predict the instantaneous permeate flux of the membrane during the hydraulic cleaning process on the membrane fouled with different foulants. This method can be embedded into the automatic cleaning program and will greatly save cleaning time and improve production efficiency.

Study on Flow Interference of Multi-group Parallel Jets between Heat Transfer Tubes

In order to find an approach to optimize the hydraulic cleaning equipment of steam generator secondary side of CPR1000 reactor, the Computational Fluid Dynamics (CFD) method was used to simulate the flow of multiple groups of parallel jets. In this simulation, the RNG k-ε turbulence model and the gas-liquid two-phase flow model is employed to distribute the jet flow between heat transfer tubes. The results show that with the increase of the jet angle, the pressure aggregation on the tube sheet decreases obviously, which is caused by the deflection force due to the pressure difference between the two sides of the jet. With the jets distance increasing, the interaction between jets decreases obviously. When the distance is up to more than nine times of tube spacing, the force that causes deflection of the jet will almost disappear. With this distance, the jets can maintain a good linearity and obtain a satisfied cleaning effect on the heat transfer tubes.

Experimental Study on Membrane Fouling and Cleaning in Hydrolytic Acidification -Membrane - Sequencing Batch Reactors Process

The process of hydrolytic acidification (HA) - membrane (M) - sequencing batch reactors (SBR) was used to deal with mixed municipal wastewater and landfill leachate. The system operated continuously for 90 days, and the changes of membrane filtration resistance and membrane cleaning were investigated. The results showed that the membrane fouling rate developed slowly during the continuous operation of the system, and the tota membrane filtration resistance increased from the initial 2.82 × 1012m−1 to 11.4 × 1012 m−1. In addition, it was found that the reversible membrane fouling was the main part of the membrane-sequencing batch filter, which accounted for 47.35% of the total filtration resistance, by observing the surface of the membrane module before and after cleaning test. What’s more, hydraulic cleaning could effectively remove the sludge and granular sediments deposited on the membrane surface, and the total resistance of membrane filtration decreased from 293.84% to 176.45%. However, by further soaking membrane components with 5%o NaClO and 5%o HCl solutions, the membrane filtration performance would be fully restored, and the total membrane filtration resistance would be restored to 104.35% of the initial state.

Enhancement of the Fouling Resistance of Zwitterion Coated Ceramic Membranes.

Ceramic membranes suffer from rapid permeability loss during filtration of organic matter due to their fouling propensity. To address this problem, iron oxide ultrafiltration membranes were coated with poly(sulfobetaine methacrylate) (polySBMA), a superhydrophilic zwitterionic polymer. The ceramic-organic hybrid membrane was characterized by scanning electron microscopy (SEM) and optical profilometry (OP). Membranes with and without polySBMA coating were subjected to fouling with bovine serum albumin solution. Hydraulic cleaning was significantly more effective for the coated membrane than for the non-coated one, as 56%, 66%, and 100% of the fouling was removed for the first, second, and third filtration cycle, respectively. Therefore, we can highlight the improved cleaning due to an increased fouling reversibility. Although some loss of polymer during operation was detected, it did not affect the improved behavior of the tested membranes.