Gas Flotation Research Articles

Performance Evaluation of Cleaning Energy of An Induced Gas Flotation Machine Using Multiple-Size-Group (MUSIG) Model

An induced gas flotation (IGF) machine is a water treatment machine used in the water treatment process of plant industries such as oil sands and chemical plants. In general, the bubble pattern formed by the rotor and stator inside the IGF is difficult to predict since the recirculation flow and the turbulent flow region are widely formed by the rotation of the rotor. In order to enhance the accuracy of the bubbly flow inside the IGF, the MUltiple-SIze-Group (MUSIG) model, which can address the spontaneous assembly of air bubbles such as bubble coalescence, is applied in this study. Numerical analysis with the rotor configuration on the flotation performance was then carried out using a commercial code, ANSYS CFX. Multiphase flow characteristics in forced air mechanically stirred with a Dorr-Oliver flotation cell were considered. In addition, the flotation performance was evaluated based on the results of flow fields, such as the void fraction, the power consumption, the air residence time, the mean air bubble diameter, and the drag coefficient. By comparing the result of each case, the newly designed model of IGF rotor with aspect ratio of 3.36 exhibited the void fraction increased by 41% and power number decreased by 23% than those of the reference model.

Removal of 2,4-D herbicide in soils using a combined process based on washing and adsorption electrochemically assisted

Abstract In this work, it is presented an innovative soil remediation technology consisting of the combination of soil washing, GAC adsorption and electrolysis. This technology is applied for the remediation of soil polluted with herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). The new combined process involves three steps into a single chamber: first step is related to the washing of soils using groundwater as soil washing fluid, the second step is related to the herbicide removal from the produced soil washing effluent by adsorption onto granulated active carbon and the third step is the use of electrolysis to oxidize the 2,4-D and provide bubbles that enhance the mixing and separation by dissolved gas flotation. All processes are studied alone and in combination. The obtained results pointed out the possibility for total removing of the herbicide content in the contaminated soil, simultaneously to the herbicide removal contained in soil washing effluent, which become ready to be recycled as a fresh soil washing fluid. The proposed combined treatment for complete decontamination of soils polluted with 2,4-D herbicide was successfully tested for 0.1 kg soil, contained 20 mg herbicide per kg of soil, using 1 dm3 of synthetic groundwater as washing effluent and 10 g GAC, and passing through this mixture an electrical current of 0.5 A, during 2 h.

The mechanism of inclusion removal from molten steel by dissolved gas flotation

ABSTRACTDissolved gas flotation (DGF) is used for removing inclusions from molten steel. The supersaturated gas forms bubbles on inclusions and carry them to the melt’s surface. Inclusion removal is modelled visually by applying a water simulation system. A mathematical model is developed to simulate the removal rate of inclusions from steel melts. From the experimental results and mathematical calculation, the mechanism of the inclusion removal by DGF was discussed, and it was concluded that first the relationship between inclusion removal efficiency and dissolved gas content, second the bubble nucleation on suspended inclusion in supersaturated molten, and finally the multi-fine bubbles flotation to the surface.

익형 변화에 따른 유도공기부상기 성능특성 연구

The flotation performance of the induced gas flotation (IGF) machine is considerably influenced by geometric configurations of rotor and stator. The interaction of rotor and stator, which are the most important components in IGF, serves to mix the air bubbles. Thus, the understanding of flow characteristics and consequential analysis on the machine are essential for the optimal design of IGF. In this study, two-phase (water and air) flow characteristics in the forced-air mechanically stirred Dorr-Oliver flotation cell was investigated using ANSYS CFX. In addition, the void fraction and the velocity distributions are determined and presented with different blade configurations.

Bubble Meets Droplet: Particle-Assisted Reconfiguration of Wetting Morphologies in Colloidal Multiphase Systems.

Wetting phenomena are ubiquitous in nature and play key functions in various industrial processes and products. When a gas bubble encounters an oil droplet in an aqueous medium, it can experience either partial wetting or complete engulfment by the oil. Each of these morphologies can have practical benefits, and controlling the morphology is desirable for applications ranging from particle synthesis to oil recovery and gas flotation. It is known that the wetting of two fluids within a fluid medium depends on the balance of interfacial tensions and can thus be modified with surfactant additives. It is reported that colloidal particles, too, can be used to promote both wetting and dewetting in multifluid systems. This study demonstrates the surfactant-free tuning and dynamic reconfiguration of bubble-droplet morphologies with the help of cellulosic particles. It further shows that the effect can be attributed to particle adsorption at the fluid interfaces, which can be probed by interfacial tensiometry, making particle-induced transitions in the wetting morphology predictable. Finally, particle adsorption at different rates to air-water and oil-water interfaces can even lead to slow, reentrant wetting behavior not familiar from particle-free systems.

Composition and Dynamic Adsorption of Crude Oil Components Dissolved in Synthetic Produced Water at Different pH Values

The effect of pH on the extent and type of dissolved components in synthetic produced water samples prepared from seven crude oils was investigated. More nitrogen containing compounds, probably due to improved water solubility of pyridinic nitrogen functionalities, were seen at the low pH. The affinity of the water-soluble compounds for air–water interfaces was in most cases higher at higher pH. This was due to increased oxygen content in the water-soluble species, probably associated with carboxylic acid functionalities. Differences in the affinity of water-soluble crude oil components to gas bubbles are anticipated to influence the oil removal efficiency by gas flotation. The dynamic interfacial adsorption was followed by a maximum bubble pressure tensiometer, while the dissolved species were characterized by total organic carbon measurements, total nitrogen measurements, FT-IR spectroscopy, and UV/vis spectroscopy.

Oil Removal from Produced Water during Laboratory- and Pilot-Scale Gas Flotation: The Influence of Interfacial Adsorption and Induction Times

The significance of interfacial chemistry for the oil removal efficiency during flotation was demonstrated in a series of laboratory flotation and pilot-scale compact flotation unit (CFU) tests. Three crude oils with different physicochemical properties were used in the investigations. The differences in drop size distributions and densities of the oils could not fully account for the observed oil removal. However, taking the time for drainage and rupture (i.e., induction time) of the thin aqueous film separating the drops and bubbles into consideration resulted in good agreement with the oil removal. Moreover, it was demonstrated in a modified CFU setup that water-soluble hydrocarbons adsorbed onto the bubbles and reduced the oil removal. This was most likely as a result of increased induction times caused by the adsorbed components.

An overview of oil-water separation using gas flotation systems.

Oil concentration levels in municipal waste water effluent streams are stringently regulated in most parts of the world. Apart from municipal waste, stricter oil/grease discharge limits are also enforced in oil and gas sectors as large volumes of produced water is being discharged to open ocean. One of the feasible, practical and established methods to remove oil substances from waste water sources is by gas flotation. In this overview, gas flotation technologies, namely dissolved and induced flotation systems, are discussed. Physico-chemical interaction between oil-water-gas during flotation is also summarized. In addition to a brief review on design advancements in flotation systems, enhancement of flotation efficiency by using pre-treatment methods, particularly coagulation-flocculation, is also presented.

The size and performance of offshore produced water oil-removal technologies for reinjection

Produced water (PW) is wastewater generated from oil exploration, and requires treating for oil and suspended solids removal. The viability of an effluent treatment unit process for this duty is dependent both on its efficacy, in terms of oil removal and – for offshore applications especially – its size, in terms of its area (FA, m/h) and volume (FV, h−1) footprint per unit volume flow. The incurred footprint applies to both the individual unit (vessel, column or tank) and the collection (or array) of units/vessels in a skid.An assessment of unit process footprint based on available information has been conducted, in particular to the case where high-quality treated water is required for reinjection. The analysis encompasses technical data from specific proprietary technologies as well as generic information for process technology types. Technologies considered comprised hydrocyclones (HCs), induced gas flotation (IGF), media (nutshell) filtration (NSF), and crossflow membrane filtration (CMF).The analysis revealed the HC to incur the smallest area footprint, less than half that of an IGF, notwithstanding only ∼0.15% of the total skid volume being used for the actual separation process. The CMF had a slightly smaller area footprint and less than half the volumetric footprint of the NSF, if the requirement for backflushing is considered. The fitting of the modular HC and CMF technologies to a skid incurs a considerable increase in the footprint, particularly for the HC where the volume occupancy is increased by an order of magnitude. It was concluded that spatial efficiency gains could be attained for modular processes if spacing of the HC vessels or membrane modules can be reduced, contributing significantly to the viability of CMF in particular.

Flotation separation of gallium from aqueous solution – Effects of chemical speciation and solubility

This work aimed to investigate dispersed gas flotation for Ga(III) removal as influenced by the speciation and solubility of Ga(III). Theoretical Ga(III) solubility was the lowest (0.615*10−4mM) in pH range of 4.9–5.8, and experimental solubility of Ga(III) generally showed a good agreement with theoretical predictions. In flotation separation, removal efficiency of Ga(III) dramatically increased from 43.0% to 87.3% as pH increased from 2.5 to 6.0. In contrast, the efficiency sharply declined to 41.4% once pH further increased to 10.3. At pH 2.5, Ga(III) removal efficiency substantially increased with increasing SDS concentration; however, the removal efficiency slightly rose with SDS concentration at pH 6.0 and remained unchanged at pH 10.3. The clear correlation between SDS dose and Ga(III) separation efficiency showed that the electrostatic interactions resulted in flotation separation of cationic species of soluble Ga(III). In addition, anionic SDS became adsorbed on the positively charged surface of colloidal solid Ga(III) via electrostatic force facilitated attachment of nitrogen gas and Ga(III) separation by foam. Nitrogen flow rate accelerated reaction rate of flotation process, while ionic strength slightly hindered removal efficiency of Ga(III).

Deoiled Produced Water Treatment Using Direct-Contact Membrane Distillation

Deoiled produced water in current produced water treatment facilities for water reclamation from steam-flooded oil exploration (Webb et al. Desalination of oilfield-produced water at the San Ardo water reclamation facility, CA, SPE 121520-PP, 2009) activities is available at temperatures between 160 and 200 °F (71–93 °C). Desalination of this deoiled produced water is accomplished currently by reverse osmosis after a number of steps including cooling. Membrane distillation processes can utilize this sensible heat to achieve desalination. Direct-contact membrane distillation studies using a hollow-fiber membrane module with brine in the cross-flow have been successfully conducted using a variety of produced waters such as Chevron A [Pre-RO, Post WEMCO; the latter refers to an induced gas/dissolved gas flotation (IGF/DGF) technique], Chevron B1, and Chevron B2 having total dissolved solids (TDS) respectively of 7622, 12040, and 35000 mg/L. The brine feed temperature was varied between 50 and 85 °C. The effe...

Deinking of recovered papers with wastewater as pulping liquor and ozone as flotation gas in an internal airlift reactor

The effect of pulping reagents and gas flotation media on deinking efficiency of recovered fibers was investigated in a bubble column reactor (BCR) and in an internal loop airlift reactor (ALR). A four-step process involving pulping, washing, flotation, and secondary washing was used. Employing an ALR instead of a BCR resulted in an increase in brightness, and a decrease in number of ink spot. Subsequently, in separate experiments, the wastewater obtained from a Merox unit was used in pulping step instead of sodium hydroxide solution as pulping liquor and the ozonated reactive gas in flotation step instead of air as gas media. Comparison of all experiments suggests that using industrial wastewater in the pulping step and ozone gas associated with ALR in flotation step give satisfactory results for industrial applications, yields a quality product while considerably preserving the environment. The brightness of deinked fibers obtained by ozone flotation was higher than the brightness of initial unprinted fibers.

Performance Analysis of a Novel Compact Flotation Unit

The oil and gas industry produces large quantities of water as a by-product of petroleum production. Discharge specification of produced water requires efficient management and sophisticated technology. Conventional technologies such as those based on gravity separation, cyclonic separation method, filtration techniques, flotation technique, and natural gas/air sparge tube systems are used for treating produced water. However, most, if not all, of these technologies require a large footprint. This problem has created a challenge for the produced water industry, as well as for operators managing the offshore production facilities. Responding to the challenge at hand, Siemens Water Technologies Corporation has developed a novel compact flotation unit (CFU) equipped with a dissolved gas flotation (DGF) pump for treating produced water. The CFU has a small foot print and shorter residence time. The DGF pump is equipped with a unique, dual-sided impeller, which pulls the blanket gas on one side and the produced water on the other. Under applied backpressure, the gas entering the DGF pump dissolves in a portion of a recycled, cleaned water stream. The dissolved gas generates bubbles due to the pressure drop when the mixture of produced water and gas passes through a special valve before entering the CFU. The ratio of the inlet produced water flow rate to the DGF pump output rate plays an important role in optimum separation of oil droplets from the produced water. Besides the above-mentioned ratio, generation of an adequate number and size of bubbles provides another critical key factor in efficient operation of the CFU system. To validate our theoretical approach regarding the controlled forced vortex of the multiphase flow, we performed various tests in the shop facility of Siemens Water Technologies Corporation, as well as on a platform facility offshore Louisiana. We used a response surface methodology technique to analyze the CFU performance data and to generate an optimum surface response for free oil and grease removal efficiency. For optimizing the size of the piping and CFU dimensions, we used the rigorous yet simple principles of the constrained similitude. The free oil removal efficiency results in the shop and field tests, for CFU without the use of packing material, were satisfactory. Additionally, we found that CFU system tests resulted in the removal efficiency of water soluble oil (WSO). We did not expect this additional outcome as the CFU system was not designed to affect the removal of WSO.

X-Ray Observation of Gas Evolution, Flotation, and Emulsification of Molten Carbon Steel Immersed in Mold Flux

At two interfacial-tension measurement experiments with the same experimental conditions, steel samples and mold flux samples of the same compositions were melted in crucibles from the same batch. During the first experiment, the steel drop melted far below its liquidus and then was emulsified. At the second experiment, the steel melted at the expected temperature but did not emulsify. The difference that can be identified is the mass of the steel samples.

Use of Dissolved Gas Flotation for Clarification of Biological Solids from a Petroleum Refinery Activated Sludge System

Dissolved gas flotation (DGF) is a feasible secondary clarification technology preceding a NPDES Permitted outfall. In 2009, a DGF was installed to separate mixed liquor suspended solids (MLSS) from wastewater originating from a petroleum refinery. Operational data indicates the technology can remove over 99% of influent suspended solids on a sustained basis. DGF clarification advantages, disadvantages, design considerations, and operational performance information are provided in this case study. Notable benefits of the technology are: low effluent suspended solids concentrations, concentrated recycle/waste activated sludge (RAS/WAS) solids, no sludge bulking concerns, compact footprint, and skid construction. The primary disadvantages are higher operating cost and more operator attention. Both conventional gravity (CGC) and DGF clarifiers should be considered viable technologies for separation of MLSS from biologically treated wastewater.

The Effect of Temperature and Impeller Speed on Mechanically Induced Gas Flotation (IGF) Performance in Separation of Oil from Oilfield-Produced Water

The effect of temperature and impeller speed on the performance of induced gas flotation (IGF) systems for the removal of oil from produced water in different ranges (5–300 g/L) of total dissolved solids (TDS) was investigated in a pilot plant study. Furthermore, it was evaluated whether the IGF pilot plant effluent could reach the 15 mg/L outlet oil content as required by Article VI of the Kuwait Convention for Persian Gulf region, before being discharged to the sea. The results showed that oil removal efficiencies up to 90% could be reached at high temperature (80°C) in just one single flotation cell without adding any chemicals. Flotation unit, however, should be followed by at least one more flotation cell in series in order to guarantee the Kuwait Convention marine pollution discharge standard for the effluent oil content.

Eletroquímica de flotação de minerais de sulfetos de chumbo e zinco

Esse trabalho foi realizado com amostras provenientes da mina de Morro Agudo, visando a verificar a influência do potencial Eh na flotação de chumbo e zinco. As amostras foram provenientes da britagem primária. Durante o processo de flotação, o potencial redox foi monitorado, continuamente, usando um eletrodo de platina. Nesse estudo, foram avaliados os efeitos da adição de sulfeto de sódio e sulfito de sódio na recuperação de galena e esfalerita na presença e na ausência de nitrogênio, como gás de flotação. Uma análise estatística dos resultados de recuperação foi feita através do software MINITAB. A interação do sulfeto de sódio com o gás nitrogênio diminui a recuperação de chumbo no concentrado e o gás nitrogênio, isoladamente, aumentou a recuperação de zinco no concentrado, para uma flotação composta por dois circuitos em série, recuperação da galena, seguida da esfalerita.

Flotation of blue-green algae using methylated egg ovalbumin

The removal of blue-green algae by dispersed gas flotation was conducted. Methylated ovalbumin (MeOA) was used as frother and flocculant, which is a biodegradable substance. The continuous flotation experiments were conducted at different feed mass flow rate of the blue-green algae cells and MeOA. The operating variables were the mass flow rate of blue-green algae cell and MeOA, the initial concentration of the cells and MeOA, and superficial gas velocity. The results showed that the mass flow rate of MeOA was the most dominant variable affected by the removal efficiency and that the removal efficiency achieved ca. 0.85 when a ratio of the mass flow rate of MeOA and that of the cells was over 0.3. A proposed flotation model considering the adsorptions of MeOA to the cells, MeOA to bubble surface and the cells bearing with MeOA to bubble surface was applied to explain the experimental removal efficiency. The experimental and the calculated removal efficiency were within error 19%, indicating that the proposed model was valid fundamentally.

Integration of dissolved gas flotation and nanofiltration for M. aeruginosa and associated microcystins removal

The removal of Microcystis aeruginosa and associated microcystins was investigated by a dissolved gas flotation (preceded by coagulation/flocculation)—nanofiltration (NF) sequence. The experiments were conducted with a freshwater spiked with M. aeruginosa cell aggregates to simulate a naturally occurring bloom. Two types of gases were used in the flotation pre-treatment, air (DAF) and a mixture of CO 2/air. Very good results in terms of NF fluxes, overall removal efficiencies and final water quality were achieved with both sequences. However, the CO 2/air mixture presented no benefit to the overall sequence, both in terms of toxin release to water during flotation and lower natural organic matter removal by NF, which was due to an overall negative effect of the acid pH. NF was able to completely remove cyanobacteria (100% removal efficiency of chlorophyll a) and microcystins (always under the quantification limit), regardless of the pre-treatment used and the water recovery rate (up to 84%). Therefore, DAF–NF sequence is a safe barrier against M. aeruginosa and microcystins in drinking water. In addition, it ensures an excellent control of particles, disinfection by-products formation, and other micropollutants that may be present in raw water.

Sludge minimisation technologies

The treatment and disposal of excess sludge represents a bottleneck of wastewater treatment plants all over the world, due to environmental, economic, social and legal factors. There is therefore a growing interest in developing technologies to reduce the wastewater sludge generation. The goal of this paper is to present the state-of-the-art of current minimisation techniques for reducing sludge production in biological wastewater treatment processes. An overview of the main technologies is given considering three different strategies: The first option is to reduce the production of sludge by introducing in the wastewater treatment stage additional stages with a lower cellular yield coefficient compared to the one corresponding to the activated sludge process (lysis-cryptic growth, uncoupling and maintenance metabolism, predation on bacteria, anaerobic treatment). The second choice is to act on the sludge stage. As anaerobic digestion is the main process in sewage sludge treatment for reducing and stabilising the organic solids, two possibilities can be considered: introducing a pre-treatment process before the anaerobic reaction (physical, chemical or biological pre-treatments), or modifying the digestion configuration (two-stage and temperature-phased anaerobic digestion, anoxic gas flotation). And, finally, the last minimisation strategy is the removal of the sludge generated in the activated sludge plant (incineration, gasification, pyrolysis, wet air oxidation, supercritical water oxidation).