| The treatment of oilfield produced water, which plays an essential role in the production process, is an important research project for the development and utilization of the oilfield and also for the environmental protection. Therefore, treatment technology of oilfield produced water assorting with the tertiary oil recovery technology, is in urgent need. Besides, physical separation processes and equipments with no added chemicals, no production of poly clay, a simple operation and low energy consumption are also in great demand. The Cyclone-static micro-bubble flotation separation, which combines the conventional Hydrocyclone with conventional flotation column, is a high efficient separation equipment, integrating cyclone separation, flotation and coalescing separation. In this dissertation, researches are carried out in the areas of cyclonic separation and coalescing separation by flotation column to enhance oil removing, which provide theoretical guidance to the development and industrial application of flotation column in oilywater separation. The major research includes the following aspects:Study concerning the mechanism of cyclonic separation strengthening oil removing by flotation column is conducted. The forces of the droplets in the cyclone are analyzed and the oilywater separation process in the flotation column built-in cyclone is depicted. The operating parameters, such as frother concentration, feed capacity, circulating pressure and inflation rate influencing the oil removal rate are studied. Mathematical model of cyclonic oil removal rate is established. The velocity field of the flotation column built-in cyclone is tested by particle image velocimetry (PIV).Study on the mechanism of multiple coalescence enhancing oil removing by flotation column is conducted. Based on the deep analysis of the inner cyclonic section and pipe flow section, the behavior of the air flotation fluid and the process of oil coalescence and comminuting, the mechanisms of swirl coalescence (collision coalescence of 90o), pipe flow coalescence (collision coalescence of 0o) and laminar coalescence(collision coalescence of 180o) in the cyclone-static microbubble flotation column are proposed. Several operating conditions are taken into consideration, such as the effect of inflation rate, temperature, feed capacity, circulating pressure and viscosity on the swirl coalescence, the effect of inflation rate, temperature, feed capacity and viscosity on the laminar flow coalescence and the effect of inflation rate, circulating pressure, viscosity, pipe length, pipe diameter and oil concentration on the pipe flow coalescence. Mathematical models of swirl, laminar flow and pipe flow coalescence are established. Particle size range, which can be effectively dealt with during the process of swirl, laminar flow and pipe flow coalescence, is clarified.Oil concentration distributions and droplet size distribution nephograms of the swirl, pipe flow and air flotation sections, being processed by swirl, pipe flow and laminar flow coalescence, is obtained, after the numerical simulation of two-phase field in the flotation column using the fluid dynamics software (Fluent). Simulation results and experimental results match well.Study on the mechanism of jet-based gas holdup control enhancing de-oiling is conducted. The law that the four parameters, namely, nozzle diameter, aeration rate, frother dosage affecting the gas holdup is analyzed. The optimal gas holdup for oil-water separation, no less than 10%, is decided. Two models are established, that is, the mathematical model for predicting the gas holdup which is based on the influence of operating parameters and the gas holdup model based on the BP neural network and GRNN neural network.The law of different factors, such as adsorption time, coal rank, coal particle size, pH value and concentration of oily wastewater, affecting the oil substances adsorbing in the surface of coal particles, is researched through the static experiment. The law of oil substances in the surface of +0.046mm anthracite and -0.046mm anthracite can be fitted by Freundlich adsorption isotherm and Langmuir adsorption isotherm respectively. Pseudo-second-order kinetic model fits the process of adsorption, the form of which is the coexistence of the physical and chemical adsorption, the former being the major and the latter being a supplement.Oil recovery wastewater from polymer flooding, essentially being a produced water circulation system which includes two kinds of productions (oil production and produced water processing) and two kinds of circulations (water and polymer circulations), needs appropriate treatment, the purpose of which is to make the effluent meet the requirement of reinjection and to retain the maximum polymer at the same time. The flotation column selective adsorption flotation process of polymer flooding produced water is developed, with the cyclone-static micro-bubble flotation column as the main separation equipment, and by means of natural adsorption of coal, with coal fine being the adsorbent, crude oil being selectively adsorbed and polymer retained. Considering the effect of multiple coalescence and stuffing coalescence, coalescence floatation process of flotation column is developed, and the recycling technology of coal-oil-based adsorption material resource is developed as well. After the integration of the coalescence flotation and the carrier selective adsorption process, a 2000m3/d industrial system named coalescence flotation-selective adsorption process is constructed in Shengli oilfield Gudao No.6 joint station. The industrial test shows that this technology is featured by unique process, advanced equipment, excellent indexes and sediment-free production, for the inefluent of oil and suspended matter concentration being 1000mg/L~2000mg/L and 120mg/L respectively, a effluent of oil concentration of 23.39 mg/L and the total oil removal ratio of 97.70% were obtained. Meanwhile, every 1m3 water treatment can reduce 1.87Kg sludge emission. |
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