Several Key Techniques Of An Ultrasonic Treating System For Crude Oil Anti-Wax And Viscosity-Reduction

For a long time, the crude oil's wax deposition and high viscosity during the process of exploitation and transportation have been essential to be taken into account in the crude oil industry of China and the whole world. By comparision with the other methods for anti-wax and viscosity-reduction (AWVR), the AWVR by using high power ultrasound (the ultrasonic AWVR) takes advantages in terms of high efficiency, no pollution, safety, simplicity, no influence on refinement and a low cost. And it has been blessed with a potential strategic significance and wide market prospects.The ultrasonic AWVR is now in the early stage of development, thus some technical problems should be addressed and improved. To do so, several key techniques of an ultrasonic AWVR treating system were intensively studied in this work, which would speed up the ultrasonic AWVR for actual and extensive applications.The ultrasonic AWVR treatment chiefly takes effect through the cavitation effect. Due to the fact that the cavitation intensity is remarkably dependent on the ultrasound's frequency and sound pressure, a numerical simulation of a single cavitation bubble's radial kinematics was carried out. Accordingly, the frequency and the power of the ultrasound treatment were determined, and thus a full-wavelength concentrating piezoelectric ultrasonic transducer was developed by using the analysis method and the transfer matrix method. For rapid and exact measuring of the transducer's mechanical resonant frequency (MRF), a novel measurement method of the MRF of a transducer based on the residual vibration signal's Morlet wavelet transform was presented in this thesis.The ultrasonic AWVR treatment should be carried out in a sonochemical reactor. In order to evaluate the cavitation intensity, the sound pressure distribution (SPD) of the reactor should be studied. The SPD has been usually analyzed by using the far-field sound pressure normalized directivity method, which has deficiencies such as poor visualization and inability for near-middle field analysis. As a result, a new planar SPD analysis method in transducers'near-middle field was proposed. The SPD of the developed transducer and its 2×2 array were studied by using this method. In addition, under the condition of the certain transducers'arrangement and the reactor's dimentioins, the transducers'interval distance was optimized.The equivalent mechanical resistence of an oil-loaded transducer is large, and it is sensitive to the variations of the pressure, viscosity, flux and temperature of the crude oil. So the transducer's conjugate matching can hardly be achieved by using the conventional method, which causes heat and low reliability. Accordingly, a primary coil serial electrical matching scheme for transducers was proposed. In this scheme, the ultrasounic generator's output transformer turn ratio was optimized over the varying range of the equivalent mechanical resistence, and a primary coil reactor was applied to match the integral load including the transducer and the transformer. Using the scheme, a more efficient matching was achieved.Due to the crude oil load, the transducer degenerates to be low-quality, which results in the performance degradations of the conventional phase locked loop (PLL) frequency tracing method, such as losing lock, mis-lock, dead lock and large tracing error. Through the theoretical analysis on those above, a novel static capacitance compensation based PLL frequency tracing for transducers was suggested. For the mechanical branch phase difference of the transducer was gained by compensating the shunting effect of the static capacitance, an accurate frequency tracing with the oil-loaded low-quality transducer was realized.Finally, based on the ultrasonic treating system developed, the parameters including the ultrasound treating time, the transducer's operating current and the wax content of the oil, which have remarkable effects on the ultrasonic AWVR performance, were studied by using the viscosity-temperature curve method. The wax crystal morphology and the composition of the experimental oil and liquid wax were compared by means of the scanning electron microscope, the gas chromatogram-mass spectrum combination and the polarization microscope. And the rules of the ultrasonic AWVR were summarized.