Ultrasonic Crude Oil Demulsification
Water-bearing crude oil is a common phenomenon in the development of oil and gas fields, and water-bearing crude oil must be dehydrated and desalted before processing. Ultrasonic crude oil demulsification is a new demulsification method that can effectively solve such problems.
The principle of ultrasonic demulsification
Ultrasound is an elastic mechanical wave propagating in a medium, which has mechanical vibration, cavitation and thermal effects. Theoretical derivation and visualization experiments prove that the sound intensity of ultrasonic demulsification must be below the cavitation threshold. Therefore, ultrasonic demulsification of crude oil mainly utilizes the mechanical vibration and thermal effects of ultrasonic waves.
1. Vibration causes water "particles" to agglomerate. When the ultrasonic wave passes through the crude oil medium with suspended water "particles", it causes the suspended water "particles" to interact with the crude oil.
2. Vibrate together. Because the water "particles" of different sizes have different relative vibrational speeds, the water "particles" will collide and stick with each other, which will increase the volume and mass of the particles, and finally settle and separate.
3. Vibration can make the natural emulsifiers such as paraffin, colloid, and asphalt in crude oil evenly dispersed, increase their solubility, reduce the mechanical strength of the oil-water interface film, and facilitate the sedimentation and separation of the water phase. Thermal action reduces the strength of the oil-water interface film and the viscosity of crude oil.
On the one hand, boundary friction increases the temperature at the oil-water interface, which is conducive to the rupture of the interface film.
On the other hand, crude oil absorbs some of the heat energy converted from sound energy, which can reduce the viscosity of crude oil, which is conducive to the gravitational sedimentation and separation of oil and water of water "particles".
Factors affecting ultrasonic demulsification:
1. There are many factors for ultrasonic demulsification, such as sound intensity, ultrasonic frequency, radiation time, temperature, settling time, crude oil viscosity, etc.
2. Strength and its distribution are one of the important factors affecting ultrasonic demulsification. The sound intensity must be controlled below the cavitation threshold. Due to the large differences in the properties of each crude oil, the optimal sound intensity required for demulsification is different.
3. The size of the wave frequency only affects the distance traveled by the "particles" to the antinodes or nodes within a certain range of magnitude, and has little effect on the demulsification effect within a certain range of magnitude. Kotyusov theoretically deduces that the frequency has an effect on "particle" agglomeration, and deduces that the optimal frequency for particle agglomeration under the action of sound waves is about 21-25 kHz.
4. Emulsification and demulsification are actually a dynamic equilibrium process. The demulsification can be broken by selecting the appropriate treatment time, but if the ultrasonic treatment time is too long, the separated oil and water two-phase emulsification may be emulsified, thereby forming a more stable emulsion. Therefore, the sound wave radiation time is not as long as possible.
5. The influence of demulsification and dehydration of crude oil is obvious. The mass fraction of water after demulsification of crude oil decreases with the increase of temperature, but the decreasing range becomes smaller and smaller with the increase of temperature.