Principle of Ultrasonic demulsification of crude oil

Ultrasonic wave is a kind of elastic mechanical wave propagating in medium, which has mechanical vibration, cavitation and thermal effects. Theoretical derivation and visual experiments prove that the sound intensity of ultrasonic emulsification must be below the cavitation threshold. Therefore, ultrasonic demulsification of crude oil mainly uses the mechanical vibration and thermal effects of ultrasonic.

Mechanism of action

1. The vibration promotes the condensation of water "particles". When ultrasonic wave passes through the crude oil medium with suspended water "particles", it will cause suspended water "particles" and crude oil

2. Vibrate together. Because water "particles" with different sizes have different relative vibration velocities, they will collide and stick with each other, increasing the volume and mass of particles, and finally settling and separating.

3. Vibration can make paraffin, gum, asphalt and other natural emulsifiers in crude oil disperse evenly, increase their solubility, reduce the mechanical strength of oil-water interface facial mask, and is conducive to aqueous phase sedimentation and separation. Thermal action reduces the strength of oil-water interface facial mask and the viscosity of crude oil.

On the one hand, boundary friction increases the temperature at the oil-water boundary, which is conducive to the rupture of the boundary facial mask.

On the other hand, the crude oil absorbs part of the heat energy converted from sound energy, which can reduce the viscosity of the crude oil, and is conducive to the gravity sedimentation and separation of oil and water of water "particles".

Factors affecting ultrasonic demulsification device:

1. There are many factors for ultrasonic emulsification, such as sound intensity, ultrasonic frequency, radiation time, temperature, settling time, crude oil viscosity, etc.

2. Intensity and its distribution are one of the important factors affecting ultrasonic demulsification device. The sound intensity must be controlled below the cavitation threshold. The optimum sound intensity required for demulsification is different due to the large differences in the properties of each crude oil.

3. The wave frequency only affects the distance of the "particle" moving toward the antinode or wave node within a certain range of magnitude, and has no significant impact on the demulsification effect within a certain range of magnitude. It is theoretically deduced that the frequency has an effect on the "particle" condensation, and that the optimum frequency for particles to produce condensation under the action of acoustic waves is about 21~25 kHz.

4. Emulsification and demulsification are actually a dynamic equilibrium process. The emulsion can be broken by selecting the appropriate treatment time. However, if the ultrasonic treatment time is too long, the separated oil-water two-phase may be emulsified to form a more stable emulsion. Therefore, the sound wave radiation time is not the longer the better.

5. The influence of crude oil demulsification and dehydration is obvious. The mass fraction of water after crude oil demulsification decreases with the increase of temperature, but the decreasing range is smaller and smaller with the increase of temperature.