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 Natural settlement separation under gravity is a simple and commonly used separation method. It makes use of the relative density of suspended impurities and grease to separate them from the grease by sinking down from the oil under the natural standing state. The separation efficiency of gravity sedimentation is relatively low, and it is only suitable for the separation of large suspended impurities in crude oil, and the separation of degranulation or soap particles in the process of hydration degumming of fats and alkali refining and deacidification. The sedimentation process of a single particle suspended in grease or a group of particles sufficiently dispersed so that the particles will not cause collision or contact is called a free sedimentation process. In fact, the shape of the particles in the oil suspension system is often irregular. The smaller the sphericity of the particles, the greater the resistance coefficient, so the actual sedimentation rate is much smaller than the theoretical value. In addition, the sedimentation rate of particles is affected by the concentration of particles in the system. When the concentration increases, the sedimentation of particles and the upward displacement of fluids will generate hydrodynamic interactions, or collisions between particles will occur, and the sedimentation of particles will be affected. Disturbance, which will also make the actual settlement rate far less than the theoretical value. The sedimentation rate of particles is directly proportional to its diameter and the relative density of solid and liquid phases, and inversely proportional to the viscosity of the system. Because the diameter of the fine particles in the oil suspension problem and the relative density difference with the oil are very small, and the viscosity of the system is large, the sedimentation process is very slow. In order to increase the sedimentation rate, the method of agglomeration and reducing the viscosity of the system can be used. The increase in system temperature can reduce the viscosity of the grease, which is conducive to the sedimentation of the particles, but the increase in the temperature of the system should not exceed the critical temperature of particle aggregation. Generally, the temperature of sedimentation and separation is maintained at about 80 degrees Celsius. Adding electrolytes and water to the oil can promote the relative density of the suspended matter to agglomerate or expand after absorbing water, thereby increasing the rate of sedimentation and separation.