Analysis and Research on Separation Effect of Disc Separator

In the process of industrial production, there are many materials for liquid-solid, liquid-liquid and liquid-liquid-solid separation. Especially when the density difference between liquid-solid and liquid-liquid phases is very small, or the solid particles are very small, the gravity sedimentation method can not meet the requirement, but the centrifugal separation method is effective. Centrifugal separation can realize continuous operation, increase production capacity, improve separation effect, reduce labor intensity and improve production efficiency.

Due to its high separation factor, disc separator is used for purification, clarification and concentration separation. It is a kind of high-performance separation equipment, widely used in petrochemical, pharmaceutical, light industry, shipping, food and other industries. This article mainly analyses the factors that affect the separation effect from the structure, operating conditions and process parameters of the disc separator.

1. Separation Principle of Disc Separator

There is a group of discs in the drum of disc separator, the discs divide the drum space into many thin layers, so as to greatly shorten the settling distance and improve the separation effect.

The suspension is fed into the drum by the feed pipe, and flows radially between the discs. The light phase flows to the drum center and is discharged by the light liquid centripetal pump. The heavy phase flows to the drum wall and is discharged by the heavy liquid centripetal pump. The sediment is deposited on the drum wall and discharged intermittently by the piston.

2. Factors Affecting the Separation Effect

2.1 Structure of Disc Separator

2.1.1 Separation Factor

Separation factor refers to the ratio of the settling speed of the particles in the centrifugal force field to that in the gravity field. Separation factor is an important indicator of the separation performance of the separator. The higher the separation factor of the disc separator, the easier the materials will be separated and the better the separation effect.

2.1.2 Disc Distribution Hole

For liquid-liquid separation, the location of the disc distribution hole is an important parameter that affects the separation effect of light and heavy phases. If the location of the distribution hole is close to the center, the light phase will contain more heavy phase components. If the location of the distribution hole is deviated to the center, the heavy phase will contain more light phase components.

2.1.3 Disc Spacing

The disc spacing should meet the requirements as follows:

(1) When the particles in the material move between the discs, they can pass through the liquid flow surface to reach the lower surface of the upper disc.

(2) The particles with critical diameter settling on the disc surface will not be taken away by the liquid flow.

2.1.4 Half Cone Angle of Disc

The half cone angle of the disc is the angle between the disc generatrix and the axis, generally within the range of 30°-45°.

2.1.5 Surface Roughness of Disc

The flow of liquid in the high-speed rotating drum is a complex turbulent flow. The roughness of the disc surface affects the flow of the liquid. The larger the surface roughness, the higher the friction coefficient, the higher the flow resistance. With the increase of the flow resistance, some particles can not reach the outer circle of the disc and be taken away by the liquid flow, which finally affects the separation effect. Generally speaking, after polishing the internal and external surfaces of the disc, the roughness should not be larger than 1.6 μm.

2.2 Operating Conditions and Process Parameters of Disc Separator

2.2.1 Diameter of Gravity Ring

Adjusting the diameter of gravity ring is to change the diameter of heavy phase outlet, and adjust the separation interface of light and heavy phases, so as to achieve the best separation effect. When the diameter of the gravity ring becomes larger, the separation interface will move out of the disc, the less heavy phase is contained in the light phase. On the contrary, when the diameter of the gravity ring becomes smaller, the separation interface will move toward the disc, and the less light phase is contained in the heavy phase.

2.2.2 Diameter of Liquid Level Ring

Adjusting the diameter of liquid level ring is to change the diameter of light phase outlet, and adjust the separation interface of light and heavy phases, so as to achieve the best separation effect. When the diameter of the liquid level ring becomes smaller, the separation interface will move out of the disc, the less heavy phase is contained in the light phase. On the contrary, when the diameter of the liquid level ring becomes larger, the separation interface will move toward the disc, and the less light phase is contained in the heavy phase.

2.2.3 Outlet Pressure

The outlet pressure is used to adjust the separation interface of light and heavy phases. Increasing the pressure of the light phase, the separation interface will move toward the heavy phase, then the light phase will be more clear. On the contrary, increasing the pressure of the heavy phase, the separation interface will move toward the light phase, then the heavy phase will be more clear.

2.2.4 Slag Discharge Time-interval

The slag discharge time-interval should be determined according to the solid content of the material, and the slag discharge operation should be carried out regularly. Otherwise the solid phase will fill up the slag chamber, and even block the disc gap, which will affect the separation effect.

2.2.5 Temperature

Temperature has a great influence on the separation effect. The viscosity of the material changes with the temperature. The higher the temperature, the lower the viscosity of the material, the better the separation effect. On the contrary, the lower the temperature, the higher the viscosity of the material, the worse the separation effect. Therefore, the temperature control is conductive to the stability of the separation process, the fluctuation of the temperature should be avoided. For example, the best separation temperature of heavy oil is between 95℃ and 98℃, and the best separation temperature of vegetable oil is between 85℃ and 95℃.

2.2.6 Stirring of Materials

The separation of suspension should be fully stirred and mixed evenly, so that the solid particles will evenly disperse in the liquid. For the granular materials formed in the production process, the uneven stirring and mixing will break the particles and affect the separation effect. So it is very important to choose the appropriate stirring device and stirring speed.

2.2.7 Stability of Feed Speed

It is very important to keep the stability of feed speed, the fluctuation should be avoided. The stability of the feed speed ensures the stability of the separation interface. Once the fluctuation occurs, the separation interface will be damaged and the separation effect will be affected.

3. Conclusion

The separation effect is the result of the mutual restriction of various parameters. The flow of liquid and the movement of particles between discs are very complex. They are not only affected by centrifugal acceleration, but also by Coriolis acceleration and viscous resistance of liquid. It is necessary to determine the structure of the disc separator according to the properties of the materials to be separated. At the same time, the operating conditions and process parameters should be adjusted during operation, so as to achieve the best separation effect.