Factors Affecting Separation Effect of Centrifuge

The centrifuge is widely used to separate solid and liquid in various industries, such as pharmaceutical manufacturing, textile, food industry and chemical industry. With the development of national economy, energy conservation and environment protection has become the mainstream of industry.

1. Classification and Working Principle of Centrifuge

According to the structure and separation requirements, industrial centrifuges can be divided into three categories: filtration centrifuges, settling centrifuges and separators. There is a cylinder rotates at high speed around the axis, called a drum, which is usually driven by an electric motor. After the suspension (or emulsion) is added into the drum, it will be driven to rotate at the same speed as the drum, the solid phase and liquid phase will be separated and discharged respectively under the action of centrifugal force. Generally, the higher the rotating speed of the drum, the better the separation effect.

The principle of centrifuge is centrifugal filtration and centrifugal sedimentation.

Centrifugal filtration is: under the action of centrifugal force, the liquid phase in the suspension will pass through the filtration medium, and the solid particles will be intercepted on the surface of the filtration medium, so as to realize the solid-liquid separation.

Centrifugal sedimentation is: under the action of centrifugal force, the components with different density in the suspension (or emulsion) will settle and be separated, so as to realize solid-liquid (or liquid-liquid) separation.

Separation factor is an important index to measure the separation performance. It represents the ratio of the centrifugal force to gravity of the separated material in the drum. Generally, the larger the separation factor, the better the separation effect.

Another factor that determines the processing capacity of centrifuge is the working area of drum, the larger the working area, the larger the processing capacity. The filtration centrifuges and settling centrifuges mainly depend on increasing the diameter of the drum to expand the working area on the circumference of the drum. For the separators, in addition to the working area on the circumference of the drum, there are additional working area, such as the discs of the disc separators and the inner cylinder of the chamber separators, which significantly increase the working area.

2. The Influence of the Selection of Centrifuge on Separation Effect

The reasonable selection of centrifuge is an important link to the separation effect. Generally, for the suspension containing particles larger than 0.01mm, filtration centrifuge is the better choice. For the suspension with fine or compressible particles, it is better to select settling centrifuge. For the suspension with low solid content, fine particles and high requirement for liquid clarity, it is necessary to select separator.

3. The Influence of Rotating Speed on Separation Effect

As everyone knows, the higher the rotating speed of the drum, the better the separation effect. The settling force acting on the solid particles can reach thousands of times of its gravity, which can ensure the complete separation of the solid from the suspension.

The separation factor is the key technical index of separation capacity. The larger the separation factor, the greater the settling force, the better the separation effect. Therefore, for the suspension or emulsion with small solid particles, high liquid viscosity and difficult to be separated, it is better to use the centrifuge with large separation factor. Increasing the rotating speed or the diameter of the drum can both increase the separation factor, but increasing the diameter means more investment, so it is more reasonable to increase the rotating speed.

4. The Influence of Operation Parameters on Separation Effect

The separation capacity of centrifuge is related to the density difference between solid and liquid phases and the length of the settling zone. The closer the density of solid and liquid phases, the larger the viscosity of the suspension, the more difficult to be separated. In the actual production, the main factors that affect the separation effect are: feed temperature, feed rate and abnormal process conditions.

Feed temperature: generally, the higher the suspension temperature, the lower the viscosity, the easier the fine particles to settle, the better the separation effect.

Feed rate: excessive feed will reduce the separation effect, the main reason is that the settling time of particles in the drum is not enough. Therefore, in order to achieve a better separation effect, the settling time of solid particles on the drum wall must be less than the retention time of suspension in the drum.

Abnormal process conditions: it means that the crystal content in the feed suspension is insufficient or the crystals do not crystallize but are flocculent. In this case, the separation effect will be affected. Therefore, the physical properties of feed suspension are directly related to the separation effect. For materials that are difficult to separate, an effective method is to wash the centrifuge frequently with hot water or condensate higher than the temperature of the feed suspension.

5. The Influence of Operation State on Separation Effect

The safe and stable operation of the centrifuge is the premise of good separation effect. Therefore, interlock and alarm functions should be set to protect the centrifuge.

The abrasion of the centrifuge directly affects the separation effect, production capacity and service life. The solid particles will cause abrasion on the inner wall of the drum and the spiral blades, so the ability of slag discharge will decrease and the water content of sediment will increase. Therefore, it is effective to add an protection layer to the key components to improve the efficiency of the centrifuge and extend the service life. In addition, it is necessary to strengthen the daily maintenance. In daily inspection, the workers should check all the  components, especially check the lubrication, working temperature, vibration of main bearing and differential. If there is leakage, crack or serious abrasion, it must be handled in time to ensure the safe and stable operation of the centrifuge.