Factors affecting the separation efficiency of decanter centrifuge and ways to improve it.

Decanter centrifuge as a high-efficiency separation equipment, widely used in chemical, food, pharmaceutical, environmental protection and many other industries, in the solid-liquid separation, liquid-liquid separation and liquid-liquid-solid three-phase separation and other processes play an important role. Its separation efficiency is directly related to the energy consumption of the production process, product quality and the economic benefits of enterprises. In-depth study of the factors affecting the separation efficiency of decanter centrifuge, and explore effective ways to improve, is of great significance.

一.The factors affecting the separation efficiency of decanter centrifuge

1.Equipment structure parameters

(1)Drum diameter and length

Drum diameter and length are important structural parameters that affect the separation efficiency of the decanter centrifuge. The larger the drum diameter, the stronger the centrifugal force field, the greater the centrifugal force on the particles under the same rotational speed, which helps to accelerate the settling speed of the particles, thus improving the separation efficiency. At the same time, a larger drum diameter can increase the effective volume of the drum and improve the processing capacity of the equipment. However, the increase in drum diameter will also be limited by the strength of the material and the manufacturing cost of the equipment, too large a diameter may lead to a decline in the operational stability of the equipment and a significant increase in manufacturing costs. The effect of drum length on separation efficiency is mainly reflected in the residence time of the material in the drum. Longer drum can extend the residence time of the material in the centrifugal force field, so that the particles have more sufficient time to settle and separate, which is conducive to improving the separation effect. However, the length of the drum is too long will increase the volume of the equipment, increase the floor space, but also increase the manufacturing cost of the equipment and operating energy consumption. Therefore, in the design and selection, according to the specific material characteristics and separation requirements, need to reasonably select the combination of drum diameter and length, in order to achieve the best separation efficiency and economic benefits.

(2)Differential speed between spiral and drum

The differential speed between spiral and drum determines the conveying speed of sediment. Differential speed is too large, although the slag can be quickly transported out of the drum, but the residence time of the material in the drum is shortened, the particles can not be sufficiently settled by the spiral out, resulting in a reduction in the separation efficiency; differential speed is too small, the accumulation of slag in the drum will gradually increase, and may block the slag discharge port, affecting the normal operation of the equipment, but also increase the friction between the spiral and the slag, exacerbate the wear and tear of the equipment, reducing the service life of the equipment. Service life. The appropriate differential speed can ensure that the slag is discharged smoothly while the material has enough separation time in the drum, thus improving the separation efficiency.

(3)Overflow weir height

The overflow weir height directly affects the depth of liquid pool in the drum. When the depth of the liquid pool increases, the residence time of the material in the drum is prolonged, which is conducive to the separation of particles, but the liquid pool is too deep will make the rotational inertia of the liquid in the drum increase, increase the energy consumption of the equipment, and may lead to the formation of a large vortex of liquid in the drum, affecting the separation effect. On the contrary, the overflow weir height is too low, the depth of the liquid pool is reduced, the material residence time is shortened, and the separation efficiency will also be reduced. Therefore, it is necessary to reasonably adjust the overflow weir height according to the nature of the material and separation requirements, in order to optimise the depth of the liquid pool and improve the separation efficiency.

2.Operation running parameters

(1) Rotational speed

The rotational speed of the decanter centrifuge determines the strength of the centrifugal force field. The higher the rotational speed, the greater the centrifugal force, the stronger the centrifugal settling force on the particles, the faster the settling speed and the higher the separation efficiency. However, the increase in rotational speed can also be limited by the mechanical strength and vibration of the equipment. Too high a rotational speed may lead to increased vibration of the equipment, affecting the stability and service life of the equipment, as well as increasing the operating noise and energy consumption of the equipment.

(2) Feed flow

The feed flow has a significant effect on the separation efficiency. When the feed flow rate is too large, the flow rate of the material in the drum is accelerated, the residence time is shortened, and the particles are taken out of the drum before they can settle sufficiently, resulting in poor separation effect, lower solid phase recovery rate, and lower liquid phase clarification. On the contrary, the feed flow rate is too small, although it can improve the separation efficiency, but the processing capacity of the equipment can not give full play to the production efficiency will be reduced, increasing the production cost per unit of product. Therefore, it is necessary to reasonably control the feed flow rate according to the processing capacity of the equipment and the nature of the material, in order to achieve a balance between separation efficiency and production efficiency.

(3) Feed concentration

The influence of feed concentration on the separation efficiency of decanter centrifuge is more complicated. For the solid-liquid separation process, when the feed concentration is too high, the viscosity of the material increases, the mutual interference between the particles increases, and the settlement resistance increases, resulting in slower particle settling speed and lower separation efficiency. At the same time, the high concentration of feed will also increase the amount of slagging, increase the load of the screw conveying slag, which is easy to cause slagging or even blockage. While the feed concentration is too low, it will make the processing capacity of the equipment is not fully utilised, increasing energy consumption and production costs. Therefore, according to the characteristics of the material and the performance of the equipment, reasonable adjustment of the feed concentration, in order to improve the separation efficiency and economic benefits.

3.Material Characteristics

(1)Particle size and distribution

The size and distribution of particles in a material play a key role in separation efficiency. Generally speaking, the larger the particle size, the faster the settling speed under the action of centrifugal force, the easier to achieve separation. As for the smaller particle size, the settling speed is slower and the separation is more difficult. In addition, when the particle size distribution is wide, small-sized particles may be interspersed between large-sized particles, affecting the settlement of large-sized particles, while small-sized particles are also more difficult to be separated from the liquid phase, resulting in a reduction in separation efficiency. Therefore, pretreatment measures, such as flocculation and coagulation, may be required for materials with smaller particle sizes or wider particle size distribution to increase the particle size and improve the separation effect.

(2)Material viscosity

Material viscosity is one of the important factors affecting the separation efficiency. The viscosity of the material, its internal friction is large, the particles in which the settlement resistance is also large, the settlement speed slows down significantly, the separation efficiency is reduced. At the same time, high viscosity materials are also easy to adhere to the drum and spiral, affecting the normal operation of the equipment and separation effect. In addition, the viscosity of the material in the process of feeding and discharging slag will also encounter greater resistance, increasing the energy consumption of the equipment. Therefore, when dealing with high-viscosity materials, it may be necessary to take measures such as heating and dilution to reduce the viscosity of the material in order to improve the separation efficiency.

(3)Material Density Difference

In the process of liquid-liquid separation or liquid-liquid-solid three-phase separation, the density difference between the phases is the basis for achieving separation. The greater the density difference, the faster the stratification speed between the phases under the action of centrifugal force, the better the separation effect. On the contrary, when the density difference between the phases is small, it is difficult to stratify, and it is easy to appear the phenomenon of blurring and mixing of the phase interface, which leads to the reduction of separation efficiency. For material systems with a small density difference, it may be necessary to use special separation processes or add auxiliary reagents to increase the density difference and improve the separation effect.

二.The method of improving the separation efficiency of decanter centrifuge

1.Reasonable selection of drum parameters

According to the characteristics of the material and separation requirements, select the appropriate drum diameter and length. For materials with larger particle size and less separation difficulty, the drum diameter can be appropriately increased to improve the processing capacity of the equipment; for materials with smaller particle size and higher separation requirements, a longer drum can be selected to extend the residence time of the material and improve the separation effect. At the same time, in the design of the drum, should also take into account the strength of the material and wear resistance to ensure that the equipment is safe and stable operation at high speeds.

2.Precise control of the spiral and drum differential speed

Through tests and actual operating experience, determine the spiral and drum differential speed suitable for different materials and separation conditions. Frequency control technology can be used to achieve precise adjustment of the differential speed, according to the nature of the material and the change of the feed flow, real-time adjustment of the differential speed, to ensure the smooth discharge of the slag and the full separation of the material. In addition, the structure of the spiral blade can also be optimised design, such as the use of variable pitch, variable depth spiral blade, etc., to improve the conveying efficiency of the slag and reduce the friction between the spiral and the slag.

3.Flexible adjustment of overflow weir height

According to the nature of the material and separation requirements, the overflow weir height can be flexibly adjusted to optimise the depth of the liquid pool. Adjustable overflow weir can be designed to realise rapid adjustment of liquid pool depth by changing the height of overflow weir. In actual operation, the overflow weir height can be adjusted in time according to the feedback of the separation effect, in order to achieve the best separation efficiency. At the same time, multi-stage overflow weir design can also be considered to further improve the adjustment precision of liquid pool depth and separation effect.

4.Select the appropriate rotational speed

Within the permissible range of the equipment, select the appropriate rotational speed according to the characteristics of the material and separation requirements. For materials with larger particle size and higher density, the rotational speed can be increased appropriately to enhance the centrifugal force field and accelerate the settling speed of the particles; for materials that are sensitive to shear, a lower rotational speed should be selected to avoid the destruction of the material structure. In actual operation, the optimal rotational speed can be determined by test, and the rotational speed can be adjusted in real time according to the change of material properties and feed flow to ensure the stability of the separation effect.

5.Optimise the feeding method

Improving the feeding method can improve the distribution uniformity of the material in the drum, thus improving the separation efficiency. The feeding method of centre feeding pipe and fabric cone can be adopted, so that the materials can be uniformly distributed in the drum to avoid bias flow and local accumulation phenomenon. In addition, it can also be set on the feeding pipe to guide the material to flow uniformly along the axial direction of the drum, reduce the impact and turbulence of the material in the feeding process, and improve the separation effect.

6.Pre-treatment of materials

For materials with small particle size or wide particle size distribution, flocculation, coagulation and other pre-treatment methods can be used to make small particles aggregated to form large particles, increase particle size and improve the settling speed. Suitable flocculants and coagulants can be selected, and the optimal amount of addition and reaction conditions can be determined through tests. For high-viscosity materials, heating, dilution and other methods can be used to reduce the viscosity of the material, improve the fluidity of the material, and reduce the particle settling resistance. In addition, the material can also be filtered, centrifuged and other pre-treatment to remove the impurities and coarse particles, improve the quality of the feed, and facilitate the subsequent separation process.

The separation efficiency of the decanter centrifuge is affected by a variety of factors such as equipment structure parameters, operating parameters and material characteristics. In practical application, according to the specific nature of the material and separation requirements, comprehensive consideration of various factors, reasonable selection and adjustment of equipment parameters and operating conditions, in order to achieve efficient operation of the decanter centrifuge, improve production efficiency.