Reason analysis and countermeasures affecting the separation effect of centrifuge

Daqing Petrochemical Company Acrylic Fiber Factory (hereinafter referred to as Acrylic Fiber Factory) recycling workshop currently has two horizontal spiral discharge sedimentation centrifuges, both of which are produced by TANABE Corporation of Japan. It is mainly used in the material circulation of the acrylic device. Nearly 90% of sodium sulfate is separated from sodium thiocyanate in the crystallization separation process, and the balance of sodium sulfate is ensured. Therefore, in the entire acrylic device, the centrifuge is crucial. Important role.
1 Working principle of the centrifuge The horizontal spiral discharge centrifuge is a column-cone combination type, which is composed of two independently rotating rotors, one is a cylindrical-conical non-porous drum, and the other is a spiral with spiral blades. Coaxially nested together horizontally. The drum of the centrifuge rotates counterclockwise, the drum rotates concentrically with the spiral inside it, and the drum speed is slightly faster than the spiral. When the suspension is introduced into the spiral cavity from the feed pipe, it enters the settling area of â€‹â€‹the drum through the distribution port. Under the action of centrifugal force, the solid phase with a higher density is deposited on the inner wall of the drum, pushed out of the settling area by the spiral blade, and passes through the drying area It is discharged from the small end of the drum, and the clarified separation liquid flows along the spiral blade channel to the big end of the drum and is discharged from the overflow hole, thereby separating the solid and liquid of the suspension. 2 Cause analysis and countermeasures affecting the separation effect of the centrifuge
2.1 Rotation speed control The higher the rotation speed of the drum, the better the dehydration effect, because the materials in the drum and the spiral rotate at high speed, which can ensure the complete separation of solids from the suspension. The ratio of the centrifugal inertial force to the gravity of the separated material in the centrifugal force field is called the separation factor F. The separation factor is the main indicator of the separation capacity of the centrifuge. The larger the F, the greater the settling force of the material, and the better the separation effect. Therefore, for suspensions or emulsions with small solid particles, large liquid viscosity, and difficult to separate, A centrifuge with a large separation factor (high speed or large diameter) should be used. The method of increasing the speed of rotation is more direct and effective than the method of increasing the diameter of the drum (modifying the diameter of the drum to modify a series of related accessory sizes); and because the improvement of the separation factor is limited, the limit value of F depends on The strength and density of the drum material, so the method of increasing the speed is relatively easier to operate in practical applications. . However, there are disadvantages to increasing the rotation speed. If the rotation speed is too high, the solid phase discharge will be too hard and block the spiral, affecting the operation of the centrifuge. Therefore, the centrifuge has to be stopped for washing to remove the agglomerated sodium sulfate. The speed of the centrifuge drum can be achieved by adjusting the size of the pulley. In actual operation, the characteristics of the material liquid, the diameter and the material of the drum, etc. should be considered thoroughly to accurately calculate the speed of the drum and the corresponding The size of the pulley can be adjusted for the speed.
2.2 Speed â€‹â€‹difference control According to the working principle of the centrifuge, the spiral and the drum rotate concentrically and concentrically, but there is a speed difference between the two. If nn represents the absolute speed of the drum, ns represents the absolute speed of the spiral, an represents The difference speed of the two, an = II The rotation speed of the bo drum is faster than the spiral, that is, nb> rIB, which is a negative difference speed, and the slip rate is the ratio of the difference speed and the drum speed: slip rate a = (An / n) xlO0% (generally, a is 0.2% -3%). The crystal separation of the recovery device pursues the dryness of the solid phase. The use of such a negative slip rate is conducive to the transportation of sediment and can reduce the power transmitted by the reducer. The negative slip can be achieved by changing the differential speed of the drum and the screw, that is, the size of the pulley on the rotor can be changed to change the slip. This method is easier to operate in production practice.
In addition, the aging belt or uneven belt tension may also lead to changes in the speed difference and change the solid phase discharge, which is also a point to be noted when analyzing the solid phase discharge of the centrifuge.
2.3 Process conditions control The separation capacity of the centrifuge depends on the solid and liquid phase density difference and the length of the sedimentation zone. The closer the solid and liquid phase density difference is, that is, the greater the viscosity of the feed slurry, the more difficult it is to separate and settle. get on. In actual production, there are three main factors that affect the separation effect of the centrifuge: the feed temperature, feed rate, and abnormal process conditions.
2.3.1 Feed temperature The temperature of the slurry can directly affect the viscosity of the mother liquid. The higher the solution temperature, the lower the viscosity, the thinner the liquid film on the solid phase, the easier the fine particles to settle, and the capillary pore The less liquid, the better the separation effect will be for centrifuges that pursue solid-phase dryness.
2.3.2 Feeding rate Sometimes, an excessively large amount of feed will result in a poor separation effect, mainly because the sedimentation time of the particles in the drum is insufficient. The premise of achieving the separation conditions designed by the centrifuge is that the time for the solid particles to settle on the drum wall must be less than the residence time of the particles in the drum, that is, the effective residence time of the slurry to be separated in the drum must be guaranteed, So that the solid particles have enough time to settle out. For the same material, when the feed volume is 1 m3 / h, the separation effect is not good, but when the feed volume is 0.5 m3 / h, the separation effect is very ideal.
2.3.3 Abnormal process conditions mainly refer to insufficient crystal content in the feed slurry or the crystals are not crystallized but flocculated, which is very difficult for the centrifuge to obtain the ideal separation effect.
For materials that are more difficult to separate, a good method is to clean the centrifuge frequently, and use hot water or condensate that is higher than the temperature of the liquid to rinse the centrifuge. It can replace the viscous mother liquor and can also block the screw. The harder solid phase discharge is replaced. Normally, the centrifuge is cleaned twice a day, but when the production is abnormal, especially the material liquid is abnormal and the centrifuge cannot be stopped, it is a good treatment for the centrifuge to clean it at any time as needed.

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