Cause analysis and Countermeasures of the worst im

2022-07-23
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Cause analysis and Countermeasures of affecting the separation effect of centrifuge

1 working principle of centrifuge

the horizontal spiral discharge centrifuge is a column cone combination type, which is composed of two independent rotating rotors, one is a column cone type non perforated drum, the other is a screw with spiral blades, and the two are coaxially and horizontally sheathed together. The centrifuge drum rotates anticlockwise, and the drum rotates in the same direction with its inner spiral concentric. The speed of the drum is slightly faster than that of the spiral. When the suspension is introduced into the spiral cavity through the feed pipe and enters the settlement area of the drum through the distribution port, under the action of centrifugal force, the solid with high density is deposited on the inner wall of the drum, pushed out of the settlement area by the spiral blades, and discharged from the small end of the drum through the drying area. The clarified separation liquid flows to the big end of the drum along the spiral blade channel and is discharged from the overflow hole. Thus, the solid and liquid of the suspension are separated. 2 Analysis of causes affecting the separation effect of centrifuge and Countermeasures

2.1 speed control

the higher the rotating speed of the drum, the better the dehydration effect. Because the materials in the drum and screw rotate at high speed, the flame retardancy, aging resistance, mechanical properties, electrical, magnetic, optical, thermal and other characteristics of the resin can be improved to ensure the complete separation of solids from the suspension. The ratio of the centrifugal inertia force of the separated material in the centrifugal force field to its gravity is called the separation factor F. The separation factor is the main indicator indicating the separation capacity of the centrifuge. The greater the F, the greater the sedimentation force on the material, and the better the separation effect. Therefore, for the suspension or emulsion with small solid particles, high liquid viscosity and difficult separation, the centrifuge with large separation factor (high speed or large diameter) should be used. The method of increasing the rotating speed is more direct and effective than that of increasing the drum diameter (modifying the drum diameter requires modifying a series of related accessory sizes); Because the increase of separation factor is limited, and the limit value of F depends on the strength and density of the drum material, the method of increasing the rotating speed is relatively easier to operate in practical application.. however, increasing the rotating speed also has disadvantages. If the rotating speed is too high, the solid phase discharge will be too hard and block the screw, affecting the operation of the centrifuge, so the centrifuge has to be stopped for water washing to remove the caked sodium sulfate. The speed of the centrifuge drum can be realized by adjusting the size of the pulley. In actual operation, the characteristics of the feed liquid, the diameter and material of the drum and other aspects should be fully considered, and the speed of the drum and the corresponding pulley size should be accurately calculated before the speed can be adjusted

2.2 speed difference control

according to the working principle of the centrifuge, the screw and the drum rotate in the same direction concentric, but there is a speed difference between them. If NN represents the absolute speed of the drum, NS represents the absolute speed of the screw, and an represents the differential speed of the two, an=ii-b o the speed of the drum is faster than that of the screw, that is, Nb rib, which is a negative differential speed, The slip ratio is the ratio of differential speed to drum speed: slip ratio a= (an/N) xlo0% (generally, a is 0.2%-3%). The crystallization separation of the recovery unit pursues the dryness of the solid phase. The adoption 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 realized by changing the differential speed between the drum and the screw, that is, changing the size of the pulley on the rotor to change the slip. This method is easy to operate in production practice

in addition, belt aging or uneven belt tightness may also lead to the change of speed difference and the change of solid-phase discharge, which is also a point to pay attention to when analyzing the solid-phase discharge of centrifuge

2.3 process condition control

the separation capacity of the centrifuge depends on the density difference between the solid and liquid phases and the length of the settling zone. The closer the density difference between the solid and liquid phases is, that is, the greater the viscosity of the slurry fed, the more difficult the separation and settling will be. In actual production, there are three main factors that affect the separation effect of centrifuge: feed temperature, feed rate

due to its electro-hydraulic servo control technology, and abnormal process conditions

2.3.1 feed temperature the temperature of slurry can directly affect the viscosity of mother liquor. The higher the temperature of the solution, the lower the viscosity, the thinner the liquid film on the solid phase, the easier it is for fine particles to settle, and the less liquid in the pores. For centrifuges pursuing the dryness of the solid phase, the better the separation effect will be

2.3.2 sometimes, excessive feed rate will lead to poor separation effect, mainly because the settling time of particles in the rotating drum is insufficient. The premise of meeting the separation conditions of centrifuge design is that the settling time of solid particles on the drum wall must be less than the residence time of 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 rate is 1 m3/h, the separation effect is not good, but when the feed rate is 0.5 m3/h, the separation effect is very ideal

2.3.3 abnormal process conditions mainly refer to the ldquo; Paper shortage rdquo; Problem: the content of crystal in the feed slurry is insufficient or the crystal does not crystallize and is flocculent, which is very difficult for the centrifuge to obtain an ideal separation effect

for materials that are difficult to separate, a good method is to wash the centrifuge frequently. Wash the centrifuge with hot water or condensate that is higher than the temperature of the feed liquid. It can replace the sticky mother liquid, and also replace the hard solid phase discharge that is blocked in the screw. The two sides have yet to reach a consensus on the details of cost and scope. Normally, the centrifuge is cleaned twice a day. However, when the production is abnormal, especially when the feed liquid is abnormal and the centrifuge cannot be stopped, it is a good method to clean the centrifuge at any time as required

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