1 Centrifuge development and use
A centrifuge is a machine that uses the powerful centrifugal force generated by the high speed rotation of a centrifuge rotor to separate liquid and solid particles or liquid and liquid mixtures. Industrial centrifuges were born in Europe. In the middle of the 19th century, there were three-legged centrifuges for textile dehydration and upper-suspension centrifuges for separating granulated sugar from sugar factories. These early centrifuges were intermittently operated and Manually draining slag. With the improvement of the slag removal mechanism, a continuously operating centrifuge appeared in the 1930s, and the intermittent operation of the centrifuge was also developed due to the realization of automatic control.
At present, centrifuges have been widely used in metallurgy, chemical, petroleum, food, pharmaceutical, mineral processing, coal, water treatment and shipbuilding sectors.
2 How the centrifuge works
Industrial centrifuges can be classified into three types: filtration centrifuges, sedimentation centrifuges and separators according to the structure and separation requirements. The centrifuge has a cylinder that rotates at a high speed about its own axis, called a drum, which is usually driven by an electric motor. After the suspension (or emulsion) is added to the drum, it is rapidly driven to rotate at the same speed as the drum, and the components are separated under the action of centrifugal force and discharged separately. Generally, the higher the drum speed, the better the separation.
The centrifugal separator has two working principles: centrifugal filtration and centrifugal sedimentation. Centrifugal filtration is the centrifugal pressure generated by the suspension under the centrifugal force field, acting on the filter medium, causing the liquid to pass through the filter medium to become a filtrate, and the solid particles are trapped on the surface of the filter medium, thereby achieving liquid-solid separation. At present, the SGZ1000-è¦ three-legged lower discharge automatic centrifuge selected for the grinding and immersing workshop of our factory belongs to the centrifugal filter.
The working principle of the SGZ1000-è¦ three-legged lower discharge automatic centrifuge.
When the control system opens the feed valve, the treated suspension reaches the full-speed running disc from the feeding tube and is evenly rubbed onto the filter medium on the inner wall of the drum under the action of centrifugal force. At this time, the suspension is in filtration. The liquid phase in the separated state is taken out through the small hole in the rotating drum through the filter medium under the action of centrifugal force, and is discharged from the liquid discharging pipe by the inner wall of the casing and the collecting of the chassis. The solid phase particles remain on the filter medium, and after washing and dehydration, when the separation requirement is reached, the discharge mechanism is started to be discharged from the discharge port at the bottom of the body.
3 Status survey
The electromechanical workshop of the Fukang Smelter is responsible for the overhaul of all equipment in the two major production systems of copper and nickel.
The nickel system leaching centrifuge mainly undertakes the liquid-solid separation work of the thickener filtrate, and the filtrate is returned to the nickel system to recover the nickel metal, and the filter residue is used as a raw material of the copper system to be used in the next process.
The indicators for measuring the working state of the centrifuge are mainly copper slag moisture and slag containing nickel, which are 11%.3.9% respectively.
Since the centrifuge was put into operation, there have been problems of severe vibration and incomplete dehydration, resulting in two important indicators exceeding the standard for a long time, directly affecting the recovery of nickel metal and the process operation of the copper system, and resulting in serious consumption of spare parts. According to the production situation of our factory's nickel system from May to July 1999, the investigation of nickel, copper slag moisture and material consumption of copper slag is shown in Table 1.
4 failure analysis and solution
4.1 Principle analysis 牦犌犣1000-è¦Three-legged lower unloading automatic centrifuge The main body of the whole machine is mainly composed of unloading mechanism, rotary body, frame, braking device and transmission device. Among them, the factors that may increase the vibration amplitude of the body are: (1) the firmness of the frame; (2) the assembly accuracy of each part; and (3) the degree of adaptation of the mechanism.
4.2 Troubleshooting
The frame firmness can be timely reinforced according to the actual situation of the site, and the assembly accuracy of each part depends entirely on the technical quality of the employees. It is a controllable factor, so the factors that cause the vibration of the body and the incomplete dehydration are only applicable to the mechanism. Sex. Through the analysis of the particle size and concentration of the suspension, combined with the on-site detection and mechanical principles, we believe that the main reasons for the poor dewatering efficiency and severe vibration of the centrifuge are:
(1) The 牦犌犣1000-è¦ three-leg lower unloading automatic centrifuge selected by our factory is suitable for liquid-solid separation work with lighter specific gravity of suspension, such as sugar production and pharmaceutical industry. At present, according to the production process of our factory, it is thick. The bottom particle size of the machine is only 325 mesh, but the concentration is as high as 40% to 50%. During the solid-liquid separation process, the filter medium is clogged, resulting in incomplete dewatering.
(2) The fabric mechanism of the original machine is restricted by the characteristics of the underflow liquid. During the operation of the machine body, it is not expected to "form a uniform material layer on the inner wall of the drum" according to the design, but a layer accumulation phenomenon in the middle direction is formed.
4.3 Formulating countermeasures
For the above reasons, combined with the characteristics of the underflow liquid, the performance of the filter medium and the mechanical principle, we have taken corresponding countermeasures:
Change the distribution pattern of solid particles on the drum during the operation of the machine: cut the upper edge of the centrifuge to 60 犿犿 to reduce the total amount of deposits inside the drum during one operation cycle; at the same time, perform the disc cloth mechanism Improvement: Remove the original cloth tray, replace it with a flat-mouth dispenser, and lengthen the feed tube. The modified mechanism is more suitable for the production process. Under the action of centrifugal force, the material distribution on the inner wall of the drum will be upward, and the solution that has not been removed will climb upward and be discharged from the upper part.
5 effects
5.1 effect comparison
The transformation began in May 1999 and was basically completed by the beginning of 2000. After it was put into operation, it achieved remarkable results. The comparison data of the indicators for the same period of two years are shown in Table 2 and Table 3.
5.2 Economic benefits
(1) The modification of the cloth device and the drum not only solves the vibration problem during the operation of the machine body, but also solves the problem of incomplete dewatering of the material liquid. The two control indexes of the centrifuge have reached the process requirements.
(2) After the transformation, the vibration of the body is reduced, which greatly prolongs the service life of spare parts and reduces the maintenance cost. (3) Increasing the recovery rate of metals in raw materials, increasing product output and total production value.
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