[Key words] PVC; centrifuge; failure; improvement
[Abstract] This paper introduces the operation status and problems encountered by Chongqing Jiangbei Machinery Co., Ltd. and France Kenner Co., Ltd. in the production process, and proposes corresponding improvement measures.
In the production process of polyvinyl chloride, the vinyl chloride monomer is suspension polymerized in a polymerization tank to form a polyvinyl chloride suspension containing 70% to 75% of water, which is carried out before the material enters the drying process. Dehydration treatment, the water content of PVC is controlled below 25%, and then enter the drying bed for drying. At present, the domestic polyvinyl chloride industry adopts a spiral decanter centrifuge to complete the dehydration process. It can be seen that the centrifuge is one of the main equipments in the production process of polyvinyl chloride.
Due to the expansion and reconstruction, our company ordered 2 D5MC centrifuges manufactured by Chongqing Jiangbei Machinery Co., Ltd. and France Kenner in March 2002. The centrifuge was specially designed for the characteristics of PVC materials. Installation, commissioning and industrial operation began in March. The designed production capacity of the machine is 3.5 ~ 4. 5 t / h, the solid content of the clear liquid is ≤ 4 × 10 - 4 , after six months of continuous operation of our company, the equipment performance is good, which can meet the production needs of our company. . The following is a description of the structure of the centrifuge, the main technical parameters, and the problems and improvements in the production process.
1 Centrifuge structure, main technical parameters (1) The structure of the centrifuge is shown in Figure 1.
(2) The main technical parameters of the centrifuge are: drum diameter, 520mm; drum length, 1 664 mm; differential speed, 50 ~ 65 r / min; drum speed, 2 500 ~ 2 800 r / min; motor power , 75 kW; start mode, frequency converter; differential form, cycloid; differential speed ratio, 25; output, 3. 5 ~ 4. 5 t / h; spiral, double head, left-handed.
2 Problems and improvement measures in the production process
2. 1 Operation and Cause Analysis On March 3, 2002, our company started to produce PVC-SG5 resin on March 10-23, 2002 using two D5MC decanter centrifuges produced by Chongqing Jiangbei Machinery Co., Ltd. The continuous phenomenon of the centrifuge feed tube fracture occurs, which reduces the production capacity and severely restricts production.
Here, our company sent a special person to track and inspect the centrifuge feed tube randomly. It was found that there were plasticized sheets and a large number of yellow spots on the wall of the feed tube of the centrifuge. In response to the above problems, we set up a research team and conducted special research and discussion. Zui finally determined that there may be two reasons for the centrifuge feed tube to break: (1) The centrifuge feed tube is in the auger State, due to large material concentration, uneven feeding, pressure fluctuations, causing the feed tube to vibrate until the fatigue breaks.
(2) The centrifuge feed pipe is in the screw conveyor. During the feeding process, due to the pressure of the material and the back splashing, it accumulates in the gap between the feeding pipe and the screw conveyor, and feeds for a long time, so that the back splashes back. The more and more material is accumulated, the plasticized sheets are gathered in the feed pipe and the screw conveyor, and the feed pipe is broken.
2. 2 Improvement measures The feed pipe before and after improvement is shown in Figure 2. The feed process is shown in Figure 3. The two centrifuges are sent to the high-level suspension buffer tank by the feed pump. The feed amount of the centrifuge is adjusted by the feed valve, and the pump is directly fed after the improvement.
3 Improved understanding of D5MC centrifuge (1) After the company improved the feed pipe and feeding process, the centrifuge did not break for 6 months, and the centrifuge did not have a feed tube. The diameter changes, and the output is reduced. On the contrary, the centrifuge runs smoothly, the current fluctuation is small, and the output is above 4 t/h, which fully meets the design requirements.
(2) Considering the process design pipeline, in order to ensure uniform feeding of the centrifuge, the material can not have the opportunity of precipitation in the process pipeline. The pipeline does not have a 90° bend to ensure the inlet pressure of the centrifuge is stable.
Our company has a pump capacity of 100 m3/h, a head of 50 m, an outlet pipe diameter of DN 80 mm and a return pipe diameter of DN 50 mm. When selecting the pump, consider the larger return flow, which can play the role of mixing. The centrifuge feed current is controlled below 85 A to ensure the centrifuge can run for a long time.
(3) Only a few domestically produced D5MC centrifuges are used in the PVC industry in China, and most manufacturers use imported centrifuges. Our company considers that the imported centrifuge is expensive, the maintenance technical requirements are high, and the maintenance is difficult. Therefore, the domestic centrifuge is decided.
(4) The domestic D5MC centrifuge is compact in structure, convenient in maintenance, high in automation, and can automatically display the main technical parameters. It is an ideal equipment for PVC dehydration separation.
(5) Conduct inspections on time and carefully maintain them. The differential should be inspected for oil quantity when running for 1 month. If oil shortage is needed, it should be replenished in time. When refueling, be sure to pay attention to whether the oil quantity is sufficient. Add the main bearing every day. The amount of oil should be 5 to 10 mg.
(6) D5MC centrifuge can be said to have a much higher technical content than the ML450 centrifuge, both in terms of structure and electrical control. Since the D5MC centrifuge is controlled by computer program, the work reliability is greatly enhanced and the fault is reduced. The rate has enabled our company to complete the remote control of large-scale key equipment to ensure the completion of production capacity and product quality, thus further broadening the sales market of PVC.
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