Extension Of Centrifuges In High-density Polyethylene Process Based On PLC

High density polyethylene (HDPE) is new plastic material with wide usages, and centrifuge is the crucial equipment in HDPE production process. Solid-liquid separation made by centrifuge can collect the solid components, and meanwhile the liquid from the slurry by centrifugal force. However, because centrifuge’s auxiliary process system and control logic are sophisticated, and it is under continuous operation, its automatic control and interlock system are very important to the machine. The plant in question has3operating centrifuges, which are controlled by PLC. During normal operation,3centrifuges are operating in parallel. When the output of HDPE inject-moulding grade JHC-7260is raised, the centrifuges encounter the problems of burn-down thrust bearing and broken torque block, and output of3centrifuges can not reach the rated value, and therefore hinder the plant’s overall production. As a result, more centrifuge shall be applied in this HDPE plant to meet higher production output demand.The article chooses the centrifuges of HDPE plant of Petrochina Jilin petrochemical company as its subject, and gives a detailed analysis of these machines,their control logic and PLC technology. According to the demand of the newly added centrifuge, the article suggests to use SIMENS S7-300PLC, the same as the ones used by existing3centrifuges, to control the machine, including its start, stop and interlock program. The article also suggests to use SIMENS PROTOOL touch screen as its local control interface, and MODBUS communication technique to achieve remote control. Based on centrifuge’s control demand and features, the article suggests to make advantage of PLC’s good adaptability to write appropriate programs for the machine, thus raises PLC’s reliability and ensures centrifuge’s safe and smooth running. After all these efforts, the production output of plant’s HDPE grade JHM-9455F will be increased to40t/h, and JHC-7260to42t/h (plant’s existing production outputs for JHMF-9455and JHC-7260F are36t/h and38t/h respectively). The purpose of HDPE plant’s centrifuge expanding project will therefore be achieved.