1 Overview In the petroleum processing industry, large rotating machine is an important part of plant equipment, such as fluid catalytic cracking unit of the main blower, pressure units, gas turbine and steam turbine and so on. These units power, harsh operating conditions, the control system complexity, is the key equipment in chemical production. Therefore, the equipment in the incidents of protection is essential. Now widely used in major petrochemical enterprises is dedicated ESD emergency shutdown system, the system complex and high cost (hundreds of million). In response to these circumstances, Shenyang Paraffin Chemical Co., Ltd. 80x104 t / a heavy oil catalytic cracking unit interlock pressure - self-protection system uses a PLC for system construction, and its subsequent performance of stable production process, action could be * many times in accident state of the unit and production unit to implement the self-protection, to prevent the expansion and spread of malignant accident, has achieved remarkable results. 2 process equipment and main chain parameters In the catalytic cracking unit, from the settler out of oil and gas obtained by fractionation of crude fractionator gasoline, diesel and gas-rich, rich gas from the distillation tower out by the compressed air pressure machine sent to stable tower and the tower in a stable crude gasoline fully miscible, steady gasoline. In this part of the process, air pressure machine is the most critical equipment, whether it s running smooth a direct impact on the entire process. If the air pressure machine was damaged units will greatly influence the economic benefits. Therefore, the protection of the pressure unit is essential. Plant 80x104 t / a heavy oil catalytic cracking unit used in the electrical pressure - air pressure machine - steam turbine 3 units, steam turbine used in the device starts generating units start to reach the rated speed (6000 rpm) after the open motor, dual power in the form of three-unit mainly to increase the availability * of unit operation. The main chain unit shaft displacement parameters, including excessive parking pressure, turbine shaft displacement exceeding parking, low oil pressure on parking, sealing the oil pressure is low parking, entrance to the steam turbine low-flow parking, parking turbine back down, stopping excessive rotating speed, manual emergency stop, parking and other power trip, these are the digital input capacity, including any one or more occur, requires PLC-Font-family: Times New Roman ; mso-hansi-font-family: Times New Roman "> entrance of the steam turbine can be quickly cut off the quick closing valves and electrical power, air pressure machine at the same time close the entrance valve, open the torch valve to fight to ensure the safety of air pressure machines and devices. 3 Scheme for the Self-preservation - is the interlock system will affect the safety of installations and equipment, important safety parameters, such as temperature, pressure, flow, temperature and the introduction of ESD (Emergency Shutdown System) system from ESD monitoring and to a significant form of sound and light alarm to achieve the implementation of interlock interlock conditions are automatically protected, to protect the safety of equipment and devices, and print out the failure cause and time of the accident in order to facilitate analysis. As microelectronics technology, Fa Zhan, PLC products in the function and performance indicators have been greatly enriched and improved???, and in quality and cheap in popularity. Therefore, the process of production to meet demand from the start, taking into account safety, can *, economy, scalability and other factors, using the OMRON company s CPM2AH? 0CDR-A-type PLC </ Font>, and select the OMRON s CX-Programmer software. 4 System Components 4.1 The hardware structure CPM2AH own I / O interface, can take 36-point input, 24-point output, relay output form, and through RS232C serial communication with PC-1. PC-1 in the pneumatic machine control room, use the Windows2000 operating system, through the CX-Programmer software and PLC <span style = "font-family: Arial; mso-ascii-font-family: Times New Roman ; mso-hansi-font-family: Times New Roman "> communication, to achieve the configuration, monitoring and incident records function. As I plant with decentralized control, centralized management, so called main control room can also see the captive air pressure machine interlock status. Therefore, the use of Microsoft s Windows2000 Terminal Services features, in the main control room set up PC-2, the air pressure machine in the control room PC-1 as a terminal server, master control room PC-2 as a terminal client, two PC- because of distance, to fiber optic Ethernet connection, the main control room PC-2, it can be run through the terminal services control room located in air pressure machine on a PC, a CX-Programmer software on the PLC to monitor and various operation. 4EF rushing into a dual redundant PLC PLC or three programs to achieve higher reliability.