Vinyl acetate is a very important industrial raw material, and its market is very broad. Its production process is mainly divided into two major processes: synthesis and distillation. The former is the process of chemical reaction to produce vinyl acetate, and the latter is the process of The vinyl acetate produced is purified through learning and physical processes. The process flow chart is as follows:
2. Features and difficulties of this process
The production of vinyl acetate is a system with a lot of towers, with many regulating loops, and the system is very closely related. The quality of the control of one parameter directly affects the success or failure of the control of other parameters. The fluctuation of a system may bring the entire system down. , Because the concentration of its product vinyl acetate is very high, reaching more than 99.9%, so the control requirements for parameters such as reaction temperature and flow rate are very stable. The medium temperature of the synthesis reactor requires 170 plus or minus 0.5 degrees, and the level of the acetic acid evaporator is required. Reaching plus or minus 1%, and the flow of acetylene is very unstable, and the controllability is not very good. These all put high requirements on the accuracy of control.
3. Process requirements for control system
a. Realize centralized monitoring of each unit operation, including: monitoring and control of physical quantities such as temperature, pressure, flow, and liquid level. The detection and control of dynamic parameters must be accurate and reliable. The medium temperature of the synthesis reactor is required to be 170 plus or minus 0.5 degrees, and the liquid level of the acetic acid evaporator is required to reach plus or minus 1%.
b. Necessary remote control measures. For emergencies such as power outages, the system should take corresponding protective measures to ensure that some key control points (valves, motors, etc.) are remotely controlled in an emergency or when needed.
c. Configure necessary alarms and interlocks.
d. Record of important parameters and easily check their real-time trends and historical trends.
e. The relevant parameters of relevant units or the operation of important equipment can be monitored at any time.
f. The control system has simple operation, convenient parameter setting and adjustment, easy operation, and humanized operation interface.
g. The operator station displays the entire production process, and modifies and prints various related parameters.
1. Network composition
Two on-site control stations and three monitoring stations use redundant dual buses to connect the control station and the monitoring station. Except for failures of any one of the buses, the entire system can still operate normally. The stability of the system communication is greatly increased. The connection structure diagram is as follows:
2. System configuration
This control system uses three monitoring stations and two on-site control stations. Stability. The two on-site control stations also adopt hot standby redundancy. If any one fails, it will automatically switch to the other for normal operation. Also increase To improve the reliability and stability of the system. All analog output has adopted hot standby, and important display parameters have also adopted hot standby. All analog output has adopted the photoelectric isolation from the field signal, all Field signals are isolated by safety barriers.
3. Control strategy and implementation planOver the years, the engineers of Hunan Liangyuan Automation (the company is committed to automation system integration, information system (including ERP system\MIS system and MRP system) development, DCS system development, PLC system development, low-voltage power distribution cabinet complete sets, frequency conversion Drive system development such as cabinet soft-lifting) has been committed to the development of the system and continuous optimization and improvement. The following are typical solutions. Actually, different optimization control schemes will be made according to different projects:
1. PID adjustment
In the production process of vinyl acetate, because the reactor temperature control requirements are relatively strict, reaching plus or minus 0.5 degrees, and its quality is also related to the quality of the final product, so the control of the reaction temperature is cascaded. Control. Its structure diagram is as follows:
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