1. System overview
The absolute drying quantity of pulp is an important index affecting the quality of paper making. The main line of the absolute drying quantity control system is the concentration regulation. The pulp concentration is detected by the concentration sensor before the pulp mixing box. The central controller realizes the concentration control to ensure the pulp concentration is stable and accurate. The electromagnetic flowmeter is used to measure the pulp flow rate. According to the absolute dryness set by the system and the pulp concentration detected from the concentration sensor, the absolute dry pulp flow rate per unit time in the pulp conveying pipe and the system setting value are basically the same by controlling the flow electric ball valve, so as to achieve continuous and stable control of the absolute pulp flow rate per unit time. The purpose of dry sizing is to get online.
At present, there are four sets of absolute drying control system for coated white board production line in a paper mill, including concentration transmitter, electric regulating ball valve, electromagnetic flowmeter, electric ball valve and DPS absolute drying measurement and control instrument. There are several defects in the system, resulting in unstable pulp quality, seriously affecting the continuous and stable production of paper machine.
1). DPS pulp absolute drying measurement and control instrument has poor adaptability to the environment. Environmental temperature, humidity, vibration and so on often lead to poor control effect of the instrument.
2). The instrument belongs to a special system. The system has poor exploitability and maintainability. It is difficult to judge the cause of the fault when the control system fails.
3). The monitoring function of the measuring and controlling instrument is relatively closed, and the function can not meet the needs of the real-time monitoring of pulp absolute drying quantity in the steady and continuous production.
4). The instrument is self-contained and can not realize the networking and communication with other control systems, and can not meet the user's desire to connect the flow and paper cutting, forming a closed-loop control requirements.
Therefore, it is urgent to reform the original control system, overcome the problems in the system, and meet the needs of production for stability, reliability and versatility.
2.system requirements
1). The selected control system adopts a general design scheme, which is universal, reliable and maintainable.
2). the control software has good flexibility, which is convenient for adjusting and modifying the control mode.
3). The system should have good expansibility, simple and convenient expansion of system scale, and little modification to the original control software.
4). The system has good network function and can be connected with the paper machine control system to realize the synchronization of paper cutting and flow.
3. system configuration and function realization
1). This control system is composed of SIEMENS CPU315-2DP and UniMAT I/O module of UniMAT company. It realizes density signal, flow signal and field control state. After digital filtering, signal conversion and other signal processing, the concentration and flow of pulp are closed-loop controlled to achieve the purpose of absolute dryness control.
2). SIEMENS Operating Panel OP270 is used for centralized monitoring of dry-out capacity, which accomplishes two tasks. One is to display the current parameters of the flow system in the form of system flow chart, tables, trends, etc. The other is to set the parameters of the dry-out capacity control system, including concentration setting, dry-out capacity setting and so on.
3). The dry weight control system is connected with the paper machine control system by PROFIBUS DP mode. On the one hand, the real-time parameters of the dry weight control system are transmitted to the paper machine control system for display and storage on WinCC. On the other hand, the paper machine control system sends the adjustment signal of the paper machine to the dry weight controller, and the dry weight controller is automatically suitable. It is necessary to adjust the process to realize the synchronization of the paper machine control and the flow control, and realize the dynamic realization of the whole paper-making process. Thus, the whole control process can be formulated to manage, different varieties and speed of paper for rapid system synchronization, reduce process adjustment time, provide production efficiency.
4). Dry-out control system can realize many practical functions which can not be realized before, including concentration adjustment cycle setting, manual automatic construction switching, pulp concentration multi-point calibration, sensor fault protection, concentration detection filtering and so on.
5). Through this control system, the control of slurry pump and the control of dry-out can be integrated, and the frequency converter of slurry pump can be directly controlled by this control system
4.Application effect analysis
Moisture quantitative control system has been put into operation so far. It works stably and reliably. Its regulation precision is better than the original DPS absolute drying measuring and controlling instrument. It also realizes the linkage with the paper machine control system. It is of positive significance to the continuous and stable production. It is the most competitive and cost-effective cost control solution.
