Overview of Chemical Water Treatment System
The water vapor circulation system of thermal power plant has strict water quality requirements for the water used as the working medium and cooling medium of the thermal system. For example, the high-pressure boiler feed water not only requires low hardness, extremely small dissolved oxygen, and extremely small solid and organic content. These water must be treated by high-purity water equipment such as precipitation, filtration, desalination, degassing, etc., and seawater as the supply source needs seawater desalination equipment before entering the water circulation system, water that does not meet the water supply standards will make the power plant equipment unable to operate safely and economically. Therefore, the chemical water treatment system of power plant is an important auxiliary workshop and auxiliary system of power plant, especially the chemical water treatment workshop of large thermal power plant and heating power plant has large capacity, complex process and high water quality requirements, and its operation is directly related to the safe operation and reliability of the power plant.

Composition of chemical water treatment system
The traditional chemical water treatment system is mostly monitored by analog screen, and the collection and management of various data scattered by monitoring points are not centralized, and the automation level is not high and the efficiency is low. The chemical water treatment system of our company is composed of two on-site computers and a set of redundant PLC system. The upper computer system and on-site monitoring and control points are closely combined into a whole through Ethernet to form a complete system, and a column of chemical water treatment is unified for centralized control.
The upper computer system adopts Yanhua industrial-grade computers to form a powerful remote monitoring and control system. The PLC control system adopts a dual-computer hot standby redundancy mode, which connects the points that need to be monitored and controlled on site through remote I/O. The redundant main control station can ensure zero downtime of the system and minimize human intervention in the system. High-performance industrial Ethernet is used for communication between the upper computer and the PLC control station, information transmission is reliable, safe and stable. Through reasonable system design and system configuration, the dynamic monitoring and control of the whole chemical water treatment process and equipment operation state are realized, and the functions of curve display, historical data preservation, authority management, operation query, alarm, printing and so on are realized.
The local instrument system is composed of pressure and temperature transmitter, flow meter, liquid level meter, PH value meter, acidity meter, alkalinity meter, silicate detector, conductivity detector, pressure and differential pressure switch, etc. It mainly completes the detection of water tank liquid level, pipeline pressure, inlet and outlet water flow, water temperature and water quality, and carries out automatic process control and adjustment through the detection value.
The field control equipment is composed of water pump, fan, pneumatic valve, electric valve, regulating valve, etc. The water pump and fan are controlled by motor, and the pneumatic valve is controlled by solenoid valve.

Function of chemical water treatment system
The function of the upper computer is to provide a variety of parameter monitoring screens, digitally display the water tank level, pipeline pressure, real-time and cumulative value of inlet and outlet water flow, water temperature and water quality detection in the chemical water treatment system, record the historical changes of these parameters, send out a voice alarm when the parameter value exceeds the preset value, and record the alarm history for inquiry. The operation and fault status display of each equipment, the start and stop operation of each equipment, and the operation record for query. When each equipment failure occurs, sound alarm will be issued and the failure situation (failure time, failure type, etc.) will be recorded to facilitate accident analysis. Important parameters, alarms and faults can be printed in reports.
The function of the lower computer mainly includes signal acquisition and processing, accumulation of flow and accumulation of running time, which is transmitted to the upper computer for display, accepting the operation of the upper computer, judging the automatic control conditions, and logically controlling the pump fan and pneumatic valve to complete the processing process.
The water treatment program-controlled system has perfect functions such as operation mode selection, automatic alarm of equipment failure, on-site information collection, processing, and operation display. In the control room, the operator can carry out centralized monitoring, management and automatic sequence control of the whole process system through the control system, and the operator can also operate the pneumatic valve, electric door, water pump and fan one-to-one remotely at the operator station. The system retains the local control function and provides local manual operation. Even in the case of complete failure of the program control system, manual water treatment can be realized through local control to ensure reliable water consumption of the unit boiler.
In the system, alarm and interlock protection are set through the PLC internal program. Once a fault occurs, the corresponding operation will be stopped immediately, and the corresponding alarm signal will be issued to automatically start the standby equipment. It also provides valve opening time-out/closing time-out fault alarm, valve position signal fault alarm, water pump/fan start/stop time-out fault alarm, water pump/fan protection device accident trip/power failure alarm and other systems, which can also be connected with the auxiliary control network system of the whole plant through the switch to realize remote operation parameter monitoring and management.