Pressure transmitter in the heat exchanger station control system application

The heat exchange station intelligent control system composed of pressure transmitter, temperature transmitter and other components mainly introduces the heat exchange station system composition and automatic control system design. This control system has been debugged in many power plants, and users are quite satisfied. The system has a high degree of automation, can realize remote monitoring, is safe and reliable, and is easy for inspection and maintenance.

1 Foreword

With the development of the economy, the voice of environmental protection and energy conservation is getting louder and louder across the country. Using cash science and technology, rational distribution of heat, let the existing It is the top priority of heating companies to make full use of thermal energy and provide better heating services to more users. Introducing microcomputer monitoring and automated control into the heating system, and realizing the transition from manual to automatic adjustment of the heating system, can meet the heating needs under the new situation.

2 Overview of the heat exchange station

The heat exchange station mainly uses heat exchanger equipment to seal the primary high-temperature water generated by the thermal electric field and the low-temperature return water of the user's secondary network, and transfer the heat The exchange is carried out, and then the resistance formed by the secondary network is overcome through the circulation pump equipment, and a stable water supply temperature is provided to the terminal under economic conditions. At the same time, it improves the automation level of the system, improves the management efficiency of the system and reduces the management labor intensity.

As shown in Figure 1, the control cabinet collects the pressure and temperature in the pipeline and then controls the circulation pump, water supply pump, temperature control valve, water tank level, etc.

3.2 Design of electronic control system

(1) According to the equipment operation process and controlled electrical components, arrange the PLC interface and write out the I/O address allocation table.

(2) The touch screen communicates with the PLCCOM1 port, and the printing board communicates with the PLCCOM2 port.

(3) Programming.

①Control process: After the PLC is powered on and running, first initialize the program, and set the secondary side water supply and return water pressure, temperature, primary side return water pressure and temperature, and heat exchanger outlet water temperature through the touch screen and over-temperature temperature and other control parameters. After hitting the automatic position, start the control. The program performs periodic scanning and PID control, sampling pressure, temperature and other numerical values ​​respectively. After internal calculation of the program, it is compared with the set value, and PID adjustment is performed based on the result. The calculated value gives switching and analog signals to control the water pump. Start, stop and frequency converter frequency adjustment.

② Programmable programming: The automatic control system is composed of major electrical components such as PLC, frequency converter, pressure transmitter, temperature transmitter, and liquid level transmitter. The water supply pump starts and stops under the control of return water pressure; the circulation pump operates with variable frequency, and the frequency is adjusted by the pressure difference between supply and return water; the condensate pump operates through the water level in the condensate water tank. Water replenishment pump control principle: The current signal is transmitted to the PLC through the return water pressure transmitter. Through PLC calculation, the feedback value is compared with the set value. When the pressure reaches the set lower limitWhen the pressure reaches the set upper limit, the PLC gives a signal to automatically stop the water replenishment pump; at the same time, when the water level in the replenishment tank is lower than the protection value, the replenishment pump is forced to stop.

Circulation pump control principle: The current signal is transmitted to the PLC through the return water pressure transmitter and the water supply pressure transmitter respectively. Through PLC calculation, the feedback supply and return water pressure difference is equal to the set pressure. The difference is compared. When it is lower than the set value, the PLC outputs a voltage signal to the frequency converter, and the circulation pump frequency increases linearly, and the speed accelerates; when it is higher than the set value, the PLC also outputs a voltage signal to the frequency converter, and the circulation pump The frequency decreases linearly and the rotation speed decreases; when it approaches the set value, the circulation pump runs at a constant speed.

Condensate pump control principle: The magnetic flap level gauge in the condensate water tank transmits the current signal to the PLC. Through PLC calculation, the feedback value is compared with the set value. When the water level in the water tank reaches the set upper limit, When the water level reaches the set lower limit, the PLC gives a signal to automatically start the condensation pump command; when the water level reaches the set lower limit, the PLC gives a signal to automatically stop the condensation pump command.

Example: The program in the figure below is a temperature and pressure acquisition program. First, the analog data collected in AIW0 (channel one) is transmitted to VW140, and the temperature or pressure value is obtained through calculation; in the figure The program can also detect whether the transmitter is damaged. If it is damaged, it will issue an instruction that the transmitter is damaged and please repair it. This detection function can also be canceled manually.

③Touch screen programming: This equipment uses Siemens 6AV6648-0AE11-3AX0 series touch screen, which can monitor the operating status and operating parameters of the system and equipment in real time, report equipment faults and solutions in a timely manner, and provide on-site equipment Perform operations.

4 Conclusion

The heat exchange station control system adopts PLC control technology, frequency conversion debugging technology and electronic signal technology to realize automatic control of the pressure and temperature of the heat exchange station, not only Saving equipment costs also improves the automation of the equipment, allowing the equipment to operate reliably and stably. And it can communicate through Ethernet, so that the central control room can receive various signals. It can also set parameters through the touch screen, start and stop with one button, and realize remote monitoring functions.