Abstract: This article briefly describes the scheme adopted by Rui Qianyuan Automation Co., Ltd. for frequency conversion of a boiler in a science and technology park. Siemens MM4 series inverters are used to control the blast and induced winds of the boiler to achieve manual open-loop/automatic closed-loop operation.
Control object: Including 6-ton steam boiler, blower motor and inducer motor.
Equipment parameters: Motor parameters at customer site: Blower motor power: 5.5 KW Lead wind motor power 18.5 KW
Control Objectives: To reform and form a good combustion conditions, improve the boiler combustion efficiency, reduce energy consumption and reduce emissions.
Frequency conversion control system design work principle:
This system can realize open/closed loop operation:
1. Wind control:
Through the negative pressure transmitter on the hearth, the standard electric signal of the hearth pressure is sent to the feedback channel of the PID controller of the induced-winding inverter. After processing, it is compared with the negative pressure of the set hearth and the PID controller generates the operation signal. This signal controls The inducer inverter regulates the motor speed to stabilize the negative pressure in the furnace at the set value, so as to achieve the purpose of automatically tracking the blast to keep the negative pressure of the furnace constant. The wind speed of the wind turbine changes with the change of the negative pressure of the hearth. That is to ensure the automatic operation of the boiler combustion part.
2. Blower control:
Through the pressure transmitter on the steam pipeline, the standard electric signal of the required steam pressure is fed into the feedback channel of the PID controller of the blower frequency converter. After being processed and compared with the set steam pressure value, the PID controller generates an operation signal. The signal control blower frequency converter regulates the motor rotation speed so that the pressure on the steam pipeline is basically stabilized at the set value so as to automatically track the pressure on the steam pipeline.
3. Since the original boiler is a non-energy-saving combustion method, the control of the air volume depends on the manual operation of the air baffle, and the steam pressure alone cannot be controlled by the manual combustion. Therefore, the amount of wind generated by the full-speed operation of the motor cannot be fully used, and about 30% of the power loss is caused by the baffle cutoff. The inverter can be used to adjust the motor speed according to the production requirements, so that the output air volume can be adjusted to improve the production efficiency and save energy and reduce consumption.
The frequency converter adopts Siemens MM430 series. The starting method of the control system is external remote manual control.
Speed ​​mode:
1: To control the speed of the motor by operating the external remote up/down button according to the production conditions.
2: The inverter switches to the automatic PID operation mode through the terminal BICO connection.
3: The system can also realize full open-loop operation, manual control and speed regulation can be realized through the start-stop button and potentiometer on the control cabinet or on-site operation box.
The main chain of the system:
1. Blower operating conditions: The blower is allowed to start running only when the induced draft fan is put into operation.
2. Frequency and industrial frequency chain. Frequency conversion operation with the original old frequency operation, chain control system.
3. When the frequency conversion system fails during operation, sound and light alarm signals are issued to remind the on-duty personnel to handle the problem at the right time.
System Components:
1. Principle of Boiler Frequency Conversion Control System
Configuration: GGD control cabinet 2200×1000×600
Blower frequency conversion power: MM430-7.5 KW induced wind frequency conversion power MM430-22KW
See below:
Frequency conversion control cabinet technical parameters and performance characteristics:
1. The main technical parameters:
(1) Main loop power supply: Three-phase five-wire system. 380V+10%.
(2) Control circuit voltage: 220V
(3) Vacuum pressure sensor adjustment range: To ensure the establishment of a full combustion system.
(4) Adjustment range of steam pressure sensor: It depends on actual production requirements.
2. System performance characteristics:
(1) Operation mode selection switch: frequency conversion and power frequency interlocking, power frequency operation is the original control system, frequency conversion and power frequency conversion by the transfer switch, and interlock protection.
(2) Under the variable frequency mode - Local/Remote - Select switch: Realize the local potentiometer manual speed regulation. Inverter PID closed-loop speed control.
(3) Variable frequency soft start: The motor is started by the inverter. The motor voltage adopts digital automatic slope compensation technology. When the motor is slowly increasing, the mechanical impact of the system is small, which can significantly prolong the service life of the electronic control element and fan machinery.
(4) It has perfect motor and inverter's own protection function: motor under voltage, regenerative over voltage, over current, overload, short circuit, overheat protection and so on.
(5) Cabinet meter display functions such as power supply voltage and motor current. Inverter running status indicator display function. And can transmit the speed of the frequency converter and the running current of the electrical machinery to the DCS monitoring system in the form of 0-20mA standard analog quantity.
(6) Inverter fault alarm indication, switch quantity transmission and remote reset function.
The main debugging parameters of the inverter:
