The low-voltage control technology of the electrostatic precipitator mainly includes rapping control, insulator thermostat electric heating control, ash hopper electric heating control, ash unloading control, material level control, import and export temperature display, high-voltage isolation switch in place display, and remote communication, etc.
Electrode rapping and dust removal is the main working process of the electrostatic precipitator. The dust removal effect is not only related to the rapping acceleration applied on the cathode and anode, but also the rapping cycle has a great influence on it. The traditional rapping method is tangential rapping, and its control can be divided into continuous rapping and timing rapping. When the strength and uniformity of the rapping meet the requirements, whether the rapping system is reasonable has a great impact on the dust removal efficiency of the electrostatic precipitator. The dust collected on the anode plate cannot fall into the ash hopper when the rapping is too frequent, and the secondary flying is serious, especially the secondary flying of the final electric field, which will greatly reduce the dust removal efficiency. On the contrary, if the rapping period is too long and the dust accumulation on the anode is too thick, the voltage between the anode and the cathode will be reduced, the secondary current will be reduced, the corona power will be reduced, and the dust removal efficiency will be reduced; , So that the dust that has been collected on the anode plate enters the air flow again. Therefore, choosing a reasonable rapping period will help to better clean the dust and improve the dust removal effect.
1.2 Unloading control system
After the dust that enters the electrostatic precipitator is captured by the cathode and anode, it will fall into the ash hopper by the rapping system. These ash materials should be discharged in a timely manner. The ash materials are accumulated too much, which will increase the load of the ash hopper. This causes a short circuit between Yin and Yang, which makes the electrostatic precipitator unable to operate normally. On the contrary, the ash hopper has no ash storage, and air leakage occurs at the ash hopper outlet, causing secondary dust and reducing the efficiency of dust removal.
1.3 Extreme heat control system
The objects of the heating control system include beam electric heaters, female porcelain shaft electric heaters, and ash hopper electric heaters. The commonly used control strategy is to control the electric heater with constant temperature according to the temperature signal of the temperature measuring device. When the temperature is lower limit, start the electric heater heating; when the temperature is higher than the upper limit, stop the electric heater heating.
2. Application examples of low-voltage control system of electrostatic precipitatorThe dust removal room of the low-voltage control system used by a factory in Shandong adopts the three-electric field dust removal method. The three electric precipitators have 6 rapping motors, 3 ash hopper heating controllers, 3 beam heating controllers, and 3 ash unloading motors. In addition, the alarm signal output terminal, hot air motor control, total start, fault removal, 3 electric field level meter detection inputs, beam ash hopper and other temperature, control, etc., total 20 points of digital output, 23 points of digital input , 8 points of analog input, 6TC temperature measurement input.
Based on the above calculation, the low-voltage control system of the electrostatic precipitator uses our company's CPU-224A as the main control part. The PLC module layout is shown in the figure below
Among them, the CPU224A module accepts the fault signal of the motor drive protector, the fault signal of the electric heating protection controller, the temperature signal of the temperature acquisition processor, the level signal and the electrical signal of the ash conveying and unloading equipment. After analysis and processing, according to the process flow The control signals such as the control rapping motor, heater, alarm, etc. are output to the corresponding external equipment. The digital input/output module EM223 outputs the signal of the CPU module to control the ash unloading motor to the corresponding external equipment. The analog input module EM231 sends the relevant signals of the high-voltage silicon rectifier equipment, the inlet and outlet flue gas temperature from the temperature collector, and the temperature signals at the beam, porcelain shaft, ash hopper, etc., to the CPU module for analysis and processing.
Third, the software design of the low-voltage control system of the electrostatic precipitator3.1 Rapping control design
According to many years of operating experience of the low-voltage control system of the electrostatic precipitator, in order to improve the dust removal efficiency of the electrostatic precipitator and effectively reduce the power consumption, the following requirements are made for the optimized control of the local rapping motor:
Cathode and anode rapping cannot be performed simultaneously in the same electric field;
In the multi-electric field dust collector, the front and rear electric field anode (or cathode) rapping cannot be performed at the same time;
For the electrostatic precipitator provided with the rapping slot plate, the final electric field anode rapping and the slot plate rapping cannot be performed at the same time.
3.2 Heating work
The heater adopts constant temperature interval control, that is, the upper and lower amplitudes of the set temperature are used as the working interval to control the start and stop of the heater. When the measured temperature is lower than the set temperature and the lower deviation of the set temperature, the heater starts to work. When the measured temperature is higher than the upper deviation of the set temperature, the heater stops working until the measured temperature is lower than the set temperature. When the temperature deviates, the heater starts heating again, cyclically, and complete temperature control.
3.3 Design of ash unloading control
The ash unloading method of the electrostatic precipitator can be divided into timing automatic ash unloading, automatic ash unloading at the upper and lower material positions and automatic ash unloading at the loading position. In this system, the control method of "high material level + time sequence" is adopted, that is, a comprehensive way of combining high material level timing ash unloading and periodic ash unloading. The so-called high-level ash unloading means that when the low-voltage control system detects a certain loading level signal, the corresponding ash unloading device is first activated; when the device has been working for a certain period of time, it will delay for a period of time to stop the corresponding ash conveying interlock system . In order to avoid the occurrence of level gauge damage or false alarms causing ash blockage in the electric field, a timer period ash unloading function is added to ensure that the system can automatically unload ash.
Four, concluding remarksThe low-voltage control system designed by OYES-200 series PlC is used to control the functions of rapping motor, ash unloading motor and auxiliary heating. It can give full play to the reliability and anti-interference ability of PLC. It has simple, flexible and external wiring. The software is easy to modify and easy to meet the advantages of various specific process requirements.
OYES-CPU224A, 2 communication ports, 24K program space, 10K data space, 14DI/10DO, expandable to 3 IO modules, is our company’s key product for market promotion. It is more and more popular with customers due to its superior cost performance. Favor.
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