Introduction to the application of electric actuators in the total pollution source control system
In recent years, after the EIA has analyzed, predicted and assessed the possible environmental impacts after the implementation of planning and construction projects, the environmental protection department has introduced a management system for total pollution source control, and strictly controlled pollution source emissions from the source. Once it is confirmed that the phenomenon of exceeding the total amount has occurred, law enforcement officers immediately shut the valve through the remote end of the pollution source total control system to prevent the pollution source from spreading further. This method provides an automated solution for environmental law enforcement.
The working principle of electric actuator
Electric actuator is a combination of actuator and control valve in automatic control system. Its function in the automatic control system is to receive the signal from the regulator, and adjust the flow of the process medium with its position and characteristics in the process pipeline, so as to control it within the range required by the production process.
The structure of the electric actuator
The electric actuator consists of two major mechanisms: execution and adjustment. The controller sends a current signal to the electronic control device. The electronic control device controls the rotation and displacement of the actuator (usually a motor). When the actuator turns the valve opening to a certain position, the resistance value of the sliding rheostat is driven by a simple gear unit The resistance value of the sliding rheostat in the corresponding position is converted into a current or voltage signal by the detection unit, and the control signal is compared after feedback, until it stops rotating when it matches the current sent by the controller. This series is called Adjustment unit.
On-site installation method of electric actuator
In the total volume control system, the actuator is generally installed in the direction of the flow of the medium, usually on the same section of the pipeline as the pipeline flowmeter, and needs to be installed at the back end of the flowmeter. The reason is that the vortex phenomenon occurs when the actuator is opened and closed. It is easy to produce a certain amount of air bubbles in the pipeline. In practical installation, it is generally installed at a pipe diameter 3 times the same pipe section as the flowmeter (experience value, for reference).
Proofreading method of electric actuator
In the total pollution source control system, the actuator often exhibits angular drift during execution, which causes the environmental law enforcement personnel to be unable to accurately open and close the electric actuator. To adjust the actuator opening, only two points of correction are required, which is the same as the PH meter correction. The principle is to correct at the position of the closed position and the open position.
Operation and maintenance of electric actuators
The actuator needs to lubricate the gears, shaft joints, oil seals and other places during use. For valves that do not move for a long time, they must perform slow step-by-step opening and closing operations, which not only avoids the blocking phenomenon of the motor, but also It protects the valve body from being worn out due to excessive force.
Safe operation of electric actuators
According to national standards, AC motor overload protection should comply with the following regulations: short-time or intermittently working motors may not be equipped with overload protection, but when the motor may be blocked during operation, it should be installed to protect the motor from blocking. . In the total pollution source control system, due to the ordinary changes in sewage water quality and the high probability of motor rotor blocking, it is necessary to install a protector. Select the type of protector to skip the starting current, which is less than the locked-rotor current. The following selection recommendations for single-phase and three-phase asynchronous motors are as follows:
(1) Selection of related protectors for single-phase asynchronous motors. In the total pollution source control system project, the electric actuators used are mostly single-phase asynchronous motors, and the protector can be connected to the live phase of the installed air switch by using a ceramic fuse. Ceramic fuse has no arc and other safety measures. (2) Selection of related protectors for three-phase asynchronous motors. In the total pollution source control system project, there are a small number of three-phase electric actuators, and the lower protector of the air switch can be selected: the integration of the air switch and the AC motor starter. It is also possible to use the integrated circuit breaker, AC contactor, and external heating relay. It is recommended to use the power type specification for the MCB.
Electric actuators pay attention to safety, and specially introduce two products with different safety specifications for us to choose: (1) Explosion-proof and waterproof type. Working in places with extremely harsh environments such as petroleum and coal mines, it has explosion-proof and waterproof effects. The high level of waterproofing can achieve long-term underwater operations. (2) Common type. General chemical and other manufacturing enterprises are suitable for general use.
Advantages and disadvantages of electric actuators
Corresponding to the manual valve execution method, the electric actuator closing valve has the following advantages and disadvantages:
Advantages: (1) Efficient execution, precise control of angle. People can not go to the scene, pass the control signal of the upper computer to the lower computer through the network, and then control the valve to close the valve through the lower computer. The electric actuator can perform accurate angle closing of the valve (regulating type), or directly switch off. Valve (switch type) in two ways. The transmission of control signals through the Internet of Things has become a mainstream method in today's automation and networked fields. The signal is transmitted to the scene through the underlying transmission path of the network, which can fully achieve the effect of real-time and accuracy. (2) The torque is executed safely and the switch is convenient and quick. According to the size of the valve, the speed can be adjusted by gearboxes of different specifications, and the larger valve core can be pushed with a small force. By setting the electronic limit switch as the electronic limit, the mechanical limit is set at the same time. The occurrence of safety protection over-travel phenomenon (3) Safe electrical protection. The temperature-sensing probe is pre-embedded in the internal mechanism of the actuator as an overheat protection for measuring the actuator motor's locked-rotor; the overload alarm is turned on and off, and the internal mechanical structure switch with a certain torque is transmitted to the electric control board through an electric signal to turn on Overload and off overload are used as limit protection functions.
Disadvantages: (1) The installation environment must be good. Ordinary electric actuators need to be moisture-proof and moisture-proof at the installation site. Explosion-proof treatment is also required for special occasions. The site environment is recommended to be dry, free of flammable materials, and have a certain degree of ventilation and moisture resistance. (2) Electronic accessories are consumables. After the aging of electronic components, the accuracy is easily affected, especially for regulating products; the price of electronic accessories including program software is relatively expensive, and the failure rate occurs frequently when the operation and maintenance is not in place. The maintenance cost is high. (3) The mechanical structure is relatively complicated, installation and debugging are difficult, and it is difficult for non-professionals to assemble and maintain. An electric actuator contains a complicated mechanical structure, and the use of electronic components at key points involves two industry standards, so it is difficult for non-professionals to maintain it.
