The use of air-jet looms in cotton textile companies is an important auxiliary project. The main equipments for all air pressure stations in the Tianjin Textile Park are centrifugal air compressors and refrigerated air dryers. Compressed air supply systems are made up of gas storage tanks, connecting pipes and valves, and are equipped with cooling systems and instrument air systems. , Computer detection system to achieve the air compressor station for the production line to ensure different pressures, different loads of gas demand. Under this premise, ensuring the qualified air supply quality, satisfying the stable air source pressure, and automatically adjusting the air supply flow are the basic tasks for automatic control of the air compressor station. With the continuous improvement of the level of automation, the discussion on the construction of unattended air compressor stations is an inevitable task in the development process.
Necessity of automatic control of air system
It is applied to the air compressor station of Tianfang Investment Holdings Co., Ltd. Cotton Spinning Plant. It is equipped with 4 sets of 70M3/min 4 sets, 53M3/min 4 sets, 48M3/min 2 sets, 43M3/min 4 sets of centrifugal air compressors and 1 Taiwan 42.5M3/min screw air compressor, with a corresponding processing capacity of the freeze dryer. The CMC controller of the air compressor equipment can automatically control and protect the operation of the host, automatically prompts the work information, has a fault alarm and protection shutdown function, can automatically load or unload according to the size of the air consumption, and is equipped with an LCD display. Screen for on-site observation of the process parameters and equipment status, with RS422/485 communication interface, can achieve complete connection with the site control room computer monitoring system.
At present, the automatic control system of the air compressor station uses the Siemens S7-300 programmable controller to collect part of the real-time operating data of the air compressor through the RS422/485 communication interface into the PLC control system, and transmits the data to the on-site control room computer. Display to replace traditional meters. However, there is no control of the air compressor.
The CMC controller that comes with the air compressor equipment can already control a single air compressor, but it does not have the ability to control the air compressor system as a whole. In the air pressure system, compared to the adjustment of a single air compressor, the overall automatic regulation of the air pressure system has more important significance:
â– A single air compressor cannot guarantee the stability of the overall air supply pressure of the air pressure system, and the overall automatic control of the air pressure system can effectively keep the air pressure in the system stable.
â– Overall load balancing, reducing exhaust venting, can save more energy and save labor costs.
â– It can realize unmanned operation, automatically start or load air compressor according to actual needs to maintain system pressure.
â– Can record air compressor operating data and alarms intermittently at regular intervals, such as jumping, surging, communication faults, and pressure.
In the existing PLC system, the overall control function of the air compressor system has not been realized. Since the CCM controller provided with the air compressor provides RS422/485 communication interface, all data acquisition and control functions are realized through the communication interface. Compared with the original control system, there is no need to increase investment in hardware equipment, only need to improve And add control software to achieve the overall control of the air compressor system.
In addition to the air compressor equipment, it is also possible to integrate the freeze dryer, which is provided with the air compressor, into the RS422/485 network to achieve full automatic control of the air pressure air supply equipment.
Automatic control of other systems of the air compressor station In addition to the air pressure supply system, other systems of the air compressor station also need to be automatically controlled, such as a water circulation cooling system. The control methods of these systems are different from those of air-pressure supply systems, which mainly adopt the traditional control mode. Use the instrument to collect the required operating parameters, perform data processing and analysis operations, and output the control signal to the actuator to achieve automatic control of the system.
Automatic control has the following advantages:
â– Easy to operate, unattended;
â– Good real-time adjustment to prevent human factors from lagging;
â– High reliability
â– Reduce the burden on staff;
â– Save on labor costs.
Required control parameters and possible control methods Required control requirements for the air compressor station; (1) High and low pressure supply pressure control (automatic start-stop control of the unit); (2) Automatic drainage control of the system; (3) Recirculating water level control and automatic dosing control (4) The required compressed air temperature, circulating water temperature and other parameters are controlled.
The overall automatic regulation of the air pressure system can generally be achieved using one of the following two methods:
(1) PLC system is used for communication and control.
(2) Ingersoll-Rand or its own control software can be used.
The first method is highly reliable and suitable for industrial control systems. When the monitoring computer fails, the PLC can also automatically control according to the set program.
The second method is controlled by the computer of the control system for individual analysis and calculation. It has better flexibility, but the disadvantage is that if there is a failure such as a computer crash, it may affect the normal operation of the system. Fortunately, the general recovery of computers often does not require too much time.
In addition to the automatic control of the air supply system, the air compressor station can establish the equipment control network together with the refrigeration station and the heat station system, realize centralized control, or be networked with the plant control center, real-time remote monitoring by the controller of the control center. Unattended.
System Configuration For the above discussion, if you need to achieve the overall control of the air compressor station, many mature PLC automatic control systems can be selected, and now take the example of the PLC automation system of ZH.
The automatic control system uses Siemens S7-300 series programmable controllers, with RS422/485 network interface, supporting MODBUS and other related network communication protocols. The system can use a dedicated industrial communication network technology to implement remote networking. Air compressor station automatic control equipment can be based on the actual production situation and the characteristics of each device, as well as possible problems, the establishment of a hierarchical control network implementation plan, as shown in Figure 1.
â– Hardware configuration Field instrumentation, controlled equipment, actuators, equipment with serial communication interfaces (such as air compressors, freeze dryers, etc.), PLCs, and monitoring computers.
â– The software function selects the special industrial configuration software (such as WINCC or iFIX) to monitor and operate the entire production process, provide the control system with the functions of communication, display and report management. Each device controller is a self-contained subsystem and its application Program features include: information acquisition, device control, fault alarms, interlock protection, and data processing and communications.
In the process of system implementation, fault detection and fault diagnosis procedures can also be introduced, which can increase the degree of intelligence of the system, help to further improve the effectiveness and reliability of the automation system, optimize the scheduling strategy, and automatically control the software chain protection. The application of functional modes is expected to raise the level of automation to a higher level, providing a basis for determining the state of maintenance of air compressor equipment, and thus obtaining greater benefits.
Conclusion In conclusion, through automated control, it is possible to overcome the unfavorable factors such as lag in adjustment caused by human factors, reduce the fluctuation of operating parameters, and achieve the goal of reducing labor and energy conservation. It is very important to upgrade the overall technical level of Tianfang Holding Co., Ltd.