With the development of the times, computer automatic control technology has been applied to every corner of life and production. Many industrial manufacturings have begun to use fully automatic or semi-automatic production lines to improve production efficiency. In the process of manufacturing industrial gas, the traditional production mode can no longer meet the contemporary production needs. This design applies the automatic control system to the process of industrial gas. This article first introduces the historical background of this design, then briefly introduces the composition and work flow of the air separation device designed in this design, and finally introduces this design from three aspects: the design of the measurement and control system, the design of the anti-surge control valve, and the control logic design of the anti-surge control valve.
Contents
1 Overview
2 Composition of air separators based on DCS automatic control systems
3 Design of air separation device based on DCS automatic control system
3.1 Design of measurement and control system
3.2 Anti-surge control design
3.3 Control logic design of anti-surge control valve
4 Conclusion
1.Overview
Air separation devices are instruments that liquefy air to obtain the required gas, and are mainly used to produce industrial gas. As the precision requirements of the processing industry become higher and higher, people's requirements for details of the processing industry are becoming more and more stringent. Conventional instruments can no longer efficiently produce industrial gases that meet the requirements of contemporary industrial processing. After years of research and development, the application of DCS systems in air separation technology has become more and more mature, and can efficiently produce industrial gases that meet the requirements.
2.Composition of air separators based on DCS automatic control systems
The air separation device based on the DCS automatic control system is mainly composed of air precooling device, compressor unit, fractionation device and air purification device. Taking the air oxygen generator as an example, it is composed of air expansion system, oxygen compression system, air compression system, molecular filtration system and cooling system. When running, the air is purified first, and then refrigerated.compression system, a molecular filtration system and a cooling system. During operation, the air is first purified, and then refrigerated and extracted.
3.Design of air separation device based on DCS automatic control system
3.1 Design of measurement and control system
The DCS control system is a comprehensive control system that supports multiple control bus standards and is compatible with multiple bus devices such as I/O and FF. Generally speaking, air separation devices prefer to use AC800F-level controllers and Profibus as bus control devices. The design concept includes additional functional designs such as power supply configuration, controller selection, and control station design. In the entire workflow, the equipment monitors and controls air compression, boost compression, nitrogen compression, and other processes through Ethernet. The AC800F model controller consists of multiple units, including a basic unit, a power module, a network module, and a bus interface. In this research center, the basic unit is PM802F, the power supply is SA801F, the Ethernet card is EI803F, and the bus interface model is FI830F. The control of other functions of the control device is composed of two bus control devices. The bus controller includes two network cards for wireless connection and communication between the controller and the system network and between network cards. According to actual needs, this design needs to use 3 I/O stations, each with 12 slots, to connect various master stations and other modules. In this design, the 3 I/O stations are S800I/O stations, and the network card module is mainly EI803F. The BENTLY3500 vibration coefficient monitoring system is used to monitor the axial displacement and radial vibration of the gas machine to achieve mechanical protection. The whole machine can switch the sequence of molecular sieves, control operation and automatic temperature adjustment, prevent compressor surge and related safety control. Moreover, the entire workflow is monitored through Ethernet, which is not only convenient and effective in management, but also ensures the synchronization of information between devices.
3.2 Anti-surge control design
In order to prevent the air separation unit from surging during operation, we generally need to set a return valve or a vent valve during the design process to prevent the occurrence of surge. The anti-surge control principle is that when the compressor is operating normally, its speed remains constant, but when an accident occurs, its operating speed changes in line with the adjustable blades, and the anti-surge control valve will automatically open. The controller will reduce the flow until it is reduced to a given minimum value. This minimum value needs to be determined based on the given value of the control line and is the main basis for anti-surge design. During design, it is necessary to perform anti-surge design based on this minimum value to calculate the pressure inside the machine. During the operation of the air separation unit, the equipment controls the flow by adjusting the anti-surge control valve, and ensures that the flow is below the safety line according to the value set in the control program to ensure the normal and effective operation of the equipment.
3.3 Control logic design of anti-surge control valve
In the process of anti-surge design, the anti-surge design is mainly carried out by controlling its backflow or venting volume to ensure the normal operation of the equipment. In order to ensure the normal operation of the anti-surge system, the control logic of the anti-surge control valve should be designed in the design process. When designing the control logic, the following points should be made clear first:
(1) When the proportional band constant of the inlet flow of the air compressor is 140.0, its integral constant should be guaranteed to be 2.0, that is, to ensure that its inlet flow meets FIC1110.
(2) The pressure value at the second outlet and the output value of the manual control are controlled to meet PIC1110, and the signal sent by the controller is set to a gradual signal to ensure the normal operation of the unit.
In the process of designing the control logic, the position of the air compressor operating point is calculated and analyzed by the actual flow and the flow value given by the control line, and the surge distance is calculated by FIC110. During the operation of the air compressor, once the monitoring instrument detects that the operating point of the air compressor is above the control line, the information will be fed back to the control center, and the controller will control the flow and ensure that the translation amount is DES+1. When the anti-surge compressor is working on the safe side of the anti-surge control line, that is, when the compressor is operating normally, the controller controls the anti-surge control valve to close. Once the compressor exceeds the safety control line, the controller will control the anti-surge valve to open at the FIC1110 control line and ensure that the operating point of the compressor is within the safe range.
4 Conclusion
This paper studies the design of air separation equipment based on DCS control. When designing this equipment, the design of the measurement and control system, the design of the anti-surge control valve and the control logic design of the anti-surge control valve should be taken into consideration at the same time. The air separation device of the DCS control system designed this time has great advantages over the traditional air separation device. It is not only simple and convenient to operate and has stable performance, but also has a very high degree of automation and self-adjustment function. The design of automatic anti-surge adjustment not only solves the inconvenience caused by equipment surge, but also improves the working stability and work efficiency of the equipment. In addition, the air separation device designed this time is very practical. Its simple integrated operation mode is simpler to operate and has a lower failure rate than traditional air separation machines, which can meet the needs of production and industrial development in contemporary society.
