Problems and development directions in the application of control valves
1. Problems in the application of control valves
① There are many varieties, specifications and parameters of regulating valves.In order to meet the control requirements of different industrial production processes, such as temperature, pressure, medium characteristics, etc., the regulating valve has nearly a thousand different specifications and different types of products.Control valveInconvenient model selection, inconvenient installation and application, inconvenient maintenance, and inconvenient management.
②The reliability of the regulating valve is poor.The characteristics of the control valve when it leaves the factory are quite different from the characteristics after a period of operation. For example, increased leakage, increased noise, poor valve reproducibility, etc., bring difficulties to long-term stable operation.
③ The regulating valve is bulky, which brings inconvenience to the transportation, installation and maintenance of the regulating valve.Usually, the weight of the regulating valve is several to hundreds of times heavier than the weight of a general instrument. For example, a DN200 regulating valve weighs 700kg. Transportation, installation and maintenance require the use of some mechanical equipment to complete the application of the regulating valve. Inconvenient to come.
④ The flow characteristics of the regulating valve do not match the characteristics of the controlled object in the industrial process, which causes the quality of the control system to deteriorate.The ideal flow characteristics of the regulating valve have been determined when the product leaves the factory, but the characteristics of the controlled objects in the industrial process are different, and the pressure drop ratio on the power port changes, so that the working flow characteristics of the regulating valve cannot match the characteristics of the controlled object, and the control system controls The quality has deteriorated.
⑤The noise of the regulating valve is too loud.In industrial applications, the control valve noise has become the main noise source of industrial equipment. Therefore, reducing the control valve noise has become an important research topic at present, and has attracted the attention of governments all over the world.
⑥Regulating valves are energy-consuming equipment. At the time when energy is increasingly scarce, energy-saving technologies should be adopted to reduce the energy consumption of the regulating valve and improve the utilization rate of energy.
2. The development direction of the control valve
The development direction of the control valve is mainly intelligent, standardization, miniaturization, rotation and safety.
(1) Intelligence and standardization. The intelligence and standardization of control valves have been on the agenda.Intelligence mainly uses intelligent valve positioners.Intelligence is manifested in the following aspects.
①The intelligent functions such as self-diagnosis of the regulating valve and remote communication of the running status make the management of the regulating valve convenient and the fault diagnosis easier, and it also reduces the skill requirements of the maintenance personnel.
②Reduce product types and simplify the production process.The use of intelligent valve positioner can not only easily changeControl valveThe flow characteristics can also improve the control quality of the control system.Therefore, the requirements for the flow characteristics of the regulating valve can be simplified and standardized (for example, only the linear characteristic regulating valve is produced). The intelligent function module is used to match the characteristics of the controlled object, so that the types and varieties of regulating valve products are greatly reduced, so that The manufacturing process of the regulating valve has been simplified, and has been tested and approved in production and the market.
③Digital communication.Digital communication will be widely used in control valves. Based on the HART communication protocol, some valve positioners for control valves implement the input signal and valve position signal on the same transmission line; based on fieldbus technology, the control valve and the valve positioner , The combination of PID control function modules enables the control function to be realized at the field level, disperses the danger, and makes the control more timely and faster.
④ Intelligent valve positioner.The intelligent valve positioner has all the functions of the valve positioner, and at the same time can improve the dynamic and static characteristics of the regulating valve, and improve the control accuracy of the regulating valve. Therefore, the smart valve positioner will become an important regulating valve auxiliary equipment in the future. widely used.
The standardization of the control valve is manifested in the following aspects.
①In order to achieve interchangeability, the control valves produced by different manufacturers of the same size and specifications can be interchanged, so that users do not have to spend a lot of time in choosing a manufacturer. ②In order to achieve interoperability, regulating valves produced by different manufacturers should be able to work with other manufacturers' products without signal mismatch or impedance mismatch. ③Standardized diagnostic software and other auxiliary software, so that control valves of different manufacturers can perform operating status diagnosis and operating data analysis.
④Standardized selection procedure.Control valveModel selection is still a matter of great concern to automatic control designers. Using standardized calculation procedures and according to the data provided by the process, the flow coefficient of the required regulating valve can be correctly calculated, the piping can be determined, and the appropriate valve body, valve core and valve trim can be selected. Material, etc., standardize the design process and improve design quality.
(2) Miniaturization. In order to reduce the weight of the regulating valve and facilitate transportation, installation and maintenance, the following measures are adopted for the miniaturization of the regulating valve.
①Using fine and small actuators.Lightweight materials are used, and multiple sets of springs are used instead of one set of springs to reduce the height of the actuator. Generally, the height of the regulating valve composed of a small pneumatic diaphragm actuator is about 30% lower than that of the same type of pneumatic diaphragm actuator. It is reduced by about 30%, and the circulation capacity can be increased by about 30%.
②Change the flow path structure.For example, changing the movement of the valve core to the movement of the valve seat, changing the linear displacement to angular displacement, etc., reduces the volume and weight of the regulating valve.
③Using electric actuators.It can not only reduce the air source device and auxiliary equipment required by the pneumatic actuator, but also reduce the weight of the actuator.For example, Fisher's 9000 series electric actuators have a height of 20 type less than 330mm, which reduces the quality of the entire regulating valve (with digital controller and actuator) to 20～32kg. Ball valves, etc., have the advantages of relatively small size, small flow path resistance, relatively large adjustment, better sealing, better anti-blocking performance, and greater flow capacity. Therefore, among the new varieties of control valves, the rotary valve The proportion increases.Especially in large-diameter pipelines, ball valves, butterfly valves and other types of regulating valves are commonly used. From the perspective of foreign products in recent years, the proportion of rotary valve applications is increasing year by year.
(4) The safety of the safety instrumented control system has received attention from all aspects, and the safety instrumented system (SIS) has higher and higher requirements for the regulating valve, which is reflected in the following aspects.
①The diagnosis and processing requirements for the fault information of the regulating valve are increased, not only the passive maintenance of the regulating valve after the fault occurs, but also the preventive maintenance and the predictive maintenance before the fault occurs.Therefore, it is more important to conduct statistics and analysis on the relevant components that make up the regulating valve, and to make maintenance suggestions in time.
②For regulating valves used in emergency shutdown systems or safety interlocking systems, requirements for timely, reliable and safe actions are put forward.Ensure that these regulating valves can respond sensitively and accurately.
③For regulating valves used in hazardous locations, the certification procedures should be simplified.For example, fieldbus instruments for intrinsically safe applications can be simplified to adopt the concept of FISCO fieldbus intrinsically safe, which simplifies the certification process for intrinsically safe products.
④Similar to the safety of other field instruments, for the safety of regulating valves, explosion-proof technology \ fireproof technology, increased safety technology, intrinsic safety technology, non-sparking technology, etc. can be used; for fieldbus instruments, physical concepts, Intrinsically safe concept, FISCO concept and non-flammable (FINCO) concept, etc.
(5) Energy saving, reducing energy consumption, and improving energy utilization is a development direction of control valves.There are mainly the following development directions.
①Adopt the control valve with low pressure drop ratio.Reduce the proportion of the regulating valve in the pressure drop of the entire system, thereby reducing energy consumption. Therefore, designing a regulating valve with a low pressure drop ratio is one of the development directions; another development direction is the use of low impedanceControl valve, For example, butterfly valves, eccentric rotary valves, etc. are used.
②Using self-operated regulating valve.For example, directly use the pressure of the medium behind the valve to form a self-operated control system, and use the energy of the controlled medium to achieve pressure control after the valve.
③Adopt the regulating valve of electric actuator.Pneumatic actuators need a certain amount of air pressure during the entire operation of the regulating valve. Although a small consumption amplifier can be used, the air consumption is still huge over time.Electric actuators are used. When changing the opening of the regulating valve, power is required, and when the required opening is reached, power is no longer supplied. Therefore, from the perspective of energy saving, electric actuators have obvious advantages in energy saving than pneumatic actuators.
④Piezoelectric control valve is used.The piezoelectric regulating valve is used in the intelligent electric valve positioner, and the air source is consumed only when the output signal increases.
⑤The valve core with a balanced structure is adopted to reduce the thrust or torque of the actuator, reduce the air chamber of the membrane head, and reduce the energy demand.
⑥Adopt frequency conversion speed regulation technology instead of regulating valve.For high-pressure drop ratio applications, if the energy consumption is large, the frequency conversion speed regulation technology can be used, and the frequency converter can be used to change the speed of the relevant operating equipment to reduce energy consumption.
(6) Protecting the environment Environmental pollution has become a public hazard. The main environmental pollution caused by the regulating valve is the noise of the regulating valve and the leakage of the regulating valve.Among them, the environmental pollution caused by the noise of the regulating valve is very serious.
①Reduce the noise of the regulating valve.Develop various methods to reduce the noise of the control valve, including from the design of the control valve flow path to the design of the control valve trim, from the analysis of the noise source to the measures to reduce the noise, etc.Mainly include designing noise reduction control valve and noise reduction control valve internal parts; reasonable distribution of pressure drop, use of external noise reduction measures, for example, increase isolation, use muffler, etc.
②Reduce the air pollution of the regulating valve.The air pollution of the regulating valve refers to the "running", "running", "dripping" and "leaking" of the regulating valve. These leakages not only cause waste of materials or products, but also cause pollution to the atmospheric environment, and sometimes cause personal damage. Accidents such as casualties or equipment explosions.Therefore, the development of regulating valve packing structure and packing type, and the development of regulating valve sealing will be an important research topic for regulating valves in the future.The development of high-tech science and technology such as computer science, control theory and automation instrumentation has promoted the development of regulating valves, for example, the development of fieldbus regulating valves and intelligent valve positioners, and the realization of digital communication in regulating valves.The development of control valves has also promoted the development of other science and technology, such as research on anti-corrosion materials, research on methods of attenuating and reducing noise, and research on fluid dynamics.With the development of fieldbus technology, the regulating valve will also be open, intelligent and more reliable. It will have a higher degree of connection, the control effect will be more obvious, and it will play a more important role in the modernization of our country. Other industrial automation instruments and computer control devices At the same time, it makes the function of industrial production process control more perfect and precise.