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Application of intelligent valve positioner in engineering practice

The advantages of a smart valve positioner
1) Improve the performance of the regulating valve and control system
The intelligent valve positioner has high control precision and can achieve precise control of the regulating valve, thus improving the control level of the system. In addition, the intelligent valve positioner can easily set the valve characteristic curve, such as the equal percentage characteristic, the Siemens PS2 series provides 1:25, 1:33, 1:50 three characteristics, ABB's TZID series provides 1:25, 1 : 50 two characteristics, Yamatake provides one. In addition, if the user is not satisfied with the valve characteristics of the positioner or has special requirements, the custom characteristic curve can be set by the custom characteristic curve function. Siemens and ABB each offer a 20-segment curve setup, and Yamatake offers 15 segments of curves.
2) Save gas, save energy and cost
We demand continuous integration with the international market, but why is the cost of the famous international petrochemical company well controlled? After so many years of hard work, China still has a big gap with the world's advanced level? From a small point of view, we did not calculate the economic account when we did the project. Taking the instrument wind as an example, the minimum energy consumption of a standard instrument wind is 1.6MJ, the first electricity is 3.6MJ, and the industrial electricity is generally 1 yuan/degree. It does not consider the cost of water removal, dust removal, equipment investment and instrumentation wages. The average production of a standard instrument wind is 0.44 yuan. Domestic locators and some intelligent locator manufacturers, for technical reasons, consume a lot of air per hour. In general, the steady-state air consumption of these products is 350 liters / hour. For Siemens PS2 (steady-state air consumption of 36 liters / hour) and ABB's TZID series (steady-state air consumption of 30 liters / hour), it can save 0.3 mark / hour under normal conditions. The annual fuel consumption is 0.3X24X365=2628, which is converted into RMB cost, so the energy saving can save 1156.32 RMB/year. Considering various costs, a Siemens intelligent valve positioner can save at least 1,300 RMB/year per year. For large petrochemical enterprises, the number of positioners is hundreds of units, with 1000 units as an example. Save 1.3 million. However, due to the low investment pressure of existing engineering construction in China, most of the projects use ordinary locators. Although the one-time investment is small, the production and operation maintenance and various consumption are very large. As a result, from the time of 3 to 5 years, the total cost is rather large, but the performance is generally the same.
3) Save gas and keep the pressure on the public network stable
For large petrochemical enterprises, because of the large number of gas points, the gas consumption is very large. At the end of the device or away from the air compressor station, the instrument wind pressure is very low, sometimes it can not even push the regulating valve to work normally, and can not meet the normal safety of the device. produce. If the intelligent valve positioner with low air consumption is used, the total air consumption is greatly reduced due to the small amount of air consumption, thereby maintaining the stability of the instrument wind network pressure and ensuring safe and reliable production of the device.
4) The initialization process is very simple
For most smart valve positioners, the initialization process is basically very simple. Taking the Siemens PS2 as an example, the initialization process can be completed automatically by simply pressing the 4 button and setting a few simple parameters. It is more convenient to upload the set parameters to the computer, and then download and batch copy to the positioner of the same working condition, which greatly saves manpower and time, especially when the new device is started or overhauled. .
5) Intelligent communication method
The most obvious feature of intelligent valve positioners is intelligent communication. For our process industry, the most common is HART communication, or PA fieldbus, or FF fieldbus. But not all smart valve positioners support the above communication methods. The Siemens PS2 intelligent valve positioner, which is used in many petrochemical enterprises, not only supports the above communication protocol, but also can perform AMS communication. In practical engineering applications, if HART communication is used (most commonly, other communication methods are also available), all the parameter information of the whole plant's intelligent valve positioner can be saved to the computer through the corresponding software and hardware. The terminal cannot be implemented. When the maintenance or replacement of the intelligent valve positioner is required, the instrument parameters can be conveniently retrieved from the information base and quickly downloaded to the valve positioner, which greatly saves labor time and cost, and is no longer saved. A lot of information is ruined.
6) Binary input, interlock switch valve
For intelligent valve positioners, most of them have self-protection interlocking function. ABB's valve positioner can be self-locking in the event of a power failure. Siemens PS2 can also self-lock or switch valves as required when the signal is broken. These locators also accept the input of external interlock signals while having the above functions. Although these chain action responses are not on the order of milliseconds, for many process industries, a chain of seconds is sufficient. For example, the chain of heating fuel oil valves. At the same time, the millisecond chain with high security level requirements is set separately in the design regulations and is not allowed to be placed together with the control loop. Therefore, it is not practical to require the interlock of the intelligent valve positioner to reach the millisecond level.
7) Quickly and easily set the split adjustment
According to the actual needs, the engineering design needs to control two or more regulating valves with one input signal, which requires the valve positioner to respond only to a certain range of the input signal. With the example of the Siemens PS2, it is convenient to set the start and end points of the split adjustment by software or manually.
8) Rich fault diagnosis function
The fault diagnosis function is a very important function of the intelligent valve positioner. In the actual start-up or commissioning process, we will encounter a variety of problems. How to correctly judge and solve these problems is very important for the normal and safe production of the device. For intelligent positioners, diagnosing valve leakage, valve packing, valve wear, etc., is a function provided by most intelligent positioner manufacturers. However, some manufacturers provide little or no function, so be sure to read the samples and consult the manufacturer when selecting the model.

Second, the choice of intelligent valve positioner
In engineering design, we must carefully select the appropriate intelligent valve positioner, paying attention to the following points:
1) Requirements to meet the on-site conditions and achieve intelligent requirements
We use intelligent valve positioners to get their intelligent functions and improve overall control performance. Therefore, intelligentization is an important indicator for us to meet the conditions of the site. Intelligence includes its communication capabilities, online or offline troubleshooting capabilities, and more.
2) It is convenient to request on-site operation
For some intelligent valve positioner products, due to the complicated setting, the effect of the product in actual use is affected. Therefore, we prefer products that are easy to operate.
3) Requires cost-effective, energy saving and cost saving
In addition to considering the investment of the instrument, we must also consider its operating costs. From the time period of 3 to 5 years, which product has high comprehensive performance, we choose which product.
4) Request on-site display
For some smart valve positioner products, since there is no on-site liquid crystal display, it must be adjusted by the hand-held device during field adjustment. This adds to the cost. In addition, for LCD liquid crystal display, pay attention to its display effect at extremely low ambient temperatures.
5) Requires the normal operation of remote installation in some cases
Since large petrochemical enterprises are now adopting more and more joint control rooms, the distance from the control room to the on-site intelligent valve positioner may be very far. The problem of cable voltage drop must be considered, otherwise the intelligent valve positioner will not work properly.

Application examples of three intelligent valve positioners in engineering practice
During the construction and operation of the plant, the regulating valve will produce various faults due to various reasons of design, construction and maintenance. For some problems, we can solve it with a smart valve positioner.
1) Example 1
A refinery unit found that several regulators could not be opened or could not be completely closed during the operation of the unit. After inspection, after eliminating other factors, it is determined that the actual pressure is higher than the design pressure, and the differential pressure before and after the valve causes the friction force to increase and the actuator cannot overcome. In this case, either replace the larger actuator or try to increase the air supply pressure. Since it is time-consuming and labor-intensive to replace the actuator, the most important thing is to affect the normal production of the device, so it is decided to find ways to increase the pressure of the air source. The site uses a common positioner plus filter pressure reducing valve to adjust the outlet pressure of the filter pressure reducing valve to the maximum, still can not solve the problem, but the instrument wind network pressure and the filter pressure reducing valve outlet pressure still have two kilograms of space. The test directly connects the instrument wind to the actuator head and solves the problem. However, due to fluctuations in public network pressure and other factors, the general positioner cannot be used and adjusted normally. Therefore, it is decided to use the intelligent valve positioner of a certain manufacturer in stock. Since the positioner of this manufacturer is not affected by the fluctuation of the gas source, the filter is installed on the valve before the positioner is installed, and the regulating valve works normally. The problem is solved.
2) Example 2
A device was shut down for major repairs. The detection valve has a large amount of inspection work, time is tight, and the task is urgent. Because this batch of regulating valve is equipped with a company's intelligent valve positioner, it has a wealth of fault diagnosis function, so the intelligent valve positioner is used to diagnose the regulating valve, including valve leakage, valve packing and other key parameters, according to fault diagnosis. As a result, the problematic regulator valve was removed for maintenance, and the control valve without problems was confirmed to be usable. After the start of the operation, after one year of operation, it proved that the regulating valve works well.
3) Example 3
In a factory, after the control valve was put into operation for several years, the continuous use of data and the constant changes of personnel caused the loss of data, and a considerable part could not be found. In the new project and transformation, they chose the intelligent valve positioner, and saved the whole plant positioner and related information through the corresponding software and hardware, which can be conveniently consulted and used during the subsequent production and maintenance.
4) Example 4
The control valve of a petrochemical plant has a positive effect due to the design, but the process requirements are counteracted at the start of construction, which requires adjustment of the regulating valve. Since the adjusting valve head is more troublesome to adjust, and the positioner is smart, the conversion of the positive and negative of the regulating valve is realized by simply adjusting the parameters of the intelligent valve positioner.
The above is a bit of my experience in engineering design and service. In the long-term development process, the use of intelligent valve positioners is a trend. We hope that more and more designers and users can use intelligent valve positioners to continuously improve the automation level of our factory, achieve good economic benefits, and constantly push our country's self-control level to the world's leading position.

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