Application of intelligent valve positioner in automatic control system of petrochemical plant Analysis of intelligent valve positioner and typical fault analysis
In the automatic control system of petrochemical plant, the selection of regulating valve is very important to the precision, its use affects the quality of products, and relates to the safety of the plant production. Dushanzi VINYL plant each device used regulating valves including various manufacturers of various types of products. But the vast majority of the regulator installed is a common type of valve positioner. FIELDVUE intelligent valve positioner produced by FISHER-ROSEMOUNT Company is now used in Dushanzi factory. After more than one year of operation, the performance, usage, performance and price ratio of FIELDVUE intelligent valve positioner are compared with those of ordinary valve positioner
A regulating valve with a common positioner is equipped with a regulating valve with an intelligent positioner
The basic error is less than 20% of the trip and less than 0.5% of the trip
Valve stability is stable and extremely stable
Manual adjustment on site Adjustment on site, in the cabinet or in communication with DCS through the calibrator
Signal source 4 ~ 20mA or pneumatic signal analog signal or digital signal
Performance/higher price than low
1 FIELDVUE intelligent valve positioner working principle and characteristics
1.1 Principles of the Intelligent Locator
FIELDVUE series digital Valve controllers have a modular base that can be easily replaced in the field without having to remove field wires or conduits. The module base includes submodules: I/P converters; PWB (printed circuit board) assembly; Pneumatic repeater; Instruction sheet. The module base can be reassembled by swapping submodules. The FIELDVUE series digital valve controller receives input signals and electrical power through a twisted pair of wires into the terminal box simultaneously to the PWB assembly submodule, where it is attached with many parameters such as node coordinates, limits and other values in multi-segment fold-linearization. The PWB component submodule then sends signals to the I/P converter submodule. The I/P converter transforms the input signal into a barometric signal. The air pressure signal is sent to the pneumatic repeater, amplified and sent to the actuator as an output signal. The output signal can also be sensed by the pressure sensitive element located on the PWB component submodule. Diagnostic information for valve actuators. The STEM POSITIONS OF THE VALVE AND ACTUATOR ARE USED AS INPUT SIGNALS TO THE PWB SUBMODULE AND ARE USED AS FEEDBACK SIGNALS TO THE DIGITAL VALVE CONTROLLER, WHICH MAY ALSO BE EQUIPPED WITH A GAUGE INDICATING THE AIR SOURCE PRESSURE AND OUTPUT PRESSURE.
1.2 Intelligent characteristics of intelligent valve positioner
1.2.1 Real-time information control, improved security and reduced costs
1) Improve control: two-way digital communication brings the information of the current situation of the valve to you, you can rely on the valve work information to have a basis for process control management decision, to ensure timely control.
2) Improve safety: You can select information from the site junction box, terminal board or in the control room such a safe area by using the manual operator, PC or system workstation, reduce your chance of facing dangerous environment, and do not have to go to the site.
3) To protect the environment: the valve leakage detector or limit switch can be connected to the auxiliary terminal of the intelligent digital valve controller, so as to avoid additional field wiring. The meter will alarm if the limit is exceeded.
4) Hardware savings: When FIELDVUE series digital valve positioner is used in integrated systems, the FIELDVUE digital valve controller replaces the regulator to save on hardware and installation costs. FIELDVUE series digital valve controllers save 50% on wiring investment, terminal and I/O requirements. At the same time FIELDVUE meter uses two line system power supply, does not require a separate and expensive power supply wire. They replace the existing analog instruments fitted to the valves and save the high cost of laying out the power and signal lines separately.
1.2.2 Reliable structure and HART information
1) Durable structure: The fully sealed structure prevents vibration, temperature and corrosive environment from affecting it, and the weatherproof field junction box separates the field wire contacts from the rest of the instrument.
2) Speed up start-up preparation steps: The two-way communication capability of the digital valve controller allows you to remotely identify each instrument, check its calibration, review and compare previously stored maintenance records and other more information, to achieve the goal of starting the loop as soon as possible.
3) Easy selection of information: FIELDVUE digital valve locator and transmitter uses HART communication protocol to easily select field information. See TRUTHFULLY THE BASIS OF THE CONTROL PROCESS – THE CONTROL VALVE ITSELF – WITH THE HELP OF A HANDHELD COMMUNICATOR ON THE VALVE OR IN THE FIELD JUNCTION BOX, AND WITH THE HELP OF A PERSONAL COMPUTER OR OPERATOR’S CONSOLE IN THE DCS CONTROL ROOM.
The adoption of the HART protocol also means that FIELDVUE meters can be incorporated into an integrated system or used as a self-contained control device. This adaptability in many aspects makes the system design work more convenient and easy no matter now or in the future.
1.2.3 Self-diagnosis and control ability
1) Fieldbus communication
All DVC5000f digital valve controllers include fieldbus communication capabilities, including A0 function block and the following diagnostics:
A) Key valve use tracking parameters;
B) Instrument health status parameters;
C) Predetermined format valve performance step maintenance test.
The KEY VALVE USES TRACKING PARAMETERS TO MONITOR THE TOTAL STEM TRAVEL (travel accumulation) and the number of STEM travel turns (cycle). The meter health parameter alarms if there are any problems with the meter’s memory, processor, or detector. Once a problem occurs, determine how the meter will react to the problem. If, if the pressure detector fails, should the meter be turned off? You can also CHOOSE WHICH component failure will cause THE meter to shut down (whether the problem is serious enough to cause THE meter to shut down). These parameter instructions are reported in the form of alarms. Monitoring alarms can provide instantaneous indication of a faulty instrument, valve, or process.
2) Standard control and diagnosis
All DVC5000f digital valve controllers include standard controls and diagnostics. Standard control includes A0 with P> dynamic error band, drive signal and output signal are dynamic scan test. These TESTS ARE PERFORMED TO CHANGE THE SET POINT OF THE TRANSMITTER BLOCK (SERVO MECHANISM) AT A CONTROLLED SPEED AND PLOT THE VALVE OPERATION TO DETERMINE THE DYNAMIC PERFORMANCE OF THE VALVE. For example, the dynamic error band test is hysteresis with dead zone plus “rotation”. Lag and dead zone are static qualities. However, because the valve is in motion, dynamic errors and “rotation” errors are introduced. The DYNAMIC SCAN TEST GIVES A GOOD INDICATION OF HOW the VALVE WILL OPERATE under process conditions, which will be dynamic rather than static. Standard and advanced diagnostic tests can be performed by running ValveLink software on a personal computer.
3) Advanced diagnosis
Instruments with advanced diagnostics perform the dynamic scan test included in standard diagnostics plus a fourth dynamic scan test, the valve characteristics test, and four step diagnostic tests. Valve characteristic TESTING allows YOU TO DETERMINE valve/ACTUATOR friction, bench test pressure signal range, spring stiffness, and seat closing force.
4) Process bus
Fischer Control Equipment Performance SERVICES CAN EVALUATE VALVES, processes, and TRANSMITTERS USING INSTRUMENTS WITH PROCESS DIAGNOSTIC CAPABILITIES while THE FOUNDATION FieldBUS CONTROL LOOP REMAINS AUTOMATIC AND THE PROCESS CONTINUES TO PRODUCE PRODUCTS. Using process diagnostics, performance services will be able to identify and identify which components of a process are likely to cause quality problems. Although process diagnostics need to be up and running, their end point can only be determined by process or operator intervention. Process diagnostics can be performed on multiple valves simultaneously.
2 Application and maintenance
2.1 applications
FIELDVUE Smart Valve positers were installed in April 1998 for use in 16 cracking and ethylene glycol units. Mainly used to replace some important control points circuit occasions. For example, feed flow valve of cracking furnace and feed flow valve of ethylene glycol epoxy reactor control.
We use the manual operator for its configuration and verification, its linearity can be up to 99%, zero and range and return can be controlled within the range of precision requirements, extremely stable control and anti-interference ability is particularly strong, fully meet the requirements of process control.
2.2 maintenance
The FIELDVUE locator requires minimal maintenance and is essentially maintenancefree. Its field adaptability is particularly strong. But in order to ensure long-term and stable operation, instrument personnel should do the following aspects of work.
1) In order to ensure a good working environment and prevent accidental damage, the working environment around the locator should be checked regularly. At the same time to ensure the stability and cleanliness of the working air source, reduce the external factors caused by instrument fluctuation and failure.
2) Instrument personnel should check the leakage and working conditions of valves and positioners every week to eliminate hidden dangers in time. Every month, the manual operator is used to check the characteristic curve of the positioner, check the zero point, range, linearity and return error and other parameters, and optimize and adjust it to ensure its working quality.
3) Check and maintain the regulating valve regularly to ensure the working quality of the valve. At the same time, the parameters of the DCS control loop are optimized to ensure the coordination and stability of the mutual work with the locator.
4) Due to DCS and other reasons, its fieldbus and software functions have not been fully developed and utilized, and the intelligent maintenance and diagnosis functions can not be fully used, but it still reduces the amount of daily maintenance.
According to the use effect of the chemical plant in the past two years, the intelligent valve controller has stable performance and convenient adjustment; Can realize direct communication with DCS, and has the function of self-diagnosis, simple maintenance; Can be transplanted to fieldbus, ** the direction of today’s instrument technology development. Further development and use of its software function is the target direction of our future efforts.
Analysis of intelligent valve positioner and typical fault analysis
Post time: Sep-16-2022
