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Application of Rotary Valve in Refining and Chemical Plant
1, the characteristics of rotary valves The valve is usually divided into straight-line program and rotary two categories. Straight-stroke valves allow or shut off the flow of fluid through a rectilinear moving part such as a ram. Straight travel valves are globe valves, gate valves, diaphragm valves and so on. Rotary valves allow or shut off the flow of fluid through a rotating part. Rotating parts can rotate 90 degrees rotary valve called 1/4 rotary valve. Sometimes 1/4 rotary valve classification can be expanded to less than 270 degrees of rotation of the rotary valve. As can be seen by definition, a rotary valve is a rotary valve that changes the valve from opening to closing by rotating a rotating member such as a rotating shutter by 90 degrees. Rotary valve generally has the following characteristics. (1) Adjustable Range The adjustable range is the most critical in the process industry. The rotary valve has an adjustable range of approximately 150: 1 (VALTEK's ball valves can be adjusted up to 300: 1, butterfly valves and cam-bend valves The adjustable range is 100: 1). Corresponding to the cut-off valve adjustable range of 30: 1, which means that the rotary valve can provide 5 times the width of the adjustable range. For example, at a maximum flow rate of 1000 l / min, the shut-off valve can effectively reduce the flow rate to 30 l / min and the rotary valve can adjust the flow rate to less than 10 l / min. The more accurate the critical valve control flow, The better the repeatability, the direct reduction of unqualified products in the process industry. Eccentric rotary valve features two to enhance its adjustable range, the first is its orifice design, the eccentric is an effective 1/4 of the park, eccentric spool is V-type, while the traditional spool is In the parked shape, when the eccentric rotary valve is off, its small V shape allows for very precise control at low flow rates, and for large flow rates it opens the valve almost to the same diameter as the pipe. The second feature is the implementation of the trip machine rotary valve actuator with a certain stroke of the membrane and cylinder two. 1 "shut-off valve stroke is about 3/4" ~ 7/8 "and rotary valve stroke more than 2". For any other size valve. The greater the stroke of the input, the better control is at the working end. Highly variable ratio control valves provide the exact formulation required by the recipe regardless of the flow rate of the individual flowpaths. Conventional linear or regulating valves are no longer suitable for such tasks. Rotary valves increase device performance while reducing the need for control valves. The cost of plant life cycle. A wide range of adjustable rotary valves allow users to improve their tightness and cut-off standards, thereby increasing cost / benefit metrics. The metal seat plus the village made of special material can prolong the service life of the valve and improve the performance of the valve. The simple design of the rotating structure can minimize the maintenance workload. Reduce the owners of production costs. (2) Strictly cut off the shaft of the straight stroke valve stem is the stem out of the valve body, each cycle with a product, for straight stroke design to avoid leakage is difficult, it can be unwanted products into the production process system, And can produce large unacceptable factory volatile external leakage. Rotary valve rotary design is essentially free of this problem, because the valve uses a low hysteresis, high thrust cylinder actuator can provide more accurate than the other forms of implementing agencies more stability, has been able to provide long-term tight Cut off the metal seat. (3) Circulation capacity Large size Small straight stroke valve flow capacity is the installation of the valve flow capacity of the pipeline to improve the flow capacity of the method is to improve the size of the straight-stroke valve, usually larger than the pipeline may be. Rotary valves have a capacity of about 2 to 3 times that of a straight-stroke valve of the same size. Rotary valves can be used to increase the amount of blending without changing the size of the feed line, which can greatly reduce costs. For this reason, some rotary valves have been It is designed as a flange-to-flange connection instead of a stop valve and is equipped with connecting bolts which are even cheaper than the globe valves they replace. (4) Anti-cavitation Throttling in the process industry can cause significant cavitation which can damage the pipe and create an unacceptable level of noise while disturbing the gauging system causing unclear or unreliable readings, The rotary valve has a robust design that greatly reduces valve failure due to water hammer, while its spool absorbs part of the excess energy, significantly reducing cavitation and related problems. (5) No external leakage Standard rotary valves are 100 times more leak-proof than standard stop-valve designs and the movement of the stem of the shut-off valve pulls the dust in and carries sand into the valve thereby damaging the graphite packing. In the rotary valve stem does not make any access to the movement, but for the rotation movement, so as not to damage the packing, to avoid external leakage. (6) Maintenance costs and spare parts Metal seat rotary valve spare parts than the cut-off valve is much less maintenance is usually relatively easy. 2, the type of rotary valve 2.1, according to the type of classification Rotary valve classification according to the type has three types: butterfly valve, ball valve and plunger valve. Butterfly valve is through the baffle or blade to the shaft as the center rotation angle to control the flow direction. The baffle or blade looks a bit like a butterfly. Butterfly valve can cut off or adjust the role of slurry or with suspended solids for the fluid. The ball valve spool is a spherical body with a circular hole, allowing the fluid to flow when the valve is in the open position, turning the spherical body 90 degrees to cut off the flow. Ball valve can cut off and adjust the role of its pressure drop is small, suitable for viscous and corrosive fluids, slurry cryogenic fluid. Ball valve can also be used for high temperature, high pressure fluid. Plunger valve spool is the middle of the cone-shaped or cylindrical plunger with a hole, when the plunger hole and the flow direction of the fluid can be passed, when the plunger rotated 90 degrees in any direction when the flow path is cut off. Plunger valves are commonly used for on / off control. 2.2, according to the operation classification Rotary valve in accordance with the operation mode has the following types: manual valve, automatic valve and control valve. Manual rotary valves are operated by hand and are operated by manual actuators such as handwheels, gears, handwheels, etc., and include a unit that can be rotated 90 degrees. The actuator opens and closes the valve by operating the valve stem and flow control element. Automatic rotary valve includes an automatic actuator, the use of external energy to automatically control or remote control valve switch. Automatic valves should generally be used in the following situations: Large valves (eg valves> 8 "), valves that are difficult to operate manually, in toxic or other harsh environments Manual operation of the valve is not possible. To handle an emergency the valve must Rapid closing valves, valves for all flow paths in batches, etc. Types of automatic actuators include hydraulic, pneumatic and electric, most of which are operated by electric and pneumatic actuators Rotary control valves are capable of operating on specific Of the valve opening, this type of valve includes an actuator that can generate a corresponding angle according to the size of the electrical signal.Diaphragm valve is commonly used in low pressure large diameter, less stringent requirements on the leakage control.Rotary control valve is a control valve, Control valve also includes some straight-stroke valve such as the globe valve, gate valve, diaphragm valve.Automatic rotation of the cut-off valve is not a control valve, because it can only be limited to the open and closed position .3, rotary valve application trends (1) Valve has become the trend of industrial applications With the worldwide process industry automation degree of improvement, The demand for moving and adjusting rotary valves is increasing and the demand for manual valves is reduced, which will make the future development of valve application technology focus on valve actuators and positioners so that the valves can be connected to personal computers, PLCs and DCS systems If the digital positioner improves the control performance of the valve by increasing the accuracy of the control valve, successful applications include the ability to increase the variable range of process parameters by up to 50% using the ND800 digital positioner for rotary control valves, Features of the Control Valve Matching of the electronic features of the positioner further enhances control performance. Typical applications are Field Browser software with HART network. Control valves are more suitable for continuous production than shut-off valves. By regulating functions, The valve is able to change the flow rate according to the input parameters to keep the set value unchanged In many cases both the shut-off valve and the control valve are needed, as in the refinery, the 1/4 turn shut-off valve is used as a safety shut-off Valve. A control valve is normally used with two shut-off valves to isolate and shut off the flow of fluid when the control valve is disassembled The electric actuator will gradually replace the pneumatic actuator because the electric actuator does not require installation and maintenance of the line and compressor and can be more closely connected with the positioner and can avoid converting electrical signals to gas signals. The other development direction is to improve the performance of the valve and improve the performance of the valve by improving the design of the seat and the material of the valve seat so as to reduce the external leakage of the valve etc. Intelligent valves with the functions of control and positioning will reduce costs and increase production efficiency (2) The trend of replacing linear actuators Because rotary valves can replace linear actuators (such as gate valves) in many cases, rotary valves (such as gate valves) Has many advantages (see section 1 of this article.) Especially with the implementation of the Clean Air Act (CAA) amendment, preventing leakage outside the valve becomes more and more important. The CAA Amendment, introduced in 1990, includes 189 Volatile Sources of Air Pollution (VHAPs), of which 150 are volatile organic compounds (VOCs). The latest CAA Amendment, adopted in April 1997, includes a quality improvement program in addition to the leak detection and repair (LDAR) program of the previous version. The CAA Amendments add to the investment made by chemical companies, refineries and other valve manufacturers that use straight-stroke valves to prevent leaks outside the valve. The CAA Amendment and its resulting control leakage have prompted manufacturers of manual valves, automatic valves, and control valves to adopt new techniques to design their valves to reduce external leakage of the valves. The key to reducing leakage outside the valve is the material of the valve packing system. Polytetrafluoroethylene (PTFE) and graphite are two common materials used in valve packing systems. Many suppliers combine perfluoroelastomers with some polytetrafluoroethylene and graphite to reduce the valve leakage system. Perfluoroelastomer packing systems have a much higher packing pressure than PTFE packing systems, but the packing system has a much higher packing pressure than perfluoroelastomer packing systems. The pressing force assembly causes wear and tear on the stem, causing leakage outside the valve. In general, the use of rotary valves is an effective measure to reduce external leakage, ie rotary valves have a tendency to act instead of valves. This trend is also illustrated by the market share of the Valve Manufacturer Associate VMA: According to data provided by the VMA, the volume of ball valves, industrial butterfly valves and plunger valves shipped in the United States in 1996 (VMA specifically records ball valves, In addition to this, the VMA tracks automatic valves as a separate category. Instead of recording the sales of quarter-turn regulators separately, they categorize them as automatic valves VMA provided data on the shipments of US suppliers, including exports but excluding imports, totaling 1.04 billion U.S. dollars, including manual valves and automatic valves, but excluding regulating valves. Ball valves accounted for the largest percentage, accounting for 54.2% of the total, industrial butterfly valves accounting for 26.2% and the remaining 19.6% for the plunger valves (see Table 1). Table 1 United States Shipments of manual and automatic ball valves, industrial butterfly valves and plungers in 1996 Type Sales (in millions of USD) Percentage Ball valves 565.5 54.2% Industrial butterfly valves 273.0 26.2% Plunger valves 204.0 19.6% 4. Rotary valves (1) Application in refinery blending system For blending systems in refineries, in order to improve the quality of blending, it is often required that all kinds of blending and blending oil be accurately injected and cut off at high speed, which often requires the use of Higher cut-off control valves provide precise fluid mixing regardless of flow rate in each flow path. Conventional linear or shut-off valves no longer adapt to this application in refineries. Rotary valves offer higher cost performance in this application due to their inherent advantages described above. To the user's long-term operation to bring greater benefits. (2) rotary valve is widely used in our plant specific application 1: coking plant 4 radiant feed control valve to rotary valve. Coking plant originally designed as a two-seater valve, due to the coking radiation contains a lot of coke powder particles, and the high temperature, fast flow, the control valve have a great erosion, control valve spool, valve seat quickly Flushing bad, serious leakage, can not control, a new control valve can only run for 3 months; later the control valve for the sleeve valve, the situation has changed, a new control valve can run 5 each month. In 1997 September we will control the valve for the FISHER rotary valve, due to the rotation of the cavitation resistance, effectively overcome the erosion of the media, we check in October 1998, one of the control valve, spool, valve seat intact . Four control valves have been used until now. Specific application 2: Southern distillation vacuum furnace 3 feed. The original design vacuum furnace 3 furnace feed sleeve valve, because the feed contains residual oil, impurities, often blocked the control valve, and the high temperature, easy to condense, bring a lot of work to the instrument maintenance, June 1998 The 3-way feed for the FISHER rotary valve, rotary valve has a strong flow of capacity to overcome the above problems, the normal operation. Specific application 3: Catalytic residue refining control valve. The catalytic residue recovery control valve was originally designed as a sleeve valve, the residual oil refining catalyst, serious erosion of the control valve, the control valve can not be used normally, a new control valve into operation for 6 months, 1998 June will control the FISHER rotary valve, the use so far. Specific application 4: catalytic pressure machine torch. The torch used in the catalytic pressure press originally adopted a 700 gate valve. The disadvantage is that the switching speed is slow and the amount of leakage is large. After that, a triple eccentric butterfly valve is used, the switching speed is less than 10 seconds, and the sealing can be done at level 5. There are many such specific applications, no longer enumerated. 5. Conclusions With the integration of refining facilities and the large scale of refinery and petrochemical installations, the requirements for accuracy and adaptability of instrumentation and control systems are becoming more and more stringent in the production process. As the key component of the control system, the control valve, the The impact of performance and quality on the economic benefits of petrochemical plants is growing. Whether it is for the future to expand the scale of production or to improve the quality of control (such as the advanced control or optimization control, etc.) require us to use the control valve, not only to consider one-time investment in the construction period, but also pay more attention to operating costs during the production period. With the rotating valve features increasingly recognized and accepted by the people, it will surely get more and more widely used in the increasingly large-scale oil refining and chemical plants in China.