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The Application of Rotary Valves in Refining and Chemical Processing Plants – Excerpt from China Chemical Equipment Network. Valves are generally divided into two main categories: linear-type and rotary-type. Straight-stroke valves allow or block the flow of material through a component that moves in a straight line, such as a gate. Straight-stroke valves include globe valves, gate valves, diaphragm valves, etc. A rotary valve allows or stops the flow of material through a rotating component. A rotary valve in which the rotating component can turn 90 degrees is called a 1/4 rotary valve. Sometimes, the classification of 1/4 rotary valves can be extended to rotary valves with an angle of less than 270 degrees. As defined, a rotary valve is a type of valve that changes from an open position to a closed position by rotating a rotating component such as a swing gate through 90 degrees. Rotary valves generally have the following characteristics. As actuating elements, control valves play a very important role in the production processes of the process industry. The performance of these control valves directly affects the output volume and the rate of defective products in such processes, as well as the smooth operation of production. With the advancement of process and control technologies, the economic scale of the process industry is growing larger, and the volume of material processed is increasing, which means that even a small percentage improvement in valve performance can yield significant benefits. Given this situation, the process industry has increasingly higher requirements for control valves. Coupled with the advantages of rotary valves themselves, this has led to their use becoming more widespread than that of traditional valves. I. Characteristics of rotary valves Valves are generally divided into two main categories: linear stroke type and rotary type. Straight-stroke valves allow or block the flow of material through a component that moves in a straight line, such as a gate. Straight-stroke valves include globe valves, gate valves, diaphragm valves, etc. A rotary valve allows or stops the flow of material through a rotating component. A rotary valve in which the rotating component can turn 90 degrees is called a 1/4 rotary valve. Sometimes, the classification of 1/4 rotary valves can be extended to rotary valves with an angle of less than 270 degrees. As defined, a rotary valve is a type of valve that changes from an open position to a closed position by rotating a rotating component such as a swing gate through 90 degrees. Rotary valves generally have the following characteristics. (1) Wide adjustment range: In the process industry, the adjustment range is of utmost importance. The adjustment range of rotary valves is approximately 150:1 (the adjustment range of VALTEK’s ball valves can reach 300:1, while that of butterfly valves and cam-flexible valves is 100:1). The adjustable range of the corresponding stop valve is 30:1; in other words, the rotary valve offers a 5 times wider adjustable range. For example, when the maximum flow rate is 1000 liters per minute, a globe valve can effectively reduce the flow rate to 30 liters per minute, while a rotary valve can adjust the flow rate to below 10 liters per minute. The more precisely the flow rate can be controlled by these valves, the better the repeatability in the process, which directly reduces the number of defective products in process industries. Two features of the eccentric rotary valve enhance its range of adjustment. The first is its orifice-type design: the eccentricity consists of an effective 1/4 circle, and the valve core is V-shaped, whereas traditional valve cores are circular. When the eccentric rotary valve is closed, its small V-shaped shape enables very precise control at low flow rates; at high flow rates, it almost opens the valve to a diameter equal to that of the pipe. The second feature is that the actuators of the stroke rotary valves in the actuating machines come in two types: diaphragm type with a certain stroke and cylinder type. The stroke of a 1” globe valve is approximately 3/4” to 7/8”, while that of a rotary valve exceeds 2”. For valves of any other size. The greater the stroke at the input side, the better the control at the output side. Control valves with high adjustability enable precise proportioning according to the requirements of the formula, regardless of the flow rates in various channels; traditional linear or control valves are no longer suitable for such tasks. Rotary valves can improve the performance of the system while reducing the costs associated with control valves over the device’s operational life cycle. Rotary valves with a wide adjustment range allow users to raise the standards for tight shut-off, thereby improving cost/benefit ratios. A metal valve seat, combined with a sleeve made of special materials, can extend the service life of the valve and improve its performance. The design of a simple rotating structure can minimize maintenance efforts. Reduce the owners’ production costs. (II) Tight isolation: The shaft of a straight-stroke valve is used for the valve stem to move in and out of the valve body, and product is carried out with each cycle. It is difficult to prevent leakage in a straight-stroke design, as this can allow unwanted products to enter the production system, resulting in significant and unacceptable volatile leaks within the factory. The rotary design of rotary valves essentially does not have this problem, as such valves utilize cylinder-type actuators with low hysteresis and high thrust, which offer greater precision and stability compared to other types of actuators; they also feature metal valve seats that enable long-term, tight sealing. (III) High flow capacity with small size: The flow capacity of a straight-stroke valve is a fraction of the flow capacity of the pipeline in which it is installed. To increase the flow capacity, it is necessary to increase the size of the straight-stroke valve, which is usually larger than that of the pipeline. The capacity of a rotary valve is approximately 2 to 3 times that of a straight-stroke valve of the same size. Rotary valves can be used to increase the mixing ratio without having to change the size of the feed pipelines, which greatly reduces costs. For this reason, some rotary valves have been designed with a flange-to-flange connection style that can replace globe valves, and they are equipped with connecting bolts; such valves are even cheaper than the globe valves they replace. (IV) Cavitation resistance: In process industries, throttling can lead to significant cavitation. Cavitation may damage pipes, generate unacceptable levels of noise, and also disrupt measurement systems, resulting in unclear or unreliable readings. Rotary valves feature a robust design that reduces the risk of valve failure due to water hammer effects; moreover, their valve cores can absorb some of the excess energy, thereby significantly reducing cavitation and related problems. (5) No external leakage: Standard rotary valves have a leakage rate that is 100 times better than that of standard globe valves. The movement of the valve stem in globe valves draws in dust and sand, which can damage the graphite packing. In a rotary valve, the valve stem does not move in and out but rather rotates, thereby not damaging the packing and preventing external leakage. (VI) Maintenance costs and spare parts: Metal seat rotary valves require far fewer spare parts than globe valves, and their maintenance is usually simpler as well. II. Types of rotary valves (I) Classification by type: Rotary valves can be classified into three types based on their design: butterfly valves, ball valves, and plug valves. A butterfly valve controls the direction of flow by rotating a baffle or blade through a certain angle around an axis. The baffle or blade looks a bit like a butterfly. Butterfly valves can be used for cutting off or regulating flow, and are suitable for fluids that are slurry-like or contain suspended solids. The valve element of a ball valve is a spherical body with a circular hole; when the valve is in the open position, it allows fluid to flow through, while rotating the spherical body by 90 degrees stops the flow of fluid. Ball valves can be used for cutting off flow and regulating it; they have a low pressure drop and are suitable for viscous and corrosive fluids, slurries, and low-temperature fluids. Ball valves can also be used for high-temperature, high-pressure fluids. The valve element of a plunger valve is a conical or cylindrical plunger with a circular hole in the middle; fluid can pass through when the hole in the plunger is aligned with the flow direction, while the flow path is blocked when the plunger is rotated 90 degrees in either direction. Piston valves are typically used for on/off control. (II) Classification by operation method: Rotary valves can be classified into the following types according to their operation method: manual valves, automatic valves, and control valves. A manual rotary valve is operated by hand, using manual actuators such as levers, gears, or handwheels to carry out the on/off operation; it includes a component that can rotate 90 degrees. The actuator opens and closes the valve by operating the valve stem and flow control elements. An automatic rotary valve includes an automatic actuator that uses external energy to automatically control or remotely operate the opening and closing of the valve. Automatic valves are generally recommended in the following situations: large valves (such as those larger than 8 inches), valves that are difficult to operate manually, valves that cannot be operated manually due to being in toxic or other harsh environments, and valves that require rapid closure in emergency situations ； Valves and other components for all flow paths in conjunction with the batch formulation. The types of automatic actuators include hydraulic, pneumatic, and electric ones, and most automatic rotary valves can be operated using electric and pneumatic actuators. Rotary control valves can operate at specific opening degrees; such valves include an actuator that can generate a corresponding rotation angle based on the magnitude of the electrical signal. Butterfly valves are commonly used in low-pressure, large-diameter applications where strict control over leakage is not required. A rotary control valve is a type of control valve; control valves also include some linear-motion valves such as globe valves, gate valves, and diaphragm valves. The automatic rotary cut-off valve is not a control valve, as it can only be in the open or closed position. III. Application trends of rotary valves (1) The replacement of manual valves with automatic valves has become a trend in industrial applications. As automation levels increase in process industries worldwide, there is a growing demand for automatic and regulated rotary valves, while the demand for manual valves is declining. This means that the focus of future development in valve application technology should be on the valves’ actuators and positioners, so that the valves can be connected to personal computers, PLCs, and DCS systems. By using a digital setter to improve the precision of control valves, the control performance of these valves can be enhanced. A successful application of this approach is the use of the ND800 digital setter with rotary control valves, which allows the range of variable process parameters to be increased by 50%. Further improvements in control performance can be achieved by matching the electronic characteristics of the valve setter to those of the control valve. Typical applications include the FieldBrowser software that uses the HART network. Compared to cut-off valves, control valves are more suitable for continuous production processes. Through its regulating function, the control valve can adjust the flow rate based on input parameters in order to maintain a constant set value. In many cases, both shut-off valves and control valves are required; for example, in refineries, 1/4 turn shut-off valves are used as safety shut-off valves. A control valve is usually used together with two isolation valves to isolate and cut off the flow when the control valve is removed. Electric actuators will gradually replace pneumatic actuators, as they do not require the installation and maintenance of pipelines and compressors; they can be integrated more closely with controllers, and they eliminate the need to convert electrical signals into pneumatic signals. Other development directions for rotary valves involve improving the design and material of the valve seat in order to enhance the valve’s performance and reduce external leakage. Intelligent valves with control and positioning functions are seeing an increasingly broad market, driven by manufacturers’ efforts to reduce costs and production enterprises’ need to improve efficiency. (II) The trend toward replacing linear-motion valves: Since rotary valves can replace linear-motion valves (such as gate valves) in many cases, they possess numerous advantages over such valves (see Part 1 of this article). Especially with the implementation of the Clean Air Act (CAA) amendments, preventing external leakage from valves has become increasingly important. The CAA amendments introduced in 1990 included 189 volatile toxic air pollutants (VHAPs), of which 150 are volatile organic compounds (VOCs). The latest CAA amendment, adopted in April 1997, includes quality improvement measures in addition to the Leak Detection and Repair (LDAR) program from previous amendments. The CAA amendment increases the investment by chemical companies, refineries, and other valve-using manufacturers in preventing external leaks from valves. The CAA amendments and the resulting requirements to control external leakage have prompted suppliers of manual valves, automatic valves, and control valves to adopt new technologies in valve design in order to reduce external leakage. The key to reducing external leakage from valves lies in the material of the valve packing system. Polytetrafluoroethylene (PTFE) and graphite are two common materials used in valve packing systems. To reduce external leakage from valves, many suppliers combine perfluoroelastomers with certain amounts of PTFE and graphite in the valve packing systems. The compressive force of the perfluoroelastomer filler system is greater than that of the polytetrafluoroethylene filler system, but the compressive force of the graphite filler system is many times higher than that of the perfluoroelastomer filler system. Excessive clamping force can lead to wear and damage of the valve stem, thereby causing external leakage of the valve. Generally speaking, the use of rotary valves is an effective measure to reduce external leakage; in other words, rotary valves tend to replace linear motion valves. This trend is also evident when looking at the market share rankings provided by the Valve Manufacturer Associate VMA: according to data from VMA, the shipment volumes of ball valves, industrial butterfly valves, and plug valves in the United States in 1996 are recorded. VMA specifically tracked the shipment volumes of ball valves, industrial butterfly valves, and plug valves; aside from these, it classified automatic valves as a separate category. It did not record the sales volume of 1/4 turn control valves separately, but included them under the category of automatic valves. VMA provides data on the shipment volumes of suppliers in the United States, including exports but not imports; the total amount is 1.04 billion dollars. This figure includes manual valves and automatic valves, but not control valves. Ball valves account for the largest share, at 54.2% of the total, industrial butterfly valves make up 26.2%, while plug valves hold the remaining 19.6% share. IV. Applications of Rotary Valves (I) Applications in the Blending Systems of Refineries In the blending systems used in refineries, in order to improve the quality of the blended product, it is necessary to inject and shut off the various oils involved in the blending process with precision and at high speed. This requires the use of control valves with high shut-off rates, so as to ensure accurate mixing of liquids regardless of the flow rate in each channel. Traditional linear stroke valves or globe valves are no longer suitable for such applications in refineries; rotary valves, thanks to the advantages described above, can offer a better performance-to-cost ratio in these applications. It brings significant benefits to the long-term operation of users. (II) Rotary valves are widely used in our factory. Specific application 1: The 4-way radial feed control valves in the coking workshop have been replaced with rotary valves. The coking plant was originally designed with double-seat valves. Since the radiant feed in the coking process contains a large amount of coke powder particles, and the high temperature and fast flow rate exert significant erosion on the control valves, the valve cores and seats of these valves get damaged very quickly, resulting in severe leakage and an inability to maintain proper control. A new control valve only lasts for 3 months before failing ； Later, by replacing the control valve with a sleeve valve, the situation improved; a new control valve could operate for 5 months. In September 1997, we replaced the control valves with FISHER rotary valves; since these rotary valves have resistance to cavitation, they were able to effectively counteract the erosion caused by the medium. In October 1998, we inspected one of these control valves, and found that both the valve stem and the valve seat were in good condition. The four control valves have been in use to this day. Specific application 2: 3-channel feeding for the southern distillation vacuum furnace. In the original design, the feed valves for the three pressure-reduction furnaces were sleeve valves. Since the feed contained residue and impurities, these control valves often became clogged. Moreover, the high temperatures led to easy condensation, which posed significant challenges for the maintenance of the instruments. In June 1998, these three feed lines were replaced with FISHER rotary valves; thanks to their superior flow capacity, these rotary valves overcame the aforementioned problems and allowed for normal operation. Specific application 3: Control valve for catalytic residue re-refining. The control valve for catalytic residue reprocessing was originally designed as a sleeve valve. Due to the presence of catalyst in the residue reprocessing stream, severe erosion occurred on the control valve, preventing it from functioning properly. A new control valve would only last for about 6 months before failing. In June 1998, it was replaced with a FISHER rotary valve, which has been in use ever since. Specific application 4: Catalytic air compressor flare. The flare system of the catalytic air compressor originally used 700-type gate valves; their drawbacks were slow opening and closing speeds and high leakage rates. Later, triple-eccentric butterfly valves were adopted, with an opening and closing time of less than 10 seconds and a sealing performance reaching level 5. There are many such specific applications, which need not be listed one by one. V. Conclusion As refining and chemical processing units become more integrated and their scale increases, the production processes place ever stricter demands on the accuracy and adaptability of instruments and control systems. As the core components within these control systems, control valves play a crucial role, and their performance and quality have an increasingly significant impact on the economic efficiency of petroleum chemical plants. Whether it is to expand production scale in the future or to improve control quality (such as advanced control or optimal control), when selecting control valves we need to consider not only the one-time investment during the construction phase but also the functions of those control valves.