[Daily Question 20090415] About the role of flow-limiting orifice plates in the process

As a throttling element, the flow-limiting orifice plate has the advantages of simple structure, easy processing, low manufacturing cost, and convenient installation. On the premise of meeting the process requirements, using the flow-limiting orifice plate instead of the regulating valve to limit the flow or reduce the pressure will* * Reduce investment and operation and maintenance costs. Features 1. Traffic can be limited. 2. Can reduce stress. 3． Can limit current and reduce pressure at the same time. Working Principle The orifice plate can be used as a throttling element to limit flow and reduce pressure. When there is a certain pressure difference before and after the orifice plate, the fluid flows through the orifice plate. For a certain orifice diameter, the flow rate through the orifice plate increases as the pressure difference increases. But when the pressure difference exceeds a certain value (called critical pressure difference), the flow rate of fluid through the shrinkage holes of the orifice plate reaches the speed of sound. At this time, no matter how the pressure difference increases, the flow rate flowing through the orifice plate will remain at a certain value and will no longer increase. The flow-limiting orifice plate is based on this principle to limit the flow of fluid and reduce the pressure.

1. To ensure the safe startup and normal operation of the centrifugal pump. When the centrifugal pump is started, in order to make the outlet pressure reach a certain value and reduce the starting current of the motor, it is required to start with the outlet valve closed or partially closed. However, for some centrifugal pumps, such as high-lift centrifugal pumps and centrifugal pumps that transport volatile liquids, the fluid is easy to vaporize due to the small gap between the impeller and the pump body. This type of centrifugal pump requires a certain flow rate when starting and operating. If this type of centrifugal pump is operated without liquid flowing out (i.e., closed operation), the liquid in the pump will generate vortexes, causing it to heat and vaporize, causing cavitation or pressure suppression, which can easily cause damage to the pump. In order to ensure the safe startup and normal operation of this type of centrifugal pump, the pump is required to have a minimum discharge flow. This value is called the minimum flow of the centrifugal pump. Usually the minimum flow rate is specified by the pump manufacturer. In order to ensure the minimum flow, a return line is added to the outlet pipe of the centrifugal pump, called the minimum flow line. Using a flow-limiting orifice plate on the minimum flow line can ensure the safe operation of the centrifugal pump and avoid damage to the pump even when the pump outlet valve is closed due to misoperation. 2. Replace the flow regulating valve to limit the maximum flow. In process operations, when the flow does not need to be adjusted and only the maximum flow is required to be limited, a flow-limiting orifice plate can be used instead of the flow regulating loop to prevent overflow and save investment. This is also one of the most common uses of restrictor orifice plates. 3. Prevent biased flow in each branch pipe. Under certain circumstances, the process requires the same flow rate in each branch pipe. However, since the resistance drop of each branch pipe is difficult to be completely equal, there is a difference in flow rate. The pressure drop of each branch pipe can be adjusted by using the flow-limiting orifice plate to keep the flow rate of each branch pipe consistent.

Overview As a throttling element, the flow-limiting orifice plate has the advantages of simple structure, easy processing, low manufacturing cost, and convenient installation. On the premise of meeting the process requirements, using the flow-limiting orifice plate instead of the regulating valve to limit the flow or reduce the pressure will* * Reduce investment and operation and maintenance costs. Features 1. Traffic can be limited. 2. Can reduce stress. 3． Can limit current and reduce pressure at the same time. When the fluid is gas, if it is only to limit the flow rate and there is no requirement for downstream pressure, a single-stage flow-limiting orifice plate can meet the requirements. However, if the pressure on the downstream side of the orifice plate is limited while limiting the flow rate, a single-stage flow-limiting orifice plate cannot meet this requirement, because it is unlikely that a single-stage flow-limiting orifice plate can limit the flow rate and also limit the downstream pressure. In this case, a multi-stage flow-limiting orifice plate should be used. Working Principle The orifice plate can be used as a throttling element to limit flow and reduce pressure. When there is a certain pressure difference before and after the orifice plate, the fluid flows through the orifice plate. For a certain orifice diameter, the flow rate through the orifice plate increases as the pressure difference increases. But when the pressure difference exceeds a certain value (called critical pressure difference), the flow rate of fluid through the shrinkage holes of the orifice plate reaches the speed of sound. At this time, no matter how the pressure difference increases, the flow rate flowing through the orifice plate will remain at a certain value and will no longer increase. The flow-limiting orifice plate is based on this principle to limit the flow of fluid and reduce the pressure.

The flow-limiting orifice plate is mainly used to reduce pressure and limit flow, but it must be considered to ensure that the downstream pipeline is full after flow restriction, otherwise it will affect the downstream process.

The flow-limiting orifice plate is mainly used by technology professionals to limit flow and reduce pressure. The general calculation is the same as that of the standard orifice plate, and the processing is also the same. However, the flow-limiting orifice plate has wider restrictions on its calculation than the standard orifice plate, such as aperture ratio, pressure loss, etc. The range is very wide. If the required pressure drop is too large and single-stage pressure reduction cannot meet the requirements, multi-stage pressure reduction can be used. The flow-limiting orifice plate of this multi-stage pressure reduction is generally calculated by the manufacturer itself, and there is no standard algorithm.

The flow-limiting orifice plate generally has two functions:: 1. Restrict large amounts of fluid from passing through, and are often used on some high-pressure or high-temperature liquids. 2. Keep fluid flowing through at all times to protect the system. Generally speaking, the materials transported by the forced circulation reboiler relatively contain some substances with higher boiling points. In order to prevent them from coking, their vaporization amount should be controlled. However, due to their high boiling point, it is impossible to lower their temperature to control them. Therefore, another method is used to increase their pressure. The function of adding a flow-limiting orifice plate before entering the tower is to increase its pressure, control its vaporization amount, and prevent high-boiling substances from coking.

Flow-limiting orifice plates are widely used in backflush systems and reactor nitrogen protection systems. Especially when the flow rate is limited, large-diameter air blowing device instruments are relatively expensive, and flow-limiting orifice plates are often used.

1. To ensure the safe startup and normal operation of the centrifugal pump. When the centrifugal pump is started, in order to make the outlet pressure reach a certain value and reduce the starting current of the motor, it is required to start with the outlet valve closed or partially closed. However, for some centrifugal pumps, such as high-lift centrifugal pumps and centrifugal pumps that transport volatile liquids, the fluid is easy to vaporize due to the small gap between the impeller and the pump body. This type of centrifugal pump requires a certain flow rate when starting and operating. If this type of centrifugal pump is operated without liquid flowing out (i.e., closed operation), the liquid in the pump will generate vortexes, causing it to heat and vaporize, causing cavitation or pressure suppression, which can easily cause damage to the pump. In order to ensure the safe startup and normal operation of this type of centrifugal pump, the pump is required to have a minimum discharge flow. This value is called the minimum flow of the centrifugal pump. Usually the minimum flow rate is specified by the pump manufacturer. In order to ensure the minimum flow, a return line is added to the outlet pipe of the centrifugal pump, called the minimum flow line. Using a flow-limiting orifice plate on the minimum flow line can ensure the safe operation of the centrifugal pump and avoid damage to the pump even when the pump outlet valve is closed due to misoperation. 2. Replace the flow regulating valve to limit the maximum flow. In process operations, when the flow does not need to be adjusted and only the maximum flow is required to be limited, a flow-limiting orifice plate can be used instead of the flow regulating loop to prevent overflow and save investment. This is also one of the most common uses of restrictor orifice plates. 3. Prevent biased flow in each branch pipe. Under certain circumstances, the process requires the same flow rate in each branch pipe. However, since the resistance drop of each branch pipe is difficult to be completely equal, there is a difference in flow rate. The pressure drop of each branch pipe can be adjusted by using the flow-limiting orifice plate to keep the flow rate of each branch pipe consistent. This post was last edited by Chasing Dreams on 2009-4-15 15:37 ]

I would like to ask about multi-stage pressure reduction. We encountered a flow-limiting orifice plate in the project that uses multi-stage pressure reduction, which is reduced from more than 90 kilograms to 2 kilograms, and the medium is coal slurry. The design institute designed it to be multi-stage pressure reduction, but the process engineer said that multi-stage pressure reduction is easy to block. I would like to ask if you have any good methods to solve the blockage problem. And it meets the process pressure.

The used example is that the pressure difference between the front and rear of the valve is large, which is prone to cavitation and serious erosion of the valve core, which greatly affects the service life of the valve core. Therefore, a flow-limiting orifice plate is designed behind the valve to reduce the pressure difference between the front and back of the valve and enhance the service life of the valve core. Furthermore, the backflush device of the pressure guiding tube is often used.

I have only used one of its functions, and I learned more today. Thank you.