Problems with steam throttle orifice plates~
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As shown in the figure below, this is a U-shaped steam heat exchanger, whose function is to heat the fluid. The main issue is related to the steam inlet: as shown in the diagram, the steam inlet passes through a pneumatic ball valve. Its function is to allow steam to flow into the heat exchanger and exchange heat with the fluid when the heat exchanger is in operation ； When the heat exchanger is not in operation, the ball valve closes to cut off the steam. The customer now requests that a throttle orifice plate be added, stating that it will allow a small amount of steam to flow in when the heat exchanger is not in use, thereby helping to balance the steam pressure. We are asked to design this throttle orifice plate. May I ask the experts whether there is any method for calculating the diameter of such orifice plates, what the requirements are, and whether its function indeed is as described by the customer? Thank you!
Looking at the piping system, the bypass is generally used when the main valve is removed; the addition of a throttle orifice is likely intended to prevent an excessive flow rate of gas. The calculation methods for throttle orifice plates are provided in the design manuals. However, you need to consider the pressure difference before and after, as well as the flow rate after throttling.
Can bypass flow always still serve the purpose of warming the pipes and removing condensate?
In my opinion, the reason manufacturers require bypass flow control is not necessarily to stabilize the steam pressure; this cannot be achieved using flow-limiting orifice plates, unless the total amount of steam used is very small, or the orifice plates are large enough, without considering costs. It is believed that the purpose of installing flow-limiting orifice plates is twofold: 1. To maintain a certain amount of steam excess when the heat exchanger is not in use, thereby preventing the formation of condensation water inside the heat exchanger, which could cause water hammer when it is put back into use. 2. When the heat exchanger is not in use, maintain a certain excess of steam to keep it at a specific temperature, thereby preventing leaks due to alternating hot and cold conditions after it is shut down. If this is the reason, the size of the orifice plate should be such that, after the heat exchanger is taken out of service and a small amount of steam passes through it, the temperature of the discharged water is comparable to the temperature when the heat exchanger is in normal operation.
Hello, thank you very much for your advice. The two points you mentioned are probably what the client intends. Could you please briefly explain the calculation steps? Or references, thank you!~
This isn’t very difficult; it is recommended to determine the amount of steam required based on the heat absorption and heat dissipation needed according to the weight of the metal in the heat exchanger.
Personally, I think using a pneumatic control valve is better; it allows for the regulation of the steam volume, preventing excessive steam flow after the heat exchanger is shut down from damaging the exchanger and causing waste of steam.
Well, flow-limiting orifice plates should be added, as long as the heat loss of the steam does not result in condensation
When the heat exchanger is not in use, maintain a certain excess of steam to keep it at a specific temperature, thereby preventing leaks due to alternating temperatures after it is taken out of service. The size of the orifice plate should be such that, after the heat exchanger is taken out of service and a small amount of steam passes through it, the temperature of the drainage water is comparable to the temperature when the exchanger is in normal operation.
There are specific design specifications for flow-limiting orifice plates; you can take a look at them