I would like to ask the experts here about the throttle valve issues in large air separation units
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I would like to ask the experts: In large air separation units, is the throttle valve simply a regular control valve with throttling functionality? Where is it used? What is its design and how is it controlled? Thank you
Here we use ordinary pneumatic control valves along with flow interlock control; the idea is to throttle the rich liquid and lean liquid that come out of the lower tower after passing through the subcooler, and then send them to the upper part of the tower. I’m not sure how others do it
Throttle valves are primarily used to regulate pressure and temperature. After passing through a throttle valve, the pressure of the fluid decreases, and along with that, the temperature drops, thereby serving to cool the fluid. In conventional air separation units, the liquid oxygen and liquid nitrogen from the lower column must pass through throttle valves to reach the upper column. In large-scale air separation units, these valves are usually pneumatic diaphragm control valves, with their operation being controlled from the main control room.
Below a certain temperature, as the fluid passes through the throttle valve, its volume increases and its pressure decreases; at the same time, there is a certain amount of temperature drop. This process is an isenthalpic change; isentropic expansion and isenthalpic throttling are the two main methods for refrigeration. For our air separation unit with a capacity of 56,000 NM3/H, high-pressure air must pass through a large throttle valve before entering the lower column; moreover, the oxygen-enriched liquid air, liquid air, contaminated liquid nitrogen, and liquid nitrogen that flow from the lower column to the upper column all pass through throttle valves as well. By controlling it based on the flow rate, the reflux ratio can be adjusted to a certain extent.
Using a throttle valve to reduce the temperature of the material is a very common practice in the design of air separation units