[Daily Question 20090407] How to choose the air-opening type and air-closing type of pneumatic control valve?

Generally, the adjustment is based on the temperature of the material, which is to try to adjust the temperature of the material as close to its safest temperature. Accordingly, choose the air on and off.

When selecting the above two types of pneumatic control valves, the following aspects should be considered:: 1． Under accident conditions, process equipment should be in a safe state as much as possible. For example, the liquid level regulating valve of the carbonization fixed auxiliary tower in a fertilizer plant often adopts an air-closed type to ensure that the valve is in the fully open position during an accident, so that the fixed auxiliary tower will not be filled with water and cause a high-pressure machine accident. 2. In the event of an accident, the consumption of raw materials or power is reduced to ensure product quality. For example, the feed control valve of the distillation tower in a refinery is generally open with air. In the event of an accident, the valve is closed and the feed is stopped. ； The return flow regulating valve generally uses an air-closed type. In the event of an accident, the valve is fully opened to ensure the return flow and prevent unqualified products from steaming out. 3. Consider the characteristics of the medium. For example, when the liquid in the distillation tower kettle is easy to crystallize and solidify, the reboiler steam flow regulating valve should be air-closed to prevent the materials in the tower kettle from crystallizing or solidifying in the event of an accident.

When selecting the above two types of pneumatic control valves, the following aspects should be considered:: It is mainly considered from two aspects: process perspective and safety perspective; (refer to process control instrumentation). For details, please refer to the following statement: (refer to process control instrumentation) 1. Under accident conditions, process equipment should be in a safe state as much as possible. For example, the liquid level regulating valve of the carbonization fixed auxiliary tower in a fertilizer plant often adopts an air-closed type to ensure that the valve is in the fully open position during an accident, so that the fixed auxiliary tower will not be filled with water and cause a high-pressure machine accident. 2. In the event of an accident, the consumption of raw materials or power is reduced to ensure product quality. For example, the feed control valve of the distillation tower in a refinery is generally open with air. In the event of an accident, the valve is closed and the feed is stopped. ； The return flow regulating valve generally uses an air-closed type. In the event of an accident, the valve is fully opened to ensure the return flow and prevent unqualified products from steaming out. 3. Consider the characteristics of the medium. For example, when the liquid in the distillation tower kettle is easy to crystallize and solidify, the reboiler steam flow regulating valve should be air-closed to prevent the materials in the tower kettle from crystallizing or solidifying in the event of an accident.

Mainly for safety reasons: The feed valve adopts air-opening type, and the discharge valve mostly adopts air-closing type.

How to choose the air-opening or air-closing type of pneumatic control valve? answer: When selecting the above two types of pneumatic control valves, the following aspects should be considered:: 1． Under accident conditions, process equipment should be in a safe state as much as possible. For example, the liquid level regulating valve of the carbonization fixed auxiliary tower in a fertilizer plant often adopts an air-closed type to ensure that the valve is in the fully open position during an accident, so that the fixed auxiliary tower will not be filled with water and cause a high-pressure machine accident. 2. In the event of an accident, the consumption of raw materials or power is reduced to ensure product quality. For example, the feed control valve of the distillation tower in a refinery is generally open with air. In the event of an accident, the valve is closed and the feed is stopped. ； The return flow regulating valve generally uses an air-closed type. In the event of an accident, the valve is fully opened to ensure the return flow and prevent unqualified products from steaming out. 3. Consider the characteristics of the medium. For example, when the liquid in the distillation tower kettle is easy to crystallize and solidify, the reboiler steam flow regulating valve should be air-closed to prevent the materials in the tower kettle from crystallizing or solidifying in the event of an accident. This is one of the essay questions in the instrument engineering theory test-advanced level, and the answer given is this

Mainly from the perspective of process production safety, in an accident state, that is, when the air source of the regulating valve is not supplied, the regulating object should be safe. Strongly recommended to moderators: It’s better to publish less test sets of this kind, otherwise the “question a day” activity will lose its meaning. This post was last edited by Mobei Yihai on 2009-4-7 16:04 ]