Methanol synthesis
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For the control valves (stop valves, ball valves) in the methanol synthesis system, should they be air-operated open or air-operated closed?
This valve is not necessarily air-operated for opening or closing; it depends on its installation location and the application for determining which type to use. Generally, it is air-operated for closing when in an open state, and air-operated for opening when used for draining liquid
It depends on the parameters set during design; in some cases it is a air-shut valve, while in other cases it is an air-open valve. Generally, air-shut valves are used to control pressure, while air-open valves are used to control temperature. For controlling liquid level, both air-open and air-shut valves can be used
Whether the valve should be open or closed is determined by the process, with the main consideration being whether it should be open or closed when the instrument air is cut off to ensure system safety
Yes, what was said upstairs is correct; whether the valve is closed or open is done for process safety reasons – for example, a vent valve is opened.