Regarding liquid level alarms
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In a methanol washing unit, what is the difference between a 3-out-of-2 and a 2-out-of-2 selection scheme when setting the low-low liquid level alarm for the methanol-depleted storage tank, and what is the principle behind these alarms?
From a safety perspective, the use of 3-out-of-2 and 2-out-of-1 systems is due to the fact that the safety considerations associated with them are not as high as those of the previous system.
From a safety perspective, it’s definitely a two-out-of-three rule~! An alarm is triggered as long as two of the three level indicators send a signal, mainly to prevent a cascade shutdown in the event that the instruments are damaged~! The failure of one gauge does not have a significant impact; the ‘two-out-of-one’ principle is in place to prevent a chain reaction that could lead to the shutdown of the methanol circulation process due to gauge failure