What substance is known to absorb humidity inside a boiler during dry lay up?

The substance that is known to absorb humidity inside a boiler during dry lay up is activated alumina. Activated alumina is a highly porous material that has a strong affinity for water vapor, which makes it effective in controlling humidity levels. This characteristic is particularly important in preventing corrosion and maintaining the integrity of boiler components during idle times when moisture could lead to damage.

Activated alumina works by adsorbing moisture from the air, thereby reducing the overall humidity within the environment of the boiler. Its ability to hold water without becoming saturated makes it a reliable choice for this application. In dry lay up procedures, using effective desiccants like activated alumina helps ensure that moisture does not accumulate, which could otherwise lead to problems when the boiler is brought back online.

The other substances listed, while they have various functions in different contexts, do not possess the same level of efficiency in moisture absorption as activated alumina when it comes to protecting boilers during dry lay up periods.