What is placed in the steam and water drums of dry-laid boilers to absorb moisture?

The correct choice is silica gel, which is commonly used in various applications to absorb moisture. In the context of dry-laid boilers, silica gel serves the function of ensuring that the steam and water drums remain dry by effectively trapping and absorbing excess moisture. This is crucial because maintaining low moisture levels helps prevent corrosion and ensures efficient operation of the boiler system.

Silica gel possesses a high surface area, which allows it to hold a significant amount of moisture relative to its weight. It is a desiccant, meaning it specifically absorbs water vapor from the air, making it ideal for usage in environments where moisture control is essential, such as in the steam and water drums of boilers.

While calcium chloride and desiccant beads may also be used for moisture absorption in different contexts, silica gel is most noted for its application in steam and water drums. Mud is generally not used for moisture absorption as it would contribute to fouling and operational issues within the boiler system.