In a bottom-supported boiler, how is the steam drum typically supported?

In a bottom-supported boiler, the steam drum is typically supported by the water tubes running vertically between the steam drum and the lower portions of the boiler. This method effectively utilizes the natural weight and structural integrity of the water tubes to safely support the steam drum, allowing for efficient transfer of pressure and steam while ensuring structural stability.

This support mechanism is important because the design concentrates the structural load onto the tubes, which are designed to handle high pressures and temperatures, maintaining a safe and efficient operation. The configuration also helps in minimizing the overall height of the boiler, contributing to a compact design that is easier to install and maintain.

The other options do not accurately represent the typical support method for the steam drum in bottom-supported boilers. For instance, placing the steam drum between the center line or supporting it with piers or overhead girders doesn't align with the usual design principles where the direct support from water tubes is preferred to maximize efficiency and minimize any potential for structural failure.