What type of boiler is characterized by having separate sections assembled for operation?

A sectional boiler is specifically designed with individual sections that are assembled together to create the complete unit for operation. This design allows for easier transportation, installation, and maintenance, as the boiler can be disassembled into smaller, more manageable parts. Each section typically contains its own heating surface, which contributes to the overall efficiency of the boiler.

In contrast, firetube and water tube boilers have distinct designs: firetube boilers have the combustion gases passing through tubes surrounded by water, while water tube boilers have water flowing through tubes that are heated by the surrounding hot gases. Single-pass boilers refer to a specific flow design, where water or steam only passes through the boiler once, rather than being recirculated. None of these other types of boilers utilize the sectional assembly characteristic that defines sectional boilers, making the choice of "sectional boiler" the most accurate answer.