In a firetube boiler, where is the combustion process typically found?

In a firetube boiler, the combustion process takes place surrounding the water tubes. This design utilizes a series of tubes that carry water, with the hot gases produced from burning fuel flowing through the space outside these tubes. As the hot combustion gases pass around the tubes, they transfer their heat to the water inside the tubes, leading to steam generation.

This arrangement effectively allows heat to be transferred to the water, while the products of combustion remain external to the water-filled tubes. It inherently implies that the water is protected from direct contact with the combustion process, which is crucial for both efficiency and safety in boiler operation.

The other options do not accurately describe the location of combustion in a firetube boiler. The combustion process does not occur inside the water tubes, nor is it specifically located in the superheaters. Superheaters are designed to increase the temperature of steam beyond its saturation point after it has already been generated in the boiler system. Thus, "surrounding the water tubes" correctly identifies where the heat transfer and combustion occur within the firetube boiler system.