Steam boilers

Thornycroft water tube marine boiler

The Thornycroft boiler has an upper steamdrum and a lower waterdrum connected together by banks of tubes. The tubes are very curved and all of them discharge into the steamdrum above the water level. In later models some of the tubes discharge below the level. A down comer between the steam drum and the water drum is located behind the boiler.
The flue gas pass through the banks of tubes and violent circulation arise in the tubes and the evaporated steam conveys water to the steam drum. This water heavy circulation keeps the tubes free from deposits.

These boilers have an upward narrowing shape and call for, especially if they are placed side by side, a larger space than other square-shaped boilers.

This boiler has two lower drums. Huge downcomers are installed between the steam drum and the water drums.

Thornyeroft water tube boiler with two water drums. Notice that the fire in the furnace doesn't heats the downcomers.