Types of Watertube Boilers

Watertube boilers are boiler systems that are used in conjunction with power sources that require a high pressure steam, high steam output and superheated steam. The energy from the heat source can either be radiant or convection. The radiant type contains flames that if come into contact with the boiler tubes, can cause erosion and tube failure. The convection type is designed to absorb the heat from the hot gases by convection. Large boiler systems contain several tube banks in order to gain maximum energy from the hot gases. A small water tube boiler is usually assembled into a single unit, whereas large boiler systems are typically manufactured in sections for assembly on site.

Types of Watertube Boilers

Longitudinal drum boilerr
A longitudinal drum boiler system contains a cooler feedwater which is fed into a drum placed longitudinally above the heat source. The cooler water falls down a circulation header into several inclined heated tubes. The water temperature increases as it passes up through the tubes. The steam bubbles are then separated from the water and the steam can be taken off.
Cross drum boiler

The cross drum boiler system contains a drum placed cross ways to the heat source which achieves a more uniform temperature. Risk of damage to the boiler system is higher however, due to faulty circulation at high steam loads. If the upper tubes become too dry, they can overheat and fail. The cross drum boiler systems do have the advantage of being able to serve a larger number of inclined tubes due to its cross ways position.

Bent tube or Stirling boiler

The bent tube or Stirling water tube boiler operates on temperature and density of water. Cooler feed water enters the drum, where it falls towards the water drum. The bent tube or Stirling boiler system allows for a large surface heat transfer area, as well as promoting natural water circulation.

Advantages of Watertube Boilers:

They contain small water content and have the ability to respond rapidly to load change and heat input.

The small diameter tubes and steam drum mean that much higher steam pressures can be tolerated.

Disadvantages of Watertube Boilers:

They are not as simple to assemble when compared to other types of watertube boilers and require more work on site.

The option of multiple burners may give flexibility, but the 30 or more burners used also require complex control.