What is Water-tube Boiler? – Water-tube boiler is a type of boiler with pipes containing circulated water, which is heated by a fire on the outer side of the pipe. The water-tube boiler has the opposite design with the fire-tube boiler. This boiler circulates water through the pipelines with the heat source coming from the furnace. These pipes, which become the water-vapor circulation pipes, are inside the combustion chamber blanket or the combustion hot gas duct. In modern water-tube boilers with large production loads, there are several parts of water pipes designed to be the walls of the boiler’s combustion chamber. The pipes are usually known by the term wall-tube.
A water tank, commonly called a steam drum, is one of the water-tube boiler character. Steam drums serve as a water tank to ensure there is always enough water circulated to the water pipes. Otherwise, steam drum also serves to separate the saturated steam with water. Saturated steam coming out of the steam drum will be heated further to become superheated steam.
Modern water-tube boiler, equipped with water pipes designed as the boiler walls (wall-tube). Water from the steam drum goes down through a pipe called downcomer to the header pipe (lower ring header) connected to all the lower ends of the wall-tube. The other end of the wall-tube at the top of the combustion chamber is directly connected to the steam drum. In the wall-tube, there is a phase change from water to steam. This water-pipe system produces a closed water circulation between the steam drum – downcomer – wall-tube and back to the steam drum. From steam drum only saturated steam will come out. In superheater boilers, the saturated steam will be heated further into superheated steam.
Even though the water-tube boiler has a slightly more complex design than a fire-tube boiler, this boilers tend to be more capable of producing higher steam quality, as well as a much larger capacity. Hence the water-tube boiler is more suitable to be applied to large industries, such as steam power plants, that demand more quantity, as well as high steam qualities.