Water Tube Boiler – Working Principle, Types of Water Tube Boilers

The water tube boilers are mainly used for generating steam with high temperature as well as pressure. The internal structure of this boiler includes a tiny steam drum, small width tubes. The components of this boiler generate high-volume vapor for high-capacity applications. These boilers are most frequently used boilers, which has replaced several boilers like fire tube due to some reasons like the weight of this tube is less, steam producing process is faster, custom design, high efficiency. The earlier water tubes include an arrangement of the only drum by headers that are connected by short, straight tubes and bent pipes. The hot gases will flow over the pipes in one go only. This article discusses an overview of water tube boiler, components, and its types.

What is a Water Tube Boiler?

A water tube boiler can be defined as a Steam boiler in which the flow of water in the tubes, as well as hot gases, enclose the tubes. Not like fire tube boilers, this boiler attains high-pressures, as well as high-steam capabilities, can be achieved. This is because of condensed tangential pressure on tubes which is known as hoop stress.

Water Tube Boiler
Water Tube Boiler

Components of Water Tube Boiler

The water tube boiler can be built with boiler shell, burner, mud drum or mud ring, furnace, safety valve, strainer, sight glass, feed check valve, steam stop valve, etc.

  • Boiler Shell: This shell is the external cylindrical part of a pressure container.
  • Mud Drum: This is a cylindrical formed space at the base of the water space. The impurities like mud, sediment, and others will be gathered.
  • Strainer:  This is a type of device as a filter to hold solid elements letting a fluid to supply.
  • Sight Glass: A glass tube is utilized on steam type boilers for giving observable signs of the water level in boilers.
  • Security Valve: A spring-loaded tap that unlocks when force gets the location of the valve. This can be used for stopping the unnecessary force from the construction of a boiler
  • Boiler: This is a surrounded space offered for the fuel combustion.
  • Feed-Test Tap: The high-force water flows via this tap, which releases to the boiler simply and supplies the water to the water type boiler.
  • Steam-Stop Tap: It controls the steam flow supply at outside.
  • Burner: This is one type of device for the beginning of air and fuel into a boiler at the preferred velocity. This is the most essential apparatus for the firing of gas or oil.

Working Principle of Water Tube Boiler

The working principle of water tube boiler is thermal siphoning (circulation of natural water). Basically, this type of boiler includes two drums namely steam, lower or mud drum.

The water tube boiler diagram is shown below, and these two drums are associated via two tubes such as downcomer and riser. At first, the water is supplied into the steam type drum with the help of a water pump. Whenever the fuel is burned, then hot gases will be generated that are permitted to supply in the shell part of the boiler. The hot gases which are produced by the fuel will replace heat by the water; the water gets changed into steam. Because, the water temperature increases, the concentration will increase automatically.

Clearly, the concentration of steam will be lesser than the water. Thus in the steam drum, the water, as well as steam, gets divided obviously due to variation in concentration. Here the traveling of steam will be upward because of low concentration as well as water will travel downward because of high concentration.

The flow of hot water at the base of the steam drum will be supplied into mud drum via downcomer tube as well as to heat the water in the mud type drum. Whenever cooler supply water is initiated into steam type drum due to the high concentration of cool water, and it moves down in the downcomer type tube near mud drum.

When transferring hot water from the mud type drum to steam type drum using riser tubes then it consequences in normal water circulation in the water tube type boiler. As additional steam is generated in the boiler then the force in the drum enhances & the water supply into the drum reduces which tend for decreasing the flow of steam. In the same way, when the production rate of steam reduces the force in the water-tube boiler reduces, & the water supply into the boiler enhances which tends to enhance the production rate. Like this, the water tube boiler controls the production of steam.

Types of Water Tube Boilers

The types of water tube boilers include the following.

  • Simple Vertical Boiler
  • Stirling Boiler
  • Babcock and Wilcox Boilers

1) Simple Vertical Boiler

This is one type of water tube boiler. In this type of boiler, the axis of direction is perpendicular with respect to the position. The major components of this boiler include ash pit, grate, feed check tap, fire hole, firebox, cross box, hand hole, fusible plug, water gauge, cylindrical shell, steam space, manhole, pressure gauge, steam stop tap, safety tap, chimney.

In this type of boiler, using the fire hoke fuel is added into the grate which destroys by fire to generate the warm gases. Ash pit is for collecting the ash which is converted from the fuel. Hot gases increase high and supply their heat toward the water within the cross box, then moves out using the chimney.

Simple Vertical Boiler
Simple Vertical Boiler

When the water heats up and generates vapor as a result of water heating then collects at the boiler’s vapor space. Vapor is gathered until an assured force is conquered & vapor moves out to activate engine or turbine. These boilers are used in steam power-driven vehicles as well as mobile machines like railway steam engine, steam tractor, Steam shovels, and steam cranes.

2) Stirling Boiler

The Stirling boiler is one type of water tube boiler, used for generating steam (50,000 kg steam/hour and 60 kgf /cm2 pressure) in the large area of the stationary plant. This type of boiler consists of 3 steam drums as well as 2 mud drums. The steam drums are located on the top section of the boiler whereas mud drums are located on the base of the arrangement. The steam drums and mud drums are connected through bent tube banks.

Stirling Water Tube Boiler
Stirling Water Tube Boiler

When the tubes are turned then the mechanical pressures due to pipes extension throughout heating cannot influence the system. The two drums as well as tubes are designed of steel which will support the total system.

The arrangement of the Stirling boiler is enclosed with brickwork. Here, the arrangement of bricks will avoid the heat dissipation in the surroundings

3) Babcock and Wilcox Boilers

This is a horizontal straight water tube boiler; it has a steam drum which is made of steel. The two ends of the drum are associated with a series of two end headers with short riser pipes. These are disposed at 15o0 angle to the horizontal axis of the steam drum. The disposed of the arrangement of tubes assists in the supply of water, and the water level in the drum is indicated with a water level indicator.

Babcock and Wilcox Boiler
Babcock and Wilcox Boiler

The fire door in the water boiler will be located at the bottom and the fuel will be supplied through this door and burns in a grate. The burning fuel will generate the hot gases that are forced in the grate to supply upward with baffle plates. At the bottom of the water boiler, mud collector is located for removing the mud particles using blow down a cock. Therefore, a nonstop water circulation from the steam drum toward the water tubes is maintained by convective currents because of the difference in concentration and it is called as normal circulation.

Thus, this is all about water tube boiler design, working principle, and its types. From the above information finally, we can conclude that all components of the water tube boilers are simply available for inspecting, repairing and cleaning. But they need cautious concentration. Here is a question for you, what is the difference between fire tube boiler and water tube boiler?