2. Steam Boilers - Introduction .... Page 1/1
- The function of a boiler in the steam cycle is to convert water into steam. Steam from boilers are either used for steam propulsion in steam ships or for auxiliary usage in diesel
propulsion ships. Usually, for diesel vessels the steam produced in boilers is saturated and has moderate steam pressure (less than 20 bar), while for steam propulsion, the steam is superheated
(could be as high as 500 degree Celsius or more) and at much higher pressure (60 bar or more).
2.1 Example of a 2-drum Water Tube Boiler with Front Firing
- The water tube boiler does away with the need for a strong outer shell to contain the steam pressure. Steam bubbles rise as soon as they are formed and cause the water to circulate freely
around the pipework. Water and steam are separated in the steam drum. Rapid water movement prevents a film of steam forming on the tube surfaces which would otherwise reduce heat transfer from
the metal tube to the water. This not only improves efficiency, but prevents overheating of the tubes.
Study the drawings of the water tube boiler and the scematic diagram of Natural Circulation in watertube boilers. We will learn these things in greater detail later.
