BOILERSBOILERS

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WHAT IS A BOILER?A boiler is a closed vessel

in which water or other fluid is heated.

The heated or vaporized fluid exits the boiler for use in various processes or heating applications.

A portable boiler(preserved, Poland)

A stationary boiler(United States)

MATERIALS

The pressure vessel in a boiler is usually made of steel (or alloy steel), or historically of wrought iron.

Stainless steel is virtually prohibited (by the ASME Boiler Code) for use in wetted parts of modern boilers, but is used often in super heater sections that will not be exposed to liquid boiler water.

In live steam models, copper or brass is often used because it is more easily fabricated in smaller size boilers.

Cast iron may be used for the heating vessel of domestic water heaters.

FUELThe source of heat for a boiler is combustion of any of several fuels, such as wood, coal, oil, or natural gas.Electric steam boilers use resistance- or immersion-type heating elements.Nuclear fission is also used as a heat source for generating steam.Heat recovery steam generators (HRSGs) use the heat rejected from other processes such as gas turbines.

CONFIGURATIONS

"Pot boiler" or "Haycock boiler": a primitive "kettle" where a fire heats a partially-filled water container from below. 18th century Haycock boilers generally produced and stored large volumes of very low-pressure steam, often hardly above that of the atmosphere. These could burn wood or most often, coal. Efficiency was very low.

Boilers can be classified into the following configurations:

FIRE-TUBE BOILER

A fire-tube boiler is a type of boiler in which hot gases from a fire pass through one or more tubes running through a sealed container of water. The heat energy from the gases passes through the sides of the tubes by thermal conduction, heating the water and ultimately creating steam.

Diagram of a fire-tube boiler

Sectioned fire-tube boiler from a DRB Class 50 locomotive.

WATER-TUBE BOILER

A water tube boiler is a type of boiler in which water circulates in tubes heated externally by the fire. Water tube boilers are used for high-pressure boilers. Fuel is burned inside the furnace, creating hot gas which heats water in the steam-generating tubes.

Schematic diagram of a marine-type water tube boiler.

Diagram of a water-tube boiler.

FLASH BOILER

A flash boiler is a type of water-tube boiler, whose tubes are strong and close together with water pumped through the tubes. The tubes are kept very hot so the water feed is quickly flashed into steam and superheated. They have these advantages:Less weight and bulk.Less time to raise steam from cold.A flash boiler is much easier than an ordinary boiler to overheat, as there is no large reservoir of water to keep the tubes from high temperature if the water flow is interrupted or inadequate.

FIRE-TUBE BOILER WITH WATER-TUBE FIREBOX

Sometimes the two above types have been combined in the following manner: the firebox contains an assembly of water tubes, called thermic syphons. The gases then pass through a conventional fire tube boiler. Water-tube fireboxes were installed in many Hungarian locomotives, but have met with little success in other countries.

Boiler for steam locomotive.

SECTIONAL BOILERIn a cast iron sectional boiler, sometimes called a "pork chop boiler" the water is contained inside cast iron sections. These sections are assembled on site to create the finished boiler.

BOILERSBOILERS

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