Wood Fuel

Wood fuel is wood used as fuel. The burning of wood is currently the largest use of energy derived from a solid fuel biomass. Wood fuel can be used for cooking and heating, and occasionally for fueling steam engines and steam turbines that generate electricity. Wood fuel may be available as firewood (eg. logs, bolts, blocks), charcoal, chips, sheets, pellets and sawdust. The particular form used depends upon factors such as source, quantity, quality and application. Sawmill waste and construction industry by-products also include various forms of lumber tailings.

Wood may be burned in a furnace, stove, fireplace, or in a campfire, or used for a bonfire. Wood is the most easily available form of fuel, requiring no tools in the case of picking up dead wood, or little tools, although as in any industry, specialized tools, such as skidders and hydraulic wood splitters, have evolved to mechanize production.

The discovery of how to make fire for the purpose of burning wood is regarded as one of humanity's most important advances.

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.
Application

Boilers have many applications. They can be used in stationary applications to provide heat, hot water, or steam for domestic use, or in generators and they can be used in mobile applications to provide steam for locomotion in applications such as trains, ships, and boats. Using a boiler is a way to transfer stored energy from the fuel source to the water in the boiler, and then finally to the point of end use.

Materials

Construction of boilers is mainly in steel, stainless steel, and wrought iron. In live steam models, copper or brass is often used. Historically copper was often used for fireboxes (particularly for steam locomotives), because of its better thermal conductivity. The price of copper now makes this impractical.

Cast iron is used for domestic water heaters. Although these are usually termed "boilers", their purpose is to produce hot water, not steam, and so they run at low pressure and try to avoid actual boiling. The brittleness of cast iron makes it impractical for steam pressure vessels.

For much of the Victorian "age of steam", the only material for boilermaking was the highest grade of wrought iron, with assembly by rivetting. This iron was often obtained from specialist ironworks, such as Cleator Moor (UK), noted for the high quality of their rolled plate and its suitability for high reliability use in critical applications, such as high pressure boilers. 20th century practice moved towards steel and welding.

Fuel

The 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

Boilers can be classified into the following 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.
* Fire-tube boiler. Here, water partially fills a boiler barrel with a small volume left above to accommodate the steam (steam space). This is the type of boiler used in nearly all steam locomotives. The heat source is inside a furnace or firebox that has to be kept permanently surrounded by the water in order to maintain the temperature of the heating surface just below boiling point. The furnace can be situated at one end of a fire-tube which lengthens the path of the hot gases, thus augmenting the heating surface which can be further increased by making the gases reverse direction through a second parallel tube or a bundle of multiple tubes (two-pass or return flue boiler); alternatively the gases may be taken along the sides and then beneath the boiler through flues (3-pass boiler). In the case of a locomotive-type boiler, a boiler barrel extends from the firebox and the hot gases pass through a bundle of fire tubes inside the barrel which greatly increase the heating surface compared to a single tube and further improve heat transfer. Fire-tube boilers usually have a comparatively low rate of steam production, but high steam storage capacity. Fire-tube boilers mostly burn solid fuels, but are readily adaptable to those of the liquid or gas variety.
* Water-tube boiler. In this type,the water tubes are arranged inside a furnace in a number of possible configurations: often the water tubes connect large drums, the lower ones containing water and the upper ones, steam; in other cases, such as a monotube boiler, water is circulated by a pump through a succession of coils. This type generally gives high steam production rates, but less storage capacity than the above. Water tube boilers can be designed to exploit any heat source including nuclear fission and are generally preferred in high pressure applications since the high pressure water/steam is contained within narrow pipes which can withstand the pressure with a thinner wall.

Boiler for steam locomotive[3]

* Flash boiler. A specialized type of water-tube boiler.
* 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 firetube boiler. Water-tube fireboxes were installed in many Hungarian locomotives, but have met with little success in other countries.
* Sectional boiler. In 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.