Иностранный язык (английский яз)

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 (e.g. logs, blocks), charcoal, chips, sheets, and sawdust. The particular form used de­pends upon factors such as source, quantity, quality and application. Wood may be sent into a furnace to be burned, stove, fireplace, or in a campfire, or used for a bonfire. Wood is the most easily available form of fuel, and it is a renewable source of energy.

     The use of wood as a fuel source for heating is as old as civili­zation itself.

Early examples include the use of wood heat in tents. Fires were constructed on the ground, and a smoke hole in the top of the  tent allowed the smoke to escape by convection.

    In permanent structures and in caves, hearths were constructed – surfaces of stone or another noncombustible material upon which a fire could be built. Smoke escaped through a smoke hole in the roof.

    The Greeks, Romans, Celts, Britons, and Gauls all had access to forests suitable for using as fuel.

Total demand for fuel increased considerably with the indus­trial revolution but most of this increased demand was met by the new fuel source. Coal, which was more compact and more suited to the larger scale of the new industries.

The development of the chimney and the fireplace allowed for more effective exhaustion of the smoke. Masonry heaters or stoves went a step further by capturing much of the heat of the fire and exhaust in a large thermal mass, becoming much more efficient than a fireplace alone.

The metal stove was a technological development concurrent with the industrial revolution. Stoves were manufactured or con­structed pieces of equipment that contained the fire on all sides and provided a means for controlling the draft. Stoves have been made of a variety of materials: cast iron, soapstone, tile, and steel. Metal stoves are often lined with refractory materials such as firebrick, since the hottest part of a woodburning fire will burn away steel over the course of several years' use.

The Franklin stove was developed in the United Slates by Ben­jamin Franklin. More a manufactured fireplace than a stove, it had an open front and a heat exchanger in the back that was designed to draw air from the cellar and heal it before releasing it out the sides. So-called ‘’Franklin’’ stoves today are made in a great vari­ety of styles, though none resembles the original design.

The 1800s became the high point of the cast iron stove. Each local foundry would make their own design, and stoves were built for myriads of purposes –  parlour stoves, camp stoves, railroad stoves, portable stoves, cooking stoves and so on. Wood or coal would be burnt in the stoves and thus they were popular for over one hundred years. The action of the fire, combined with the causticity of the ash, ensured that the stove would eventually disintegrate or crack over time. Thus a steady supply of stoves was needed. The maintenance of stoves, needing to be blacked, their smokiness, and the need to split wood meant that oil or electric heat found favour.

      In the 19th century the airtight stove, originally made of steel, became common. They allowed greater control of combustion, being more tightly fitted than other stoves of the day.

      Use of wood heat declined in popularity with the growing availability of other, less labor-intensive fuels. Wood heat was gradually replaced by coal and later by fiel oil, natural gas and propane heating except in rural areas with available forests.

      Today in rural, forested pails of the U.S., freestanding boilersare are increasingly common. They are installed outdoors, some distance from the house, and connected to a heat exchanger in the house using underground piping. The mess of wood, bark, smoke and ashes is kept outside and the risk of fire is reduced. The boilers are large enough to hold a fire all night, and can burn larger pieces of wood, so that less cutting and splitting is required. However, outdoor wood boilers emit more wood smoke and associated pollutants than other wood-burning appliances. This is due to design characteristics such as the water-filled jacket surrounding the firebox, which acts to cool the fire and leads to incomplete combustion. An alternative that is increasing in popularity are wood gasification boilers, which burn wood at very high efficiencies (85-91 %) and can be placed indoors or in an outbuilding.

      As a sustainable energy source, wood fuel is still used today cooking in many places, either in a stove or air open fire, in many industrial processes, including smoking meat and making maple syrup, it also remains viable for generating electricity in areas with easy access to forest products and by-products.

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