Solid fuel

Solid fuel from biomass is regarded as a renewable energy source which can contribute to climate change mitigation efforts. Solid fuel from fossil fuels (i.e. coal) is not a renewable energy.

Types

Biomass

Biomass that is used for energy production can be processed into solid fuels but also into liquid or gaseous fuels. In comparison, the term biofuel is nowadays mainly (but not exclusively) used for liquid or gaseous fuels, used for transportation.

Pellet fuels are made from compressed organic matter or biomass. Pellets can be made from any one of five general categories of biomass: industrial waste and co-products, food waste, agricultural residues, energy crops, and untreated lumber. Wood pellets are the most common type of pellet fuel.

In the context of energy production, biomass is matter from recently living (but now dead) organisms which is used for bioenergy production. Examples include wood, wood residues, energy crops, agricultural residues including straw, and organic waste from industry and households. Wood and wood residues is the largest biomass energy source today. Wood can be used as a fuel directly or processed into pellet fuel or other forms of fuels. Other plants can also be used as fuel, for instance maize, switchgrass, miscanthus and bamboo. The main waste feedstocks are wood waste, agricultural waste, municipal solid waste, and manufacturing waste. Upgrading raw biomass to higher grade fuels can be achieved by different methods, broadly classified as thermal, chemical, or biochemical.

Wood

Wood fuel can refer to several fuels such as firewood, charcoal, wood chips sheets, pellets, and sawdust. The particular form used depends upon factors such as source, quantity, quality and application. In many areas, wood is the most easily available form of fuel, requiring no tools in the case of picking up dead wood, or few tools. Today, burning of wood is 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 may be used indoors in a furnace, stove, or fireplace, or outdoors in a furnace, campfire, or bonfire. As with any fire, burning wood fuel creates numerous by-products, some of which may be useful (heat and steam), and others that are undesirable, irritating or dangerous.

When harvested in a sustainable fashion wood is usually considered to be a renewable solid fuel (renewable energy).

There is debate as to whether burning wood can be considered carbon neutral, as technically the wood cannot release more carbon than was sequestered during its growth, although this does not take account of other impacts such as deforestation and rotting has on the carbon footprint.

Peat

Peat fuel is an accumulation of partially decayed vegetation or organic matter that can be burnt once sufficiently dried. It is used widely in the country districts of Ireland and Scotland where alternatives are absent or expensive. It has a relatively low calorific value, even after essential drying.

Fossil fuels

Coal

Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. Throughout history, coal has been used as an energy resource, primarily burned for the production of electricity and heat, and is also used for industrial purposes, such as refining metals. Coal is the largest source of energy for the generation of electricity worldwide, as well as one of the largest worldwide The extraction of coal, its use in energy production and its byproducts are all associated with environmental and health effects. Variations such as smokeless coal can be formed naturally in the form of anthracite, a metamorphosed type of coal with a very high carbon content that gives off a smokeless flame when set alight. It is an important type of smokeless fuel.

Coke

Coke is a fuel with few impurities and a high carbon content, usually made from coal. It is the solid carbonaceous material derived from destructive distillation of low-ash, low-sulfur bituminous coal. Cokes made from coal are grey, hard, and porous. While coke can be formed naturally, the commonly used form is man-made. The form known as petroleum coke, or pet coke, is derived from oil refinery coker units or other cracking processes.

Smokeless fuel

Solid fuels which produce little smoke or volatiles are made from powdered anthracite coal and supplied in the form of briquettes usually for domestic use either in stoves or open fireplaces. The fuel is replacing coal as a fuel for open fires because of the reduction in particulate emissions and its increased efficiency. Smokeless fuel burns at a higher temperature and more slowly than a coal fire. The term also includes charcoal, made by restricted combustion of dry wood and widely used at open air barbecues to cook food on an open fire.

Solid fuels for special applications

Rocket propellant

Solid rocket propellant consists of a solid oxidizer (such as ammonium nitrate) bound with flakes or powders of energy compounds (such as RDX) plus binders, plasticizers, stabilizers, and other additives. Solid propellant is much easier to store and handle than liquid propellant, and has a higher energy density so requires less space for the same amount of stored energy.