biomass (energy) biomass (energy) biomass (for energy) is matter from recently living (but now dead) organisms which is used for bioenergy production. examples include wood, wood residues, energy crops, agricultural residues, 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 pellets is an example of biomass used for bioenergy production, usually for heating purposes.miscanthus × giganteus, a perennial grass can also be used for bioenergy production. the climate impact of bioenergy varies considerably depending on where biomass feedstocks come from and how they are grown. for example, burning wood for energy releases carbon dioxide; those emissions can be significantly offset if the trees that were harvested are replaced by new trees in a well-managed forest, as the new trees will absorb carbon dioxide from the air as they grow. however, the establishment and cultivation of bioenergy crops can displace natural ecosystems, degrade soils, and consume water resources and synthetic fertilisers. in 2020 biomass produced 58 ej (exajoules) of energy, compared to 172 ej from crude oil, 157 ej from coal, 138 ej from natural gas, 29 ej from nuclear, 16 ej from hydro and 15 ej from wind, solar and geothermal combined. approximately 86% of modern bioenergy is used for heating applications, with 9% used for transport and 5% for electricity. most of the global bioenergy is produced from forest resources. the iea's net zero by 2050 scenario calls for traditional bioenergy to be phased out by 2030, with modern bioenergy's share increasing from 6.6% in 2020 to 13.1% in 2030 and 18.7% in 2050. the ipcc (intergovernmental panel on climate change) believes that bioenergy has a significant climate change mitigation potential if implemented correctly. most of the ipcc's pathways including substantial contributions from bioenergy in 2050 (average at 200 ej). terminology biomass (in the context of energy generation) is matter from recently living (but now dead) organisms which is used for bioenergy production. there are variations in how such biomass for energy is defined, e.g. only from plants, or from plants and algae, or from plants and animals. the vast majority of biomass used for bioenergy does come from plants. bioenergy is a type of renewable energy with potential to assist with climate change mitigation. some people use the terms biomass and biofuel interchangeably, but it is now more common to consider biofuel to be a liquid or gaseous fuel used for transportation, as defined by government authorities in the us and eu. from that perspective, biofuel is a subset of biomass. the european union's joint research centre defines solid biofuel as raw or processed organic matter of biological origin used for energy, such as firewood, wood chips, and wood pellets.: 20–21 types and uses different types of biomass are used for different purposes: primary biomass sources that are appropriate for heat or electricity generation but not for transport include: wood, wood residues, wood pellets, agricultural residues, organic waste. biomass that is processed into transport fuels can come from corn, sugar cane, and soy. biomass is categorized either as biomass harvested directly for energy (primary biomass), or as residues and waste: (secondary biomass). biomass harvested directly for energy the main biomass types harvested directly for energy is wood, some food crops and all perennial energy crops. one third of the global forest area of 4 billion hectares is used for wood production or other commercial purposes, and forests provide 85% of all biomass used for energy globally. in the eu, forests provide 60% of all biomass used for energy, with wood residues and waste being the largest source. woody biomass used for energy often consists of trees and bushes harvested for traditional cooking and heating purposes, particularly in developing countries, with 25 ej per year used globally for these purposes. this practice is highly polluting. the world health organization (who) estimates that cooking-related pollution causes 3.8 million annual deaths. the united nations sustainable development goal 7 aims for the traditional use of biomass for cooking to be phased out by 2030. short-rotation coppices and short-rotation forests are also harvested directly for energy, providing 4 ej of energy, and are considered sustainable. the potential for these crops and perennial energy crops to provide at least 25 ej annually by 2050 is estimated. food crops harvested for energy include sugar-producing crops (such as sugarcane), starch-producing crops (such as corn), and oil-producing crops (such as rapeseed). sugarcane is a perennial crop, while corn and rapeseed are annual crops. sugar- and starch-producing crops are used to make bioethanol, and oil-producing crops are used to make biodiesel. the united states is the largest producer of bioethanol, while the european union is the largest producer of biodiesel. the global production of bioethanol and biodiesel provides 2.2 and 1.5 ej of energy per year, respectively. biofuel made from food crops harvested for energy is also known as "first-generation" or "traditional" biofuel and has relatively low emission savings. the ipcc estimates that between 0.32 and 1.4 billion hectares of marginal land are suitable for bioenergy worldwide. biomass in the form of residues and waste residues and waste are by-products from biological material harvested mainly for non-energy purposes. the most important by-products are wood residues, agricultural residues and municipal/industrial waste: wood residues are by-products from forestry operations or from the wood processing industry. had the residues not been collected and used for bioenergy, they would have decayed (and therefore produced emissions) on the forest floor or in landfills, or been burnt (and produced emissions) at the side of the road in forests or outside wood processing facilities.sawdust is residue from the wood processing industry. the by-products from forestry operations are called logging residues or forest residues, and consist of tree tops, branches, stumps, damaged or dying or dead trees, irregular or bent stem sections, thinnings (small trees that are cleared away in order to help the bigger trees grow large), and trees removed to reduce wildfire risk. the extraction level of logging residues differ from region to region, but there is an increasing interest in using this feedstock, since the sustainable potential is large (15 ej annually). 68% of the total forest biomass in the eu consists of wood stems, and 32% consists of stumps, branches and tops. the by-products from the wood processing industry are called wood processing residues and consist of cut offs, shavings, sawdust, bark, and black liquor. wood processing residues have a total energy content of 5.5 ej annually. wood pellets are mainly made from wood processing residues, and have a total energy content of 0.7 ej. wood chips are made from a combination of feedstocks, and have a total energy content of 0.8 ej. the energy content in agricultural residues used for energy is approximately 2 ej. however, agricultural residues has a large untapped potential. the energy content in the global production of agricultural residues has been estimated to 78 ej annually, with the largest share from straw (51 ej). others have estimated between 18 and 82 ej. the use of agricultural residues and waste that is both sustainable and economically feasible: 9 is expected to increase to between 37 and 66 ej in 2030. municipal waste produced 1.4 ej and industrial waste 1.1 ej. wood waste from cities and industry also produced 1.1 ej. the sustainable potential for wood waste has been estimated to 2–10 ej. iea recommends a dramatic increase in waste utilization to 45 ej annually in 2050. biomass conversion raw biomass can be upgraded into better and more practical fuel simply by compacting it (e.g. wood pellets), or by different conversions broadly classified as thermal, chemical, and biochemical. biomass conversion reduces the transport costs as it is cheaper to transport high density commodities.: 53 thermal conversion thermal upgrading produces solid, liquid or gaseous fuels, with heat as the dominant conversion driver. the basic alternatives are torrefaction, pyrolysis, and gasification, these are separated principally by how far the chemical reactions involved are allowed to proceed. the advancement of the chemical reactions is mainly controlled by how much oxygen is available, and the conversion temperature. torrefaction is a mild form of pyrolysis where organic materials are heated to 400–600 °f (200–300 °c) in a no–to–low oxygen environment. the heating process removes (via gasification) the parts of the biomass that has the lowest energy content, while the parts with the highest energy content remain. that is, approximately 30% of the biomass is converted to gas during the torrefaction process, while 70% remains, usually in the form of compacted pellets or briquettes. this solid product is water resistant, easy to grind, non-corrosive, and it contains approximately 85% of the original biomass energy. basically the mass part has shrunk more than the energy part, and the consequence is that the calorific value of torrefied biomass increases significantly, to the extent that it can compete with coals used for electricity generation (steam/thermal coals). the energy density of the most common steam coals today is 22–26 gj/t. there are other less common, more experimental or proprietary thermal processes that may offer benefits, such as hydrothermal upgrading (sometimes called "wet" torrefaction.) the hydrothermal upgrade path can be used for both low and high moisture content biomass, e.g. aqueous slurries. pyrolysis entails heating organic materials to 800–900 °f (400–500 °c) in the near complete absence of oxygen. biomass pyrolysis produces fuels such as bio-oil, charcoal, methane, and hydrogen. hydrotreating is used to process bio-oil (produced by fast pyrolysis) with hydrogen under elevated temperatures and pressures in the presence of a catalyst to produce renewable diesel, renewable gasoline, and renewable jet fuel. gasification entails heating organic materials to 1,400–1700 °f (800–900 °c) with injections of controlled amounts of oxygen and/or steam into the vessel to produce a carbon monoxide and hydrogen rich gas called synthesis gas or syngas. syngas can be used as a fuel for diesel engines, for heating, and for generating electricity in gas turbines. it can also be treated to separate the hydrogen from the gas, and the hydrogen can be burned or used in fuel cells. the syngas can be further processed to produce liquid fuels using the fischer-tropsch synthesis process. chemical conversion a range of chemical processes may be used to convert biomass into other forms, such as to produce a fuel that is more practical to store, transport and use, or to exploit some property of the process itself. many of these processes are based in large part on similar coal-based processes, such as the fischer-tropsch synthesis. a chemical conversion process known as transesterification is used for converting vegetable oils, animal fats, and greases into fatty acid methyl esters (fame), which are used to produce biodiesel. biochemical conversion main articles: biogas and biofuel biochemical processes have developed in nature to break down the molecules of which biomass is composed, and many of these can be harnessed. in most cases, microorganisms are used to perform the conversion. the processes are called anaerobic digestion, fermentation, and composting. fermentation converts biomass into bioethanol, and anaerobic digestion converts biomass into renewable natural gas (biogas). bioethanol is used as a vehicle fuel. renewable natural gas—also called biogas or biomethane—is produced in anaerobic digesters at sewage treatment plants and at dairy and livestock operations. it also forms in and may be captured from solid waste landfills. properly treated renewable natural gas has the same uses as fossil fuel natural gas. climate impacts this section is an excerpt from sustainable energy § bioenergy. the climate impact of bioenergy varies considerably depending on where biomass feedstocks come from and how they are grown. for example, burning wood for energy releases carbon dioxide; those emissions can be significantly offset if the trees that were harvested are replaced by new trees in a well-managed forest, as the new trees will absorb carbon dioxide from the air as they grow. however, the establishment and cultivation of bioenergy crops can displace natural ecosystems, degrade soils,