Biomass (energy)

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. == Types and uses ==

As seen from the table above, the chief problem with biomass, such as saw dust, as an energy source is that it has far lower energy content relative to fossil fuels. 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 maize), 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. 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 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. 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. 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 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. Torrefied biomass, biochar and bio-coke can be used in blast furnaces to produce green steel, green urea/ammonia/hydrogen and green slag cement. 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==

Short-term vs long-term climate benefits Regarding the issue of climate consequences for modern bioenergy, IPCC states: "Life-cycle GHG emissions of modern bioenergy alternatives are usually lower than those for fossil fuels." Consequently, most of IPCC's GHG mitigation pathways include substantial deployment of bioenergy technologies. Some research groups state that even if the European and North American forest carbon stock is increasing, it simply takes too long for harvested trees to grow back. Bioenergy from sources with high payback and parity times take a long time to have an impact on climate change mitigation. They therefore suggest that the EU should adjust its sustainability criteria so that only renewable energy with carbon payback times of less than 10 years is defined as sustainable, for instance wind, solar, biomass from wood residues and tree thinnings that would otherwise be burnt or decompose relatively fast, and biomass from short rotation coppicing (SRC). The IPCC states: "While individual stands in a forest may be either sources or sinks, the forest carbon balance is determined by the sum of the net balance of all stands." IPCC also state that the only universally applicable approach to carbon accounting is the one that accounts for both carbon emissions and carbon removals (absorption) for managed lands (e.g. forest landscapes.) When the total is calculated, natural disturbances like fires and insect infestations are subtracted, and what remains is the human influence. IEA Bioenergy state that an exclusive focus on the short-term make it harder to achieve efficient carbon mitigation in the long term, and compare investments in new bioenergy technologies with investments in other renewable energy technologies that only provide emission reductions after 2030, for instance the scaling-up of battery manufacturing or the development of rail infrastructure. Forest carbon emission avoidance strategies give a short-term mitigation benefit, but the long-term benefits from sustainable forestry activities provide ongoing forest product and energy resources. Most of IPCC's GHG mitigation pathways include substantial deployment of bioenergy technologies. Limited or no bioenergy pathways leads to increased climate change or shifting bioenergy's mitigation load to other sectors. In addition, mitigation cost increases. Carbon accounting system boundaries Carbon positive scenarios are likely to be net emitters of CO2, carbon negative projects are net absorbers of CO2, while carbon neutral projects balance emissions and absorption equally. It is common to include alternative scenarios (also called "reference scenarios" or "counterfactuals") for comparison. The alternative scenarios range from scenarios with only modest changes compared to the existing project, all the way to radically different ones (i.e. forest protection or "no-bioenergy" counterfactuals.) Generally, the difference between scenarios is seen as the actual carbon mitigation potential of the scenarios. In addition to the choice of alternative scenario, other choices has to be made as well. The so-called "system boundaries" determine which carbon emissions/absorptions that will be included in the actual calculation, and which that will be excluded. System boundaries include temporal, spatial, efficiency-related and economic boundaries. Many biomass-only combustion facilities are relatively small and inefficient, compared to the typically much larger coal plants. Further, raw biomass (for instance wood chips) can have higher moisture content than coal (especially if the coal has been dried). When this is the case, more of the wood's inherent energy must be spent solely on evaporating moisture, compared to the drier coal, which means that the amount of CO2 emitted per unit produced heat will be higher. This moisture problem can be mitigated by modern combustion facilities. Forest biomass on average produces 10-16% more CO2 than coal. However, focusing on gross emissions misses the point, what counts is the net climate effect from emissions and absorption, taken together.EU's Joint Research Centre has examined a number of bioenergy emission estimates found in literature, and calculated greenhouse gas savings percentages for bioenergy pathways in heat production, transportation fuel production and electricity production, based on those studies. The calculations are based on the attributional LCA accounting principle. It includes all supply chain emissions, from raw material extraction, through energy and material production and manufacturing, to end-of-life treatment and final disposal. It also includes emissions related to the production of the fossil fuels used in the supply chain. It excludes emission/absorption effects that takes place outside its system boundaries, for instance market related, biogeophysical (e.g. albedo), and time-dependent effects. The authors conclude that "[m]ost bio-based commodities release less GHG than fossil products along their supply chain; but the magnitude of GHG emissions vary greatly with logistics, type of feedstocks, land and ecosystem management, resource efficiency, and technology." Because of the varied climate mitigation potential for different biofuel pathways, governments and organizations set up different certification schemes to ensure that biomass use is sustainable, for instance the RED (Renewable Energy Directive) in the EU and the ISO standard 13065 by the International Organization for Standardization. In the US, the RFS (Renewables Fuel Standard) limit the use of traditional biofuels and defines the minimum life-cycle GHG emissions that are acceptable. Biofuels are considered traditional if they achieve up to 20% GHG emission reduction compared to the petrochemical equivalent, advanced if they save at least 50%, and cellulosic if the save more than 60%. The EU's Renewable Energy Directive (RED) states that the typical greenhouse gas emissions savings when replacing fossil fuels with wood pellets from forest residues for heat production varies between 69% and 77%, depending on transport distance: When the distance is between 0 and 2500 km, emission savings is 77%. Emission savings drop to 75% when the distance is between 2500 and 10 000 km, and to 69% when the distance is above 10 000 km. When stemwood is used, emission savings varies between 70% and 77%, depending on transport distance. When wood industry residues are used, savings varies between 79% and 87%. Since the long payback and parity times calculated for some forestry projects is seen as a non-issue for energy crops (except in the cases mentioned above), researchers instead calculate static climate mitigation potentials for these crops, using LCA-based carbon accounting methods. A particular energy crop-based bioenergy project is considered carbon positive, carbon neutral or carbon negative based on the total amount of CO2 equivalent emissions and absorptions accumulated throughout its entire lifetime: If emissions during agriculture, processing, transport and combustion are higher than what is absorbed (and stored) by the plants, both above and below ground, during the project's lifetime, the project is carbon positive. Likewise, if total absorption is higher than total emissions, the project is carbon negative. In other words, carbon negativity is possible when net carbon accumulation more than compensates for net lifecycle greenhouse gas emissions. Typically, perennial crops sequester more carbon than annual crops because the root buildup is allowed to continue undisturbed over many years. Also, perennial crops avoid the yearly tillage procedures (plowing, digging) associated with growing annual crops. Tilling helps the soil microbe populations to decompose the available carbon, producing CO2. Albedo and evapotranspiration == Environmental impacts ==

The environmental impacts of biomass production need to be taken into account. For instance, in 2022, IEA stated that "bioenergy is an important pillar of decarbonisation in the energy transition as a near zero-emission fuel", and that "more efforts are needed to accelerate modern bioenergy deployment to get on track with the Net Zero Scenario [....] while simultaneously ensuring that bioenergy production does not incur negative social and environmental consequences." Sustainable forestry and forest protection IPCC states that there is disagreement about whether the global forest is shrinking or not, and quote research indicating that tree cover has increased 7.1% between 1982 and 2016. IEA Bioenergy writes: "forests managed for producing sawn timber, bioenergy and other wood products can make a greater contribution to climate change mitigation than forests managed for conservation alone." Three reasons are given: • reducing ability to act as a carbon sink when the forest matures. • Wood products can replace other materials that emitted more GHGs during production. • "Carbon in forests is vulnerable to loss through natural events such as insect infestations or wildfires" Data from FAO show that most wood pellets are produced in regions dominated by sustainably managed forests, such as Europe and North America. Europe (including Russia) produced 54% of the world's wood pellets in 2019, and the forest carbon stock in this area increased from 158.7 to 172.4 Gt between 1990 and 2020. In the EU, above-ground forest biomass increases with 1.3% per year on average, however the increase is slowing down because the forests are maturing. United Kingdom Emissions Trading System allows operators of CO2 generating installations to apply zero emissions factor for the fraction used for non-energy purposes, while energy purposes (electricity generation, heating) require additional sustainability certification on the biomass used. Biodiversity Biomass production for bioenergy can have negative impacts on biodiversity. Oil palm and sugar cane are examples of crops that have been linked to reduced biodiversity. In addition, changes in biodiversity also impacts primary production which naturally effects decomposition and soil heterotrophic organisms. Win-win scenarios (good for climate, good for biodiversity) include: • Increased use of whole trees from coppice forests, increased use of thin forest residues from boreal forests with slow decay rates, and increased use of all kinds of residues from temperate forests with faster decay rates; • Multi-functional bioenergy landscapes, instead of expansion of monoculture plantations; • Afforestation of former agricultural land with mixed or naturally regenerating forests. Win-lose scenarios (good for the climate, bad for biodiversity) include afforestation on ancient, biodiversity-rich grassland ecosystems which were never forests, and afforestation of former agricultural land with monoculture plantations. Lose-win scenarios (bad for the climate, good for biodiversity) include natural forest expansion on former agricultural land. Lose-lose scenarios include increased use of thick forest residues like stumps from some boreal forests with slow decay rates, and conversion of natural forests into forest plantations. Pollution logs). Other problems are pollution of soil and water from fertiliser/pesticide use, and emission of ambient air pollutants, mainly from open field burning of residues. The traditional use of wood in cook stoves and open fires produces pollutants, which can lead to severe health and environmental consequences. However, a shift to modern bioenergy contribute to improved livelihoods and can reduce land degradation and impacts on ecosystem services. When combusted in industrial facilities, most of the pollutants originating from woody biomass reduce by 97-99%, compared to open burning. Combustion of woody biomass produces lower amounts of particulate matter than coal for the same amount of electricity generated. ==See also==