Biomass energy
Biomass energy refers to a renewable energy source derived from recent biological materials, including natural vegetation, agricultural residues, and purposefully grown energy crops. This form of energy can be transformed into various gaseous and liquid biofuels or used directly for heating. In 2022, the United States sourced approximately 5% of its energy from biomass, demonstrating its role as an alternative to fossil fuels like coal and oil. Biomass can be processed through thermal, biological, and chemical methods, each producing different types of fuels. Thermal conversion methods, such as combustion and gasification, utilize heat to generate electricity or produce syngas. Biological conversion, involving anaerobic digestion, leads to the creation of biogas, while chemical conversion produces biodiesel through transesterification of plant oils or animal fats.
While biomass energy can help reduce environmental waste and support energy sustainability, it also raises concerns regarding land use, soil health, and carbon emissions. The cultivation of energy crops can lead to soil nutrient depletion and erosion, while burning biomass contributes to greenhouse gas emissions. As the demand for biomass energy increases, balancing its benefits and potential environmental impacts remains a critical consideration.
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Biomass energy
Summary: Biomass energy describes a diverse category of alternative energy resources derived from recent biological sources, which can be used to produce various gaseous and liquid biofuels or to produce heat directly through several different processes.
Biomass energy is derived from materials of recent biological sources and is considered a renewable energy resource. Unlike fossil fuels, which are energy resources that result from ancient biomasses that have undergone geologic transformation into such forms as petroleum or coal, biomass energy specifically refers to biological feedstock for energy, the material that will be used to generate energy, produced recently by organisms. According to the US Energy Information Administration, the United States got 5 percent of its energy from biomass in 2022. Broadly, biomass resources can be classified into three categories based on the origins of the feedstock: natural vegetation, residues and wastes, and purposefully grown energy crops. Energy derived from feedstock harvest from natural vegetation, such as through the burning of lumber from forests, represents one of the oldest sources of energy used by humans. Residues are by-products of agriculture and food production, forestry operations, and other manufacturing and production practices that process organic materials, while waste used for biomass comes from animal farm waste, sewage, and municipal solid waste from agricultural, residential, commercial, and industrial sectors. Particular grasses, such as switch grass or fescue, and aquatic crops, such as kelp and algae, can be purposefully grown to derive biomass energy. Biomass can be used to generate heat directly through combustion, and can be harnessed to produce electricity, providing an alternative to oil and other kinds of energy fuels.
Additionally, biomass can be converted into various biogases such as methane, carbon dioxide, and synthesis gas (or syngas, a mixture of hydrogen and carbon monoxide that can be used as fuel), and liquid biofuels such as ethanol, methanol, and biodiesel. Biogases and liquid biofuels can be used in furnaces and boilers that would normally use conventional fuels like natural gas or oil for heating and electricity generation purposes, with little to no conversion of the equipment necessary. The three major processes that can be undertaken to convert biomass into viable fuels are thermal, biological, and chemical.
Thermal Conversion
Thermal conversion of biomass resources into viable fuel involves the application of increased heat in four processes: direct combustion, pyrolysis, gasification, and liquefaction. Industrial conversion of biomass to viable fuel may use a combination of these processes. Direct combustion of biomass materials such as wood can be used to produce heat, which is either used for heating purposes or for the generation of electrical energy. Electrical power generation from direct combustion, which is harnessed indirectly through turbines, is a generally inefficient means of producing electricity, since there is an often significant amount of waste heat (heat energy that is not harnessed for use in some capacity). Another method of converting biomass feedstock into a viable fuel is through the process of pyrolysis, the process of inducing decomposition in organic materials by applying high heat without oxygen. Depending on the specific origins of the biomass feedstock and the conditions of the pyrolysis, such as temperature or pressure, the resulting viable fuel can be in the form of gas, liquid, solid, or a combination of the three. An analogue to crude oil called bio-oil, or pyrolytic oil, can be produced through pyrolysis. Pyrolytic gas that is produced through pyrolysis is often fed back into the pyrolysis system as fuel in order to reduce the need for additional fuel to perform the conversion process. Solid residue called char may result from pyrolysis of organic materials and is usable as fuel.
Through gasification, the biomass feedstock converts into syngas by undergoing exposure to high temperatures and specific quantities of hydrogen and oxygen. Before gasification, the biomass might be pretreated by undergoing pyrolysis. The syngas that results from gasification can be used as fuel. The last major form of thermal conversion that can be applied to biomass feedstock is the process of liquefaction. Liquefaction produces liquid fuels such as ethanol from biomass resources.
Biological Conversion
Biological conversion consists of the feedstock undergoing processes of anaerobic digestion, digestion without the presence of oxygen, by biological agents such as yeast and various bacteria. A product of anaerobic digestion by bacteria and other biological agents is biogas, a usable gaseous fuel that is rich in methane. A digester is a tank where biomass feedstock is added, fed to biological agents that consume the resource and subsequently produce biogas. Biomass feedstock must be degraded by three kinds of bacteria before becoming usable fuel. First, the feedstock is broken down by fermentative bacteria and acetogens, organisms that produce acetate. Acetate and other simpler intermediary organic compounds that are produced by these two groups of organisms are converted into carbon dioxide and methane that become biogas by methanogens. The combination of digested biomass feedstock and anaerobically digesting organisms housed in the digester form a slurry or broth. Liquid biofuels that are mixtures of various alcohols, such as ethanol, can be derived from biomass feedstock through anaerobic digestion as well through additional distillation processes. As is the case with thermal conversion, the resulting viable fuel from biological conversion depends on the specific components of the biomass feedstock as well as the conditions of biological conversion, such as the biological agents used, pH levels, and general temperature. High moisture feedstock such as waste, sewage, and crop residues are especially well suited to produce fuel through anaerobic digestion. Biological conversion of biomass feedstock is currently performed in countries such as China, India, South Korea, Brazil, and Thailand.
Chemical Conversion
Biodiesel is a specific diesel fuel derived from vegetable oil or animal fat feedstock through chemical conversion. Oils such as vegetable oil, olive oil, and sunflower oil can be combined with an alcohol through a process called transesterification to produce biodiesel and glycerol, a viscous liquid used in pharmaceutical and soap manufacturing. The biodiesel produced through transesterification can be used directly or can be mixed with regular diesel before use. In addition to its use as a heating fuel, biodiesel can be used to fuel vehicles such as automobiles, trains, and airplanes. While plant oils can be used directly in diesel engines, doing so will result in shortened operating life of the engine. Biodiesel is a biodegradable fuel alternative to petroleum and produces fewer carbon emissions. There are currently many biodiesel refineries worldwide in such countries as Brazil, Argentina, Cambodia, Germany, Malaysia, Indonesia, and the United States.
The United States and Brazil produced approximately 80 percent of the world’s ethanol and biodiesel in 2023. The top consumers of biofuels include Germany, Brazil, France, Italy, and the United States. The United States in particular has increased its consumption of biodiesel as federal and state legislation has provided incentives for biodiesel use. Oregon and Minnesota, for example, are implementing legislation that will require the incorporation of biofuel into gasoline sold in the state; gasoline will contain 10 percent bioethanol, and diesel fuel will contain 20 percent biodiesel. In many northeastern states, buildings and homes have increasingly reduced the burning of oil for heating purposes by consuming biofuels instead. In most states, biodiesel consumption has increased because of its usage in government and civic transportation and vehicle needs, such as waste management, postal service, and military vehicles, as well as buses for public transit and school systems.
Environmental Effects
There are both environmental benefits and concerns regarding the use of biomass as a source of energy. Of the benefits, the use of residual, by-product, and waste materials to produce energy reduces the amount of environmental waste caused by agriculture, industrial manufacturing, and other human activities. Fertilizers can be produced from the solid end products of biomass energy conversion. With respect to environmental concerns associated with biomass energy, like any land-intensive human activity, purposefully grown energy crop production can adversely affect natural land and soil conditions in a given geography. One way this occurs is through the removal of nutrients from the land by the harvesting of plant material that would otherwise decompose and recycle nutrients back into the soil. The removal of vegetative matter, particularly with livestock and agricultural machinery, can affect soil texture and compaction, which can impact the ability for land to absorb water. Without vegetation, where plant roots help to keep soil in place, large tracts of land become susceptible to rapid erosion.
In addition to the effects on land, erosion deposits particulate matter into rivers, lakes, and other bodies of water, which can become a problem to wildlife. The resident soil fauna can also be adversely affected through heavy harvesting, as well as pesticide and herbicide usage. As with other forms of fuel, biomass energy can produce carbon dioxide emissions if burned to produce heat or electricity. Large carbon sinks, such as forests, act to store carbon, which reduces the amount of carbon dioxide in the atmosphere. In addition to increasing atmospheric carbon dioxide and other greenhouse gases in combustion, the large-scale harvesting of such carbon sinks reduces the capacity for and prevents future carbon sequestering, the process that removes carbon from the atmosphere and stores it into a carbon sink, which can contribute to the greenhouse effect.
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