Biomass contains stored energy. That's because plants absorb energy from the sun through the process of photosynthesis. When biomass is burned, this stored energy is released as heat. Burning biomass releases carbon dioxide. However, plants also take carbon dioxide out of the atmosphere and use it to grow their leaves, flowers, branches, and stems.
That same carbon dioxide is returned to the air when the plants are burned. Many different kinds of biomass, such as wood chips, corn, and some types of garbage, are used to produce electricity. The lost energy and mass can be used to fuel the torrefaction process.
During torrefaction, biomass becomes a dry, blackened material. It is then compressed into briquette s. Biomass briquettes are very hydrophobic , meaning they repel water. This makes it possible to store them in moist areas. The briquettes have high energy density and are easy to burn during direct or co-firing. Direct Firing and Co-Firing Most briquettes are burned directly. The steam produced during the firing process powers a turbine , which turns a generator and produces electricity.
This electricity can be used for manufacturing or to heat buildings. Biomass can also be co-fired, or burned with a fossil fuel. Biomass is most often co-fired in coal plants. Co-firing eliminates the need for new factories for processing biomass. Co-firing also eases the demand for coal. This reduces the amount of carbon dioxide and other greenhouse gas es released by burning fossil fuels.
Pyrolysis Pyrolysis is a related method of heating biomass. This keeps it from combusting and causes the biomass to be chemically altered. Pyrolysis produces a dark liquid called pyrolysis oil, a synthetic gas called syngas, and a solid residue called biochar.
All of these components can be used for energy. Pyrolysis oil , sometimes called bio-oil or biocrude, is a type of tar. It can be combusted to generate electricity and is also used as a component in other fuels and plastics. Scientists and engineers are studying pyrolysis oil as a possible alternative to petroleum.
Syngas can be converted into fuel such as synthetic natural gas. It can also be converted into methane and used as a replacement for natural gas. Biochar is a type of charcoal. Biochar is a carbon-rich solid that is particularly useful in agriculture. Biochar enriches soil and prevents it from leach ing pesticide s and other nutrients into runoff. Biochar is also an excellent carbon sink. Carbon sink s are reservoirs for carbon-containing chemicals, including greenhouse gases.
Gasification Biomass can also be directly converted to energy through gasification. The molecules break down, and produce syngas and slag. Syngas is a combination of hydrogen and carbon monoxide. During gasification, syngas is cleaned of sulfur, particulates, mercury, and other pollutants.
The clean syngas can be combusted for heat or electricity, or processed into transportation biofuels, chemicals, and fertilizer s. Slag forms as a glassy, molten liquid. It can be used to make shingles, cement, or asphalt. Industrial gasification plants are being built all over the world. Asia and Australia are constructing and operating the most plants, although one of the largest gasification plants in the world is currently under construction in Stockton-on-Tees, England.
This plant will eventually be able to convert more than , tons of MSW into enough energy to power 50, homes. Anaerobic Decomposition Anaerobic decomposition is the process where microorganisms, usually bacteria , break down material in the absense of oxygen. Anaerobic decomposition is an important process in landfill s, where biomass is crushed and compressed, creating an anaerobic or oxygen-poor environment. In an anaerobic environment, biomass decay s and produces methane, which is a valuable energy source.
This methane can replace fossil fuels. In addition to landfills, anaerobic decomposition can also be implemented on ranch es and livestock farms. Manure and other animal waste can be converted to sustainably meet the energy needs of the farm. Biofuel Biomass is the only renewable energy source that can be converted into liquid biofuels such as ethanol and biodiesel. Biofuel is used to power vehicles, and is being produced by gasification in countries such as Sweden, Austria, and the United States.
Ethanol is made by ferment ing biomass that is high in carbohydrates, such as sugar cane, wheat, or corn. Biodiesel is made from combining ethanol with animal fat, recycled cooking fat, or vegetable oil.
Biofuels do not operate as efficiently as gasoline. However, they can be blended with gasoline to efficiently power vehicles and machinery, and do not release the emissions associated with fossil fuels. Ethanol requires acres of farmland to grow biocrops usually corn. About 1, liters gallons of ethanol is produced by an acre of corn. But this acreage is then unavailable for growing crops for food or other uses.
Growing enough corn for ethanol also creates a strain on the environment because of the lack of variation in planting, and the high use of pesticides. Ethanol has become a popular substitute for wood in residential fireplaces. When it is burned, it gives off heat in the form of flames, and water vapor instead of smoke.
Biochar Biochar, produced during pyrolysis, is valuable in agricultural and environmental use. When biomass rots or burns naturally or by human activity , it releases high amounts of methane and carbon dioxide into the atmosphere. However, when biomass is charred, it sequester s, or stores, its carbon content. When biochar is added back to the soil, it can continue to absorb carbon and form large underground stores of sequestered carbon—carbon sinks—that can lead to negative carbon emissions and healthier soil.
Biochar also helps enrich the soil. It is porous. When added back to the soil, biochar absorbs and retains water and nutrients. This enhances the soil and leads to significantly higher plant growth. Black Liquor When wood is processed into paper, it produces a high-energy, toxic substance called black liquor.
Until the s, black liquor from paper mills was considered a waste product and dumped into nearby water sources. With the invention of the recovery boiler in the s, black liquor could be recycled and used to power the mill. In the U. More recently, Sweden has experimented in gasifying black liquor to produce syngas, which can then be used to generate electricity.
Hydrogen Fuel Cells Biomass is rich in hydrogen, which can be chemically extracted and used to generate power and to fuel vehicles.
Stationary fuel cells are used to generate electricity in remote locations, such as spacecraft and wilderness areas. Burning municipal solid waste MSW , or garbage , in waste-to-energy plants could result in less waste buried in landfills.
On the other hand, burning garbage produces air pollution and releases the chemicals and substances in the waste into the air. Some of these chemicals can be hazardous to people and the environment if they are not properly controlled. The U. Environmental Protection Agency EPA applies strict environmental rules to waste-to-energy plants , which require waste-to-energy plants to use air pollution control devices such as scrubbers, fabric filters, and electrostatic precipitators to capture air pollutants.
Scrubbers clean emissions from waste-to-energy facilities by spraying a liquid into the combustion gases to neutralize the acids present in the stream of emissions.
Fabric filters and electrostatic precipitators also remove particles from the combustion gases. The particles—called fly ash—are then mixed with the ash that is removed from the bottom of the waste-to-energy furnace. Ash from waste-to-energy plants can contain high concentrations of various metals that were present in the original waste. Textile dyes, printing inks, and ceramics, for example, may contain lead and cadmium. Separating waste before burning can solve part of the problem.
Because batteries are the largest source of lead and cadmium in municipal waste, they should not be included in regular trash. Florescent light bulbs should also not be put in regular trash because they contain small amounts of mercury. The EPA tests ash from waste-to-energy plants to make sure that it is not hazardous. The test looks for chemicals and metals that could contaminate ground water.
Some MSW landfills use ash that is considered safe as a cover layer for their landfills, and some MSW ash is used to make concrete blocks and bricks. Biogas forms as a result of biological processes in sewage treatment plants, waste landfills, and livestock manure management systems. Biogas is composed mainly of methane a greenhouse gas and CO2. Many facilities that produce biogas capture it and burn the methane for heat or to generate electricity. This electricity is considered renewable and, in many states, contributes to meeting state renewable portfolio standards RPS.
This electricity may replace electricity generation from fossil fuels and can result in a net reduction in CO2 emissions. Burning methane produces CO2, but because methane is a stronger greenhouse gas than CO2, the overall greenhouse effect is lower. Biofuels are transportation fuels such as ethanol and biomass-based diesel fuel. The federal government promotes biofuels as transportation fuels to help reduce oil imports and CO2 emissions. In , the U. As a result, nearly all gasoline now sold in the United States contains some ethanol.
Biofuels may be carbon-neutral because the plants that are used to make biofuels such as corn and sugarcane for ethanol and soy beans and oil palm trees for biodiesel absorb CO2 as they grow and may offset the CO2 emissions when biofuels are produced and burned.
Growing plants for biofuels is controversial because the land, fertilizers, and energy for growing biofuel crops could be used to grow food crops instead.
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