Biomass
Biomass—renewable energy from plants and animals
Source: Adapted from The National Energy Education Project (public domain)
Source: Adapted from The National Energy Education Project (public domain)
Biomass is organic material that comes from plants and animals, and it is a renewable source of energy.Biomass contains stored energy from the sun. Plants absorb the sun's energy in a process called photosynthesis. When biomass is burned, the chemical energy in biomass is released as heat. Biomass can be burned directly or converted to liquid biofuels or biogas that can be burned as fuels. Examples of biomass and their uses for energy:
· wood and wood processing wastes—burned to heat buildings, to produce process heat in industry, and to generate electricity
· agricultural crops and waste materials—burned as a fuel or converted to liquid biofuels
· food, yard, and wood waste in garbage—burned to generate electricity in power plants or converted to biogas in landfills
· animal manure and human sewage—converted to biogas, which can be burned as a fuel
Converting biomass to other forms of energy
Burning is only one way to release the energy in biomass. Biomass can be converted to other useable forms of energy such as methane gas or transportation fuels such as ethanol and biodiesel.Methane gas is a component of landfill gas or biogas that forms when garbage, agricultural waste, and human waste decompose in landfills or in special containers called digesters. Crops such as corn and sugar cane are fermented to produce fuel ethanol for use in vehicles. Biodiesel, another transportation fuel, is produced from vegetable oils and animal fats.
How much biomass is used for fuel?
Biomass fuels provided about 5% of the primary energy used in the United States in 2016. Of that 5%, about 48% was from biofuels (mainly ethanol), 41% was from wood and wood-derived biomass, and about 11% was from the biomass in municipal waste. Researchers are trying to develop ways to use more biomass for fuel.
Biofuels are transportation fuels such as ethanol and biodiesel that are made from biomass materials. These fuels are usually blended with petroleum fuels (gasoline and diesel fuel), but they can also be used on their own. Using ethanol or biodiesel means less gasoline and diesel fuel is burned, which can reduce the amount of crude oil imported from other countries. Ethanol and biodiesel are also cleaner-burning fuels than pure gasoline and diesel fuel.
What is ethanol?
Ethanol is an alcohol fuel made from the sugars found in grains such as corn, sorghum, and barley.
United States Department of Agriculture (USDA) research geneticists study switchgrass as a source of ethanol.
Other sources of sugars to produce ethanol include
· Sugar cane
· Sugar beets
· Potato skins
· Rice
· Yard clippings
· Tree bark
Most of the fuel ethanol used in the United States is distilled from corn. Scientists are working on ways to make ethanol from all parts of plants and trees rather than just grain. Farmers are experimenting with fast-growing woody crops such as small poplar and willow trees and switchgrass to see if they can be used to produce ethanol.
Ethanol is blended with gasoline
Nearly all of the gasoline now sold in the United States is about 10% ethanol by volume. Any gasoline-powered engine in the United States can use E10 (gasoline with 10% ethanol), but only specific types of vehicles can use mixtures with fuel containing more than 10% ethanol. A flexible-fuel vehicle can use gasoline with ethanol content greater than 10%. The U.S. Environmental Protection Agency ruled in October 2010 that cars and light trucks of model year 2007 and newer can use E15 (gasoline with 15% ethanol). E85, a fuel that contains 51%–83% ethanol, depending on location and season, is mainly sold in the Midwest and can only be used in a flexible-fuel vehicle.
What is biodiesel?
Biodiesel is a fuel made from vegetable oils, fats, or greases—such as recycled restaurant grease. Biodiesel fuel can be used in diesel engines without changing the engine. Pure biodiesel is non-toxic, biodegradable, and produces lower levels of most air pollutants than petroleum-based diesel fuel. Biodiesel is usually sold as a blend of biodiesel and petroleum-based diesel fuel. A common blend of diesel fuel is B20, which is 20% biodiesel.
Geothermal reservoirs are naturally occurring areas of hydrothermal resources. These reservoirs are deep underground and are largely undetectable above ground. Geothermal energy finds its way to the earth's surface in three ways:
· Volcanoes and fumaroles (holes in the earth where volcanic gases are released)
· Hot springs
· Geysers
Most geothermal resources are near tectonic plate boundaries
The most active geothermal resources are usually found along major tectonic plate boundaries where most volcanoes are located. One of the most active geothermal areas in the world is called the Ring of Fire, which encircles the Pacific Ocean.
When magma comes near the earth's surface, it heats ground water trapped in porous rock or water running along fractured rock surfaces and faults. Hydrothermal features have two common ingredients, water (hydro) and heat (thermal).
Geologists use various methods to find geothermal reservoirs. Drilling a well and testing the temperature deep underground is the most reliable method for locating a geothermal reservoir.
U.S. geothermal power plants are located in the West
Most of the geothermal power plants in the United States are in western states and Hawaii, where geothermal energy resources are close to the earth's surface. California generates the most electricity from geothermal energy. The Geysers dry steam reservoir in Northern California is the largest known dry steam field in the world and has been producing electricity since 1960.
Geothermal power plants use hydrothermal resources that have both water (hydro) and heat (thermal). Geothermal power plants require high-temperature (300°F to 700°F) hydrothermal resources that come from either dry steam wells or from hot water wells. People use these resources by drilling wells into the earth and then piping steam or hot water to the surface. The hot water or steam powers a turbine that generates electricity. Some geothermal wells are as much as two miles deep.
Types of geothermal power plants
There are three basic types of geothermal power plants:
· Dry steam plants use steam directly from a geothermal reservoir to turn generator turbines. The first geothermal power plant was built in 1904 in Tuscany, Italy, where natural steam erupted from the earth.
· Flash steam plants take high-pressure hot water from deep inside the earth and convert it to steam to drive generator turbines. When the steam cools, it condenses to water and is injected back into the ground to be used again. Most geothermal power plants are flash steam plants.
· Binary cycle power plants transfer the heat from geothermal hot water to another liquid. The heat causes the second liquid to turn to steam, which is used to drive a generator turbine.
· The environmental effects of geothermal energy depend on how geothermal energy is used or how it is converted to useful energy. Direct use applications and geothermal heat pumps have almost no negative effects on the environment. In fact, they can have a positive effect by reducing the use of energy sources that have more or greater negative effects on the environment.
· Grand Prismatic Spring, Yellowstone National Park, Wyoming
· Geothermal power plants have low emission levels
· Geothermal power plants do not burn fuel to generate electricity, so the levels of air pollutants they emit are low. Geothermal power plants emit 97% less acid rain-causing sulfur compounds and about 99% less carbon dioxide than fossil fuel power plants of similar size. Geothermal power plants use scrubbers to remove the hydrogen sulfide naturally found in geothermal reservoirs. Most geothermal power plants inject the geothermal steam and water that they use back into the earth. This recycling helps to renew the geothermal resource.
· Many geothermal features are national treasures
· Geothermal features in national parks, such as geysers and fumaroles in Yellowstone National Park, are protected by law.