Biomass refers to living and recently dead biological material that can be used as fuel or for industrial production. Although biomass includes both plant and animal matter, it is most commonly referred to plant matter grown biofuel, production for fibres, chemicals or heat. Some of the more common plants include miscanthus, switchgrass, hemp, corn, poplar, willow, sugarcane and oil palm.

Fossil fuels are not considered as biomass, although they have their origin in ancient biomass techniques. This is due to them containing carbon that has been “out” of the carbon cycle for a very long time.

Environmental Impact

Biomass is part of the carbon cycle. Carbon from the atmosphere is converted into biological matter by photosynthesis. On death of combustion the carbon goes back into the atmosphere as carbon dioxide (CO2). This happens over a relatively short timescale and plant matter used as a fuel can be constantly replaced by planting for new growth. Therefore a reasonable stable level of atmospheric carbon results from its use as a fuel. It is accepted that the amount of carbon stored in dry wood is approximately 50% by weight.

Though biomass is a renewable fuel and is sometimes called a “carbon neutral” fuel, its use can still contribute to global warming.

This happens when the natural carbon equilibrium is disturbed. However, when biomass is used for energy production it is widely considered carbon neutral, or a net reducer of greenhouse gasses because of the offset of methane that would have otherwise entered the atmosphere. The carbon biomass material which makes up approximately fifty percent of this dry-matter content is already part of the atmospheric carbon cycle.

Energy produced from biomass residues displaces the production of an equivalent amount of energy from fossil carbon in storage. It also shifts the composition of the recycled carbon emissions associated with the disposal of the biomass residues from a mixture of CO and CH4 to almost exclusively CO2. In the absence of energy production applications, biomass residue carbon would be recycled to the atmosphere through some combination of rotting (biodegradation) and open burning. Rotting produces a mixture of up to fifty percent CH4, while open burning produces five to ten percent CH4. Controlled combustion in a power plant converts virtually all of the carbon in the biomass to CO2. Because CH4 is a much stronger greenhouse gas than CO2, shifting CH4 emissions to CO2 by converting biomass residues to energy significantly reduces greenhouse warming potential of the recycled carbon associated with other fates or disposal of the biomass residues.

The existing commercial biomass power generating industry in the United States, which consists of approximately 1,70-0 MW of operating capacity actively supplying power generation avoids approximately two million tons per year of CH4 emissions from the biomass residues that, in the absence of energy product ion, would otherwise be disposed of by burial, by spreading and by open burning.

How Biomass Power Technology Works

There are many types of plants in the world, and many ways they can be used for energy production. In general there are two approaches: growing plants specifically for energy use, and using the residues from plants that are used for other things. The best approaches vary from region to region according to climate, soils, geography, population, and so on.

Energy Crops

Energy crops, also called "power crops," could be grown on farms in potentially very large quantities, just like food crops. Trees and grasses, particularly those that are native to a region, are the best crops for energy, but other, less agriculturally sustainable crops such as corn tend to be used for energy purposes at present.

Trees. In addition to growing very fast, some trees will grow back after being cut off close to the ground, a feature called "coppicing." Coppicing allows trees to be harvested every three to eight years for 20 or 30 years before replanting. These trees, also called "short-rotation woody crops," grow as much as 40 feet high in the years between harvests. In the cooler, wetter regions of the northern United States, varieties of poplar, maple, black locust, and willow are the best choice. In the warmer Southeast, sycamore and sweetgum are best, while in the warmest parts of Florida and California, eucalyptus is likely to grow well.

Grasses. Thin-stemmed perennial grasses used to blanket the prairies of the United States before the settlers replaced them with corn and beans. Switchgrass, big bluestem, and other native varieties grow quickly in many parts of the country, and can be harvested for up to 10 years before replanting. Thick-stemmed perennials like sugar cane and elephant grass can be grown in hot and wet climates like those of Florida and Hawaii.

Other crops. A third type of grass includes annuals commonly grown for food, such as corn and sorghum. Since these must be replanted every year, they require much closer management and greater use of fertilizers, pesticides, and energy. While corn currently provides most of the liquid fuel from biomass in the United States, there are more sustainable ways to produce energy from plants.

Oil plants. Plants such as soybeans and sunflowers produce oil, which can be used to make fuels. Like corn, though, these crops require intensive management and may not be sustainable in the longer term. A rather different type of oil crop with great promise for the future is microalgae. These tiny aquatic plants have the potential to grow extremely fast in the hot, shallow, saline water found in some lakes in the desert Southwest. In 2004, Green Fuel Technologies, a Massachusetts-based company, harnessed the ability to capture and use carbon dioxide emissions from power plants as a means to stimulate algae growth.[2] The algae is then converted into a various range of fuels. This technology, known as Emissions-to-Biofuels, is demonstrating great promise and has the potential to transform the way utilities produce energy.

Biomass Residues

After plants have been used for other purposes, the leftover wastes can be used for energy. The forestry, agricultural, and manufacturing industries generate plant and animal wastes in large quantities. City waste, in the form of garbage and sewage, is also a source for biomass energy.

Forestry. Forestry wastes are the largest source of heat and electricity now, since lumber, pulp, and paper mills use them to power their factories. One large source of wood waste is tree tops and branches normally left behind in the forest after timber-harvesting operations. Some of these must be left behind to recycle necessary nutrients to the forest and to provide habitat for birds and mammals, but some could be collected for energy production. Other sources of wood waste are sawdust and bark from sawmills, shavings produced during the manufacture of furniture, and organic sludge (or "liquor") from pulp and paper mills.

Agriculture. As with the forestry industry, most crop residues are left in the field. Some should be left there to maintain cover against erosion and to recycle nutrients, but some could be collected for fuel. Animal farms produce many "wet wastes" in the form of manure. These wastes are commonly spread on fields, not just for their nutrient value, but for disposal. Runoff from over fertilization threatens rural lakes and streams and can contaminate drinking water. Processing crops into food also produces many usable wastes.

Cities. People generate biomass wastes in many forms, including "urban wood waste" (such as shipping pallets and leftover construction wood), the biodegradable portion of garbage (paper, food, leather, yard waste, etc.) and the gas given off by landfills when waste decomposes. Even our sewage can be used as energy; some sewage treatment plants capture the methane given off by sewage and burn it for heat and power, reducing air pollution and emissions of global warming gases.

Converting Biomass to Energy

The old way of converting biomass to energy, practiced for thousands of years, is simply to burn it to produce heat. This is still how most biomass is put to use, in the United States and elsewhere. The heat can be used directly, for heating, cooking, and industrial processes, or indirectly, to produce electricity. The problems with burning biomass are that much of the energy is wasted and that it can cause some pollution if it is not carefully controlled.

An approach that may increase the use of biomass energy in the short term is to burn it mixed with coal in power plants—a process known as "co-firing." Biomass feedstock can substitute up to 20 percent of the coal used in a boiler.[3] The benefits associated with biomass co-firing include lower operating costs, reductions of harmful emissions, and greater energy security. Co-firing is also one of the more economically viable ways to increase biomass power generation today. In 2000, the Chariton Valley Biomass Project, a joint effort including Alliant Energy, the U.S. Department of Energy, and local biomass groups, began testing the co-firing of switchgrass with coal at Alliant's Ottumwa Generating Station in Iowa. The project has proved so successful that in 2005, Alliant received permission to build a permanent biomass processing facility at the plant, capable of co-firing up to five percent of its energy with switchgrass.[4]

A number of noncombustion methods are available for converting biomass to energy. These processes convert raw biomass into a variety of gaseous, liquid, or solid fuels that can then be used directly in a power plant for energy generation. The carbohydrates in biomass, which are comprised of oxygen, carbon, and hydrogen, can be broken down into a variety of chemicals, some of which are useful fuels. This conversion can be done in three ways:

Thermochemical. When plant matter is heated but not burned, it breaks down into various gases, liquids, and solids. These products can then be further processed and refined into useful fuels such as methane and alcohol. Biomass gasifiers capture methane released from the plants and burn it in a gas turbine to produce electricity. Another approach is to take these fuels and run them through fuel cells, converting the hydrogen-rich fuels into electricity and water, with few or no emissions.

Biochemical. Bacteria, yeasts, and enzymes also break down carbohydrates. Fermentation, the process used to make wine, changes biomass liquids into alcohol, a combustible fuel. A similar process is used to turn corn into grain alcohol or ethanol, which is mixed with gasoline to make gasohol. Also, when bacteria break down biomass, methane and carbon dioxide are produced. This methane can be captured, in sewage treatment plants and landfills, for example, and burned for heat and power.

Chemical. Biomass oils, like soybean and canola oil, can be chemically converted into a liquid fuel similar to diesel fuel, and into gasoline additives. Cooking oil from restaurants, for example, has been used as a source to make "biodiesel" for trucks. (A better way to produce biodiesel is to use algae as a source of oils.)