Biomass

Background

Biomass refers to energy stored in biological materials that can be used to generate energy specifically heat, electricity and biofuels.¹ Biomass is a chemically complex and heterogeneous resource, with different biomass resources offering varying energy product potential. More than half of the world's population (52%) cook and heat with solid fuels, including biomass fuels and coal.² Biofuels derived from biomass provided 1.8 percent of the world’s transport fuel in 2008. ³   Biomass also includes plant or animal matter used for production of chemicals, fibers and plastics. Biomass alcohol fuel, or ethanol, is derived mostly from corn and is used as an oxygenate in gasoline.⁴

Biomass excludes organic materials such as fossil fuels which have been transformed by long-term geological processes and whose carbon has been “out” of the carbon cycle for long periods. ⁵

Biological materials absorb carbon dioxide (CO2) from the air as they grow, and when the biomass is burned, or decomposes through natural means, it emits carbon back into the atmosphere. This allows for a "closed carbon cycle" that results in a marked decrease in life cycle greenhouse gas emissions as compared to petroleum or other fossil fuels.⁶

Sources

Examples of biomass include wood, agricultural crops for alcohol fuels, solid waste, and landfill gas (primarily hydrogen gas). Industrial biomass can be grown from different types of plants including miscanthus, switchgrass, hemp, corn, poplar, willow, sorghum, sugarcane, and a few tree species, such as eucalyptus and oil palm. ⁷

Biomass Production

Thermal conversion refers to combustion technology facilities which can burn multiple types of biomass including wood, agricultural residues, wood pulping liquor, municipal solid waste and refuse-derived fuel. Combustion technology converts biomass into several forms of energy for commercial or industrial use such as: hot air, hot water, steam and electricity.

Biochemical conversion makes use of the enzymes of bacteria and other micro-organisms to break down biomass. Major scientific research is also focused on improving the efficiency of cellulose enzymes in breaking down cellulose into sugar which can then be converted to biofuels such as ethanol.

Using biomass as an energy source offers many advantages over petroleum: it is more evenly distributed over the Earth, can be accessed through less intrusive means, and it represents a renewable resource. The most common technique used to generate energy from biomass is through direct combustion, but biomass can be used in three main ways:
1. In the form of gas through gasifiers for thermal applications
2. In the form of methane gas to run gas engines and produce power
3. Through combustion to produce steam and thereby power⁸

Integrated biorefineries are the most economical and efficient way to use biomass. These can produce multiple out-puts such as fuels, power and value added bioproducts such as plastics and fibers. The goal is to minimize waste and use non-plantation surplus biomass for energy production. ^{9 10}

The United States receives 45 billion kilowatt-hours of electricity from biomass, about 1.2 percent of the nation's total electric sales. The US also produces nearly four billion gallons of ethanol, about two percent of the liquid fuel used in cars and trucks.

Health and Environment Impacts

Biomass energy recycles carbon dioxide during the plant photosynthesis process and uses it to make its own food. In comparison to fossil fuels such as natural gas and coal, which take millions of years to be produced, biomass is easy to grow, collect, utilize and replace. Perennial biomass crops offer potential for carbon sequestration due to their increased root biomass and buildup of non-harvested biomass. Co-firing biomass as a secondary fuel in a coal-burning power plant using high-sulfur coal could help reduce sulfur dioxide and nitrogen oxide emissions. Also, Co-firing decreases net carbon dioxide emissions from the power plant if the biomass fuel comes from a sustainable source.¹¹

Because of incomplete combustion, biomass burning emits many chemicals such as: small particles (also called particulate matter, PM), CO, NO2, Formaldehyde, Acrolein, Benzene, Toluene, Styrene, 1,3-Butadiene, polyaromatic hydrocarbons, etc.¹²   These and others pose potential health risks as well as form Black Carbon. Studies of the black carbon cloud that periodically covers South Asia show most 14C content related to recent plant life rather than fossil fuels.

In developing countries, direct biomass combustion in homes has been linked to health risks associated with high airborne particulate levels and released endotoxins leading to respiratory illness especially in young children. According to the WHO indoor air pollution generated mostly by improperly ventilated stoves burning biomass such as wood, crop waste, dung, and coal, cause an estimated 1.6 million deaths annually. Dependence on solid fuel biomass exasperates issues with deforestation, contributing to buildup of greenhouse gases and thus exacerbating climate change issues.