Biomass is defined by Wikipedia as “biological material derived from living, or recently living organisms.” It includes plant material and animal wastes. Combustion of biomass has been used throughout human history to provide heat, ever since the discovery of fire, and is the oldest form of renewable energy (it has an extensive literature). It is still widely used for heating purposes but other ways to obtain useful energy from biomass have now been developed, including gasification and conversion to liquid fuels. Each of these applications and biomass’ significant potential are discussed below.
A lot of biomass is produced each year in the world, about half in the oceans and half on land. It is biologically-produced matter based in carbon as well as hydrogen and oxygen. Estimated annual production is 100,000 billion kilograms of carbon. An important point to keep in mind is that the chemical arrangements of these organic materials can be changed, an important focus of biomass research.
On land biomass can be obtained from a variety of sources:
Wood, in the form of trees, tree stumps, branches, wood chips, and yard clippings remains the largest source of biomass energy today. In many developing countries it is still the only combustion fuel source for domestic use. Other common fuel sources include municipal solid wastes, animal wastes (e.g., ‘cow chips’ or bio-digested manure), and landfill gas (primarily methane and carbon dioxide).
In recent years pellet fuels, made from compressed biomass. have been used increasingly for heating in power plants, homes, and other applications. Wood pellets are the most common type, but grasses can also be pelletized. Pellets are extremely dense and can be produced with a low moisture content that allows them to be burned with a high combustion efficiency. Further, their uniform shape and small size facilitates automatic feeding. According to the International Energy Agency global wood pellet production more than doubled between 2006 and 2010 to over 14 million tons. In a 2012 report, the Biomass Energy Resource Center anticipated another doubling of wood pellet production in North America within five years.
An important application of biomass is its direct conversion into liquid fuels, or biofuels, that can replace petroleum-based fuels such as gasoline, diesel and jet fuel. These ‘alternative’ fuels fall into two categories, first generation biofuels such as ethanol that are derived from sugarcane and corn starch (and therefore compete with food crops) and second generation biofuels that use as feedstock non-food and low value agricultural and municipal wastes that are not edible. Production of first generation biofuels is well underway in Brazil and the U.S. but second generation production is still limited by high production costs. The problem is the difficulty in breaking down the lignocellulosic biomass that constitutes the bulk of plant matter. Governments and many private sector firms are attacking this problem and 2014 could be a breakthrough year as a number of second generation production plants come on line.
Ethanol, which is usually mixed with gasoline to produce E-10 (90% gasoline and 10% ethanol) can also be produced by gasification of biomass. Gasification processes use high temperatures in a low-oxygen environment to convert biomass into synthesis (or ‘syn”) gas, a mixture of hydrogen and carbon monoxide. This gas can then be chemically converted into ethanol (C2H5OH) or a wide variety of other C-H-O molecules and fuels.
An emerging and potentially major biomass field is the production of alternative fuels using algae (algaculture). Algae is Latin for ‘seaweed’ and are “..photosynthetic organisms that occur in most habitats. They vary from small, single-celled forms to complex, multicellular forms, such as the giant kelps that grow to 65 meters in length.” ‘Photosyntheic’ refers to algae’s ability to capture light energy to power the manufacture of sugars, carbohydrates composed of C-H-O that can then be converted to other C-H-O molecules. . Algae differ from plants in that they are primarily aquatic.
Interest in algae was triggered by the need for alternatives to petroleum fuels and the world food crisis. Algae produce lipids (a variety of organic compounds) that can be used for making biodiesel, bioethanol, biogasoline, biojetfuel, biomethanol, biobutanol, and other biofuels, using land that is not suitable for agriculture (e.g., land with saline soil). They can be produced using seawater, brackish water, and wastewater, and are biodegradeable. An important, and perhaps critical, aspect of algaculture is that it is claimed that algae farming can yield 10-100 (one claim says 300) times more fuel per unit area than other second-generation biofuel crops. It is estimated that growing enough algae to replace all U.S. petroleum fuels would require only 0.4% (15,000 square miles) of the U.S. land area, or a small fraction of land currently devoted to corn production. Algae crops also have a short harvesting cycle – 1 to 10 days – and so can be harvested repeatedly in a short time-frame.
The biggest barrier to greater use of algae-derived biofuels is the cost of scaling up to commercial production levels. Another concern, for open-pond algae facilities, is contamination by invasive algae and bacteria and vulnerability of monocultures to viral infection. Many schemes for reducing costs and potential contamination are being explored, given the large potential markets available. One obvious target is ground transportation. Another such market is the U.S. military which is already testing biofuels in aircraft and ships. A third large potential market is commercial air transportation. Finally, like all energy sources, biomass has environmental impacts and risks – e.g., water demand and deforestation if land is cleared for biomass production.
A brief word on biochar, a form of charcoal that is created by pyrolysis (low- or no-oxygen heating) of biomass. It is believed that pre-Columbian Amazonians used biochar to increase soil productivity. In addition, biochar has attracted growing attention because of its ability to sequester carbon for centuries (and thus reduce global warming) and its ability to attract and retain water because of its porous structure and high surface area. its production also does not compete with food production.
In my view, and that of many others, biomass will be a major part of our renewable energy future. It is available world-wide, grows in great and diverse quantity, can be used for direct heating and electricity production via heating of water, can be converted to liquid fuels and other C-H-O commodities, and, if used carefully, has significant potential to reduce greenhouse gas emissions. . The Union of Concerned Scientists has estimated that biomass can provide up to 248 GWe of power generation capacity if fully utilized in the U.S. Current U.S. generating capacity is just over 1,000 GWe. Costs, the major barrier, will come down and our children and grandchildren (and probably many of us) will be traveling in biofuel-powered cars, trucks, trains, airplanes, and ships before too long in the 21st century. It is an exciting option and real possibility that is just over the horizon.