Figure I. Energy density of various biomass-based materials (BC = biocarbon) compared with coal
Categories: General
Date: Mar 23, 2009
Title: Biomass -> Biocarbon -> Bioenergy
No industry is better positioned to meet the challenges of the global thirst for renewable energy and innovative bioproducts than the biomass industry. Read about Alterna Energy in the April 2009 edition of BioEnergy Canada magazine.
By Gerry Kutney
The forestry industry is undergoing a change brought on by the unprecedented natural disaster of the mountain pine beetle and other infestations that have devastated part of the nation’s richest resources, the competitive plight of our industry in the market place, and the U.S. housing meltdown. The forestry industry however, is looking beyond, lumber, pulp and paper in an effort to mitigate these challenges to include energy and biobased products.
The greatest opportunity for the forestry industry is its access to the most efficient solar, carbon-capture technology in the world designed by Mother Nature. Through photosynthesis, using sunlight, a forest grows carbon structures (trees) by recycling carbon dioxide from the air. Thus, wood products, bioenergy and bioproducts from forests are renewable. More importantly, bioenergy is greenhouse gas (GHG) neutral, and some bioproduct applications are carbon negative, therefore both improve the impact of climate change.
As the world realizes the value of renewable energy and bioproducts, and the GHG crisis continues to threaten our planet, the forestry industry is prepared to respond. “Our forests are one of the most important allies we have in the battle against climate change,” said Gordon Campbell, premier of British Columbia in 2008. “Living forests convert carbon dioxide into oxygen, while sustainable wood products play an important role in sequestering carbon.” The opportunities from Canada’s “damaged” forestry resources and residual fibre are plentiful. “B.C. is considered to be the Saudi Arabia of the world when it comes to the potential for bioenergy,” says John Rustad, member of the legislative assembly for Prince George, British Columbia.
Wood-based bioenergy for example, was revolutionized through the development of wood pellets which nearly double the energy density of green wood chips, producing approximately 9.5 gigajoules per tonne (GJ/t). Wood pellets have emerged as a significant fuel supply for various areas of the world, most notably in Europe. Building the new bioenergy industry though, is not without its challenges. Wood fibre is bulky, therefore expensive to transport, and the material must be densified to open up the global potential for bioenergy in Canada. Biocarbon, while produced from the same type of biomass as wood pellets, has an energy density equivalent to that of coal, which yields an energy density of approximately 30 GJ/t, or 60 per cent more energy than wood pellets. (Figure I.)
Figure I. Energy density of various biomass-based materials (BC = biocarbon) compared with coal
Biocarbon, also called biochar or charcoal, is a renewable replacement for coal manufactured for industrial markets. The material can be produced from biomass resources such as wood, municipal and agricultural waste, and tires through a controlled heating process called “carbonization,” which heats organic (carbon-containing) materials to elevated temperatures in an environment of controlled and reduced oxygen levels. During the carbonization process all of the energy necessary to fuel the process can be supplied by the biomass.
Carbonization is a thermochemical refining technology that involves a myriad of complex reactions of the components of biomass. At temperatures of 300 C, a sharp rise in the carbon content or energy density of the biomass occurs and biocarbon production takes place (Figure II). When temperatures exceed 500 C, gasification of the volatile components in the biocarbon commences and the remaining solid becomes predominately purer forms of graphite-like carbon. At this stage of pyrolysis, activated carbon is generated.
Figure II. Carbon content of biocarbon with increasing carbonization temperatures
(graph modified from: Schenkel, Y. Modelisation des Flux Massiques et Energetiques dans la Carbonisation du Bois en Four Cornue. Ph.D., Dissertation, Universite´ des Sciences Agronomiques de Gembloux, Gembloux, Belgium, 1999; also available on page 1621 of Ind. Eng. Chem. Res., Vol. 42, No. 8, 2003)
Activated carbon is commonly utilized to remove organic impurities in water and air, in addition to many industrial purification processes such as sugar refining and pharmaceutical manufacturing.
Above 700 C, another group of reactions is possible where the residual biocarbon is reacted with limited amounts of oxygen and gasified (Figure III). In the biocarbon gasification process, synthesis gas (syngas) is produced, which is composed of hydrogen and carbon monoxide. Syngas can be combusted to produce heat; utilized in a turbine, internal combustion engine, or fuel cells to produce electricity, or in a Fischer-Tropsch reaction to produce biodiesel and related fuels. An advantage of biocarbon over the direct gasification of biomass is that the wood tars have already been removed, producing a much cleaner syngas.
Figure III. Thermochemical Refining of Biomass and Biocarbon
Biocarbon has the unique ability among renewable energy sources to utilize electrical generation equipment that has already been installed. Since the physical and chemical properties of biocarbon are sufficiently similar to coal, biocarbon can be utilized in existing coal-fired generating stations, with minimal modifications. Among renewable energy sources, biocarbon also has the ability to be utilized in a variety of applications beyond simple power generation. The thermochemical biorefining technology uses biomass to produce carbon in a solid form making it available for energy production, steel manufacturing, water and air purification and agricultural production (terra preta). Biocarbon can be used to offset the use of fossil carbon, reducing the overall emissions of GHGs for every unit of energy consumed. In the case of agricultural use, the carbon is directly sequestered, permanently removing carbon dioxide from the atmosphere; a form of carbon capture and sequestration.
Living in a carbon-based world, it is important to focus on the research and development of renewable biocarbon for sustainable transportation fuels, large and small combined heat and power technologies, green electricity, trace contaminant adsorbents, increased food production and a myriad of others that all contribute to the reduction of carbon dioxide from fossil fuels. In oil refining, hydrogen and carbon molecules are manipulated to produce a number of everyday products. Refining, gasification and other technologies and processes are already available which can provide a base for similar manipulations of renewable biocarbon materials. Further biocarbon research and development would help grow Canada’s new biocarbon industry, intellectual property could be exported around the world, and the wealth created would amount to billions of dollars as new renewable-carbon industries evolve and the traditional forestry industry is revitalized.
Biomass has been the energy staple of mankind through the ages. Fossil fuels, such as coal and oil, have only superseded biomass for a brief period in the grand scheme of civilization. For example, the world did not burn more coal than wood until the beginning of the 20th century. Now biomass is biomass beginning to resume its traditional position in history.
This article is found in the April 2009 issue of Bioenergy Canada
magazine (www.bioenergymagazine.ca).