Integrated Forest Biorefineries: Current State and Development Potential

LEW P. CHRISTOPHER

Center for Bioprocessing Research and Development and Department of Civil and Environmental Engineering, South Dakota School of Mines and Technology, Rapid City 57701, South Dakota, USA

Email: lew.christopher@sdsmt.edu; Tel.: + 1-605-394-3385

1.1 Introduction

The motivation for development and use of biofuels is currently driven by several important factors: 1) diminishing reserves of readily recoverable oil; 2) increasing demand and prices of petroleum-derived fuel; 3) concerns over increasing greenhouse gas emissions and global climate change; 4) growing food needs; and 5) desire for energy independence and security. The total energy world consumption in 2005 was 488 EJ with U.S. consumption of 22% of the world total, which is expected to surpass 650 EJ by 2025 and grow approximately 40% over the next 25 years. Future oil supply is not unlimited or assured as currently available petroleum fuel reserves are estimated to become nearly depleted within 40 years. Crude oil prices have risen from less than $20/ barrel in the 1990s to nearly $100/barrel in 2007 with a current annual volatility of crude oil prices exceeding 30%. Government-controlled national oil companies and organizations, many in countries that are unstable or prone to conflict, command and control more than 75% of the world's known oil reserves and global oil production. The U.S. imports 10 million barrels of oil per day of the existing oil reserves of 1.3 trillion barrels.

In 2004, fossil fuels accounted for 86% of the U.S. total energy consumption, with an additional 8% from nuclear power and only 6% from renewable sources, including 3% of biomass-derived biofuels. Biomass, however, is the single renewable resource on earth, reproduced at 60 billion tons per year (as organically-bound carbon), that has the potential to supplant the use of liquid transportation fuels and help create a more stable energy future. In general, around 30% of the world's primary energy is derived from biomass with around 430 g carbon produced per square meter of land per year. The U.S. and other regions of the world have abundant biomass resources which are much more evenly distributed and accessible throughout the planet than the oil reserves. In their "billion ton vision", the U.S. Department of Energy (DOE) reported that nearly 1.3 billion dry tons of biomass could become available to produce biofuels and displace more than 30% of the nation's consumption of liquid transportation fuels. However, the biomass share of the U.S. energy supply in 2004 was less than 3% of the total, compared to 40% and 23%, derived from petroleum and coal, respectively. Although biomass ranks well below petroleum, natural gas, and coal and is about one-half of nuclear, it surpasses hydroelectric and other renewable sources, and in 2009, the share of biomass in the total U.S. energy consumption exceeded 4% for the first time.

While ethanol production from corn and sugarcane (first generation biofuels) is a well-established process, cellulosic ethanol (second generation biofuels) is yet to be commercialized. The DOE Roadmap envisages large-scale production of second generation biofuels to become a nation-wide reality beyond 2020. The cellulosic biomass base is composed of a wide variety of forestry and agricultural resources that include forest thinning, wood mill residues, logging residues, paper waste, tree trimmings, grass clippings, energy crops such as switchgrass and miscanthus, sugarcane waste (bagasse), wheat straw, rice straw, corn stover and corn cobs.

According to the "billion ton vision" of DOE, two-thirds of the biomass resources in the U.S. represent agricultural waste, whereas about a third is forest-based. Forests cover 30% of the earth (about 3.9 billion hectares) and play a major role in preservation of biodiversity, soil conservation, and prevention of climate change serving as a major carbon dioxide sink. The forest resources are sustainable and provide long-term economic benefits to more than 1.6 billion people with a market of forest products estimated at $327 billion per year. Wood is used to produce heat for domestic and industrial purposes, and due to its strength properties, it is the primary construction material in more than 145 countries around the world. Wood is also used as a chemical feedstock to produce charcoal, tar, pitch, pulp fibers, paper, etc. Therefore, the wood-based value chain includes wood products, paper products, energy, and wood-derived chemicals. Due to the wood's increasing use and demand, approximately 130 000 km2 of forest are lost as deforestation every year. In addition, large areas of forest lands are littered with an unnatural accumulation of stunted, overcrowded trees and woody debris. Decades of fire suppression have disrupted the natural fire cycle of U.S. forests. Fires on these overstocked stands are more intense and harder to control than forest fires in previous decades, and they often result in catastrophic crown fires that kill large areas of forestlands. An estimated 8.4 billion dry tons of material needs to be removed from the national forests to reduce the risk of fire hazard, insect infestation, and disease. This vast source of biomass is available for production of wood products, chemicals, and energy. The biomass-derived energy use is projected to grow 35% from 2010 to 2024.

To combat the above processes, sustainable forest management practices need to include activities such as forest carbon credits, afforestation, reforestation, and the active support of government, forest companies and landowners. Government policies, carbon credits and carbon markets can be used as a tool to offset greenhouse gas (GHG) emissions. "Carbon credit" is a generic term for any tradable certificate or permit representing the right to emit one ton of carbon dioxide or the mass of another greenhouse gas with a carbon dioxide equivalent to one ton of carbon dioxide. Since GHG mitigation projects generate credits, this approach can be used to finance carbon reduction schemes between trading partners and around the world though carbon markets. Plant-derived biofuels as a carbon-neutral technology have to achieve at least 60% lower emissions than petroleum fuel based on lifecycle studies that include all emissions resulting from making the fuel from the field to the tank. Meeting these goals will require significant and rapid advances in biomass feedstock and conversion technologies; availability of large volumes of sustainable biomass feedstock; demonstration and deployment of large scale, integrated...