Biomass — the ultimate renewable feedstock

While power generation based on coal gasification provides several advantages to traditional coal-fired power generation, this approach still relies on coal — a non-renewable fossil fuel. By comparison, the ability to power gas turbines using syngas that is produced by gasifying biomass — a diverse category that includes plant materials (such as fast-growing trees and grasses), agricultural residues (such as grains, corn and sugar cane, and even the woody, cellulose-rich leaves and stalks), and paper mill and lumber mill scrap— offers process developers a way to generate electricity using a truly renewable resource. Meanwhile, when it comes to producing liquid fuels from biomass feedstocks, corn and sugar cane are already widely used in commercial-scale facilities to produce ethanol, while soybeans are already being used to produce biodiesel (these technologies are beyond the scope of this report, and are not discussed further). As with coal gasification, syngas is produced when biomass is gasified in a partial oxidation reactor (without a catalyst), at temperatures ranging from 900 to 1,400°C, depending on whether oxygen or air is used. While such feedstocks will not likely ever replace fossil fuel feedstocks entirely, the ability to commercialize technologies that convert “bushels into barrels,” as the saying goes, promises to play an increasingly important role, as society continues in its quest to achieve more environmentally friendly, renewable sources of fuels, electricity and chemical feedstocks, and achieve greater overall energy self-sufficiency. Today, a variety of promising processes are being pursued to convert biomass into valuable fuels and other feedstocks.

Generating electricity from biomass To generate electricity from biomass, renewable feedstocks such as forest residues, agriculture, landfill gases, and municipal wastes are typically used in one of four ways: via direct-firing, co-firing, gasification and anaerobic digestion. Direct-fired systems are the most widely used. With this approach, biomass is burned directly, in lieu of oil or natural gas in a boiler that produces steam, which drives a steam turbine to generate electricity. However, such systems tend to have relatively low efficiency — on the order of 20% — due to the relatively low heating value of the biomass-based feedstocks compared to traditional fossil fuels. To attain higher fuel heating values, co-firing systems mix biomass with coal or other fossil fuels, and use this fuel blend in a conventional power plant. According to a 2006 report by the Worldwatch Institute (Washington, D.C.; www.worldwatch.org), more than 100 U.S. coal-fired power plants are now burning biomass together with coal. Experience has shown that biomass can be substituted for up to 2-5% of coal at very low incremental cost; higher rates — up to 15% biomass — are possible with moderate plant upgrades. When burned with coal, biomass can significantly reduce the overall emissions of SO2, CO2 and other greenhouse gases produced by the facility. And, by burning biomass that would otherwise be destined for landfills, this approach reduces the amount of organic waste that would ultimately decompose and release methane —a greenhouse gas that is 21 times more potent than CO2.

Biomass gasification systems use a gasification process (described above) to convert the biomass into syngas. Once this syngas (carbon monoxide and hydrogen) is cleaned to remove unwanted pollutants, it is burned (in lieu of fossil fuels) in either a boiler that provides steam for a steam turbine, or in a gas turbine that generates electricity directly. Such power plants are said to achieve efficiency ratings of 60% of better. The fourth option — anaerobic digestion — uses engineered systems to promote biomass decay, in order to capture the methane (the primary constituent of natural gas) that is produced during the process. The captured methane is then used to power a conventional power plant that generates electricity. Such highly engineered systems rely on a particular blend of bacteria that promotes the decomposition processes in the absence of oxygen, in a closed bioreactor. The bioreactor must be designed and operated in such way as to maintain the precise balance of nutrients and operating conditions (such as pressure, temperature and pH) that is required by this colony of fragile bacteria, in order to sustain the bacteria and maximize the desired reactions. Lurgi AG (Frankfurt, Germany; www.lurgi.de) and Karlsruhe Research Center (Karlsruhe, Germany; www.fzk.de) are constructing a pilot plant that will use flash pyrolysis at 500°C to convert biomass into pyrolysis oil and coke (up to 40 wt.%). This product can then be gasified to produce syngas, which can then be further processed to produce various sulfur-free biofuels. For instance, researchers at Japan’s National Institute of Advanced Industrial Science & Technology (Tsukuba, Japan; www.aist.go.jp) have developed a new catalyst (1 wt.% rhodium supported on oxides of cerium and silicon) that allows biomass gasification to be carried out at lower temperatures — on the order of 650 to 700°C. The resulting synthesis gas (a mix of CO, H2, CH4, and CO2, with solid carbon generation of only 1% and no tar), is suitable to produce power in a gas turbine, or can be used as a chemical feedstock. Scaleup efforts are underway. Researchers at the University of Wisconsin (Madison, Wisc.; www.wisc.edu) are also developing a milder process to convert biomass-derived oxygenated hydrocarbons into a syngas that consists of hydrogen with less than 60 ppm carbon monoxide. Because it uses a nickel (not platinum) catalyst, and is carried out at milder conditions (roughly 225°C, versus 600-1,000 deg C), the process is being pursued as a less costly alternative to conventional steam reforming of natural gas to make CO-lean H2 for fuel cells and other purposes. The use of supyngas stream — before it is combusted in the gas turbine.

Researchers at the University of Wisconsin (Madison, Wisc.; www.wisc.edu) are also developing a milder process to convert biomass-derived oxygenated hydrocarbons into a syngas that consists of hydrogen with less than 60 ppm carbon monoxide. Because it uses a nickel (not platinum) catalyst, and is carried out at milder conditions (roughly 225°C, versus 600-1,000 deg C), the process is being pursued as a less costly alternative to conventional steam reforming of natural gas to make CO-lean H2 for fuel cells and other purposes. The use of supercritical water (SCW) is key to the one-step process for making hydrogen from biomass (including black liquor from the pulp-and-paper industry, municipal garbage and paper sludge) that has been developed by researchers at Japan’s Shizuoka University (Hamamatsu, Japan; www.u-shizuoka-ken.ac.jp). The continuous process, which has thus far been demonstrated at bench scale, is said to produce two to fives times more hydrogen than conventional reforming and gasification processes. The researchers are currently seeking commercial partners for scaleup. Together Shell Deutschland Oil GmbH (Hamburg; www.shell.com) and Choren Industries GmbH (Freiberg-Saxony; www.choren.com/de/) are constructing the world’s first commercial facility to convert biomass into a synthetic fuel called “SunFuel,” using Choren’s Carbo-V three-stage gasification technology. The SunFuel can then be further converted into methanol or diesel using Fischer-Tropsch synthesis. According to Shell, the fuels that will be produced at the 15,000-m.t./yr plant can be used without modification in any diesel engine. Meanwhile, Neste Oil Corp. (Helsinki, Finland; www.neste.com) is building a 170,000-m.t./yr plant, slated for startup in 2007, as the first commercial-scale demonstration of its NExBTL (“next generation biomass-to-liquid”) process at its Porvoo, Finland, petroleum refinery. The process produces diesel fuel from renewable raw materials, and, according to the company, can be adapted to use many types of vegetable and animal fats. Meanwhile, Neste Oil and Total S.A. (Paris, France; www.total.com) have signed a memorandum of understanding to evaluate the possibility of building a large-scale production plant for biodiesel fuel using the NExBTL process at one of Total’s petroleum refineries. While many biomass-conversion processes rely on partial oxidation reactors (using either air or pure oxygen), several groups are also developing biomass-conversion processes that rely on pyrolysis in an oxygen-depleted environment. For instance, DynaMotive Energy SystemCorp. (Vancouver, B.C.; www.dynamotive.com) has developed a fast pyrolysis-based process to produce “BioOil” from a wood-residue feedstock. In the process, pulverized biomass is pyrolyzed in a bubbling fluidized-bed reactor that operates oxygen-free at 450-500 deg C. Once it’s operational, the pyrolysis plant that will process 100 tons/d of plywood residue and produce 70 m.t./d of BioOil (along with 20 m.t./d of char and 10 m.t./d of non-combustible gases), which will to fuel a turbine to generate electricity in a cogeneration plant (up to 2.4 Mwe) operating at Erie Flooring and Wood Products facility in West Lorne, Ont. DynaMotive Energy Systems is also in the process of developing a larger, 200-m.t./d pyrolysis plant for producing BioOil for other clients. Researchers at the Pacific Northwest National Laboratory (PNNL; Richland, Wash.; www.pnl.gov) are also involved in developing a pyrolysis-based biomass-conversion process for producing both gaseous and liquid fuels. Winds of Change The first commercial-scale wind farms were constructed in California in the early 1980s. With wind power increasingly viewed as a more environmentally friendly alternative to traditional fossil-fuel-powered electricity generation, the worldwide wind energy market has been experiencing dramatic growth in recent years. Today, “wind farms” consist of anything from a single turbine to as many as several hundred turbines, and are becoming an increasingly important component of the world’s electricity pool. U.S. wind activity According to figures released in mid-2006 by the American Wind Energy Assn. (AWEA; Washington, D.C.; www.awea.org). The total worldwide wind-based power generation capacity at the end of 2005 was 59,322 MW. In the U.S., the total installed capacity for U.S. wind-based energy was nearly 10,000 MW (enough to serve the annual electricity needs of 2.5 million homes), by the American Wind Energy Assn. (AWEA; Washington, D.C.; www.awea.org). About 3,000 MW of new capacity (representing investment of over $4 billion) is expected to be added in the U.S. by the end of 2006. Today, "wind farms" consist of anything from a single turbine to as many as several hundred turbines, and are becoming an increasingly important component of the world's electricity pool. AWEA also notes that wind-based power generation was the second-largest source of new power generation capacity added in the U.S. in 2005, after facilities powered by natural gas, and this trend is likely to continue through 2006. According to AWEA, the 10,000-MW capacity of the U.S.’s current wind turbine fleet offsets the equivalent of 73,000 tons/yr of SO2, 27,000 tons/yr of NOx, 16 million tons/yr of CO2, every year, as well as mercury and other pollutants (the emissions that would result from the production of 10,000 MW of power using the average U.S. utility fuel mix). In addition, today’s 10,000 MW of wind power saves about 0.6 billion cubic feed per day (bcf/d) of natural gas — about 3.5% of the natural gas currently used in the U.S. to generate electricity. In 2005, 2,431 MW of new capacity was installed in the U.S. (across 22 states) making wind-based power generation the second-largest source of new power generation capacity in the U.S, after natural-gas-fired power plants, according to AWEA. Based on total installed capacity at the end of 2005, California (2,150 MW), Texas (1,995 MW), Iowa (836 MW), Minnesota (744 MW) and Oklahoma (475) are currently lead the pack, according to AWEA, although Texas is expected to overtake California as the leader by the end of 2006. In terms of manufacturers with installed U.S. wind capacity delivered during 2005, GE Energy (Atlanta, Ga.; www.gepower.com) dominated the market with 1,433 MW (representing 60% of total annual capacity), with Vestas (Randers, Denmark; www.vestas.com) in second place with 700 MW (nearly 30% of total installed capacity). Mitsubishi Electric (Tokyo, Japan; www.mitsubishielectric.com) with 190 MW Suzlon Energy Ltd. (Mumbai, India; www.suzlon.com) with 55 MW, and Gamesa (Huelva, Spain; www.gamesa.es) with 50 MW, sharing the top five positions, according to AWEA. European wind activity While the installation of wind-based power generation capacity is on the rise in the U.S., most of the wind-based activity has been in Europe. For instance, while the U.S. had 9,150 MW of installed capacity by the middle of 2006, the total installed capacity for wind-based power generation across the European Union (EU) was 40,504 MW by the end of 2005, according to the European Wind Energy Assn. (Brussels, Belgium; www.ewea.org). In fact, cumulative wind power capacity in the EU grew by an average 32%/year between 1995 and 2005, from a base of 1,638 MW in 1994, and this bullish growth rate helped the EU to achieve the European Commission’s 40,000-MW target five years ahead of time, according to EWEA. Germany, Spain, Portugal, Italy and the U.K currently top the list of individual markets in terms of installed capacity. By 2010,wind power is expected to deliver 33% of all new electricity-generation capacity, and provide electricity for 86 million Europeans, according to a 2004 estimate by the EWEA. One of the challenges associated with harnessing wind energy is the fact that wind is —by its very nature—unpredictable, and its strength and reliability are dependent on location. Sometimes the wind doesn’t blow, and it often blows in unpredictable gusts. To cope with such variations in wind energy, developers of commercial-scale wind farms tend to install hundreds or even thousands of wind turbines. However, because of its inherent variability, wind-based energy is not typically used as the sole source of power for a given application (as is often the case for solar-energy-based solutions, which are discussed below). Rather, wind farms more commonly produce electricity that is fed into the power grid. Wind technology has progressed mightily over the past quarter century. For instance, at a given site, a single modern wind turbine now produces 180 times more electricity, and at less than half the cost per kilowatt-hour (kWh) than an equivalent system of 20 years ago, according to EWEA. Nonetheless, to better understand the fundamentals of wind-based power generation, fundamental and applied research remains ongoing. For instance, researchers at the U.S. Dept. of Energy’s Sandia National Laboratories (Albuquerque, N.M.; www.sandia.gov) are working to gain better understanding of the effects of wind gusts and turbulence, both of which can significantly reduce the life expectancy of turbine blades and airfoils, and to develop more robust and reliable turbine designs, which can more cost-effectively generate power via wind energy. While it might seem like a quaint relic of bygone days, wind turbine blades are typically fabricated by hand, by laying down multiple layers of fiberglass cloth and resin in a mold, using the same fabrication techniques that are used in the boat-building industry. However, the imperfections that result from this type of composite structure can lead to premature failure of wind turbine blades. To improve performance, the Sandia researchers are also investigating a variety of advanced materials— carbon fiber and carbon/glass hybrid composites, advanced resins, additional fiber treatments — in order to develop blades that are lighter and less costly while still offering sufficient reach, and more structurally reliable to minimize fatigue-related failures. They are also working to develop more-efficient blade designs and better (automated) manufacturing techniques. The goal is to create rotating blades that encompass the greatest possible sweep area, so as to maximize the amount of electricity that can be generated by the wind energy. Sandia researchers are also developing a range of computational tools to significantly improve the design and structural analysis of longer, thinner and more durable blade geometries with greater sweep area (to increase energy capture), and to perfect non-destructive testing techniques that can help researchers to evaluate and improve the design of existing blades. The challenge is to design blades that are both stiff and strong to span greater areas, while remaining both lightweight and able to adapt to varying system loads. In addition, to mitigate the high-frequency loads on wind turbine blades that result from periodic wind gusts and turbulence, the Sandia researchers are also developing small, fast-acting sensors and control devices that can be used to optimize turbine operation, and improve the maintenance procedures for gears and bearings, which are most often to blame for extended outages related to wind turbines. Proven condition-monitoring sensors and systems are now widely used with wind turbines, to track vibration signatures, temperature, shaft speed, torque, wind velocity and other machinery parameters. As with other condition-monitoring efforts, this allows operators to evaluate the ongoing condition of all rotating parts over time, so that progressive wear and other issues can be watched in realtime, and preventive (and even predictive) maintenance can be undertaken to improve efficiency and reduce failures. In addition, most state-of-the-art wind turbines now routinely include monitoring devices to track the performance of gears and bearings, which are most often to blame for extended outages related to wind turbines. Researchers at the National Wind Technology Center (NWTC; Boulder, Colo.; www.nrel.gov/wind), a world-class research facility managed by the U.S. Dept. of Energy’s National Renewable Energy Laboratory (NREL; Golden, Colo.; www.nrel.gov), are also working to reduce the cost of wind energy through ongoing research and development of state-of-the-art wind turbine designs. For instance, NWTC has been working with The Wind Turbine Company (WTC; Bellevue, Wash.; windturbinecompany.com), which has focused its R&D efforts on developing so-called “downwind” turbines. WTC’s design features two rotor blades, which are oriented on the downwind side of the tower. By contrast, conventional upwind turbines feature three rotor blades that are oriented on the upwind side of the tower. According to WTC, its patented lightweight design allows the units to be constructed using 40-50% less materials compared with similarly rated, conventional “upwind” turbines. With both lower price and lower operating cost, WTC’s wind turbines also produce electricity for 30% less than today’s most economic units, according to the company. TWC is currently testing its prototype 750-kilowatt (kW) wind turbine at DOE/NREL’s National Wind Technology Center. Testing on earlier 250-kW and 500-kW prototypes has already been completed. To improve the preventive and predictive maintenance of wind turbines, and assist in both diagnostic efforts and root-cause failure analysis, Bently Nevada Corp. (Minden, Nev.; www.bently.com) has developed a variety of condition-monitoring systems, which monitor vibration signatures, temperature, shaft speed, torque, wind velocity and other machinery parameters. In May 2006, Siemens Power Generation (Erlangen, Germany; www.siemens.com) announced that it would be supplying 17 new wind turbines for three “repowering” projects in Germany. Specifically, the company will be providing larger, more robust units to replace some of the smaller, aging wind turbines that have been in operation for several years. For instance, in one project —the Marienkoog project operated by Buergerwindpark Galmsbuell GmbH — Siemens will provide seven 3.6-MW machines, to replace 15 older units. With an installed capacity of more than 50 MW, this project will become the largest wind farm in Germany once one it begins commercial operation by mid-2007. Buergerwindpark has also ordered seven 2.3-MW wind turbines for its Norderhof Wind Park. Meanwhile, in late 2006, Siemens received an order worth 350 million Euros, for what it claims will be Europe’s largest commercial wind farm (slated for 322-MW capacity upon completion). The installation will include 140 2.3-MW wind turbines for the Whitelee Wind Farm south of Glasgow, Scotland. Completion is set for the summer of 2009. GE Power has installed more than 8,500 wind turbines, with a total rated capacity of 7,600 MW worldwide, according to the company. In 2006, the company expanded its line of “multi-megawatt” wind turbines by launching a new platform in Europe, which will be followed by similar product rollouts in the U.S. and Asia in 2008, says the company. Evolving from GE’s proven 1.5-MW unit (which are typical sold in multiples to gain the needed generating capacity at a given site), GE’s newer machines will include a 2.5-MW unit (with a 100-meter rotor diameter) and a 3-MW unit (with either 90- or 94-meter rotor diameters). The increased rotor sizes will offer higher energy capture, says the company, and the units also include a number of other industry innovations, including a highly efficient, permanent magnet synchronous generator (enabling higher efficiency at lower wind speeds), a modular converter with full power conversion (which allows for more effective power quality control), improved bearing and lubrication system design, and advanced control technologies (which provides, among other things, improved pitch regulation, power/torque control, and load-dampening capabilities). Meanwhile, one of the early projects being undertaken as part of BP’s expanding alternative-energy portfolio (mentioned above), is a 9-MW wind farm currently being built at the company’s oil terminal in Amsterdam, whose electrical output (enough to power 5,000 homes) will eventually be sold into the Dutch grid. BP also operates the Nerefco wind project at the (jointly owned) BP/Chevron Texaco (jointly owned) refinery near Rotterdam. That project, which began commercial operations in 2003, produces nearly 23 MW of electricity, enough to power 20,000 homes. http://www.cheresources.com/energy_future/novel_power_generation01.shtml