In this issue

This column features helpful information, innovative equipment, systems and applications utilities around the nation can use to save energy and improve service.

Biofuels—More than Just Corn for Cars

Biofuels can be derived from almost any type of “biomass,” a broad term encompassing living or recently alive biological material. Because biomass is produced on a short time scale, it is considered a renewable resource. 

How are biofuels used?

Biofuels are already used to supply a small fraction of our energy needs, with significant opportunities to expand their use as infrastructure is developed. In addition to ethanol and biodiesel for transportation, biofuels are currently used for power production, heating and cooling of buildings and the thermal needs of industry. 

Biomass is today the largest non-hydroelectric renewable source for electricity in the U.S. Most of this is produced in pulp and paper mills, which often generate electricity by burning wood chips, bark or the sludges and “liquors” that are byproducts of the paper-making process.  At the same time, they recover waste heat from electricity generation to meet the thermal needs of the mill. This highly efficient combination is referred to as combined heat and power (CHP) or cogeneration. The electricity generated may be used onsite and/or supplied to the local utility for distribution to the public.   

Biofuel production issues

Issues concerning the use of biofuels include the ratio of a fuel’s energy content to the energy input required to produce and deliver the fuel, competition with food production, the cost of collecting feedstocks, infrastructure development, land and water use, diversion of biomass out of ecological systems, climate change and the sheer magnitude of our current energy consumption. Also, non-energy uses of biomass may be more cost effective, less energy intensive overall, more environmentally benign or more needed than the production of biofuels. Examples of non-energy biomass products include food, animal feeds, clothing, “bio-plastics,” and recycled paper.

Resources from crops and wastes

Biofuel crops include corn, soy, sugar cane and palm, as well as non-food crops such as algae, grasses and trees. The energy and land area required to produce and deliver crop-based biofuels varies dramatically.  For example, ethanol produced from corn has been estimated to reduce global warming emissions on average by only about 15 percent compared to petroleum-based fuels (considering the complete carbon cycle and energy inputs in production and transportation). 

In comparison, ethanol produced from cellulosic materials, such as woods, grasses, straw, leaves and stocks can reduce these emissions by 90 percent or more. Of course, how much (if any) is avoided in any particular case depends on how the feedstock and biofuel are produced and transported. Regarding land use, it has been estimated that growing algae as a biofuel feedstock requires only about 2 percent of the land area needed to produce soybean oil for biodiesel.

The waste produced by our cities, farms and industries represents a vast energy resource that, if tapped, could avert much of the need for energy crops.  Waste—or “co-product”—streams include:

• Food and beverage processing waste such as trimmings, peelings, husks and floor waste; wastewater rich in fruit or vegetable biosolids; broken eggs; cheese whey and spoiled milk products; waste vegetable oil; the oily wastewater sludge from meat and fish processing; spoiled and off-spec beer, syrup and juices.
  
  
• Agricultural wastes such as animal manures; the stalks, chaff and “stover” (dried husks and leaves) from field crops; weather-damaged crops.
  
  
• Forest products industry wastes such as residue from logging, lumber milling and furniture manufacturing; and sludges and liquors from paper manufacturing.
  
  
• Municipal and urban wastes such as sewage, construction and demolition debris, landscaping debris, landfill gas and solid waste; and leftover food from restaurants, supermarkets, schools and hospitals.
  
  
• Other industrial wastes such as glycerol from biodiesel production.   

A major hurdle in taking advantage of wastes is the cost of collection.  Often an individual facility does not produce enough waste to make it cost effective to use for its own thermal or electrical needs, or for producing biofuels for market. 

Transportation costs to collect wastes on a community or regional level may be too high for a cost-effective project in today’s energy market. On the other hand, productively using wastes often reduces the financial or environmental costs of disposal.     

Summary of biofuels

Ethanol, currently used as a gasoline additive, is produced by fermentation and distillation. Cellulosic materials must also be delignified prior to fermentation. The lignin may be used to fuel the energy intensive distillation process, increasing the net energy output of cellulosic materials. 

Recent advances—such as combining fermentation with evaporation to eliminate distillation, and converting syngas (see below) to ethanol by an alternative process—improve efficiency and show promise to improve cost effectiveness.

Biodiesel is derived from the oils of wastes and crops such as canola, soy, sunflower seed, mustard, safflower and some types of algae. Biodiesel is usually winterized to reduce the temperature at which it congeals in cold weather, typically by blending it with petro-diesel. Other ways of winterizing include using additives and de-esterification. Glycerol is a waste generated from the production of biodiesel that may be used as a feedstock in producing ethanol and biogas.

Syngas (a.k.a. wood gas or producer gas) refers to a synthetic gas largely containing carbon monoxide and hydrogen. Syngas may be produced from almost any carbon-containing materials, such as wood, stalks, grasses, vegetable oils and food wastes, but also plastics, rubber and coal. Syngas may be burned in engines, turbines and boilers to generate electricity, process heat and steam. Its bio-hydrogen may also be separated for use in fuel cell or internal combustion vehicles. 

Burning syngas derived from wood is more energy efficient overall than either wood-based ethanol production by fermentation or incinerating wood in wood-fired boilers. Gasification plants are now considered commercially feasible and may be cost effective even on a relatively small scale. Production of syngas results in marketable byproducts, such as pure carbon.

Biogas usually refers to methane-rich gas (55 to 60 percent methane) produced from biomass (although the term biogas is sometimes applied to syngas.) Biogas is most commonly produced in anaerobic digesters from agricultural and food wastes and from the wastewater of municipal and industrial facilities. Biogas may be burned onsite or in a nearby industrial facility to offset natural gas use, after removing (or “scrubbing”) corrosive components.

While serving thermal needs on-site is most efficient, biogas may also be scrubbed to produce pipeline-quality natural gas, burned in turbines to generate electricity, and used in fuel cell vehicles or in commercially-available natural gas-fueled vehicles.

Solid Biofuel, or “hog fuel,” is wood waste that is ground into wood chips. Sources include logging residue, forest thinnings, lumber milling, furniture making and construction debris.  Just as with coal, hog fuel may be incinerated in solid-fuel boilers or gasified.

More information

• Clark, Catherine and Yao Yin, “The Sustainability of Biomass Energy in the Pacific Northwest,” Oregon State University, 2007.
  
  
• Database of State Incentives for Renewables & Efficiency: Biomass renewable energy projects often qualify for financial incentives from government and other organizations.
  
  
• Haq, Zia, “Forecasts: Biomass for Electricity Generation,” Energy Information Administration, 2002.
  
  
• Pellerin, Cheryl, “Organic Material Largest U.S. Source of Renewable Energy,” April 2005.
  
  
• U.S. DOE Energy Efficiency and Renewable Energy, Biomass Program.
  
  
• Whittelsey, Frances Cerra, “Bio-Hope, Bio-Hype, A users' guide to biofuels,” Sierra Club, September/October 2007.