Biofuel vs Bioelectricity : Grasses mostly used for Biofuel Production, Bioelectricity for Biorefineries and Possible CHP on Farms

It is estimated that millions of acres will be set aside for the purpose of growing energy crops such as switchgrass in future years. Debates are common as to whether it would be more efficient to use switchgrass to produce electrical power (bioelectricity) versus it's use in producing cellulosic based ethanol for vehicles. Several factors should determine the use of grasses for bioenergy purposes. One of the most important factors, which many scientists agree upon, is the location of the bioenergy farms in relation to the nearest Biomass Conversion Facility (BCM). In fact the USDA offers a Biomass Crop Assistance Program for farmers that intend to grow, harvest, collect and transport bioenergy crops to selected BCM's. The more common Biomass Conversion Facilities most likely will be ethanol biorefineries. Since many BCM's will have a large manufacturing capability, the most common application for bioelectrical power - should be for biorefineries. Thermochemical manufacturing processes common to an Integrated Biorefinery should allow for ample sized power plants to be built along with the refinery, which would also use biomass (ie grass) as a (shared) power source. If the biorefinery is large enough, it may produce ample amounts of electrical power. For example, a Biomass operated Integrated Gasification Combined Cycle (BIGCC) power plant that can produce at least 100 MW of electrical power can also provide additional heating needs for ethanol processing and also put back a net of around 20 MW of electricity back into the power grid for an estimated 40 million gallon per year ethanol capacity manufacturing plant [1. De Kam et al 2009].

Switchgrass also has the potential to produce an array of different chemicals, other than ethanol, such as mixed alcohols and organic acids. This allows different types of biorefineries to coexist using the same biomass source. The manufacture of these kinds of chemicals also allow for the production of hydrogen which would be used to make electrical fuel cell power. A power plant such as an IGCC is designed to operate on a number of different fossil fuel and/or biomass sources. In the near future, ethanol biorefineries based on corn should be retrofitted to allow the production of cellulosic ethanol from grasses. A larger amount of ethanol should be produced from switchgrass versus corn or sugarcane in the USA. Several years ago a DOE study determined that ethanol made from grasses are more efficient to produce than using corn and should produce enough ethanol to help satisfy vehicle fuel demand. This is no small task, since it is estimated that 1 ton of grass produces around 80 gallons of ethanol. It was then estimated that 30 % of petroleum used for gasoline could be displaced at 2004 consumption levels if there were around 600 cellulosic ethanol biorefineries that produced around 100 million gallons of ethanol per year [2. Houghton, Weatherwax & Ferrell 2005] -- (Link to Publication). In summary, grasses most likely will be used to produce electrical power and biofuels/chemicals simultaneously. Switchgrass could also be used on local farms to help produce further electrical power and biogas. The use of Anaerobic Digesters are commonly used in farms in Europe and are significant in use since they are another source of natural gas that can be used for Combined Heating and electrical Power (CHP). In 2007, 6 million tons of oil equivalents (called Mtoe) - as related to overall power generation, was produced from biogas in Europe with Germany being the largest energy biogas producer with the thousands of farms implementing biogas digester units [3. Weiland 2010].


1. "Biomass Integrated Gasification Combined Cycle for Heat and Power at Ethanol Plants", Energy Conversion and Management vol 50 no 7 pg 1682-1690 [2009], De Kam MJ, Morey RV, Tiffany DG

2. "Breaking the Biological Barriers to Cellulosic Ethanol : A Joint Research Agenda - A Research Roadmap from the Biomass to Biofuels Workshop Sponsored by the US Department of Energy", Office of Energy Efficiency and Renewable Energy, Office of the Biomass Program, December 7-9 2005, Houghton J., Weatherwax S., Ferrell J.

3. "Biogas Production : Current State and Perspectives", Applied Microbiology and Biotechnology Vol 85 pgs 849-860 [2010], Weiland P.

Photos taken from NREL (Department of Energy) Photographic Information Exchange Archive

KEYWORDS: Cellulosic Ethanol, Anaerobic Digerstors, Integrated Gasification Combined Cycle Power Plants, Biogasifiers, Biorefineries, Biomass Conversion Facilities, Biogas, Power Cogeneration, Switchgrass, Petroleum Displacement

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