Cellulose-To-Ethanol Plants Offer Efficiency, Lower Emissions
If the ethanol industry can reduce the amount of energy used to produce ethanol -- and therefore the emissions from the process -- it could offer itself as a truly greenhouse-friendly fuel, according to experts. When looking at the total life-cycle, the most energy-efficient plants are cellulosic-to-ethanol, and the entire ethanol industry could be moving in that direction.
One reason why cellulosic ethanol is so efficient is that it uses renewable energy. "If an integrated ethanol production and utilization cycle is considered, such as exists in Brazil, the CO2 released during the cycle is continuously counterbalanced by the CO2 uptake during sugar cane growth, through photosynthesis," said a report done by Gabriel Murgel Branco and Alfred Szwarc experts from CETESB, the Sao Paulo State Environmental Protection Agency. "Therefore, each ethanol vehicle, that substitutes for a gasoline or diesel vehicle, 'saves' the CO2 emissions which would have been emitted."
Cellulosic-to-ethanol plants are notably more energy efficient as well. "As the ethanol industry expands, it may increasingly rely on more abundant and potentially lower-cost cellulosic crops," according to a study done by the Institute for Local Self-Reliance (ILSR) entitled, How Much Energy Does It Take to Make a Gallon of Ethanol? "When that occurs, the net energy of producing ethanol will become even more attractive," ILSR said.
Supporting this statement, the study charts the net energy percent gain for an average ethanol plant versus a cellulosic crop-based plant at 38% and 162% respectively (see chart). "The data suggests a very large energy gain from converting cellulosic crops into ethanol," said the 1995 report. "Cellulosic crops use relatively little fertilizer and use less energy in harvesting than annual row crops. The crop itself is burned to provide energy for the manufacturer of ethanol and other co-products."
In addition, biomass-to-ethanol plants are far less subject to feedstock limitations. "The availability of cellulosic feedstock dwarfs what you can get from grain supplies. It is almost limitless," said Bill Wells, vice president of marketing for Delta-T Corp. "Also, because of the economy-of-scale, the price will come down and the technology will get better." This could eliminate the need for subsidies, said Wells.
Seeing this opportunity, Arkenol Inc. will soon begin construction on a number of plants in the U.S. and abroad, including one in Sacramento, CA, using rice-straw as the feedstock. Arkenol's goal is to have the 12-million-gallons-per-year plant online by the end of 1999. But biomass-to-ethanol is far from being a well-developed industry, as currently there are only six biomass-to-ethanol plants worldwide and only one in the U.S.
"If annual ethanol sales expand beyond 2 billion gallons, cellulosic crops, not starch, will probably become the feedstock of choice," said the ILSR report. But while ethanol continues to grow regardless of the feedstock, U.S. ethanol sales over the past five years (see graph) do not indicate the U.S. is close to reaching that level of demand. "If there was a nationwide RFG fuel standard and ethanol captured 30% of the oxygenate market it would be the equivalent to 2 billion gallons of ethanol," noted Burl Haigwood, consultant for Information Resources, Inc.