By Mukesh Patir
The Renewal Fuels Standards (RFS) of US Energy Independence and Security Act 2007 requires replacing 39 billion gallons of gasoline use by 2022 with renewal fuels and of these 21 billion gallons is expected to come from cellulosic ethanol. The USDA provide loan up to $ 250 million dollars for research into renewal fuels and recently it has awarded loan to Range fuels to build a 100 million gallons cellulosic ethanol plant in Georgia using mostly woods and forest residues. Is it going to be sustainable or would intensive forest management practice be able to supply feedstock for producing ethanol?
Increasingly unreliable scenario of foreign oil import coupled with record surging high prices of gasoline in the US have led to much R & D efforts in the field of renewal energy for achieving energy independence in the country. US Farm Bill 2008 and the Energy Independence and Security Act 2007 enacted in recent times have provisions which support development of alternative renewal fuels. Renewal Fuels Standards (RFS) of the Energy Independence and Security Act 2007 require replacing 39 billion gallons of gasoline use by 2022 with renewal fuels and out of which 21 billion gallons is expected to come from non food crops based cellulosic ethanol(CRS report for congress, 2007). The USDA provides fund up to $ 250 million for research into renewal energies and has awarded loan to Range fuels a bio fuel firms to build a 100 million gallons capacity cellulosic ethanol production plant at Soperton Georgia (Christopher Doering 2009) which is expecting to use woods and forest residues. Is it going to be sustainable or would intensive forest management practice be able to supply required feedstock for producing cellulosic ethanol?
This paper provides an overview of ethanol production in the US, its current state of manufacturing processes and explores the potential of intensive forest management practices to supply regular feedstock and analyzes its feasibility at a commercial scale. It discusses the conversion process and efficient production of cellulosic ethanol that use agriculture residues; woodchips etc and examine the potential of intensive forest management practices for ethanol production. And finally it analyzes the feasibility of producing ethanol from forest woods or wood wastes and its impact on atmospheric carbon balance.
Current production process of ethanol and its projected consumption
Ethanol consumption in the US mostly comes from corn based production which was estimated to be little over 5 billion gallons annually in 2006 (Range fuels 2007). However its use is increasing and is supposed to be around 9 billion gallons per annum. The new Renewal Fuels Standard (RFS), one of the provisions of US Energy Independence and Security Act 2007 sets a higher annual standard for renewal fuel use of 9.0 billion gallons in 2008 and 36 billion by 2022 then its previous old RFS standards of 5.4 billion gallons 2008 and 7.5 billion gallons in 2012. Figure 1 shows the trends of ethanol consumption in the US from 2008 and a projected utilization of 36 billion gallons for 2022. Of these 36 billion gallons the new RFS require that 21 billion gallons of ethanol has to come from non food crop based ethanol such as cellulosic ethanol (CRS report for congress 2007). This is supposed to lessen the impact on the prices of food crops and wean away ethanol producers from corn ethanol and focus on non food crops based ethanol such as cellulosic ethanol using agriculture residues, municipal wastes, forest residues wood chips and woods from fast growing energy crops.
Cellulosic ethanol may be produced either by Biochemical process which involve breaking down the biomass into sugars and ferment into ethyl alcohol using enzymes or Thermo-chemical process using heat and steam to break down biomass into synthesis gas then passe over catalysts to convert it into ethyl alcohol (Coskata 2009). Range fuels one of the ethanol producing firms based in Colorado use a two steps thermo-chemical process for converting biomass into ethanol (Range fuels 2007). Coskata Biofuels Company uses a conversion process called thermo-biological which uses combination of the biochemical and thermo-chemical process for producing ethanol (Coskata 2009). The US Department of Energy targets both biochemical and thermo-chemical processes for producing ethanol.
Conversion efficiencies of these technologies are different depending on biomass types, moisture content. According to “Growing Energy report” (Dian Greer 2005) the conversion efficiency would improve from 50 gallons per dry ton to over 100 gallons per dry ton with advanced in technology. In a study by National Renewal Energy Laboratory it has been observed that conversion efficiency from Corn stovers is 70 gallon of ethanol per ton dry biomass of corn stovers (Robert Wallace et al 2000) while another firm Coskata claims to have technology to produce 100 gallon of ethanol per ton of dry biomass from any cellulosic sources. In order for ethanol production to be efficient and operating at economy of scale the processing capacity of the plant should be at least 2000 dry ton per day or an average of 5000 to 10000 dry ton of biomass, John Sheehan, National Renewal Energy Laboratory (Diane Greer 2005).
Short rotation forest management practices in Michigan to produce cellulosic ethanol
Michigan has a total forest area of 19,280,000 acre roughly about 53 percent of the total geographical area of the state. Of this approximately 98 percent is timberland with 61 percent private ownership. Average biomass productivity of timberland in Michigan is 40 dry ton per acre that amounts to a total biomass production of 758.5 million dry ton every year in 2007 (Earl C. Leatherberry and Gary J. Brand 2003). These biomass resources may not be enough to support production of 21 billion gallons of ethanol as required by Renewal Fuels Standards. However it may support production of a smaller scale of 1 billion gallon every year which is about 4.7 % of the total RFS requirement by 2022. This would require a feedstock supply of 10 million dry ton of biomass to the 1 billion gallon of ethanol every year. This premise is based on the assumption that at least 82 % of all privately owned timberland i.e. 9500000 acre would be used for producing biomass.
Short rotation forestry is being suggested for supplying 10 million dry ton of biomass to produce 1 billion gallon of ethanol every year with the following management practices:
Growing of fast growing tree species like Quaking Aspen (Populous tremuloides), Big – tooth Aspen (Populus grandidentata) or Balsam poplar (Populus balsamifera) most of which are found abundantly in Michigan. These species grows very fast and ready for harvest within 30 years (Russel P Kidd and Melvin Koelling 1988). Based on the dry biomass productivity of 40 dry ton per acre it has been found that 10 million dry ton of biomass could be produced in 25000 acre for a 1 billion gallons ethanol plant. Biomass productivity could be increased by producing hybrid species through biotechnology.
Rotation harvesting and natural regeneration: Of the total 9500000 acre of privately owned timberland approximately 250000 acre could be harvested for biomass every year and each year it should be properly managed for natural regeneration and through plantation. After harvest the root systems of aspen trees have been found to produces 3500 to 3600 suckers per acre and this stand would contain on average 4000 – 6000 stems per acre (Russel P Kidd and Melvin Koelling 1988). As these species have been found to be ready for harvest in just 30 years this management practice would ensure continuous annual supply of an average of 10 million dry ton of biomass for at least 30 years in a cycle to produce 1 billion gallons of ethanol every year.
Discussion and conclusion
Above discussion supports the premise that 1 billion gallon/annum of ethanol can be produced with 10 million dry ton/ annum through short rotation forestry management practices in 9500000 acre of Aspen forest. This 1 billion gallon per annum of ethanol production would contribute towards 4.7 % of the total RFS goal of 21 billion gallons as motor fuels in the US by the year 2022. Production facility could be located close to the sources to reduce cost of transportation of the feedstocks. This could be put forward as an efficient and eco-friendly process of renewal energy. The biomass productivity of 40 dry ton/ acre of this forest management practice far exceed the biomass productivity of the most promising biomass species, Switch grass which is just around 12.4 dry ton per acre (Diane Greer 2005). Since ethanol would not release carbon dioxide into the atmosphere so this is a carbon neutral activity to produce renewal energy. Every unit of ethanol used can displace 66 % of the use of fossil fuels and thus to that extent reduces atmospheric carbon dioxide emissions.
CRS report for congress, 2007, Energy Independence and Security Act 2007: A summary of major provisions, 12th April 09, http://energy.senate.gov/public/_files/RL342941.pdf
Christopher Doering 2009, Cellulosic output could explode, Reuter, 12 April 09, http://www.reuters.com/article/smallBusinessNews/idUSTRE50869B20090109?feedType=RSS&feedName=smallBusinessNews
Range fuel 2007, 12 April 09, http://www.rangefuels.com/what-is-the-federal-government-doing-to-support-ethanol.html
Coskata 2009, 12th April 09, http://www1.eere.energy.gov/biomass/pdfs/Biomass_2009_Adv_Biofuels_I_Roe.pdf
Range fuels 2007, 12th April 09 http://www.rangefuels.com/range-fuels-technology.htmlDiane Greer 2005, Creating cellulosic ethanol: spinning straw into fuel, Bio-cycle, http://www.harvestcleanenergy.org/enews/enews_0505/enews_0505_Cellulosic_Ethanol.htm
Robert et al 2000, Feasibility study for co-locating integrated ethanol production plants from corn starch and lignocellulosic feedstock, 12th April 09, http://www1.eere.energy.gov/biomass/pdfs/37092.pdf
Earl C. Leatherberry and Gary J. Brand 2003, Michigan forest resources in 2001, USDA forest service 12th April 09, http://www.ncrs.fs.fed.us/pubs/rb/rb_nc224.pdf
Russel P Kidd and Melvin Koelling 1988, Aspen Management in Michigan, 12th April 09, Forestry AOE team, http://www.for.msu.edu/extension/ExtDocs/aspen.html