Linda F. Benedict, Niu, Huizhen, Zapata, Hector O.
Hector Zapata, Michael Dicks, David Maradiaga and Huizhen Niu
Ethanol in small quantities is used to supplement gasoline. While corn starch is the primary source of this fuel, research continues on converting a range of plant fibers (cellulose) into ethanol. The LSU AgCenter is a member of the Sun Grant consortium of universities involved with the analysis of the potential for cellulosic ethanol and the development of the technologies to make the conversion of plant fibers to ethanol economically viable. One driver of the ethanol market is the Energy Independence and Security Act of 2007, which requires that 36 billion gallons of renewable fuel be produced in the United States by 2022. Cellulosic biofuels, produced from lignocellulose, will comprise 16 billion gallons (45 percent) of this total.
Louisiana has several sources of plant material available after harvest of major crops that could be used to produce ethanol and electricity. For example, rice hulls have been used in southwest Louisiana to produce electricity, and sugarcane bagasse is used by sugar factories as burning fuel. This study measures the total potential amount of crop material left in fields from the production of Louisiana’s main commercial crops – including corn, cotton lint, rice, wheat, grain sorghum, soybeans and sugarcane – and the total potential ethanol and electricity that could result from conversion.
Measuring Total Biomass
Crop residues from agricultural fields have intrinsic value. Corn and soybean residue, for example, increases soil moisture, nutrient and organic matter content of soils while reducing soil erosion. These beneficial functions of crop residues should be maintained when estimating potential total biomass. Conversion factors for dry matter and available residue for corn stover, for example, are estimated at 30 percent of total residues. Using historical yield data for Louisiana, average straw to grain ratios were multiplied by average yields and by average acres harvested to obtain an estimate of crop residue tonnage for each parish over the past 10 years. Total biomass is converted to Btus per pound by source of feedstock. Corn stover, sorghum straw, wheat straw, soybean and cotton biomass are converted to fuel using 7,500 Btus per pound of dry matter; rice straw is estimated at 6,811 Btus per pound of straw. For sugarcane, energy value (dry matter) was calculated at 7,899.5 Btus per pound and feedstock yield (bagasse) was estimated at 22 percent of a historical yield average. For the conversion of biomass to kilowatt hours, it is assumed that 1 kwh is equivalent to 3,413 Btus at an average efficiency of 20 percent; for liquid ethanol, the conversion factor is 84,000 Btus per gallon.
Potential Ethanol Production
Total biomass production available from crop residues in Louisiana is presented in Figure 1. Bagasse from sugarcane production (for sugar) accounts for 30 percent of total biomass from crop residues using average parish crops yields from 2000-2010. Rice yields have been increasing over the past few decades in Louisiana, although acreage has been on a downtrend since the late 1960s, resulting in 23 percent of the state total biomass potential. Corn acreage and production have grown exponentially, with corn production now concentrated in the northeast corner of the state. This increasing trend in corn production makes corn the third (19 percent) dominant crop residue biomass supplier in the state. The remaining feedstocks – cotton, sorghum, soybeans and wheat – supply about 26 percent of total biomass.
The conversion of total biomass into total gallons of ethanol is presented in Figure 2. Again, sugarcane bagasse dominates as a potential source of ethanol resulting in a total production of 147 million gallons, followed by rice straw with 112 million gallons, and corn stover with 94 million gallons. The remaining crops could generate a total of 134 million gallons of ethanol. This suggests that the total state potential ethanol production from crop residues included in this study is about 486 million gallons.
The number of housing units that could be supplied with electricity from crop residues is equivalent to the Btus that can be generated from the various feedstocks divided by 18,000 kwh/year required to power an average home in Louisiana. The resulting estimates are shown in Figure 3. The findings suggest that close to 132,971 homes could be supplied with electricity from crop residues produced in the state, given that the sources of agricultural residue remain in the same proportions as those calculated for ethanol (Figure 2).
It was assumed for this study that those parishes with maximum biomass production could become primary suppliers as shown in Figure 4. These estimates suggest that parishes in the top 50 percentiles (the two darker green shadings) are located in northeast, south central and southwest Louisiana. A radius of 50 miles from the physical address to Agrilectric Power in Lake Charles, which uses rice hulls to produce electricity, is illustrated for the southwest corner of the state as a point of reference to an existing operation and to a potential supply zone.
While the viability of using crop residues for ethanol production is a subject of research and development, estimates of potential production of ethanol and electricity from agricultural crop residues in Louisiana are valuable in planning the development of such an industry. This study shows that potential total biomass production from agricultural crop residues is located mainly in the northeast, southwest and south central areas of the state. These are areas most likely to benefit from crop residue cellulosic ethanol production if commercially viable technologies are developed. The potential economic impact from developing a crop-residue based ethanol industry is significant. The estimates from this study suggest that there is enough biomass from crop residues to provide electricity for about 130,000 homes; this would be the equivalent of supplying sufficient electricity for two large cities such as Baton Rouge and Lake Charles. Equivalently, this biomass potential could be used to develop about 10 ethanol plants, each with a capacity of 50 million gallons per year.
The majority of U.S. ethanol plants are in rural communities where agriculture is the dominant economic activity. Because the economic impact of ethanol production is mostly local, it is an appealing industry because wages in ethanol production tend to be higher than those in many other alternatives. Whether the development of this industry becomes a reality for Louisiana would require a closer examination of the economic feasibility and risks associated with markets, technologies and natural factors.
Hector Zapata, Professor, Department of Agricultural Economics & Agribusiness, LSU AgCenter; Michael Dicks, Professor, Department of Agricultural Economics, Oklahoma State University; David Maradiaga, Research Assistant, and Huizhen Niu, Instructor, Department of Agricultural Economics & Agribusiness, LSU AgCenter, Baton Rouge, La.
(This article was published in the winter 2012 issue of Louisiana Agriculture magazine.)