Published on January 2, 2008
Slide1: Bio-Energy From Mesquite on Texas Rangelands Jim Ansley Texas Agricultural Experiment Station Vernon, TX Slide2: Much of the Southern Prairie (USA) Today Advanced woody plant (i.e., “brush”) encroachment reduces herbaceous (forage) production, reduces off-site water yields, and interferes with livestock gathering Slide3: Increasing Mesquite Cover Reduces Grass Yields This chart shows how C4 (warm season) mid-grass production in interspaces between mesquite declines sharply when mesquite cover exceeds 30% (from Ansley et al 2004; J. Range Mgt 57:49-57 – full article can be found in the publications list on Dr. Ansley’s web site) Slide4: Costly Brush Treatment Options Mechanical $50-80/acre Herbicides $15-25/acre Fire $5/acre (but limited as to when and where it can be used) Slide5: Overall Objective Determine the feasibility of developing a bio-energy industry in rural Texas based on rangeland woody plants Emphasis is on Honey Mesquite but other shrubs could be used, depending on size, density and access Slide6: Drought hardy; fixes own nitrogen; can grow on dry, nutrient poor soils Requires no cultivation, seeding, fertilizing, or irrigation Resprouts vigorously after an aboveground disturbance (i.e., “top-kill”) Mesquite as a BioFuel Source Slide7: Managing Mesquite Harvest for Multiple Benefits Slide8: Potential Uses of Mesquite Biomass Feedstock for Combustion Fire Wood Electricity Feedstock for Liquid Fuels Ethanol Biodiesel Other Biofuels BioProducts Plastics Polymers Mesquite Wood Products Furniture Particle Board Cooking Chips Yellow = Area currently emphasized by Dr. Ansley’s project Slide9: WHY ETHANOL??? Slide10: How Is Petroleum Used? United States Type of Use Percent of Total Use Cars and Trucks 66% Jets and Airplanes 10% Power Plants <10% Source: Richard Heinberg, “The Party’s Over”, Gabriola, B.C., Canada Energy Sources for Power Plants Coal (56%); Nuclear (21%); Gas (10%); Hydroelectric (10%); Other (3%) Where we need the most help is fuel for vehicles – ETHANOL!! Slide12: Mesquite BioFuel Research Needs Harvest Technology Cutting Lifting Baling Transport Ethanol Conversion Grinding Gasification Optimum Refinery Locations Economics Supply Size/Mass/Density Relationships Regrowth Rates Regional Supply Ecological Effects Grasses Soils Wildlife Nutrient Cycling Water Yield Waste Disposal Energy Balance Water Balance Yellow = Research areas currently emphasized at Vernon Blue = Process being developed by private industry cooperators Slide13: Mesquite Supply There are 51 million acres of mesquite in Texas (SCS 1984; SCS is now NRCS) Scifres (1980) estimates 56 million acres Of this total, about 30 million acres are moderate to dense mesquite Slide14: Mesquite Distribution In Texas (SCS,1984) Texas Mesquite Supply 30 million acres of moderate to dense mesquite Pink and yellow areas have highest density Slide15: Mesquite Supply Summary 15 million acres available for harvest (if leave the remaining 15 million acres for wildlife habitat) Estimated wood yield 12 tons per acre in moderately dense stand (240 trees/ac x 100 lbs per tree). Assume 80-85% harvest efficiency: Yield 10 tons/acre 10 years regrowth needed before re-harvest in north Texas. Important to understand we need to manage the regrowth and not kill the tree. Note – Mesquite standing crop and regrowth yield estimates are based on data recently collected at TAES in Vernon. These data are not yet published. Slide16: Harvesting Technology Two Phase Process 1. Cutting (Felling) 2. Collecting Slide17: Harvesting Technology Cutting- (Felling) Machines such as this Barko 775C Specialized cutter heads Wood debris left Little damage to grasses or soils Slide18: Harvesting Technology - Collecting - Recently constructed a harvester to collect the wood mulch (Patent pending) The harvester is pulled and powered by one of the brush cutter machines. Requires >100 hp. Slide19: Harvest Test Trials Typical Test Stands 50-70% canopy cover 250-350 trees per acre Avg. tree height 3-4 m Time: 2 hours per acre (0.4 for felling) (1.6 for collecting) Daily Rate One Harvester 4-5 acres Slide20: Harvest Test Trials Total Fuel Use: Dense Stand (300 tr/ac) 23 gallons per acre Moderate Stand (140 tr/ac) 16 gallons per acre Slide21: Ecological Effects of Harvesting Mesquite stump Slide22: Wood-to-Ethanol Conversion Slide23: Ethanol & Cellulose Chemistry Wood Cellulose + Lignin: Cellulose has thousands of 6-carbon chain glucose residues linked by oxygen bridges: (C6H12O6 x thousands) Lignin has combinations of phenolic subunits such as coniferyl alcohol that have 6-carbon benzene rings: (C10H12O3 x thousands) H OH C C H H H H Ethanol: Ethanol by comparison is a very simply 2-carbon molecule: (C2H5OH ). It has a higher percentage of hydrogen (13%) than cellulose or lignin (7%). Slide24: We are working with private companies that are developing cellulosic ethanol technologies. The details of these processes are proprietary so we are unable to provide these data in this presentation. However, for the purposes of projections, we will assume ultimately a 150 gallon per ton yield. Currently, fermentation of 1 ton of corn yields about 100 gallons of ethanol. Cellulosic materials such as wood or grass may have higher yields but the technology for conversion of cellulosic materials to ethanol is not currently available. The maximum possible ethanol yield from one ton of dry wood is about 300 gallons. This is based on the amount of carbon in wood plus the addition of extra hydrogen because there is a greater percentage of hydrogen in ethanol than in wood. Wood-To-Ethanol Yields Slide25: Regional Projections These projections are based on a cellulosic refinery that can yield 5 million gallons of ethanol per year. Currently, this is well below the corn ethanol standard of 50-100 million gallons annually. However, with a feedstock source such as mesquite we have to take into consideration the transport costs of the feedstock. Therefore, a lower yielding refinery is needed to minimize transport costs. Slide26: Wood and Acreage Per Refinery 5 Million Gallon Per Year Commercial plant - 5 million gallons ethanol per year > Assume 150 gallon per ton yield (this is not yet commercially available) > Need about 34,000 tons mesquite feedstock per year > If refinery runs 340 days per year, need 100 tons per day. > Therefore, need to harvest 10 acres per day. 3,400 acres of mesquite needed per year (assuming 10 tons per acre and 34,000 tons per year). Re-harvest every 10 years. Therefore to indefinitely sustain such a refinery, one needs 10 x 3,400 or about 34,000 acres. This assumes that the mesquite regrowth is allowed to grow!! If we add 15,000 acres for brush sculpting for wildlife habitat, the total acreage needed for the harvest “system” is about 50,000. Travel distance from wood source to refinery < 10 miles. It is ESSENTIAL that refineries are small capacity and located near the feedstock source to minimize travel distance. Slide27: Rural Economic Development Slide28: Will It Make A Dent in Texas Oil Use? Slide29: Note Regarding Data Sources: This presentation represents the combined efforts of Dr. Ansley’s research at the Texas Agricultural Experiment Station near Vernon and data generated by industry collaborators. All projections regarding mesquite availability and the costs to harvest mesquite have been developed by Dr. Ansley either through field measurements or reference to available literature. Wood-to-ethanol yields (i.e., gallons of ethanol per ton of mesquite wood) are considered estimates at this time and are used only to generate regional projections. It should be emphasized that this represents a very preliminary projection and is subject to continual modification in the future as more data are gathered. No commercial refinery using cellulosic conversion technology has yet been constructed. If you have questions please contact me at [email protected] Thank you for your interest.