|Texas had 3.8 million acres with moderate to dense mesquite in 1984; that has climbed to 6 million acres.|
A Texas Agricultural Experiment Station researcher is exploring the feasibility of harvesting and using rangeland woody plants, such as mesquite and red berry juniper, as an ethanol feedstock for a distributed bio-energy industry in rural West Central Texas.
The prime area to harvest mesquite is the middle third of the state: a band bordered on the west by a line from Childress to Del Rio and on the east from Decatur to Austin. This mesquite-covered area could provide fuel for about 400 small (5 million gallons per year) ethanol plants, according to Dr. Jim Ansley.
We’ve had so much more interest in this since gas prices went up last summer. That’s going to be a real driving variable. If gas prices continue to go up, I think we could very well see a first generation refinery built in Texas to handle mesquite within five years.—Jim Ansley
Ansley is working with Pearson BioEnergy in Aberdeen, Mississippi to study the supply, harvest technologies, ethanol conversion rates and ecological effects of mesquite-to-ethanol production.
Pearson is the developer of a combined gasification/Fischer-Tropsch process for the conversion of the mesquite feedstock to a syngas, and then its subsequent conversion to ethanol.
In a trial with Pearson, one oven-dry ton of mesquite wood yielded 214 gallons of ethanol with a conversion efficiency of greater than 98%, according to Ansley.
By comparison, fermenting corn yields about 124 gallons per ton (EERE), and the yield from switchgrass cellulosic ethanol is about 80 gallons per ton (Iogen). (Iogen believes it can increase the switchgrass cellulosic ethanol yield to 100 gallons per ton in the future.)
An acre of the densely populated mesquite standing 10 to 12 feet tall will yield about 8 to 10 tons of wood. A commercial refinery producing 5 million gallons of ethanol per year will require about 30,000 acres to sustain it, assuming a 10% annual harvest and 10 years for regrowth.
The thing that will make this fail is if people think a bigger refinery in the big cities is better. That’s where it will fail. The transport costs to get the feedstock to the refinery will kill you.—Jim Ansley
Building smaller refineries in the rural regions where the mesquite is located is the key to making this work, Ansley said.
A State Energy Conservation Office grant is supporting the team’s study of different regrowth rates, as well as develop a mechanized system of harvesting mesquite. Working with private cooperators, Ansley has helped design a harvester that is in the patent-pending stages, and hopes to have it ready for a field demonstration on 5 October.
We’re in the process of trying to measure how much energy it takes to harvest mesquite in the field. That’s probably our least researched area. Now that we have this machine constructed, we can start working on that.—Jim Ansley