New process design improves energy balance of ethanol production considerably

Using the sheer power of mathematical programming, chemical engineers from the Carnegie Mellon University in the U.S. have devised a new process that considerably improves the efficiency of ethanol production, a major component in making biofuels a significant part of the world's energy supply.

The researchers have used advanced process design methods combined with mathematical optimization techniques to reduce the operating costs of corn-based bioethanol plants by more than 60 percent. The key to the new strategy involves redesigning the distillation process by using a multi-column system together with a network for energy recovery that ultimately reduces the consumption of steam, a major energy component in the production of corn-based ethanol.

For a long time, corn-based ethanol was considered a questionable energy resource, and doubts still remain over its final energy balance (for more on this concept, see the excellent overview of the principles behind the notion of 'net energy' at the Encyclopedia of Earth, and a new lifecycle assessment of corn ethanol's energy efficiency). Today, 46 percent of all U.S. gasoline contains some percentage of ethanol. Until now, demand was driven by a federal mandate that 5 percent of the American gasoline supply – roughly 7.5 billion gallons – contain some ethanol by 2012.

But since President Bush held his State of the Union address, the biofuel has received a far bigger boost. The new U.S. energy agenda aims to replace not less than 20% of all gasoline consumption (roughly 2 million barrels per day) with renewables, mainly ethanol, in 10 years time ("20 in 10") (earlier post). This will require a gigantic investment in finite resources, and so each increase in processing efficiencies is more than welcome.

"This new design reduces the manufacturing cost for producing ethanol by 11 percent, from $1.61 a gallon to $1.43 a gallon. This research also is an important step in making the production of ethanol more energy efficient and economical." Chemical Engineering Professor Ignacio E. Grossmann, who completed the research with graduate students Ramkumar Karuppiah, Andreas Peschel and Mariano Martin.

In the U.S., corn is the main feedstock used to produce ethanol, but the biofuel can be made from a wide variety of starch and sugar rich crops. The increased efficiency derived from the enhanced energy recovery model can in principle be applied to most other processing facilities:
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The research was conducted through the Chemical Engineering Department's Center of Advanced Process Decision-Making in collaboration with Minneapolis-based Cargill, an international provider of food, agricultural and risk management services and products. More particularly, it drew on the work of Professor Grossman's team, which is united in a research group, whose main aim is the development of discrete-continuous optimization models and methods for problems in process systems engineering.

Grossman's group addresses "problems in the areas of process synthesis, planning and scheduling of process systems, through novel mathematical programming approaches, which rely on linear and nonlinear models with discrete and continuous variables. These include mixed-integer programming (MILP and MINLP), General Disjunctive Programming (GDP) and global optimizationand multiperiod optimization. Both deterministic models as well as models with uncertainty are considered."

Luca C. Zullo, technical director of Cargill Emissions Reduction Services, said about the cooperation: "As a result of the explosive growth of the U.S. fuel ethanol industry, we decided to collaborate with Professor Grossmann's team to verify how process synthesis tools could be applied to improve the production of ethanol from corn. The work done at Carnegie Mellon demonstrated the potential for considerable capital and energy cost savings in the corn to ethanol process. We look forward to the time when the tools developed by Carnegie Mellon researchers will become part of industry's new toolkit for making the process even more economical and sustainable."

Efficiency increases in biofuel processing are one of the areas in which tremendous progress remains to be made. An example of what is possible is offered by Brazil's experience. There, in less than 25 years time, ethanol producers succeeded in reducing costs by up to 75%, mainly through increases in processing efficiency. This trend is set to continue, making the energy balance of the biofuel better than it already is.

Without wanting to be be too deterministic (or assuming the existence of some hidden finality within scientific evolution), the exponential increase in scientific and technological breakthroughs allows us to assume that in the field of biofuels production too, large efficiency increases will be made in the not so distant future (in plant biology, agronomy, engineering, biochemistry and process engineering).

More information:
Barttfeld, M., Aguirre, P.A. and Grossmann, I.E. "A Decomposition Method for Synthesizing Complex Column Configurations Using Tray-by-Tray GDP Models," [*.pdf], sine dato, submitted for publication.

Barttfeld M., Aguirre P.A. and Grossmann I.E. "Alternative Representations and Formulations for the Economic Optimization of Multicomponent Distillation Columns." [*.pdf] To appear in Computers & Chemical Engineering.

Cleveland, Cutler; Peter Saundry, 2007. "Ten fundamental principles of net energy." In: Encyclopedia of Earth. Eds. Cutler J. Cleveland (Washington, D.C.: Environmental Information Coalition, National Council for Science and the Environment).