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Renewable fuel mandates can't be met by ethanol

احدث اجدد واروع واجمل واشيك Renewable fuel mandates can't be met by ethanol

Even many of its most ardent supporters have come to recognize that corn-based biofuels may not make much economic sense. But efforts to develop alternatives such as biodiesel and cellulosic ethanol have continued in the hope of meeting an ambitious goal: a 2007 law that mandated renewable fuel use to reach 36 billion gallons a year by 2022. Considering that the US currently consumes about 140 billion gallons of fuel, and gas mileage will be rising significantly soon, the mandate will require that a substantial fraction of the fuel used in the country come from renewable sources in the near future.

At a recent meeting of the Agricultural and Applied Economics Association, some researchers considered what we'd need to do to reach that target; their conclusions were published in the American Journal of Agricultural Economics in December. They conclude that the focus on ethanol production in general is misguided regardless of the source, simply because consumption will hit what they call a "blend wall" unless radical (and expensive) changes are made to our automotive infrastructure. As such, they recommend we focus on converting biomass into a gasoline-like fuel if we're to reach the mandated biofuel targets.

Right now, the majority of ethanol consumed as fuel in the US is blended with gasoline to make a mix called E10. That's ostensibly 10 percent ethanol, but its average concentration is a bit less, since a full 10 percent blend would create problems during summer months. Right now, even if every gallon of gasoline in the nation was E10, the authors calculate that we'd consume about 12.6 billion gallons of ethanol annually. "US ethanol production capacity already exceeds this level," the authors conclude. "Thus, our ability to consume ethanol has reached a limit called the blend wall.

Once it hits the blend wall, the ethanol manufacturers dump it on the market at about the same price as the raw material it was created from, generally corn. At least 3 billion gallons of production capacity also was kept inactive for most of 2009.

The authors consider several combinations of options that will increase ethanol uptake. One option is to increase the allowance for a regular fuel blend to E15, which can still be burned in current vehicles. Another is to dramatically increase the use of E85, which requires special flex-fuel vehicles and a separate supply infrastructure. A final option is to divert cellulosic fuels stock from ethanol production entirely, and perform a more energy-intensive conversion to a gasoline-like fuel stock.

Keeping the current blend at E10 and increasing the use of E85 could potentially get us to the renewable fuels mandate, but it would be ugly. In 2010, it's estimated that we'll have consumed 20 million gallons of E85; that will have to rise to 23.5 billion gallons by 2022. Supplying that much would require about $30 billion in upgrades to gas stations alone, and an average increase of 8.7 million flex fuel vehicles every year until then. Because of its lower energy density, E85 provides lower gas mileage, so consumers would also be filling their tanks much more often.

Taking this route would also cut into the amount of regular gasoline used, and thus the ethanol that goes into E10 right now. Thus, switching from E10 to E15 changes the trajectory a bit, but not dramatically.

The only thing that really changes things is diversion of a lot of the biological material that might be converted to ethanol into what the authors term "thermochemical biofuels." These require the breakdown of the raw material through a high-temperature process, recombining it into fuels that are a lot more similar to current gasoline. Thus, the energy used is likely to be higher than ethanol, but the output can be blended at any level or completely substitute for standard gasoline.

Combined with a shift to E15, this could potentially eliminate the need to change the nation's transportation infrastructure to support more E85, as well as its associated costs. The "blend wall" never materializes.

The analysis seems to be solid, given the assumptions made by the authors, and it certainly highlights the problems we'll face as we try to figure out how best to integrate renewable fuels into our existing infrastructure. But the scope of the study, with 2022 as its end point, limits the discussion severely.

Long term, given a finite supply of oil and the resultant increase in prices, the US is going to want to produce as much biofuel as it can. Eventually, that won't run into any sort of blend wall; it'll run into limits on the availability of biological material to convert into fuel. What will matter most is not which technology will get us to a 2022 target, but which most efficiently converts raw materials to useable fuel

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