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Martin Laplante

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Thu, 11 Jan 2007

How much ethanol do we need in gasoline?

Canada is increasing the amount of ethanol in gasoline. This is supposed to reduce greenhouse gas emissions without reducing energy use. But at the same time we are increasing the amount of synthetic crude from tar sands, which increases greenhouse gas emissions without changing energy use. How much alcohol do we have to use to compensate for the tar sands.

The U.S. DOE claims that the "net energy balance" of making fuel ethanol from corn grain is 1.34. That means that one barrel of oil is required to make ethanol with the energy equivalent of 1.34 barrels of oil.

They should really say the balance "can be" 1.34 since to achieve this you need the latest high efficiency processes, and you have to assume that all of the by-products are recovered and used as animal feed, thereby reducing the necessity to grow that feed. The fact that we have to replace the missing corn crop with other food without using any more land is not included in the calculation. We could become vegetarians, but who would eat all that animal feed from the industrial by-products? So, pretty big assumptions, but 1.34 is a number we can use.

This is just a back of the envelope calculation. A barrel of conventional oil releases about 450 kg of CO2, plus another 28.6 kg used in processing. For tar sands it's 80-90 kg, or 13% more. I'm not counting the opportunity cost of using up all our cleaner natural gas production (3 000 cu ft per barrel) in the process. Do the math and you have to mix 2/3 of a barrel of synthetic crude with 1/3 of a barrel of ethanol to do the same amount of damage as we did in the 90's.

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