David’s post about ethanol and coal inspired me to do a bit of research on just how much coal goes into producing G.W. Bush’s favorite “renewable,” “clean-burning” fuel source.

What I found is … disturbing. First, some background. Before you can distill corn into fuel, you have to crush it. There are two ways to do so: wet milling and dry milling.

According to this USDA document, dry milling accounts for about two-thirds of ethanol production, wet milling the rest. Traditionally, dry-milling relies on natural gas for power, while wet milling leans on natural gas and coal in roughly equal proportions.

In addition to traditionally not using coal, dry milling is a bit more energy-efficient than wet milling, which according to this Energy Star document (PDF) ranks as “the most energy intensive industry within the [food-processing sector], using 15% of the energy in the entire food industry.”

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Thus, if corn-based ethanol must exist, dry-milled ethanol beats wet-milled. (Note: I think corn-based ethanol is an environmental and economic disaster no matter how it’s milled.)

Here’s where we get to the disturbing part of the Christian Science Monitor piece David points us to. According to CSM (via Alternet), the new coal-burning plant in question uses dry-milling. The article states:

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The Goldfield refinery, and the other four coal-fired ethanol plants under construction are called “dry mill” operations, because of the process they use. The industry has in the past used coal in a few much larger “wet mill” operations that produce ethanol and a raft of other products. But dry mills are the wave of the future, industry experts say. It’s their shift to coal that’s causing the concern. [Emphasis added.]

The article claims high natural-gas prices are inspiring dry-millers to shift to coal. “It just made great economic sense to use coal,” one newly launched dry-mill ethanol plant manager tells CSM.

Since two-thirds of ethanol plants are dry millers currently relying on natural gas, that’s a disturbing statement. So is CSM’s claim that industry buzz about “retrofitting existing refineries for coal is growing.”

Think it would “just [make] great economic sense to use coal” for dry-milled ethanol if David ruled the world and he imposed a stringent carbon tax?

Of course, if I ruled the world, the point would be moot: Ethanol and industrial corn would cease to exist — and the Midwest would be a magnet for foodies indulging in some of the best vegetables and grass-fed meats available anywhere.