Dave's Energy

Tuesday, May 22, 2007

Coal-to-liquids diesel vs. Ethanol

An AP article earlier this month by H. Josef Hebert entitled "Ethanol Bill Heads to Full Senate, Prompts Debate over Coal as Motor Fuel" points out the bipartisan support for a bill that would try to replace a quarter of all our gasoline consumption with ethanol. Then it goes on to say that a measure to encourage production of clean diesel from coal-to-liquids processes was defeated along party lines. The reasons cited were concerns over global warming and specifically that coal-based fuels generate more CO2 than conventional gasoline. Unfortunately, that may be somewhat of an invalid argument.

I feel compelled once again to remind my friends that burning ethanol in your car produces CO2 at the tailpipe, as we have pointed out here in the past (see prior post titled: "Burning ethanol in your car releases CO2" . In fact, when you take into account that a typical E-85 flex-fuel vehicle gets a likely 15 MPG and a typical diesel powered car might get 30 MPG, then the ethanol burning car emits MORE CO2 on a per-mile-driven basis than the coal-based diesel car at the tailpipe.

The tailpipe distinction is key, because processing coal into liquid fuel emits CO2 at the plant level, and the process of making ethanol at a plant also emits CO2 (yet much less than the coal process). The difference is that a coal-to-liquids plant puts off CO2 in relatively pure, elemental form. This means the CO2 can readily be sequestered and put into a pipeline to move around the country for uses such as injection into EOR projects, etc.

I don't mind so much the coal-to-liquids process being dismissed if the reasons were based in fact, but I have a hard time when the same politicians accept the concept that we can just mandate our way to making 30 billion gallons of ethanol a year in just a few short years. We've said it before and will gain: there isn't enough land to do it with corn, there isn't the climate to do it with sugar, and there isn't enough time to do it with cellulosic material (we are trying to undo millions of years of plant evolution that has made cellulosic material very difficult to break down).

If we want to reduce CO2, the solution is clear: burn less fuel. Don't try to come up with a new fuel. So to burn less fuel, you have to use more efficient engines. That is where various technologies come into play. Not just hybrids, but also diesels and possibly compressed natural gas engines. Finally, if you really want to burn less fuel, just allow it to be more expensive. But that is the subject for another day...

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