Tuesday, February 12, 2008

current best bio-fuel, a quick analysis

ZeaChem, a newish company here in the PNW is planning to produce ethanol from trees instead of corn. they currently own 35,000 acres of short rotation hybrid tree crop producing land and recently announced an agreement for how they will acquire additional production from another grower in the area.

aside from the inherent problems of ethanol (like difficult storage, delivery, and use), this seems worthwhile to talk about. i figure their process is producing ethanol because that is what the gov't will reward them to do. if we ever get smart and push butanol instead (a direct replacement for gasoline, with none of ethanol's storage, delivery, or use problems), i'm assuming that ZeaChem's process will be modified to produce butanol.

so, what they say is that:

"Other approaches have theoretical restrictions that limit ethanol production to 60-100 gallons per dry ton of biomass. The ZeaChem technology will produce fifty percent more ethanol per ton of feed than the current best-in-class technology."

so, let's be generous and say ZeaChem can produce 150 gallons ethanol/ton of dry biomass. we can even be excessively generous to the point of lying to ourselves a little bit and say that they could produce a gallon of butanol as a direct replacement for a gallon of ethanol. there is more energy in a gallon of ethanol, so this is almost certainly a false assumption, but let's pretend.

so, 1 ton of trees will give you 150 gallons of gas. they own 35,000 acres growing trees. the best hybrid poplar trees in the best soils will produce 10 tons of biomass per year. 35,000 acres x 10 tons/acre x 150 gallons/ton = about 50 million gallons of bio-fuel per year. the average american uses about 500 gallons/year. so, this process will support the driving habits of 3 Americans per acre of productive soil. given that we were a bit too generous in our assumptions and that there will be energy inputs into the system, i think scaling that back to 2 American drivers/acre should bring us pretty close to reality.

i'm impressed. assuming there are 200 million American drivers, that means we only need to use a land area of 100 million acres (an area the size of California) to provide a biological source for our current transportation consumption. this may not be so disruptive or impossible, actually. there are probably hybrid poplar trees that will happily grow on marginal soils that are currently unused or underused, so we may not have to displace food crops or native forest in order to provide a sustainable forest fuel crop.

1 comment:

KVMAPR said...

Interesting thumb nail sketch, but a number of other inputs may tend to bring the efficiency of this equation down. For instance, 10 tons per acre on "marginal" lands is unlikely, even with the best hybrids available. But using those lands is a good way to avoid competing with food supply production.

Then how do you do it? Same approach you use for crops, increased nutrient input. Poplars will grow well even in marginal lands, but you have to up the fertilizer and water supply to get a respectable result.

An alternative to hybrid poplar that may do well on marginal lands with less nutrient and water input is a plant that's better adapted to such an environment, switch grass for instance. You may get less ethanol per acre, but your inputs per ethanol gallons produced could be significantly lower. And there are a lot of "marginal" acres out there that could be used.