Robert Rapier who writes the R-Squared Blog offered up a useful post yesterday that describes Mr. Rapier’s thinking in two important areas. All of us can use Mr. Rapier’s quick and easy guides in forming thoughts about where to invest, have expectations and judge how to save for future investments in tools that use energy. The relevant parts of his post deal with the mass balance and energy balance. The two sections can be roughly applied to most all biomass sources for making fuels.

The first Mr. Rapier addresses is mass balance or the mass entering has to stay constant by coming out or accumulating in a system. Using wood in the post because of the Coskata commentary Mr. Rapier tracks the carbon from wood sources through to the Coskata ethanol output. Wood at 50% carbon becomes 1,000 pounds of carbon per ton times 454 grams yielding 37,833 moles of carbon. Going through the conversion to ethanol with carbon2 you get 18,917 moles of ethanol which divided by 454 again gets you 1917 pounds or 290 gallons. A good exercise and Mr. Rapier offers that a ton of woody mass can through the Coskata process yield 34% of the carbon back into ethanol to be used again. Basically its good work, well worth your looking it over.

On the other hand, any process that seeks to convert carbon in one form to another will need this very assessment done somewhere along the due diligence path. What applies to wood applies to any other source. What Mr. Rapier does is point out a couple of glaring issues. The first is by omission, in that the hydrogen (you need six hydrogen atoms for ethanol) for making the ethanol is not accounted for. It comes from the process’s other inputs, adds part of the ethanol mass, and skews the end result to an actually lower use of the original carbon. Add the missing oxygen atom and the proportion of original carbon goes down even more.

The results, as innovative, technologically feasible and low in cost of the end product still throws off some 5/6ths of the original woody mass as some sort of effluent. I’m impressed and a little bewildered that all of this wood to ethanol is so exciting. It’s not making a great deal of market sense to me. Mr. Rapier deals with it as going into “microbe production, carbon dioxide and lost tail gas.” In any case the remaining 5/6ths of the original mass is going to be quite a pile before long.

The next section deals with energy balance. Simply put and for most applications energy balance is the values going in to a process as compared to the product values coming out. Here Mr. Rapier gets it together in the fourth paragraph with a “crude illustration” which isn’t so crude as just incomplete of accounting for all the inputs. The point he makes is that the energy going in to distill off the water is more than the energy in the ethanol remaining. (Not to nitpick Mr. Rapier, but the distillers I know distill off the ethanol at its lower vapor temperature, thus a lower BTU input.) This one part is just one of several beginning at planting the tree and on to the exit of the fuel product at the process end. Mr. Rapier makes it very clear that we have to be conscience of the energy inputs to get worthwhile results. The market won’t tolerate products that consume more than they deliver, as they would be even more expensive than the energy used to make them. Grasping this principle is critical for understanding what technologies will get to market and succeed.

These two concepts, the mass balance and the energy balance offer two perspectives for you to consider. One common truth in chemical reactions is that the more simple the product you seek the more likely it will be easier and cheaper to make when compared to more complex molecules. There are lots of exceptions, but on the whole you’ll find it’s easier to make methane than a complex hydrocarbon or make methanol than ethanol or butanol. It’s usually much easier to crack large molecules to smaller ones than to make big ones from small ones.

That said, many will correctly think that the adage of the “KISS” method would apply and justifiably so. While ethanol has a huge following it is more difficult to make than the smaller alcohol methanol. Little is said about the comparison between the two in the press and research isn’t getting onto the discussion with hard analysis. But practical experience and both biological and chemical processes suggest that the cheaper fuel product would be methanol or even more likely methane. There’s something Mr. Rapier could apply his considerable skill towards.

Long-term readers will recall this site is about the energy and fuel science to maintain and improve our standards of living. As much as ethanol and its following make a lot of news the allegiance here is to our cost for units of work. Mr. Rapier offers a glimpse into two useful metrics for assessment that are easy to use and very informative when taken further out. What can be made cheap would be a better guide to the cars, tools and equipment we buy in the future than any other input.

That makes it BTUs per dollar as the main end metric. That comparison tells me what choices I’d make for the tool, be it a car, a furnace or backyard grill. Things in this field are interesting enough, but its time to get on with looking for real long term fueling solutions that the market can deliver in quantity. Biomass to fuel is a path from a seed to disposing of the pile of leftovers. Mr. Rapier offers a broad-brush stroke look, and its not all that far from being something almost everyone can understand, even politicians.

Biomass by itself has a great future, even though many suggest that it’s not enough. Actually it could be if the hydrogen to add to the biomass carbon can be added to the process cheaply, so making the theoretical 100% of carbon returned fully to the fuel cycle. But that’s another issue.


1 Comment so far

  1. Theron Tataris on April 12, 2011 10:40 PM

    I must say, I assumed this was a pretty attention-grabbing read when it involves this topic. Liked the material.

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