Sunday, February 24, 2008

Ethanol's perpetual motion process

Hat tip to Jib for linking to this well researched analysis of ethanol production by Chuck Angier, The Futility of Ethanol. It is a good read, but two areas jump out needing clarification and refutation. I will address the first in this post.
The energy efficiency ratio of Ethanol is 1.06 without byproduct credits and 1.67 with byproduct credits. (Ethanol.org). In other words, ethanol generates 6% more energy than is required for production. If you were to allocate 34% of the required energy to the production of the byproduct, then it produces 67% more energy than it consumes.
It took a while to comprehend this statement, because it is physically impossible. The energy efficiency ratio is defined as a value between 0 and 1.
In physics and engineering, including mechanical and electrical engineering, energy efficiency is a dimensionless number, with a value between 0 and 1 or, when multiplied by 100, is given as a percentage. The energy efficiency of a process, denoted by eta, is defined as

where output is the amount of mechanical work (in watts) or energy released by the process (in joules), and input is the quantity of work or energy used as input to run the process. Due to the principle of conservation of energy, energy efficiency within a closed system can never exceed 100%.
In mechanical engineering terminology, the ethanol proponents are making a claim that violates the First Law of Thermodynamics.
The change in the internal energy of a closed thermodynamic system is equal to the sum of the amount of heat energy supplied to the system and the work done on the system.
I think what these alchemists really mean is that for every one human supplied energy unit used in producing ethanol, 1.06 energy units of ethanol are produced. Fair enough and with a scientifically researched basis. But this calculus ignores the huge amount of solar energy converted to potential energy as the corn grows.
The misstatement of energy efficiency is made by the ethanol hucksters to put their product in an impossibly good light. This can be used to fool a scientifically ignorant audience, the Wisconsin State Legislature, for example.

The aspect of BIG ETH's efficiency claim that includes production of byproducts in the computation to come up with an efficiency of 1.67 is contrary to standards for engineering evaluations of process efficiency.
For example, in the generation of electricity at a coal fueled power plant, both flyash and steam are byproducts of the process. However, the BTU's that may be attributable to production of these byproducts are not considered in the thermal efficiency of the energy conversion. The desired output of this process is electrical energy, not an adjunct for road construction or waste heat discharged to Lake Michigan.

Same goes for the Milorganite produced from last Friday's burrito and the waste byproducts from ethanol production. The Milorganite has no nutritional value and distillers grains have no use as motor fuels. Therefore, these byproducts do not get considered in determining the efficiency of the process, be it digestive or ethanol distillation.

The implications to the analysis in The Futility of Ethanol of disregarding byproduct production will be addressed in a later post.

CORRECTION:

I have reviewed the Net Energy Balance of Ethanol Production issue brief from Ethanol.com and found that they use the term "Energy Ratio" not "Energy Efficiency." Therefore, my above rant misses the mark.

3 comments:

Chuck said...

Ethanol nets 6% more energy than it consumes (1.06), AND generates 3.43 lb. of byproduct per gallon. Proponents qualify the 1.06 with a position that (arbitratrily) 34% of the energy consumed in the process is allocated to the byproduct, thus the energy cost of producing the ethanol is reduced. This is why I could care less about energy efficiency but would like to know what the "dollar" efficiency is. If the byproduct had the value of gold, then the ethanol would be very inexpensive and we would be an ethanol society already. I felt that I was "violated" when, in my research, I read that the energy efficiency of Ethanol was 1.67 but only after allocating 34% of the energy to the by-product.

Chuck Angier

Headless Blogger said...

Chuck - I understand where you are coming from.

If the byproduct is something that is already produced and with an existing demand, then the "allocation" of energy could have a basis. They'd essentially be using an improved process to make that byproduct and getting the ethanol for the difference in energy use.

I don't know a thing about distillers grains, but from your essay I conclude that the above conditions do not apply.

Chuck said...

The original document at www.ethanol.org where I got my data has been removed. I wonder why?
You might want to check out at new PDF file they have that looks interesting. Go to page 10. They are still allocating 35% of the energy costs to byproduct. http://www.ethanol.org/pdf/contentmgmt/Issue_Brief_Ethanols_Energy_Balance.pdf