Modern Alchemy: The Conversion of Anergy to Exergy
John A. “Skip” Laitner, a visiting fellow of the American Council for an Energy-Efficient Economy, says in his paper Linking Energy Efficiency to Economic Productivity: Recommendations for Improving the Robustness of the U.S. Economy, “it turns out that the U.S. economy converted only 14 percent of the total energy consumed in 2010 into useful work. In other words, the American economy wasted 86 percent of all the energy used in the production of goods and services. One can easily imagine that waste of this magnitude creates an array of costs that can easily weaken the nation’s economic and social well being.”
This wasted energy is mostly in the form of heat, which is cumulative on an already overheating planet.
In essence current energy regimes are performing reverse Alchemy.
Katherine Tweed, quotes Laitner in here post Forget Energy Efficiency, Think Exergy: “What most people call energy, for example, is what physicists and engineers are more likely to call exergy, or high-quality energy that is available to do work. Energy that is either wasted or useless -- in effect, energy that has no capacity to perform work such as the heat in the atmosphere -- is referred to as anergy.” Add up anergy and exergy and you get total energy. Capture that waste heat, however, and it becomes something useful.
It becomes effectively the Alchemists dream of turning lead into gold.
In his ACEEE paper Laitner estimates the waters in the Gulf of Mexico contain sufficient heat to power the U.S. economy for about 3600 years but says, “the energy within those waters is simply too diffuse, and the average temperature too low, to be available as a major source of power for the U.S. economy.”
In other words, he says the Gulf of Mexico contains a lot of anergy and the following OTEC resource map, bearing in mind a temperature differential between the surface and the ocean water at a depth of 1000 meters should be minimally 21C in order to produce power by this process, for the most part bears him out.
Surface temperatures over 26C are the breeding ground for hurricanes however, therefore in certain months Gulf of Mexico waters are conducive to generating OTEC power in the alternative.
This is not to say that there isn’t a whole lot of ocean accumulating over 90 percent of the heat attributed to global warming that can’t be put to useful work year round.
The means for doing this is a heat engine.
The efficiency “n” of such an engine = 1-Tc/Th where Tc is the temperature in degrees Kelvin of the cold sink and Th is the temperature of the hot source, which in this case is the ocean’s surface.
Assuming the ocean temperature at 1000 meters is generally 4C or 277K and the surface should be at least 25C or 298K, then the theoretical efficiency of the OTEC heat engine is about 7 percent or about half of the current conversion rate of U.S. energy.
Statistically this seems like no great shakes, but one has to consider that ocean heat is what is, and will for centuries to come, doing the damage of global warming and the conversion of this heat to work is the reverse of the U.S. situation. Not only does OTEC “capture” some of this otherwise more than useless energy and put it to work, due to the low thermodynamic efficiency of the process it moves about 20 times more heat into the cold sink of the ocean, which has a great capacity to receive it plus half the coefficient of expansion of the tropical surface. It is a process that replicates the events that have led to the recent atmospheric warming hiatus and is effectively the most efficient use of otherwise wasted and damage producing heat.
It can strengthen global economic and social well being even as it mitigates environmental damage; both useful and necessary outcomes.
OTEC done properly is contemporary energy and environmental Alchemy.
Other Posts by Jim Baird
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