Heat transfer, as we know from high school, takes place by con-duction, convection or radiation. That is, from excitedly quivering molecule to its neighbor, or by the excited molecule itself moving (in a liquid or gas), or by the excited molecule emitting radiation (in a spectrum of colors, most of it, at reasonable temperatures, infra-red). In a solid such as oil shale, only conduction and radiation will transfer the heat from one place to another.
A body receiving radiated heat will partly absorb it, partly trans-mit it through its interior, and partly reflect it. On a warm day, a piece of metal in the sun gets so hot that it cannot be touched, yet the air is only pleasantly warm: the air transmits most of the radia-tion, the metal absorbs most of it (but if painted white, will reflect it and remain cool). A body absorbing all incident radiation, or a "black body," like many concepts in physics, is a non-existent ideali-zation, but one that can be closely approximated
¾just as skating on ice closely approximates an idealized absence of friction.Oil shale is sedimentary rock that contains small globules of organic matter. The composition of the base rock and the concen-tration of organic matter varies so widely that the name "oil shale" is one of convenience; it is not a geological or mineralogical term. When the shale is heated, the organic matter, often called kerogen, liquefies and yields oil. The heat is transferred to the inside of the shale by conduction, but since the shale is not a good conductor, much heat must be put into it to reach the kerogen inside. When the temperature of the heater is raised, more heat will be conducted, as shown in the figure. The pilot projects retorting oil shale worked with temperatures of up to about 900øF, producing little oil and a lot of hot spent shale.
[DIAGRAM]
But Prof. Nielson's laboratory tests disco- vered a critical point: when the temperature is raised higher, radiative transfer takes over. That is, conduction increases at the same rate as be- fore, but the kerogen globules act as near- black bodies, whereas the shale is partly trans- parent to heat radiation. The cross-over point is at about 1,000øF, and at higher temperatures radiation is the more important mechanism of transfer.
Since the radiated heat is absorbed far more by the kerogen than by the shale (at least for the same volume), more heat goes more efficiently to where it is wanted
¾in the kerogen, and less is wasted in heating the shale. The process developed by Prof. Nielson works at 1,200øF; at that temperature the kerogen turns into a gas¾ natural gas.Previous projects failed because they did not reach high enough temperatures, and because they went for the oil dripping down;
Nielson's goes for the gas bubbling up to the surface.
Gas? I started out with oil. Yes, but gas can substitute for oil in many places, for example, as a feedstock in the chemical industry, though admittedly not in transportation.
Beyond that, the Los Alamos National Lab announced on Dec. 4 [1987] that it has succeeded in converting natural gas into a liquid fuel (methanol) that can either be used directly in automobile engines or converted to gasoline. Natural gas (methane) burns in a surprisingly complicated chain of reactions whose end product is CO
2 and water. The trick is to stop the oxidization as soon as the methanol stage is reached.This could turn out to be a momentous discovery not only for the process under discussion, but for the transportation of gas
¾ for example, from the Alaskan oil fields (where it is now pumped back into the ground) to the contiguous states.|
Vol. 15, No. 5
Newsletter: Access to Energy Newsletter Archive Volume: Issues Issue/No.: Vol. 15, No. 5 Date: December 01, 2004 10:29 AM (For actual publication date see newsletter.) Title: Peace in Our Time
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