FOSSIL FUELS

There is no question that the use of fossil fuels will continue to dominate world's energy supply in the foreseeable future. The following diagram summarizes U.S. energy supply and demand in 1993. Close to 90% of the overall supply (84 quadrillion BTU) came from coal, oil and natural gas. So it is important to take a closer look at the technical virtues and vices of these energy sources. Once these are understood, and once their potential environmental impact is placed into perspective, it will be easier to make economic and political judgments about their future prospects.

The vast majority of fossil fuels is burnt with oxygen from air to produce heat. [Heat is either the ultimate objective or it is subsequently used in a heat engine (for example, turbine of a power plant or automobile engine) to produce mechanical work.] This process is called combustion. It is the most important chemical reaction known to man. The molecules of fossil fuels (for example methane, CH4, consisting of one carbon atom bound by four hydrogen atoms) react with the oxygen molecules (O2, two oxygen atoms connected to each other) and a rearrangement of their constituent atoms takes place. When the reaction is completed, carbon dioxide (CO2, one carbon atom bound by two oxygen atoms) and water (H2O, one oxygen atom bound by two hydrogen atoms) are produced. A consequence of this rearrangement of atoms is a release of heat. The quantity of heat released is called the heating value of the fuel. For example, a gallon of most petroleum products (gasoline, fuel oils, etc.) has a heating value of approximately 140,000 BTU. A barrel of oil (42 gallons) releases about 5.8 million BTU. A pound of coal has a heating value anywhere between 6,000 and 15,000 BTU. A cubic foot of natural gas has a heating value of about 1,000 BTU. (A useful rule of thumb, sufficiently accurate for many purposes, is that 1 gallon of oil is equivalent to about 10 pounds of coal and to about 150 cubic feet of natural gas. When these quantities of fuel are burnt, approximately the same quantity of energy is released in the form of heat.)

We shall see that in nuclear reactions, in contrast to this rearrangement of atoms to form new molecules, the internal constituents of the nucleus of an atom (protons and neutrons) are rearranged. Such a rearrangement also results in the release of heat, a tremendous amount of heat in fact. To give you an idea, a quarter-inch by half-inch pellet of conventional nuclear fuel (uranium) produces as much heat as 1800 pounds of coal, or 150 gallons of oil.

Because fossil fuels are of interest for their heating value, a very important comparison of their virtues is in terms of cost of a given quantity of thermal energy. A convenient choice is a million British thermal units (BTU). While the prices of fuels may vary considerably with time and place of purchase, the procedure outlined below is valid always. It allows us to compare 'apples' with 'apples'. It is also the key to formulating energy policies at both the microeconomic and the macroeconomic level.

NATURAL GAS:

COAL:

PETROLEUM:

Petroleum looks decievingly cheap in this comparison. It is never used before it is refined (see petroleum products). The refined products are obviously more expensive than crude oil. For example, gasoline and residential fuel oil cost about $1.25 and $0.85 at the station. Their comparable prices are then close to nine and six dollars per million BTU, respectively. This is much higher than the current prices of coal or natural gas. It's too bad you can't put coal into your 'gas' tank; some time soon, though, you may be able to use compressed natural gas (CNG). But if you are just interested in heating your home, these simple calculations are quite revealing. (For a more complete story on this, see Residential Comfort.)

For an illustration of current prices of fossil fuels, as reported by the media, see here.

lrr3@psu.edu (last revised 6/22/95)