Hydrocarbons – The Weapons of Mass Combustion™

There is much debate regarding the need for energy self sufficiency in the US.  The discussions are also shaded by opinion on the possible problems of global warming.  All this public debate is for good reason even if the debate is not always well reasoned.  Of course the US should wean itself from imported oil if we want to improve the environment and reduce our balance of payments deficit.  The problem is difficult to solve not because of lack of discussion but rather because of fundamental thermodynamics.  Hence, I chose the title Hydrocarbons – The Weapons of Mass Combustion ™ for this article.

First we need vivid analogies to describe energy content.  The sad truth is no lay person, politician, or most techies can describe the energy contained in a kilowatt hour in simple terms.  Here are some clearly understood analogies of a kilowatt hour of stored energy (not necessarily fully recoverable but stored).  A water tank with 1,000 gallons of water on top of a structure or hill 315 feet above the reference point has the potential energy of 1 kilowatt hour.  A 12 volt automobile battery with 83 amp hours of capacity has one kilowatt hour of stored energy.  Now the kicker 3.1 fluid ounces (80 ccs) of diesel has one kilowatt hour of stored energy.

From the above analogies one can see that diesel has massive energy density per unit volume.   Volume is the method by which things are stored in the three dimensional space that we live within.  While many tout the high energy density of hydrogen per unit mass, the energy density per unit volume of liquid hydrogen is only one fifth that of diesel.   Forgetting how expensive and inefficient it is to produce and store liquid hydrogen, it simply makes no sense to store a fuel that contains only 20% of energy content of another fuel when considering personal or other transportation vehicles.  The space shuttle jettisons its external hydrogen tanks for this very reason.  This space vehicle would be too large and too heavy if it did not have throw away hydrogen tanks.  I doubt we can litter the roads with throw away hydrogen tanks for Hummers even if Arnie likes to say “hasta la vista baby”..

Why does diesel have such a high energy density per unit volume?  The simple answer is that the carbon hydrogen bond (hence hydrocarbon) when oxidized (burned) releases substantial energy.  The second part of the answer is also that the specific gravity or density of diesel is much greater than that of liquid hydrogen.  Diesel is more than 15 times denser than liquid hydrogen and more than 10,000 times denser than gaseous hydrogen.   While the density of our politicians may not be tolerable, high density of fuels are a desirable quality.

Self service gasoline stations are now the norm in the US.  There is hardly ever any mention in the news of accidents occurring while the least technical amongst us fill their vehicle tanks with gasoline or diesel.  The amount of energy transferred into a 15 gallon tank from the diesel pump equals more than 600 kilowatt hours of stored energy.  The transfer of the 15 gallons of fuel is accomplished in approximately 3 minutes.  This implies a rate of energy transfer greater than 12,000 kilowatts or about the capacity of an electrical substation for a housing development with 8,000 homes.  Another analogy is as follows: If the Hoover Dam’s entire electrical output is used to fill the kilowatt hours in the fuel tanks of personal vehicles, the Hoover Dam could simultaneously fill 165 vehicles.  These vehicles would be filled with their energy in 3 minutes.  Therefore 3,300 vehicles could be filled in an hour, or about 2,900,000 vehicles could be filled with their energy in a year.  This is about half the number of vehicles in the San Francisco Bay Area.  I guess we are not going to build two Hoover Dams soon in the Bay Area just to fill our cars with fuel only once a year.

Methane is another weapon of mass combustion™.  This fuel has 4 carbon hydrogen bonds in each molecule just waiting to release a mushroom cloud of energy when burned.  Methane is 8 times as dense as gaseous hydrogen and as fuels are stored on a volume basis, methane gas compressed to the same pressure as hydrogen has approximately 3.5 times energy content compared with hydrogen.  We all know, how relatively few vehicles in the US fleet have been converted to run on compressed natural gas (methane).    Compressed methane in fact is a good candidate for substituting for gasoline or diesel as a transportation fuel for urban travel, however the logistics are more complicated and consumer prefer convenience to reduced emissions.  Methane is gaining market share as the fuel of choice for electric power generation.  As the US has no active policy to include new nuclear power stations in the generation mix, methane has taken up the challenge of adding generation capacity to the grid.  There will be increased importation of pipelined methane from Canada and liquefied methane (LNG) transported by the US in specialized ocean freighters.  Methane will continue to play a major role as a weapon of mass combustion ™ well into the future.

Now we come to the heavyweight weapon of mass combustion™ – Coal.  This carbon compound is a solid and holds a prominent position in our energy mix.  More than 55% of the electric power generated in the US is from coal fired stations.  There is significant interest in coal gasification and ultra supercritical coal fired power generation stations.  These technologies that soon will be widely deployed, produce electricity more efficiently than older coal fired stations.   Coal is relatively abundant in the US and China and is a likely candidate for remaining in medal position (gold or silver) in the Olympic stage of weapons of mass combustion™.

Other heavily carbonaceous fuels such as tar sands and shale will be extracted in increasing quantities and will perform that wonderful trick of breaking the carbon hydrogen to release energy to the energy hungry world.  The Chinese are trading bicycles for Buick Rendezvous SUVs so that they can enjoy the full energy content of an American lifestyle.  Why not, they too have been allowed in the club that enjoys the security of weapons of mass combustion ™.

The brave new world does have a few arrows in our quiver to combat the weapons of mass combustion™.  These are the hybrid drive train, mass transportation, mini personal vehicles, telecommuting, bicycling, and walking.    There is no doubt that these measures can and will hold back and delay the date when the stockpiles of the weapons of mass combustion™ are exhausted.  The folly of the modern lifestyle is best expressed in the universal term of TV Hours ™.  The TV Hour ™ not only refers to supposed enjoyment that mankind obtains from watching the 1.5 billion tube TVs that are connected to replays of the Brady Bunch, but also refers to the universal constant for energy content.  A TV Hour ™ is the amount of energy in electrical form needed to power a 20” tube TV for an hour.  Just so we can relate energy usage in transportation, my governator Arnie driving his Hummer 15,000 miles each year uses over 550,000 TV Hours ™ or energy in the process.  Arnie could therefore have 62 TV’s running 24/7 with the replay of that wonderful film “The Terminator”.  I doubt that even this “Mr. Universe” has enough peripheral vision to take in this amount of visual stimulation.  Even my favourite vehicle the Toyota Prius driven 15,000 miles per year could power 12 TVs constantly. 

By comparison the 2,000 calorie daily diet, equals one TV running constantly.  Having reduced life to the number of TVs running, I suggest we stop and have a 20 fluid ounce Venti® sized cup of Starbucks® coffee.  Incidentally, the quantity of energy needed to heat 20 fluid ounces of water to make the Starbucks® coffee equalled approximately half a TV Hour™.  I guess we will never escape Starbucks®, TVs, or hydrocarbons.

© Lindsay Leveen 2004.

Some thoughts on Energy units

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