The Types of Fossil Fuel We Use Makes a Difference in Global Warming

Add a Comment

May 16, 12:20 PM

by John Ryden, Global Warming Examiner

 

 

If we shut down the production of new oil resources such as from the Arctic National Wildlife Refuge and we buy more oil produced from Canadian Tar Sands, we increase the amount of carbon dioxide released into the atmosphere. The Tar Sands have much higher carbon content than light oil from Alaska. It also takes a considerable amount of energy from burning fossil fuels to extract the tar and then more carbon releases from the natural gas used to produce the hydrogen that is used to process the oil into products like diesel fuel.

Following is the chemical details on carbon content in fossil fuels:

Carbon Dioxide (CO₂) is a simple gas consisting of one carbon atom bonded to two (2) oxygen atoms. It is created by burning fuel containing carbon. Fossil fuels, which constitute the majority of fuel sources currently used on earth, are made up of carbon and hydrogen in various molecules.

The most basic of these molecules is methane. The chemical composition of methane is one (1) carbon atom and four (4) hydrogen atoms in a single molecule: CH₄. The process of burning methane combines one (1) methane molecule with two (2)  oxygen molecules to produce heat plus one (1) carbon dioxide molecule and two (2) water molecules:  CH₄ + 2O₂ -> CO₂ + 2H₂O.

Carbon dioxide can’t be removed or eliminated because the creation of carbon dioxide is what releases the energy from the fuel. There has been some discussion of sequestering (storing) the resulting carbon dioxide, but this has not been demonstrated on a commercial scale.

Not all fossil fuels produce an equal amount of carbon dioxide for the amount of energy released. Methane is the simplest of the fossil fuels having a ratio of 4 hydrogen atoms to each carbon atom. It is a gas at room temperature. Diesel fuel is made up of a group more complex hydrocarbons having an average chemical composition of C₁₂H₂₃, ranging from approx. C₁₀H₂₀ to C₁₅H₂₈. The extra carbon changes the physical properties and makes diesel fuel a liquid at room temperature. The average composition of diesel fuel has a ratio of approximately 2 hydrogen atoms to each carbon atom. Methane has an energy density of 55 MJ/Kg while diesel has an energy density of 48 MJ/Kg. When you burn diesel fuel you release more than 1.5 times as much carbon into the atmosphere than burning methane.

Coal is even worse. There are various types of coal. Sub-bituminous coal, bituminous coal and anthracite are together known as black coal or hard coal. Brown coal (lignite) is a relatively soft material that has a heating value only about one-quarter that of black coal. It has lower carbon content and higher moisture content than black coal.

Coal is classified according to its heating value and according to its relative content of elemental carbon. For example, anthracite contains the highest proportion of pure carbon (about 86%-98%) and has the highest heat value—13,500–15,600 Btu/lb (British thermal units per pound)—of all forms of coal. Bituminous coal generally has lower concentrations of pure carbon (from 46% to 86%) and lower heat values (8,300–15,600 Btu/lb). Bituminous coals are often sub-divided on the basis of their heat value, being classified as low, medium, and high volatile bituminous and sub-bituminous. Lignite, the poorest of the true coals in terms of heat value (5,500-8,300 Btu/lb) generally contains about 46%-60% pure carbon. (Link)

Coal ranges from about 10 MJ/Kg to about 30 MJ/Kg. The ratio of hydrogen to carbon is about 0.75 hydrogen atoms to each carbon atom. The higher concentration of carbon in coal gives makes it a black, solid material. Burning coal can releases twice as much carbon into the atmosphere as methane (natural gas). Coal with lower heat value will release even more carbon than coal with a higher heat value. This is one reason that China, which has an economy only 1/3 the size of our economy, produces just a much carbon dioxide emissions. This is because the Chinese burn mostly low quality coal to generate electricity.

   Subscribe   Feed

Include other special offers from Examiner.com
Terms of Use