Fossil Fuels How do they give us energy? Kate Johnston 2009

How are fossil fuels formed? Formed from heat and pressure acting on dead plants and animals (containing carbon) Takes hundreds of millions of years Original energy source??? Sun!

Nonrenewable 86% of the primary energy production in the world comes from burning fossil fuels. –63% hydroelectric –6.0% nuclear –0.9% other Nonrenewable: takes millions of years to form – reserves are being depleted faster than formed.

What are they made of?? Fossil fuels are a mixture of hydrocarbons Hydrocarbons are compounds composed of carbon and hydrogen atoms Eg: methane CH4

Alkanes: Saturated Hydrocarbons

Alkenes: Double Bonded Hydrocarbons

Alkynes: Triple Bonded Hydrocarbons The simplest alkyne is ethyne (acetylene):ethyneacetylene

What do we do with these hydrocarbons?? Combustion! –Fuel (any hydrocarbon) + Oxygen  Carbon Dioxide + Water

Combustion

Combustion CH4 + 2 O2  CO2 + 2 H2O Bonds need to be broken Bonds Put Together Endothermic Reaction Exothermic Reaction Takes Energy Releases Energy (as heat, sound, light)

What do we do with this energy? Combustion of different hydrocarbons will result in different levels of energy release Different hydrocarbons are used to power different things

Combustion of Fossil Fuels Most fossil fuels contain more than just Carbon and Hydrogen Burning methane releases only carbon dioxide and water. Since natural gas is mostly methane, the combustion of natural gas releases fewer byproducts than other fossil fuels.

Natural Gas Primary use: heating and cooking LNG = liquefied natural gas – made from cooling natural gas. –Used in transport, since it takes up to 1/600 of the gas volume Usually found above oil reserves

Natual Gas ~ Pros Cheaper than oil Know US reserves should last >125 years Produces less air pollution than other fossil fuels Can be used in highly efficient fuel cells

Natural Gas ~ Disadvantages Must be converted to LNG before it can be shipped (expensive and dangerous) Can leak into atmosphere (methane is a greenhouse gas and more potent than CO2. Pounds of CO2 per billion of BTU of energy = 117,000

How do we get OIL and what do we do with it? Mixture of Hydrocarbons, with some oxygen, nitrogen, and sulfur impurities. 1 barrel of oil = 42 Gallons = 6 million BTUs

Recovery of Oil Oil (and natural gas) are found in the ground, not freely drifting up. An oil reservoir is not a vast underground lake, but a solid layer of rock that is porous.

Oil Recovery Drill wells through non-porous rock (the barrier that traps oil) Primary Recovery: 30% of oil trapped can be economically recovered by pumping

Secondary Oil Recovery 10 % more is removed by flooding well with high-pressured water or gas

Tertiary Oil Recovery Sometimes 10% more can be removed by heating the oil and scrubbing it out

How do you find it?? Used to be hit or miss Now, it is found by seismic or sound waves, then 1.Exploration Wells are dug 2.Rock samples are analyzed and identified 3.Wells are formed to tap into source (hopefully more than one at a time). Location is major challenge. 4.Oil travels from well to refinery (pipeline or tanker) 5.At refinery hydrocarbons are separated by distillation

Distillation Column Hydrocarbons are heated Hydrocarbons with lowest boiling point (lightest) go to the top of column and are collected Heaviest, highest boil point, hydrocarbons are collected at bottom

Cracking Heavy, large molecules at the bottom of the distillation column are not very useful as a fuel…. So they are cracked! Cracking = high temp. and pressure breaks the molecules into smaller hydrocarbons.