Fossil fuels, which consist of coal, oil and natural gas, are currently the world's primary energy source. Fossil fuels are formed from organic material over the course of millions of years. Over the past century, it has fueled the U.S. and has been a pivotal significance in global economic developments. As of 2011, 42% of electricity supplied in the U.S. is primarily coal. In 2010, 19.2 million barrels per day of petroleum were consumed. It is most primarily used in transportation. Additionally, in 2010, 22% of natural gas was utilized. It is commonly used to provide electricity to buildings or industrial processes.

American coal production is currently the second highest in the world (behind China) delivering 997 million short tons in 2014. The process of fossil fuel power plants incorporates the milling of coal into a fine powder, which is burned in the combustion chamber of a boiler at a high temperature. The hot gases and heat energy produced, converts water (in tubes lining the boiler) into steam. The high pressure steam is passed into a turbine containing thousands of propeller-like blades. The steam pushes these blades causing the turbine shaft to rotate at high speeds. A generator is mounted at one end of the turbine shaft and consists of carefully wounded wire coils. Electricity is generated when these coils are rapidly rotated in a strong magnetic field. After passing through the turbine, the steam is condensed and returned to the boiler to be heated again. The electricity generated is transformed into higher voltages (up to 400,000 volts) used for economic, efficient transmission via power line grids. When it nears the point of consumption, such as peoples’ homes, the electricity is transformed down to the safer 100-250 voltage systems used in the domestic market [1].

Based on the schematic of the fossil fuel power plant below, subsystem A supplies the energy needed to vaporize the power plant working fluid into vapor required by the turbine. Subsystem B is where the energy conversion from heat to work occurs. Regardless of the source of energy required to vaporize the working fluid and the type of working fluid, the vapor produced passes through the turbine, where it expands to lower pressure, developing power. In subsystem C the turbine power shaft is connected to an electric generator. The vapor exiting the turbine passes through the condenser, where it condenses on the outside of tubes carrying cooling water. In subsystem D, cooling water is sent to a cooling tower, where energy received from steam condensing in the condenser is rejected into the atmosphere. Cooling water then returns to the condenser [2].

Oil is the world’s primary fuel source for transportation. Most oil is pumped out of underground reservoirs, but it can also be found imbedded in shale and tar sands. Oil as the working fluid works in the same manner as coal, in which, air is drawn into the compressor where it forms a mixture with oil and is burned. The combustion of hot gases expands through the turbine which is connected to a generator and electricity is produced.

Natural gas is collected from wells on land, offshore drilling platforms or offloaded from overseas tankers (liquefied natural gas). Natural gas as the working fluid can operate efficiently in a combined cycle consisting of a gas turbine (Brayton) cycle with excess heat going to a steam turbine (Rankine) cycle. The gas turbine compresses air and mixes it with fuel. The heated air-fuel mixture moves through the gas turbine blades, making them rotate. This fast-spinning turbine drives a generator that converts a portion of the rotated energy into electricity. The heat recovered from the generator captures exhaust heat from the gas turbine that would otherwise escape through the exhaust stack. The heat recovered from the generator creates steam and is delivered into the steam turbine. The steam turbine sends its energy to the generator drive shaft, where it is converted into additional electricity.

[1] Dorsey, Piccirilli. "Fossil Fuels." Environmental and Energy Study Institute (EESI). 2014. Web. 4 May 2015. <http://www.eesi.org/topics/fossil-fuels/description>.

[2] “Combined-Cycle Power Plant - How It Works.” General Electric (GE).2014.Web. 6 May 2015. <https://powergen.gepower.com/plan-build/tools-resources/power-generation-basics/combined-cycle-power-plants.html>.

[3] Avro, Samuel R. U.S. Electricity Net Generation by Fuel-2012. Digital image. Energy Trends Insider. 21 Feb. 2012. Web.

[5] Moran, Micheal J., Howard N. Shapiro, Daisie D. Boettner, and Margaret B Bailey. "Chap.8 Vapor Power Systems." Fundamentals of Engineering Thermodynamics. 7th ed. John Wiley & Sons, 2011. 430-455. Print.