CoalNatural GasPetroleum

How Fossil Fuels are Used to Generate Electricity 

The world is constantly in need of electricity, as it drives human activities and keeps the world in motion. To cater to practically every need, every year we consume more than 24 PWh of electricity. That is 24,000,000,000,000,000 Wh/year (Longo, 2019). While 10.7 percent of this is comes from nuclear power, and 23.9 percent from renewable sources, fossil fuels are the dominant source of electricity, creating two-thirds of this enormous quantity of electricity that we consume.

In the United States, fossil fuels supply most of our energy needs, including roughly two-thirds of US electricity generation (UCS, 2019). Even in the UK where clean energy has charted a course for the country’s electricity generation needs, in the third quarter of 2019, some 39 percent of UK electricity generation was from coal, oil, and gas, and staying true to their commitment to clean (or in this case cleaner energy), 38 percent came from natural gas and less than 1 percent from coal and oil combined. (Evans, 2019). 

To create electricity, fossil fuel power plants are put to work. They do this generally by burning carbon fuels such as coal, oil, or gas to generate steam that drives large turbines that in turn produce electricity. There are many ways to produce electricity. The presence of electrons flowing between relevant materials may be used to provide current. To provide large amounts of steady power demanded by modern societies, large power plants have been built. Most power plants make electricity with a generator. The electricity generated is transformed into the 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 our homes, the electricity is transformed down to the safer 100-250 voltage systems used in the domestic market.

Most traditional power plants make energy by burning fuel to release heat. Thus, they are called thermal (heat-based) power plants. They burn fuel with oxygen to release heat energy, which boils water and drives a steam turbine. This is majorly the one used by coal and oil plants. Natural gas uses a different process. Instead of making steam, they burn a steady stream of gas and use that to drive a slightly different design of the turbine (called a gas turbine) instead (Wodford, 2019)

Although these plants are able to reliably generate their share of electricity for extended amounts of time, they produce large amount of carbon dioxide when burning carbon fuels, contributing to climate change. Additionally, these come with sulfurous oxides – leading to acid rain, among other pollutants. There is a  large amount of coal, oil, and gas that needs to be transported long distances for the plants, and when there is a shortage of fuels, the prices rise quite a bit.

Oil

Oil, otherwise known as crude, is a thick black liquid composed primarily of hydrogen and carbon. Power plants that burn oil to produce electricity are called oil-fired plants. As a matter of operation, they generally operate similar to fossil-fueled counterparts, the coal-fired and natural-gas-fired plants.

Thus, oil is burned to heat water. When the water is heated, it creates steam to spin a turbine, which has magnetic coils that may be used to generate electricity. This may be referred to as the Conventional steam system.

Another means of using oil to generate electricity is the internal combustion engine, which works by converting the explosive potential of burning petroleum into mechanical energy and making use of that mechanical power to run a generator. This is similar to the gasoline-burning version of the system present in conventional motor engines. Oil-fired combustion engine generators are common in circumstances when a fixed generator is needed but the power demand is too small to make a steam turbine practical.

Finally, there is the combined-cycle technology, where oil is first combusted in a combustion turbine, using the heated exhaust gases to generate electricity. The exhaust gases are then recovered and undergo the conventional steam system to heat water in a boiler, creating steam to drive a second turbine.

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Coal

Coal is a solid fossil fuel formed over millions of years by the decay of land vegetation. When layers are compacted and heated over time, deposits are turned into coal. Coal plays a vital role in electricity generation worldwide. Coal-fueled power plants currently provide about 38 percent of global electricity, and although the creation might generally be lower in some countries, coal fuels a higher percentage of electricity (WCA).

The process in the case of a coal-fired generating station begins when the coal is brought into the station on a conveyor belt after stored in large coal piles just outside the station. The conveyor feeds the coal into large pulverizers that crush the coal into a fine powder, thereby increasing the surface area and allowing it to burn more quickly. Large fans then blow the coal powder into a giant furnace or combustion chamber of a boiler where it is burned giving off vast amounts of heat. The temperature can reach over 3,000 degrees Celsius (CNS, 2018).

The furnace is surrounded by tubes filled with water, and the immense heat from the burning coal turns the water in the tubes into steam. The steam is then transferred under pressure through large pipes at high speed to a turbine. The process then pushes the turbine’s blades causing them to spin. A generator is mounted at one end of the turbine shaft and is made of carefully wound wire coils. To create electricity, these turbines are rapidly rotated in a strong magnetic field. After passing through the turbine, the steam is condensed back to water using cooling water. It is then pumped back into the water tubes surrounding the furnace to continue the process.

A practical example is noted in the Kingston Fossil Plant near Knoxville, Tennessee, which burns coal to heat its boilers to about 1,000 degrees Fahrenheit, thereby creating high-pressure steam. The steam is piped to the turbines at pressures of more than 1,800 pounds per square inch. The turbines are connected to the generators and spin them at 3,600 revolutions per minute to make alternating current (AC) electricity at 20,000 volts. Water is then pumped in a condenser to cool and condense the steam coming out of the turbines. The Kingston plant generates about 10 billion kilowatt-hours a year, enough electricity to supply 700,000 homes. To meet this demand, Kingston burns about 14,000 tons of coal a day (TVA).

Natural Gas

During the 1970s and 1980s, the preferred choices to power electric utility generators were large coal or nuclear-powered plants. However, due to economic, environmental and technological changes, natural gas has become the fuel of choice for new power plants built since the 1990s. Natural gas has gained support in use over time. This is because it has been observed that natural gas burns more cleanly than other fuels such as petroleum and coal since it produces less carbon dioxide (EIA). Gas-fired power stations also attain very high-efficiency rates, converting a larger proportion of the energy in natural gas into electrical energy, given the nature of the fuel. For example, the power station, Irsching 4, near Ingolstadt, achieved an efficiency rate of 60.75 percent shortly after it was commissioned in 2011, a first-time result. In comparison, coal-fired power stations can reach an efficiency rate of 50 percent at best (WG).

Electricity can be generated from natural gas through cogeneration, gas turbines, and steam turbines. The process is through what is known as combined heat and power (CHP), which involves the use of a heat engine or power station to generate electricity and heat simultaneously. It is the assembly of heat engines working together from the same source of heat (the source of the heat being produced from burning natural gas), converting it to mechanical energy. High efficiency can be achieved through the combination of gas and steam turbines in a combined cycle mode. A semi-closed or closed gas turbine may be used where fuel (natural gas in this case) is combusted with oxygen. 

A gas turbine is a type of continuous combustion engine. It can be particularly efficient in recovering waste heat from the turbine by a heat recovery steam generator to power a conventional steam turbine in a combined cycle system. A steam engine extracts thermal energy from pressurized steam and uses it to engage in mechanical work on a rotating output shaft. Natural gas is also well suited for combined use with other forms of renewable energy sources such as solar, water, and wind energy. CHP plants can achieve an 80-90 percent rate of efficiency, but there must be a user for the energy near the vicinity of the plant (WG). Locally produced electricity and power through a natural gas-powered CHP plant is considered to be the most efficient and rapid means of cutting carbon emissions (AL, 2012).

Alternatively, electricity from natural gas may be derived by piping natural gas underground to power plants. Similar to the process with coal, the power plants burn natural gas to boil water to produce steam. The steam spins the blades of a turbine that are connected to a generator. The generator then spins magnets to generate electricity. The electricity then passes through power plants (EPSC, 2017).

Locally produced electricity and power through a natural gas-powered CHP plant is considered to be the most efficient and rapid means of cutting carbon emissions (AL, 2012).

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Challenges in the Use of Fossil Fuels to Generate Electricity

 Like with every useful thing, there are consequences to using fossil fuels in the generation of electricity. For instance, supplying electricity to homes and businesses is an almost uniquely challenging enterprise. Electrical energy is either expensive or inconvenient to store, meaning supply and demand must be balanced in real-time. It is also difficult to transport it over long distances, and should, therefore, be made locally in where it is required (CB, 2017) . 

Another unavoidable consequence of burning any fossil fuel is that the process generates greenhouse gases, mostly Carbon dioxide (CO2) but also Sulphur dioxide (SO2) and Methane (CH4), all of which contribute to global warming. The burning of fossil fuels produces around 6.3 billion metric tons of carbon dioxide per year. It is estimated that natural processes of the Earth can only absorb about half of the amount, resulting in a net increase of 3.2 billion tons of atmospheric carbon dioxide per year which may lead to global warming.

The operation of power plants also impacts the environment. That is the water, land, and air. Conventional steam plants require large amounts of water for steam and cooling, and can negatively impact local water resources and aquatic habitats by contaminating the water or by reducing the availability of such resources. Fossil fuel residues that are not consumed during combustion became a waste burden and contain toxic and hazardous wastes that may negatively affect the environment. (PS).

Even with the advent of natural gas, which is the cleanest of fossil fuels, it still produces a significant amount of greenhouse gases that affect the environment and contribute to climate change. Given that fossil fuels are set to meet about 84 percent of global energy demand through 2030, it is important to look for alternative sources to generate electricity.

Sources

Alfagy Limited (2012). “Biomass drying from CHP heat recovery.” Alfagy Limited.                     

Carbon Brief (2017). “Mapped: How the US generates electricity”. Carbon Brief. Available at: https://www.carbonbrief.org/mapped-how-the-us-generates-electricity

CNS. (2018). “Fossil Fuel”. Canadian Nuclear Society. Available at: https://teachnuclear.ca/all-things-nuclear/energy-demand-and-sources/present-energy-sources/fossil_fuels/

EIA. “World Carbon Dioxide Emissions from the use of Fossil fuels”. US Energy Information Administration.

EPSC. (2017). “How Natural Gas Generates Electricity” Energy Providers of Southern California. Available at: http://conserveenergysocal.com/how-natural-gas-generates-electricity/

Evans, S. (2019). “Analysis: UK renewables generate more electricity than fossil fuels for the first time”. Carbon Brief. Available at: https://www.carbonbrief.org/analysis-uk-renewables-generate-more-electricity-than-fossil-fuels-for-first-time

Gray, R. (2017). “The Biggest Energy Challenges Facing Humanity”. BBC. Available at: https://www.bbc.com/future/article/20170313-the-biggest-energy-challenges-facing-humanity

Longo, L. (2019). “The end of coal, the rise of natural gas”. Eniday. Available at: https://www.eniday.com/en/education_en/gas-vs-coal-climate-change/

“Electricity from Oil”. PowerScorecard. Available at: http://www.powerscorecard.org/tech_detail.cfm?resource_id=8

Thomas, E. (2017). “How Does an Oil Power Plant Work?”. Sciencing. Available at: https://sciencing.com/oil-power-plant-work-4570209.html

TVA. “How a Coal Plant Works”. Tennessee Valley Authority. Available at: https://www.tva.com/Energy/Our-Power-System/Coal/How-a-Coal-Plant-Works

UCS. (2019). “Fossil Fuels”. Union of Concerned Scientists. Available at: https://www.ucsusa.org/energy/fossil-fuels

WCA. “Uses of Coal”. World Coal Association. Available at: https://www.worldcoal.org/coal/uses-coal/coal-electricity

“Natural Gas and Electricity”. WinGas. Available at: https://www.wingas.com/en/raw-material natural-gas/electricity-from-natural-gas.html

Wodford, C. (2019). “Power Plants”. Available at: https://www.explainthatstuff.com/powerplants.html

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