Energy Sources: Fuels, Nuclear Power, and Hydro and Thermal Electricity Generation

Energy sources can be ranked by several criteria, such as whether they are primary or secondary, renewable or non-renewable, and how efficiently they convert into usable energy.

Fuels and Their Properties

Calorific power: the energy released per unit mass or volume of fuel when it undergoes complete combustion.

Heat capacity: the amount of heat a substance must receive to raise its temperature by 1 K or 1 °C.

Solid Fuels

Coal is formed through the carbonization and pyrolysis of plant matter, and is extracted from coal mines.

• Peat: contains about 60% carbon and a large amount of moisture.
• Lignite: a low-calorific-value coal, typically found in shallow deposits that can be mined by opencast methods.
• Hard coal: a high-carbon coal with a high calorific value.
• Anthracite: the oldest and most highly carbonized coal, with a carbon content of around 95% and the highest calorific power.

Processing Petroleum

Crude oil is transformed into products suitable for consumption through several processes:

• Fractional distillation: crude oil is heated until its components vaporize, then separated in distillation towers according to their boiling points.
• Cracking: the decomposition of heavier hydrocarbons into lighter, more useful ones.
• Polymerization: the opposite of cracking, in which small molecules combine to form larger ones.
• Reforming: the conversion of light, low-octane hydrocarbons into heavier, higher-octane compounds, using high temperatures and a catalyst.

Radioactivity and Nuclear Energy

Radioactivity is the phenomenon of nuclear transmutation, or transformation, in which unstable nuclei emit radiation.

• Alpha radiation: consists of helium nuclei. It has low penetrating power and can be stopped by a sheet of paper or the skin.
• Beta radiation: consists of fast electrons or positrons. It has medium penetrating power and can be stopped by a thin sheet of aluminium.
• Gamma radiation: consists of high-energy electromagnetic photons. It has the greatest penetrating power and requires thick lead or concrete shielding.

Nuclear fusion: the union of light nuclei to form a heavier nucleus, releasing large amounts of energy.

Nuclear fission: the splitting of a heavy nucleus into smaller nuclei, releasing energy and neutrons. These neutrons can trigger a chain reaction when the mass of fissile material reaches a critical mass.

Energy and the Environment

Greenhouse effect: the atmosphere is heated because it lets visible solar radiation pass through while absorbing the infrared radiation emitted by the Earth, which raises global temperatures.

Atmospheric pollution: emissions of sulfur and nitrogen oxides react with water vapour, oxygen and sunlight to form sulfuric acid and nitric acid, which fall to the ground as acid rain.

Power Generation Plants

Hydroelectric Power Plants

Components: dam, gravity intake, pressure pipes (penstocks), water channels, powerhouse, and transformers. The transformer raises the voltage so electricity can be transported efficiently to consumption centres.

Turbine types:

• Francis turbine: suited to medium heads and variable flow.
• Pelton turbine: suited to high heads and regular flow.
• Kaplan turbine: suited to low heads and highly variable flow.

Plant types: base load, peak load, reserve, and pumped-storage plants. Peak hours are periods of high demand, while off-peak hours are periods of low demand.

Advantages: no particulate or polluting emissions into the atmosphere, and river flow can be regulated.

Disadvantages: loss of fertile land and farmland, alteration of river flow, erosion and sedimentation problems, changes to vegetation and fauna, organic accumulation of residual water sediments, and possible effects on the local climate.

Thermal Power Plants

In a thermal plant, energy is converted in stages: chemical energy becomes thermal energy, then kinetic energy of rotation, then electrical energy.

Main components: boiler, heater, turbine, condenser, cooling tower, chimney, electrical equipment, and water treatment plant for the feedwater.

Fluidized bed combustion: a combustion system that operates at lower temperatures, which reduces most pollutant emissions and also reduces nitrogen oxide emissions into the atmosphere.

Combined cycle plants: combine a gas turbine, compressor, combustion chamber, heat recovery boiler, and steam turbine, followed by a generator and condenser.

Cogeneration plants: produce electrical energy and use the residual heat to obtain hot water or steam for other uses.

Nuclear Power Plants

Reactor components: reactor vessel, moderator, control rods, and coolant.

• PWR (Pressurized Water Reactor): uses pressurized water in a two-circuit cooling system.
• BWR (Boiling Water Reactor): water boils directly inside the reactor, producing steam for the turbine.

Transformation stages: the electrical network uses several transformers, for example 20 kV/400 kV at generation, 400 kV/110 kV for transmission, and 20 kV/400 V for final distribution.

Natural Gas Processing

Diesel and natural gas processing: impurities are removed, and the gas is transported in gaseous form to the distribution plants. Several stages of cooling are needed to obtain liquefied natural gas, which is then distributed in cylinders at different pressures.