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Thursday, January 3, 2019

Coal fired power plants

Coal fired power plants are a type of power plant that make use of the combustion of coal in order to generate electricity. Their use provides around 40% of the world's electricity and they are primarily used in developing countries. Countries such as South Africa use coal for 94% of their electricity and China and India use coal for 70-75% of their electricity needs, however the amount of coal China uses dwarfs most other countries (see the data visualization below). The use of coal provides access to electricity to those who previously didn't have it, which helps to increase quality of life and reduce poverty in those regions, however it produces large quantities of different pollutants which reduces air quality and contributes to climate change.

Burning huge amounts of coal

Coal plants require enormous amounts of coal. Shockingly: a 1000 MWe coal plant uses 9000 tonnes of coal per day, equivalent to an entire train load (90 cars with 100 tonnes in each!). The amount of coal used during a full year would then require 365 trains, and if each is 3 km long then a single train carrying all of this coal would need to be about 1100 km long; about the same distance as driving from Calgary AB to Victoria BC. If this train were to pass by your house at 40 kilometers per hour, it would take more than a day to pass!
 The conversion of this coal to the end goal of electricity is a multi-faceted process:
  1. The coal must be unloaded from the train. Traditional ways of doing this require the use of cranes picking up the coal from the cars, however newer plants have the floor underneath the train tracks drop away, allowing the coal to be dropped into underground containment. Doing so doesn't even require the train to stop moving! . Many coal plants are mine mouth which means the plant was put where the coal mine is, so the coal doesn't need to be transported by train.
  2. Once unloaded, the coal is then pulverized into a fine powder by a large grinder. This ensures nearly complete burning of the coal in order to maximize the heat given off and to minimize pollutants.
  3. The pulverized coal is then input to a boiler, where combustion occurs and the coal provides heat to the power plant. This heat is transferred to pipes containing high pressured water, which boils to steam.
  4. The steam then travels through a turbine, causing it to rotate extremely fast which in turn spins a generator, producing electricity. The electricity can then be input to the electrical grid for use by society.
Coal fired power plants follow the Rankine cycle in order to complete this process. Since they require plenty of water to be circulated in this cycle, coal power plants need to be located near a body of water. The process of coal fired plants can be seen below in Figure 

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