What is 1 kg of coal?

Bituminous coal, courtesy of Wikipedia

This is a kilogram of coal – okay, so I have no idea how much it actually weighs, but let’s work under this assumption – and its primary use is to be burnt for electricity. What is in a kilo of coal [1]? Primarily, it is made of:

  • 860 g of carbon;
  • 50 g of hydrogen;
  • 70 g of oxygen; and
  • 10 g of sulphur.

Let’s imagine that we have a device that can burn this fully: no energy wasted into forming ash, no incomplete combustion creating carbon monoxide, etc. What would the products be?

  • 3 150 g of carbon dioxide;
  • 900 g of water;
  • 20 g of sulphur dioxide; and
  • 40 MJ of heat.

This estimate is about double the amount of energy usually produced [2], largely due to omitting ash formation, moisture content, and other factors that impede complete combustion. Still, maintaining this generous assumption, and taking into account the 40% efficiency of coal plants [3], and 6% loss from transmission [4], we find that one kilogram of coal can produce about 15 MJ of electricity, about enough to boil 25 kettles of water.

However, there are other trace elements in coal that can be of concern: this kilogram of coal also contains 1 mg of uranium, 1 mg of arsenic, 3 mg of thorium, 5.8 mg of lead, 98 mg of fluorine, 320 mg of chlorine, and 21 μg of mercury [5]. This means that, over an entire day, the average coal power-plant (burning 1.3 kt of coal [6]) will release 520 MBq of uranium & thorium, 1.3 kg of arsenic, 7.5 kg of lead, and 27 g of mercury.

It should be noted that this isn’t an exceptional amount of radiation, but over time it does build up: the area around a coal plant is generally significantly more radioactive than around a nuclear plant, and can be significantly enriched in toxic metals.

Real life, however, is more complicated that this ideal: as noted before, coal only produces half the calculated energy (about 22 MJ of heat per kilogram), many toxic elements remain in the coal ash (making its disposal an issue), and large amounts of contaminants leach from coal stockpiles into the water.

Unlike what the Australian government keeps propounding, coal is not a harmless black rock, and it isn’t good for humanity.

What is 1 kg of coal?

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