Someone once put the words ‘Clean’ and ‘Coal’ together and thus created the phrase ‘Clean Coal’.
However the idea that this phrase represents does not have a counterpart in physical reality, and will not form part of a sustainable energy future.
In case you are unfamiliar with this fantasy, the idea is that by using some unspecified ‘Clean Coal’ technology, we will be able to burn Earth’s vast abundance of coal while releasing only minimal amounts of carbon dioxide.
It is important to understand that ‘Clean Coal’ technology, like ‘Flying Cars’, can be built.
Scientific American (SA) this month (January 2016) covers the technology – sometimes called ‘Carbon Capture and Storage‘. The article is a litany of expensive failure after expensive failure.
SA look in detail at the 582 MWe Kemper coal plant currently under construction. SA tells us that this is ‘the most advanced coal plant in the US‘.
When it starts working – it’s about 2 years late – it will have cost 6.3 billion dollars (3.9 billion dollars over-budget) – a price tag more normally associated with nuclear power stations – and rather defeating the whole point of the exercise.
However the real craziness comes when SA describe the plans to put Kemper’s CO2 into the Tinsley Oil Field.
This will be done to to force more oil out of the ground which will then be refined and burned and so release more CO2!
However SA do not explicitly calculate the ratio of the amount of CO2 that will be buried in the Oil Field, to the amount of CO2 that will be released when the oil produced is subsequently burned.
SA states that currently 770 million cubic feet of CO2 are used in the Tinsley field annually, “boosting oil production from 50 barrels a day to more than 5000 barrels a day”.
Readers, I know you are busy and the units are confusing, so on your behalf I have done the sums for you:
- The mass of 770 million cubic feet of CO2 is approximately 42 million kilograms.
- The CO2 released by burning 4950 barrels of oil every day for a year is about 777 million kilograms of CO2
In other words, for every kilogram of CO2 buried, 18.5 kilograms of CO2 will eventually be released to the atmosphere.
Of course, it would be possible to bury the CO2 without extracting any oil. But that would make the plant even more expensive to run than it currently is.
Overall, the Kemper plant is useless for sequestering CO2. It would be cleaner to just burn the coal directly.
Now that I think about it, comparing ‘clean coal’ with ‘flying cars’ is an insult to flying car builders.
A better comparison would be with ‘flying toasters’: an utterly pointless distraction from reality.
The calculation (skip if you don’t like this kind of thing)
770 million cubic feet of CO2 corresponds to a volume of 21.8 million cubic metres
Using the ideal gas law PV = nRT I calculate that at STP, this corresponds to about 960 million moles of CO2
Each mole of CO2 weighs 0.044 kg and so the mass of this gas is 960 x 0.044 =42.3 million kilogrammes
The EPA tell me that 1 barrel of oil is equivalent to 0.43 tonnes of CO2: This is 430 kilogrammes
The Tinsley Well produces an additional 4950 barrels of oil per day which corresponds to 365 x 4950 = 2.12 million barrels of oil per year.
So this corresponds to 2.12 million barrels x 430 kg = 777 million kilograms of CO2