This is a thoughtful reply to a post of mine on THE Oil Drum.

He thinks fuel cells will work, which I don’t, and I’m not sure where he stands on the exponential maths thing, but this is a good guy, and a thinker. Let the debate roll….   He also added (further into the interchange, that lignite gives 15 megajoules/kg, whereas coal gives 24 megajoules/kg. But……it has the same CO2 output per ton. So, we are indeed at about 50% loss for sequestration.
majorian on October 9, 2009 – 10:00am Permalink | Subthread | Parent | Comments top

Coal mining is very efficient.
Surface mining requires 5-10 kwh of energy per ton of rock and typically 1.5 tons of rock is required to produce 1 ton of coal.
Underground mining requires 15-30 kwh of energy per ton of rock
and typically 2.5 tons of rock yields 1 ton of coal.
Therefore around 10 kwh per ton is required for surface mines and 60 kwh per ton is required for underground mining.
An ‘average’ ton of coal produces 2000 kwh of electricity.
Typically a coal train uses 900 BTU to transport 1 ton of coal
one mile. So a 2000 mile train trip would use 1800000 BTUs of diesel(13 gallons).
The energy density of coal is falling slowly about 1/2 a percent per year in part because lower BTU western coal is being mixed in to reduce sulfur emissions.

My guess on sequestration is 50% energy taken, so even if it happens, halve your resource. Then add the exponential function – which Heading Out seems to overlook.

The amount of energy required to separate and compress CO2 to 150 bar by the 1930s amine process is about 200 kwh per ton of CO2. A ton of coal produces 2.2 tons of CO2 so that’s about 440 kwh per ton of coal. The preferred method of sequestering CO2 is by the more efficient coal gasification IGCC
method where the CO2 is already compressed to about 50 psi in the process.

If a ton of coal produces 2000 kwh of electricity 440 kwh represents a 22% energy penalty for CO2 capture, not 50% as you guessed.

The amount of energy required for pipeline transport is about 200 BTU per ton mile so a 1000 mile pipeline would require 132 kwh of energy to move the CO2 produced by burning a ton of coal 1000 miles.

The thermal efficiency of new IGCC is about 45% versus 35% for existing coal plants.
2000 kwh x 45%/35% = 2571 kwh per ton of coalso subtracting 440 kwh and 132 kwh for transport leaves us back at about 2000 kwh per ton of coal for the grid.

I will repeat that we have 30 years experience sequestering CO2(2000 feet underground) in the US
despite skepticism by Gail and others.
I agree that if we burn carbon we must bury it as I believe the IPCC who fully endorse CCS technology.
Clean coal allows us energy to responsibly extend civilization for another century when hopefully new energy technologies can be developed.

It seems EROEI mainly serves as a way for lazy people to avoid doing the math.


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