<Open ThreadThe Oil DrumA little more on coal mining>

114 comments on A new thread for the weekend

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Boof on January 14, 2006 - 9:38pm Permalink | Subthread | Parent | Comments top
CTL takes carbon from the ground and puts it into the atmosphere, exacerbating GW. One day even coal will run out. In an all-biofuels economy the carbon would be recycled indefinitely. Preferably the plant material would be leftovers from food production. Conservative estimates say to get both food and fuel we need at least 20 acres or 8 hectares of productive land per person. In the absence of new clean energy sources this probably requires a 50% reduction in the population.
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LevinK on January 15, 2006 - 12:20am Permalink | Subthread | Parent | Comments top
If I can recall correctly over the half of the energy needed to produce ethanol goes into the destillation process which by itself uses electricity. If the additional electricity comes from coal (the obviuos choice if you don't want nuclear) then with a 40% efficient power plant and EROEI of 1.34 we are going to need 0.5/0.4 = 1.25 Btu of coal energy to produce 1.34 Btu of ethanol energy; That is coal to ethanol EROEI is less than 1.1
On the other hand a Fischer-Trops conversion has an efficiency in the range of 70% so the coal to diesel EROEI is 0.7 which is not that far - again for ethanol I omitted the other energy inputs for fertilizers etc.

The CO2 arithmetics is even worse for ethanol because the ethanol itself is releasing CO2 in the atmosphere. If instead we yielded the farmland to forests the net result would be a reduction of C02 so I can not not agree that ethanol is costless on this point - there is an alternative cost here. My fear is that if we allow this idea to go to a really large scale, there may come a day when we will have all our forests replaced by energy crops just like it seems to be already happening in Brazil. No need to comment on the CO2 emissions effects from that prospect.

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