If ethanol were to become a more prominent source of fuel in automobiles, there would presumably be a reduction in air pollution. At least, I understand that is one benefit of the increased use of ethanol, in addition to the reduction in reliance on foreign oil. If I am correct in that assumption, then that increased use will be accompanied by an increase in air pollution by the plants that make the ethanol, most of which will be powered by coal, according to one website that is promoting their construction. Is there a way to estimate the nature of the trade off at this point? Which way will the balance tip? Are there folks out there making some reasonable calculations? I did a SDMB search but couldn’t find any discussions that addressed this one. I thought I’d find plenty. Maybe my search terms missed it. Any help, dopers? xo, C.
Ethanol is carbon neutral since plants take carbon from the air wheras fossil fuels take carbon from the ground so you reduce CO2 emissions. However, the growing, harvesting refining and transportation of ethanol requires conventional fuels which contribute to CO2. Theres a lot of debate as to exactly how much fossil carbon is burnt for every litre of ethanol.
In these sorts of discussions, it’s not unusal for someone to whip out a misapplication of the laws of thermodynamics and insist that the amount of energy available from burning the ethanol cannot exceed the amount of energy that went into producing it - baldly stated like that, it is of course true - however, the mistake that is often made is to forget that the primary energy input for the ethanol production is not the fossil fuels used to harvest or process it, but is in fact sunlight - driving photosynthesis in the crop plants to make sugar.
Not that I observe any of this fallacy in the posts so far, but I just thought it would be as well to mention it.
I think the reason there hasn’t been any discussion is because there is no real fossil fuel saving in producing ethanol.The only difference is that instead of pumping gas into cars we pump gas into tractors and irrigation pumps to grow plants. We then turn those plants into ethanol that exactly matches the amount of gas we used in the tractors and pumps.
Since producing ethanol doesn’t save any fossil fuel then of course it can’t have any effect on pollution. We are still burning burning exactly the same amount of gas. The only difference is that we are burning it in Iowa rather than in New York.
There have been plenty of discussions on the fossil fuel saving, or lack thereof, of ethanol production. You could start with Cecil’s column on the subject, then move on to the discussion that prompted. Then you can add “Peak oil” to our search terms for discussion unrelated to Cecil’s column.
But basically at this point producing ethanol doesn’t mean we use less gasoline. It just means we use the gasoline somewhere else. There is debatable evidence that large scale cane fed ethanol plants in Brazil may be producing some saving in gasoline, but not in the US using current technology and level of commitment
Well, one big difference is that we’re pretty much at the end of our efficiency improvements with conventional fossil fuels wheras we have just barely begun with ethanol. We have a pretty good idea what the efficiency of an idealised 4 stroke engine is and what we can practically achieve with Internal Combustion Engines. We have a fairly good idea how to refine gasoline and how to transport it. Theres not likely to be much improvement in mile per gallon from pure gasoline. On the other hand, we have barely any idea what the most efficient way to produce ethanol is. True, right now it might take something like 1 gallon of fossil fuel to produce 1 gallon of ethanol, but there could easily be orders of magnitudes of improvement in that figure as more money gets put into development.
An alternative viewpoint may be that instead of complaining that ethanol requires equivilant amounts of fossil fuels to produce, you might marvel that it has achieved parity with fossil fuels in such a short time.
There are no doubt efficiencies to be taken advantage of, but also, it might be quite workable to power some parts of the production process directly from sustainable (and fairly cheap) sources, for example: distillation of ethanol requires heat; this may be obtained directly from solar power (i.e. without converting the solar energy to electricity and back - just by focusing an array of mirrors on the boiler).
I expect the fermentation process requires some kind of agitation and there will certainly be pumping operations; these could again be directly obtained as mechanical work from wind or possibly from flowing water.
It’s not that even that efficient. A Cornell-Berkeley study found that it takes 28% more fossil fuel to produce ethanol from corn than the corn produces. But I think the ethanol produced from sugar in Brazil is more efficient.
I’d not heard this misconception before, though I can understand how it arises. Fortunately, Mangetout has already debunked it.
What the “emissions neutral” argument ignores, however, is the fact that in order to plant massive quantities of sugar or corn for ethanol production, you need to remove whatever was on the land previously. I have no idea what this might have been for corn fields in Iowa, but in Brazil we are talking about rainforests. Does a field of sugar cane remove as much CO2 from the air as an equivalent area of rainforest? Assuming that leaf surface area is the principal consideration, I would imagine not. The other environmental disadvantages of replacing rainforest with commercial agriculture are well documented, and not worth repeating here.
For the record, I don’t think Blake is actually guilty of any such misconception; I think he’s just describing the current state of play.
Actually, I wouldn’t be surprised if it did; sugar cane produces lots of sugar (obviously), which is chock-full of carbon; rainforests might be bigger in terms of biomass per unit area of land (although maybe not), but that biomass takes a while to develop, whereas sugar cane grows comparatively quickly and is repeatedly harvested, leaving the land vacant to be grown again (notwithstanding issues of soil fertility, soil erosion and crop rotation).
That’s still not to say that I think slash-and-burn replacement of rainforests with sugar cane fields is a great idea; I think it’s a terrible idea.
If you believe there is a misconception in anything that I posted then by all means present facts to the contrary. I am quite happy to posts references to support everything that I have said. Mangetout certainly never debunked anything I wrote, nor does he claim to have done so.
Ahh, no, we are not. There is some rainforest cleared for cane in Brazil but most of it is woodland
Speaking of misconceptions. It seems like I have to clear this one up every 6 months or so.
Look, rainforests don’t remove any CO2 from the air. In fact the prepondereance of evidence at the moment suggests that tropical rainforests are a net carbon source.
Sugar cane doesn’t remove any carbon either. We are replacing one completely carbon neutral system with another completely carbon neutral system.
The only carbon balance consideration is the carbon release from rainforest as a result of the initial clearance.
I guess I’m going to have to have you clear this one up again. What do you mean by this? The trees don’t use any CO2? Wha?
Trees absorb carbon from the atmosphere when they grow but they release it all back out again when they decay/get burnt.
Trees can only absorb carbon by converting it into solids, initially sugar but later into cellulose, lignin etc. Since the tree is converting a gas into a solid in this process it also has to be gaining weight. So a tree can only absorb carbon so long as it is gaining weight, and it can only absorb an amount of carbon equivalent to its weight gain.
What applies to trees also applies to forests. A forest can only absorb carbon while it is gaining weight. A mature forest isn’t gaining any weight. A new tree only starts growing when an equivalent mass of old tree has died.
Logged forests can absorb carbon because the trees are being continuously killed and removed from the forest to be replaced with young growing trees. In unlogged forests the old trees rot where they fall, releasing all that carbon straight back into the forest.
The only time a rainforest (or any forest for that matter) can absorb carbon is if it is suffering the effects of some form of recent disturbance. Undisturbed old growth forests are carbon neutral.
I suppose you know a good deal more about this than I do, but I don’t know why this statement is true. Solids don’t automatically weigh more than gases. Three grams of CO2 as a gas would produce three grams of CO2 as a solid.
While I understand your basic point that when substantial growth is no longer occurring, there is much less CO2 taken in, I still wonder about the basics of photosynthesis that must still occur, even in a mature forest. Doesn’t the process still happen? Isn’t sugar still produced in the leaves? And doesn’t that mean that CO2 is taken in? I’m still perplexed.
That’s correct and…
A 1000g tree in an atmosphere containing 3g of CO2 will weigh 1000g.
A 1000g tree with 3g of dry ice hanging from its leaves will weigh 1003g.
It doesn’t matter what form it exists in, when you weigh all the solid mass in a tree you weigh all the solid mass. And if you convert material from a gas to a soild and add it to the tree the solid mass of the tree must increase.
I’m sure I’m missing something here, but this all seems self evident. We are discussing the ability of trees to sequester gaseous carbon as soild biomass. It doesn’t really matter what form they sequester it as, the amount of mass in solid form must be increasing if the amount in gaseous form is decreasing. It’s a balanced equation. The amount of matter is a constant, it can only change form,it can’t change mass.
Yes CO2 is still being taken in and converted to sugar, and that sugar is then oxidised to CO2 again as part of the the TCA cycle.
Unless the tree contains more sugar today than it contained at the same time yesterday it can not have sequestered any carbon.
And if it does contain more sugar today than yesterday then it must have more mass in solid form than it did yesterday.
And if it has more mass in solid form than it did yesterday then it must weigh more than it did yesterday.
Ok, Blake, I see what’s happening here. We’re talking past each other. When you said, “rain forests don’t remove any CO2 from the air,” you meant on balance. I took that statement to mean that plants do not remove CO2 from the air, a statement that created cognitive dissonance, to say the least, as we say in the edubiz. That wasn’t what you meant, but that’s how it reads. In any case, it’s clear now. Thank you for clarifying.
Hopefully we’ve had enough about rainforests. I’d like to return to the question of Brazilian ethanol. Personally, I think American ethanol is a huge sham meant to throw money at farmers, and if the current excitement about ethanol focuses only on them then it will soon fizzle because of the impracticality of the reality. However, I have heard very encouraging things about producing ethanol in Brazil. Apparently, they’re already selling it locally at prices considerably lower than that of gas (that is, than that of gas a year ago), sometimes even twice less. I think they also manage to do this without any subsidies. Does this not indicate that when they produce ethanol they are also using much less input energy (which is now fossil fuels but could also be ethanol itself)? Am I still correct in believing that Brazilian ethanol is as close to the energy holy grail as we’ve so far come? Someone said that Brazillian ethanol is better, but apparently not by much. This got me worried.
I’ll bite.
My source is this BusinessWeek article datelined 19 May 2006. Here are a couple relevant sentences, as I attempt to comply with fair use rules for copyrighted material.
Oh dear.
The ‘facts to the contrary’ that Blake was requesting would be those supporting the notion that he had asserted ethanol production could not be achieved without expending at least an equivalent quantity of fossil fuels; i.e. fact supporting the notion that Blake was suffering from the misconcieved application of the laws of thermodynamics.
No such facts are forthcoming, because Blake clearly made no such assertion and is clearly not labouring under that false impression; he describes the state of the art at this point (a phrase explicitly appearing in the thread title) as being a roughly equivalent trade-off in terms of ethanol out per gasoline in.
It is crystal clear from even the most cursory reading that Blake is NOT asserting that it is impossible for ethanol production to be done in a way that does not consume an equivalent quantity of fossil fuels; he’s just saying that right now, we are not achieving that.