Depolimerizarea termala nu intra in calcul ca energie alternativa. Acest proces transforma gunoiul cu baza organica inapoi in combustibili din hidrocarburi. Este foarte folositor si va atenua mult din socul energetic, dar nu va inlocuii combustibilii fosili. De ce? Pentru ca gunoiul a fost produs initial din si cu ajutorul combustibililor fosili. Acest proces nu va avea niciodata rata energetica pozitiva a combustibilului original. Pe masura ce sursa scade (petrolul, gazul natural) si materialul de baza necesar acestui proces se va diminua.
The biggest problem with TD is that it is being advertised as a means to maintain business as usual. Such advertising promotes further consumption, provides us with a dangerously false sense of security, and encourages us to continue thinking that we don't need to make this issue a priority.
Avionul cu soia. De ce zāmbiti? Nu e deloc ridicol. Va rog sa nu rādeti. E absolut normal. American Chemical Society in Anaheim, California, sustine ca amestecul de soia in kerosen este solutia crizei petroliere.Dar au uitat sa calculeze cāte hectare de soia va trebuiesc pentru un zbor, sa zicem de la Bucuresti pana la Brasov. Si asta ar fii doar una din probleme. http://www.eurekalert.org/pub_releases/2004-03/ns-sp032404.php Una din problemele majore este faptul ca flota actuala de avioane (11.000) , nu poate fii facuta sa zboare cu altceva in loc de kerosen. Airbus au studiat cāteva variante cu hidrogen dar nu au ajuns nicaieri.
Schematically, there are two types of cultures that allow to obtain a liquid fuel from a field (which is the usual way to obtain a biofuel !) :
On the grounds of gross outputs, we can make a first rough calculation of the surface that it is necessary to allocate to "energetic crops" to replace by biofuels produced in France all oil used for transportation in France, that is 50 millions tonnes (or 50 Mtoe) :
The above percentages, obtained on the grounds of gross outputs, are already significant : we understand right away that we (in France) will never substitue all gasoline by "oily biofuels". Nevertheless, it remains possible, when looking at there figures, to think that we have a real potential with beets. Alas, things are not so simple, and we must reason with the NET output of this line. Indeed, to obtain these biofuels, it is necessary to spend some energy :
If we want to totally replace oil (and natural gas, that is no more renewable) by biofuels, it is not by using oil (and gas, for fertilizers) to produce these biofuels that we will manage to do so ! Therefore we must deduct from the gross energy obtained the upstream consumptions, for fertilizer manufacturing, culture, cropping, and processing after crop.
Well taking into account all these upstream consumptions will lead to net outputs much inferior, and almost null for ethanol ex-wheat.
Why such a drop for beets ? It is that distillation consumes a lot of energy, about the 2/3rds of the energy "enclosed" in the alcohol obtained. The energy required for fertilizer manufacturing and powering the tractor do the rest. Thus "all crops are equal" and yield a net output of 0,75 tonne oil equivalent per hectare, except wheat that yields almost nothing on a net basis.
To produce 50 millions tonnes oil equivalent, we should thus mobilize, in rough figures, 3 to 4 times the present arable land surface of our country. Of course this is not possible, and even producing 10% of this amount out of biofuels would require 30 to 40% of the present cultivated land, and we did not mention oil for heating so far.
One can therefore easily realize that biofuels will not allow to substitute "one day" the oil that we presently consume, and not even a significant fraction of it. In other words, to consider that it is not annoying to have a way of life heavily dependant on fossil fuels because, "one day", we will all be able to drive (and heat ourselves) on biofuels is alas to cherish an illusion. http://www.manicore.com/anglais/documentation_a/carb_agri_a.html
Wood and other biomass. Wood has long been used as a fuel, now to the extent that large areas worldwide are being deforested resulting in massive erosion in such places as the foothills of the Himalayas, and the mountains of Haiti. Wood can be converted to a liquid fuel but the net energy recovery is low, and there is not enough wood available to be able to convert it to a liquid fuel in any significant quantities.
Other biomass fuel sources have been tried. Crops such as corn are converted to alcohol. In the case of corn to ethanol, it is an energy negative. It takes more energy to produce ethanol than is obtained from it (Pimentel, 1998). Also, using grain such as corn for fuel, precludes it from being used as food for humans or livestock. It is also hard on the land. In U.S. corn production, soil erodes some 20-times faster than soil is formed. Ethanol has less energy per volume than does gasoline, so when used as a 10 percent mix with gasoline (called gasohol), more gasohol has to be purchased to make up the difference. Also, ethanol is not so environmentally friendly as advocates would like to believe. Pimentel (1998) states:
Ethanol produces less carbon monoxide than gasoline, but it produces just as much nitrous oxides as gasoline. In addition, ethanol adds aldehydes and alcohol to the atmosphere, all of which are carcinogenic. When all air pollutants associated with the entire ethanol system are measured, ethanol production is found to contribute to major air pollution problems.
With a lower energy density than gasoline, and adding the energy cost of the fertilizer (made chiefly from natural gas), and the energy costs (gasoline and/or diesel) to plow, plant, cultivate, and transport the corn for ethanol production, ethanol in total does not save fossil fuel energy nor does it's use reduce atmospheric pollution.
A comprehensive study of converting biomass to liquid fuels by Giampietro and others (1997) concludes:
Large scale biofuel production is not an alternative to the current use of oil, and is not even an advisable option to cover a significant fraction of it.