Avionul cu soia. De ce zāmbiţi? Nu e deloc ridicol. Vă rog să
nu rādeţi. E absolut normal. American Chemical Society in Anaheim,
California, susţine că amestecul de soia īn kerosen este solutia
Ok, poate nu cu soia, dar de spanac ce ziceţi? Spinach Could Power Better Solar Cells.Metan există īn cantităţi enorme īn apa mări. Există microbi care produc metan. Chiar īn Marea Neagră. Problema e cum īl extragi?
Depolimerizarea termală nu intra
īn calcul ca energie
alternativă. Acest proces transforma gunoiul cu baza organica īnapoi īn
combustibili din hidrocarburi. Este foarte folositor şi va atenua mult din şocul
energetic, dar nu va īnlocui combustibili fosili. De ce? Pentru că gunoiul a
fost produs iniţial
cu ajutorul combustibililor fosili. Acest proces
nu va avea niciodata rata energetică pozitivă a combustibilului original. Pe
masură ce sursa scade (petrolul, gazul natural) şi materialul de bază necesar
acestui proces se va diminua.
Depolymerization (TD) is a process being developed by
World Technology. The process turns waste into oil. It is often
touted as a "solution" to the oil crisis
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
Dr. Walter Younquist points out:
It might be thought that the heavy yields available from sugarcane would allow far better energy capture than 1.9 kW/ha. We have written a separate working paper on this, Sugarcane and Energy, since some of the “supplementary data” in Pimentel and Pimentel, 1996 pp. 236-239, relating to sugarcane are incorrect. We got correct data from the Mauritius Sugar Industry Research Institute. The calorific value of sugarcane is about 1212 kcal/kg. After allowing for inputs, the net output as raw sugarcane is 10.5 kW/ha. However this is an unrealistic assessment, because it fails to take into account that a considerable part of the inputs needed are higher grade fuels, such as ethanol. Thus the more realistic question is this: what is the energy value of the ethanol yield that can be obtained from 1 ha of sugarcane, that will be available for use (rather than needed as input)? For the U.S., assuming the average sugarcane yield of 74 tonnes/ha, the answer is 2.1 kWyr/ha/yr. In other words a steady supply of 2.1 kW/ha.Incidentally, the 0.1 percent datum mentioned earlier, for temperate zone plant-energy-capture, receives confirmation from the forestry data used by Wackernagel et al (1997) in their spreadsheets.
The truth is ethanol is no replacement for oil. It's not
even a viable supplement.
The U. K. carrying capacity estimate of 6 million, based on biomass, derives from the estimated 1.9 kW/ha and the March 1997 data of Wackernagel et al as follows. To replace the current U. K. fossil fuel use of 5.19 kW/cap at a rate of 1.9 kW/ha requires 5.19 / 1.9 = 2.73 ha/cap. United Kingdom citizens are estimated to currently use 0.11 ha/cap of arable land, 0.27 ha/cap of pasture, and 0.10 ha/cap to provide forest products (all these are U. K. areas, not worldwide productivity areas). This gives a total of 3.21 ha/cap. Dividing this into Britain’s 20 million hectares of ecologically productive land gives a carrying capacity of 6 million people. In the calculation for the United States, the sustainability buffers used for our normal carrying capacity calculations were retained, as well as the 12% biodiversity buffer; this gave an ecologically productive area of 439 million ha, and a total “footprint” of 7.98 ha/cap, giving a population limit of 55 million. These calculations are purely to demonstrate the general effect of energy-capture at 1.9 kW/ha. U. K. forests, and U. S. forests (just possibly), may be nearly three times as productive as world averages. Forest yield factors are very hard to estimate.
For the average U.S. sugarcane yield of 74 t/ha, the gross calorific value is 74,000 x 1212 = 89.7 million kcal. On a pro rata basis, using P&P page 237, the input needed to produce this 74 tons is 10.3 million kcal/ha. Thus net energy-capture = 79.4 million kcal/ha = 10.5 kW/ha.
The ethanol calculation for sugarcane is made simple because all the heat needed for conversion is provided by the bagasse, the non-sugar part of the crop. Thus all additional inputs are higher-grade fuels. Thus we can take the additional inputs (beside the bagasse) as being taken from the ethanol output. The amount of the gross ethanol output which is needed to feed the input is about 0.47, leaving 0.53 as net output. However the biggest attenuation comes in the conversion itself: 13 kg of sugarcane, — to take an intermediate figure — with a calorific value of 13 x 1,212 = 15,756 kcal, produces 1 liter of ethanol, with a calorific value of 5,130 kcal. Energy attenuation is therefore 5,130 / 15,756 = 0.326. The aggregate attenuation is therefore 0.53 x 0.326 = 0.173. Applying this to the gross calorific value of 74 tonnes, amounting to 11.91 kW/ha, gives 2.1 kW/ha. Note a steady flow of 2.1 kW/ha can also be described, in terms of an amount of energy, as 2.1 kWyr/ha/yr.
Worldwide forest absorption capacity should be a rough guide to temperate-zone photosynthesis — which presumably lies somewhere between boreal and tropical forest productivity. In their March 1997 spreadsheets, Wackernagel et al (1997) used a worldwide forest carbon absorption capacity of 1.8 metric tons of carbon per ha. This datum derived from Yoshihiko Wada’s (1994) survey of the literature. In the November 1997 revision to the spreadsheets, the data used came from the Intergovernmental Panel on Climate Change, which reduced the absorption capacity datum to 1.42 tC/ha. Wood has an energy/carbon ratio of about 38.46 GJ/tC = 1.22 kWyr/tC. Thus the earlier and later datums indicate energy outputs of about: 1.8 x 1.22 = 2.2 kW/ha and 1.42 x 1.22 = 1.7 kW/ha. These estimates, 2.2 kW/ha and 1.7 kW/ha, bracket the 1.9 kW/ha figure which we derived from the temperate-zone, agricultural, plant-energy-capture datum of 0.001.
Oil from biomass
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.