Reply #15: I'm still skeptical [View All]

[JohnyCanuck]

Oct. 27, 2003 – A staggering 98 tons of prehistoric, buried plant material – that's 196,000 pounds – is required to produce each gallon of gasoline we burn in our cars, SUVs, trucks and other vehicles, according to a study conducted at the University of Utah.

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Unlike the inefficiency of converting ancient plants to oil, natural gas and coal, modern plant "biomass" can provide energy more efficiently, either by burning it or converting into fuels like ethanol. So Dukes analyzed how much modern plant matter it would take to replace society's current consumption of fossil fuels.

He began with a United Nations estimate that the total energy content of all coal, oil and natural gas used worldwide in 1997 equaled 315,271 million billion joules (a unit of energy). He divided that by the typical value of heat produced when wood is burned: 20,000 joules per gram of dry wood. The result is that fossil fuel consumption in 1997 equaled the energy in 15.8 trillion kilograms of wood. Dukes multiplied that by 45 percent – the proportion of carbon in plant material – to calculate that fossil fuel consumption in 1997 equaled the energy in 7.1 trillion kilograms of carbon in plant matter.

Studies have estimated that all land plants today contain 56.4 trillion kilograms of carbon, but only 56 percent of that is above ground and could be harvested. So excluding roots, land plants thus contain 56 percent times 56.4, or 31.6 trillion kilograms of carbon.

Dukes then divided the 1997 fossil fuel use equivalent of 7.1 trillion kilograms of carbon in plant matter by 31.6 trillion kilograms now available in plants. He found we would need to harvest 22 percent of all land plants just to equal the fossil fuel energy used in 1997 – about a 50 percent increase over the amount of plants now removed or paved over each year.

http://www.eurekalert.org/pub_releases/2003-10/uou-bm9102603.php

I'm skeptical that this depolymerization process will entirely be able to replace fossil fuels at our current and projected rates of consumption. While it could help alleviate some of the shortages we will no doubt face, it will be a mistake to think that we can continue our energy intensive, industrialized societies by just growing our energy as crops or reprocessing manufactured waste products back into oil.

As this University of Utah study indicates to grow the material would mean a 50% increase increase in the amount of land devoted to agriculture (to meet just the 1997 consumption figures). As for the argument that the depolymerization process can be used to retrieve oil from waste products, the laws of thermodynamics will dictate that each time the conversion process takes place energy will be lost in the process and the useful energy derived from the output will always be smaller than the energy used to create the input. In a closed system that would mean eventually the process would grind to a halt. However, if outside energy is available to supplement the energy obtained from the material produced by the depolymerization process, it might make some economic sense to derive as much oil as possible from the process in order to alleviate the shortages that will occur after peak oil.

I certainly would not count on depolymerization to mean that life will continue as normal and we'll get to continue our energy hungry North Amercian lifestyles, driving our single occupant SUVs 30 miles from the suburbs to work each day, jetting off each winter to Hawaill or the Caribbean for our vacations etc. etc.

From the article Nine Critical Questions To Ask About Alternative Energy:

Ethanol is another case in point. Some research has shown a negative EROEI for ethanol. Newer research from Oregon shows a slightly positive return. Ethanol is, at best, a slightly beneficial temporary alternative - not a substitute.

Claims that cars can run on vegetable oil never take into account the amount of energy necessary to generate the vegetable oil (farming, vegetable transport, extraction, etc.).

Devices that recycle plastic into oil don't mention the fact that plastic is oil, and that a great deal of energy was used to make it into plastic in the first place.

Similarly, new technology of thermal depolymerization is not a legitimate alternative energy source. This process transforms carbon-based wastes back into hydrocarbon fuel. This technology is useful, and may help us on the downside of the Hubbert curve, but it will never replace fossil fuels. Why? Because the wastes were produced by the use of fossil fuels (my emphasis JC)

EROEI = Energy Returned on Energy Invested.

For more info on the coming Peak Oil crisis see:
www.gulland.ca/depletion/depletion.htm www.peakoil.net www.hubbertpeak.com