April 08, 2007
Biomass Energy Sources Compared On Greenhouse Gases
A recent study attempts to measure the net changes in greenhouse gas emissions from using different forms of biomass energy.
The study, "Net greenhouse gas flux of bioenergy cropping systems using Daycent", was completed by Paul Adler (United State Department of Agriculture - USDA), Stephen Del Grosso (USDA and Colorado State University), and William Parton (Colorado State University). Results appear in the April issue of Ecological Applications.
"Biofuels have a great potential to reduce our dependence on gasoline and diesel fuel," says Parton. "We have performed a unique analysis of the net biofuel greenhouse emissions from major biofuel cropping systems by combining ecosystem computer model data with estimates of the amount of fossil fuels used to grow and produce crop biofuels."
Adler, Del Grosso and Parton used the Daycent biogeochemistry model, developed by Parton and Del Grosso to asses greenhouse gas fluxes and biomass yields for corn, soybean, alfalfa, hybrid poplar, reed canary grass and switchgrass.
I am guessing they are assuming the development of cheap and scalable methods to do biomass processing using cellulosic technologies. That seems a safe bet.
How could ethanol or electricity made from switchgrass and poplar reduce greenhouse gas emissions by more than 100%? By keeping some of the carbon anchored in roots after the surface biomass gets harvested?
The results of the study showed that when compared with gasoline and diesel, ethanol and biodiesel from corn and soybean rotations reduced greenhouse gas emissions by almost 40 percent, reed canarygrass by 85 percent. Greenhouse gas emissions were reduced by about 115 percent for switchgrass and hybrid poplar. Both switchgrass and hybrid poplar offset the largest amounts of fossil fuels reduced emissions compared to other biofuel crops and offset two times as much fossil fuels if they are used for electricity generation via biomass gasification.
On second thought: If the poplar gets burned in order to generate heat to generate electricity this creates the possibility of carbon sequestration. If the carbon dioxide from burned poplar trees gets captured and sequestered then the net effect would be to pull carbon out of the atmosphere! Such a process would go beyond carbon neutral to carbon negative. Using such an approach on a large scale to generate electricity the amount of carbon in the atmosphere would gradually go down.
Biomass energy production produces oxides of nitrogen.
Study results showed that nitrogen (N2O) emission resulting from production of the biofuel crops is the largest greenhouse gas source, while displaced fossil is the largest greenhouse gas sink followed by soil carbon sequestration.
Leave aside for the moment that the global climate computer models are huge simplifications of reality with huge errors in their predictions. Never mind that assorted confidently stated projections of future world temperatures are therefore not real science if by science we mean the ability to predict. Leave all that skepticism aside for the moment for the skepticism cuts both ways. While it is true that we do not know for a certainty that we are warming the planet we also do not know for a certainty that we aren't. All we know is that we are pumping up the concentration of CO2 in the atmosphere and that gas does - all else equal - cause warming. Therefore the possibility exists that we really are warming the planet. Those who can handle the state of uncertainty have to admit that, well, we don't know if we face a big problem or not.
Having said all that, here's my most important point: We might eventually find that we really are going to heat up the planet by several degrees Fahreneit or Celsius and that doing so will cause what most of us will decide is morally unacceptable damage to some peoples (e.g. Pacific islanders and Bangladeshis who'd get flooded by rising sea levels due to melting ice). In spite of the obvious benefits to humans living in northern Russia and other cold places we might decide we want to stop global warming. In that case it is good to know we could always shift to using poplar tree biomass to generate electricity with carbon sequestration and then use electricity for most transportation needs. Then we could pull down the level of atmospheric carbon dioxide and (since by the assumptions in this scenario CO2 really does heat the planet) cause as much cooling as we want to cause.
Mind you, we'd still probably need to generate most electricity using nuclear, wind, and solar power. Otherwise too much land surface would get used for poplar forests and switchgrass fields. But we could use some land areas for forests in order to do large scale atmospheric carbon extraction and help pay for these CO2 extraction operations by using the poplar to generate electricity.
While hype over the threat of global warming has recently taken the pattern of a crescendo leading up to the release of the latest IPCC report my own thinking is heading in the direction of worrying less about it. Why? In a nutshell: We are going to have the technological tools to stop and reverse it if necessary. Gregory Benford sees a cheap way to cool the planet. Should the need arise we could use his proposal as a temporary measure to cheaply buy time while we ramp up poplar forests to extract CO2. We'd still use nuclear, wind, and solar photovoltaics to provide most of our energy.
Technologies for biomass gasification, photovoltaics, batteries, nuclear power, and other needed elements will all get much cheaper. In a few decades time the potential problem of global warming will become solvable for an affordable price and pieces of the solution will become popular anyway because they'll become cheaper ways to get energy.
These studies (at least as reported popularly) are meaningless, because it
is unclear what the baseline is for comparison. If land is NOT being used
for these biofuel crops, what do they assume it IS being used for? The
relevant baseline would seem to be letting the land grow up in natural
vegetation. This might lead to considerable carbon sequestration, perhaps
so much that this do-nothing approach actually comes out ahead. (And note that
it requires no labour or other resources, as well, so even if it's not quite
the winner in carbon terms, it may well be the winner in broader terms.)
Here is the reason why the bio-fuel scenario is so daunting to me.
Let us just start with current consumption. According to the EIA the US used approximately 13,825,000 barrels a day of petroleum based fuels in 2005.
There are 42 gallons in a petroleum barrel (approximately 159 l). So in 365 days the US used about 800 Billion l of petroleum.
Taking gasoline (~725g/l) as about 3/5 of the total and diesel as 2/5 (~850 g/l), I get about 620 Billion Kg or 620 Million Tonnes of fuel.
Diesel is on the average C12H26 and Gas is ~C8H18. Averaged as C9H20 it would have a molecular weight of 9*12 + 20 = 128, so it would be 84% Carbon, and the 620 Million Tonnes of fuel would be ~525 MT of Carbon.
Now to get that much carbon from biological sources, most of it will be in the form of carbohydrates, which have molecular formula of HCOH. The oxygen atom is heavier (16) than the Carbon and Hydrogen (12+2) so carbohydrates (and most plant matter) are 40% Carbon.
To get 525 MT of Carbon in the form of carbohydrates requires 1.3 GT of plant matter.
Could it be done? ORNL published a report "Biomass as Feedstock for a Bioenergy and Bioproducts Industry: The Technical Feasibility of a Billion-Ton Annual Supply, April 2005" (PDF 8.5 MB)
From the "Executive Summary" of the report:
Looking at just forestland and agricultural land, the two largest potential biomass sources, this study found over 1.3 billion dry tons per year of biomass potential
Forestlands in the contiguous United States can produce 368 million dry tons annually. This projection includes 52 million dry tons of fuelwood harvested from forests, 145 million dry tons of residues from wood processing mills and pulp and paper mills, 47 million dry tons of urban wood residues including construction and demolition debris, 64 million dry tons of residues from logging and site clearing operations, and 60 million dry tons of biomass from fuel treatment operations to reduce fire hazards. All of these forest resources are sustainably available on an annual basis. For estimating the residue tonnage from logging and site clearing operations and fuel treatment thinnings, a number of important assumptions were made:
* all forestland areas not currently accessible by roads were excluded;
* all environmentally sensitive areas were excluded;
* equipment recovery limitations were considered; ...
From agricultural lands, the United States can produce nearly 1 billion dry tons of biomass annually and still continue to meet food, feed, and export demands. This projection includes 428 million dry tons of annual crop residues, 377 million dry tons of perennial crops, 87 million dry tons of grains used for biofuels, and 106 million dry tons of animal manures, process residues, and other miscellaneous feedstocks. Important assumptions that were made include the following:
* yields of corn, wheat, and other small grains were increased by 50 percent;
* the residue-to-grain ratio for soybeans was increased to 2:1;
* harvest technology was capable of recovering 75 percent of annual crop residues (when removal is sustainable);
* all cropland was managed with no-till methods;
* 55 million acres of cropland, idle cropland, and cropland pasture were dedicated to the production of perennial bioenergy crops;
* all manure in excess of that which can applied on-farm for soil improvement under anticipated EPA restrictions was used for biofuel; and
* all other available residues were utilized.
However the assumptions for bio-fuel production from agriculture make me very nervous. Do they represent soil mining that will leave us with depleted and unproductive land? Will increasing crop yields require additional applications of fertilizer and pesticide that could create their own problems? Would converting that much cropland into fuel production adversely affect food prices and harm people in poor countries?
Further, It would require an enormous input of energy to turn carbohydrates into alkane fuels. to make C12H24O12 into C12H26 requires the addition of 13 H2. The source of that H2 and the process heat required to drive the process, if it is not more bio-fuel or fossil fuel must be wind, solar or nuclear, and in large quantities. This is not to say that it is impossible -- just that it would be an enormous task.
The wait-and-see approach does nothing to address ocean water acidification. The chemistry of how atmospheric CO2 lowers the pH of seawater is simple and not subject to any controversy. Seawater pH has dropped .1 unit since the Industrial Revolution started. Since much of the base of the ocean's food chain depends on dissolved calcium, the utilization of which depends on pH, the rapid acidification of seawater bodes ill for the planet.
Even aside from climate change, seawater acidification is enough reason to move away from fossil fuel combustion ASAP. Of course, I'm open to hearing about cheap and easy ways to ameliorate this process, or reasons why it isn't actually a looming problem. So share it if ya got it.
Global warming is a scare story for little kiddies and big kiddies who never grew up. They gots to have a crisis or lots of crisises all the time. Drama queens on parade. It ain't science. It's alarmism wrapped in pseudo-science.
Leave aside for the moment that the global climate computer models are huge simplifications of reality with huge errors in their predictions.
Global climate models have huge errors in their predictions? Where did you get this? The range of variability from climate models typically comes from variations in the input assumptions (for example, how much CO2 we will actually emit in the future), not the models themselves.
If anything, Hansen's predictions of two decades ago appear to be pretty much on the money (judging by warming seen since then), and current models are better than the ones he used.
Global warming is a scare story for little kiddies and big kiddies who never grew up.
Keep telling yourself that, if it makes you feel comfortable. While you're at it, if you're a smoker, tell yourself that won't cause lung cancer.
Some of us prefer objective science to wishful thinking. The science of global warming is rather well established, and no one -- not even oil or coal companies, who'd have a lot to gain from it -- has been able to come up with a realistic climate model that fails to predict warming as greenhouse gas concentrations increase.
Hmmm... do we have enough fresh water left to use biofuels? I mean we are currently consuming or exporting the vast majority of what we grow, so if we increase the amount we use for fuels were either have to eat less or export less (which means someone else is eating less) right? The other alternative is to use more land for fuel production which would mean more water usage.
They gots to have a crisis or lots of crisises all the time.
Not to mention lots of pluralses.
A planetary scientist of my acquaintance who studies asteroids recently told me the climate models have such huge simplifications and errors that they can't predict.
Science is when you can predict. The models are too simple to have predictive value.
I'd quote the guy by name but was in a private conversation when he told me this. Maybe I can get him to show up here and repeat what he told me.
This isn't to say that the CO2 is not changing the climate. It may well be. But those models are not objective science at this stage in their development.
Water is a problem for efforts to scale up agriculture. Farmers can move to more water-efficient methods. But that's not going to allow a huge increase in acreage farmed.
I'd expect tree planting to be a less water-dependent path. The trees will grow more slowly in drier years but probably won't die. Their longer lifespans will let them use variable amounts of rain.
But, again, I'm taking the position that we shouldn't shift to biomass for most purposes. Better to go with nuclear, wind, solar, and geothermal.
Maybe crops can learn to use brackish water and suboptimal soil? Maybe all the research in plant genetics will yield crops that produce abundant food, and as a side product, concentrate hydrocarbon fuels in the waste and stubble? Nothing wrong with using plant waste to make fuel as long as you keep recycling the carbon by growing more plants.
This isn't to say that the CO2 is not changing the climate. It may well be. But those models are not objective science at this stage in their development.
And yet, no one has come up with a realistic model (that is, one that predicts current and historical climate) and yet fails to predict additional warming as GH gas concentrations increase.
If warming under increased GH gas concentrations were so dependent on model artifacts, you would think it would have been easy to come up with such models. But warming is a robust consequence of the basic physics of radiation transport in the atmosphere, other approximations notwithstanding.
I'd expect tree planting to be a less water-dependent path.
I am not so sure about that. See "transpiration". Trees are very efficient water pumps.
Those two plants that reduce greenhouse gas emissions...do they reduce it enough to make growing them (which requires energy, tractors --aka gas/diesel--, water, space, etc) especially efficient? do they outweigh the massive ammount of work that would be required to switch our modern economy, or whatever you want to call it, to one effectively based on the use of those two plants?
Sorry about being an ignorant 10th grader, but those questions just popped up into my head right after i read it. It wasnt very clear what the processes were, in order to use the plants.
Also....with everything else that was said. I am fully aware that CO2 is a greenhouse gas, we make it, and it affects the climate change...Coming from a believer in Global Warming, i think that while any reduce in CO2 emissions is a very good thing, CO2 is not the main greenhouse gas. Water Vapor is (it accounts for 95% of global warming, go look it up), and i firmly believe that the solution to global climate change will have to focus on reducing this gas as well.
Once again, i would like to stress that i do comprehend what CO2 emissions do to our planet. Even a change of .01 degree Farenheit potentially melts thousands of tons of ice worldwide, and every little bit DOES matter. a lot. squared to the 66th. Because not only will you have to reduce the temperature to make it freeze again, as if it were normal water, you will have to contend with thousands of tons of warmer water pushing you back all of the time, that have now mixed with the lovely salt water to lower the freezing point, so in the end, its about 1.4-1.8 times harder to counteract (assuming PERFECT conditions, across the board --- that means that, 100% instantly, you will have all of the equipment needed, every person in the world following the rules, and everything green and ready to work MILISECONDS after it melts). umm....thats all i got. discuss.