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Thursday, April 26, 2007

The Case for Burying Charcoal

Research shows that pyrolysis is the most climate-friendly way to consume biomass.

By Tyler Hamilton

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Carbon capture: Heating biomass such as wood pellets (right) in an oxygen-free environment produces char (left) and byproducts such as methane that can be burned. Research shows that turning biomass into char and burying the char is a good way to avoid releasing greenhouse gases into the atmosphere.
Credit: U.S. Department of Energy

Several states in this country and a number of Scandinavian countries are trying to supplant some coal-burning by burning biomass such as wood pellets and agricultural residue. Unlike coal, biomass is carbon-neutral, releasing only the carbon dioxide that the plants had absorbed in the first place.

But a new research paper published online in the journal Biomass and Bioenergy argues that the battle against global warming may be better served by instead heating the biomass in an oxygen-starved process called pyrolysis, extracting methane, hydrogen, and other byproducts for combustion, and burying the resulting carbon-rich char.

Even if this approach would mean burning more coal--which emits more carbon dioxide than other fossil-fuel sources--it would yield a net reduction in carbon emissions, according to the analysis by Malcolm Fowles, a professor of technology management at the Open University, in the United Kingdom. Burning one ton of wood pellets emits 357 kilograms less carbon than burning coal with the same energy content. But turning those wood pellets into char would save 372 kilograms of carbon emissions. That is because 300 kilograms of carbon could be buried as char, and the burning of byproducts would produce 72 kilograms less carbon emissions than burning an equivalent amount of coal.

Such an approach could carry an extra benefit. Burying char--known as black-carbon sequestration--enhances soils, helping future crops and trees grow even faster, thus absorbing more carbon dioxide in the future. Researchers believe that the char, an inert and highly porous material, plays a key role in helping soil retain water and nutrients, and in sustaining microorganisms that maintain soil fertility.

Johannes Lehmann, an associate professor of crops and soil sciences at Cornell University and an expert on char sequestration, agrees in principle with Fowles's analysis but believes that much more research in this relatively new area of study is needed. "It heads in the right direction," he says.

Interest in the approach is gathering momentum. On April 29, more than 100 corporate and academic researchers will gather in New South Wales, Australia, to attend the first international conference on black-carbon sequestration and the role pyrolysis can play to offset greenhouse-gas emissions.

Lehmann estimates that as much as 9.5 billion tons of carbon--more than currently emitted globally through the burning of fossil fuels--could be sequestered annually by the end of this century through the sequestration of char. "Bioenergy through pyrolysis in combination with biochar sequestration is a technology to obtain energy and improve the environment in multiple ways at the same time," writes Lehmann in a research paper to be published soon in Frontiers in Ecology and the Environment.

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Comments

  • Burying Energy
    hsfrey on 04/26/2007 at 1:37 AM
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    The energy we get from burning carbon fuels comes from the oxidation of the carbon. Charcoal represents a large proportion of the carbon, and hence the energy in the fuel. By not burning the fuel completely, we'd simply get less energy out of it, so we'd have to burn more OTHER fuel to make up for the fuel we buried.
    This is like saying that you put half as much CO2 into the atmosphere if you dump half of your gasoline onto the ground and don't burn it.
    What am I missing here?
    Rate this comment: 12345
    • Re: Burying Energy
      Buckwheat469 on 04/26/2007 at 2:32 AM
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      It does sound a bit odd to have all of this usable energy in the form of carbon that we would just be burying. I like the idea of using it in fertilizers of some sort to enhance the growth of plants, but I know that the governments, in their infinite wisdom, will just bury it in fear. The point is that we would be reducing the CO2 in the atmosphere by burying a large portion of the plant byproduct, but if the plant produces a net zero CO2 footprint, then what is wrong with using the char for fuel and releasing the CO2? In the long-run, if we use the char in place of coal then we would be reducing the CO2 emissions by not using buried stores while allowing other plants (like grasses and mosses and other things) to grow while we used crops and trees and other biomass for fuel.
      Rate this comment: 12345
      • Re: Burying Energy
        RickJ on 04/26/2007 at 4:03 AM
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        The paper sumamry notes that displacing coal combustion by burning the char is better than burying - which makes sense, but the tech review summary does not make this clear.
        Rate this comment: 12345
        • Re: Burying Energy
          tjh on 04/27/2007 at 12:45 PM
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          The paper does say it may be better to displace coal with biomass than to turn the biomass into char and bury it, but that conclusion excludes the benefits that come from the byproducts of the analysis (i.e. hydrogen, methane, bio-oil) and the benefits of using the char to enhance soil fertility (i.e. more trees, more growth, larger carbon sink) and absorption of greenhouse gases such as nitrous oxide because of reduced decay. Factor these in and the pyrolysis/bury approach has better carbon savings. And if you can achieve that with coal, this is an even better proposition when it comes to less carbon-intensive fossil fuels such as natural gas, and even oil. In this regard, it may be better to replace coal with natural gas and save the biomass to create and bury char.
          Rate this comment: 12345
          • Re: Burying Energy
            RickJ on 05/02/2007 at 6:25 AM
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            I agree there are wider sustainability benefits to making char, but burning biomass (or the char) to replace gas in a heating application, then using the gas to make power and displace coal has some pretty compelling GHG reduction numbers - none of which are relevent in many parts of the world where transport of the fuel to create grid power is prohibitively expensive. Certainly, this is an excellent idea & worth further investigation.
            Rate this comment: 12345
      • Sequestering Carbon their goal
        nekote on 04/26/2007 at 5:35 AM
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        The goal would seem to be to sequester Carbon that mostly comes out of the atmosphere.

        In essence, an entry for Branson's prize of $25 million for the best way to sequester a Gigaton, per year, of Carbon (or is it CO2?).

        This effort is to have a negative - not 0 - carbon foot print.
        Rate this comment: 12345
      • Re: Burying Energy
        green_tech_watch on 04/28/2007 at 4:33 PM
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        Locking carbon in a solid form also makes it easier to transport for the purpose of sequestration. It is a lot of carbon per square centimetre.

        Think of capturing C02, compressing it, piping it or putting it into tankers. There would need to be much infrastructure to get this to happen. Then you have to find out where you can put the CO2.

        Carbon in solid form can be easily scattered on farmland.
        Rate this comment: 12345
    • Re: Burying Energy
      zephod on 04/26/2007 at 5:29 AM
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      I think you're missing the crucial difference between fossil and bio-fuel. Using fossil fuels is always carbon-positive (ie adding carbon to the cycle); burning biomass is carbon-neutral. But this burying of char, indeed energy inefficient, would have the benefit of making the whole process carbon-negative (ie taking carbon out of the cycle). Plus, the char works apparently as a natural soil enhancer. It almost sounds to good to be true, doesn't it?
      Rate this comment: 12345
    • Re: Carbon Plus What?
      nick47g on 04/26/2007 at 1:40 PM
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      Pure carbon in the form of char, coke or petroleum coke is a Godsend to matalurgy, phamacuticles etc.  Moreover it has no sulfur, mercury or heavy metal in it that have to be delt with!!! So defacto sequester the coal and keep the toxics where they've been for 200 Million years!
      Rate this comment: 12345
  • a better use than burying
    djs on 04/26/2007 at 4:33 AM
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    Higher temperature pyrolysis of biomass, to a CO + H2 mixture looks better. Adding more hydrogen (from water electrolysis, powered by solar cells) produces liquid fuels (methanol, gasoline by Fischer-Tropsch, etc) - the biomass thus can serve to make a "hydrogen economy" actually work by carrying the hydrogen in a convenient form in addition to furnishing the biological energy content.
    Rate this comment: 12345
    • Re: a better use than burying
      mbmurphy777 on 04/26/2007 at 2:49 PM
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      True, but the solar electrolysis and high temp nuc electrolysis and all the conversion steps would be less efficient than using the solar pannels or nuc plants to create electricity for electrified transportation.
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      • Re: a better use than burying
        djs on 04/27/2007 at 4:04 AM
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        electrified transportation is beautiful, but liquid fuels will remain necessary for some forms of transport (air; sea [when the wind can't help]; remote locations).
        Rate this comment: 12345
  • Credit due to South American Indians
    ericzundel on 04/26/2007 at 6:46 AM
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    Charles C. Mann's book, "1491" describes how South American Indians used controlled burning to enrich the soil in a similar manner described in this article.  Their slow burning of biomass created carbon rich soil that greatly improved agricultural yields.  Furthermore, the effects are much more long lasting than other soil amendments, such as adding nitrogen fertilizer.  The "black earth" created hundreds of years ago is still supporting crops today.
    Rate this comment: 12345
    • Re: Credit due to South American Indians
      AlanM on 04/26/2007 at 2:31 PM
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      The title is '1491' of course, not 1941. It's a great book about the people who lived in the Americas before Europeans arrived and settled. One of its themes is that there were lots more people here than we used to believe, and that they had richer civilizations than we want to believe. European diseases decimated them.
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  • Water retention and land reclamation.
    Hardheadjarhead on 04/26/2007 at 9:55 AM
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    What would the char do for soils in arid areas?  Would we be able to increase soil fertility using stuff like this?

    If the char makes for increased crop yields, I see it as a money making and exportable product. 
    Rate this comment: 12345
  • Forest fire?
    Viv on 04/26/2007 at 12:13 PM
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    Loading the soil with charcoal is not going to sound a good idea to a fireman, not when the severity and incidence of fires is on the increase.
    Rate this comment: 12345
    • Re: Forest fire?
      mbmurphy777 on 04/26/2007 at 2:55 PM
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      Terra preta (the charcoal rich black earth) is not any more flammable than regular dirt.

      Fires need oxygen to burn, and packed dirt just doesn't allow for sufficient penetration.
      Rate this comment: 12345
  • Slash,chip & char
    abcarterjr on 04/26/2007 at 2:09 PM
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    FireSafeLandscaping near the Sitgreaves National
    Forest generates Juniper slash & string cut high
    plains grass that can be run thru a chipper then
    charcoaled into compost for the kitchen garden.
    Rate this comment: 12345
  • Good essay on possible uses of char from biomass
    mbmurphy777 on 04/26/2007 at 2:45 PM
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    Some of the tech are not quite ready, of course, but there are several things to like here:


    http://ergosphere.blogspot.com/2006/11/sustainability-energy-independence-and.html



    It could allow replacement of natural gas and coal fired electricial generation and offset some liquid fossil fuels.  Transitioning to electrified transport would dramatically reduce the liquid fuels requirement, hence some of the surplus char could be sequestered.

    Rate this comment: 12345
  • win win
    farmboy on 04/26/2007 at 6:53 PM
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    Sequestering char has many advatages,the most important one is making use of waste stream products that add to the carbon in the atmosphere as they decompose. Items like agricultural, forestry, and manufacturing waste, why burn them, leave them on the forest floor or bury them in the land fill. Char benefits the soil through water retention and nutrient retention. Improved soil grows more biomass that takes more carbon out of the air, and needs less supplemental nitrogen which is derived from natural gas. Bring me your char and I will gladly bury it on my farm.
    Rate this comment: 12345
    • Re: win win
      TrueGrit on 04/27/2007 at 12:04 AM
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      You are right on track farmboy.  If you would like to enhance your position with substance I would recommend your review of http://www.eprida.com/news.php4
      Eprida suggests that they have a method of converting basic charcoal into a soil fertilizer and paying farmers to bury it with their crops.  Farmers could have an endless supply.
      Rate this comment: 12345
  • Net of Char process
    rlindsl on 04/27/2007 at 3:28 PM
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    Logging will be a significant source of potential char. It would be most carbon efficient to use excavators to return to a logging site the next fall after the debris has cured/dried and then bury it and ignite it. After it has charred it could be exhumed and used at that site or trucked to other locations.

    If you are going to truck the char, you should do an analysis comparing that to trucking the raw biomass to a char facility that could utilize the waste heat in the process.

    The most efficient use of char sequestration would be onsite and it would enrich the depleted soil lowering the cost and total use of fertilizers in silviculture.

    The onsite char utilization would be a benefit to the thinning of high fuel load forsets in the western United States where the biomass is remote and of little economic value.  These forest lands tend to have marginal soils that would benefit from this treatment. A sequestration subsidy might move these fuel load reduction projects into... the black.  Sorry.
    Rate this comment: 12345
  • Make coal or soil from biomass in hours!
    Greg on 05/26/2007 at 12:41 PM
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    A similiar aproach for a negative CO2 balance from biomass was published by Max Planck Institute already last year. But here we can get other valuable materials like coal or topsoil for vegetation of eroded areas.

    Have a look at the following link:

    http://www.mpg.de/english/illustrationsDocumentation/multimedia/mpResearch/2006/heft03/3_06MPR_20_25.pdf
    Rate this comment: 12345
  • Heavy Metals Adsorption
    erinbyers on 06/25/2007 at 11:09 AM
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    If bio char can adsorb heavy metals from the rain, to me this begs the question of whether this increases the amount of heavy metals absorbed by the plants, and entering our diet.  Any comments?
    Rate this comment: 12345
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