[Terrapreta] Brown Haze from Cooking Fires Cooking Earth, Too

[Sean K. Barry]

Hi Larry,

Tom Miles can correct me on any of this, but I believe the production of "smoke" from making charcoal is really a function of things like the moisture content of the biomass feedstock, the temperature of the pyrolysis reaction, biomass residence time in the reactor, air control; both flow direction through the reactor and oxidant levels, and the configuration and depth of the charcoal bed in the reactor.

The charcoal, once made will naturally produce less smoke when it is burned.  This is because charcoal "burns" hot.  It all primarily combusts completely, into invisible hot gases; CO2 and H2O, at a higher temperature than when pyrolyzing the biomass.

Pyrolysis is partial combustion and destructive distillation of biomass and occurs just below complete combustion temperatures and oxygen levels.   When is biomass heating to combustion temperature, lower temperature pyrolysis is occuring in any fire.  There is more partial combustion, and a high production of vaporized partial combustion products.  These cooling vapors and the chunks of charcoal blown off the biomass are what form the smoke and soot.  In any open fire at atmospheric pressure and open to the air, the pyrolysis products will bloom voluminously away from the flames as they cool.  It can be mixed with a lot of cooling water vapor too, adding a big steam plume.

Using a drier biomass feedstock, enclosing the heated biomass and gases when pyrolizing it, keeping this all hot (>450C), blowing the pyrolysis products down through a hot bed of charcoal, and limiting the amount of air/oxidant that get to the pyrolysis reaction will control and even stop the production of smoke.  The reaction will more completely char the biomass, will produce more fuel gases; H2, CO, CH4, and produce less combustion gases (CO2 and H2O), and ash.  Simple charcoal retorts do not do this.  There is more air and more complete combustion going on in them, with less resulting charcoal, and more smoke and heat loss.  It will take something like a "stratified down-draft gasifier" with a deep moving charcoal bed to prevent the production of lots of smoke when making charcoal from biomass.

Depending on how fast the biomass is moved through the reaction zone, the air flow, and reactor temperature, etc; adjusting these can make a difference in the relative amounts of the products, fuel gases vs. charcoal.  This is called the "superficial velocity" of the gasifier.  There is a number called lambda, too, which relates the actual (in reaction) air/fuel ratio (oxygen mass to feedstock mass ratio) to the stoichiometric ratio; which is the air/fuel ratio required for complete combustion.  When lambda is held to around 0.25, and the pyrolysis reaction is kept hot (>450C), then the reaction will produce more fuel gases (less smoke and less charcoal), than at any other ratio.

Building a device which can pyrolyze biomass, make charcoal, and make fuel gases that are usable, is not trivial.   It has been done, though, and is doable with some fairly simple control systems.  I have not completely built one yet and I am not a chemical engineer.  But, I read well, and I can understand the concepts that go into building one of these devices, I think.  So, this is what I am at doing.

SKB
  ----- Original Message ----- 
  From: Larry Williams<mailto:lwilliams at nas.com> 
  To: Tom Miles<mailto:tmiles at trmiles.com> 
  Cc: Haard Richard<mailto:richrd at nas.com> ; Kraus Jeff<mailto:jeff at nakedclothing.com> ; Barry Sean<mailto:sean.barry at juno.com> ; John Flottvik<mailto:jovick at shaw.ca> ; adkarve<mailto:adkarve at pn2.vsnl.net.in> 
  Sent: Sunday, August 26, 2007 2:25 PM
  Subject: Brown Haze from Cooking Fires Cooking Earth, Too


  Tom-------I wonder if the soot is from the production of charcoal is a greater contributer to the haze event that cooking fires. From my use of making charcoal for a high volatile organic content and from the pictures of charcoal making around the world, there seems to be a greater amount of smoke (soot) from the production side rather than the user side of charcoal's story. This article leads me believe that it is all the more important that charcoal be buried in the soil and that solar cookers are very important on a world wide basis even if used seasonally in the higher latitudes.


  You should have received the link regarding a small group of American's using solar cookers at stylish barbecue parties---the gourmet crowd. See:When the sun is shining, break out the solar oven by Sarah Elton @http://www.theglobeandmail.com/servlet/story/LAC.20070822.LSOLAR22/TPStory/Life<http://www.theglobeandmail.com/servlet/story/LAC.20070822.LSOLAR22/TPStory/Life> . As we work with charcoal to improve the plant production we have a dual problem. First, to accomplish the burial of black carbon in the soil that correlates, in some fashion, to Terra Preta and secondly to reduce the amount of carbon dioxide and methane released to the atmosphere.


  Also see:The Darkening Earth, Less sun at the Earth's surface complicates climate models by David Appell @http://www.sciam.com/article.cfm?articleID=000C3AAE-D82A-10F9-975883414B7F0000&modsrc=related_links<http://www.sciam.com/article.cfm?articleID=000C3AAE-D82A-10F9-975883414B7F0000&modsrc=related_links> . This article places importance of soot in dimming surface light energy and storing heat within the layer of atmospheric smog.




  Being a landscaper gardener allows me to see the "on-the-ground" practices with managing vegetation. Locally, individual and government agencies burn vegetation with no thought to their contribution to atmospheric changes. From what I see practiced, even with the potential burial of charcoal in the soil, Western society's use and disposal of vegetation releases huge amounts of carbon to the atmosphere. Entropy, retarding the flow of energy (dissipative energy use), is not in our collective mind. Of course, the pictures of charcoal production in Ghana and India, also, show a release of smoke.


  We are on a tight rope and need to appreciate the trends in economics, social acceptance and the alterations to Earth's resources that we face. Sunlight is a resource. I understand the need for this list, Terra Preta, to remain focussed on process because we do not have sufficient scientific backup to easily sell the concept. At the same time burying charcoal is only part of the solution for removing greenhouse gases.


  Tom, at this point, I am not asking for any action by you except to dialog with you and Rich. Jeff Krause, sells solar water systems and I thought this post might stimulate his interest in solar cookers.


  In a couple hours I should be ready to fire off my retort south of Bellingham at Oyster Creek. It is a little isolated if the burn smokes. I plan to capture the condensate from the smoke and will direct the remaining smoke to the fire.Thanks for the work that you do-------Larry






  -----------------------------
  @http://www.sciam.com/article.cfm?articleID=235006DA-E7F2-99DF-30481E19A0C76818<http://www.sciam.com/article.cfm?articleID=235006DA-E7F2-99DF-30481E19A0C76818>
  August 01, 2007
  Brown Haze from Cooking Fires Cooking Earth, Too
  The brown haze over Asia warms the atmosphere just as much as greenhouse gases


  By David Biello










       Image: COURTESY OF NASA 

   
       BROWN CLOUD: Aerosols from cooking fires cover India and other parts of Asia with a thick haze that contributes as much to global warming regionally as greenhouse gases. 



  Drone aircraft flying in loose formation through the brown cloud that forms over the Indian subcontinent have revealed that the nearly two-mile thick haze exacerbates atmospheric warming by 50 percent. This means the soot in the cloud more than cancels out any cooling from its fellow aerosolsand causes as much warming as carbon dioxide (CO2), the leading greenhouse gas.


  Atmospheric physicist Veerabhadran Ramanathan of the Scripps Institution of Oceanography at the University of San Diego and his colleagues flew 18 missions with three unmanned aircraft from a base on the island of Hanimaadhoo in the Indian Ocean. Launched via radio control (model plane enthusiasts take note), the aircraft (each weighing more than 60 pounds and with wingspans of nearly six feet) followed programmed routes.


  They flew in vertical formation: one drone directly above the brown cloud, one below and one in the thick of it. The plane above measured how much solar radiation bounces back while the one below measured the amount that penetrated. "The difference between the two tells how much sunlight is getting trapped in the atmosphere," Ramanathan says. The craft inside the cloud measured how water vapor and other cloud components were affected. But the key is, he says, "they all had to sample the same column of real estate."


  The researchers found that "this brown cloud was as much as 50 percent of the background heating," he says. "We are sometimes thinking that aerosols might save us from global warming" by reflecting sunlight and dimming Earth below, but "our study shows us not necessarily. While they may be cooling the globe, they are causing mischief in other places."


  The primary culprit seems to be the black carbon in soot, which soaks up any sunlight it can, thereby warming whatever it touches. And the dominant source for all this black carbon is cooking fires, Ramanathan says. All these cooking fires are, in effect, drying the region, both by contributing to the melting of glaciers that feed Asia's major rivers as well as by decreasing the evaporation that drives rainfall. Aerosols across the board, from black carbon to sulfates, appear to be increasing across Asia as it industrializes.

   
       

   
       
        Image: SCRIPPS INSTITUTION OF OCEANOGRAPHY, UCSD 

   
       
        UNMANNED AIRCRAFT: The drones pictured here with climatologist Veerabhadran Ramanathan allow real-time monitoring of atmospheric phenomenon from many different angles. 

  But the problem can be solved by swapping other fuels and methods for the wood in cooking fires. "The aerosol lifetime is two weeks," Ramanathan says. "If the world pays attention and puts resources to it, we will see an effect immediately. I'm talking weeks, at most a few months, not decades or centuries."

  That contrasts with solutions for CO2 emissions, which will require much longer periods to show effects. Because the brown cloud appears to be at least as important, eliminating it could buy time to implement more far-reaching solutions before catastrophic glacial melt and other climate change impacts occur, Ramanathan argues.

  Ramanathan and colleagues plan to demonstrate this on a small scale over the next few years in the Himalayas, over a 12-square-mile area in the foothills. "We want to create a black carbon hole," he says.

  In addition, the unmanned drones provide a new and relatively cheap method for measuring such atmospheric effects, such as powerful storms or the absorption of sunlight in regular clouds. "To address that you need many aircraft to look at the cloud from all sides," he notesand only unmanned, autonomously navigated drones will do.

  Previous efforts, such as the one that identified the Asian brown cloud in the 1990s, cost millions of dollars to keep conventional aircraft airborne and could only capture data over relatively short time spans. "It's going to be a revolution," he says, "in the way we can look at the planet."
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