[Terrapreta] ? GHG emissions from Biomass Combustion ?

[teelws at jmu.edu]

Tony,

Your questions is quite complicated because it is species dependent when you get down to the actual numbers.  It even varies with soil type and location.  The chemistry is relatively simple in a qualitative sense, but quantitatively then it gets messy.

Most carbon in plants is in the form of repeated sugar chains that make up cellulose.  The basic formula is (CH2O)n, with n representing the total number of repeated segments.  If your grass is naturally dried, like in the late fall here is Virginia, then almost everything in the plant is cellulose.  However, each dry species will have some levels of calcium, magnesium, potassium, phosphorus, and in some species silica.  Some grass species use silica as a repellent to grasshoppers.  (Some grasshoppers have evolves aluminum-based mandibles to get around the silica - life is complicated and fascinating).  When you burn most of the biomass is lost as H20 and CO2 as long as oxygen is not a limiting factor.  Peter Read's numbers are approximately correct, though I usually use 40%C for grass.  It is a little different with woody biomass because some of that is lignin, which has a higher C percentage.  What remains after burning is often a very light white powder, less than 1% of tot!
!
al weight, made up mainly of oxidized forms of the elements I listed above.

Green grass is different.  It is higher is nitrogen, phosphorus, and many of the other elements as well.  The plant tends to withdraw these elements into their root systems for next years growth if they dry naturally.  If you cut them green they, of course, stay in the stalk or leaf.  Drying these then burning could yield small amount of nitrogen oxides, including some N2O, the worst of the plant-based greenhouse grasses, produced more when composting or low oxygen pyrolysis to make biochar, which explains why many of the list members want to make sure the off-gases from making biochar are burned.  The C:N ratio is most green grasses is around 20:1.  In naturally dried grasses it is closer to 100:1, at least according to the literature.  Different species will have slightly different ratios.  

I hope this helps some.  You should not produce any greenhouse gasses other than CO2 and water with burning naturally dried grasses in open flame.  Limited oxygen situations are the problem, and worse with cut and dried grasses.

Wayne

---- Original message ----
>Date: Mon, 10 Mar 2008 14:12:22 +1000
>From: "Tony Lovell" <tonyl at soilcarbon.com.au>  
>Subject: Re: [Terrapreta] ? GHG emissions from Biomass Combustion ?  
>To: "'Peter Read'" <peter at read.org.nz>, <Shengar at aol.com>
>Cc: terrapreta at bioenergylists.org
>
>   Peter
>
>   Thanks for such a prompt response - which of course
>   leads to more questions!!
>
>   What happens to the other 50% of material in the
>   biomass that is not C? And if the combustion
>   happened in a less than complete manner, eg in a
>   bushfire or burn to clear land, what would the mix
>   of GHG's be like?
>
>   Tony
>
>    
>
>    
>
>   ----------------------------------------------------
>
>   From: Peter Read [mailto:peter at read.org.nz]
>   Sent: Monday, 10 March 2008 2:01 PM
>   To: Shengar at aol.com; tonyl at soilcarbon.com.au
>   Cc: terrapreta at bioenergylists.org
>   Subject: Re: [Terrapreta] ? GHG emissions from
>   Biomass Combustion ?
>
>    
>
>   Hi
>
>   provided it is fully combusted there should be no
>   CH4 or CO
>
>   how much CO2 depends on the particular biomass but a
>   good rule of thumb is 50% C by weight in dry biomass
>
>   So 1 tonne Biomass contains ~500Kg C yielding
>   500*44/12 Kg CO2 = ~1800Kg CO2
>
>   Peter
>
>     ----- Original Message -----
>
>     From: Shengar at aol.com
>
>     To: terrapreta at bioenergylists.org
>
>     Sent: Monday, March 10, 2008 4:38 PM
>
>     Subject: [Terrapreta] ? GHG emissions from Biomass
>     Combustion ?
>
>      
>
>     Hi All,
>
>     Could anyone provide the figures Tony Lovell is
>     asking for below;
>
>      
>
>     "Erich
>
>     Thanks you for sharing our work with your
>     colleagues at TP.
>
>     Would you or any of your colleagues be able to
>     assist me with finding some information?
>
>     I am looking for general parameters on how much of
>     what GHG's are produced due to the combustion of
>     biomass. In particular if we were to combust say
>     1,000kgs dry matter of switchgrass or similar
>     material how much CO2, CH4, CO, etc etc would be
>     released.
>
>     Any assistance you can provide is greatly
>     appreciated.
>
>     Take care,
>
>     Tony Lovell
>
>     Soil Carbon (Australia) Pty Ltd
>
>     PO Box 157, BOND UNIVERSITY QLD 4229
>
>     Suite 102, 20 Lake Orr Drive, VARSITY LAKES QLD
>     4227
>
>     Ph: +61 (0)7 5553 7900 Fax: +61 (0)7 5553 7999
>     Mob: +61 (0)418 730340
>     Email: tonyl at soilcarbon.com.au
>
>      
>
>      
>
>      
>
>     Thanks
>
>     Erich
>
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Wayne S. Teel
MSC 4102 ISAT
James Madison University
Harrisonburg, VA 22807
Tel: 540-568-2798
Fax: 540-568-2761