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<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">Dear Crispin,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">thanks for your comments. I have several Chinese journal papers on NO reduction by char. Do you mean this group (Li Dong, Shiqui Gao and Guanwen Xu,
NO Reduction over Biomass Char in the Combustion Process, Energy & Fuels 24, 446-450, 2010)? The authors are from</span><span lang="EN-US" style="font-family:"Calibri",sans-serif"> Chinese Academy of Sciences.
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">As I wrote 16.10.2017 to the list, we studied NO formation and reduction from char (and from fuel bed). It was mainly in connection with grate combustion
in an European project “Reduction of Nitrogen Oxide Emissions from Wood Chip Grate Furnaces (Low-NOx Wood Chip Project;
</span><span lang="EN-GB" style="font-family:"Calibri",sans-serif">Contract JOR3-CT96-0059)” but we had also another national research programme focusing on stoves or fireplaces “TULISIJA” (=fireplace).<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-family:"Calibri",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-family:"Calibri",sans-serif">NO is formed in parallel with oxidation of char from a single particle. Part of NO diffuses into the same particle and reacts to N2. When the particle size decreases with combustion,
the conversion of char-N to NO increases. This is due to the fact that the rate of escape of NO increases with decreasing particle size and there remain less possibilities for the reduction of NO with char in the same particle it is formed. This applies to
single particles and can be explained with a model (Saastamoinen, J., and Hämäläinen, J., Release of nitrogen from wood. International Energy Agency (IEA) - Workshop:”NOx/N2O Formation and Destruction in Fluidized Bed Combustors”, 16.5.1999, Savannah, USA,
16 p.). If someone is interested, I can send a copy.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-family:"Calibri",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-family:"Calibri",sans-serif">In a fuel bed, NO formed from a single particle can also be reduced to N2 by other surrounding char particles. For example, in fluidized bed batch combustion of char, the conversion
of char N to N2 increases with increasing batch size, because with large batch size there are more particles acting as reducing material. The same applies to char particles in a fixed bed. NO is already partly reduced in the particle it is formed but it can
further effectively be reduced in other particles later along the gas flow.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-family:"Calibri",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-family:"Calibri",sans-serif">Jaakko<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
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<div style="border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0cm 0cm 0cm">
<p class="MsoNormal"><b><span lang="EN-US">From:</span></b><span lang="EN-US"> Stoves [mailto:stoves-bounces@lists.bioenergylists.org]
<b>On Behalf Of </b>Crispin Pemberton-Pigott<br>
<b>Sent:</b> maanantaina 29. tammikuuta 2018 17.58<br>
<b>To:</b> Discussion of biomass cooking stoves <stoves@lists.bioenergylists.org><br>
<b>Subject:</b> Re: [Stoves] why does charcoal produce more CO?<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span lang="EN-CA" style="mso-fareast-language:EN-US">Dear Jaakko</span><span lang="EN-CA" style="font-size:11.0pt;mso-fareast-language:EN-US"><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">This is fascinating. Thanks so much for sending such a detained report.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">I recommend, based on recent information and a visit to the Chinese Academy of Sciences in Beijing, that you contact Prof Xue from the Beijing University of Chemical Technology. He has been modeling the behaviours you
describe and one additional product (not mentioned below) is that NO produced from fuel N can be reduced to N2 and O2 if the bed has certain characteristics. It is an interesting assumption in the US stove tests that the heat available from fuel is for all
fuel N to be ‘burned to NO<sub>2</sub>.” Now, with an understanding of how to do it, it can rather be converted to the molecular form N<sub>2</sub>.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">They built a stove with several optimisations in mind which I hope to test at CAU shortly. There are two extant copies and they look really good. They are low pressure boilers (water heaters for homes).<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">If you can’t locate Prof Xue contact me and I will find an intermediary.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Regards<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Crispin<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-CA"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Dear stovers,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">the question of CO release from char bed is interesting. We developed models for the combustion of a char bed [1] and CO [2].
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">[1] Saastamoinen, J., Huttunen; M., Kilpinen, P., Kjäldman, L., Oravainen; H, and Boström, S., Emission formation during wood log combustion in fireplaces - Part II: Char combustion stage. Progress in Computational Fluid
Dynamics 6 (4/5), 209-216, 2006.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">[2] Saastamoinen, J.J, Kilpinen, P.T, and Norström, T.N., New simplified rate equation for gas-phase oxidation of CO at combustion. Energy & Fuels, Vol. 14, No 6, pp. 1156-1160, 2000.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Input values in the model are the particle size, bed thickness, inlet air rate and air inlet temperature (and inlet air composition, H2O etc.). Equations describing the particle and gas temperatures and the gas composition
(species O2, CO, CO2, H2O, H2, NO) as function of location (distance above the air inlet) are solved. Oxygen reacts with the char particles producing CO and CO2 in exothermic reaction. There is some literature on the product ratio CO2/CO on the char surface.
Endothermic gasification reactions, where H2O and CO2 react with char take also place. CO may be burning in the gas depending on the temperature. All the reaction rates (kinetics) depend on the temperature.
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Initially one has to assume some temperature for the char bed. Then iterative calculations are needed using the equations of the model, which lead to actual temperature and species distributions as function of the distance
from the air inlet. Interestingly two solutions for the same problem were found depending on the initial guess. If one assumes relative low temperature (for example 700 oC), the iterative calculations lead to one stable solution for the temperature and species
distributions. If one assumed higher initial temperature, iterative calculations lead to another solution at higher temperature level. After some consideration, it was reasoned that both solutions could be existing. Assuming low temperature, CO produced at
char surface did not burn in the gas and the temperature level remained low but assuming higher temperature it did burn producing heat keeping the bed at higher temperature level and sustaining burning of CO. Actually, there are three stable solutions. Assuming
initial temperature 20 oC, there is no burning.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">So there are some reasons for high CO emissions:<o:p></o:p></span></p>
<ul style="margin-top:0cm" type="disc">
<li class="MsoNormalCxSpMiddle" style="margin-bottom:8.0pt;mso-add-space:auto;line-height:105%;mso-list:l1 level1 lfo3">
<span lang="EN-US" style="mso-fareast-language:EN-US">The fuel bed is disturbed so that temperature deceases (for example too high air rate cools it). Then it may be difficult to get CO again burning. Preheating of combustion air could promote burning of CO.
Burning of CO is shown by the blue flame.<o:p></o:p></span></li><li class="MsoNormalCxSpMiddle" style="margin-bottom:8.0pt;mso-add-space:auto;line-height:105%;mso-list:l1 level1 lfo3">
<span lang="EN-US" style="mso-fareast-language:EN-US">In the end stage usually, the temperature becomes too low to sustain burning of CO. I usually burn thin sticks in the end stage in my fireplace on the char bed, so that much of CO from the larger char particles
is burnt with the volatile flame from the sticks. <o:p></o:p></span></li><li class="MsoNormalCxSpMiddle" style="margin-bottom:8.0pt;mso-add-space:auto;line-height:105%;mso-list:l1 level1 lfo3">
<span lang="EN-US" style="mso-fareast-language:EN-US">In a thick char bed, CO may burn inside the bed producing CO2 and rising the temperature. However, CO2 may again react with char upper in the bed producing CO.<o:p></o:p></span></li><li class="MsoNormalCxSpMiddle" style="margin-bottom:8.0pt;mso-add-space:auto;line-height:105%;mso-list:l1 level1 lfo3">
<span lang="EN-US" style="mso-fareast-language:EN-US">Burning rate of CO depends on the H2O level even in the simple reaction CO+O2/2=CO2 there is no H2O. In reality the reaction scheme is more complicated, where radicals formed from H2O promote the reaction
rate. If there is no H2O in the air, the burning rate of CO becomes very low. Usually there is some H2O in the air, but in dry weather conditions, CO release may become higher.<o:p></o:p></span></li></ul>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Jaakko<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><b><span lang="EN-US">From:</span></b><span lang="EN-US"> Stoves [<a href="mailto:stoves-bounces@lists.bioenergylists.org">mailto:stoves-bounces@lists.bioenergylists.org</a>]
<b>On Behalf Of </b>Andrew Heggie<br>
<b>Sent:</b> perjantaina 26. tammikuuta 2018 20.45<br>
<b>To:</b> Discussion of biomass cooking stoves <<a href="mailto:stoves@lists.bioenergylists.org">stoves@lists.bioenergylists.org</a>><br>
<b>Subject:</b> Re: [Stoves] why does charcoal produce more CO?<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On 26 January 2018 at 01:31, Darpan Das <<a href="mailto:darpandasiitb@gmail.com" target="_blank">darpandasiitb@gmail.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal"><img border="0" id="_x0000_i1025" src="https://mailtrack.io/trace/mail/e69f256f0f88a1aa36e8809aa9d03574740386e1.png?u=1788967"><o:p></o:p></p>
<p class="MsoNormal"><br>
Thanks Andrew.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I was also wondering if the decrease in bound oxygen content would have any role to play in the increase in co emissions. My ultimate analysis results for wood and charcoal show that charcoal has negligible O/C content. This probably is
because of the pyrolysis process for wood has already removed the volatiles. Now the charcoal is more energy densified containing most of it part as carbon.<o:p></o:p></p>
</div>
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<p class="MsoNormal"><o:p> </o:p></p>
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<div>
<p class="MsoNormal">Can this less O present in the solid fuel matrix be attributed as a reason for formation of high CO?<o:p></o:p></p>
</div>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Darpan<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Crispin has replied to this.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">By the time the fire is reduced to a glowing bed of coals there will be little oxygen bearing compounds left.
<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">In the early stages of pyrolysis CO is given off and this is a result of the decomposition of wood, so yes the CO is a product from the decomposition of oxygen beariing compounds in the wood.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">The reduction of CO2 by carbon to CO only takes place at higher temperatures by which time the char is nearly all carbon with no oxygen bearing compounds remaining.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">If the firebed is thin and able to radiate its heat freely so it looks like "black" heat the conditions for making CO from char don't exist and the char should oxidise directly to CO2, as the bed gets deeper and the heat cannot escape then
the conditions are there.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I cannot imagine what -56C is like +40C was bad enough<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Andrew in balmy England<o:p></o:p></p>
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