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</o:shapelayout></xml><![endif]--></head><body lang=EN-CA link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US'>Dear Tom R<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US'><o:p> </o:p></span></p><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0mm 0mm 0mm'><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US'>So when we provide very hot secondary air into a gas stream at about 700 C it is (mostly) burning C, not CO? Maybe?<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D;mso-fareast-language:EN-US'>Thanks<br>Crispin<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif"'><o:p> </o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><div><p class=MsoNormal>Dear Richard and All combustors, gasifiers and Pyrolysers:<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Good question, "Why is the match flame blue near the base, but turns yellow in the outer region?"<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal><><><><o:p> </o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>As the wood in the match heats, the cellulose in the wood breaks down to form CO and H2. (The lignin in the wood turns to charcoal.) <o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>I could write a long equation using cellulose (C6H10O5)n, but the chemistry is easier if I approximate it for Carbo-Hydrates, "CH2O", an approximate formula for all sugars, starch and cellulose. <o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal> CH2O ===> CO + H2 <o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Solids emit black body radiation mostly proportional to their surface temperature. But burning gases emit arbitrary colors due to the flame reactions. So the flame close to the match shows these blue flame colors. <o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal><><><><o:p> </o:p></p></div><div><p class=MsoNormal>So why does the flame give off black body radiation at a greater distance from the burning match? <o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Carbon monoxide is a queer duck. It is THE MOST STABLE molecule at high temperatures. However, at low temperatures (below ~700C as the flame gas cools) it disproportionates to carbon and CO2. <o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal> 2CO ===> C(soot) + CO2<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>This is known as the Reverse Boudouard reaction. However, it takes a while for the soot to form. <o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>The same thing is true if you look very closely at a candle flame.<o:p></o:p></p></div><div><p class=MsoNormal><><><><o:p> </o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>I started to answer your question this morning, but did not have a good answer. When I returned to the question in the afternoon my subconscious must have accessed "Reverse Boudouard". Funny how the mind works. <o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Your flame chemist, <o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Tom Reed <o:p></o:p></p></div><div><p class=MsoNormal><br>Thomas B Reed<span class=apple-style-span> </span><o:p></o:p></p><div><p class=MsoNormal><span class=apple-style-span>280 Hardwick Rd</span><o:p></o:p></p></div><div><p class=MsoNormal><span class=apple-style-span>Barre, MA 01005</span><o:p></o:p></p></div><div><p class=MsoNormal><span class=apple-style-span>508 353 7841</span><o:p></o:p></p></div></div></div></body></html>