Dear Ron
>>“For those not having experience with TLUDs, Dean's reference to "no primary >>air can make it up", means that the oxygen is "entirely" used to produce >>carbon monoxide.” … >>It is really rare to find a normalised CO emissions factor (not concentration >>in the emerging gases) above 100,000 ppm. I have only see it once and I work >>with some of the wildest devices the imagination has produced. > [RWL: This part I don't understand. Neither Dean or I were talking > about anything other than primary air. I see that you did not follow. I am sure is it my method of describing it. Here is a short version: You can’t get pure CO from biomass pyrolysis for inherent chemical reasons. Proof that I offer: I have measured CO production across a wide range of conditions and it is almost impossible to get more than 10% CO even when it is theoretically possible (from the elemental composition) to get 40%. >>CO(ppm) * (EA+100%) = CO(EF) at O2=0% (the O2 is factored out). > [RWL3: The subject of excess air for testing the completeness of > combustion (after adding secondary air and releasing the majority of the > energy) is extraneous to the sentence under discussion.] That is how to work out what the CO level is, in ppm. 100,000 ppm is 10%. >>I mention this to support my conclusion that the O2 tends to create ‘fuel >>moisture’ very easily. >I have personally measured the gases coming up through the fuel bed in a TLUD >(a borrowed high quality tool) and the dominant gas was CO (many millions of >ppm). That is impossible. 1 million parts per million is 100% CO. >> RWL4: My main concern is with Crispin's above next-to-last sentence: "I >> am expressing doubts that level could be created in a TLUD that was not >> first run as a regular fire. The word "TLUD" should say to all that the test operation was NOT run as a regular fire. They are as near to polar opposites as the stove world can get. So this is to ask Crispin what he is saying here and what part of my response he is objecting to? I am offering a method of how to get a CO content as high as 10%. Start a regular fire, get it going well, then enclose it in a vessel while hot and running. This can produce 10% CO, but a TLUD cannot. That is my contention. Biomass needs just a little more air (Oxygen) to completely use up the H2 and then breathe in whatever additional air would burn all the Carbon. In any real file, some of the C becomes CO and CO2 (surface reactions mentioned by Dr Tom Reed in a previous discussion). >> [RWL: I hope we can get a specific citation for/from Tom here. He addressed it directly previously on two occasions. >At the hot surface from which (very complicated and numerous [1000's of >species??]) pyrolysis gases are emerging, my understanding of the pyrolysis >surface effect literature is that "all" (given control of the incoming oxygen >flow) are turned into CO and water. My point is that if there is NO air entering, virtually all the O2 in the fuel is turned into water. The great proportion. Some of the H2 is left in the gas but is it hard to find an H2(EF) of 15,000 (1.5%). I have no problem with others contradicting this with real measurements. >>The relatively small amount of CO2 that is produced near the surface (not ON) >>is converted back to CO as it interacts with the hot char above it This only happens under certain conditions and not when it is cool. Dr Tom was mentioning C=> CO2 reactions taking place above 400 C on the surface. CO can also be formed, and volatiles (which contain carbon) can break down into CO as well. The CO in the gas is not necessarily produced from CO2 and is unlikely if the temperature is low because it has to absorb a lot of heat to do so (24 MJ/kg). > So I repeat - I am mystified by this message and about what is at dispute. I am not sure there is a dispute. Perhaps the clarification will suffice. Regards Crispin
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