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</o:shapelayout></xml><![endif]--></head><body bgcolor=white lang=EN-CA link="#0563C1" vlink="#954F72"><div class=WordSection1><p class=MsoNormal><span style='color:#1F497D'>Dear Alex<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Very good question and complex to answer so I will have to put down some rules.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Let’s define ignition as the first 30 minutes and the pyrolysed state (poorly defined) as the second important point in the measurement.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>The 30 minute window is the time taken to get the thing lit well and running at an even power level. <o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Let’s take the traditional stove as the baseline. These pics are quite high resolution so you can zoom them.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-CA'><img width=567 height=254 id="Picture_x0020_1" src="cid:image002.jpg@01CEDC57.6BB93B50"></span><span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>The purple line is the burn rate so when it stabilises at a constant rate (straight, angled line) the power level is constant. <o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>The yellow line shows the accumulated PM to that point. So after 30 minutes it has not quite stabilised but is at 35 minutes. It does not last long before the burn rate starts to drop. This is typical of the product. </span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>The initial smoke for 7 minutes is the wood lighting with maybe or maybe not a couple of pieces of coal being affected. The huge blast of PM is the coal being put on top of the wood fire (roasting it) or else it is being lit crossdraft meaning the fire is hitting a pile of coal next to it. This is the main portion of the total PM.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>After it gets going, there is very little smoke. The second ‘puff’ is the refuelling of a hot stove at 70 minutes. It has a much shorter stabilisation time and a similar burn rate profile. <o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>I would say that the ignition is responsible for more than 90% of total emissions, if you include refuelling. <o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Now let’s look at a clean igniting stove (this is not a TLUD).<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-CA'><img width=567 height=292 id="Picture_x0020_2" src="cid:image005.jpg@01CEDC57.6BB93B50"></span><span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>First note that the vertical scale is not quite the same.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>This is a crossdraft stove with a hopper. The wood ignition can be seen starting at minute 4 then dropping to nearly zero then the coal starts and is burning very well by minute 25. The burn rate is constant by 30 minutes indicating that the fire is established and constant. At minute 78 when the traditional stove needed refuelling, it was only necessary to shake the grate which made the spike in PM (ash, maybe a little BC).<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>This particular stove went through 6 more iterations until the smoke was pretty much undetectable after 12 minutes. I would say that the ignition period was responsible for more than 95% of total emissions.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Finally a TLUD (I have to hide the product name in this case) :<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-CA'><img width=566 height=248 id="Picture_x0020_3" src="cid:image009.jpg@01CEDC57.6BB93B50"></span><span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>First note that the reported emissions rate is per net MJ, not per MJ as is the case in the older tests above. <o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>The ignition goes well with the wood (almost always larch or in some cases pine). There is some smoke as the coal lights on top, largely due to the cold combustion chamber and an excess of air in the chamber. <o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>The increase in smoke at 55 minutes is not caused by someone fiddling or refuelling. It is a problem found with many TLUD’s that are created without adequate testing. There is a lot of heat generated in the combustion chamber and the primary air supply is not controlled well enough to limit the power adequately. It heats the stove body and chamber (cast iron typically) so much that at some point the pyrolysation rate exceeds the available air supply. This took 55 minutes with this stove. As the gas production rate starts to overwhelm the air supply combustion quality deteriorates and it starts to make more smoke than it did during ignition. This is a common problem and nearly no one is listening to us so we are starting a stove design training centre to bring real time measurements to the attention of the producers.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>I would say that in the case of TLUD’s the major part of the emissions comes when the pyrolysation reasons the bottom of the pile and it flashes the remaining volatiles into gas over a 15 minute period. The effect is common in all TLUD’s that burn to the bottom. There is no new raw fuel below to cool the hot zone with new moisture. So it becomes in effect a self-heating retort with thermal runaway.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Only a few TLUD’s have proper and controllable secondary air. Some have it but it is not preheated. The TLUD’s with a cold supply of air at the top blowing across the top of the chamber have the worst results of those with secondary air. There is still a chance that the effect above will emerge. The problem at root is a runaway pyrolysation effect caused by trying to have the fuel be part of the air control system. If the fuel is not exactly right there will inevitably be negative consequences. In other words the stoves are too simple to work properly except in ‘certain circumstances’. The call to chip fuel to a particular size and density is in part to keep the stove simple. It is OK if you can organise it.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>So what does a really clean lighting stove look like?<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>This is again a cross draft stove with a hopper:<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='mso-fareast-language:EN-CA'><img width=567 height=291 id="Picture_x0020_4" src="cid:image012.jpg@01CEDC57.6BB93B50"></span><span style='color:#1F497D'><o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>This is the result of 18 months of work on ignition and fuel feeding processes. It has a small amount of wood in the combustion chamber that is lit on top to get the initial smoke out of the way and then it lights to the side and runs constantly thereafter. It can be refuelled at will without consequences and in fact this stove was refuelled. You can’t see where. The change in power was caused by shaking the grate.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>It is with some annoyance that I see these stoves were specifically excluded from the Berkeley comparative assessment of stoves they wrote for the GACC on the excuse that people should not burn coal (which is what is says in the introduction). There is a whole group of stoves which would all sit in the bottom left corner of the stove performance chart deep into the Tier 4 section – cleaner than anything burning wood. In fact some of these stoves can burn wood very well too. <o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>The final example (remembering to correct for the different metrics) is 1293 times cleaner than the baseline for a +99.9% reduction in PM2.5. That is something to be praised, not hidden. What is the problem with letting people know that coal can be burned <i>this</i> cleanly? A modern power station cannot deliver electric heating and match the PM or CO numbers per net MJ. Those producing stoves of this calibre are in Turkey, Mongolia and China. There is a Japanese stove I have not seen which may also be in this league.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Incidentally, all the best stoves (the four approved for subsidy this year, for example) produce no smoke after a certain time of running and starting removing ambient PM, meaning they have negative emissions for at least part of the time. The best ones, perhaps half, are able to scrub the air entering the stove completely of all particles even if the ambient air has 200 or more µg/m<sup>3</sup>. They literally clean the air to zero PM while burning wet lignite in a natural draft 10 kW fire. <o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>So far three types of combustors have achieved this: downdraft (BLDD), end-lit down-angled crossdraft (ELCD) and updraft (TLUD).<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Regards<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Crispin watching the early morning snowfall<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><div><p class=MsoNormal>Crispin,<br><br>This may be an affront to your technical cred, but if you could humour me with an educated guess, I have a question. How much of the improvement/reduction in emissions is due to 'top ignition', better start up and how much is due to improved steady state combustion?<br><br>Alex<br><br><br><o:p></o:p></p></div><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Times New Roman","serif";mso-fareast-language:EN-CA'><o:p> </o:p></span></p></div></body></html>