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<DIV><FONT face=Arial>Dear Crispin</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<BLOCKQUOTE
style="BORDER-LEFT: #000000 2px solid; PADDING-LEFT: 5px; PADDING-RIGHT: 0px; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="FONT: 10pt arial; BACKGROUND: #e4e4e4; font-color: black"><B>From:</B>
<A title=crispinpigott@gmail.com href="mailto:crispinpigott@gmail.com">Crispin
Pemberton-Pigott</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A
title=stoves@lists.bioenergylists.org
href="mailto:stoves@lists.bioenergylists.org">'Discussion of biomass cooking
stoves'</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Tuesday, February 26, 2013 5:57
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: [Stoves] combustion of char
-- spontaneous and dangerous</DIV>
<DIV><BR></DIV>
<DIV class=WordSection1>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US">Dear
Kevin<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US">Wow.
Well I had not considered either of those two. What is perhaps the logical
approach is to look at the processes that could account for 100 g of
gain.</SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US"></SPAN> </P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US"><STRONG>#
Firstly, I can't see the weight gain, in that the weight at 2815 is virtually
identical to the weight at 6567, as shown on your previous chart. However, the
range of your scale seems to be from 0 to at least 100 kilograms. 100
grams in 100 kilograms = 1 in a thousand = 0.1%. It may be a question of
electronic precision being significantly more than the mechanical accuracy of
the scale.</STRONG></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US">You
can take it that the initial fire was with 5 kg of coal and then a reload with
4.6 = 9.6 kg of coal, 25% moisture, roughly 10% ash. From that we could
calculate the missing fraction of fuel mass which would be most of the non-ash
portion. I can’t see there being enough carbon left to pick up that much
O<SUB>2</SUB>.</SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US"></SPAN> </P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US"><STRONG>#
With 10% Ash, the ash would be about 1 kg. A weight change of 100 grams would
thus be about 10% CaCO3 is 44% CaO, and 56% CO2. The addition of the CO2 to
CaO roughly doubles its weight. To get a 100 gram weight gain, one would need
roughly 100 grams of "free" CaO in the ash. This would be roughly 10% CaO, or
roughly 20% limestone in the final ash. Free lime in that quantity is
unlikely, in that it would most likely be tied up with other reactive ash
components, such as Feo, Sio2, and Al2O3. Equally, it is unlikely that
the3re would be free FeO, in that it is very reactive to silica.
</STRONG></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US">There
is no doubt that the reversal idea is not correct because there is a
temperature record and the interior air temperature remained well above the
outdoor temperature (the building is heated).</SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US"></SPAN> </P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US"><STRONG>#
If these reactions jhad occurred, then it is likely that there would be a bump
in ash temperature, in that these slagging reactions are exothermic.
Note that these reactions, if they were present, are independent of room
temoperature.... Lime calcines at about 897 C, and Fe3O4 is formed when FeO
drops below about 680C in the presence of oxygen. I can't see any "roughness"
in any of the other lines, at the time of the "weight gains", so this seems to
confirm it is not an oxidation effect.</STRONG></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US"><STRONG></STRONG></SPAN> </P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US"><STRONG>#
Yet another possibility is that your "Heavy stove + sensitive scale" was
actually functioning as a seismograph.... is it possible that there might be a
quarry nearby doing blasting, or heavy trucks or trains going down their
respective roads?</STRONG></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US"><STRONG></STRONG></SPAN> </P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US"><STRONG>Best
wishes,</STRONG></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US"><STRONG></STRONG></SPAN> </P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US"><STRONG>Kevin</STRONG></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US">Here
is the set of temperatures with the Mass, test date 12 Jan
2010:<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><IMG id=Picture_x0020_1
src="cid:B27FB08E3A3F4FCFB6315C2CE6ED9D60@usera594fda0bf" width=680
height=319><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US"><o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US">You
can save and stretch that. The 1 deg rise in temperature to -12.5° as the sun
comes up is visible at the end. The temperature in the stove is slightly
higher than the air in the room. The mass curve is generally the same shape as
the charts by Battacharyya for coal (with a different time scale – but
remember this is coke).<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US">It
was hardly an ideal set of measurements. We were just looking to see the
cooling. The thermal efficiency of the stoves drops to -250% at times because
it pulls in more cold air than it generates as heat – the fire just acts as a
fan to throw heat from the room up the chimney.<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US">I
am still prepared to write off the mass change as an instrument artifact –
wind or something but it is a curious phenomenon to
consider.<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US">Regards<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US">Crispin<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><o:p> </o:p></P>
<DIV>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Arial','sans-serif'; COLOR: windowtext">Dear
Crispin</SPAN><SPAN style="COLOR: windowtext"><o:p></o:p></SPAN></P></DIV>
<DIV>
<P class=MsoNormal><SPAN
style="COLOR: windowtext"> <o:p></o:p></SPAN></P></DIV>
<DIV>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Arial','sans-serif'; COLOR: windowtext">I can think of
two possibilities for the possible weight gain:</SPAN><SPAN
style="COLOR: windowtext"><o:p></o:p></SPAN></P></DIV>
<DIV>
<P class=MsoNormal><SPAN
style="COLOR: windowtext"> <o:p></o:p></SPAN></P></DIV>
<DIV>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Arial','sans-serif'; COLOR: windowtext">1: If there was
backdraft, as a result of the windy conditions, it might be possible that
particles of char or creosote fell from the chimney, or were blown back, to
the stove system, creating an increase in weight of the stove system. This
material then burned off. Note that the weight at about 2815 is the same as at
the very end of the chart, where the red line continues past 6567</SPAN><SPAN
style="COLOR: windowtext"><o:p></o:p></SPAN></P></DIV>
<DIV>
<P class=MsoNormal><SPAN
style="COLOR: windowtext"> <o:p></o:p></SPAN></P></DIV>
<DIV>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Arial','sans-serif'; COLOR: windowtext">2: The oxygen
that was picked up would be not only as oxygen, but as CO2. What might have
happened is that is that the ash, containing FeO could easily pick up oxygen
and become oxidized to Fe3O4, and limestone components in the ash could have
been calcined to CaO, which could easily react with CO2 from the atmosphere,
to "airslake" back to CaCO3. The "jiggle in the weight" may be a result of
"local fire" re-calcining" the lime fraction, or "re-reducing the iron
components.</SPAN><SPAN style="COLOR: windowtext"><o:p></o:p></SPAN></P></DIV>
<DIV>
<P class=MsoNormal><SPAN
style="COLOR: windowtext"> <o:p></o:p></SPAN></P></DIV>
<DIV>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Arial','sans-serif'; COLOR: windowtext">Any likelihood
that either of these guesses might be accurate?</SPAN><SPAN
style="COLOR: windowtext"><o:p></o:p></SPAN></P></DIV>
<DIV>
<P class=MsoNormal><SPAN
style="COLOR: windowtext"> <o:p></o:p></SPAN></P></DIV>
<DIV>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Arial','sans-serif'; COLOR: windowtext">Best
wishes,</SPAN><SPAN style="COLOR: windowtext"><o:p></o:p></SPAN></P></DIV>
<DIV>
<P class=MsoNormal><SPAN
style="COLOR: windowtext"> <o:p></o:p></SPAN></P></DIV>
<DIV>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Arial','sans-serif'; COLOR: windowtext">Kevin</SPAN><SPAN
style="COLOR: windowtext"><o:p></o:p></SPAN></P></DIV></DIV>
<P>
<HR>
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