<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML xmlns="http://www.w3.org/TR/REC-html40" xmlns:v =
"urn:schemas-microsoft-com:vml" xmlns:o =
"urn:schemas-microsoft-com:office:office" xmlns:w =
"urn:schemas-microsoft-com:office:word" xmlns:x =
"urn:schemas-microsoft-com:office:excel" xmlns:m =
"http://schemas.microsoft.com/office/2004/12/omml"><HEAD>
<META content="text/html; charset=iso-8859-7" http-equiv=Content-Type>
<META name=GENERATOR content="MSHTML 8.00.6001.23487">
<STYLE>@font-face {
font-family: Cambria Math;
}
@font-face {
font-family: Calibri;
}
@page WordSection1 {size: 612.0pt 792.0pt; margin: 72.0pt 72.0pt 72.0pt 72.0pt; }
P.MsoNormal {
MARGIN: 0mm 0mm 0pt; FONT-FAMILY: "Times New Roman","serif"; FONT-SIZE: 12pt
}
LI.MsoNormal {
MARGIN: 0mm 0mm 0pt; FONT-FAMILY: "Times New Roman","serif"; FONT-SIZE: 12pt
}
DIV.MsoNormal {
MARGIN: 0mm 0mm 0pt; FONT-FAMILY: "Times New Roman","serif"; FONT-SIZE: 12pt
}
A:link {
COLOR: blue; TEXT-DECORATION: underline; mso-style-priority: 99
}
SPAN.MsoHyperlink {
COLOR: blue; TEXT-DECORATION: underline; mso-style-priority: 99
}
A:visited {
COLOR: purple; TEXT-DECORATION: underline; mso-style-priority: 99
}
SPAN.MsoHyperlinkFollowed {
COLOR: purple; TEXT-DECORATION: underline; mso-style-priority: 99
}
SPAN.hoenzb {
mso-style-name: hoenzb
}
SPAN.EmailStyle18 {
FONT-FAMILY: "Calibri","sans-serif"; COLOR: #1f497d; mso-style-type: personal-reply
}
.MsoChpDefault {
FONT-FAMILY: "Calibri","sans-serif"; mso-fareast-language: EN-US; mso-style-type: export-only
}
DIV.WordSection1 {
page: WordSection1
}
</STYLE>
<!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]--></HEAD>
<BODY lang=EN-CA link=blue bgColor=#ffffff vLink=purple>
<DIV><FONT size=2 face=Arial>Dear Chrispin</FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial>Thank you for the edifying comparison and
explanation on refractory issues. Dr Goreau advise he believes biorock
</FONT></DIV>
<DIV><FONT size=2 face=Arial>would not work in an internal stove application,
unless we want to make quick lime or use with betel nut. However a
mesh</FONT></DIV>
<DIV><FONT size=2 face=Arial>or wire frame for the external housing might
work. </FONT></DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV>----- Original Message ----- </DIV>
<BLOCKQUOTE
style="BORDER-LEFT: #000000 2px solid; PADDING-LEFT: 5px; PADDING-RIGHT: 0px; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px"
dir=ltr>
<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> Saturday, June 01, 2013 5:18
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: [Stoves] stoves by the
millions</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
Paul O<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">You
have given another good example of the difference between a refractory
material (which means it can withstand very high temperatures) and a material
designed to resist thermal shock. High temperature shock resistance is not
synonymous with ‘refractory’. The word ‘refractory’ is often used incorrectly
in stove discussion. Stoves do not necessarily benefit from having a
refractory rating on the combustion chamber.<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">Stove
combustion chambers must resist rapid temperature changes in a short period of
time at a moderate temperature (600-1000° C). Industrial ceramics designed for
refractory applications often have a very slow heating rate, particularly when
fired for the first time.<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">When
a refractory material is capable of doing both jobs (unusual) and it is new,
it usually has to be fired at a very low rate – taking from 1 to 2 days to
reach max temperature when initially commissioned. This to remove moisture and
in some cases, to do a final firing. Castable ceramics are all in this
category (the ones I have seen, anyway). They have to breathe out the crystal
water otherwise steam pockets break through the material.</SPAN><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; FONT-SIZE: 11pt"
lang=EN-US><o:p></o:p></SPAN></P>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt">There
is a paper on the ProBEC website explaining why ceramic parts crack and what
to do about it.<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt">Stress
and Strain: <o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt">A
Rocket type-stove has all the air coming from one side and this drives the
flame against the back all of the combustion tube. This is about the most
demanding possible arrangement as the temperature of the flame varies rapidly
and frequently applying large internal stresses on the material particularly
on the top 1mm which flakes off, even if the body does not crack (though
usually it does).<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt">In
order to minimise this effect, you can bring the air from both sides (as one
list member has done recently with a distillation device) to counter each
other and keep the flame in the centre. Xavier was also experimenting with
this layout in Benin and was successful in bring the ceramic failure problem
under control (right Xavier?).<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt">Of
critical importance when creating a ceramic for stove combustion chambers is a
low thermal expansion rate and a strong suppression of the silica transition
from á to â phase at 573 degrees.<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt">The
wall temperature can easily exceed 573° C but does not often reach 1200 so the
challenge is not a refractory one but an expansion issue. If a simple clay
body is hot on one side and cool on the other (insulating) is it very likely
to fail catastrophically after a few cycles.<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt">Regards<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt">Crispin<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p> </o:p></SPAN></P>
<DIV>
<DIV>
<DIV>
<P style="MARGIN-BOTTOM: 12pt" class=MsoNormal>Art,<o:p></o:p></P></DIV>
<P style="MARGIN-BOTTOM: 12pt" class=MsoNormal>Not long ago I made reactor
using refractory ceramic pipe. This pipe is designed to handle molten metal
and is supposed to withstand temperatures up to 1,750 C. In less than two
minutes into a TLUD burn with rice hulls, it cracked. It is hard to imagine
that a reef-formed reactor will last very long.<o:p></o:p></P></DIV>
<P class=MsoNormal>Paul Olivier<o:p></o:p></P></DIV></DIV>
<P>
<HR>
<P></P>_______________________________________________<BR>Stoves mailing
list<BR><BR>to Send a Message to the list, use the email
address<BR>stoves@lists.bioenergylists.org<BR><BR>to UNSUBSCRIBE or Change
your List Settings use the web
page<BR>http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org<BR><BR>for
more Biomass Cooking Stoves, News and Information see our web
site:<BR>http://stoves.bioenergylists.org/<BR><BR>
<P>
<HR>
<P></P><A></A>
<P align=left color="#000000" avgcert??>No virus found in this
message.<BR>Checked by AVG - <A
href="http://www.avg.com">www.avg.com</A><BR>Version: 2013.0.2904 / Virus
Database: 3184/6368 - Release Date: 05/29/13</P></BLOCKQUOTE></BODY></HTML>