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<DIV><FONT size=2 face=Arial>Dear Crispin</FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial>Excellent presentation and analysis!</FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial>Your point about over-firing, and not knowing when
to turn down the damper is a good one. </FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial>Would a simple bimetal magnetic stack thermometer
be able to tell you the temperature of stack gases, so that the Operator could
turn down the damper to maintain the stack temperature to the temperature
observed at minute 35, where maximum efficiency occurs?</FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial>Best wishes,</FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial>Kevin</FONT></DIV>
<BLOCKQUOTE
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dir=ltr>
<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> Monday, November 01, 2010 12:04
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: [Stoves] Chimneys</DIV>
<DIV><BR></DIV>
<DIV class=WordSection1>
<P class=MsoNormal><SPAN style="COLOR: #1f497d">Dear
Joyce<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">There are two answers to your
question. The first is that CO is not all that big a problem for most people.
Yes it is a problem in certain places, Johannesburg and the col burning
Highveld regions for example, but smoke exposure is a much larger concern in
my experience.<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 second is that chimneys
are relative expensive. If you put a chimney on a stove that is not very clean
burning, it quickly gets clogged and is a maintenance problem. An
example of this is the stoves made from clay and sand in Kenya. In the high
regions (tea estates especially) there are ‘fuel efficient stoves’ promoted by
the tea estate corporations as a beneficial idea. They have chimneys but are
pretty dreadful is terms of combustion efficiency. In as little as 3 months a
3 inch diameter chimney gets clogged with condensed, boiled biomass vapours.
The stove have chimneys but don’t really save much fuel and waste a great deal
of it by simply not burning the gases. <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 chimney are not as easy to
work with as one would hope. Cleaning up the combustion is actually the most
important if there is nearly zero money in the community.
<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">Chimney stoves, in answer to
your question about the effect of putting on a chimney, have to have pretty
good air control or they are not very efficient.<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">Attached is a chart of a coal
stove with a chimney attached, and no flue damper to control the draft. There
is really no way for anyone to know how and when to close or partially close a
damper for optimum efficiency. This is the result of an open chimney attached
to a fairly large fire. The peak burning rate can be seen by looking for the
steepest portion of the brown line. That is the mass burned during the
operation.<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">As you can see the initial
burn rate is low so the line is nearly horizontal, then it gets going like
crazy to about 16 kW. Then the coal runs out and the burn rate slows. Then it
is refuelled with a sharp jump up which tapers off in the end after about 200
minutes.<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 thermal efficiency is the
green lines, The darker one that moves up and down is the instantaneous
efficiency calculated from the temperature of the gases in the chimney and the
excess air at the time. The smoother green line is the cumulative efficiency,
meaning how things have gone so far, all things considered. Two features are
noticeable. The first is that it is pretty constant at about 65% efficient
when the fire is large and burning at a high rate. The second is that as the
fire dies down, the thermal efficiency drops to zero and in fact goes
negative. Because it is negative (the fire is actually cooling the room by
throwing more heat up the chimney than it is generating) the average for the
whole burn drops from 60% at minute 100 to 33% at minute 200. That is amazing,
eh?<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 putting on a chimney does
not guarantee overall success. The main reason for the poor performance is
excessive draft – there is simply too much air getting into the stove,
allowing it to operate at a high power level – too high to be useful actually.
This is followed by a period when the stove cools the home drawing, as it
does, about 50 cubic metres of -35 degree C air into the house to feed the
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, chimneys make things a lot
more complicated providing expected results and additional expense. The
expense is not just for the chimney which might cost $5, but also for a stove
that is air tight enough to control the combustion reasonably and now waste
fuel.<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">Best
regards<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="COLOR: #1f497d">Crispin<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><o:p> </o:p></P>
<P class=MsoNormal><SPAN lang=EN-US>Why is no one talking about chimneys that
get rid of the CO safely? And doesn’t the addition of a chimney change the
dynamics of any stove?<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN lang=EN-US><o:p> </o:p></SPAN></P>
<P class=MsoNormal><B><I><SPAN
style="FONT-FAMILY: 'Arial','sans-serif'; FONT-SIZE: 9pt" lang=EN-US>Joyce M
Lockard<o:p></o:p></SPAN></I></B></P>
<P class=MsoNormal><I><U><SPAN style="FONT-SIZE: 9pt" lang=EN-US><A
href="mailto:rj.lockard@frontier.com">rj.lockard@frontier.com</A><o:p></o:p></SPAN></U></I></P>
<P class=MsoNormal><SPAN style="FONT-SIZE: 9pt" lang=EN-US>503-533-4190
Home<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="FONT-SIZE: 9pt" lang=EN-US>503-201-9548
Cell<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN style="FONT-SIZE: 9pt" lang=EN-US>503-533-4209
Fax<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN lang=EN-US><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN lang=EN-US><o:p> </o:p></SPAN></P></DIV>
<P>
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