KilnProbe Story and the
Wood firing
Philippe Langlois <philippelanglois@free.fr>
The Idea
The idea for the KilnProbe came to me when Francois Eve told me about
his huge wood firing project, a kiln of a 100 cubic meters which took Francois,
Gaelle and Linda three years to prepare.
I thought to myself "Wow, that would be great to show on the Internet and
have realtime temperature data with graphics available there!"
It became more reallistic when Alain Regnier built a special device from
a pyrometer.
That device would commute at command between the two temperature probe,
and send the result to a computer. The idea was taking shape.
The technology
The computer in charge of taking temperature measurements every 10 seconds
from each probe is setup on an old Pentium 200 MMX box running Windows 98.
The collecting program was developped in Visual Basic to retrieve the data
from the serial port.
The graphing and Internet gateway is setup on my Linux laptop. It runs
Apache, RRD Tools (which is a generalization of MRTG), rrdexplorer, rrdcgi,
PHP4 and a variety of custom made scripts to generate and archive these
precious data. The upload is then done using lftp on our hosting server.
The network on the site is constructed with a 10/100 Mbit/s ethernet switch,
in order to enable easy and fast communication between computers.
The temperature probes themselves are 20 meter long K-couple (Chromel -
Alumel) thermocouples. They are linked to a microcontroller-based meter made
by Alain Regnier.
The story during the firing
Here, I'll try to sum up the events of the wood firing and the KilnProbe
project.
Saturday 20th of september
First time we meet with Alain, we've been working on the project remotely
and only knew our voice and email styles. We set up the different computers,
switch, thermocouples probes, converters etc...
Francois and Linda fire up the kiln around 19:00 (7 PM). It's the "bassinage"
(pre-firing) and the goal is to chase the humidity from the kiln and the
pots. The peep holes of the chimney (the "tetin") are closed with a brick
during this time to keep the heat in the kiln and prevent "hot pathways".
The goal is to keep the heat inside the kiln, that it goes everywhere in the
pots piles.
We had a little apero to celebrate the event.
The KilnProbe live experiment starts this afternoon!
No graph yet, but we can see the temperature on the computer.
Sunday 21st of september
Real nice <g> graphics star to show today. Yeah!*^$@($@&*(
Legend: September, Sunday 21st and Monday 22nd.
The green curve "cheminee" [###] represents
the heat in the back of the kiln, one meter from the chimney. The probe
is placed in the middle of a pile of pots. It reflects the temperature inside
the kiln load, at the coldest spot of the kiln.
The red curve "alandier" [###] represents
the heat in the firebox.
All temperature are in Celsius Degrees.
On this graph, you can see the impact of the warm weather of the afternoon
on the "cheminee" [###] curve. In the evening,
the atmospheric temperature cooled down and so the temperature inside
the kiln did also.
We noticed with Linda that the speed of the air in the chimney was much
more intense in the afternoon (17:00, 5 PM) than at noon time (12:00, 12 AM).
Francois explained that there was an intense "tirage" (draft) for this very
early period of the bassinage, and that meant that a lot of air was going
in the kiln, including cold air.
He suggested to reduce the entry of air by removing the bricks from under
the logs so that no air would flow around them. So we blocked the entry of
air in front of the burning logs with bricks, and lowered the logs on to the
coals.
You can notice on the previous and following graphs that this way of placing
the logs has an effect on the temperature inside the kiln. The temperature
read by the "cheminee" [###] curve is increasing
at 01:00 (1 AM) monday morning. This cannot come from the atmospheric temperature
outside.
Monday 22nd of september
The "bassinage" firing at this point is concentrated on getting the temperature
up inside the kiln load. The curve to watch for this is the "cheminee"
[###] curve indicated the temperature of the
pots which will be the hardest to heat.
The temperature in the alandier [###] must
not cross the 100 Celsius degrees because water would then boil in the pots
and then the pots would explode. Neither the "cheminee" [###] curve should cross 100 Celsius but it's highly
unlikely ;-)
Legend: Night from September, Sunday 21st to Monday 22nd.
During this night between sunday and monday, the laptop harddrive got filled
up and I started to look for an alternative so that a tower computer sit
there, dedicated to making the graphs and pushing content to the Internet.
You can see during this night that new wood was placed in the firebox around
midnight and around 03:00 and left there to burn without touching.
The effect of the human activity constantly touching the burning wood is
noticeable starting at 08:00 this morning as you can see the spike happening
much more than during the night, with no effect on the "cheminee" [###] curve.
Around 13:00, the weather started to turn to rain. And the wind before the
rain started. The flames were boosted quite a bit by this wind and the temperature
in the alandier [###] "clicked" twice over
100 degree Celsius between 13:00 and 14:00.
The temperature of the "cheminee" [###] grows
steadily, reaching 25 degrees Celsius, maybe due to the warmth of the day
(which is less warm than sunday).
Tuesday 23rd of september
It rained this morning and the air temperature dropped, so did the temperature
inside the kiln.
We are a little bit worried about the variation of temperature inside the
kiln ("cheminee" is "probe2", here on this special graph). I suggested the
idea to put hay in the rose holes in the chimney, at the back of the kiln.
Linda corrected that by the fact we want to have the kiln open somewhere
for the humidity to come out. She also wants to block the top holes so that
no draft is coming there.
The difficulty here comes with the chimney that is being built to reinforce
the back of the kiln. It will prevent us from accessing the bricks there,
removing or adding them if needed. So we need to foresee what needs to be
done on the chimney before finishing the back wall.
Wednesday 24th of september
Last night, it was really cold and the outside temperature dropped a lot.
We are trying to check if the probe at the back of the kiln (chimney probe)
is working.
Either it's not working or it's so deep in the pot piles that it doesn't
register any temperature change because the heat is going around the pots.