Hank Murrow on thu 17 nov 05
On Nov 17, 2005, at 12:27 PM, Jennifer Boyer wrote:
> Hi Hank,
> Can you describe how the water is added to the kiln? Is it like Jeff
> Oestreich's method, using a gardening water sprayer like those used to
> apply pesticide to apple orchards?
During my MFA work in the middle 60s, I was adding water to the plates
of my oil fired kiln. Perhaps 5 gallons over a two hour period. The
soda kiln at ACC required a sprayer as you describe. both worked well.
> Would it work without soda, just water? I have one cold spot in my
> kiln: typical bottom back.
Yes, and placing a broken kiln shelf leaning up against but out from
the flue opening will help too. makes the gases go around the shelf to
get out the flue.
Cheers, Hank in Seattle after a day of set up in the Gallery
www.murrow.biz/hank
Fredrick Paget on thu 17 nov 05
Tony,
The explanation is simple enough: If you blow steam through a bed of
hot coals it comes out the other side as a mixture of hydrogen and
carbon monoxide. BOTH WILL BURN.
Before natural gas was brought into use back in the 1930's they made
gas that way. It uses up the coals and any sooty smoke that is in
the kiln and converts it into gas. The other side of this is that the
reaction soaks up heat energy from the coals so you can't go too far
with it or the reaction stops. The gas plants used to have two units
going and switch from one to the other and blow air into the cooling
one to get the heat back up.
Yes, they were burning coal and were polluters. There is a 2 block
square site where one of these gas plants stood in San Rafael,
California, near here, and it is a toxic waste site. They finally
paved it over as a parking lot. The toxic effects came from the coal
and don't worry - your kiln won't become toxic.
I expect that we will be back to this kind of gas in another decade
or so when we run out of natural gas.
--
From Fred Paget,
Marin County, CA, USA
fredrick@well.com
Charter Member Potters Council
C + H2O-->H2+CO, ABSORBS HEAT
H2+O-->H2O, CO+O-->CO2 RELEASES HEAT
clennell on thu 17 nov 05
Pyro Gang : I need a an explanation to a half baked theory i have.
I had a firing where the front of the woodkiln was at Cone 10 (1300C on the
pyro) and I needed to bring the back up to temperature. I opted to throw
green wet wood into the firebox while I side stoked the back. to my
amazement the front kept going up to around 1375. I had to start putting
bigger and bigger pieces in to slow the damn thing down.
I wrote John Neeley about this suggesting that I was getting heat from
water. He referred me to the water gas reaction. It is too big for my brain
still.
Mel mentioned a chinese guy throwing a balloon of water in the kiln and
almost decapitating himself- steam explosion.
has anyone any information that a half wit like myself can understand to
support my theory that the water in the wood released oxygen that made the
combustion more complete and the kiln gets so friggin hot.
Thanks for your collective brain power.
cheers,
Tony
Tony and Sheila Clennell
Sour Cherry Pottery
4545 King Street
Beamsville, Ontario
CANADA L0R 1B1
http://www.sourcherrypottery.com
http://www.sourcherrypottery.com/current_news/news_letter.html
Hank Murrow on thu 17 nov 05
On Nov 17, 2005, at 5:21 AM, clennell wrote:
> Pyro Gang : I need a an explanation to a half baked theory i have.
> I had a firing where the front of the woodkiln was at Cone 10 (1300C
> on the
> pyro) and I needed to bring the back up to temperature. I opted to
> throw
> green wet wood into the firebox while I side stoked the , I fired the
> cross draft soda kiln and was . to my
> amazement the front kept going up to around 1375. I had to start
> putting
> bigger and bigger pieces in to slow the damn thing down.
> I wrote John Neeley about this suggesting that I was getting heat from
> water. He referred me to the water gas reaction. It is too big for my
> brain
> still.
Dear Tony;
I don't really know if there is a boost in BTU from green wood, but I
do know that the absorption of energy at the firebox in turning the
water to steam, is given up at the rear of the chamber. It is an old
trick with cross draft kilns and long kilns. You get to Cone 12 at the
front, and cone 8 at the back.......add water, whether brine as in soda
fires, or wet wood as in your firing, and the heat is absorbed from the
firebox and given up at the other end. My terminal project at the U of
Oregon dealt with this phenomenon. Cross draft kiln that fired real
evenly after an application of brine. More recently, at Vince's beloved
ACC, I fired the cross draft soda kiln, and realized despite my best
efforts that the cone 12 was going down in the front, with 8 not going
in the bottom back. I hurriedly brined the kiln with 2.5 gallons of hot
water and 2000 grams of soda....... the result was really lovely soda
everywhere, and the cones at the end of the firing(an hour later) were
down to a 1.5 cone difference. Ain't fire grand......especially with a
little water!
Cheers, Hank, departing in ten minutes for a show at the Glenn Richards
Gallery in Seattle....opens Saturday from 6 to 9 pm.......... you
Seattleites be there. Lots of nice ware!
www.murrow.biz/hank
pdp1@EARTHLINK.NET on thu 17 nov 05
Hi Tony,
My guess would be that with a large enough contained mass and contents at
those temparatures, the amount of 'cooling' provided by the moisture of the
Green Wood, was simply absorbed by and overcome in the larger contribution
of Calories the Wood itself made, as Wood...especially if these pieces were
smallish.
At a much lower temperature, and or in a smaller Kiln as well, I would
expect Green Wood to have some cooling effect...
I do not believe this scenario has anything to do with a release of Oxygen
from the influence of heat on Water or moisture, to support combustion
processes.
So, in summary, I believe your temperature rose because you in effect, were
stoking the Kiln with smaller fast burning pieces of Wood, whose moisture
content offered less cooling than the fuel potential of the Wood itself
offered to increase the heat.
Did these make any sound when they went it?
Any muffled 'Booms'?
Lol...
Phil
Las Vegas
----- Original Message -----
From: "clennell"
> Pyro Gang : I need a an explanation to a half baked theory i have.
> I had a firing where the front of the woodkiln was at Cone 10 (1300C on
the
> pyro) and I needed to bring the back up to temperature. I opted to throw
> green wet wood into the firebox while I side stoked the back. to my
> amazement the front kept going up to around 1375. I had to start putting
> bigger and bigger pieces in to slow the damn thing down.
> I wrote John Neeley about this suggesting that I was getting heat from
> water. He referred me to the water gas reaction. It is too big for my
brain
> still.
> Mel mentioned a chinese guy throwing a balloon of water in the kiln and
> almost decapitating himself- steam explosion.
> has anyone any information that a half wit like myself can understand to
> support my theory that the water in the wood released oxygen that made the
> combustion more complete and the kiln gets so friggin hot.
> Thanks for your collective brain power.
> cheers,
> Tony
Jennifer Boyer on thu 17 nov 05
Hi Hank,
Can you describe how the water is added to the kiln? Is it like Jeff
Oestreich's method, using a gardening water sprayer like those used to
apply pesticide to apple orchards?
Would it work without soda, just water? I have one cold spot in my
kiln: typical bottom back.
Jennifer
On Nov 17, 2005, at 10:42 AM, Hank Murrow wrote:
> On Nov 17, 2005, at 5:21 AM, clennell wrote:
>
>> Pyro Gang : I need a an explanation to a half baked theory i have.
>> I had a firing where the front of the woodkiln was at Cone 10 (1300C
>> on the
>> pyro) and I needed to bring the back up to temperature. I opted to
>> throw
>> green wet wood into the firebox while I side stoked the , I fired the
>> cross draft soda kiln and was . to my
>> amazement the front kept going up to around 1375. I had to start
>> putting
>> bigger and bigger pieces in to slow the damn thing down.
>> I wrote John Neeley about this suggesting that I was getting heat from
>> water. He referred me to the water gas reaction. It is too big for my
>> brain
>> still.
>
> Dear Tony;
>
> I don't really know if there is a boost in BTU from green wood, but I
> do know that the absorption of energy at the firebox in turning the
> water to steam, is given up at the rear of the chamber.
> ************************
Jennifer Boyer
Thistle Hill Pottery
Montpelier, VT
http://thistlehillpottery.com
Mary & Wes on thu 17 nov 05
Air dried wood has 15% to 20% water in it and this requires roughly 33% of
the heat potential to vaporize. No heat gain there. It takes a much higher
temp to disassociate hydrogen and oxygen, if you could get the process to
work at a lower temp this an endothermic (takes heat) reaction, so no heat
gain there. But, let's assume that you do get free oxygen, what's it going
to burn? All that free hydrogen isn't going to go to waste and guess what
it's in the perfect ratio to burn completely, why go looking for carbon to
burn? So there would be no net gain of oxygen to speed up your wood
burning. A guess may be put forward by what Mel mentioned about the Chinese
gentleman, you are creating steam, this increases the pressure in the kiln
pushing more gases up the stack, maybe this acts like an increase in the
draft of kiln which draws more air in. Also, think about what happens to
the wood, I'll bet there was a lot of snap, crackle, pop coming from the
firebox, that's the wood being splintered as pockets of moisture inside the
wood are being vaporized. Smaller wood size translates to more surface area
for oxygen that is already there from the air inlets to burn the wood at a
faster rate. It's about BTU's per hour input that raises the temp in a
kiln, so if you were watching a pyrometer the temp should have gone down
more than normal during a normal stoke (water being boiled off) and then a
faster than normal heat rise from the now dry, splintered wood burning
faster.
The story that Mel told makes sense by the way, if you introduce 1 pint of
water into a 2400 degree kiln it's roughly equivalent to setting off 3
sticks of dynamite based on the expansion of water when converted to steam.
If you ever get the chance go to a power station and look how small the
steam inlet is in relation the backend of the turbine.
And as always I may be totally wrong about this, this is just my mind
wondering down strange paths.
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of clennell
Sent: Thursday, November 17, 2005 7:21 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Help fire bring me water!
Pyro Gang : I need a an explanation to a half baked theory i have.
I had a firing where the front of the woodkiln was at Cone 10 (1300C on the
pyro) and I needed to bring the back up to temperature. I opted to throw
green wet wood into the firebox while I side stoked the back. to my
amazement the front kept going up to around 1375. I had to start putting
bigger and bigger pieces in to slow the damn thing down.
I wrote John Neeley about this suggesting that I was getting heat from
water. He referred me to the water gas reaction. It is too big for my brain
still.
Mel mentioned a chinese guy throwing a balloon of water in the kiln and
almost decapitating himself- steam explosion.
has anyone any information that a half wit like myself can understand to
support my theory that the water in the wood released oxygen that made the
combustion more complete and the kiln gets so friggin hot.
Thanks for your collective brain power.
cheers,
Tony
Tony and Sheila Clennell
Sour Cherry Pottery
4545 King Street
Beamsville, Ontario
CANADA L0R 1B1
http://www.sourcherrypottery.com
http://www.sourcherrypottery.com/current_news/news_letter.html
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Lee Love on fri 18 nov 05
On 2005/11/18 8:55:12, mary.handrow@verizon.net wrote:
> It's about BTU's per hour input that raises the temp in a
> kiln, so if you were watching a pyrometer the temp should have gone down
> more than normal during a normal stoke (water being boiled off) and then a
> faster than normal heat rise from the now dry, splintered wood burning
> faster.
Actually, when I stoke wet wood, I get a large heat jump. Defies
common sense, doesn't it? Other people who wood fire have noticed the
same thing.
A big thing people always forget about wood kilns, is that
heat is made from fuel, plus oxygen. Folks, especially new to
stoking, think the more fuel you put in the firemouth, the more heat you
will get. This is not the case, especially in traditional kilns with
limited airflow.
I think what causes the heat jump, is that the water slows
and evens out the release of gasified fuel and this better matches the
amounts of oxygen in the kiln, making it fire more efficiently.
Part of the reason water helps even out the temp, is that
the increased backpressure forces the heat back. It is a way to add
backpressure without putting in more fuel than the oxygen can handle.
Wet wood will cause problems earlier in the firing, when you
are trying to get up to temp. That is why folks want seasoned
wood. But when you have the temperature rolling, then you can use wet
wood to modify the atmosphere.
--
Lee in Mashiko
"Where the spirit does not work with the hand, there is no art."
--Leonardo da Vinci
Bruce Girrell on fri 18 nov 05
Lee Love wrote:
> Actually, when I stoke wet wood, I get a large heat jump. Defies
> common sense, doesn't it? Other people who wood fire have noticed the
> same thing.
It wouldn't surprise anyone who has ever been in a sauna. When the water
goes on the rocks, it gets hot and it gets hot fast.
Since a sauna is a somewhat closed system and the heat rise takes place over
a fairly short period of time, it's pretty safe to say that there is no net
heat change in the system. Assuming no net heat change, the evaporation of
the water means that it got all of its energy from the sauna rocks. It takes
539 calories/gram to change water to steam. So the sauna rocks are cooled
down by an equal amount. The energy that the water has picked up is now free
to move about in the form of steam and it is capable of transferring its
energy to anything with which it comes into contact.
I see the sauna rocks as a major heat/energy reservoir that is fairly well
insulated because it is surrounded by air, an excellent insulator. Adding
the water to the rocks first transfers a significant portion of energy to
the water which expands and, as a gas, can move by convection to allow it to
transfer some of that energy to the sauna occupants.
I believe that a similar effect may occur in the wood kiln. The firebox
represents a huge energy store. Adding wet wood (or spraying a mist) would
transfer a significant amount of energy to the water and then that water
would move as a gas throughout the kiln, delivering some of the additional
energy to the kiln contents. There is no free lunch. The firebox would be
cooled by the amount of energy transferred to the water and that energy will
have to be replenished.
Less scientifically, I have always felt, but don't have a shred of evidence
to substantiate it, that water vapor is more efficient at conducting heat
than air. A damp, cool day feels colder than a dry, cool day of the same
temperature (more heat is being conducted away from your body), for example.
If this is true, then the addition of water to a kiln would have two
effects. One effect is to act as a transfer medium for stored heat from the
firebox and the second effect would be to improve heat transfer efficiency.
Bruce Girrell
in SNOWY northern Michigan where the lake effect machine is in high gear.
Ivor and Olive Lewis on sat 19 nov 05
Dear Tony,
Every time we go to or through the Clare Wine Region I have a bit of a =
giggle. We pass through Bungaree Station (Sheep farm). I call it "Indian =
Country". Sign point to a side track stating "Fire Water".
I seem to recall this is a discussion I have contributed to during the =
past five or six years on Clayart.
No ! ! It is not a half baked idea.
Yes, you can enhance your firings by using the "Water Gas Reaction" =
provided you have a Carbon Rich Fuel System, which wood firing is, and =
know how to exploit it without blowing up the kiln. It does take some =
understanding to utilise the Water Gas Reaction effectively but the =
elementary chemistry is that Steam at +1100=BA C reacts with free Carbon =
at +1100=BA C to give Pure Hydrogen and Pure Carbon Monoxide. Both of =
these are high calorific fuel gases. Both burn with High Flame =
Temperatures. The down side is that the energy has to come from =
somewhere so the white hot charcoal cools, the reaction stops and the =
fire goes out. My take is that you had the damper wide open keeping a =
good draft which would keep the coals above the critical temperature and =
also supply enough Oxygen to make the Carbon Monoxide and Hydrogen burn =
freely.
What's hard about Chemistry?
Enjoy your local reds. Good for the Heart.
All the best,
Ivor.
Steve Slatin on sat 19 nov 05
Bruce --
Somewhere in the back of my mind I remember doing
the numbers once for a similar reaction. The only
way you can figure out if you can conceivably gain
heat from this series of reactions is to count out
each and every one of the reactions, endothermic
and exothermic, and see if IN SUM there is an overall
gain or loss.
'Cracking' the water is endothermic, then free O2
and carbon can react with the Hydrogen yadda yadda --
the thermal absorbtion and production of each reaction
should be fairly easy to find, I have a weak
recollection
of finding what I needed all together in one book ...
a
red cover? An ancient 'rubber handbook?' I don't
have
one any more ...
Steve S
--- Bruce Girrell wrote:
> First off, let me say that I have no question that
> the water-gas reaction
> can and does occur. But I am not convinced that it
> is the primary
> explanation for the temperature rise described in
> this thread. Ivor rightly
> points out that the reaction requires a carbon rich
> fuel system and also
> rightly points out that to take advantage of the H2
> and CO produced,
> additional oxygen is required to burn it. With the
> overabundance of carbon,
> the kiln atmosphere should be a reduction
> atmosphere, leaving scarce oxygen
> to react with the H2 and CO.
Steve Slatin --
And I've seen it all, I've seen it all
Through the yellow windows of the evening train...
__________________________________
Yahoo! Mail - PC Magazine Editors' Choice 2005
http://mail.yahoo.com
Bruce Girrell on sat 19 nov 05
Ivor Lewis wrote:
>Yes, you can enhance your firings by using the "Water Gas Reaction"
>provided you have a Carbon Rich Fuel System, which wood firing is, ...
and also
>...a good draft ... would keep the coals above the critical temperature and
>also supply enough Oxygen to make the Carbon Monoxide and Hydrogen burn
freely.
First off, let me say that I have no question that the water-gas reaction
can and does occur. But I am not convinced that it is the primary
explanation for the temperature rise described in this thread. Ivor rightly
points out that the reaction requires a carbon rich fuel system and also
rightly points out that to take advantage of the H2 and CO produced,
additional oxygen is required to burn it. With the overabundance of carbon,
the kiln atmosphere should be a reduction atmosphere, leaving scarce oxygen
to react with the H2 and CO.
In fact, as has also been pointed out earlier, water gas was produced and
_collected_ for the purpose of delivering to customers to use for heating
and cooking. In other words, when the conditions exist that produce the
water gas, the water gas is not immediately reburned. And it is immediate
reburning of the water gas that is being used as an explanation for the kiln
temperature rise.
Let me amend the sauna model a bit. Instead of saying that water vapor
carries stored heat from the firebox to the remainder of the kiln, I'll say
whatever gases evolve from the application of water to the kiln carry stored
heat from the firebox to the remainder of the kiln. And forget what I said
about evaporation. All that really matters is that the water takes on a
great deal of energy from the mass of the firebox and its contents.
The distinction that I would still make is this: I suggest that the heat
rise in a kiln resulting from an application of water is due to energy being
transferred from the mass of the firebox contents to the water, heating it,
whereupon the water expands rapidly, filling the kiln and transferring some
of its energy to the ware and pyrometers. If water gas is formed it, too
will spread about the kiln transferring some of its energy to the kiln
interior. But I suggest that reoxidation of any water gas formed is
responsible for, at most, a small portion of the observed temperature rise.
I think that the following experiment could determine which is actually
dominant: simple energy transfer or reoxidation of water gas. I'll have to
risk a high fire load of ware, though, and we have a show on Dec. 3, so even
though I consider the risk small, I'm not willing to do the experiment until
the loss of a load would be less critical.
Our kiln is propane fired, so the charcoal part of the reaction is missing.
If spraying water into the burner ports results in a significant temperature
rise, then simple thermal transfer is the most likely mechanism. If there is
no temperature rise then reoxidation of water gas is more likely the
explanation.
I think that simply opening the damper until the kiln is neutral should be
sufficient to limit available carbon to the point that no significant water
gas production would be expected. To be absolutely sure, I could turn off
the gas, but then the heat taken on by the water would not be replenished by
the combustion energy.
Sound good? Anybody see any holes?
Bruce "sticking my neck out" Girrell
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