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How much propane?



 
 
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  #1  
Old July 3rd 07, 01:34 PM posted to rec.crafts.pottery
Alex S
external usenet poster
 
Posts: 1
Default How much propane?


If I am firing stoneware in a propane kiln of 8 cubic feet (something I am
thinking about) does anyone have a ball park idea of how much propane might
be required per firing?

Sort of related to this, and apologies for going over old ground, I am
interested in the idea of the "greenest" approach to firing pots. I doubt
if propane is ... I suppose wood must be better since it is renewable. But
there's also the question of how much can be fired per unit of heat/energy -
what sort of firing is the most efficient and/or economical. This is a
topic I am hoping to research further.


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  #2  
Old July 4th 07, 12:45 PM posted to rec.crafts.pottery
Bob Masta
external usenet poster
 
Posts: 96
Default How much propane?

On Tue, 3 Jul 2007 13:34:44 +0100, "Alex S"
wrote:


If I am firing stoneware in a propane kiln of 8 cubic feet (something I am
thinking about) does anyone have a ball park idea of how much propane might
be required per firing?

Sort of related to this, and apologies for going over old ground, I am
interested in the idea of the "greenest" approach to firing pots. I doubt
if propane is ... I suppose wood must be better since it is renewable. But
there's also the question of how much can be fired per unit of heat/energy -
what sort of firing is the most efficient and/or economical. This is a
topic I am hoping to research further.


I'm also interested in "green" issues. One thing to consider is that
fuel firing typically wastes a lot of the fuel energy, due to
combustion inefficiencies and due to heat lost up the flue
after combustion. I don't have any numbers for kilns, but
old "standard"-type gas furnaces were typically about 50%
efficient. (The new high-efficiency models don't seem
relevant to kilns, since they extract so much heat that the
flue termperatures are very low.)

On the other hand, electric heat (kilns or furnaces) is
100% efficient at converting electricity to heat. The
problem is really heat losses through the insulation.
I am planning to build a small "super-insulated" electric
kiln to learn more.

One of the issues for any type of kiln is that the energy that goes
into heating up the insulation mass is a loss, so you ideally want low
mass insulation like fiber, but that's not very durable for facing.
I'm thinking of one 2.5" layer of IFB, followed by several inches
of perlite (low cost) in a metal shell. Still haven't figured out
details of how to handle peepholes through this much
thickness... won't be much of a view down a narrow hole!

Best regards,


Bob Masta

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Signal Generator
Science with your sound card!
  #3  
Old July 4th 07, 08:50 PM posted to rec.crafts.pottery
Andrew Werby
external usenet poster
 
Posts: 49
Default How much propane?


"Bob Masta" wrote in message
...
On Tue, 3 Jul 2007 13:34:44 +0100, "Alex S"
wrote:


If I am firing stoneware in a propane kiln of 8 cubic feet (something I am
thinking about) does anyone have a ball park idea of how much propane
might
be required per firing?

Sort of related to this, and apologies for going over old ground, I am
interested in the idea of the "greenest" approach to firing pots. I doubt
if propane is ... I suppose wood must be better since it is renewable.
But
there's also the question of how much can be fired per unit of
heat/energy -
what sort of firing is the most efficient and/or economical. This is a
topic I am hoping to research further.


I'm also interested in "green" issues. One thing to consider is that
fuel firing typically wastes a lot of the fuel energy, due to
combustion inefficiencies and due to heat lost up the flue
after combustion. I don't have any numbers for kilns, but
old "standard"-type gas furnaces were typically about 50%
efficient. (The new high-efficiency models don't seem
relevant to kilns, since they extract so much heat that the
flue termperatures are very low.)

On the other hand, electric heat (kilns or furnaces) is
100% efficient at converting electricity to heat. The
problem is really heat losses through the insulation.
I am planning to build a small "super-insulated" electric
kiln to learn more.


[While it may be true that converting electricity into heat is (almost) 100%
efficient, you neglect the fact that the process of producing the
electricity from fuel is far less efficient, more like 30%. Then there are
losses in transmission to account for. So if "green-ness" is what we're
talking about, we should look at the whole cycle, not just the part that
happens between the wall-plug and the kiln. Perhaps your electricity is made
from hydro or wind turbines, geothermal sources, solar panels, or a nuclear
plant (not that these don't have problems of their own) but most electricity
in the US is made by burning fuel, often coal. Fuel-fired kilns, where the
heat energy is used directly instead of for electricity generation, are a
lot more efficient than the process of burning fuel to make electricity,
sending it down a wire, and using it to heat a kiln.

I suppose the "greenest" kiln would be one that's directly solar-heated.
Solar kilns are widely used for drying wood; ones capable of firing ceramics
are theoretically possible, but I couldn't find any solid information on
them online, although there's plenty of rumor and speculation around the
topic. It seems that a solar furnace is easier to achieve; Sandia Labs has
one they use to simulate nuclear events, and test refractory materials to
failure. But while devices like that are good at concentrating the heat of
the sun into a small spot, getting from there to heating a kiln efficiently
is a different problem, which doesn't seem to have been solved yet.]

One of the issues for any type of kiln is that the energy that goes
into heating up the insulation mass is a loss, so you ideally want low
mass insulation like fiber, but that's not very durable for facing.


[People often coat their ceramic blankets with a heat-reflective refractory
coating (ITC), which helps with its fragility issues. Personally, I'm highly
suspicious of that fibrous ceramic material and what it does in the lungs. I
would hesitate to use it in a kiln; I like the old-fashioned light
firebricks better.]

I'm thinking of one 2.5" layer of IFB, followed by several inches
of perlite (low cost) in a metal shell. Still haven't figured out
details of how to handle peepholes through this much
thickness... won't be much of a view down a narrow hole!


[I'm not sure about the perlite; it's not really refractory, and will fall
out your peephole. I suppose you could whip it up with some other
ingredients to make a light castable material, but it would only be good for
back-up insulation behind a real high-temperature refractory board, blanket
or brick.]

Andrew Werby
www.unitedartworks.com


Best regards,


Bob Masta

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Signal Generator
Science with your sound card!



  #4  
Old July 5th 07, 02:04 PM posted to rec.crafts.pottery
Bob Masta
external usenet poster
 
Posts: 96
Default How much propane?

On Wed, 4 Jul 2007 12:50:11 -0700, "Andrew Werby"
wrote:


"Bob Masta" wrote in message
...


I'm also interested in "green" issues. One thing to consider is that
fuel firing typically wastes a lot of the fuel energy, due to
combustion inefficiencies and due to heat lost up the flue
after combustion. I don't have any numbers for kilns, but
old "standard"-type gas furnaces were typically about 50%
efficient. (The new high-efficiency models don't seem
relevant to kilns, since they extract so much heat that the
flue termperatures are very low.)

On the other hand, electric heat (kilns or furnaces) is
100% efficient at converting electricity to heat. The
problem is really heat losses through the insulation.
I am planning to build a small "super-insulated" electric
kiln to learn more.


[While it may be true that converting electricity into heat is (almost) 100%
efficient, you neglect the fact that the process of producing the
electricity from fuel is far less efficient, more like 30%. Then there are
losses in transmission to account for. So if "green-ness" is what we're
talking about, we should look at the whole cycle, not just the part that
happens between the wall-plug and the kiln. Perhaps your electricity is made
from hydro or wind turbines, geothermal sources, solar panels, or a nuclear
plant (not that these don't have problems of their own) but most electricity
in the US is made by burning fuel, often coal. Fuel-fired kilns, where the
heat energy is used directly instead of for electricity generation, are a
lot more efficient than the process of burning fuel to make electricity,
sending it down a wire, and using it to heat a kiln.


Your point is well taken. One issue is that electricity generation
is more amenable to emissions controls (stack scrubbers and the
like), and eventually perhaps CO2 capture (though I'm not holding my
breath on that one).

But I'd sure love to see some overall efficiency numbers for fuel
kilns for comparison. g

I suppose the "greenest" kiln would be one that's directly solar-heated.
Solar kilns are widely used for drying wood; ones capable of firing ceramics
are theoretically possible, but I couldn't find any solid information on
them online, although there's plenty of rumor and speculation around the
topic. It seems that a solar furnace is easier to achieve; Sandia Labs has
one they use to simulate nuclear events, and test refractory materials to
failure. But while devices like that are good at concentrating the heat of
the sun into a small spot, getting from there to heating a kiln efficiently
is a different problem, which doesn't seem to have been solved yet.]


Then there's the issue of completing the entire firing while the sun
shines!

One of the issues for any type of kiln is that the energy that goes
into heating up the insulation mass is a loss, so you ideally want low
mass insulation like fiber, but that's not very durable for facing.


[People often coat their ceramic blankets with a heat-reflective refractory
coating (ITC), which helps with its fragility issues. Personally, I'm highly
suspicious of that fibrous ceramic material and what it does in the lungs. I
would hesitate to use it in a kiln; I like the old-fashioned light
firebricks better.]


I'm thinking of one 2.5" layer of IFB, followed by several inches
of perlite (low cost) in a metal shell. Still haven't figured out
details of how to handle peepholes through this much
thickness... won't be much of a view down a narrow hole!


[I'm not sure about the perlite; it's not really refractory, and will fall
out your peephole. I suppose you could whip it up with some other
ingredients to make a light castable material, but it would only be good for
back-up insulation behind a real high-temperature refractory board, blanket
or brick.]


I'm also wary of fiber, hence the insulating fire brick with perlite
as a backup. The beauty of perlite (besides being cheap) is that
it is a really good insulator at low temperatures (under 850C or so),
much better than IFB (roughly the same as Kaowool at 850C,
depending on packing density of each). So there are limits to
how thick a backing layer you can use, since if you add too much
insulation the cold face of the IFB will end up being hotter
(more of the temperature drop is across the back-up insulation)
and that has to remain low enough to not degrade the perlite's
R-value.

As you note, I will have to use a castable behind the peeps.
Perlite is a common basis for castables, so I will probably start
out there. From what I have been able to find on the Web,
it looks like perlite bound with sodium silicate may be a good
starting point.

Best regards,



Bob Masta

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Signal Generator
Science with your sound card!
  #5  
Old July 5th 07, 03:19 PM posted to rec.crafts.pottery
charlie
external usenet poster
 
Posts: 29
Default How much propane?


"Bob Masta" wrote in message
...
On Tue, 3 Jul 2007 13:34:44 +0100, "Alex S"
wrote:

One of the issues for any type of kiln is that the energy that goes
into heating up the insulation mass is a loss, so you ideally want low
mass insulation like fiber, but that's not very durable for facing.
I'm thinking of one 2.5" layer of IFB, followed by several inches
of perlite (low cost) in a metal shell. Still haven't figured out
details of how to handle peepholes through this much
thickness... won't be much of a view down a narrow hole!

Best regards,


Bob Masta


maybe a large window instead of a peephole?

regards,
charlie
http://glassartists.org/chaniarts


  #6  
Old July 5th 07, 03:27 PM posted to rec.crafts.pottery
STEPHEN MILLS
external usenet poster
 
Posts: 5
Default How much propane?

Bob,

Re your experimental kiln.
There was some research done by the late Donald Shelley in the UK which
found that there is a point at which increased insulation begins to have a
reverse effect and heat starts to accelerate through the wall rather than
being retained.
I came across this in the late '70s when a former associate of his was
designing my last production kiln, using Ceramic Fibre (board hot face, then
1260oC grade fibre, then Lo-Con, then Rockwool) the most efficient wall
thickness they came up with for a 55 Cu. Ft. gross capacity was 7 inches.
the kiln was certainly economical (Natural Gas), but the outer surface still
got very hot.

I have done some searching, but I'm afraid I can't do better than memory of
past information currently.

Steve
Bath
UK

"Bob Masta" wrote in message
...
On Wed, 4 Jul 2007 12:50:11 -0700, "Andrew Werby"
wrote:


"Bob Masta" wrote in message
...


I'm also interested in "green" issues. One thing to consider is that
fuel firing typically wastes a lot of the fuel energy, due to
combustion inefficiencies and due to heat lost up the flue
after combustion. I don't have any numbers for kilns, but
old "standard"-type gas furnaces were typically about 50%
efficient. (The new high-efficiency models don't seem
relevant to kilns, since they extract so much heat that the
flue termperatures are very low.)

On the other hand, electric heat (kilns or furnaces) is
100% efficient at converting electricity to heat. The
problem is really heat losses through the insulation.
I am planning to build a small "super-insulated" electric
kiln to learn more.


[While it may be true that converting electricity into heat is (almost)
100%
efficient, you neglect the fact that the process of producing the
electricity from fuel is far less efficient, more like 30%. Then there are
losses in transmission to account for. So if "green-ness" is what we're
talking about, we should look at the whole cycle, not just the part that
happens between the wall-plug and the kiln. Perhaps your electricity is
made
from hydro or wind turbines, geothermal sources, solar panels, or a
nuclear
plant (not that these don't have problems of their own) but most
electricity
in the US is made by burning fuel, often coal. Fuel-fired kilns, where the
heat energy is used directly instead of for electricity generation, are a
lot more efficient than the process of burning fuel to make electricity,
sending it down a wire, and using it to heat a kiln.


Your point is well taken. One issue is that electricity generation
is more amenable to emissions controls (stack scrubbers and the
like), and eventually perhaps CO2 capture (though I'm not holding my
breath on that one).

But I'd sure love to see some overall efficiency numbers for fuel
kilns for comparison. g

I suppose the "greenest" kiln would be one that's directly solar-heated.
Solar kilns are widely used for drying wood; ones capable of firing
ceramics
are theoretically possible, but I couldn't find any solid information on
them online, although there's plenty of rumor and speculation around the
topic. It seems that a solar furnace is easier to achieve; Sandia Labs has
one they use to simulate nuclear events, and test refractory materials to
failure. But while devices like that are good at concentrating the heat of
the sun into a small spot, getting from there to heating a kiln
efficiently
is a different problem, which doesn't seem to have been solved yet.]


Then there's the issue of completing the entire firing while the sun
shines!

One of the issues for any type of kiln is that the energy that goes
into heating up the insulation mass is a loss, so you ideally want low
mass insulation like fiber, but that's not very durable for facing.


[People often coat their ceramic blankets with a heat-reflective
refractory
coating (ITC), which helps with its fragility issues. Personally, I'm
highly
suspicious of that fibrous ceramic material and what it does in the lungs.
I
would hesitate to use it in a kiln; I like the old-fashioned light
firebricks better.]


I'm thinking of one 2.5" layer of IFB, followed by several inches
of perlite (low cost) in a metal shell. Still haven't figured out
details of how to handle peepholes through this much
thickness... won't be much of a view down a narrow hole!


[I'm not sure about the perlite; it's not really refractory, and will fall
out your peephole. I suppose you could whip it up with some other
ingredients to make a light castable material, but it would only be good
for
back-up insulation behind a real high-temperature refractory board,
blanket
or brick.]


I'm also wary of fiber, hence the insulating fire brick with perlite
as a backup. The beauty of perlite (besides being cheap) is that
it is a really good insulator at low temperatures (under 850C or so),
much better than IFB (roughly the same as Kaowool at 850C,
depending on packing density of each). So there are limits to
how thick a backing layer you can use, since if you add too much
insulation the cold face of the IFB will end up being hotter
(more of the temperature drop is across the back-up insulation)
and that has to remain low enough to not degrade the perlite's
R-value.

As you note, I will have to use a castable behind the peeps.
Perlite is a common basis for castables, so I will probably start
out there. From what I have been able to find on the Web,
it looks like perlite bound with sodium silicate may be a good
starting point.

Best regards,



Bob Masta

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Signal Generator
Science with your sound card!



 




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