Rosanne Cleveland-King on mon 21 sep 98
I have just moved and have the opportunity to use natural gas instead of
having my propane bottle moved. I am on a tight deadline with my next
firing and am rather reluctant to go the natural gas way. Scared is more
like it. I would like to know what is involved with the burner setup.
Is the gas pressure any different? Is the firing procedure any
different? Any ideas?
Thanks is advance
Rosanne Cleveland-King
Mud Pies Pottery
carla@iclub.org
Cameron Harman on tue 22 sep 98
To Roseaane,
Check with Marc Ward of Ward Burner Systems, he is on this list.
The only difference should be the size of the burner orifices to
accommodate the natural gas. You also have to be sure you have
enough gas pressure at the burner, as I say, check with Marc, he
knows this stuff very well.
Cameron
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**********************************************************
Cameron G. Harman, Jr. 215-245-4040 fax 215-638-1812
e-mail kilns@kilnman.com
Ceramic Services, Inc 1060 Park Ave. Bensalem, PA 19020
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Donn Buchfinck on thu 24 sep 98
if you are going to fire with propane, you cannot beat Dedell gas burners
they are the best, they look different but they are great.
ransome ventury burners are great too, a bit pricy, but what the hell, it all
is
ward power burners are easy to build yourself if you do not want to have the
safty system on it, it takes a little work and persistance but it can be done
propane has pressure with it and that can be used for the burner
where as natural gas normaly come with low pressure and the blower is needed
to mix and get the combustion right. in some instances you can get the
natural gas delivered in a higher pressure
both firing methiods are great but you should also look at your kiln you are
building before you choose, if you have a choice.
1st with natural draft kiln ie not forced air, the configuration of the kiln
or shape of the inside needs to be inside a cube or as close to it, for an
even firing.
with forced air the kiln can be a little out of cube and work
think of a kiln, think of it with water, turn the kiln upside down in your
mind
the natural draft kiln is a siphon with the stack creating the draw to pull
the water/ gasses through it, the forced air is a pump. so you do not need a
tall stack to draw the water/ gasses through it
gas pressure is important, because if you have a lot of pressure you do not
need a tall stack, it will be like having forced air. the high pressure comes
through the ventury burner and draws the air from behind it. mixing before it
hits the flame retention tip.
if you do not have a lot of pressure then you need a tall stack to create the
draw in the kiln, sucking the gas and air from the burner, the damper becomes
very important in this type of firing, controling the secondary air supply.
if you have a choice, of high pressure vs low pressure this is the real
question, high pressure will make for a cheaper kiln, you will not need to
build such a tall stack for the kiln.
one has to create a formula to decide on the kiln burner system, if there is
a choice about the type of gas you have to think about cost.
natural gas in the long run I would think would be cheaper than propane, do
you have enough bricks to build a stack for low pressure natural gas or you
could go with a low stack and use forced air
just DO NOT build a high stack then put forced air burners on it, it creates
too many problems
need any other questions answed i will give it my best
once again forgive me for my meager grammar and spelling
Vince Pitelka on fri 25 sep 98
A couple of things here are a bit misleading -
>if you are going to fire with propane, you cannot beat Dedell gas burners
>they are the best, they look different but they are great.
>ransome ventury burners are great too, a bit pricy, but what the hell, it all
>is
Dedell burners ARE ransome venturi burners.
>propane has pressure with it and that can be used for the burner
>where as natural gas normaly come with low pressure and the blower is needed
>to mix and get the combustion right. in some instances you can get the
>natural gas delivered in a higher pressure
Venturi burners work great on low-pressure gas if you have the right burner
and the right orifice size to deliver the BTUs you need. The first kilns I
ever built were 7 to 10 WCI (water column inches), and worked great with
natural draft burners.
>just DO NOT build a high stack then put forced air burners on it, it creates
>too many problems
I have seen many forced-air downdraft kilns with very tall stacks which work
just fine. As long as you have proper damper control, and as long as you
manipulate the flue to draw evenly from throughout the bottom of the kiln,
the height of the stack should not negatively affect firing.
- Vince
Vince Pitelka - vpitelka@DeKalb.net
Home 615/597-5376, work 615/597-6801, fax 615/597-6803
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Cameron Harman on sat 26 sep 98
Donn Bunchfinck wrote about relationships between the kiln stack
and the type of burners being used. He indicated that the height
of the stack was somehow related to whether you had forced air
burners or venturi burners. He also indicated that the shape of
the kiln was somehow related to the type of burners.
I hesitated to write, but this whole note is so wrong I cannot let
it pass.
The kiln pressure inside any fuel fired kiln (gas, oil, coal,
whatever) should always be the same. It is the arrangement of the
stack internally and externally that will control this function.
It doesn't matter whether it is updraft, down draft or forced
draft the pressure is ALWAYS set to the same point. The very idea
that forced air burners somehow push air out of the kiln is so
terribly wrong it makes me shudder.
All of the comments I saw were obviously based on experience with
very poorly designed kilns. a well designed kiln has a shape that
is related to heat transfer, not to the type of burners used.
The bottom line is that natural gas, where available, is the
cheapest source of energy ( the only exception being occasional
spot purchases of diesel oil). Either natural gas or propane is
capable of firing beautifully in a properly designed kiln.
The only difference between venturi burners and forced air burners
has to do with efficiency and "throw". The type of forced air
burners used by hobby kiln builders are not much different in
effect from venturi burners except that when properly set up they
can produce reduction fires a little more easily. The forced air
burners used in industrial kilns are so well controlled that they
can be made to easily fire either oxidizing or reducing. In
addition you can buy higher velocity burners that are more suited
for firing long distances (say seven feet or more). That is they
"throw" even heat over a longer distance.
The burners used for the kilns you are familiar with are chosen
over the industrial burners because the cost of the flame safety
is less and the cost of the blower is less or non-existant.
The stack on a kiln is the "pump" that clears the products of
combustion out of the kiln. Whether a kiln is fired with forced
air or not, the cubic feet per hour of gasses to be removed from a
kiln are EXACTLY the same at the same BTU input. Therfore, the
action of the flue and stack MUST be the same for either type of
burner or you have some real design problems.
In order to control pressure in a kiln all the gas and air that
you put in must be removed. If not you have either a positive or a
negative pressure in the kiln. The kiln pressure should be 0.000
inches water column at the base. Nature will cause the pressure to
rise approximately 0.01 inches water column per foot of interior
height above the base (for example two feet above the base should
be 0.02 inches). This happens regardless of the type of exhaust,
the height of the stack or the type of burners. All that you can
change is the level of the 0.000 inches point.
If your burners are venturi burners and draw air from the room
through openings around the burner, then the zero point should be
at that location. If those burners are also at a raised elevation
(that is, burners both high and low), you have a kiln that will
always be difficult, if not impossible to control. If you have
forced air burners, then their vertical location is of less
importance.
I don't mean to be quite so technical, but the answers are found
in the physics of the situation. Kiln design is very complicated
in spite of the fact that it looks so easy. However, once the
fundamental physics is known it becomes a lot easier.
I hope this helps more than it confuses.
Cameron Harman
--
**********************************************************
Cameron G. Harman, Jr. 215-245-4040 fax 215-638-1812
e-mail kilns@kilnman.com
Ceramic Services, Inc 1060 Park Ave. Bensalem, PA 19020
get your free ezine: http://www.kilnman.com/ezine/ezine.html
THE place for total kiln and drier support
**********************************************************
Donn Buchfinck on sun 27 sep 98
To: Vince Pitelka - vpitelka@DeKalb.net
Dedel is a great burner
he puts them together and they WORK
you have a lot of variables to control when you put forced air burners on a
kiln with a high stack
If the stack is too tall then secondary air comes in around the burner flame
retention tip and creates an oxidation flame around the reduction flame, this
is why sometimes we get copper reds and celedons that have a side of them not
reduced. the height of the stack for a forced air kiln should be no taller
than the height of the top of the arch on the out side of the kiln. then some
type of hood should be mounted 2-3 feet above the stack to catch the flue
gases. This saves money in creating a tall stack. In school we had an
instructor get three different colors of copper red from his copper red glaze
in three different firings, because he knew how to set the kiln up and deal
with the primary air vs secondary air.
a tall stack makes the damper very sensitive and adjustments can be difficult.
also on windy days it also affects the firing, but with the method I
described the stack is not connected to the kiln so wind does not play a
factor.
I believe in the simpiest way to do things.
I try not to be an expert in these instances, just giving an opionion, I
realy dislike people who think they know the only way to do things. and feel
they have to point out other peoples mistakes. also in kansas city where I
went to school we only had 4-5 inches of pressure, so at times it was
difficult to fire the kilns.
good luck
and keep on making that stuff
Donn
Donn Buchfinck on sun 27 sep 98
In a message dated 9/27/98 3:56:19 AM, you wrote:
<>
I hesitated to write, but this whole note is so wrong I cannot let
it pass.
well I just thought I would write and say that as a hobby potter, with My BFA
from the Kansas City Art Institute 1990, where I learned about kilns from
Peter Pinnell and from Penn State for my MFA 1995, where I learned about
updrafts from Dave Dontigny, I find you comments and lack of flexibility
annoying, and I would hope that anyone who comes in contact with you, turns
and runs away because your ego does try to crush other people to your
concepts.
I have a geil downdraft kiln that does not have a stack on it and it fires
great, it fires with ventury burners that pressurize the kiln, the damper is
what controls that pressure. I might be wrong on the physics of the thing ,
but I know that it works pretty good. I am a potter not a pysics major.
when I was in undergrad school, Peter Pinnell, you might have heard of him,
he has built some kilns, had a forced air downdraft kiln he built. It was a
marvel, he could get three different copper reds from three different firing,
with the same glaze. He knew how to fire a kiln. The kiln had secondary air
cages on it, you can purchase them from pyronics corporation. They
controlled the secondary air that flowed into the kiln. On top of the kiln
there was a stack but it was connected to a hood several feet above the kiln,
this allowed for ambient air to cool the gases so not to burn the stack up.
He had total control over the kiln.
my giel is very friendly also cone 10 even with two adjustments
I find that a forced air system is a pump
natural draft is a syphon
look at a wood kiln, it is a syphon, and you need to get the stack hot to
draw the air through the kiln, through the firebox for combustion. This is a
natural draft kiln. I might be wrong, if not for those summers I spent at
the Archie Bray Foundation firing wood kilns, or the one I rebuilt at Penn St.
The problem with some kilns that have forced air blowers is that they do not
have enough power, so they need the stack to draw in more air around the
burners. Then it is like hooking up a pump to a syphon system, it confuses
the system. Making the damper super sensitive.
if the burner system has pressure, either from forced air or from gas pressure
in a ventury system, a tall stack is not needed. And a person can save the
cost of building a very high stack.
as to kiln design, I thought I read in the kiln building books that for
natural draft kilns it was best to have the whole inside of the kiln as close
to a cube as possible, and if one was to have forced air the kiln could be
somewhat out of square. I am just repeating what I had read from people who
thought they knew what they were doing, when your book comes out I will read
it with an open mind also.
this whole conversation is somewhat amusing to me because we have not even
touched on updraft designs, the whole discussion has been about downdraft.
I have fired both forced air updrafts, "alpine" and ventury based systems,
Dave Dontigny who started the Penn St. Program and created the Supermud
conferences back in the 70's built some of the best updrafts I have ever had
the pleasure to fire. He had a 160 cubic foot kiln that went to cone 10 even,
a monster of a kiln that fired so great it was unbelievable. These kilns do
not have a stack, the damper controls the pressure within the kiln.
Kilns are like people, they have their own idiosycracies, I have found that
if someone builds the same kiln next to each other, they will be different in
how they fire. I am an intuitive based potter. And I try to learn the kiln I
am going to fire. And I am open to other ideas, but I find your rigidity
sad. Because I must be lucky, for I have seen what I have talked about put
into practice and have had great results. There are a lot of different
schools of thought as to how to build and fire a kiln. People are probably
very happy with what you build for them, but are glad when you leave.
Several weeks ago I wrote a comment about ego based people who feel it is
their right to say that someone else is WRONG, I find this amusing and sad.
I understand you feel you are right, and your methods do work for you. But
please do not begin to comment on other people's opinions and ideas. There is
no ONE WAY to accomplish a goal. Maybe we are saying the same things, but
differently. Good luck
Donn Buchfinck
Vince Pitelka on sun 27 sep 98
>The stack on a kiln is the "pump" that clears the products of
>combustion out of the kiln. Whether a kiln is fired with forced
>air or not, the cubic feet per hour of gasses to be removed from a
>kiln are EXACTLY the same at the same BTU input. Therfore, the
>action of the flue and stack MUST be the same for either type of
>burner or you have some real design problems.
This is a bit misleading. It may be that in the final analysis the cubic
feet per hour in the stack is the same in the flue of a forced draft kiln or
a natural raft downdraft kiln, but the action of the stack is very
different. The terms themselves say it. Natural draft requires the
"natural" convection currents in the stack in a downdraft kiln, or the kiln
body in an updraft kiln, to draw in secondary air during oxidizing or
neutral stages of the firing, therby maintaining efficient combustion. With
forced-air systems we can regulate the air input with the burners
themselves, and the stack in a downdraft or the kiln body in an updraft need
only exhaust the combustion gases. Therefore, a forced air downdraft needs
to have a stack only as tall as the kiln, whereas a natural draft downdraft
needs a much taller stack to maintain the required convection.
- Vince
Vince Pitelka - vpitelka@DeKalb.net
Home 615/597-5376, work 615/597-6801, fax 615/597-6803
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Vince Pitelka on mon 28 sep 98
>you have a lot of variables to control when you put forced air burners on a
>kiln with a high stack
You have a lot of variables to control when you put any burners on any kiln.
>If the stack is too tall then secondary air comes in around the burner flame
>retention tip and creates an oxidation flame around the reduction flame
No, that's not true as long as you close down the damper enough.
>the height of the stack for a forced air kiln should be no taller
>than the height of the top of the arch on the out side of the kiln.
If you are stating opinions, then do not state them as facts. The height of
the stack for a forced draft kiln doesn't HAVE to be any taller than the
kiln, and it certainly saves money to make it that short, but it does not
hurt at all to have it be taller. In some cases, we reuse a chimney which
was already there. If we are changing over to forced draft, we may still
wish to use the same chimney. There is no reason not to, because it will
not adversely affect the kiln.
>realy dislike people who think they know the only way to do things. and feel
>they have to point out other peoples mistakes.
When you state things on this list, make sure they are accurate, or else you
can expect someone to correct you. The things I say on this list are based
on thirty years of professional experience in ceramics. They are still only
my opinions.
- Vince
Vince Pitelka - vpitelka@DeKalb.net
Home 615/597-5376, work 615/597-6801, fax 615/597-6803
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Cameron Harman on tue 29 sep 98
Vince,
I appreciate the thinking that went into your comments about the
stack. I think that we are saying the same thing in different
ways. Here are a couple of things to consider that might clarify
my meanings and, hopefully, make sense with your comments.
The action of the the gas movement inside a stack and the action
of gas movement inside a kiln are two separate, but equally
important considerations.
In a stack its sole purpose is to provide enough negative pressure
at its opening into the kiln to remove the gasses generated there
and still maintain the pressure level inside the kiln that you
desire. The term 'natural draft' in the industry means that the
stack itself has no fans attached. There are kilns with fans in
the flue system, these are 'forced draft' kilns. Forced draft
kilns are used in special situations where there are too many
pressure drops in the system or where large quantities of excess
air involved.
The action of the currents in side the kiln are extremely
important, as you point out. The benefit of a downdraft compared
to an updraft is simply that the downdraft can be connected
tightly to a flue system that is built into the load of ware . An
updraft kiln does not allow a tight connection because the top of
the ware would have to be sealed from the top of the kiln allowing
only a predetermined slot for the sir to go through. I know that
this is confusing, and I am sorry I cannot make it more clear in a
short note, call me and I'll try to explain more fully.
There is nothing wrong with either updraft or downdraft, its only
that you can design a kiln with very much more uniformity with a
downdraft.
If you can coordinate the ware setting and the flue openings
inside the body of the kiln, you can then control those "natural"
convection currents you refer to, but this must be built into the
kiln design in the first place. The thing that allows you to draw
more secondary air into the kiln is the slightly negative pressure
inside the kiln at the point where the burners are located. If the
burners are sealed (secondary air provided by a blower) they are
still sensitive to the pressure inside the kiln, but not as much
so.
When I design a kiln, I first do an energy balance to determine
the amount of BTU required under varying conditions including
reducing, excess air and faster firing. The very next thing I do
is design the exhaust (read flue, stack, etc.) system. The flue
system is designed to provide the amount of negative pressure I
want at the burner location. The stack, flue openings, etc. are
all designed to fit those conditions. In that process I can
determine the type of stack I need to use, straight stack or
collector hood, for example.
When that system is worked out the stack will be easy to control.
Usually the only changes necessary are the adjustments that you
would make for substantially different firing conditions. For
example, reduction firing with venturi burners need more flue
control than oxidizing, but still easily within control.
It is important to know what kind of burner you are starting with
only to be sure that the internal kiln pressure is suitable for
that burner. In a kiln with sealed burners I would operate the
kiln with a zero pressure at the base, with venturi burners I
would possibly need a negative pressure at the burner level. ( I
am sorry that I messed up and did not make this point clear
before).
I agree, that with forced air burners you regulate the air to
burners and with venturi burners you regulate the gas pressure
(and the kiln pressure). However, in some kilns with forced air
burners the air is left at some constant value and the gas is
regulated. In other words either systems works, its just that some
methods are easier than others or some might be more efficient
than others.
In neither case the height of the stack is directly determined by
the type of burner other than the necessity to pull more draft on
a venturi kiln to get the higher negative at the burner location.
If the flue system is properly designed, then the stack control
will not be overly sensitive.
I am not trying to challenge your position, only to clarify the
technical end somewhat. As I have said elsewhere, my purpose is to
open the dialog between the end user and the kiln designer. I
regret that in all these years there has been very little of this
dialog. Believe it or nor, I learn a great deal from these
interactions.
Cameron
--
**********************************************************
Cameron G. Harman, Jr. 215-245-4040 fax 215-638-1812
e-mail kilns@kilnman.com
Ceramic Services, Inc 1060 Park Ave. Bensalem, PA 19020
get your free ezine: http://www.kilnman.com/ezine/ezine.html
THE place for total kiln and drier support
**********************************************************
john eden on tue 29 sep 98
I agree with Vince, here at the College I have sixty-five foot chimneys with
venturi type fans in them AND I use downdraft kilns with forced air burners.
If you use an atmospheric damper which is cheap and easy to install in
addition to the regular damper you shouldn't have any trouble with tall
chimneys.
Cheers, John.
I would also like to add that tall chimnies are not always a matter of
choice, particularly in educational institutions. The local codes
concerning "height of chimney relative to roof peak height" and the head of
facilities is more likely to be the governing factor. Just my opinion of
course. :-)
Cheers, John.
John Eden / Ceramics
John Abbott College
Ste. Anne de Bellevue
Quebec, H9X 3L9, Canada
Tel. # 514-457-6610 ext.395
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