rlg@desktalk.com on tue 9 sep 97
Marc,
Learn something new every day!
Is there a rule of thumb for inlet port diameter to burner inside or
outside diameter?
Thanks,
Richard
At 11:23 PM 9/6/97 EDT, you wrote:
>----------------------------Original message----------------------------
>Hey folks,
>
>Following this thread and I noticed this part of a post;
>
><<<>burner port. That way it will draw in secondary air and you will be
>fine.>>>>
>
>No burner that is designed for open port applications (open port meaning you
>can see the flame or look into the port from the outside) should be put into
>the port. Zero. Zip. Nada. None. The rule of thumb is to back off the burner
>1/4" for every inch of flame tube diameter. So a two inch pipe on a burner
>requires a 1/2" back off. These are industry standards that deal with clean
>firings, no fiddle'n around making "tuned flues", ect. Potters tend to "fire
>incorrectly" as far as industry is concerned, so consider the setbacks above
>as a minimum. You can go as much as a 1/2 - 3/4 inch setback per inch of
>flame tube diameter. If the perimeter of your port glows, you've gone too far
>or your port is too small. I am not an advocate of small ports and flues,
>especially for forced air. Venturi burners typically entrain only 30-50% of
>their primary air through the mixing bell. You have to have adequate space
>around the burner to entrain the necessary secondary air and to help cool the
>burner head.
>
>Happy firings to ya'll
>
>Marc Ward
>Ward Burner Systems
>PO Box 333
>Dandridge, TN 37725
>USA
>423.397.2914 voice
>423.397.1253 fax
>wardburner@aol.com
>
>
WardBurner@aol.com on wed 10 sep 97
Richard,
You asked;
<<<outside diameter?>>>>
If you go with the industry standard of 1/4" set back for every inch of flame
tube diameter, You would then use a burner port that is 1 inch larger in
diameter than the outside diameter of the burner head...ie. a burner head
that measures 3.5" at it's outside diameter needs a 4.5" diameter burner
port.
Now, the key words up above are "industry standard." When industry sets their
burner at that distance it is usually placed outside a Tuyere Block...A WHAT?
A Tuyere Block is a precast burner port that has a taper of around 15 degrees
that enlarges as it enters the kiln or furnace. The flame has a tendency to
do the same thing. This is also why Venturi burners are flared larger as the
gas moves down the tube. This flaring helps to increases the low pressure
area behind the orifice in the case of the Venturi and increases the low
pressure area around the burner head in the case of the Tuyere block. What
happens is more air gets pulled into the burner or the kiln.
OK, most all potters don't use Tuyere blocks or tapered burner ports. So what
do they do? As you back your burner off, you may need to enlarge your burner
port more than the 1" over head size recommended above. It is better to err
on the side of too large than too small. If the edges of your port glow, your
burner is too far back/port too small. That's an "either/or" thing. So, for
potters, there is no strict rule of thumb. That's because they are using all
sorts of beasts to fire kilns.
But wait, your thinking that the ole' Alpine has it's burners crammed way up
in the port. Some manufacturers have decided to solve problems related to
spark ignition, thermocouples, wind, back pressure, ect., by sacrificing
burner heads (that's why Alpine has those funky little clay tips). You can
get away with this easier with forced air because you are not as dependent on
secondary air to provide all your combustion air. Venturi's need secondary
air.
Hope I helped more than I confused....
Marc Ward
Ward Burner Systems
PO Box 333
Dandridge, TN 37725
USA
423.397.2914 voice
423.397.1253 fax
wardburner@aol.com
Vince Pitelka on wed 10 sep 97
>Is there a rule of thumb for inlet port diameter to burner inside or
>outside diameter?
Richard -
This is no rule of thumb, but it's worth relating. One of the best-firing
kilns I have ever used was a big car kiln I built in my studio in Northern
California many years ago. I used six industrial cast-iron tube burners
which were 2" I.D. and 2 1/2" O.D. at the flame-retention tip. I carved
softbrick inserts to fit into the burner ports, with a hole 3 1/2" diameter,
tapering larger towards the inside of the kiln. The burner tips were spaced
about 1/2" away from the face of the inserts, which corresponds with Marc's
specs, which I am glad to hear, considering that it was a total shot in the
dark for me at the time. This kiln had a good tall TAPERED stack, and a
very tight fitting damper, and it fired more evenly and more quietly than
any other kiln I have seen.
- Vince
Vince Pitelka - vpitelka@DeKalb.net
Home 615/597-5376, work 615/597-6801, fax 615/597-6803
Appalachian Center for Crafts
1560 Craft Center Drive, Smithville TN 37166
Karl P. Platt on thu 11 sep 97
To add a bit here.....
The most essential function of a burner block is to provide flame
stability at low temperatures. Simply put, it gets hot fast and guards
against the flame being quanched by its surroundings. Many studio
ceramists who fire through non-designed holes in the kiln wall are obliged
to fire rich until what ever the arrangement is gets hot enough to permit
a stable flame. There are a lot of downsides to this and they should be
obvious. Burner blocks are so simple and cheap to make that it really
doesn't make sense to fire without them.
KPP
Grace Liu on thu 11 sep 97
Marc,
I've been following this thread on burners, very interesting &
enlightening.
Is there an industry standard for the diameter of the actual burner in
relation to the size of the kiln. I imagine there must be. What would
the ideal burner diameter be for a downdraft kiln about 1 cubic meter
(about 35 cubic feet)? How many burner ports would you recommend?
Trying to get my hands on a comprehensive kiln building book, but gotta
wait for a few weeks for delivery.
Thanks in advance for your advice.
grace
WardBurner@aol.com wrote:
>
> ----------------------------Original message----------------------------
> Richard,
>
> You asked;
>
> <<<> outside diameter?>>>>
>
> If you go with the industry standard of 1/4" set back for every inch of flame
> tube diameter, You would then use a burner port that is 1 inch larger in
> diameter than the outside diameter of the burner head...ie. a burner head
> that measures 3.5" at it's outside diameter needs a 4.5" diameter burner
> port.
>
> Now, the key words up above are "industry standard." When industry sets their
> burner at that distance it is usually placed outside a Tuyere Block...A WHAT?
> A Tuyere Block is a precast burner port that has a taper of around 15 degrees
> that enlarges as it enters the kiln or furnace. The flame has a tendency to
> do the same thing. This is also why Venturi burners are flared larger as the
> gas moves down the tube. This flaring helps to increases the low pressure
> area behind the orifice in the case of the Venturi and increases the low
> pressure area around the burner head in the case of the Tuyere block. What
> happens is more air gets pulled into the burner or the kiln.
>
> OK, most all potters don't use Tuyere blocks or tapered burner ports. So what
> do they do? As you back your burner off, you may need to enlarge your burner
> port more than the 1" over head size recommended above. It is better to err
> on the side of too large than too small. If the edges of your port glow, your
> burner is too far back/port too small. That's an "either/or" thing. So, for
> potters, there is no strict rule of thumb. That's because they are using all
> sorts of beasts to fire kilns.
>
> But wait, your thinking that the ole' Alpine has it's burners crammed way up
> in the port. Some manufacturers have decided to solve problems related to
> spark ignition, thermocouples, wind, back pressure, ect., by sacrificing
> burner heads (that's why Alpine has those funky little clay tips). You can
> get away with this easier with forced air because you are not as dependent on
> secondary air to provide all your combustion air. Venturi's need secondary
> air.
>
> Hope I helped more than I confused....
>
> Marc Ward
> Ward Burner Systems
> PO Box 333
> Dandridge, TN 37725
> USA
> 423.397.2914 voice
> 423.397.1253 fax
> wardburner@aol.com
Karl P. Platt on fri 12 sep 97
On Thu, 11 Sep 1997, Grace Liu wrote:
> Is there an industry standard for the diameter of the actual burner in
> relation to the size of the kiln. I imagine there must be. What would
> the ideal burner diameter be for a downdraft kiln about 1 cubic meter
> (about 35 cubic feet)? How many burner ports would you recommend?
Can I chime in here? There is no such standard. The ideal case would be a
kiln in which there were an infinite number of little burners covering the
walls. Of course, this isn't practiIn industrial practice the type of
combustion hardware used is very different from studio practice. Where an
industrial kiln will typically use noxxle mixing type burner (where both
gas and air are pressurized), studio practice is to use a low pressure
venturi of some tye-- often operating with pressurized gas. There are many
advantages to nozzle-mixing burners. These include extreme stability,
a very wide array of available flame shapes, sizes and velocities, highly
repeatable input (the amount of gas and air and their proportion), etc.
Nozzle mixing burners do not necessarily cost more than
inspirator/aspirator(venturi) driven burners.
cal. The actual dimensions of a burner
are determined by how much gas/air mix needs to pass through it and how
much pressure there is available to move it -- the gas, the air or both
may be pressurized.
Industrial burners are, in general, operated at higher "energy density"
than studio burners -- the number of BTU/cubic foot of flame is higher -
and they also operate with higher "flame speeds" -- the gases leaving the
burner have higher velocities. This is used to promote temperature
uniformity within the kiln -- using the least number of burners
possible/practical. It should be noted that there are also burners which
have a zero forward flame speed (flat-flame ot hot-spot type burners)
these have specific applications usually out of the ceramic field -- and
they're noisy as *&$%. Of course, nozzle mixing burners using high
pressures (8 osi+) are also generally more noisy than low pressure
imspirators/aspirators.
All of this is to note that there aren't tables somewhere that say x
burners need to cover y volume. Many factors need to be considered --
desired firing rate, mass of the kiln/load, heat losses, etc. Flue sizing
is, however, something that can be predicted once it is known how much
fuel/air is going to be put into the kiln and how hot the kiln will be
operated.
> Trying to get my hands on a comprehensive kiln building book, but gotta
> wait for a few weeks for delivery.
If there exists such a thing please forward However, as yet, I haven seen
that our colleague Marc has put anything in print -- which is unfortunate
-- hint,hint.
> > But wait, your thinking that the ole' Alpine has it's burners crammed way up
> > in the port.
Does anyone from Alpine read Clayart? I hope so as these lame
self-destructing burner arrangements need to be resolved.
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