Vince Pitelka on wed 7 apr 04
> It's not that I love the Alfred burners...it's more that I can afford
them,
> and they do the job I need doing. I don't want weed burners, mega
burners,
> power burners. I make some large pots, and I single fire everything. I
> need to have a slow firing. I actually did a burner search for something
> that would give me 100,000 BTUs with low pressure and natural draft.
Maybe
> I'm blind, or not looking in the right place, but it was very hard to find
> anything like that. Going through Marc Ward's catalogue, I found that I
> could rig up six underpowered burners with thermocouple and pilot for over
> three thousand bucks.
Richard -
Mark Ward sells the GACO MR-100 cast iron venturi burner for $58 each. They
don't have the finnesse of a Ransom, but they are wonderful burners, and
they turn down very low with no problems. Michael McDowell's kiln is 40
cubic feet, softbrick, and with six of them at 7 WCI it is way overpowered.
I really do not know if six MR-100s at 7 WCI would be enough for a sixty
cubic foot kiln with a hardbrick interior, but if you could double the
pressure I'll be they would work great. Raising the line pressure would
also balance out your manifold pressure.
You have no doubt done lots of gas plumbing. If you are using Alfred pipe
burners, then obviously codes and inspections are not an issue, so why not
assemble the burners yourself and save a big chunk of money? I have brand
new Johnson Controls low-pressure basos and target pilot burners at school,
and I can email you the model numbers. You can order them from your local
commercial plumbing supplier along with all the other parts you need to
build your own burners.
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
Richard Aerni on wed 7 apr 04
Before too much time goes by, I wanted to extend a big thank you to all who
took the time to consider and respond to my situation with my kiln. It's
heartening to feel the good vibes from the distant masses!
I've printed everything up and will spend some time considering and mulling
while waiting for the utility complany to get to my issue. At first glance
there seems to be a fairly broad spectrum of points of view, some of which
appear to be contradictory.
For those of you who asked more questions...
The burners are Alfred aspirating burners. Orifice size Morris Twist Drill
#19, which at 7 WCI should provide me with approx. 100,000 btus per hour.
There are six burners for a kiln which has 62 cubic feet of interior
space. This ratio of btus/cubic foot is pretty much the same as I've had
in earlier models of this kiln, which have all worked fine. I understand
that in shrinking the cubic feet by 30% from my earlier models, I have
effectively made the kiln less effective, since the proportion of wall
space (heat loss area) to interior space has increased.
My stack is square, about 15 1/2 feet high, starts out 13 1/2 by 13 1/2 and
tapers to 12 x 12. It does come out of the roof into an area which is
sheltered by an adjacent wall, and this may present some vacuum/drafting
issues. I was up on the roof during the firing, though, and draft seemed
to be fine. During the firing, and in particular in the latter stages of
the firing, there was never a point at which there was significant back
pressure at the burner ports or in the kiln. I had to work to get that
lazy flame of which I spoke. I am considering raising the stack another
five feet to bring it above the height of the adjacent wall. I cannot
determine gas velocity through the kiln at present as I fired it alone, and
can't do the oily rag test, as the smoke would have exited the chimney by
the time I could run around to a point where I could view the chimney. I
did leave the kiln firing for four hours after cone eight began to tip,
thinking I'd let time and not btus bring down the remaining cones, but
sadly, they did not tip further.
The bag walls are 22 1/2 inches high. This is a height that has worked for
me in the past.
I am now firing with natural gas. Typical household pressure of natural
gas is 7 WCI. My previous kiln was propane. Typical household pressure of
propane is 11 WCI, which was the pressure I had in the old kiln. The
orifices were #31 Morris Twist Drill size, which should provide approx.
100,000 btus per hour at 11 WCI.
The burner ports are 4 1/2 x 5 inches, expandable to 4 1/2 x 7 1/2.
Together their area is 132 1/2 cubic inches, while my exit flue is sized at
125 cubic inches, though I never had the damper open more than 3 1/4 inches
during the firing, meaning that the effective exit flue was 40 cubic
inches, at most. The burner ports and exit flue have been shrunk
marginally from the previous kiln.
I'm intrigued by Hank's observation about the decreasing manifold size
supplying constant pressure. Hank, is there a chart or graph anywhere
where I can get an estimate on the proper decrease in pipe size to maintain
constant pressure?
I may have forgotten some questions. If so, I apologize. I'm going to
head off to the studio to try to make some pots while mulling all this
over. Big thanks to Sabra Wood (my new studio mate...still looking for
other intrepid souls who may wish a workspace) for printing all your
replies out and bringing them down to me.
Best,
Richard Aerni
Rochester, NY
Hank Murrow on wed 7 apr 04
On Apr 7, 2004, at 6:14 AM, Richard Aerni wrote:
> Before too much time goes by, I wanted to extend a big thank you to
> all who
> took the time to consider and respond to my situation with my kiln.
> For those of you who asked more questions...
> Snip.....I am now firing with natural gas.
Dear Richard;
You are going to love Natural gas. It has from 8 to 12% water vapor
included, which will make it easy to get nice reduction at higher
temperatures.
> I'm intrigued by Hank's observation about the decreasing manifold size
> supplying constant pressure. Hank, is there a chart or graph anywhere
> where I can get an estimate on the proper decrease in pipe size to
> maintain
> constant pressure?
Pipe sizes offer the most cost effective way to accomplish this. Start
with the largest size at the front burner(closest to the supply) on the
manifold, and drop one pipe size to the next. Then drop one more pipe
size to the third burner. That shoud do it if your main supply line is
big enough. You can check the resulting pressures with a homemade
manometer made from a "U" shaped clear tubing half filled with water or
light oil. Make a mark where the first burner maxes out, and then check
the others. I am betting that if you step down the pipe sizes as
described herein that you will have even pressure at all three burners.
Richard, I know how much you love those Alfred Style pipe burners, but
Sometime in the next year or so I will convince you to try some Eclipse
mixers. One on each side feeding the gas/air mixture to three Sticktite
tips will amaze you with both full on capacity and gentle turndown. You
can run these at a whisper. But that can wait until you have a few
loads out to pay your immediate bills in the new studio!
Cheers and Good Luck!
Hank in Eugene, heading your way to do workshops during May/June in
Annapolis, Greenbelt, Far Hills, and Storrs. Hope to meet you for a
studio visit.
www.murrow.biz/hank
Richard Aerni on wed 7 apr 04
Hank,
It's not that I love the Alfred burners...it's more that I can afford them,
and they do the job I need doing. I don't want weed burners, mega burners,
power burners. I make some large pots, and I single fire everything. I
need to have a slow firing. I actually did a burner search for something
that would give me 100,000 BTUs with low pressure and natural draft. Maybe
I'm blind, or not looking in the right place, but it was very hard to find
anything like that. Going through Marc Ward's catalogue, I found that I
could rig up six underpowered burners with thermocouple and pilot for over
three thousand bucks. I've no trust fund, my prices are modest, as is my
income. If that's what I have to pay for burners, well, maybe I should go
into low fire electric.
I'll gladly accept referrals about suitable burners that can be had
relatively cheaply.
And many thanks for the explanation about the manifolds.
Richard Aerni
Craig Martell on wed 7 apr 04
Hello Again Richard:
If your kiln is 62 cubic feet total space with a hard brick interior and
you factor in the minimum recommended btus for that type of kiln to be
fired to cone 10 (16,000 btus per cubic foot), a value of 920,000 btus per
hr is what you would need at peak input. With your current setup, you are
more than 300,000 btus short. When you fired with propane at your old
digs, I would assume that you had about 10psi coming out of the tank which
gives a more positive backup for equal pressure at each burner and will
also determine your btu input for any given orifice size.
Your current situation requires about 165,000 btus per burner and if you
increased your manifold pressure and your working pressure against the
orifices the burners would entrain primary air more efficiently and your
btu input would be at a point where cone 10 would be down in good
order. Aspirating burners need a certain pressure drop value across the
orifice to function well. The higher the pressure against the orifice, the
greater the drop as gas passes into the mixer where this drop creates a
negative pressure that entrains the air. I think this is the most
practical solution for you current shortfall. I don't think that resizing
each burner supply line is as practical and would be unnecessary with a
higher manifold pressure. Hank's thinking is very sound but maybe a bit
too creative, I think it would be more practical to increase the supply
pressure. My hard brick kiln uses four venturis. I put 10 psi in the
manifold and max the burners at 2 psi with no pressure difference at any of
the burners because of the higher manifold pressure.
Your stack diameter could be part of the problem. 13.5" is humongous and
even 12" is too large from my experience. If the stack is hard brick too,
it's a total heat wick and is causing problems with temp in the ware
chamber. Are you seeing a lot of flame at the damper when you are at peak
input? If so, you're losing heat to the stack that is better used in the
ware chamber. Those big diameter stacks will cause a real severe drop in
exit velocity of gasses too. I have a 66 cubic foot soft brick kiln that
has a 9 by 9 inch exit that goes just over the damper, maybe 18 inches
total height. I then have a 10inch steel pipe that's lined with 1 inch
kaowool risers for a diameter of 8.5 inches and I get very good draft with
little heat loss to the stack.
If you want rock solid, right on advice on how to fix this problem in the
quickest, most effective way, I would talk to either Marc Ward or Cameron
Harman. These dudes ain't free but they know kilns and how to make them work.
regards, Craig Martell Hopewell, Oregon
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