Reid Harvey on sat 1 sep 01
Friends,
This is my second time posting this:
Venturi burners are made here in Bangladesh and there is a good supply
of gas. So several of us are anxious to build a gas kiln or two, to
substitute for the more widely used electric kilns. Electricity is more
expensive and the power supply is not dependable. We would like to build
a small production kiln of 1.0 to 2.0 cubic meter capacity, probably a
catenary arch, and we'd appreciate any observations on appropriate
burner size, as well as dimensions of ports and flue. I suspect we'll
end up doing cross draft.
Also, any insights on a simple way, at the beginning of firings, not to
get a kiln full of unburned gas would be appreciated. A lot of the
automatic equipment used in the U.S. and elsewhere is not available
here, so we won't be able to use the same kind of pilots, fail safe
shutoff, etc. Worst case we'll just have to eyeball the flame, pretty
much until it's self igniting. This approach makes me a bit nervous. At
some time in the past I'm sure the burners were successfully used
without these devices. Or maybe we could make a primitive pilot. Any
ideas?
I would imagine that some potters can do successfully do without the
extra equipment, but would imagine they went through a tenuous breakin
period, and have come to know their kiln inside out. My experieince with
gas is limited to use smaller kilns back in the dark ages, but the
bigger kilns seem to be a different ball of wax.
Reid Harvey
To read a recent presentation on earthenware water purifier candles,
click:
http://phys4.harvard.edu/~wilson/remediation/ACER.html
vince pitelka on sat 1 sep 01
> Venturi burners are made here in Bangladesh and there is a good supply
> of gas. So several of us are anxious to build a gas kiln or two, to
> substitute for the more widely used electric kilns. Electricity is more
> expensive and the power supply is not dependable. We would like to build
> a small production kiln of 1.0 to 2.0 cubic meter capacity, probably a
> catenary arch, and we'd appreciate any observations on appropriate
> burner size, as well as dimensions of ports and flue. I suspect we'll
> end up doing cross draft.
Reid -
It is pretty difficult to give specific recommendations based on the
information you give above. You could email Marc Ward at wardburner@aol.com
and explain your situation and I expect he will be very generous with
information. A one cubic meter kiln is about thirty cubic feet, and I think
that the heat requirements will be about 400,000 BTUs per hour to reach cone
10 in a timely fashion. In very general terms, the venturi burners we use
for such a kiln, such as the MR-100 GACO burners Marc sells, are about 3
1/2" or 4" in diameter, and four of them produce the needed BTUs for a kiln
this size when operating on low pressure propane. If you go for a kiln
closer to two meters, you will of course have to increase the number of
burners. Also, if you increase the gas pressure you will produce more BTUs
per burner, but the burners will also become much more noisy. I always
prefer natural gas or low-pressure propane, so the burners run quiet. It
might take more burners, but it will be worth it for general peace of mind.
> Also, any insights on a simple way, at the beginning of firings, not to
> get a kiln full of unburned gas would be appreciated. A lot of the
> automatic equipment used in the U.S. and elsewhere is not available
> here, so we won't be able to use the same kind of pilots, fail safe
> shutoff, etc. Worst case we'll just have to eyeball the flame, pretty
> much until it's self igniting. This approach makes me a bit nervous. At
> some time in the past I'm sure the burners were successfully used
> without these devices.
Baso valves are small, so overseas shipping would be relatively cheap.
They could be ordered from the States, and they do not require any external
power supply, and therefore would work fine on your system, if you can order
them from Marc Ward or some other supplier. The Baso valve and pilot
assembly will cost you about $150 per burner, but may well be worth it for
the peace of mind, depending on the nature of your installation. As another
option, you could install a "ring burner," a continuous tube burner (like an
oven burner) with small holes all along its length. The ring burner
supplies flame to ignite all the venturi burners. With this system you
would only need a single Baso valve on the main feed to the kiln burners
(the ring burnes AND the venturis), with a pilot light which ignites the
ring burner. The ring burner is necessarily a low-pressure device, and the
flame is very low, and its primary fault is that it is easily blown out by
cross drafts from the weather. If the pilot is also a low-pressure,
low-velocity pilot, it will also blow out easily, and thus your system is
prone to shut off easily and frequently when the wind is up. If you need to
have the kiln in a location where it is exposed to powerful gusts of wind,
the ONLY solution is to have higher-pressure burners and pilots, which are
relative immune to weather effects.
I am ALWAYS in favor of proper safety devices, but I will readily admit that
as a hippie potter in Northern California we often fired outdoor kilns with
no safety devices at all. I do not recommend it under any circumstances.
It just is not worth it. But in your situation it may be the only option.
Such a kiln should always be located away from any buildings, under its own
shed, with abundant ventilation. As long as you light the burners the
instant you turn on the gas, you will not fill the kiln with gas. I would
ONLY use this system with at least 5 PSI of propane, so that the burners run
with considerable velocity, drastically reducing the chance of blow-outs due
to the weather. Please keep in mind that I tell you this in case it is the
ONLY available option. For anyone else, always use Baso valves at the
least.
You can make very efficient pilot burners. If you decide to go this way, I
can give you some pointers.
Good luck and best wishes -
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://www.craftcenter.tntech.edu/
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