isnorchd on thu 13 jan 00
------------------
1/13/00
A friend is building a gas kiln and is running into some problems with which
someone on the list might be able to help. Last night he faxed me the =
following
and asked me to post it:
What is the correct dimension and relationship of the EXIT at the =
back
of the fire chamber, going into the collecting chamber in front of the =
chimney?
The kiln is a downdraft 63=22 X 63=22 X 63=22 using eight (8) gas inlets =
9=22 X 4 1/2=22 -
TOTAL 324 Sq. In.
The chimney will have a base 18=22 X 18=22 inside, 324 Sq. In.
Thanks very much for your help.
Don Beckerman
isnorchd=40nk.ksc.co.th
Isan Orchid Guest Lodge
Thabo, Nongkhai, Thailand
The Gateway To Indochina
ferenc jakab on fri 14 jan 00
Don, I don't know what the "correct" ratio is, though I think I did find out
when I built my Kiln. I used a ratio of 1:4.. I.e. my 8 burner ports add up
to 576 sq inches and I used a flue exit size of 144 sq inches, 12"x 12" but
this is reduced by a full brick on end in the middle of the "throat" used as
support. The collecting chamber size is roughly 24 x24 x 24 inches. I find
that at 1250 deg Celsius I have the baffle open about 2" and it is
oxidising. The baffle is an 18"sq 3/4"kiln shelf.
Hope this is of some help. I found that the collecting chamber size was the
most critical thing with my kiln. If your exit is too large you can use the
baffle to reduce the venting gas's flow, but if it's too small then the kiln
is forever reducing.
Feri.
Dorothy Weber on fri 14 jan 00
I believe the exit flu should be at least the same size as the entrance flu,
but your entrance flu seems exceptionally large. Let the real guru's on
clayart comment.
Peter Jones on fri 14 jan 00
Don: That is a whopping big chimney your friend is putting on a relatively
small kiln. Most chimneys need only be 9X9" unless the stack height is very
short. With a chimney that large, he is liable to get such a strong draft
that all the heat will be literally sucked straight to the back of the
stacking area and cause all sorts of uneven fired results. Even having a
small outlet at the back of the kiln will only increase the speed of the
flow of gases, not cut down on the draft itself.
Comparatively speaking, my kiln is roughly the same size, maybe a bit
taller. I use two forced air burners that run along the bagwall as opposed
to hitting it directly. They also come from opposing corners of the kiln:
one from the left front, the other from the right rear. This sets up a bit
of cyclonic effect in the stacking area. I also have extended the flue out
into the middle of the stacking beneath the bottom kiln shelf layer so that
the gases are all drawn towards the center of the kiln rather than the back
of it. Fired results are extremely even, front to back, top to bottom,
usually only 1/4 cone difference.
The burner port openings (only two of them) are 4 1/2" X 7 1/2" The flue is
about 9" X 7 1/2", chimney is 9" X 9" and 14' tall. As it is, I usually
keep the damper pushed way in so as not to create too much draft. No point
in sucking out all that heat when the idea is to keep it inside the kiln
where it does the most good.
If it's not too late, I suggest he make a smaller diameter chimney and make
the flue opening the same as the chimney size: about 9" x 9". He can
always close it down, but it's near impossible to make it larger. Also no
point in making it larger than the chimney diameter since it is only as
effective as the largest diameter in the whole design.
Peter Jones
----------
>From: isnorchd
>To: CLAYART@LSV.UKY.EDU
>Subject: Re: Fire chamber exit
>Date: Thu, Jan 13, 2000, 4:42 PM
>
>----------------------------Original message----------------------------
>------------------
>1/13/00
>
>A friend is building a gas kiln and is running into some problems with which
>someone on the list might be able to help. Last night he faxed me the following
>and asked me to post it:
>
> What is the correct dimension and relationship of the EXIT at the back
>of the fire chamber, going into the collecting chamber in front of the chimney?
>
>The kiln is a downdraft 63" X 63" X 63" using eight (8) gas inlets 9" X 4 1/2"
>TOTAL 324 Sq. In.
>
>The chimney will have a base 18" X 18" inside, 324 Sq. In.
>
>Thanks very much for your help.
>
>Don Beckerman
>isnorchd@nk.ksc.co.th
>
>Isan Orchid Guest Lodge
>Thabo, Nongkhai, Thailand
>The Gateway To Indochina
>
>
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