Paul Taylor on fri 10 jan 03
Dear Hank and all
Thanks for the reply. I have not had much time over christmas for any more
study. Just before christmas I went to change the tap washers in the
bathroom and ended up putting in a new bath room plastering the walls and
all . the job did not go well as I have metric fittings on the tap and
heating end (Ireland uses imperial sizes) and lead on the other - all set in
concrete. God knows I need a holiday to recover from the holidays.
The mail saga
I am the sort of person that goes where angels fear to tread regardless of
expertise . This explains the E mail not working. Where as most people take
their computer to the server or a friend 'that knows all about that sort of
thing' and there after leaves well alone; my independent streak tends to go
it my own way. Even if I do get something off the shelf I have mixed
emotions. especially when it goes wrong: one of obvious annoyance and one of
excitement - cause I get to undo it and look in side to see how it works.
Any way the e-mail was a 'botch' up between, me, my server, and my computer.
Me because I tinkered with my settings - something a dyslexic should not be
doing.
My server, accepts two addresses taylor@anu.ie and taylor@mail.anu.ie I
decided this was confusing so I changed my settings to just use the former
and made a mistake.
My server is still is a bit choosy about the other servers it will deal with
so when I asked for advise they defended this position. Which did not help
because that was not the problem.
And for the most mischievous reason My computer resets the old inaccurate
settings every time I turn the darn thing on . So if in doubt use the 'go'
address I will keep an eye on the return address settings-- I need a
holiday so badly.
Kilns and burners, which unlike bathrooms and computers, I should know about
------------------------
I expect the weather in your part of the globe is similar to the West of
ireland where I live Wet and windy . In fact your post has completely
undermined my thinking . If Hank can get a decent reading off his manomiter
there by controlling his kiln so can I. So I am going to do some more
experiments with the equipment I have before spending money . Including The
venturi flue bit that Neils recommends.
--------------------
I am still trying to get my head round the subtile differences between the
three burner systems and their various nuances.
What I think so far is that the three systems have their advantages and
disadvantages that change with context.
The system most used is similar to the one I use, except I have
misunderstood how to run it efficiently. It seems from what you are saying
that the atmospheric system runs best with lots of burners giving off soft
flames ( lots of secondary air) . This is not wasteful of gas and gives an
even firing.
I imagine lots of soft flames washing slowly through the ware.
So I tried a little experiment in my kiln 40 cu ft and turned the burners up
full 'whack' What I got was a faster but very uneven firing with any
discrepancy in draft through out the kiln exaggerated by hot spots. So I am
tempted to put another two venturi burners into the kiln to improve its
efficiency - a broader flame spread
I am supposing The criteria for a kiln using venturi burners is that it is
very well built because you need to have the secondary air coming in near
the burners and not as a draft through cracks . I suspect that your kiln is
extremely well insulated. Is it and with what?
The next bit of technology is the forced air blower the advantage of this is
that you can blow the heat round the kiln which allows the flame to give off
its maximum amount of heat before it leaves the kiln and also allows for a
positive pressure in the kiln so the chimney is not so important . The
damper setting only control the kiln pressure but not the amount of
secondary air . The rub is that the flames from such burners can give hot
spots where the burners go into the kiln and cold spots where the flame does
not travel so fast. You can compensate for this with an open kiln setting
and or blowing the flames onto a brick (Baily's) do this. The flame smashes
off the brick and ricochets in all directions giving an even firing . My
question would be once the flame has hit the brick and or other methods of
dispersal. Is it traveling any faster than a venturi system even with lots
of secondary air. Or are all my friends on clayart swimming a against the
tide of progress due to their refusal to rely on our highly efficient
electricity suppliers:)
There are advantages in the forced air system in that you can measure more
easily the amount of gas and air you are using and that the negligible use
of secondary air means that the reduction is even through out.
There is another idea which some have mentioned, but I do not know if this
is a theory or if someone has it working. It is to run the burners so there
is a swirling of gases around the kiln with the flue exit at the middle
bottom of the kiln. I have seen this suggested with venturies also (firing
the venturi burners round the side and then the excess disappearing down a
plughole in the middle) whether this gives an even flame distribution I do
not know - it looks good in theory.
The third option is a nozzle mix burner that blasts a flame through the kiln
at such a speed that it all ends up evenly fired. You can measure exactly
the proportion of gas to air for perfect reduction control and the flames
that are swirling round the kiln give off all their heat before leaving the
kiln. The rub is that these burners take no prisoners and need a safety
system that looks like a small oil refinery That cost more than the burners.
I have not been able to 'suss' out which part of the safety systems that I
have seen on nozzle mix burners are essential, which parts are paranoia, and
which parts give superior computerized firing control. Or is the basic
safety system so expensive it makes the rest seem economic. Also we are
relying on those champions of efficiency and customer service at the
electricity supply company (I must be related) ....
As I said before I think some of all this depends on the context of how big
your kiln is and how accurate you want it to fire . If I was building any
kiln over 40cu ft I would go for a nozzle mix system and be tempted to
incorporate preheated air because the economy of scale would make the safety
and controls of the nozzle system worth while.
However with any thing under this size I am not quiet sure if any of the
forced air systems are more even or more accurate than a venturi atmospheric
system. If there is no difference, I can do with out reliances on the
electricity. If there is some improvement with a forced air system I am
tempted to use it. And if there is a minimum safety system that does not
break the bank I might try a nozzle mix system for the greatest of accuracy.
I expect for now I will use the venturi system but build two forced air
burners as well to try out the difference and I can use the forced air in a
salt kiln later on if I find it at all efficient.
By the by
into my 40cuft kiln I have four two inch venturi burners firing at 3 ppsi
this will get me to 1260 with heavy reduction in eleven to twelve hours
depending on the load. However the secondary air for these burners enters
the kiln through the bottom of a side wall and is ducted underneath the
burners which are set into the side walls of the kiln.
This works but I do not know enough about combustion to know if there is any
inefficiency in this as opposed to letting the secondary air in around the
burner set an inch out side the kiln. (apart from the safety ).
I use
The kiln is built with an inch of fiber stuck onto 4.5 in HTI's (k24s I
suspect) then 4.5 in of vermiculite brick laid dry.
the kiln is downdraft with a flue running the length of the kiln
I am tempted to close off all the flue except the middle and restrict the
opening to encourage an acceleration of air at the entry point (nils Lis).
I have writain some to Craig who is still with me on my pedantic quest.
--
Regards from Paul Taylor
tamlin1952@go.com
http://www.anu.ie/westportpottery
Phone International 00 353 98 21239
From the Republic of Ireland 098 21239
Paul Taylor
Westport pottery
Liscarney
Westport
County Mayo
Ireland
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