Paul Taylor on sat 28 sep 02
Dear All
I am thinking of building a new kiln 17 to 15 cu foot packing space.
I am keeping my old kiln 40 cu foot
I also plan to leave room for a salt kiln which I plan to share the same
chimney (built outside) as the new kiln. The fire bricks are scrounged for
a chimney all ready.
I am also thinking of using preheated primary air for all my kilns .
Fortunately I have the space . Behind my large kiln is enough space to put
a heat recuperator and I can design a space in the new chimney for one
easily.
I am hoping that once I have learned the techniques for building the
system I should be able to build it into all the kilns easily and cheaply.
The only information I have is in the Energy Efficient Potter by Regis C
Brodie . The essay on preheated air is by Buddy Francis . The information on
building the heat recuperator is very clear but I am worried that the burner
information is a little scanty.
My experience of building burners is limited to the venturi type with
internal ceramic cup burners - with slightly preheated secondary air coming
in at the bottom of the kiln . Preheated with the heat bellow the burners -
which I do not think is that efficient. For greater kiln control I would
like to cut out secondary air altogether.
Again I am not quiet sure how Buddy's burners work or how easy they are
to light and to keep alight . I am ok with building the manifolds for the
recuperators and I have some Ideas of my own on these. But in the burners
there are flame pilot ports and observations ports with no explanation of
how they are managed. I am not that worried about 'turndown' I will add the
odd venturi burner to the kiln for 'Candeling' and 'Ramping'
Does any body have any direct or indirect experience with the burners
shown in Buddy's article? I suppose the burners to be internally fitted
in to the kiln. Does any body know what safety feachers are needed and
where they go and how they are managed?
I would dearly like to get in contact with Buddy Francis if he is still
about.
Does any body have a contact number or an address?
Does any body know about other essays or books that would be helpful ?
I have not read Buddy Frances article from Studio potter ( 7 pp 61-66)
because I suppose it contains the same information I have from the 'Essay in
the energy efficient potter' book. But may be it contains a more detailed
drawing of the burner?
There is a book for sale 100$ aprox called Boilers and Burners: Design and
Theory (Mechanical Engineering Series) -- by Prabir Basu, et al. Has any
body any read or used this book and how helpful would it be? I can
understand grafts and formula and piece to gether most bits of jargonese but
I am wondering if the book is over kill for the information I need.
Also The Energy Efficient Potter book is twenty years old -- are there new
and better ideas in circulation?
I have access to help from engineers and a supplier of bits like blowers
and valves, and also access to, welding, threading, and forge, facilities.
The building of any thing is not a problem once I understand what I am
doing.
Grateful for all replies
--
Regards from Paul Taylor
There is no such fury as self interest posing as moral principle.
http://www.anu.ie/westportpottery
Bruce Girrell on mon 30 sep 02
Paul Taylor wrote:
> I am also thinking of using preheated primary air for all my kilns ...
> The only information I have is in the Energy Efficient Potter by Regis C
> Brodie . The essay on preheated air is by Buddy Francis .
I'm curious about this. It would seem to me that using preheated air would
_decrease_ combustion efficiency because of the less dense (hence less
oxygen available) preheated air.
I searched for the article that you quoted and did not find it. I did find a
site by Regis Brodie, www.brodieco.com, and maybe if you contact him he
could point you to Buddy Francis.
Bruce Girrell
in northern Michigan where fall is coming late this year.
Glad to be home from Kazakhstan.
Gavin Stairs on mon 30 sep 02
Hi Bruce and Paul,
Of course the blast furnace is predicated on the use of preheated air, so
that may be the origin of the idea. But...
The blast furnace burns coke or charcoal, basically solid carbon, and is
therefore limited in its top temperature by the energy balance of that
reaction. Higher temperatures can only come from preheating the fuel or
oxygen (air), or decreasing the inert load from nitrogen and gangue
(non-iron material in the ore charge). The blast furnace preheats by
recycling some of the furnace heat through air pipes called tuyeres to
preheat the blast air, which is of course blown in under slight
pressure. This raises the top temperature, but does not directly save any
energy.
Gas pottery kilns do not have any problem reaching temperature, as the
flame temperature is well above the target temperature, and heat transfer
is in no way limited. The value of preheating the incoming air would
therefore depend on the relative cost of heating the air by the gas flame
or by whatever preheater was arranged. If the preheat was scavenged from
the waste kiln heat, by means of a jacket around the chimney or the whole
kiln, there could be some economies. I doubt that preheating by means of a
gas or electric heater would save anything. The cost of the heat exchanger
would not be insignificant, so the benefit would have to be weighed against
that, and the cost of running the auxiliary blowers.
If you are talking about a wood kiln, then I think an air preheat could be
useful, especially in getting the kiln to heat fast. The best (simplest)
preheater would be a gas burner running in the primary air vent. Just a
smallish gas burner with a whole lot of secondary air. That would
immediately raise the temperature of the wood flame, and thereby increase
the rate of heat transfer to the ware, etc. It would also reduce the ash
burden, so it would be good for those not using wood for heavy ash deposits.
And Bruce, the energy balance is not much affected by the density of the
air. Just the mass. Of course the air handling system has to accommodate
the lower density air.
Gavin
At 10:12 AM 30/09/2002 -0400, Bruce Girrell wrote:
>Paul Taylor wrote:
>
> > I am also thinking of using preheated primary air for all my kilns ...
> > The only information I have is in the Energy Efficient Potter by Regis C
> > Brodie . The essay on preheated air is by Buddy Francis .
>
>I'm curious about this. It would seem to me that using preheated air would
>_decrease_ combustion efficiency because of the less dense (hence less
>oxygen available) preheated air.
Bruce Girrell on tue 1 oct 02
Gavin Stairs wrote:
> And Bruce, the energy balance is not much affected by the density of the
> air. Just the mass. Of course the air handling system has to accommodate
> the lower density air.
Yes, of course. I was somehow stuck in thinking only about natural
convection or venturis. Certainly a powered burner could deliver however
much air would be required for proper combustion.
Bruce "had my head in a dark place" Girrell
Bill Karaffa on wed 2 oct 02
-----Original Message-----
From: Ceramic Arts Discussion List [mailto:CLAYART@LSV.CERAMICS.ORG]On
Behalf Of Paul Taylor
Sent: Wednesday, October 02, 2002 3:20 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Building Burners ? ( a bit technical)
Check out Nils plans for using preheated air for forced air burners in his
book "The Art of Firing". This is a pretty simple system. While I haven't
tried it myself I would be tempted to give it a try in a future kiln.
Bill Karaffa
Firemouth Pottery and Gallery
Boulder Junction Wisconsin
http://fp1.centurytel.net/karaffa
Paul Taylor on wed 2 oct 02
Tanks Gavin
The recuperator I am thinking of building is set in the exit flue and
pushed through the recuperator and burners by a fan. I received a warning
privately that these ceramic systems were subject to leekage . I suspected
as much, even so a saving in fuel may be more economic here in ireland since
we pay over twice as much as americans.
As I said even the idea of learning to build a forced air burner seems a
good idea but its early days - I shall research a little longer.
The recuperator I have drawings for is made from a ceramic based on
silicone carbide . From what i remember silicone carbide is so refractory it
stands any thing except a knock. I will pack the whole thing with fiber
gaskets and buffers to allow for expansion.
A friend of mine (lost contact) told me about experiments they did at
Stoke on Trent collage . I may try to get hold of information from them.
I will also contact Mr Brodie.
I am also interest in building my own nozzle mixed burners these burners
would have to work with cold and hot air. Thats probably more down to
control of the blower.
--
Regards from Paul Taylor
http://www.anu.ie/westportpottery
In time the biggest hammer will fail to smash a nut that is the nature of
'disaster' - but also 'hope'.
> From: Gavin Stairs
> Reply-To: Ceramic Arts Discussion List
> Date: Mon, 30 Sep 2002 14:54:38 -0400
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Re: Building Burners ? ( a bit technical)
>
> Hi Bruce and Paul,
>
> Of course the blast furnace is predicated on the use of preheated air, so
> that may be the origin of the idea. But...
>
> The blast furnace burns coke or charcoal, basically solid carbon, and is
> therefore limited in its top temperature by the energy balance of that
> reaction. Higher temperatures can only come from preheating the fuel or
> oxygen (air), or decreasing the inert load from nitrogen and gangue
> (non-iron material in the ore charge). The blast furnace preheats by
> recycling some of the furnace heat through air pipes called tuyeres to
> preheat the blast air, which is of course blown in under slight
> pressure. This raises the top temperature, but does not directly save any
> energy.
>
> Gas pottery kilns do not have any problem reaching temperature, as the
> flame temperature is well above the target temperature, and heat transfer
> is in no way limited. The value of preheating the incoming air would
> therefore depend on the relative cost of heating the air by the gas flame
> or by whatever preheater was arranged. If the preheat was scavenged from
> the waste kiln heat, by means of a jacket around the chimney or the whole
> kiln, there could be some economies. I doubt that preheating by means of a
> gas or electric heater would save anything. The cost of the heat exchanger
> would not be insignificant, so the benefit would have to be weighed against
> that, and the cost of running the auxiliary blowers.
>
> If you are talking about a wood kiln, then I think an air preheat could be
> useful, especially in getting the kiln to heat fast. The best (simplest)
> preheater would be a gas burner running in the primary air vent. Just a
> smallish gas burner with a whole lot of secondary air. That would
> immediately raise the temperature of the wood flame, and thereby increase
> the rate of heat transfer to the ware, etc. It would also reduce the ash
> burden, so it would be good for those not using wood for heavy ash deposits.
>
> And Bruce, the energy balance is not much affected by the density of the
> air. Just the mass. Of course the air handling system has to accommodate
> the lower density air.
>
Gavin Stairs on wed 2 oct 02
Hi Paul,
I doubt you need to use ceramic tubes. They are very expensive. I think
you might do well enough with thin wall steel tubing, and replace it when
it blows out, which it will soon enough. The thing to do would be to
arrange a counter-flow heat exchanger in the stack, with simple tubing
(perhaps stainless steel exhaust pipe for gas fired domestic appliances)
such that the hot gas is always only a wall thickness away from the
counter-flowing air. That will tend to reduce the temperature of the tube
wall to something a bit above the mean temperature of the two gasses. So
you blow cold air in at the top of the stack and bring it out at the bottom
of the stack, and then run as short as possible a duct to the air intake of
the kiln. This outside duct should be insulated with fibre if
possible. The system will tend to corrode at the bottom of this
arrangement, so you should make that section as easy to replace as possible.
The stack will have to be made about twice as large as normal, to
accommodate the reverse flow duct. There will also be a reduction in the
flue draught, as the temperature of the chimney will be reduced. So you
will probably have to use a blower. One at the cold end of the ductwork
may suffice. The damper would be at the hot end of the exchanger, and be
of the bypass sort, so that there is always a stream of cold air flowing
through the exchanger to prevent it from overheating.
This arrangement will not seal out all the flue gasses from the draft air,
but that shouldn't be too much of a problem: just allow you to recycle some
CO as well as the heat.
I would start out with the simplest possible arrangement, and then improve
it by degrees as it teaches you what it needs.
Gavin
At 09:19 PM 02/10/2002 +0100, you wrote:
>The recuperator I am thinking of building is set in the exit flue and
>pushed through the recuperator and burners by a fan. I received a warning
>privately that these ceramic systems were subject to leekage . ...
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