[Stoves] Crispin´s kiln. (was Re: Traditonal Charcola Making Process / retort

Thu Jul 5 01:54:57 EDT 2007

Crispin and all,

Subject changed to refect what we are actually discussing here!!

I am just a novice at this stuff, but I think I can assist in a practical way.

A question or two and comments:

1.  You say you need power of 35 KW.  But at is an electric kiln, right?  Is
that 35 kWe, and on a 10% cycle?  And can you translate that into total energy
needed in terms of kWt (thermal kW is what we are after), and also the time
schedule for the delivery of the heat.  We want to determine the specifics of
the power kWt/hr during the duration of the firing.  If it is on a 
hourly basis
then the kW energy and the kW/hr power are equal, right?.  But if you want ¨X¨
of kWt energy delivered in 30 minutes, you need ¨2X¨ kWt/hr, right?   (AJH and
the 2 Tom´s, please help me here.)

2.  With a professor/engineer here in Managua, we have been discussing a
semi-continuous-operation kiln (for bricks) that does not need to cool down
after each load of bricks.  Pretty simple design.  Are you wanting 
batch firing
or continuous operation?  If continuous, then the size of the main kiln 
chamber
can be much reduced and still produce the desired number of units per 
day. Here we are talking of 2 cubic meters, with the volume of bricks 
much larger
than your volume for the stoves.

3.  Gasifiers are the answer.  At Chip Energy, my partner and I are 
developing a
biomass furnace that does about 60 kWt/hr (200,000 BTU/hr).  We can go much
lower in power and probably higher, or add a second gasifier.  (This is
continuous operation using the AVUD (Another Variation UpDraft) gasification
technology.  See the prototype at   www.chipenergy.com   ).  We have excellent
control of the primary and secondary air, so there should not be much surplus
air into the kiln.  But the amount of air plus gases that enters must also
exit, and that means some waste but also means circulation and flow to reach
all the items.

Paul

-- 
Paul S. Anderson, Ph.D., Geography professor - Emeritus
Telephone:  USA-309-452-7072 (residence and office)
Internet site:  www.ilstu.edu/~psanders
For my gasifier stoves info, go to:
http://bioenergylists.org/contributors#Paul_Anderson

Quoting Crispin Pemberton-Pigott <crispinpigott at gmail.com>:

> Dear Tom
>
>> How many stoves per batch and what size kiln do you need?
>
> Well...this will be an interesting piece of math.  I have to heat the oven
> at the fastest rate that will not melt the material (PK11).  We melted about
> 200 stoves working out how to do this!  This problem is visible in the
> temperature ramping I described before - as it gets hotter I have to slow
> down of the stoves near the elements melt.
>
> The duty cycle of the electric elements is only 50% or less at any time.  I
> am hoping that the gas fire will circulate the heat much better than the
> electric oven so that I can increase the temperature much faster.  This will
> decrease the cycle time and give me more stoves per day.
>
> At the moment the experiments are being run in a 0.7 M^3 kiln with 28 stoves
> in it.  It will hold 29 but I can't get good enough circulation of the air
> (even temp) unless I move the shelves around.
>
> Thus getting a better kiln design is a top priority.  I am looking at 3
> cubic metres with a gas flow path that ensures more even heat distribution.
> More heat is wasted using gas but it solves a difficult heat distribution
> problem.
>
> So the power required will be higher than an equivalent electric oven
> because a) it wastes heat and b) it will be ramping faster and c) there will
> be more MCS mass relative to the oven wall mass (which is insulative).  So I
> want to model the power demand before ordering the kiln, and the gasifier
> will have to match that.
>
> The power demand is non-linear.  The power required at the beginning (on the
> present 2 identical ovens) is 35 KW, and the duty cycle is 10% to start
> with.  Because of poor air circulation, it is on full power for 10% of the
> time on a 30 second cycle.  This allows the heat to distribute well.  This
> phase is for drying the clay.  Later the crystal water is driven off at a
> higher power rating, then the charcoal burned out at a low power (but at 600
> C) then it is ramped as fast as possible without melting the stoves.  The
> gas + air movement will really help with that.  At 1170 it is held for 3 hrs
> at a low power mostly to ensure the heat distribution is good.  I want to
> reduce that to perhaps 30 minutes.  Then the power is shut off.
>
> So the determination of gas volume from the gasifier will be decided by the
> ramping rate from 600 to 1170 (or 1250).  I have a reasonable model of what
> is happening now which is why I could tell you that there is 3.5 KWH in the
> firing of one stove.  In a large stove that will drop - perhaps to 3 KWH or
> less.
>
> Ideally we should get the cycle time down to 12 hours so we can do two loads
> a day per kiln.  That would be good - and the gasifier would have to produce
> for 8 of that I think.
>
> If it was 3 cubic metres it would hold about 125 stoves.  The total power
> demand would be in the neighbourhood of 420 KWH.  With Kevin's analysis
> taken into consideration and your 2.75 Kg we are talking about loading
> 350-400 kg of wood into the gasifier.  Let's go for 450 kg or 1000 pounds.
>
> That sounds manageable.
>
> If the gas fire temp is reliably in the 1300 range I can raise the firing
> temp and reduce the production cost which I like as a side benefit.  That
> would require going back to the ceramics lab for a new formula but it would
> be worth it.
>
> The spreadsheet will not look too complicated and we can bounce if back and
> forth.  The things I want to see clearly are
>
> Gas volume produced
> Heat content
> Variable production rate assured
> Temperature max
> Sustainable power max
> Charcoal yield (which takes a back seat, however but I like the $$)
>
> Thoughts, anyone?
>
> Regards
> Crispin
>
>
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