[Terrapreta] Farm Scale Batch Charcoal Furnace for Homestead orFarm

[Sean K. Barry]

I have a 200,000 BTU outdoor wood burning furnace 100' from my house.  I have burned 10-12 full 4'x4'x8' cords of red and white oak each winter since 2001.  I get 10 (or 20) cords of oak logs delivered every year (it's about ~2 tons cord green, 10 cords on a 40' flatbed).  I have to cut 10-12 cords of 8' logs into <36" pieces for the furnace (3 x 32" = 96", 2 cuts), split more than half of it, and stack it next to the furnace each year.
My 17 year old son, Kevin, helps now.  With a chainsaw, a power splitter, splitting wedges and sledges, a four-wheel drive ATV, a trailer, and a covered woodshed, it takes us both 5-6 weekends, all weekend, in the summer and fall to ready the winters wood.  We heat a 4200 sq foot, two story log house, we make no charcoal, as yet, and we do not harvest combustible fuel gases.

An atmospheric pressure pyrolysis reactor/furnace, which could simultaneously produce an extraordinarily efficient 35-40% yield if "fixed Carbon" (fC) and 200,000 BTU of sensible heat would either produce little or no combustible fuel gas, or heat, or would need to have both a high throughput and extraordinarily efficient performance.  I load our furnace in the winter about 1 cord of dry oak every 1 1/2 weeks, twice a day  (~3500 lbs dry every 21 days).

The manufacturer of the furnace I own, HeatMor, claims 70% efficiency with a water only.  It's rated at 200,000 BTU/hr (200CCSS).
I thought about sucking air down through its chimney, out the bottom and burning the ejected gas to make charcoal inside it.  It would have been cumbersome to remove the charcoal.

If one wanted to produce a 25-35% fC yield from the biomass, this would reduce by about 50-60%, the amount of chemical energy from the biomass that would be available for heating (or harvesting combustible fuel gases).  Only 28-35% (0.70 * 0.40-050) of the biomass energy would ever make it to warming the house.  This means, that if I wanted to make charcoal at 25-30% yield and still heat the house, Kevin and I would need split more than 3-4 times as much wood as we do now.  And all we would get for our labors is charcoal and heat.

If you add harvesting combustible fuel gases to the desired product stream, then this will decrease the other two or increase the total amount of biomass feedstock, which is required.  Unless the system is highly automated and there is a ready cheap available source of a large feedstock usable biomass for that particular reactor design, then getting combined heat and electricity CHP from biomass isn't doable.

You might try to make an energy budget estimate for your farm, then convert that to BTUs and see how much biomass you'd need at say run at 70% heat efficiency and 35% KWe efficiency.  Then figure in tons of wood multiplied by the labor cost of the steps to process it; cut it, split it, chip it, stack it, lift it, move it, load it, unload it, etc.

Regards,

SKB


  ----- Original Message ----- 
  From: Sean K. Barry<mailto:sean.barry at juno.com> 
  To: terrapreta at bioenergylists.org<mailto:terrapreta at bioenergylists.org> ; AJH<mailto:list at sylva.icuklive.co.uk> 
  Sent: Monday, April 07, 2008 6:58 PM
  Subject: Re: [Terrapreta] Farm Scale Batch Charcoal Furnace for Homestead orFarm


  Hi David Stewart,

  I've seen your last few posts and have been reading along to find out more of what you are interested in.  Pyrolysis of biomass for the production of charcoal, heat, and/or combustible fuel gases is very interesting thermodynamic process.  The first thing to keep in mind is that there is a finite amount of chemical energy in the biomass.  Desiring to produce all of charcoal, heat, and combustible fuel gases at usable levels necessarily requires more biomass fuel.  Secondly, the configuration of the pyrolysis process (top-load-up-draft, down-draft, fluidized-bed, etc) and management of the thermodynamics and chemical stoichiometrics is critical to the efficient operation of the device.

  There exist few devices that are even close to fully automated.  Take a look at the Community Power Corporation website (http://www.gocpc.com/<http://www.gocpc.com/>) for an example of a $500,000 15kWe biomass fueled generator.

  Regards,

  SKB
    ----- Original Message ----- 
    From: AJH<mailto:list at sylva.icuklive.co.uk> 
    To: terrapreta at bioenergylists.org<mailto:terrapreta at bioenergylists.org> 
    Sent: Monday, April 07, 2008 12:10 PM
    Subject: Re: [Terrapreta] Farm Scale Batch Charcoal Furnace for Homestead orFarm


    On Mon, 7 Apr 2008 10:12:06 -0500, David Stewart wrote:

    >No. Didn't mean to take it off list, just new to the whole concept and
    >wasn't sure that I would be responding to you directly if I put it on
    >list.  Please feel free to post anything you write on the list and I
    >will endeavor to do the same.

    OK I've copied the conversation to [terrapreta], although it's all a
    bit upside down now.
    >
    >I'm guessing that most of the wood would be "lop and top", if that
    >means branches and the like.

    Then you'll need to decide how to get that down to a size that will
    fit in the kiln, bearing in mind bigger pieces take longer to dry and
    pyrolyse.
    >
    >On Mon, Apr 7, 2008 at 8:42 AM, AJH <ajh at sylva.icuklive.co.uk<mailto:ajh at sylva.icuklive.co.uk>> wrote:
    >> On Mon, 7 Apr 2008 07:28:07 -0500, David Stewart wrote:
    >>
    >>  >About 200,000 btu is the size of the furnace that I've anticipated for
    >>  >the house.
    >>
    >>  I think 200k Btu/hr is about 60kW(t) so fairly modest. Also oil and
    >>  gas fired furnaces tend to run for shorter periods, so you can have a
    >>  wood fired device running more nearly constantly and have a smaller
    >>  power. Having said that I'd guess we could have a pyrolyser no more
    >>  than 1.2m by 1.2m (4' by 4') for the actual reactor. With half the
    >>  energy being left in the char this equates to about 23kg/hr (50lb/hr)
    >>  of bone dry wood.
    >>
    >>
    >>  >Fuel would be primarily wood.  It's what we have in abundance in the NH.
    >>
    >>  Sizes are an important consideration, would it be solid billets,
    >>  lop&top or woodchip?
    >>
    >>  Did you mean to take the conversation off the terapreta list?
    >>
    AJH
    >>
    >>


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