[Terrapreta] More trials

[Greg and April]

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  From: Greg and April [mailto:gregandapril at earthlink.net] 
  Sent: Wednesday, 14 May 2008 3:06 AM
  To: MFH; Terra Preta
  Subject: Re: [Terrapreta] More trials

   

  Interspaced in Blue. Mine in green  More replies in Fuchsia.



   

    ----- Original Message ----- 

    From: MFH 

    To: Terra Preta 

    Cc: jameskater at onetel.net 

    Sent: Monday, May 12, 2008 19:43

    Subject: [Terrapreta] More trials

     

    If you can bear with me here is some info from last weekend's trials. Various conclusions are probably of little scientific merit and may well be blindingly obvious but I'll include for those who maybe don't have one of these exciting toys.

     

      1.. The original second-hand house brick kiln had 15cm/6" (when will the US join the rest of the world?) gaps between the drum and the bricks on both sides, and a relatively shallow space under the drum for the initial fire. The idea was that it would be easier to add fuelwood on the sides, but in fact this reduced the effectiveness of the insulation.    We did join the rest of the world ( officaly that is ), I didn't know that    Remember that's officaly ( like things in science, the military, goverment work ).    I do fairly well with both, and can usualy mentaly convert when dealing with inches, cm's, and mm's - I have to think abit when it's miles and km's.    I find that metric is good when dealing with smaller measurements ( and is very good when dealing with divisions of ten ), but starts to get fairly clumsy when you want to split in to half's, quarters, and so on and with very large measurements ( instead of 18 gal it's 68 liters )  it's just that un-officaly most Americans still find it easier to say they want a 6ft 2"x4" than a 2 meter 50mm x 100mm ( or 5cm x 10 cm ).  You're right - a 100x50 piece if timber will always be a 4x2 for me. In Oz the larger dimension is first as opposed to the US          
      2.. I re-laid the bricks to give a greater fire space under the drum for the initial fire, and moved the side walls inwards so that the only gap was between the ridges of the drum and the bricks. The basic concept was to apply the heat from underneath, and to insulate as best possible (under the primitive circumstances) against any unnecessary heat losses.    Why heat only from the bottom?    I would think that something like a 5 cm gap between the walls and the retort would alow heating from the sides as well ( without loosing excess heat from below ) - and heat from as many directions would decrease the time needed per batch.  There was about a 20mm gap anyway, and I think this is adequate, or would be if the top insulation was more effective. Ideally I would have a 20mm gap between the drum and the cast refractory kiln on the front, back, sides and top. This should give a very even heating effectt.    Perhaps - I just don't see alot of chimney effect ( to draw the heat along the sides of the barrel ) going on there, with that small a gap.    Have you tried insulating the top with bat's of bock wool?        
      3.. The drum was loaded with around 100kg of old dry dense hardwood, plus 2 x 75mm thick telephone books and some tyre scraps I had collected from beside the highway.    How did the tire scraps work out?    Any of that nasty burning rubber smell?    I would have thought that they would have been better used as fuel, once you had a hot fire going.  They came out of the charring in much the same physical shapes as they went in, but crumbled easily to fine C. I haven't tried them as a fuel but have tried sump oil and at the high temps of the fire under the drum this burnt without smoke. I'll collect some more tyre scraps and try these next w/end. If they turn out to be suitable one restriction on the use of old tyres would be the need to have the firebox large enough to take whole tyres, unless I contemplated a new career as a Highway Tyre Scrap Removalist.    I am still scratching my head over the tires.    There are pro's and con's to using them either as fuel or as material to char.    Just the simple fact that they are some what associated with heavy metal contamination will probably keep me from using them untill more results are avalable. 
      4.. 
      5.. SNIP
      6.. 
      7.. By 18:00 the first gas burn had started and by 18:15 the 8 x 8mm holes in the base of the drum were all roaring.    Any reasion that you chose 8mm over another size?    Why only 8?    Was it to prolong the burn and decrease the rate of off gassing?  Started with 6 x 6mm but these couldn't handle the gas volume. 8x8 seems a good compromise. Any larger and there could be a risk of air entry towards the end of the cycle allowing the char to ignite.    I have been thinking about running the off gasses through a pipe, with a ball valve on it.    That way I can vent at a very high rate, but, when the burn is done, I can sut it off to prevent air form getting to the hot char.    I'm thinking that such a set up would make a good taping point for later rerouteing 9 and taping the gasses for other uses.
     

      8.. SNIP

      9.. 

      10.. Around 21:00 the gas burn started to slow down, and by 22:00 the last flame was gone.    So 5 hrs from start to finish.    How much time did you actualy spend fueling the retort and how material did you use to fuel it?  This is all relative to the economics of the process, but I have some advantages, like a ready source of old dry timber that's been lying on the ground for years from previous felling or storm damage. So, once I'd re-shaped the kiln and placed the drum it would have taken around 30 minutes to saw, split and load 100kg+ of timber into the drum, and maybe 50kg for the fire.     So you loaded up the all fuel at the beginning and not refuel it partway through the burn?
      11.. 
      12.. SNIP
     

      12.. The charring was complete, including the tyre rubber, the 2 phone books, and dense hardwood as large as 20cm/8" in diameter.    No metal in the tire scraps?  Yes there was reinforcing wire in some. This separated readily and for a commercial process could be separated in a sloped mesh tumbler.    The reasion I ask, is that ground up tires have been assoseated with leaching of zinc and possably even lead and cadmium - I'm not sure that I would want to deal with those metals my self - especialy if I'm going to be putting char that was made from tires into the ground to grow things.

      12.. Volume loss was in the region of 20% at a guess. 
     

    It is the energy output that continues to stun me. The volume of gas that escaped through the poor lid seal was very substantial and burnt for over 2 hours. In addition, the gas burning under the drum was obviously far in excess of the volume required to maintain the char process, just using the red heat of the drum as an indicator. And on top of that was the vast heat energy given off to the atmosphere despite the attempts to provide insulation.

     

    I'll continue making batches using this crude system every weekend, but there's not a lot more to prove and I now really need to take the lessons learnt and build a decent drum and kiln. In particular the effectiveness of the insulation will be a considerable determinant in the efficiency of the process. I will aim for a castable refractory kiln in a similar shape to the current brick one, with relatively narrow gaps between the drum and the refractory except for the "firebox" underneath. It will have two hinged doors at the front - the upper one allowing the drum to be slid out above the lower firebox door. A similar upper door also for the rear, and this will also have an adjustable vent to allow heat to escape rearwards. This would lead into a second chamber where another drum loaded with wood is waiting its turn in the queue, being pre-heated at the same time. When one drum has completed the char process, it will be slid out to cool, the drum in the heat chamber at the rear is slid in to take its place, the refractory is at high temp already, the gas jets are lit, doors closed, the third drum is loaded and slid into the warming chamber..

     

    The drums to be fabricated from boiler plate, and maybe with domed lids and toggle screws to clamp down. Then I need to work out how to plug in a pipe or hose to vent off excess gas, plus a compressor and a pressure vessel to store. And that pre-supposes a capacity to record temperatures inside the drum so that this info can be fed to a controller that will make decisions when and if to pipe off some gas for storage. Plus a serious gas burner system under the drum, because I believe we can eliminate the need for wood fuel and just use some of the stored excess gas. And then some boiler tube at an upper level through which water can be piped and fed into a large storage tank as a heat bank, and then into the house and/or a greenhouse in winter through sub-floor piping, radiators, or a concrete storage tank under the slab. I don't have a house at the farm yet or even a greenhouse much less an electricity supply but that just adds some more interesting challenges. Its down to time and dollar availability.

     

    In the meantime I'm continuing with the garden trials, and certainly there is visible evidence of improved growth and vigour in the plots which had the char added. The best is the one that also had some cocopeat organic matter added, as well as some worm castings. Digging down a few inches and grabbing a handful gives this sweet-smelling crumbly mix, laden with organic matter and just seeming to be bursting with goodness. Hardly a scientific analysis but I've been handling and smelling soil for a long time and this lot is just about good enough to eat.

     

    Max H

     

     

     


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