[Stoves] here are my additional answers sir!

[Ron Larson]

Stovers  (cc Alexis);

    Alexis has asked that I forward his further responses to my five questions.  I add a part "A" for today's dialog:
          [RWL1:  Can you cite a reference in the stove literature?  This is new to me for stoves (especially your type of combustion stove), although I have seen use of steam in larger gasification units.  ] 

  Alexis:  I saw this technology only in Kunming City at Yunan Province.  You can contact Dr. Paul Anderson or Mr. Dean Still.  They saw this technology there also during our seminar last July if I remember.  I did only a small improvement on it using rice husk as fuel!  You can visit that manufacturing plant if you have a chance.
                  [RWL1A:  Paul has written a nice introduction to your earlier report on your TLUD stove.  Dean has a wonderful background in stove comparisons.  It would be good to hear their thoughts on the appropriateness of adding a steam jacket to power simple stoves.  I have thought for some time that a jacket around the outside would be a great way to capture some of the heat loss radially.  A spigot could be placed on the outside from which to draw hot (pasteurized) water - as an extra benefit.    I have a feeling that the steam jacket idea is allowing some reduction in height - and therefore a way to lower cost.    
     
          {RWL2:  My point is that char output and efficiency are (closely) related.  When talking about efficiency, even for stoves that have little charcoal production, the standard efficiency formulas all you to deduct the energy content of the produced char  (and I think those formulas are wrong).  So I urge you to weigh the charcoal and your reported efficiencies will be m comparable to those of others.]

  Alexis:  YOu suggestion are well taken.  I will do that in my next tests.  Kindly send me the methodology for my guidance.  Thanks a lot for the new learning sir!
                  [RWL2A.   I wonder if Dean can do this, as I don't know the present standard.  Briefly, the energy in the obtained char (using perhaps 28-30 MJ/kg - in your  rice hull case: 15) is subtracted from the energy in the input wood (using perhaps 18 MJ/kg) (to be used in the denominator of the efficiency computation).  My "beef" is that in cases where charcoal is a desired output, its energy value should be in the numerator of the efficiency computation.  Since 1+x is very nearly 1/(1-x) for small x - one doesn't usually care.  but if 30% of the weight ends up in charcoal and your previous measured efficiency was 20% ignoring the charcoal and using 18 and 15 MJ/kg), then the three approaches would give these calculated efficiencies:  

  1.  Your effic. (ignoring weight and energy value of the char) = .2

  2.   "standard" approach =  .2 / (1- .3*15/18) = .2/.75 = .267
          (Note it would be .2/.5= .4, if your 15 was replaced by 30 )

  3.   When valuing the char as an output for efficiency purposes:
  efficiency3 = .2 + .3*15/18 = .2+.25 = .45  (a lot larger than .267)
          (and if done with charcoal @ 30:  .2 + .5 = .7  (a lot larger than .4)

      While on the subject of efficiencies, I think you will find your efficiency could be increased a lot with another "shield" surrounding the vessel containing the water.  Dr. A.D. Karve has several designs that show very large gains with this added means of improving the convective heat transfer to the cook pot.  I presume others have equal gains to report.  I'll bet your reported 20% can go up above 40%.


       [RWL3:  Agreed.  your value of 3500 kcal/kg is about 15 MJ/kg - which are units I prefer.  About half  the 30 MJ/kg that we often talk about for char.  But there is talk about silicon perhaps being valuable as a soil amendment (of course not for the CO2 climate issues that are driving my interests  now).]

  Alexis:  Silica from rice husk is a good material for making a locally mix refractory cement.  I am using that already.  Char is the black one after burning and is good material to increase the water holding capacity of the soil. 
              [RWL3A:  Thanks.  Still hoping to hear more about any work in your area on the soil productivity gains with charcoal additions.
                  No need to repeat anything on Q4.]
    
          [RWL5:  Thanks.  I had been assuming this new unit was more like your 2003 charcoal-making stove.  Bottom lighting makes sense now, but I am still surprised that adding steam helps so much with a clean burn.  I am still uncertain how the continuous feeding of fuel is accomplished (but thanks for the added detail on removing charcoal.)   Do you get mostly ash if you don't use the scraping lever often?  When  the lever is used and you drop char to the lower container,  I would think the char could continue to combust.  How do you prevent that?  It would seem that this design would work for a variety of fuels (maybe limited to small size?), not just rice hulls.
  Not understanding yet your feed mechanism,  I can't tell, but do you think it might work with wood pellets?]

  Alexis:  In the rice husk gasifier I have in 2005, the lighting of fuel is on top since the operation is a batch mode.  In the super turbo stove, the lighting is at the bottom since it operates on a continuous mode.  the two are entirely different because the 2005 is purely gasification while the later one is direct combustion.
                  [RWL5A1:  It appears that you are operating MUCH  cleaner than any other direct combustion stove - one of the reasons for my continued interest.  In part this must be the steam jet.  But it probably is also because of your method of feeding fuel.  How often should the user "hit" this scraping lever?  is there a substantial change in output power as one empties some char?]

  In the super turbo burnt rice husk is replaced once the char is removed from the grate.  If you move the lever, the char will be drop from the grate and rice husk will replenish the char automatically since the grate is at 45 degree angle.  This process will continue until you stop the operation.
                  [RWL5A2:  Sort of understood.  Not yet clear exactly how one prevents loss of fuel as well as char during this tilting operation.  I need to see your unit  in operation, I believe.]
              
  If you let the char stay there for a longer period in the pan, it will continue to burn until it becomes white.  Hpowever, this would take a longer period.  If you put it in water, it will immediately quench and stop burning.
                  [RWL5A3:   Understood.

  You can use other kind of fuel but you need to redesign the stove to fit the fuel.
                  [RWL5a4:  Apparently extra fuel  (needed for non-batch operation)sits in the lower inverted cone, but outside the combustion area.  Does the inner cone fit tightly against this lower inverted cone - or is there a continuous air gap that allows the outer fuel to slide in as char/ash is released?  Those on the list interested in making "raw" briquettes from leaves, paper, straw, etc might find that small pellets might work well in this design.]

  PS.  the attached is the video of the super turbo stove for your file sir.
                [RWL:  This 6 second clip was sent to Tom Miles today - and everyone may be able to see Alexis' unit in operation.  It had a surprising "roar", with a very stable, apparently very intense flame.
                  I haven't commented earlier on the nice look of the uppermost flame holding region.  This flame looks very much like one would expect from a propane  or gas stove set on "High" - capable of serious heat output (reportedly 5kW?)
                  I am looking forward to Alexis' response to Crispin on why and how the steam helps.  
                  This clip shows something that doesn't look like any natural draft unit I've ever seen - so I believe this steam innovation  (and ability to feed continuously, with considerable char creation capability) needs further consideration by the many stove designers on this list.  Hopefully some size reductions and simplifications can be found that will allow a lowered cost.  (Crispin's VESTO is selling [locally, not in the US and a loer power output] at  about 10% the cost reported by Alexis.)
                  Again thanks to Alexis for another complete response.    Very helpful.    Ron]