[Stoves] Wattle cuttings

[Ronal W. Larson]

Dave,  list,  Paul:

	1.   I feel a need to pipe in (apologies in advance for getting carried away).  I met Dave at ETHOS-2016, but have failed till now to follow his considerable progress.   Dave has a wonderful set of videos and information that are worth most list members looking at.  See also my 11 inserts in his message.  This first part not related to anything he wrote.
	
	2.  See this recent video on making his stove:  https://www.youtube.com/watch?v=bhfHAiGqFQQ <https://www.youtube.com/watch?v=bhfHAiGqFQQ>  April 2017.  I see some clever construction techniques here - which will allow flat shipments and local assembly.  Apparently a recommendation for using waste tin cans - that I’m anxious to hear more about.  He is striving for low cost, but has a high efficiency (I think;  Dave: any measurements yet?) product.

	I see here statements about secondary air hole total area being 6 times that of the primary air inlet area.  But somewhere else I saw a ratio of 3 times.  I think this latter to be more probable, when considering the large air flow resistance of the fuel bed.  I wouldn’t be surprised to hear even 2:1.  Anyone know of any studies on this ratio - and how it would change for different fuels and different fuel bed heights?

	It is also important that Dave has a single supply for both primary and secondary air - but is apparently able to change the air hole size ratio to optimize performance.

	3.  Somewhat similar is at this site:	   http://docplayer.net/42354628-The-khaya-power-kettle-cooker-market-need-for-a-smokeless-biomass-cooker-the-khaya-cooker.html <http://docplayer.net/42354628-The-khaya-power-kettle-cooker-market-need-for-a-smokeless-biomass-cooker-the-khaya-cooker.html>

		Dave:  I see both “Khaya” and “Ekasi“ associated with you and your cooker.   The former seems to have some stoves with similar features.  Any remaining connections?

	4.   More related to his winning a South Africa competition:
	http://southafrica.cleantechopen.org/2016/12/14/tia-and-ekasi-energy-co-fund-biomass-stove-pilot-project/ <http://southafrica.cleantechopen.org/2016/12/14/tia-and-ekasi-energy-co-fund-biomass-stove-pilot-project/>  (Dec.  2016)
		Dave talks about his stove at https://www.youtube.com/watch?v=APwQ7Mx6NEg <https://www.youtube.com/watch?v=APwQ7Mx6NEg>  (June 2016) and
		https://www.youtube.com/watch?v=-HYWwuGQPDc <https://www.youtube.com/watch?v=-HYWwuGQPDc>  (Nov. 2016)

	5.   Dave:    I haven’t yet found statements on recommended uses (and values) of the produced char - especially placement in soil as biochar.   Can I hope that will also be coming along?   Do you try to discourage consumption of the char in your stoves?
	
	6. I got into all of the above for my own curiosity and stove design reasons, not because I found some of the following numerical data to be a tad confusing - although no numbers are incorrect..  This below is to respond to Dave’s request “ Please tell me if my logic and math is correct here/“
 
More below.

> On May 6, 2017, at 12:39 AM, Paul Anderson <psanders at ilstu.edu> wrote:
> 
> dave,  Your   al culations and    commens seeem  ocorrect.
> 
> \
> 
> Whqt sizes will woek for instututional cooking sto es
> 
> Paul
> Doc  /  Dr TLUD  /  Prof. Paul S. Anderson, PhD
> Email:  psanders at ilstu.edu <mailto:psanders at ilstu.edu>
> Skype:   paultlud    Phone: +1-309-452-7072
> Website:  www.drtlud.com <http://www.drtlud.com/>
> On 5/5/2017 6:41 AM, Dave Lello wrote:
>> Hi Paul
>> 
>> Attached is a picture of bark stripped and  dried wattle from cut down saplings. The bundle will fit into a fire chamber about 150mm wide and 280mm deep. The sticks are cut at about 220mm.
	RWL1:  All the other “FAAB” material talked of pellets.  (Dave has a nice acronym for FAAB, that I’d like to hear more about).  Is there any story on why today’s message is about sticks?  Striving for lower operating costs?  A new market?

	Are you happy with use of the sticks shown?  Any problems not seen with your pellet designs?

	Also,  I am surprised that you don’t have more vertical height above the secondary air holes - to allow time for more complete combustion.  What sort of soot buildup do you see on your cook-pots?


>> 
>> It's weight is about 1kg and at about 15 MJ for air dried wood should produce about 4kw of heating power. (Of which we use 70 % in the gasifier).
	[RWL2:  I see numbers above 15 MJ/kg for wood (and you use 18 MJ/kg for pellets).   

	Dave clearly knows this - but for beginners: 1 W = 1 Joule/sec.   Since there are 3600 seconds in an hour, then 1 kWh = 3.6 MJ.  This has the nice feature that 1 kg of pellets = 18 MJ = (exactly) 5 kWh .   In electrical terms, 1 kWh is about 10 cents, but because there are all sorts of differences, we don’t want to say that 1 kg of pellets is worth 50 cents (or a tonne worth $500).  But there is some favorable comparisons if the electricity is used for cooking; wood is generally a factor of about ten cheaper.

	I presume the “about 4 kW” is the same as the slightly lower 3.8 kW below?  Or - the ratio of 15 MJ/18 MJ would give a little higher than 4 kWh (not kW).   But Dave is also talking in operating times of about 1 hour.  We must be careful (my main point below) to distinguish between power (kW) and energy (kWh).

	Same about “use 70%”?  This is an energy value, whereas 4 kW is power - so we have to be careful (This implies 30% of the input energy remains in the 20% by weight char mentioned below.   The EPA (Jim Jetter) and other folks measuring stoves are very careful on knowing both the input energy density (like 15 and 18 MJ/kg) and the produced char unused energy density (a number like 30 MJ/kg).  Weighing everything is easy;  knowing energy content is not.

>> 
>> My previous burn test is that these sticks will burn down in the TLUD in about 45mins.

	[RWL3:  Dave: elsewhere I saw that you have achieved at least a 2:1 TDR (Turn Down Ratio).  Can you expand on this 45 minute number’s possible range for 1 kg of pellets (and or wood).  Is 45 minutes on the fast or slow end?
>> 
>> Meaning we get about 2.8 kw over 45 mins or 3,7 kWe.
	
	[RWL4:   a)   The number 2.8 kW comes from (15 MJ/kg) * (1 kg) * (.70)  = 10.5 MJ potentially useful and the remaining 4.5 MJ is to be found in the char.    Since 18 MJ = 5 kWh (or 1 MJ = .27777 kWh)  , then 10.5 MJ converts to 10.5 * .27777 = 2.91666.. kWh (so Dave, being conservative, might have rounded 10.5 to 10).  

	More importantly,  I believe Dave intended to say the energy output in his stove test was 2.8 kWh (NOT 2.8 kW - which would say this is a power number)

	b)  For Dave:  EE’s (I once “were one”) are very choosy about always capitalizing the W (based on the name Watt).  Same statement should be in my comment RWL2 about the needed capitalization of “w”.  Same reason for capitalizing J - meaning the person Joule.
  
	c)   The larger number 3.7 (a power, not energy) comes from productively utilizing that valuable 2.8 kWh in only 45 minutes = 3/4 hour, so (2.8) *4/3 = 3.7333…  Here I like the unit kW, but not sure why Dave adds the subscript e.   In usual EE parlance, that subscript usually means “electrical” (to distinguish from kWth, with “th” meaning thermal).  So I would recommend against using the “e” subscript.  
	 I presume the 3,7 was a typo and should be 3.7.  

>> 
>> When compared to the pellet stove (100mm diameter), we use ,75 kg per hour. Pellets are about 18,000 MJ / kg or 5 kWh. 
	[RWL5:   Dave is here saying he is recommending a larger diameter for the less dense wood stick fuel.  From here on, we have a new subject.

>> 
>> 70% of 5 kWh is 3,5 kWe.
	[RWL6:  Dave is here asserting that his two stoves operate about the same in terms of char produced.  But again, both terms have to have the same (energy) units: 3.5 kWh  (not 3.5 kWe or kW)

>> 
>> In both cases if we achieve a 50% heat transfer efficiency, this is effective heating of about 1,8 kWe.
	[RWL7:  Dave is saying that his two stove-fuel combinations have an average per rating of (3.7 + 3.5) / 2 = 3.6 kW

>> Thus my estimate is that 150mm gasifier for dried saplings will produce to same heat output as a 100mm pellet gasifier.
	[RWL8:  This is, to me, a new finding.  Again we are talking about POWER - which will determine the time to boil.   Dave is here giving us valuable information -  only possible from one trying to meet consumer demands.

>> 
>> The floor standing model can be used for wood burning, but will NOT meet institutional needs only  rural domestic needs.
	[RWL9:   Here we learn more about the 280 mm height, apparently a good bit taller than his pellet-using-unit.  I think we can see easily why;  Paul Olivier’s units for much less dense rice husks have are very tall - to get adequate running time.  The diameter is influencing Power (kW) , not Energy  (kWh).  The height is influencing Energy (kWh). not Power (kW

>> 
>> Please tell me if my logic and math is correct here.
	[RWL10:   I like all the logic and math.  My only concern is with mixing up power and energy terminology.  BOTH kW and kWh are hugely important - to stove users.

>> 
>> Working on drawings for 1st laser prototype.
	[RWL11:  Dave - this sounds like a new and different business model then.  You would supply (for a price, presumably) the way to punch flat stock anywhere in the world?  

	Thanks for giving us so much new data to consider.  Congratulations on your recent major award.  Please keep us informed.  Best of luck. 

Ron

	ps.  (This not meant to be a plug for Dave and FAAB.  I hope we can hear from other stove manufacturers in a similar manner.)

>> 
>> Dave
>> 
>> 
>> <Mail Attachment.jpeg>
>> 
>> <Mail Attachment.jpeg>
>> 
>> 
>> Sent from my iPhone
> 

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