[Stoves] Request for technology proposals - Clean Stove Initiative, Indonesia

[Paul Anderson]

Crispin,

Thank you for that carefully expressed statement with examples. More of 
us need to master these calculations, or find simple ways (spreadsheets 
perhaps?) to make the calculations easier.

Still 10 days before I get back home from Brazil.   This will be one of 
my priority tasks then.

Paul

Doc  /  Dr TLUD  /  Prof. Paul S. Anderson, PhD
Email:  psanders at ilstu.edu
Skype: paultlud      Phone: +1-309-452-7072
Website:  www.drtlud.com

On 2/21/2014 1:16 PM, Crispin Pembert-Pigott wrote:
>
> Dear Ron
>
> I think there is an assumption which is not always true: that a TLUD 
> makes char. It is true that stoves can be designed to produce char 
> from the fuel placed in them -- many types -- but it is not the case 
> that all TLUD's have to make char.
>
> Where there is a fuel consumption metric based on the total fuel used 
> per cycle, whether the stove makes char or not is up to the producer. 
> A water boiler could have an heat transfer efficiency that was very 
> high, make some char, and still meet the minimum 1-Star target of an 
> overall thermal efficiency of 45%.
>
> You will perhaps recall the discussions we have had in the past where 
> the calculations were laid out in such a way that the energy 
> accounting is plainly stated so that each portion of the process is 
> identified and the overall raw fuel needed to achieve the result also 
> given.
>
> If you have a 10 litre water boiler, it will require about 3.5 MJ to 
> be delivered to the water container. At a fire heat to water container 
> efficiency of 65% it means a fire generating a bit more than 5.2 MJ. 
> Suppose that is 1/3 of a kg of wood pellets.
>
> The baseline device has an efficiency (based on raw fuel consumed) of 
> about 17% which means it would take 1.3 kg of those same pellets to do 
> the same thing.
>
> 1/3 x (65/17) = 1.3
>
> I am not saying there is a local baseline pellet stove, just using 
> biomass fuel with the same energy per kg.
>
> So if you were to achieve an overall thermal efficiency of 40%, while 
> actually having a heat transfer efficiency of 65%, the difference can 
> be produced as unburned charcoal. In fact a dedicated water boiler 
> should be able to achieve a heat transfer efficiency of 75% or better 
> so this is not a stretch.
>
> Take a mass of raw fuel, calculate the energy content. Suppose it is 
> 20 MJ from 1 kg.
>
> Transfer 40% of that to the water vessel, that is, 8 MJ to boil 22 
> litres of water.
>
> Actual heat transfer efficiency is 65%, i.e. 13 MJ available were all 
> the fuel to be burned.
>
> The difference, 5 MJ, could instead be char. At a heat content of 172 
> g of char or 17.2% char yield.
>
> In this example, the water boiler would complete the boiling task, it 
> would receive 1 Star for overall thermal efficiency and it would also 
> produce 172 g of char.
>
> If the overall thermal efficiency was lower (not for this programme 
> however) say, 25%, the char producible would quite a bit higher: an 
> additional 138 g for a total of 310 (31%). I think at the moment no 
> TLUD is produce 31% char yield.
>
> I have encouraged everyone for several years to make this sort of 
> calculation because if you have a char production target, say 18-20%, 
> and you have a fuel efficiency target, there is a heat transfer 
> efficiency target that will produce all the results simultaneously.
>
> I am confident that with the larger boilers, 20 litres, the heat 
> transfer efficiency will be in the high 80's. It is, after all, a gas 
> flame burning in constant, perfect circumstances each time with no 
> need for control.
>
> To calculate that, let's use 85% HT eff and 3.5 MJ/10 litres:
>
> 1 kg fuel @ 17MJ/kg AR (As received) total 17 MJ
>
> 2 Stars needs 55% overall thermal efficiency (Heat in the fuel v.s. 
> heat in the pot)
>
> 20 litres needs 7 MJ in the pot.  7/0.85 = 8.235 MJ of fire heat
>
> 2 Stars means using up to 7/.55 = 12.727 MJ of heat
>
> Difference is 4.49 <J or 155 g of char
>
> Mass of fuel used including making the char = 749 g with 155 g left as 
> char (21%)
>
> This is technically possible.
>
> For reference: Baseline 17% eff = 1.211 kg fuel per 10 litres boiled
>
> Someone who built a boiler that burned the great majority of the char 
> would of course use far less raw fuel. Customers may prefer that.
>
> You were correct in your earlier comment that I proposed a 10% 
> efficiency gift to the char makers but that was not accepted by the 
> programme. Maybe next year, if there is judged to be a benefit from 
> having the char, and people are willing to deal with handling it -- 
> something not yet proven.
>
> I hope this clarifies everything.
>
> Regards
> Crispn
>
> *From:*Ronal W. Larson [mailto:rongretlarson at comcast.net]
> *Sent:* Friday, February 21, 2014 1:22 PM
> *To:* Discussion of biomass; Crispin Pemberton-Pigott
> *Subject:* Re: [Stoves] Request for technology proposals - Clean Stove 
> Initiative, Indonesia
>
> Crispin:
>
> I think TLUD companies might find it interesting to enter on the 
> water-boiling side of this RFTP.   But it is not clear how charcoal 
> will be counted.  I can see at least three formulas for calculating 
> the efficiency; one ignoring the char, by which no TLUD could ever win 
> if they wanted to save the char.  The two formulae that count char as 
> a useful co-product could either (or both) place the char in the 
> numerator or the denominator.  One of these formulas will make the 
> proscribed efficiencies quite achievable.  I can't find the intended 
> formula(e) in what you have sent.
>
> Ron
>
>
>
> _______________________________________________
> Stoves mailing list
>
> to Send a Message to the list, use the email address
> stoves at lists.bioenergylists.org
>
> to UNSUBSCRIBE or Change your List Settings use the web page
> http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org
>
> for more Biomass Cooking Stoves,  News and Information see our web site:
> http://stoves.bioenergylists.org/
>

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.bioenergylists.org/pipermail/stoves_lists.bioenergylists.org/attachments/20140222/f5d0643f/attachment.html>