[Stoves] stoves and credits again

Mon Sep 25 04:29:42 CDT 2017

I carried out a thought experiment.

In case 1, a cookstove burning wood boiled 5 litres of water at an energy efficiency of 30%.  The useful energy provided was 5*4.186*(100-15) = 1779kJ. This required 5*4.186*(100-15)/0.3 = 5930kJ.  If the as-fired wood had a LHV of 15MJ/kg, it would have needed 5930/15000 = 0.395kg wood

In case 2, the same stove was operated to produce charcoal while also boiling 5litres of water.  More wood would be needed, because not all the wood would be combusted – some would be left as char. If you fed 0.395kg wood to be turned into char at 29% efficiency, and the char had an LHV of 28MJ/kg, then the char would have an energy of 0.395*28000*0.29=3163kJ. The wood from which it was prepared had an energy content of 5930kJ, which was what was needed to boil the water in the absence of char production. So 5930-3163 = 2768kJ of additional energy* would be needed to boil the water if there was char production. At 15MJ/kg, this is 2768/15000 = 0.185kg extra wood, or an increase of 47% in the wood supply. The total energy supplied would then be 5930+2768 = 8698kJ.  The energy efficiency of cooking would therefore fall to 1779/8698*100 = 20.5%, while the efficiency of char production would have been 3163/8698*100 = 36.4%.  The system efficiency would have been 20.5+36.4 = 56.9%

If you used the WBT formula, the efficiency of boiling with char production would have been 1779/(8968-3163)*100 = 32.1%.  Given the measurement errors inherent in the WBT method, this would have been statistically indistinguishable from the efficiency with no char production – i.e. it would have shown no benefit to char production. 

Prof Philip Lloyd

Energy Institute, CPUT

PO Box 1906

Bellville 7535

Tel 021 959 4323

Cell 083 441 5247

PA Nadia 021 959 4330

*This assumes that there is no endotherm in the pyrolysis of wood in the presence of air, and that all the pyrolysis products except the char burn to provide heat. There is evidence in the literature of no endotherm in the presence of air.

From: Stoves [mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of Paul Anderson
Sent: Sunday, September 24, 2017 11:27 PM
To: Discussion of biomass cooking stoves
Cc: ndesai at alum.mit.edu; Andrew Heggie; Crispin Pemberton-Pigott
Subject: Re: [Stoves] stoves and credits again

Philip, Tom and all,

Philip is mostly correct.  Actually wood takes up (has) too much WEIGHT.  Wood has 3 times (or more, if the char is poorly made) the ENERGY value of charcoal that could come from that char.   But it has about 5 times the DRY weight of the char, plus there can be 20 to 50% moisture  content to make the wood even heavier.   

And the charcoal has  almost double (30 vs. 16) the energy content by weight, but char is so much lighter per unit of volume.  So the trucks are buldging upward and sideways with the sacks of charcoal strapped to them.  Weight of charcoal is not a problem for most transport.

Apart from the transportation issue, I believe that the appeal of charcoal is that it does not smoke (not much).   CO is invisible and deadly, but the people learn to cook on the balcony or keep some  air flowing.  And it does not turn the bottom of the pots black.

Charcoal is an attractive fuel.   Too bad it is made by processes that throw away 2/3rds of the energy.    (So, let's promote TLUD stroves and collect the char for sale to the urban folks.  Only one third of the cutting of wood/forest.) 

 So, if 100,000 households (mainly in rural or peri-urban areas) would use TLUDs, the resultant char would equal to the energy needed for an approximately equal number of households (mainly urban) that would want to burn charcoal.  

Now that would be FUEL efficiency measured by communities, not by single stoves.

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 9/24/2017 11:40 AM, Tom Miles wrote:

That's probably why charcoal use is increasing 5% per year in SSA compared with wood fuel at 1% per year. 

T R Miles Technical Consultants Inc. 

tmiles at trmiles.com

Sent from mobile. 

On Sep 24, 2017, at 8:50 AM, "plloyd at mweb.co.za" <plloyd at mweb.co.za> wrote:

Just a thought on Sub Saharan charcoal use. As Africa urbanizes, so it needs energy to cook. Wood takes up too much volume, and the roads are primitive. So it makes sense to use charcoal. A bicycle load will keep ten homes cooking for a week. 
The use of char oal has everything to do with logistics and nothing to do with the environment.
Philip

Sent from my Huawei Mobile 

-------- Original Message --------
Subject: Re: [Stoves] stoves and credits again
From: Nikhil Desai 
To: Ron Larson 
CC: Andrew Heggie ,Crispin Pemberton-Pigott ,Discussion of biomass cooking stoves 

Ron: 

What makes you believe that users of biomass-fuelled stoves are predominantly growers (of biomass)? 

Saw the figures for urban charcoal markets in Sub-Saharan Africa lately? Or looked at non-household cooking (in my view roughly 50% of cooking energy consumption worldwide)? 

Nikhil

On Thu, Sep 21, 2017 at 10:54 PM, Ronal W. Larson <rongretlarson at comcast.net> wrote:

Andrew and list:

There appears to be a win win situation here and I gather there is
still a vast part of equatorial Africa where annual burning  takes
place. However it brings me to another reason I like the idea, though
not the practicalities, of a householder-subsistance farmer being paid
a subsidy funded by the developed world. The trouble is I have a
parochial view and not a good worldview of what types of persons
depend on biomass fuelled stoves. Are they also predominantly growers?

[RWL9:  Yes to Andrew’s last question.  I disagree with Andrew calling himself “parochial” - when he supports (as do I) the ethics of “a subsidy funded by the developed world”.

[RWL10:   Agree totally.  And I think this is what will eventually kill the geoengineering technology that is often placed ahead of biochar - BECCS.  In BECCS, as with “clean coal”, the CO2 from combustion (never pyrolysis) is placed, as  liquid, deep underground.   Major expenses needed to protect the world’s soil are not needed for biochar.  Soil quality is closely linked to carbon content - and biochar does this with no penalty - while apparently being the cleanest and most efficient of all possible solid-fuel stoves.

`Andrew - thanks for your above rebuttal to Crispin.

Ron

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