Crispin and list 1. Re non-sustainable biomass, the Geres folk also seemed to be bothered by the rules. I will re-read. My hope is that biochar somehow can find a different path (whch adds to the available credits). I do not claim to understand this yet .
2. Re the use of 18 vs 15 - I agree. I have just gotten used to working with nice easy divisible numbers so folks could easily follow the math. I apologize; I should have put in a warning to that effect. Any idea how the energy value of char should be similarly devalued by humidity? I just want to work with the simple example of 1 kg of char - as that is what we have cost data for. I can't redo without some energy value for char at the same place where wood's energy value is 15 MJ/kg. Might it be about 30 * 15/18=25? I am hoping that the main point of cook-earnings using char-making stoves won't change much. I personally think time savings will be a bigger issue - and the GERES material has some nice numbers on this topic. I have been amazed at how uniform power levels can be once one has set a desired power level; that converts to saved time.(and therefore another income aspect of a cost comparison. I still need to respond to your recent list of TLUD deficiencies; I haven't forgotten. We just need to also talk about balancing factors such as these two above. There are others. 3. I give a talk at ETHOS on the handling of char in stove efficiency computations - that will take issue with some of your thoughts below. Let's revisit this after you have heard my view on this topic. Ron ----- Original Message ----- From: "Crispin Pemberton-Pigott" <[email protected]> To: "Discussion of biomass cooking stoves" <[email protected]> Sent: Wednesday, January 23, 2013 7:57:17 PM Subject: Re: [Stoves] Example of missed opportunities was Re: is this new? Dear Ron and Everyone There are some really good points here which bear a little analysis. 4. On p 50, we read (emphasis added): "Biomass is generally considered to be a renewable fuel. When it is burnt any CO2 released is assumed to be reabsorbed through re-growth of biomass. If biomass is not re-grown, then the emissions from biomass can be considered to be a non-renewable fuel. Therefore, cooking stove projects can only generate emission reductions where it can be shown that the biomass used is non-renewable ." For a list of rules on what constitutes fundable biomass use reduction you could see the UNFCCC documents on calculating it. > c. But we got a fair amount of cooking out of that 28 cent investment. We > started out with about 4 kg * 18 MJ/kg = 72 MJ, and ended up with 1 kg * 30 > MJ /kg in char - a difference of 42 MJ. This needs slight editing. It is a tropical, humid country and drying fuel is a difficult business. Assume 15 MJ/kg and that is probably the best you are going to get. That is 60 MJ. It is unlikely you will get 1 kg of char – more likely 25% of the dry mass . There is often confusion about the initial fuel dry mass and the charcoal dry mass yield. Just be careful about the units. > f. Since char-making stoves are reported by EPA (and others) to be the > highest efficiency reported (in part because the power level is > controllable), maybe the economic argument is even more in favor of the > char-maker. The tests you refer to used a WBT that credits the unburned char as ‘fuel not consumed’ then calculates backwards to get a ‘dry mas fuel equivalent of the energy released during the burn. This ‘dry mass fuel equivalent’ is considerably less than the actual fuel consumed. Thus the ‘fuel efficiency’ is not the stated final number. This was discussed in detail here where after Jim Jetter and I agreed that if the char is not ‘fuel’ to the stove it was created in, it has to be considered ‘lost’ with the ash. As the thermal efficiency is determined from the heat released, not the fuel consumed, the overall efficiency is somewhat misrepresented by the test method. In short, char making TLUD’s have been given efficiency ratings and fuel consumptions numbers that far exceed their actual performance as viewed from the fuel pile’s and fuel buyer’s points of view. A pretty comprehensive restatement of stove performance is required to get a realistic picture of stove performance comparisons as the issue of wasted charcoal affects stoves differently. The more they create charcoal during cooking, the greater has been the padding of their fuel performance numbers. Regards Crispin _______________________________________________ Stoves mailing list to Send a Message to the list, use the email address [email protected] 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://www.bioenergylists.org/
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