Crispin As near as I can tell, like Kevin, you have not understood what I am attempting. Forget everything about joules as the fundamental variable. Of course joules are needed in doing what I want, but do appropriate computations where the fundamental variable is kgs of C or CO2. Think about comparing the carbon neutrality and carbon negativity values of stoves.
A few more notes below. I am not necessarily agreeing with paragraphs where I make no comment. On Nov 28, 2012, at 2:10 PM, "Crispin Pemberton-Pigott" <[email protected]> wrote: > Dear Ron > > I am so pleased to read that you understand the core of my problem relating > to the char calculations. I know there are a number of others who are > following the chain of calculations. > > >The present GACC handling of char weight is to compute its energy content > >and subtract this from the input biomass energy in the denominator of an > >energy efficiency computation. > > I am not so sure it is the GACA that is doing this, but it certainly is the > calculation done in the WBT 4.1.2 and the CCT 2.0 if I recall correctly. That > is the correct way to get the heat transfer efficiency as measured between > the fire (and its combustion efficiency, it you are precise about it) and the > contents of the pot (including the pot mass if you are precise about it). The > char is unburned so it was not generating heat. The heat value of that char > is usually guessed at which is where a quite large error may be introduced as > it could be between 12 and 32 MJ/kg. So the number resulting is a proxy for > the heat transfer efficiency, and that is what people take it to be. It is > thought of as the heat transfer efficiency which is really the efficiency as > measured from the hot gases to the surface of the pot – something difficult > to quantify. > > >This bothers some on this list, but I think is relatively OK if the char is > >eventually productively used. > > I am not sure who that would be because everyone so far has agreed that the > correct measure of thermal efficiency is done exactly as described. > > What is invalid is to divide the energy number (a number Joules) by the heat > content of dry fuel and then claim that the resulting fuel mass equivalent of > that number of Joules is equal to the fuel used by the stove to perform the > test. > > I case that is not totally clear: the energy efficiency is being correctly > calculated by deducting for char not burned. If that char is never going to > be burned in that same stove, then the fuel that was loaded into the stove to > create it has to be counted as part of the raw fuel that stove consumes each > time it performs that same task. > > With the advent and popularity of char-making stoves, this error – the > difference between the two methods of determining ‘fuel consumed’ – is so > large as to give very misleading comparisons between stoves of different > types. > > What happens to the char after the stove finishes producing it is not a > function of the stove and the stove cannot be credited with ‘not burning it’ > if each time the stove is used new raw fuel has to be taken from the > environment to load it. What is happening now is that the ‘test result’ is > claiming that the necessary fuel is not really being taken from the > environment because of mathematical trickery. It is being taken – just watch > a char-making stove and see how much fuel goes into it each time it is loaded. > > >…The source of the char should be emphasized when you report on the > >efficiency of jikos. > > The maker of the Jiko has no control over the production method or raw > materials used to make the char. The char might be from another stove. The > jiko can only be evaluated for fuel consumption on the basis of how much fuel > it consumes. It is a metric applicable to that product. Its thermal > efficiency is (relatively easily) calculated from the fuel consumed to > perform a thermal task. Its fuel efficiency can be measured doing any chosen > task. None of these related to how the charcoal was made or what happens to > waste char from the Jiko. > > For a systems perspective, the whole environment, there are many combinations > of products that can intersect to create less CO2, or not waste fuel, or > create more heat total by burning fuel in stages on different devices. Those > are all legitimate calculations that one might want to do for the whole > system. For example a TLUD gasifier usually has a high heat transfer > efficiency. When viewed from the point of fuel consumption, the overall > efficiency is not so good because of all the char, but that char could be > used in a second stove to raise the combined efficiency of the pair of > stoves. Great. They do that in Indonesia in the ‘improved kitchens’. The > system efficiency is higher than any of ites parts. However when rating the > components of the system they are still examined and rated individually. > RWL. My note had to do with carbon, not energy. In my mind, the jiko should be as out of place on this list as a coal- burning stove - both because they are so wasteful In most cases, and because almost any char- making stove is superior in every testing category. > >We absolutely need two efficiency numbers we can add together - and I do not > >now see them. > > I too see a need for two efficiency numbers – the heat transfer efficiency > (of interest to designers) and the system efficiency (of interest to policy > managers). You can’t add them though because one is a sub-set of the other. > > RWL: I am claiming my two carbon-based numbers can be added. I am making no > claims here about your two energy efficiencies. > > >But the production of biochar is necessarily accompanied by a reduction in > >energy. > > I think that is a step too far. Are you assuming that the stove producing the > char is more efficient than stoves that do not? If is a reduction in the > efficiency of the use of energy available in the raw fuel, yes. But to > accomplish any task, the energy required is not a function of the fact it > makes char, it is a function of the heat transfer efficiency which might be > high or low depending on the stove. I have tested a TLUD char-making stove > recently with a thermal efficiency of about 19%. > RWL: I am certainly claiming that a stove with favorable carbon negative attributes needs to be recognized by stove performance monitoring groups. Energy efficiency is similar, but not the same. I do happen to believe that many char-making stoves are more energy efficient (because they can easily control power level and excess air) - but I did not make any such claim in my note, where I have tried hard to say I was only talking about C/CO2. > >Biochar enthusiasts recognize that we can't have both high energy output and > >high char output. > > Totally agree. There is to be double-counting. > RWL. I don't understand last sentence. Ron > 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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