[Stoves] Shields E450c as a way to test char-making stoves (attn: GACC testers)

[Ronal W. Larson]

Crispin, list, and ccs  (adding Jim Jetter and Frank)

   1.  I have to apologize to Frank Shields if Crispin is correct on Frank's motivation in paragraph 1.  I was confused by an early statement by Frank that one didn't need to measure the weight of produced char.  This is to ask Frank to clarify.  Did he mean not measure the energy content?

   2.  Crispin seems to be implying again here that stove test results that report char produced (weight and its energy content) is fundamentally illogical/improper/unscientific.  Jim Jetter is reporting char-pertinent numbers and I am happy with the present reporting by Jim.   I ask Crispin (again) what he would report for a stove intentionally designed to produce char.

   3.  In the 5th paragraph, we see "….'50% fuel saving' under the old method".  My understanding is that this is both the old and the present method - and I might argue it undervalues the production of char - not overvalues.  My reasoning has been to ask Jim about inefficiencies.  I believe that Jim agrees that you don't get the right inefficiency answer by subtracting the 50% from 100% when analyzing a char-making stove.
      For those new to this, the 50% comes from a formula of the form  A/(B-C).  I think that there is merit to the formula (A+C)/B, which gives almost the same result when C  (char energy) is small, but gets wildly further apart when C is large (as in char-making stoves).  A is energy to the pot, B is the input energy.  This A/(B-C) formula has been around for a long time.  I think it offers some comparison value, but I prefer the (A+B)/C version - which is easy to obtain from Jim's data, although not specifically given.  My perception (correct?) is that Crispin doesn't want B to be provided. 
      The whole argument here is about how one handles "apples" and "oranges".  I think the jury is still out - but not on whether both numbers are important to some people.

  4.  I see nothing below to help me in reporting on char-making stoves.  I believe that Crispin wants all char to be considered uninteresting (illogical/improper/unscientific) when he says in Paragraph 4  (highlighted below)
> "Where a char making stove, or any other stove that produces char or other bits of fuel remaining which it cannot burn as fuel, that remaining fuel is not to be considered ‘unburned fuel’. It is considered ‘consumed’ even if not ‘burned’."
     Jim Jetter is already producing this number.  He is also giving other efficiency numbers that I support.

  5.  But there is a portion of the population using Jim's data that think Crispin is not understanding the important potential use of char as biochar.  We are not understanding Crispin wanting to use the word "consumed" when it wasn't.   This is to again ask Crispin whether there is any number that Jim can report (that he is not already doing) that would accurately tell char-interested users of his data about stove differences as to their char-producing capabilities?

Ron


On Oct 19, 2013, at 8:37 AM, "Crispin Pemberton-Pigott" <crispinpigott at gmail.com> wrote:

> Dear Jim and Frank and All
>  
> 1.  The approach proffered by Frank is to determine the energy content of a ‘fuel remainder’. I think to is fair to ask why the number is sought and then to be clear what happens with the number generated. In that way we are clear there is a good reason to make such a determination, and exactly how the result of the measurement will affect something reported in the performance evaluation.
>  
> 2.  There are several opinions on what should be measured and reported. If you are programme manager and are selecting a technology to promote, or to subsidise while someone else promotes it, the number usually sought are:
>  
> Energy consumed in the form of fuel
> Carbon monoxide emitted into the dwelling, or into a chimney (i.e. personal or community exposure)
> Particulate matter emitted into the dwelling, or into a chimney (i.e. personal or community exposure)
>  
> 3.  In the past test methods have favoured the idea that the ‘heat transfer efficiency’ or the net gain in useful heat in the pot expressed as a percentage of the heat released by the fire are an indicator of the energy consumption. Because with the passage of time and the invention of stoves that have remaining after a fire significant quantities of energy in the form of char, there has been a breakdown in the relationship between the ‘heat transfer efficiency (however defined) and the fuel consumed to feed the fire to generate that heat.
>  
> 4.  As a result of long investigation and consultation including the exchange of worked examples demonstrating this breakdown, Jim and I agreed some time ago that the situation was such that the consideration of whether or not ‘fuel remaining’ is fuel for that same stove was essential. If a stick burning stove can burn remaining sticks, it is fair to consider that to be ‘fuel not burned’. Where a char making stove, or any other stove that produces char or other bits of fuel remaining which it cannot burn as fuel, that remaining fuel is not to be considered ‘unburned fuel’. It is considered ‘consumed’ even if not ‘burned’.
>  
> 5.   The main reason for this is that stoves which consume as much fuel as a baseline stove were being given a ‘50% fuel saving’ rating under the old method. This is not reasonable and is in fact misleading. Thus we both propose that the fuel remaining be examined in the light of its usefulness to that same stove. A relevant cell in the spreadsheet is needed to enter this consideration.
>  
> If a stove can burn the fuel remaining, and the test is going to be an analogy of cooking or ‘actual use’ then such remaining fuel should be used in the test. Why? Because we want to limit cheating and misleading reporting of performance. One might create a stove that is claimed to be able to burn all fuel remaining but when trying to do so, the performance suffers greatly. That raises difficulties: how shall such a stove be rated? What if it can indeed burn charcoal with a retro-fitted container? Is that two stoves or one?
>  
> Before grasping that nettle it should first be established that if a stove has fuel remaining that it cannot burn, the fuel consumption, expressed in the form of energy contained in that fuel, be reported correctly.
>  
> The second thing to accept is that it was decided some time ago, and appears in the IWA, that the energy getting into the pot shall be the measure of the ‘work done’. Emissions are expressed in terms of the ‘net heat gained’ not on the basis of either a mass of fuel consumed or per unit of energy from the fuel consumed nor the fuel burned.  The reason is that people cook until the meal is done, not until the fuel all is burned. The emissions are related to the cooking, not the burning of a certain mass of the release of a certain amount of energy. Cooking requires energy, the energy is what is gained by the pot.
>  
> There are two schools of thought about what energy is available to do the cooking. As is well known, a massive stove retains heat and this can be used for cooking late in the cycle. In the same way a massive pot (a No.25 three-legged pot weighs 61 kg) stores heat that is available for cooking. That is why several test methods consider the thermal mass of the pot as well as the contents. Consider a South African cast iron 3 litre pot weighing 7.1 kg. The thermal mass of the pot is similar to that of the contents. If we specify a pot for all tests, we run the serious risk of misrepresenting the performance of stoves not tuned to that pot size.  Plus there is no need to make such a restriction. If we consider the Cp of the pot and its mass, we get a more accurate determination of the useful heat gained by the pot. This in turn provides a more accurate determination of the overall energy performance as is understood by someone seeking to reduce fuel consumption.
>  
> It for that reason that the Indian thermal efficiency test, and the British Standard upon which it is based, consider the mass of the pot and its thermal properties. There are a number of other examples of this approach but one should suffice.
>  
> For stoves that are able to ‘recycle’ all the fuel remaining, there is no need at all to determine the exact heat content of the fuel because during any series of replications it will be fed into the next fire, and the average of all the energy consumed and heat gained will greatly limit the errors in calculation. This means treating a performance test as being one in a series of identical replications reflecting actual use.
>  
> When there is a portion of the fuel remaining that can be recycled (the more common situation, there is again no real need to analyse the useable fuel because it is going into the next fire to be consumed again. If a test series is analysed as a group to get an average performance (which is about the only thing that can correctly be reported) it makes little difference. If the initial and final mass of ‘fuel remaining’ are recorded and the difference after several identical replications is large, the energy value can be determined, and the best way to do that is a bomb calorimeter. But this need only be done once, at the end, not for each and every test because the test are analysed as a group. 
>  
> With respect to the fuel remaining that is not usable, there is no need to determine the energy content because it forms part of the fuel consumed, whatever its form and analysis.  If 20 g of char remains in unusable form after each burn cycle, the new raw fuel needed to produce it is known from the fuel mass in and out.
>  
> When the lab test method reasonably replicates fueling behaviour, the result in the field is a reasonable match. One of the reasons why there have been such large discrepancies between these two tests is because the test method tries to consider each test as a stand-alone even with 100% new raw fuel at the beginning and ‘leftover’ fuel at the end with an unknown energy content.
>  
> By far the largest proportion of improved cooking stove projects intend to save fuel. This is because it favours the user and the demands on their time and effort. There is no point at all in having a ‘terribly clever’ stove that uses the same amount of fuel (saving no time or effort) and which gets a fuel consumption rating that is different (‘better’) from its actual fuel requirement.  The metric is Energy consumed during the cooking cycle (which I take to be the burn cycle, i.e. including ignition and burn-out phase if there is one).
>  
> Similarly there is no point in rating the emissions from a stove in a manner than is not directly tied to the heat needed in the pot to do the cooking.  The relevant metrics are CO and PM mass per MJNET in the pot. I prefer to consider the energy in the pot material for reasons explained above.
>  
> There is a simple test of the appropriateness of a method: if changing the pot or the load in the pot changes the reported performance of the stove, there is something wrong (un-universal) in the test method. Because peopledo use different pots and pot loads, the calculation method should account for the energy correctly so such changes to not influence the performance reported. Otherwise it is a test of the pot, not of the stove.
>  
> While it is tempting to ‘fix the pot’ or ‘fix the task’ or ‘fix the fuel’ it is simple unnecessary to do so. All we have to be is learn to use the correct metrics and methods of analysis and the necessary information can be delivered to the policy managers. The intention of these methods is to be able to make predictions of future performance. If the rating a stove receives is not predictive of future performance in the hands of target communities, it is not a ‘skilled’ method.
>  
> The fact that target communities vary and the ways they use their stoves is complex does not absolve the technicians from having to report properly. The fact that a really good test method will require complexity on the technical front is not the issue. ‘Being simple’ and getting the wrong answer, misleading policy mangers, is not acceptable. Stoves are complicated. The patterns of use in a community must be known before designing a test cycle. It is not difficult, it is just that to date social scientists have not dominated the technical portion of testing. They have been warning is from the sidelines that the ratings are not relevant in the communities. Well, we should listen and adapt.
>  
> If a programme is spending $1m on a stove programme, one should expect to see about 5% of that spend on testing, analysis and validation of methods, confirmation of findings and refinement of the protocol. The goal is a rating method that can make predictive comparative ratings of performance for baseline and candidate technologies. There is a whole social science aspect to this as well that relates to how the stove performs the tasks anticipated in that community. Those questions are deserving of equal status and must also be predictive of acceptance, uptake, use and something Cecil wants to see, ‘transferability’ of the technology.
>  
> Regards
> Crispin
>  
>  
> Subject: Re: [Stoves] Shields E450c as a way to test char-making stoves (attn: GACC testers)
>  
> Hi Jim
>  
> Our experience in Vietnam and now in Peru is that if you separate the biomass from the combustion as per the stove Mr Khoi and I developed then we see nearly 100% pyrolysis and the temperate doesnt vary that much.  Properties of biochar between 425C and 500C dont vary that much for a given feedstock and anyway the properties change once the biochar goes into the soil (Good paper by     Harvey OR, Herbert BE, Kuo LJ, Louchouarn P. Generalized Two-Dimensional Perturbation Correlation Infrared Spectroscopy Reveals Mechanisms for the Development of Surface Charge and Recalcitrance in Plant-Derived Biochars. Environ. Sci. Technol., 46(19), 10641-10650 (2012).
>  
> Thats a whole other story.  Read Joseph et al 2010 An Investigation into the reactions of biochars in soils Soil Research.
>  
> You can read more on Mr Khois stove in the article I wrote for IBI.
>  
> Sorry for the short answer but preparing to run the 2nd international biochar workshop in China.  We will teach people how to run Mr Khois stove as well as a Jolly Roger plus seeing a 1 tonne/hr commercial plant that has just been built.
>  
> Regards
> Stephen Joseph
>  
> On 18/10/2013, at 6:59 AM, Jetter, James wrote:
> 
> 
> Paul and All,
> 
> I would be very interested to hear Dr. Reed's opinion of this idea.
> 
> From the publication Dr. Reed co-authored, entitled An Atlas of Thermal Data for Biomass and Other Fuels:
> http://www.nrel.gov/docs/legosti/old/7965.pdf
> "Thermal analysis data is useful both for researchers and practicing engineers.  For researchers the thermal analysis data provide the information for the identification of different reaction mechanism, determination of kinetic parameters and optimization of conditions to favor one reaction over the other.  The specific temperatures at which various heterogeneous reactions occur, their reaction rates and the energies involved in these reactions are invaluable information for engineers involved in system design."
> 
> Thermal analysis of fuels is valuable for basic research and for understanding system design, but it seems to me that it would have limited value as an alternative method for efficiency testing. If all the biomass fuel in a stove is completely pyrolyzed at (or near) 450C, then I think the proposed idea may work, but what if a portion of the fuel is not completely pyrolyzed or is pyrolyzed at a different temperature?  What if a portion of the char is combusted? We have seen variation in the energy content and composition of remaining char.
> 
> Jim
> 
> 
>  
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