[Stoves] Energy content of 'what is burned' in a TLUD

[Ronal W. Larson]

 List  cc Crispin

	My interpretation of Crispin’s response below to my question yesterday (“If a TLUD is being tested, will char amount be measured automatically?”)  is No.

Ron





On Nov 26, 2014, at 11:17 AM, Crispin Pemberton-Pigott <crispinpigott at outlook.com> wrote:

> Dear Paul
>  
> This is mostly for you as you asked on the side, with Ron L on the side in that conversation, but this will be of interest to others as well.
>  
> I have been getting a new set of stove performance results ready for the annouvement of approved products for the CSI-Indonesia Pilot. There are several TLUD’s submitted.
>  
> Your question was about the heat content of what is being burned during these TLUD tests. The rules allow for ‘left over fuel’ to be re-used in the same stove if it is possible (this applies to all stoves – see the test method previously linked in the CSI Call for Technology Proposals). For TLUD’s this matter has not been discussed in detail here on the Stoves list.
>  
> Usually, each test has been made, so it seems, with new raw fuel each time.  In real life, if one were to turn over the stove and empty it, there would be re-usable fuel in the mix. The charcoal doesn’t burn so there is no point in putting it back, but the ‘other stuff’ is burnable.
>  
> The CSI-WHT (which is a SeTAR HTP) test method allows for such fuel to be re-used. Generally speaking it gives a more accurate picture of the actual day to day performance. This is the calculation:
>  
> 1.       Mass of new raw fuel loaded, its moisture content and elemental analysis.
> 2.       Mass of recycled fuel loaded, its moisture content and elemental analysis.
> 3.       Mass of leftover re-usable fuel, which is assumed to be the same moisture and elemental analysis as that produced by the same stove the last time the same cycle was run (and it is a reasonable assumption).
> 4.       Mass of leftover char that cannot burn in the next operation – typically having the elemental analysis of charcoal and virtually no moisture.
>  
> The consumption (by mass) is 1+(2-3)-4.  That is OK, but they have quite different compositions and therefore heat energy. What is needed to get a proper thermal performance is the knowledge of the heat available in each. That is included.
>  
> Heat transfer efficiency requires the denominator to be by mass 1+2-3-4 each factored for heat content. No problem.
>  
> Overall thermal efficiency (which is directly related to fuel consumption) is 1+2-3 with no deduction for char because it is produced from raw or recycled fuel and not used.
>  
> The question you were asking relates to the actual heat available per missing kg of fuel. The fuels in question are (1) Albasia pellets, (2 and 3) slightly roasted and partially dried Albasia pellets, and (4) Albasia pellet charcoal.  The moisture levels are respectively (1) 5.21%, (2 and 3) 4.29% and (4) 0-1%.
>  
> The heat available from the burned combination in one actual test is 12.32 MJ/kg. This is the heat available from the burning of wood gas and some of the carbon. It is corrected for the moisture change in the unburned fuel that is heated by the pyrolysis. I am seeing test after test some value in the ≈12.5 range so I think that it is reasonable to assume that is a ‘good guess’ if you have to make one.
>  
> Note that this number is not compensated for CO produced. Where the CO concentration is high it has a significant (consistently detectable) impact on the number.
>  
> It happens that we have a couple of locally made (Indonesia) ND-TLUD stoves that are extremely clean (better than a fan stove) with good power control and a high enough heat transfer efficiency to overcome the wasted char. By ‘overcome’ I mean the system efficiency is high enough to get ‘one star’ meaning they can enter the programme. This combination you may recall being discussed between us on this list a couple of times. If the heat transfer efficiency is in the 50% range, and the char production is in the 20% of dry mass range, it is still possible to get a system efficiency of over 25%. The CO produced is getting so low it is close to the quantification limit of the equipment so has little influence. (But never assume anything – there are lots of high-CO TLUD’s! Just not these.) The CO level is much lower than most ethanol stoves.
>  
> For PM, they are getting close to the range of the very cleanest coal burning stoves on the Mongolian market which – that range is under 10 mg/MJ delivered to the pot during the cooking cycle. One achieved less than 1/10th of the amount permitted by the CSI’s top tier which meets my personal target of a 98% reduction compared with the baseline. The key ingredient is the proper preparation of the fuel (pellets). The same could be done with coal and manure.
>  
> Regards
> Crispin
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