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

Crispin Pemberton-Pigott crispinpigott at outlook.com
Wed Nov 26 12:17:20 CST 2014


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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