[Gasification] Weight, power and temperature Tests

[Thomas Reed]

Dear Gasers and Stovers

Someone asked recently how hot the TLUD stoves got during operation.  I made a number of tests below on gasifying several fuels.  The highest temperature I measured during the pyrolysis operation with the Cen-Tech IR pyrometers was 190 C.  However, when the yellow flame disappeared and charcoal was gasifying the temperature rose to 350C.  

MESQUITE, LIGNIN, AND PINE TLUD  PYROLYSIS

THE FOLLOWING FUELS WERE BURNED IN A 4" D X 6" TALL TLUD STOVE AND THE WEIGHT CHANGE RECORDED. 









Note:  The tests were done on a scale weighing to 1/2 g and time recorded every minute.  

Dry wood typically has an energy content of 21 kJ/g.  However in the TLUD stove only the cellulose contributes is vaporized, approximately 16 kJ/g of weight loss, while the lignin is carbonized to charcoal.  

MESQUITE
Mesquite is said to have a very high lignin content, compared to other woods, 64%!
If lignin is the precursor of charcoal, mesquite should give a very high yield of charcoal.

152 g of mesquite chips were placed in the Wanderer stove and ignited with the propane torch.

Time.  Weight.     DW (weight change)
0.         152
1.         141.            11          Mesquite  Chunks too big, requires lots of ignition with propane torch
2.         135.            14
3.         128.              7
4.         121.              7
5.          110.           11
6.           98.            12
7.            86.        .  12.          Highest Temperature with Cen-Tech IR pyrometers 190 C.  
8.           72.            14 
9.            60.           12
10.          46.           14
11.          34.5.        11.5
12.          21.          13.5
13.            9.         12.       End of yellow flame,  put charcoal in can and weighed

Yield:    38 g ==> 38/152= 25.0%

COMMENT - this is a High charcoal yield, but not enormous.  The pine chunks below yielded 15% charcoal.  

<><><><>

Same experiment with lignin chunks from a brown forest lignin log broken up by hand.  Incredibly light.  Probably the first time anyone ever gasified pure lignin - and maybe the last.  It is a very low density fuel, since all the cellulose was eaten by microorganisms.


Time     wt.             dW
0.           54
1.           47.            7
2.           40.            7
3.           32.5.       7.5               Some soot in flame
4.           27.5.       5
4.5.      26.            1.5               Yellow out

Yield 6.5 g,  12%. 

I have long believed that it is the lignin that is the precursor to charcoal.
This experiment suggeststhis is probably not true.

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Pine block - Wanderer

3/4 sq x1" pine blocks

0.      96.5.      dW
1.         89.          7.5 
2.        85.         4.0
3.        80.5.    4.5
4.        76           4.5.               Can maximum temperature 190C.  
5.         71.            5
6.         65.          6
7.          57.          8
8.         51.5.       5.5
9.          46.         6.5
10.        39.           7              Flame low
11.           31.5.       7.5          Flame much higher, end effect
12.         22.           9.5           big fire
13.         13.              9             All block surfaces on fire, but centers still outgasing
14.         5.5.          7.5          Can temp 350 with Cen-Tech IR pyrometers

15 g charcoal = 15.5%

Note: dry wood has a typical heat of combustion of  21 kJ/g, so complete combustion would generate (21000/60) 350 Watts/Gm-min. 

However in the TLUD this is reduced to maybe 16 kJ/Gm-min or 270 Watts/g-min, because mostly cellulose and water are volatilized and the remaining charcoal generates  26 kJ/g, or 433 W/g-min. 

So a burn rate of 12 g/min would yield a (270 X  12) 3.2 kW flame.  
Fuel bed 4"D  x 3" deep

I hope this information is useful, but needs digesting.

Tom Reed
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