[Stoves] Concentrators in ND TLUDs

Sun Feb 24 19:19:40 CST 2013

Dear Paal

There is something fundamentally wrong with this list of figures. Perhaps someone can explain to why it looks so strange. Please see the blue lines I have inserted.

Aprovecho 2009

Rocket

Mud with skirt

Rocket

Haiti side air 

Rocket

Haiti

 Peko Pe

Multi Use stove

Toucan

TLUD

Champion 

Fuel to Cook 5L 

(8 50/1500) g

g

666.6

1046.4

809.1

768.8

2749.5

925.2

1075.7

Carbon content of the fuel @50% C

g

333.3

523.2

404.6

384.4

1374.8

462.6

537.9

CO to Cook 5L (20)

g

59.2

2 50.5

27.4

23.0

67.3

52.0

90.5

PM to Cook 5L (1500)

mg 

1656.2

3267.8

3060.6

223.1

3191.6

2059.9

9904.4

Energy to Cook 5L15,000/25,000mkJ

kj

12,839

20,153

15,582

14,807

52,954

17,818

20,718

Time to boil 5 litres min

min

48.4 

47.7

26.4

28.1

30.6

18.9

25.0

CO2 mass based on fuel consumption (assumes no CO)

g

1222.1

1918.4

1483.5

1409.5

5040.9

1696.2

1972.3

CO2 to Cook 5L

g

1307.7

1716.7

1395.5

708.6

843.8

1052.5

1098.4

Ratio of CO2 in the fuel said to be used and the CO2 said to have been emitted

g/g

0.935

1.117

1.063

1.989

6.777

1.611

1.796

While the possibility exists that the stove emitting less CO2 than the fuel contains means it was producing char, the production of more CO2 than there is Carbon available in the fuel is impossible, certainly not by a factor of 6. In other words, the stated fuel consumption would have produced the mass of CO2 shown in the Third Last Line. In all but one case this did not happen.  Adding to the CO2 mass the mass of CO (factored in both cases for the mole mass) the figures get worse. In short, these emissions are chemically imbalanced. In the case of the first stove, there was more CO2 emitted than there was Carbon available to make it.

I think what is happening is that stoves which produce a lot of charcoal are being rated on the heat of the wood gas produced, and that heat is converted to an equivalent mass of dry wood (at 19.25 MJ/kg). In the case of the ‘Multi-use stove’ it seems to have produced nearly no carbon in the exhaust at all, meaning almost all the cooking was done by hydrogen in the fuel which means a very high char production rate.

What it means on a practical level is that if the stove in question cannot use the char that was created in a future fire in the same stove, the fuel consumption number should be treated, as agreed by several testing labs recently, as ‘fuel used’ even if the char was not consumed. 

This particular error in accounting for the difference between the raw fuel consumed by a stove and the “dry fuel equivalent” of the energy released by the fire is a major source of confusion about the fuel efficiency of stoves. It would be good for everyone to familiarize themselves with the calculation methods involved so as to be able to explain some of these large discrepancies in emissions and reported performance. In theory it should be possible to calculate the amount of char produced in each test. If the measured mass of char does not match that value, then there may be something amiss with the calculation method. It is a good method for checking data quality.

Regards

Crispin

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