[Stoves] TLUD Test with Switchgrass Pellets

Wed Nov 16 20:34:07 CST 2011

Dear Roger S and Switchgrass Fans

Roger this will be of interest because the fuel came from you!

In preparation for the demo to the Chinese stove delegation I ran a single
test with 8.85mm diameter switchgrass pellets in a Grasifier TLUD stove.

The stove weighs 645 grams. The fuel added was 1050 grams.

After it was running well (perhaps 10 minutes because it lit slowly) I put
on a donut-shaped steel plate with 4 bolts that served as pot rests. It
boiled 1.7 litres of water quickly but I was not tracking the heating rate.
I was looking at burn quality and the char produced. Boiling times another
time.

There was too much primary air after a while though it was good to have
during ignition. The pyrolysation rate was too high after a while so I
closed all the 6mm holes (there were 5) but one.  It 'cooked' the pot for
about two hours. The char remaining was in the form of pellets which
remained quite strong. A picture of the char is attached. It evaporated
nearly all the water by the time the flame went out. Some 340 g of water
remained in the pot (with lid).

The char was spread on a concrete floor where it smoked for a few minutes.
Nothing done except spreading it out to cool. Afterwards it was collected
and weighed.

Fuel (air dry, est 10% moisture): 1050 g

Dry fuel mass 945 g

Char yield: 365 g

Char yield as % of initial fuel mass: 34.8%

The ash content is about 10% for switchgrass, right? If so:

Ash content of the initial fuel: 94.5 g

Ash content of the char: 94.5 g

Dry Ash-free content of the initial fuel: 850.5 g

Dry Ash-free content of the char: 270.7

Carbon content of the char (est 88% of non-ash content): 238 g

Estimated heat content 16 MJ/kg, x 1.05 kg = 16.8 MJ

Water heated 1.7 litres =  0.676 MJ

Water evaporated = 1360 g = 3.070 MJ

Total heat applied = 3.746 MJ

Average thermal efficiency from for the entire burn = 22.3%.

Final note: the char will not burn in this device.

Regards

Crispin

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