Banjo
04-09-2006, 04:35 PM
Thought I'd share these numbers I worked out the other week.
If you assume 50% efficiency (not sure if this is reasonable, likely in the right ballpark) then you can boil off 5.6 litres of water (vapour) per litre of propane.
Seems these days a "20 pound" propane tank is now 8kg, which is about 15.3 litres of propane. So a tank full will boil about 85 litres of sap per tank.
This is based on ...
Propane has 25.3 MJ/litre
Heat of vapourization of water is 539.5 cal/g
cal x 4.184 = J
Note that it takes 1 cal/g to heat water 1°C, so taking sap from 10 to 100 °C adds about 17% more to the energy needs.
I think I'm on my 5th tankfull (might be 6th) and I've made about 14 litres of syrup or so.
The moral of the story is that I need to be burning wood next year, I've got lots of fencerows that need to be cleared up.
FWIW, Andrew
PS. The same book lists air dried hardwood at 30,600 MJ/cord, softwood at 18,700 and "mixed hardwood" at 25,000. These are full cords
If you assume 50% efficiency (not sure if this is reasonable, likely in the right ballpark) then you can boil off 5.6 litres of water (vapour) per litre of propane.
Seems these days a "20 pound" propane tank is now 8kg, which is about 15.3 litres of propane. So a tank full will boil about 85 litres of sap per tank.
This is based on ...
Propane has 25.3 MJ/litre
Heat of vapourization of water is 539.5 cal/g
cal x 4.184 = J
Note that it takes 1 cal/g to heat water 1°C, so taking sap from 10 to 100 °C adds about 17% more to the energy needs.
I think I'm on my 5th tankfull (might be 6th) and I've made about 14 litres of syrup or so.
The moral of the story is that I need to be burning wood next year, I've got lots of fencerows that need to be cleared up.
FWIW, Andrew
PS. The same book lists air dried hardwood at 30,600 MJ/cord, softwood at 18,700 and "mixed hardwood" at 25,000. These are full cords