A very modest centrifugal blower got the burn rate up , the close exhaust temp cherry red, exhaust clean, and dry steam generation working for efficient remote heat transfer of high temperature heat, & downdraft pump of clean exhaust working for nearby scavenge of low temp heat.
My eyeball calc of heat effectiveness was that the heat from 20# dry wood chips or dust approximates+-20% the heat from 20#propane of direct application flame.
The efficiency of heat application may bias that very rough observation.
Does anyone know a source of calorie bomb test specs comparing fuel heat contents that would include different woods?
Cj Verde wrote:
I don't think 20lbs of propane = 20 lbs of wood.
Dry Wood appears to already have about 40% oxygen. Propane 0%.
Air dried cord wood or wood chips have about 20% moisture and when burned produce 7,100 Btu/lb ( page 13 of http://cardi.cornell.edu/cals/devsoc/outreach/cardi/programs/loader.cfm?csModule=security/getfile&PageID=1118149 )
From page 16 I get that propane has 91,333 BTU per GALLON.
Now how many pounds of propane in an at sale temperature gallon of propane? 6? 91,333/6= 15,222 BTU/Lb propane?
I think my application of propane may have been less efficient. But not 50% less efficient. The wood dust fire was much bigger that the propane -> I guess more time for heat loss with my application of propane.
Cj Verde wrote: Still, pound for pound may not be the best way to compare.
Engineering-wise #/# rationality is good for estimating capacity and handling cost issues - when scaled by density and also rheology (or flow).
Then $/$ rationality is possible without wild guesses.
I buy propane at about $0.60/ lb and wood chips at about $0.04/lb.
My propane hardware cost (tank, regulator, hose burner) cost me about the same on a BTU burn rate as my 3cf wood dust batch burner -IF I price the wood dust burner parts at full retail rather than scrounge cost. I scrounge well on wood dust furnace parts - saved most of the cost by my scrounging.
When my process is out of test mode I think the burner labor management cost will be very close - that is assuming that my work heat * batch time requirents match the wood dust stoves capacity.