There was recent discussion in a few places about energy density per hopper volume. Since I have both charcoal and also less than 3% moisture content hardwood chips; I thought I would weigh both fuels in identical weight 5 gallon buckets. So this gets us both weight and volume density for comparison.
Ill start with the chips, the common BTU value I have found with a google search seems to be 8000 btu per lb of dry wood. These chips are very dry and my meter will not register anything. But Im sure there is some moisture in some of it. They were just sun bathed for around the 3 days of good weather we had here. These chips were screened with 1/4" screen and filled even to the top the of the bucket.
Weight was exactly 10 lbs. per 5 gallon pale.
BTU Value = 80,000 btu.
Ok now the charcoal. This fuel was also made from hardwood. I also screened this fuel. Google tells me 9700 btu per lb of charcoal.
Weight was 6.45 lbs per 5 gallon pale.
BTU Value = 62,565 btu.
Ok so by volume near 0 MC wood chips are around 21.8% greater in energy density. Ok now when comparing charcoal verses wood fuel, you can not just stop here. We also must factor in differences technology efficiencies. General consensus is wood fuel gasification reaction process has a loss of 25 to 30%.
Charcoal, I dont know what the consensus is and I have not personally figured it out. I can only guess and if any one has some real numbers I will edit this. For now Im going to make an educated guess of a 10% loss and I think that more than actual.
Wood chips BTU net value after gasification 80,000 - 30% = 56,000 btu
Charcoal BTU net value after gasification 62,565 - 10% = 56,308 btu
Ok now start adding in the moisture and these figures will change again. Because you are typically not going to be running bone dry wood fuel. so that number is going to come down the more moisture that is the fuel. Now Charcoal it will be just the opposite with water injection as you adding more BTU’s
This is just some rough figures, different fuels, different gasifiers and many other factors will play into these numbers from one to the other.