one pound of wood has around 7,000 british thermal units to it. a pound of charcoal has around 9,000. coal, depending on the type, could range from 9,000 to 17,000.
could you think of a way to agglomerate charcoal, whether from wood or some other bio-source, into denser pellets or lumps that can approach the BTU and purity of sub-bituminous to bituminous coal? applying pressure onto powdered charcoal will take too much energy. if you bind it with some material containing a volatile hydrocarbon like propane or methane, it might end up more expensive than mined coal.
any ideas? yep, i’m thinking of a renewal alternative for cement plants, solid-fuel powerplants, and furnaces/smelters.
But on reflection, why bother to compress it into blocks if you just want to use it as a convenient fuel? Why not just feed it to the furnace as a powder? (OK, powder explosions are a risk, but a manageable one)
current biomass briquettes are basically just charcoal dust with accelerants like nitrates and wax. not much improvement over nice hardwood charcoal but already acceptable for steam generation.
That extra energy got into the coal by compression. As you say, doing it artificially would be expensive. Doing it naturally would take a while. No free lunch etc.
Wait just a minute. Aren’t you comparing apples and oranges?
Burn one pound of wood to get 7,000 BTU and you then have a considerable less weight of charcoal and less available energy from its combustion. Cost analysis will also be miserably uneconomical.
OK, wood has fewer BTU’s per pound than charcoal because of its oxygen content, largely CHOH units. Charcoal is relatively pure carbon? Is coal’s relatively higher content due to hydrogen compounds, coal tars? If so, compressing charcoal would only mean the pound took up less space, not much more energy.
Did coal gain energy from compression, or did that just make it compact? If the latter, then there’s no particular relationship between the energy required to compress and the energy available in the final product - in the same way that the energy in oil is not dependent on the amount of energy required to extract it from the Earth, or refine it.
Have a look at the table under types in the wikipedia article on coal. The energy content appears to be almost entirely based on the oxygen content. (Surprising, yes?)
I’d be willing to bet that relationship extends to charcoal.
It depends on the analysis basis and moisture content. Moisture content is the single biggest variable for wood heating value.
It’s a much wider range than that; I can find charcoal with 14,000 Btu/lbm.
Where are you getting 17,000 Btu/lbm coal? A better range would be 4,500 (for a lignite B) to 14,000 (for a low-vol bituminous).
9,000 Btu/lbm is already well in the sub-bituminous coal range, more like a Sub B or even Sub A.
Torrefaction.
I guarantee ANY charcoal is going to be more expensive than coal per mass or per BTU, unless you have some special tax incentive, subsidy, or sweetheart deal with the supplier.
Torrefied biomass, especially some crop like hybrid willow or poplar.
Note that I do this work professionally, and have for decades.
Pulverized coal (PC) units tend to grind coal to a fineness of about 70% passing a 200 mesh (74 micron) screen size, which is very, very fine. CFB, BFB, stoker, and cyclone-fired units all use much larger pieces, sometimes as large as 3x0 (essentially, passing through a 3-inch screen).
Recapping, biomass is not going to be competitive with coal unless there are serious tax incentives, or other factors at play. I’ve conducted or been the principal consultant on scores, yes scores of industry studies over the years, in a variety of different countries. Your best bet might be torrefied biomass, but even then you’re still looking at costs of $5/MBtu and up in any serious quantity.