Hi Steve,
That's very interesting information mate. Could you possibly let me know of unsuitable woods for use? From my firewood database (in my head
) I'm thinking stuff like laburnum, laurel etc. Please put me right however - I'm always happy to learn new stuff! I'd also be very interested to know if the charcoaling process would convert woods considered unsuitable for firewood because of toxic releases etc - into suitable charcoal - all the volatiles having been driven off in the charcoaling process? My guess is that the answer may well be yes - but I'll try to find out for sure. Anyway - that's another conversation!
The briquettes as you suggested are pure 100% wood. The production is similar to wood pellets in that huge pressures heat up the feedstock and soften the lignins naturally present in the wood - these then act as a natural "glue" that holds the briquette together when it cools.
There is quite a variation in briquette type and quality across different manufacturers. Many are produced from predominantly softwood residues, and these types - generally cylindrical and having the appearance of a number of discs stuck together (like a pile of weetabix) tend to expand susbstantially when burning. They will also tend to fall to pieces resulting in a pile of hot sawdust if poked or disturbed by other briquettes being loaded on top of them. I don't know if it's ever been tried, but I'm guessing this type of briquette would not charcoal successfully.
The briquettes I deal with are produced in a screw extruder as opposed to a piston machine, and are made mainly from hardwood residues. They are harder and denser than the type above, and do not expand when burning. They also hold their shape until completely burned, and have a longer burning time, and a more even heat output throughout that time. Many other types (which are still a very good product by the way) tend to be high output to begin with, but then tail off fairly rapidly after an hour or so. The ones I deal with now - and I've trialled a lot over the years - are without a doubt the best I've had, and I believe they're the best on the market today.
Briquettes are traditionally (I say traditionally though these are a relatively new product to the UK market) used as a direct replacement for firewood, where they have a number of advantages. They are clean, dry and pleasant to handle. Compact and very dense so require minimal storage space - a tonne of briquettes occupies 0.9m3 - a tonne of firewood will be between 3 and 5m3 depending on species and moisture content. Have a much higher heat value than firewood - one tonne of briquettes has about the same energy as just over four tonnes of seasoned logs, due in a large part to the much lower moisture levels - around 6.6% for briquettes as opposed to around 25% for most seasoned logs. Even kiln dried logs have around twice as much moisture.
The idea of charcoaling these briquettes was originally to produce a fuel with similar properties to coal for people wishing to get the heat without the associated carbon footprint. Although we lose the flame picture you get with coal, the heat output of these briquettes is very close to that of anthracite on a per kilo basis - so it's pretty hot stuff. Because the briquettes it's made from are so dense to begin with - much denser than natural wood, you end up with a long burning high energy charcoal.
I'll certainly keep you guys posted with any developments - and stop here first for testers!
Cheers all,
Andy