Luk,
You are absolutely right in that charcoal takes away some problems but introduces new ones. And I think you're right in saying every man has to build what is right for himself.
Now, I am going to try to argue my case for charcoal... It doesn't get much attention, and there are many false assumptions with the "difficulty" of making charcoal, or the inferior nature of charcoal to biomass systems. Of course, the above statement holds true... Every man needs to build what is right for him... I am simply going to make a case that charcoal is not only easier, but perhaps even superior
All in good fun, Luk... You has to make your case with the DriZzleR when it was first introduced, and I am going to make my case for OUR version of charcoal gasification...
I think you may be overestimating the effort it takes to make charcoal. For us, with our retort, we simply chip wood with an average wood chipper (not a special PTO size chunker), throw the chipped wood (even somewhat green/wet wood), light it and walk away. In 1.5 hours, we have charcoal, ready to be used... No drying time necessary, however dry feedstock takes the least energy to pyrolyze. So, I can't help but think that there is not much difference at all with a wood gasser chipping wood, vs. our method. No more hassle at all... I can't say that for other peoples retort, however. Just ours.
As I stated in my last comment, our retort is not ready yet to make use of all those extra BTU's... But it will be. And when that happens, we can stand up against any "BTU" argument with traditional wood gas systems. The BTU's from our retort can go to many useful things:
- Hydronic heating (house)
- Water distillation/sanitation
- Wet feedstock drying (radiator with fan)
- Refrigeration (adsorption refrigeration)
- Etc.
If you are following me so far, I am saying that once we re-design our retort to make use of the waste BTU's, we will be on par with wood gas systems. Wood gas BTU's from the pyrolysis gasses are kept and used in the actual gasifier, while ours is detached, and not exactly tied to the gasifier. We have the option to be tied with an auger, but it isn't necessary. Flexibility.
Now, wood shrinks about 40% in size when it's turned to charcoal. But the energy density of charcoal is greater by volume. So when considering a hopper of wood, and a hopper of charcoal, the charcoal has the greater energy, even though we need an additional 40% raw wood to fill the same hopper. I prefer to use the BTU argument because it's easier.
Here are a few more items that might persuade someone thinking about using charcoal:
- Our advantage over wood gas systems is that our reduction zone has 100 times the surface area than wood chunks.
- We use MUCH smaller charcoal chips (less than 1/2"), and the gas reduces through the entire hopper, not just in the "hearth" zone.
- We can stick a nozzle anywhere we want, and get perfect reduction, which is why our "dynamic gas flow nozzle" will work. Having one gasifier be able to match a vast range of needs is very appealing.
- We are able to use water for 30-50% of our fuel. This alone puts us back closer to wood gas, even though we brought in an outside element. Can't do this with a wood gasifier.
- We also don't need a radiator, if we can balance the steam as a coolant.
- If we insulate the core / copper coils, the heat will be tremendous! That simply means we use more steam (which makes more H2)... i.e. more free fuel.
- When enough steam is used to cool the exothermic reaction, the steam displaces the ambient air that would have been drawn in. This means much less nitrogen in our gas flows. Maybe as much as a 20% reduction.
- We can recirculate the exhaust pipe gasses as a coolant, and as a fuel... CO2 + C --> 2CO. Can't do this with a wood gasifier.
- Recirculation with the exhaust gasses results in longer lasting feed levels (less carbon is needed if we are converting CO2 to CO)... See the "Boudouard reaction"
- Charcoal will store for 10,000 years without rotting. How long will wood last?
- Charcoal can be used as biochar, an amazing soil amendment
- Etc.
So, in summary...
I think I've made a strong case for charcoal... It's not much more work to make the char than it is to make wood chunks. And it can be used quite effectively in CHP systems with an auger and airlock. If the retort heat is used wisely, the BTU's are put to use, and on par with wood gas. And lastly, charcoal is versatile!
Thanks Luk for letting me passionately state my case for charcoal!
Troy