h a l f b a k e r yYou think: Aha! We go: ha, ha.
add, search, annotate, link, view, overview, recent, by name, best, random
news, help, about, links, report a problem
browse anonymously,
or get an account
and write.
register,
|
|
|
A forestry scheme and power station in one. A large conveyor belt extends from the power plant and all fuel to the left of it is harvested. A lower deck on the conveyor is used to transport seedlings outward to replant the area to the right of the conveyor.
As time advances, the conveyor is slowly
rotated around the power station until it reaches the same point years later when the trees are ready to harvest again.
By definition the power plant is carbon neutral as the same volume of biomass is being burnt and regrown. However, partially burnt wood could also be buried to make the plant have a negative carbon footprint.
A further refinement would be to have radial hoses e.g every few degrees or arc to pipe the power station's exhaust gases around the growing foliage. Thus providing a CO2 rich environment for the crop.
http://forestry.abo...ics/blsilsalnig.htm
[pertinax, Jul 26 2009]
Prior Art (Non-Circular)
Intensive_20tree_20...ing_20for_20country
[loonquawl, Jul 27 2009]
Energy Forestry
http://en.wikipedia...iki/Energy_forestry
in which a fast-growing species of tree or woody shrub is grown specifically to provide / biofuel [BunsenHoneydew, Jul 27 2009]
Biofuel yields
http://en.wikipedia...biofuel_crop_yields
And the winner is algae [BunsenHoneydew, Jul 27 2009]
Methane high jinks.
http://www3.signons...facilitys-excess-g/
[bungston, Jul 27 2009]
Algae fuel
http://en.wikipedia.org/wiki/Algae_fuel
[BunsenHoneydew, Jul 27 2009]
[link]
|
| |
Suppose trees taking 100 years to grow to maturity. |
|
| |
That means this thing rotates through 3.6 degrees of arc per year. At that rate of rotation, do you really want a conveyor belt planting seeds to the right, when seeds are probably being sown naturally from overhanging trees whose trunks are still to the left? |
|
| |
I s'pose it might be different nearer the perimeter, where 3.6 degrees of arc might represent a more substantial distance, but that still leaves the question of what wonderful, low-carbon-footprint mechanism will place appropriate seedlings on that outbound conveyor. |
|
| |
Also, have you done any back-of-envelope on the energy consumption of this creeping conveyor belt itself, especially the tree-harvesting teeth it would need (array of chainsaws?), and subtracted the result from the likely energy output of the wood-burning hub? |
|
| |
holy crop man. move Mohammad to the mountain not the other way around. If you're just going to burn a bunch of trees just build a huge crawling power plant and have it make a huge convoluted loop, harvesters on one side, planters on the other. a central power hub should be able to give you around 1500 acres of coverage and you could run it like a circle crop. |
|
| |
//just build a huge crawling power plant// |
|
| |
You misunderstood. Not the triffid kind, but the kind with concrete foundations and big generators. |
|
| |
There are many tree crops that grow to maturity in far less than 100 years. Willow, paulonia, bamboo (technically a grass), and others. |
|
| |
I would suggest the power plant first pyrolyze the wood and run on woodgas. That leaves you a charcoal soil improver you can return to the soil, which should retain most of the important minerals and trace elements. This would help to prevent soil depletion. |
|
| |
While you're at it, you might as well pipe the exhaust back out into the forest - the extra CO2 would aid plant growth, up to a point. /edit/ Ah, as your closing paragraph suggests. |
|
| |
From link: "Black willow is short lived;[...] The average black willow is mature in 55 years" |
|
| |
So, still only about 7 degrees of arc per year. |
|
| |
Wood chucks would chuck wood....unless you have some form of relocating the wildlife that sets up home in a given, soon to be feedstock, part of your forest. |
|
| |
//unless you have some form of relocating the wildlife// |
|
| |
It would just be like normal forestry with the majority running ahead of the sound of buzz-saws. This scheme might actually offer some advantage there as the deforestation is predicatable and always leaves the same area of forest in the vicinity. |
|
| |
There's an open-cast coal mine in Germany (couldn't find a decent link) that basically does this, but linearly and for coal.
A single massive machine clears, digs up and transports the coal to the (fixed) power station. It's trundling its way across the German countryside, until it runs out of coal (er, may be lignite...?).
(It was in a documentary on Discovery or National Geographic channel recently.) |
|
| |
[pertinax]: Paulonia is mature in three years. Bamboo can be cropped annually. Willow can be coppiced several times a year. |
|
| |
I do seem to recall a French feasibility study which was essentially the same as [bigsleep]'s proposal, using willow coppicing and piping exhaust CO2 back into the forest. |
|
| |
//piping CO2 exhaust back into the forest//
given the diffusion rate, would that even be worth it ? |
|
| |
//Bamboo can be cropped annually// okay, but what's its carbon composition ? |
|
| |
The sources I find recommend about 5 years for bamboo
growth, with a biomass production of 86 tonnes per
hectare, with an additional 43 tons of carbon sequestered
as underground growth (roots and such). Fast growing
willow (does not have to be black, faster growing species
will produce useable biomass, just not lumber), coppiced
at 5 year intervals will run as high as 48 tonnes/hectare,
depending on environment. Both can be harvested
annually with an approximately proportional
production.
|
|
| |
I'm having trouble finding the wood volume requirements
for a power plant of any given size, however. |
|
| |
I do see one problem with the continuos approach however. Coppiced trees are generally cut in the winter while the tree
is dormant. Cutting them in the growth season will damage
the stump, potentially killing your tree. The same, to a
lesser extent, applies to planting new trees every time, at
least in areas with defined seasons. Midwinter and
midsummer plantings are unlikely to survive, I would assume
the same goes for dry seasons in areas that have dry and
rainy. |
|
| |
[MechE], You're right the replanting would need to be seasonally modulated. We could also choose some depleted forestry area to remain empty for a while e.g. with a 20 year system, 5 years worth could be left as a buffer. At some point in the far distant future, this could be used to manage atmospheric CO2 levels. |
|
| |
I wonder how much CO2 is taken in by Kudzu in a year. |
|
| |
for the back-of-envelope people:
Wood burns with about 3kWh per kg. A forest has ~ 250m3 wood per 10.000m2, weighing 500kg per m3. |
|
| |
So the square meter of forest nets ~40kWh (I rounded up, as a forest nets more burnable material than just wood). |
|
| |
For a turning speed of 3,6°, this means ~1/100th° per day, 1/2.400th° per hour. |
|
| |
A Circle has an area of piR2, so a circle of 20m diameter has 314m2, producing a steady 5W. |
|
| |
A solar cell of ~1/3rd m2 (1/1000th of the forest...) and a battery can do the same, but still - better than i thought. |
|
| |
//I do seem to recall a French feasibility study which was essentially the same as [bigsleep]'s proposal//
So, what you're saying is, this will be invented by someone French? |
|
| |
Admittedly not that efficient. Wiki cites around 2% for tree solar capture efficiency. Mixed planting I reckon you could get that up to 5-10%. One of the most important aspects though is the possibility for carbon capture and modulating CO2 capture through growth schemes. |
|
| |
[loonquawl]: would you care to redo those sums assuming an open algae pond, yielding 80,000kg of oil/ha/y? [link] |
|
| |
Reed canarygrass is the thing for this scheme. No need to replant since it will grow back from the roots. |
|
| |
I was impressed to read of methane generation at our local sewage treatment plant. It is burnt off on site. They are aware that methane can be used to generate power but there was apparently no good way to get the methane to a place where it could be burned, and no good powerlines to transmit electricity generated for burning on site. They are talking about trucking the methane out in tank trucks. If a sewage plant which has been in place for decades cannot figure out a financially sound way to turn methane into dollars, I despair of any other biomass to energy scheme. |
|
| |
//If a sewage plant which has been in place for decades cannot figure out a financially sound way to turn methane into dollars//
Unless your local plant is a private operation they won't care ("they" of course meaning Local Government) until it's politcally expedient to do so. |
|
| |
Most local sewage treatment plants do not produce enough
methane to generate power on a significant scale. Quite a
few cattle farms, however, are starting to do so. It can be
made economical, and minimizing transport costs is a big
part of it. |
|
| |