Friday, October 13, 2006

Biofuels Revisited II

Ah. Here's the relevant quote from Den Beste.

Biomass: I'm a bit embarrassed that I forgot this one to begin with. Biomass is, at its core, an extremely roundabout form of solar power. The idea is to use farmland to grow greenery, and then to burn the greenery to generate energy, but depending on who is making the proposal the details can vary wildly. Ethanol as a fuel is one example of this, but it is exceedingly inefficient because it is based on corn and only utilizes the grain, and wastes most of the energy in that and uses none of the energy in the rest of the plant.
A more efficient form of biomass is methanol, which can be created from the entire plant. The most efficient form is to burn the entire plant in a big power facility, for instance as a substitute for coal in electrical generation. There are some engineering issues involved, such as the fact that the biomass has to be dried or somehow have its water content reduced substantially, but that's a detail of the process.
It's an attractive idea, but I'm not sure the numbers make sense. I'm not sure I believe it's possible to actually supply a significant portion of our current energy use this way. You're only talking about actually harvesting greenery from the fields once or at most twice per year, and you're only going to get a few tons of dried fuel per acre each time you harvest. The US uses about 60 million short tons (about 55 million metric tonnes) of coal per month, or about 650 million metric tonnes per year.
According to this page at Oak Ridge National Laboratory, anthracite and bituminous coal (which make up most of the coal we use) contain 27-30 gigajoules per metric tonne. Agricultural residues are 10-17 gigajoules per metric tonne (as a function of water content). As an approximation, that means about 2 tonnes of biomass would be needed to replace each tonne of anthracite. Are we actually capable of producing, collecting and transporting 1.3 billion tonnes of dried biomass per year? The US currently has about 200,000 square kilometers of irrigated land; can we generate seven thousand tons of biomass per square kilometer? Or even a tenth of that? Not easily, if it's possible at all.
One of the reasons we can produce that much coal is that it's concentrated; a given coal mine can produce millions of tonnes of coal with a relatively small amount of machinery. But biomass would be extremely spread out, and you'd need an impressive infrastructure investment for all the trucks to collect it and bring it to rail yards for transport to the power plants. And a non-obvious part of the problem is that right now our agricultural practices are using that same biomass, partly to stop soil erosion and partly to reduce fertilizer usage. (Also, a lot of it is used as animal feed.)


Blogger Sir Henry Morgan said...

Hi qwerty

Thanks for viewing and commenting on my page. I've commented a reply. And I'll have two small posts (no numbers) up today and tomorrow).

Yes yes yes - "Quigley Down Under". Apart from my youngest bro (I made him sit and watch my copy with me one time) I've never ever encountered anyone who's even heard of it. I place it up there with Jeremiah Johnson (my out and out all time favourite film) and Duel at Diablo. And apart from the Rings, I have all your favourites in my collection. What do you think of B5, and the latest version of Battlestar?

Orson Scott Card - yes (of them all my favourite is Ender's Shadow). What do you think of A.E.van Vogt? I've got most of his stuff - I had every last bit of it once, but I lent a heap of books to my brother and never saw them again. Live and learn.

Actually, going by your books, I rather fancy you might like Steven Pressfield's Gates of Fire and Tides of War (you have to know a little of the history and mores of those times to fully appreciate them). "The Goat Song" by Frank Yerby is a favourite of mine too.

Space travel - my body may be stuck here on this little rock - but my head's out there between the stars. And as for the Air Force - I enlisted in the RAF when I was only 15, as a "Trenchard Brat", at Halton.

Sorry to be so OT.

Sunday, October 15, 2006 8:38:00 AM  
Blogger qwerty182764 said...

"Sorry to be so OT."

Hey, thanks for commenting. I'm happy with comments about any topic at all.

Sunday, October 15, 2006 10:10:00 AM  
Blogger Randy said...

Can't send to or comment on the USS site, damn work filters ;o)

But in the main his commentary suffers from the same 'problem' as your orginal. False assumptions that 'biomass' has to mean 'standard agriculture' process' which is incorrect.

On a 'side' note he DID point out that some have put forth the proposal that oil is NOT made from fossil plant materials as assumed. He's also 'mostly' correct in saying this has not been 'proven' in the real world yet as most of the attempts to find oil resources using the 'deep-hot-biosphere' theories has come up empty.

But I also noted that neither he nor you have noted that we already have a working 'waste-to-oil' process that is proven to work:

Economical or not is the current question but one that perhaps misses the point since this process will render safe AND produce usable by-products from such currently 'un-usable' wastes such as toxic and biohazardous waste.

He's also a bit quick to dismiss things like 'tidal' power by ridicule without refering to more near term and simpler technologies being used to harness said power than his assumed 'monster' systems.
Tidal power stations are being built in England and Scotland that consist of small staions powered not by the 'tidal' action directly but by air flow induced by wave action. This has proven to be a very simple and turn-key solution to utilizing ocean power WITHOUT having to resort to such 'cumbersome' systems as huge tidal pools.

I'm more in agreement with the Ambivelent Engineer; what we can replace at an economical cost we SHOULD replace. We may not ever have enough alternatives to completly replace oil, but I suspect we have enough to greatly reduce our current demands.


Thursday, October 19, 2006 7:01:00 PM  
Blogger qwerty182764 said...

Thanks for your posts. I'll investigate your comments on alternative sources for biofuels. Like I said, I'm somewhat openminded to newer ideas, so I'll check out this algae production.

However, whatever method eventually pans out for manufacturing biofuels will have to be a "monster system" (at least in terms of our present generating capacity) almost by definition. That terrawatt-order power supply has to come from somewhere.

Some monsters will be easier to create than others, though. :-P (cue creepy organ music for haloween)

Friday, October 20, 2006 6:19:00 PM  
Blogger qwerty182764 said...

I also think Den Beste was commenting specifically on implementing an alternative fuel source within the timescales needed to make a difference in our conflict with the Middle East.

On other timescales, some of these things may come into play, but on the order of one or two decades, we're probably not going to see a global demand drop for oil to impoversh these backwards donkey-powered sandholes.

Friday, October 20, 2006 6:29:00 PM  

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