The OTEC plantship held position off the coast of Florida. It was going to be a busy day-- they were running out of limestone, and it was also time to empty the fuel reserves and send to oil ashore.
Everyone knew the inefficiencies of the process, even though it had been improved over the years. The thing was, demand for that good old-school oil outstripped hydrogen and LNG bang for buck, and cryogenic transport systems never really took off. Thus, here they were, making gasoline, as it were, out of thin air.
Well, not exactly. The capital costs of the ship were staggering. High oil prices guaranteed a healthy return on investment nonetheless. And the "thin air" was actually manufactured air-- hydrogen from the water, carbon dioxide from the limestone. The energy, originally from the sun, was stolen from the heat of the ocean via thermoelectrics exploitation of the temperature differential of the surface and the deep cold water.
The plant could of have supplied ample electric energy, fresh water, or hydrogen from electrolysis to any coastal city, but they weren't buying. Too many other OTEC ships keeping the cities awash in hydrogen and water.
So, instead of a "stripped down" OTEC ship, this lumbering hulk of a ship had much bigger, more diverse factories. First, a powerful, very hot furnace stripped limestone of it's carbon dioxide.
CaCO3 >>> CaO + CO2
Next, the reverse water gas shift (RWGS) reaction further preps the gases:
CO2 + H2 >>> CO + H2O
Then, finally, the carbon monoxide is sent out to be reacted with even more hydrogen:
9H2 + 8CO = C8H18 (octane)
The octane is pumped onto an oil tanker for the trip to miami, a much shorter trip than mideat crude use to make. The ship delivering the limestone is filled back of with lime (CaO), to be sent to local cement firms and other industrial users of CaO.
For better or for worse, the fossil fuel economy survived, and was in fact aided by it's archrival H2.-- Madai, Sep 26 2005 (???) Fischer-Tropsch history http://www.pacificr...fischer-tropsch.htmwow. [Zimmy, Sep 26 2005] (??) Biofuels http://www.sciencen.../20051001/bob10.aspA fine review [bungston, Oct 10 2005] Offshore Technological Energy Conversion?-- Zimmy, Sep 26 2005 That, of course, works, but the acronym is Ocean Thermal Energy Conversion.-- Madai, Sep 26 2005 Fishbone for releasing yet more carbon into the atmosphere. The basic science is sound though. If you could source your carbon from the atmosphere, making the process greenhouse-neutral, I might be tempted to change my vote.-- BunsenHoneydew, Sep 27 2005 "carbon moxide" - hm, missed that one in chemistry class.-- DrCurry, Sep 27 2005 Bunsen, lime, when exposed to air, sucks carbon out of the atmosphere, and becomes limestone. That's what happens when lime-based concrete "sets".
The problem with "sourcing carbon from the atmosphere" is that you would have to do it in a city, where cars, humans, etc, are releasing plenty of carbon, or do it someplace where plant life won't otherwise suffer, or do it very slowly.
If we sucked the carbon out of the atmosphere in mass quantities in the middle of the ocean, woops, all nearby algae would die.
Right now, my idea is phrased so as to be "carbon indifferent". If people want to use the lime to sequester carbon, great. If people want to sequester carbon by storing the oil produced at the FTOTEC plant, great. This idea does not depend on greenhouse gas politics. I use limestone as the carbon transport medium because it is cheap, abundant, renewable, and very safe/easy to transport.
I thought about adding stuff about atmospheric sourcing, but I figured the idea was complex enough as is, plus, in order to change the greenhouse gas problem, you'd have to shut down all coal mines, and all oil pumps. Nice sentiment, but not in the scope of this idea.
Fretting over the atmospheric sourcing for FTOTEC will only add an extra layer of cost to the FTOTEC plantship, delaying FTOTEC's ascendancy over mined fossil fuels.-- Madai, Sep 27 2005 Alternate fossil carbon: OK. I likes. Also good to see an anno from [BunsenHoneydew]. Storing and moving fuel in the form of hydrocarbon does make sense. The infrastructure is all in place, and the technology reliable. With unlimited energy, one could run a number of reactions which stored the energy as hydrocarbon.
I once posted a request to convert barrels of oil currently required by the world into acres of oilseed required to grow it as a crop. No takers.-- bungston, Sep 27 2005 Planned thermoclines? hunh? I'm sorry but thermoclines are not planned. Meanwhile, I've already done an "ocean life promoting" idea. It was fishboned. And, of course, again. the idea is complex enough as is, adding a layer of complexity by feeding the fishies is out of scope.
Meanwhile, adding nutrients from a stationary point doesn't seem wise. Would be better to have a more mobile ship doing so.
What's with the "I'll vote if you change your idea" stuff? Sounds like a bribery, and frankly, I'm offended. If you have something to add to the idea which is in scope, I'll modify the idea whether or not you attempt to bribe me.
Bungston, right now, the cost of fuel is too cheap to consider replacing food crops with energy crops. There's ethanol in the US, but that's not a good energy scheme, that's farm aid.
I think salicornia will really take off as an oilseed crop, since seawater can be used to feed them. But it depends on land costs, food costs, etc.-- Madai, Sep 28 2005 //"I'll vote if you change your idea"// Hey, everybody says that. If you can't take a little bribery and corruption, and heavy doses of gratuitous insults, you're in the wrong place.
As it happens, I'm not changing *my* vote whatever you do to the idea.-- DrCurry, Sep 28 2005 There's a difference between "not liking it" and "not being able to take it".
//As it happens, I'm not changing *my* vote whatever you do to the idea.//
Sounds like you're the one who can't take it.-- Madai, Sep 28 2005 No, I'm the one (one of the ones) who doesn't like it.-- DrCurry, Sep 28 2005 I was thinking more about this idea, which I like because of the demonstrated nonmagicalness of it. Consider a situation where you have plentiful carbonate rocks, an oxygen atmosphere, and nuclear power. This could be a desert region somewhere like Utah (sand cooled nuke?), another planet, or a nation with little in the way of natural resources or fertile soil.
The proposed method would make nuclear energy easily portable and salable by storing it as hydrocarbon, a medium with proven means of transportation and use. A small or underpopulated country could use its nuclear plant to process its limestone as described, then make it into alkanes for sale on the world market. This method could also be used by a Mars station (presuming there are ancient carbonates on Mars) - you want to have vehicles and distant outposts, but dont want to string powerlines from your nuclear plant hither and yon: convert it into liquid alkanes and off you go in your diesel Rover.
The other nice thing about this method on Mars: the CaO waste product would go into the CO2 scrubbers for living spaces (vehicles, remote sites) that did not have incorporated greenhouses for this purpose.
You already had my bun, [M]. See linked article, a fine review on processing carbon into alkanes (but no mention of limestone!).
One more thing: why don't you change this title into something which reflects the idea a little better, without an acronym? The HB gets a lot of hits from Google. Then people interested in this approach will find your idea, and maybe stick around.-- bungston, Oct 10 2005 The concept is great. Sequestering carbon is always going to be good for ol' Mother Earth and the folks who live on her when all the folks are releasing massive amounts of already sequestered carbon. You should always put back what you take away...it keeps the balance of things.-- Blisterbob, Oct 10 2005 Bungstun, I just typed it into yahoo. This HB idea is at the top whether I type in "Fischer-Tropsch OTEC" or "Fischer-Tropsch Ocean Thermal Energy Conversion". I understand your concerns, but I'm not sure how to address them. Do you have an idea for a new title?-- Madai, Oct 18 2005 How about for a summary: Limestone is a fossil fuel, too! That is at the core of this scheme, but does not appear until halfway down the idea.-- bungston, Oct 18 2005 Mmm... there's no energy in the limestone. It's just a convenient carbon transport. There might well be a better way to transport it.-- Madai, Oct 19 2005 The links dont work anymore.-- pashute, Jan 05 2011 //I once posted a request to convert barrels of oil currently required by the world into acres of oilseed required to grow it as a crop. No takers.//
World oil consumption is about 87 million barrels per day, or 6*10^12 W. Average insolation at the earth's surface is about 250 W/m². A reasonable upper limit for efficiency of conversion to biomass by plants is 0.08, based on sugar cane growing under ideal conditions. That gives an area of 3*10^11 m², or 3*10^5 km², or 74 million acres. For comparison, the United States is about 9.8*10^6 km², and the entire land area of the earth is 149*10^6 km².
Those are optimistic figures. Net energy production, factoring in agricultural inputs and processing, and considering that seed oil production is less photosynthetically efficient (perhaps about a quarter) than total sugarcane biomass production, would make the actual land area much larger - perhaps a third of the US.
[Calculations revised; I multiplied where I should have divided first time, and got an area that was far too big.]-- spidermother, Jan 20 2012 random, halfbakery