The Ergosphere
Saturday, September 24, 2005

Scribblings for September 2005

This post will collect links and calculations posted in comments elsewhere.  This may become a monthly feature.

Friday the 16th:  Item 3 added
Friday the 16th:  Item 1 updated

You mean, aside from the lack of suitable land for growing cane in the USA and the huge subsidies which are already applied to sugar in this country?  (Subsidies are as big a fiscal problem as EROEI is an energetic problem.)

Sugar cane is, like bamboo, a grass.  I have to admit, hybrid Miscanthus seems to have amazing potential if that 60 Mg/ha/yr can be reproduced and sustained (update to post body is coming).  But every crop has its preferred growing conditions, and trying to run the US vehicle fleet on ethanol from cane looks as impossible as feeding the Alberta and Saskatchewan beef herds on locally-grown corn.
I traded a couple of e-mails with Steve Long, the researcher quoted in the Reuters story. He claims he was misquoted.

He says Miscanthus can meet 50% of Illinois electricity needs on an average yield of 14 dry tons per acre and an energy content of 18 MJ/kg.
This comment has been removed by a blog administrator.
Excuse my ignorance, but where does the ZnO required for ZAFCs come from, in a renewable form? I realise it is produced as a result of the reaction, but where does it come from to start with without mining and therefore becoming 'non-renewable'?

Sounds like a great concept though.
@Gitch: Yes, you need to mine the zinc, but it is not consumed in the process. The ZnO dug out of the ground is reduced to Zn in the SOLZINC process, and then oxidised in the ZAFC, releasing the energy taken up in the reducing reaction. That leaves the same quantity of zinc+oxygen from the air=i.e, zinc oxide ready to be fed back into the SOLZINC plant.

@EngrP: It's just struck me that this algal hydrogen process (German link), which is an improvement of 13x over previous ones anyway and is to be prototyped this winter, could integrate nicely with SOLZINC. After all, you need undifferentiated carbon and you also need to recapture the CO2 exhaust.

So - you run the algal H2 process next to the SOLZINC plant, and pyrolyse the waste algae to C (perhaps using waste heat from the CO-to-CO2 gas turbine?). That gives you the input carbon, and sucks up the CO2. And it also throws off a nice bonus of H2. (You could also use the process-heat and CO2 output of the SOLZINC to hothouse the algae, that is if you are aiming for maxH2.)
glitch:  Expanding on Alex's explanation, the zinc has to be mined from ore once and is then (in theory) cycled indefinitely.  You have the thermal and electrolytic reduction processes:

    1. ZnO + C + Δ -> Zn + CO
    2. Zn++ + 2e- -> Zn + CO

And you have the fuel cell anode reaction:

     Zn -> Zn++ + 2e-

The zinc ion combines with hydroxyl ions (OH-) to form Zn(OH)2, which in turn decomposes to ZnO and H2O at 125 C.  This forms a closed loop with no carbon emissions in the power production phase, no airborne emissions at all, and perhaps 50% efficiency end to end (the Electric Fuel FC's appear to be about 62% efficient, with the rest of the losses on the reduction end).

Alex:  I don't read German and I've learned not to trust the translation engines on technical stuff.  What's the efficiency up to?

The point of the algal hydrogen process is that it doesn't lose any carbon, so no carbon needs to be replaced; you could run it in a closed environment with no inputs except distilled water, eliminating issues of contamination.  Having competing algae or bacteria (or viruses) which prey on them could be a huge headache in any open system.  You might want to keep it closed.

On the other hand, you could get the carbon from elsewhere including some other algae grown in open ponds (let them compete, all you want is biomass).  If you can get a stream of hydrogen from the specialists, you could use the hydrogen to make any number of products:

1.   ZnO + C + Δ -> Zn + CO

2a.  CO + 2 H2 -> CH3OH (methanol)
2b.  CO + 3 H2 -> CH4 + H2O (methane)
2c.  2 CO + 8 H2 -> C2H4 + 2 H2O (ethylene)

Ethylene is the starting point of many chemical syntheses, including polyethylene.  I'm of the opinion that most of the carbon going through such a process should be sequestered underground, but it occurs to me that cramming it back into the earth as medium-chain polyethylene is going to be a lot more stable than liquid CO2.  And, of course, plastic would be dirt cheap as it would be almost a waste product...
Electric Fuel's figures indicate an efficiency of about 62% for their Zn-air FC, so presumably 38% of the energy is converted to heat.  They mention a separate air stream (from the reaction air) for cooling, so this could presumably help to supply cabin heat.  It might need some juicing up to be hot enough, but if you can't justify a heat pump system to bring the temperature high enough, you have a fair amount of energy to use for resistance heaters (my least favorite option).

If you're sitting at a standstill, the battery won't be doing much and won't be creating much heat.  Whether you go with heat pumps or resistance heat, cabin heat is going to slice something off the range in those situations.  Will you have "enough" left?  Looks like the answer is "It depends".
What about attaching a Sterling engine or something else that can make use of the excess heat? I'm guessing since they have twin-engine helicoptes that spin one primary rotor, it's possible to have a twin engine vehicle spinning one drivetrain. Or is the heat not likely to be enough to power an externally heated engine like a Sterling? I know power to weight ratio is still problematic for Sterlings running off a minimal temperature differential.
The Zn-air cells have to be kept cool enough that the water doesn't boil out of the electrolyte.  Just trying to grab the heat means keeping it from going straight into the environment, which defeats the purpose of keeping the cells cool.

For most purposes, it's useless to try to extract useful work from heat less than a couple hundred degrees F.
I see there are other types of Metal-Air fuel cells around too. Magnesium-Air and Aluminium-Air are two that I could find references to online. Is there any reaon you prefer ZAFCs to these? I would have thought Zn and Al, with their low atomic weights, would also be useful.
This comment has been removed by a blog administrator.
Aluminum cannot be regenerated using wet chemistry, and magnesium is a potential fire hazard.

Aluminum is a particular difficulty for a carbon-free energy cycle.  It's possible to make it by electrolysis of a molten chloride bath (which produces chlorine gas - nasty stuff) but the usual way is to dissolve Al2O3 in molten cryolite and electrolyze that using carbon anodes.  The anodes are consumed by the oxygen, forming carbon dioxide.

Zinc can be electrolyzed in a water bath with no carbon consumed.   Not only is this a lot easier to do on small scales, if carbon emissions are an issue the zinc process has no emissions and nothing to clean up.
You might want to look at your annual energy consumption vs. the amount of zinc required to store it and consider how suitable it is for storage on the duration of a season as opposed to, say, a week.
You might find that it is not only more convenient to ship electricity via wires than on trucks, it's probably cheaper too.  The losses are certainly lower.

Few off-grid RE users have storage for more than a few days of electric consumption; there is going to be some more coming along in a while, and at some point the RE system hits the point of diminishing returns and it makes more sense to have a generator than more batteries.  At 424 Wh/lb of zinc, your annual 9125 kWh would require nearly 10 metric tons of metal.

Contrast to inventories of gasoline.  I understand that US gasoline stocks amount to roughly 190 million barrels, or roughly 1 barrel per passenger vehicle.  If we assume an average fuel economy of 25 MPG (generous), that's about 1050 miles of driving per vehicle "in the bank".  If you were going to bank that much mileage capability as zinc, and your car uses 300 watt-hours per mile at the battery terminals, you'd need 315 kWh of storage which could be provided by less than 750 pounds (about 340 kg) of zinc metal.

I see now that my estimate for zinc inventory in "miracle metal" was rather low if all energy has to be stored as zinc, but that's not necessary as long as it can be regenerated as required.
Sugar cane should not be dismissed as an alternative just because it doesn't grow i most of the US. Massive imports from the Caribbean could help them as well as us.

Unfortunately, agricultural politics in the US has driven the focus to stuff that *is* grown here (in many states) regardless of the efficiency.
If you think it's expensive to ship the oil that powers the USA, think what it would take to do it with bales of sugar cane.
Well, let's see.  If there was a rail line through Central America to the USA (which I believe there is not), and if it was acceptable to convert so much other land away from forest and food production to making energy for the US (which I don't believe it would), what would it take?

US coal consumption in 2004 was about 1.1 billion short tons.  Biofuels have less energy per ton than coal, so call it 1.6 billion tons of cane needed to replace the coal alone.  If a loaded train car can hold 100 tons of cane, it would take 16 million car-loads per year to satisfy the demands of the US.

That's a car-load every 2 seconds, every minute of every day of the year.  If the cars are 70 feet long, they would have to move at a minimum speed of about 25 MPH just to pass fast enough.  And heaven help you if someone decides to sabotage the rail line!

Anything with a bottleneck like that is simply not going to work.

If the Brazilians want another product they might try processing the bagasse into charcoal, burning the off-gas for distillery fuel and selling the remaining char as "synthetic coal".  It would slash the weight and bulk to be shipped, though I'm not sure how much excess they'd have.  Maybe they'd be best off using it to fire local electric plants instead of shipping it overseas.
The question of "bridging" is a knotty one.  On the one hand, ethanol can keep a gasoline-driven system running; on the other hand, the existence of liquid fuels (especially if subsidized) cuts the pressure to convert to something else.

I don't think ethanol helps get to EV's or zinc-air fuel cells.  As I see it, the migration path looks like this:

ICEV --(add batteries)-> hybrid ICEV
hybrid ICEV --(add storage, charge from grid)-> GO-HEV
GO-HEV --(exchange ICE for Zn-air FC)-> Zinc/grid powered vehicle

Ethanol doesn't seem to fit anywhere.
A privately-owned zinc regeneration company might branch out to serve the public too, but I'm not sure that the countryside isn't also "fertile" territory.  If the regeneration process is simple enough, some people might convert their equipment to electric and run their own zinc cycle.  Some of those are bound to be willing to sell to whoever comes by.

"Smith's Sorghum Source and Zinc Fuel", anyone?
Post a Comment

<< Home
Talk largely about energy and work, but also politics and other random thoughts

Mail Engineer-Poet

(If you're mailing a question, is it already in the FAQ?)

Important links

The Reference Library

Blogchild of

Armed and Dangerous

Blogparent of


The best prospect for our energy future:
Flibe Energy

January 1990 / February 2004 / March 2004 / June 2004 / July 2004 / August 2004 / September 2004 / October 2004 / November 2004 / December 2004 / January 2005 / February 2005 / March 2005 / April 2005 / May 2005 / June 2005 / July 2005 / August 2005 / September 2005 / October 2005 / November 2005 / December 2005 / January 2006 / February 2006 / March 2006 / April 2006 / May 2006 / June 2006 / July 2006 / August 2006 / September 2006 / October 2006 / November 2006 / December 2006 / January 2007 / February 2007 / March 2007 / April 2007 / December 2007 / January 2008 / May 2008 / June 2008 / August 2008 / October 2008 / November 2008 / December 2008 / February 2009 / March 2009 / April 2009 / May 2009 / June 2009 / July 2009 / August 2009 / September 2009 / October 2009 / November 2009 / December 2009 / January 2010 / April 2010 / May 2010 / June 2010 / July 2010 / August 2010 / September 2010 / October 2010 / November 2010 / December 2010 / January 2011 / February 2011 / March 2011 / April 2011 / May 2011 / July 2011 / August 2011 / September 2011 / October 2011 / April 2013 / November 2013 / December 2013 / January 2014 / February 2014 / March 2014 / April 2014 / July 2014 / August 2014 / September 2014 / October 2014 / November 2014 / February 2015 / April 2015 / October 2015 / March 2016 / April 2016 / May 2016 / June 2016 / July 2016 / November 2016 / December 2016 / February 2017 / May 2017 / June 2017 / September 2017 / October 2017 / November 2017 / March 2018 / May 2018 / June 2018 / October 2018 / December 2018 / January 2019 / March 2019 / June 2019 / October 2019 / November 2019 / March 2020 / June 2020 / December 2020 / March 2021 / April 2021 / May 2021 / July 2021 / January 2022 / February 2022 /

Powered by Blogger

RSS feed

Visits since 2006/05/11: