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.

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

 
Comments:
here's some pics of the Weitzman Institute in Israel.

http://www.isracast.com/tech_news/090905_tech.htm
 
What if sugar cane was used instead of corn to produce Ethanol?

I saw a show on the History Channel last night that showed that Brazil is using massive sugar cane acreage to produce all the ethanol that they need.

Apparently after the sugar crystals are extracted, the brown pulp that is left over can be burned to generate steam for electrical generation with the waste steam used to help distill the sugar/yeast batches. You wouldn't need to burn Natural Gas to distill the Alcohol in this case.

Of course, the current agrigultural laws that severely limit who can grow sugar in the U.S. would need to be repealed. I think Peanuts and Tobacco have similar restrictions, although Tobacco restrictions have recently been dropped.

Also the U.S. areas where sugar could be productively grown continuously would be limited to the Southern States. Also Sugar Cane takes a lot out of the land, so you might need to rotate crops or let the land lie fallow to recover.

Is there some compelling reason to remove Sugar Cane from consideration? I'm growing tired of seeing you beat the corn-based ethanol like a pinata.
 
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 think the subsidy problem is related to the fact that the amount of acreage allowed for sugar production is tightly controlled. The government also "guarantees" a market price 3 or 4 times the world market price and refuses to allow imports. Its a great racket if you had a sugar plantation in place before the "New Deal". But the lack of supply has forced people like soft drink makers to go with alternatives like high-fructose corn syrup.

You have a point about the lack of suitable arable land for Sugar Cane production in the USA. You would almost be forced to irrigate large sections of New Mexico or Nevada, which presents a whole new set of problems in itself.

I wonder if we could "outsource" sugar cane production to Mexico or other Latin American countries where growing conditions are more favorable. The administration is always complaining about farmers in S. America growing Coca. Maybe a massive program to produce Sugar Cane instead would be a viable alternative.
 
"Hydrogen is a boondoggle."

Yes -- not to mention that hydrogen fuel cells remain finicky, expensive and difficult to commercialize. Electric motors are a mature technology that is cheaper, more reliable, more flexible, and still improving. A vast infrastructure already exists to manufacture and service electric motors, but nothing comparable is in place for fuel cells.
 
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...
 
EP,
How much heat might be available from ZAFC for space heating? For example, a car in winter. Would it be enough?
 
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.
 
What does everyone think of the feasability of a (zinc only) one fuel society? Lets say 30 years from now?

Zinc for cars, electricity and heating.


I am imagining a home like mine in Canada where there is plenty of heat and sun in the summer. With some improvements in efficiency, solar cells on the roof could provide all energy needs.

In the winter I would buy zinc fuel to provide the extra power I need to run a ground source heat pump and the extra electricity requirements. I could even use extra capacity in the summer to recharge some cells and produce some of my own zinc fuel.

If I got really aggressive, I could sequester some of the heat in a sink in the back yard, making my heat pump really efficient.

It seems reasonable to combine solar and zinc since they can presumably share the power conversion equipment.

The added bonus is I get a UPS in the bargain. No more blackouts. We could dismantle most of the grid which will save me tax money from subsidies and it will make my neighborhood look better without the wires.
 
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.
 
Coincidentally, I was just doing the annual calculation. Just for electricity (not heating), with lots of simplifying assumptions .

Using Electric Fuels cells:
(25 kWh/day * 365) / 17.4 = 524 cells/ year. Take away half that for the winter only and another 1/3 for solar available during winter. It comes out to 175 cells.

Volume: 175*79 l = 13.8 cubic metres.

Not terribly large, but adding heating would be a problem. I used the volume of the cell, so raw fuel would be smaller. Looks like I would still need deliveries monthly during the winter.
 
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.
 
Not that I disagree in general, my vision as stated is not feasible.
But, you used the entire year's supply, and came up with 10 metric tonnes.
I estimated a storage requirement for 1/3 that. i.e. 3.3 metric tonnes.

To put that in perspective, my Honda Odyssey (with me in it) is just over 2 Metric tonnes.

Shipping 3 Tonnes to my house could not cost that much. (I realize 3 T of zinc might cost alot in itself, but it is essentially borrowed.)

I have no idea how much my government spends maintaining the grid and the nuclear plants etc. But I know they are in debt and we are paying for it somehow.

If renewables are going to provide all of our energy needs, the disparity between summer and winter and day and night has to be handled some way. Whether the energy is stored at my house or centrally, the macroeconomic problem is the same.

Furthermore, if zinc is produced with solar power, I suspect it is more efficient to ship that to my house than to convert to electricity and ship it on the grid.

Right now we don't store much energy because we rely on fossil storage. The future, eventually, will be without fossil fuels.

This is not a criticism of anybody, but how are we going to do it? Anybody?
 
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.
 
If you were going to grow sugar cane in the carribbean, you would probably want to process it there as well. Brazil does this and sends out tankers of ethanol to California already.

If you wanted to utilize the whole sugar cane plant to fire steam electrical generation to help distill the sugar into Ethanol, you could grow it in South America and ship it by train to the U.S.

We already have the infrastructure to ship huge quantities of Coal by Train, we could probably extend this to shipping sugar cane in bulk from Mexico and points South.
 
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.
 
I wasn't arguing for replacement of coal that is currently being used for electrical generation.

I thought the point was to boost the alternate fuel supply after peak oil is reached to buy you the time to convert to a zinc based system. Even if Sugar Cane based ethanol couldn't 100% replace existing petroleum stocks, it might mitigate shortages.

In this way, while petroleum winds down you can use dual fuel/hybrid cars to buy time rather than get caught in a downward spiral.

Your point about rail line security is well taken. I doubt anyone would ever bother with a Sugar Cane "Supertanker" due to loading/offloading issues.
 
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.
 
I would think that zinc-air refueling would first take hold in major metropolitan areas. With a larger base of potential customers, investing in zinc refueling infrastructure makes more sense. Hopefully the zinc could be reprocessed near the point of use.

The smaller cities and countryside would be slow to convert to zinc-air because they lack the economy of scale and have more shipping issues. A system where major cities were the first adopters seems like the most likely scenario.

That would go a long way to reduce the USA petro demand.
 
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?
 
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