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
Posted 2005-Sep-11 at Peak Oil Optimist in a story about biomass:
Well, let's see. Land area of Illinois: 57918 square miles, or about 37.1 million acres. 8% of that is 2.97 million acres; call it 3 million. (This is about 1/4 of the 11.8 million acres planted to corn in Illinois in 2004.) Yield of Miscanthus or switchgrass: roughly 10 tons/acre/year. Call the yield 30 million tons/year. Heat of combustion: 10 million BTU/ton? Total available energy would be 300 trillion BTU; converted to electricity at 33% efficiency, it would yield 100 trillion BTU or 29,300 million kilowatt-hours. Total electric consumption in Illinois in 2001 was 92,358 million kilowatt-hours. So no, growing grass to fire electrical generators wouldn't satisfy the state's needs. Not even close. (continuing) Boosting efficiency from 33% to 40% isn't going to make up for a 3:1 gap. If you can get 2.5 tons/acre of corn stover from the crop acreage, the ~30 million tons of biomass from that would get you closer but not all the way there. But riding my hobby horse for a bit... 30 million tons of biomass with 30% conversion to char would make 9 million short tons of charcoal. If each pound of char can make 5.448 lb of zinc metal and you can get 423.6 Wh/lb out of the zinc, you'd get 41,500 million kWh out of it. That's better than 45% of requirements. Double the 8% of land area to 16% and you've hit 90%; add 30 million tons of corn stover and you're up to 135%. That looks good, especially if you add some wind (if I were designing this I'd shoot for wind capacity of 30-50% and use zinc to run transport). (continuing) Heiko Gerhauser posted figures that I'd missed (glossed over or mis-read) or didn't have:12-60 (!) metric tons per hectare (5.4-27 short tons/acre).
"17.4 million BTU per metric tonne" (15.8 million BTU/short ton) Switchgrass is capable of yielding upwards of 10 short tons/acre, so the performance of Miscanthus is less impressive than it first appears; still, 27 tons/acre is nearly twice the best prospective yield I've seen for switchgrass. However, such figures appear exceptional and may not be available absent very favorable conditions. If it is possible to get a consistent 13.5 dry tons/acre from a grass crop and it produces 15.8 MMBTU/ton, the annual available energy over 3 million acres would be 640 trillion BTU or 187,000 million kWh thermal. The electric production would be 62,500 million kWh from a 33% efficient steam plant, or 75,000 million kWh from a 40% efficient combined-cycle plant. If 30 million tons of corn stover is added to the grass and it has a similar energy content, the total electric output would be sufficient to supply Illinois' 2001 requirements.
Over at The Energy Blog, zinc got a mention... but only as a way of making hydrogen. I took issue with the concept of hydrogen as the best product:
The ΔHf of zinc oxide from solid zinc is 84670 cal/mol; the ΔHf of water is 70600 cal/mol, so the conversion from metallic zinc to hydrogen is about 83% efficient. PEM fuel cells are roughly 60% efficient, so the overall efficiency of the zinc-hydrogen-PEM FC system is just about 50%. According to Electric Fuel's published figures for their electric bus system, the efficiency of a zinc-air FC is about 62%. That's 24% more energy out of a given amount of zinc than you get by taking a detour through hydrogen. Hydrogen is a boondoggle.Posted 2005-Sep-15 at Green Car Congress in a story about hybrids, drifting to the suitability of zinc-air cells for running semi-tractors:
Well, let's see. If you can devote 7500 pounds of a tractor to its combined "fuel" and "engine" (electric motors are light) and you use Electric Fuel's bus cells, you'd be able to carry 38 of them. Total energy would be 38 * 17.4 kWh = 661 kWh. If you did some aerodynamic cleanup to let the semi achieve 10 MPG and its engine efficiency is 35%, it would be using 1.5 kWh/mile [1] and the batteries would allow 440 miles of range. That's not much compared to what you'd get from 200 gallons of diesel at even 6 MPG, but it's clearly not impractical. If you combined this with a dual-mode (road/rail) system like Blade Runner and electrified the rail system, you'd have unlimited range on the rails and several hundred miles off-rail range. That's sufficient for most everything. [1] If diesel fuel has 19,110 BTU/lbm and 7.67 lbm/gallon, each gallon has 146,600 BTU/gallon (42.9 kWh/gallon). Conversion at 35% efficiency yields 15.0 kWh/gallon, so 10 MPG would be equivalent to 1.5 kWh/mile.
Comments:
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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.
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.
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.
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.
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.)
@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...
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".
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.
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.
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.
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.
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.
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.
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.
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?
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"Smith's Sorghum Source and Zinc Fuel", anyone?
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