The Ergosphere
Wednesday, June 29, 2005

Zinc: Miracle metal?

Research at ETH Zürich (News release) have implemented a pilot-scale thermochemical process to capture solar energy using a zinc cycle and a supply of free carbon (diagram) (hat tip: Green Car Congress).  This process converts zinc oxide (ZnO) and carbon to metallic zinc and carbon monoxide; the zinc can be used to make either hydrogen or electricity, and the ZnO product completes the cycle.  The carbon source can be anything from coal to biomass.  The researchers claim 30% conversion efficiency in the pilot plant, with full-scale plants expected to hit 50%-60%.

The adjective "impressive" is, I believe, an understatement.

When I read this, I was initially troubled by the use of carbon (coal!) in what was represented as a solar energy system (bait and switch).  However, the researchers claim that the amount of carbon required to reduce the zinc is reduced to 1/5 of that required by pure chemical processes and that biomass can be used as the carbon source.  It's also obvious that the off-gas (CO) retains much of the energy from the original carbon fuel.  The big questions are:
  1. Is this true?
  2. How much energy is retained?
  3. What are the follow-on possibilities?

Is it true?

This one starts with the chemistry:  specifically, heats of formation.  (Elements have zero heat of formation by definition.)

Table 1:  Heats of formation
  Compound    ΔH, gram  
  ZnO (from zinc solid)   -84670
  ZnO (from zinc gas)   -115940
  CO   -25400
  CO2   -93960
  H2O (liquid)   -70600

A process with the inputs of elemental carbon, zinc oxide and heat and the outputs of zinc gas and carbon monoxide has the following energy balance:

ZnO + C + 90540 cal/mol -> Zn (gas) + CO

The energy supplied by heat vs. the total is 90540/115940 = 0.78, or 78% (the remaining 22% comes from the oxidation of carbon to CO).  This is close enough to the author's claim of 4/5 to count the latter as correct.  However, it is not the whole truth; out of the chemical energy output of the process, 61% comes from the input carbon and only 39% from the thermochemical additions.  But that's misleading too; the outputs are not equivalent.

How much energy is retained?

The reaction inputs include carbon with a heat of combustion of 93960 cal/mole (plus the thermal energy required to bring the inputs up to reaction temperature, but which are not quantified here).  The outputs include: The chemical energy of the outputs (at room temperature) is 153230 cal/mol, while the chemical energy of the input carbon is 93960 cal/mol.  The thermal process has increased the total energy substantially, but the carbon input still accounts for 61% of the total input energy (chemical and thermal).

A conservative estimate of the sensible and latent heat of the products, assuming the zinc is condensed to liquid and the CO is cooled to 200 C, is 20420 + (7 * 1000) = 27420 cal/mol.  Perhaps 25% of this could be converted to work via a steam turbine, so the net output would be 6855 cal/mol (7.97 Wh/mol); this is about 7.6% of the input solar energy.  This would retain the full chemical energy of the products for other purposes, but this is not the only option.

What are the follow-on possibilities?

The zinc can be used in one of three basic ways, all of which convert it back to zinc oxide:
  1. Use in a stationary zinc-air fuel cell to make electricity for the grid.
  2. Use in a vehicular zinc-air fuel cell for as a motor-fuel replacement.
  3. Reaction with water to make H2.
Examining these possibilities in turn:

Stationary fuel cell:  The carbon monoxide is surplus in this process, and could be burned in a combined-cycle powerplant.  At 50% efficiency, the CO would yield 34280 cal/mol or 39.8 Wh/mol electric output; this electricity would be added to the 7.97 Wh/mol from the thermal output, for a total of 47.8 Wh/mol from the heat and off-gas.

The real surprise is the output from the zinc-air process.  At 1.65 volts per cell and 100% coulomb efficiency (ha!), a Zn-air cell will deliver 91.4 watt-hours per mole of metallic zinc (about 78600 cal/mole).  The total output is 139.2 Wh/mol.  An IGCC powerplant burning carbon (coal) at 40% efficiency would only yield 37580 cal/mol (43.7 Wh/mol).  The total useful energy output is more than tripled.

Mobile fuel cell:  There are already projects to run vehicles such as buses on zinc-air fuel cells.  If these could be moved down to cars, the results could be quite impressive; a vehicle using 250 Wh/mile would require only 179 grams of zinc (2.74 moles) per mile.  Zinc is a reasonably dense metal at 7.14 g/cc; solid zinc would yield about 40 miles to the liter, or upwards of 150 miles per gallon (powdered forms would not be quite so energy-dense).  The carbon monoxide would also be surplus in this scenario.

The actual available energy (electricity) from a Zn-air fuel cell is several times as great as what can be obtained from the same chemical input of gasoline to an internal combustion engine.  The metallic zinc contains about 90% as much energy as the input carbon, and it can be converted to motion with very high efficiency.  It appears likely that a solar-mediated zinc reduction process using coal could power 3.5 times as many vehicle-miles as a conversion of coal to liquid fuel.

Reaction with water to make hydrogen:  This one is interesting, because the efficiency of conversion is relatively high (83% conversion of zinc metal to hydrogen).  But what do you do with the hydrogen?  Among possibilities like the manufacture of ammonia for fertilizer, you could use it to convert half of the carbon monoxide (CO) off-gas to methanol (CH3OH).  Each mole of reactants would yield 19.9 Wh/mol of electricity and 1/2 mole (16 grams) of methanol; methanol has 173.6 kcal/mol heat of combustion (86.8 kcal/mol of reactants).

Methanol is an excellent motor fuel, powering a great many racing vehicles and mixing well with gasoline.  At a density of 0.79, it packs about 55% of the energy of the same volume of gasoline.  A vehicle achieving 30 MPG of gasoline could be expected to get about 16.5 MPG on methanol; each mile of travel would require about 5.66 moles of methanol.

Suppose that a solar power system is set up on a square kilometer of land in a sunny locale.  It receives an average of 5400 Wh/m^2 per day, or 5.4 GWh/day over the whole array.  It converts this thermal energy to zinc with an efficiency of 50%, plus the carbon inputs and outputs.  How much does it process each day, and what could it do?

At 50% capture and 90540 cal/mol captured thermal energy, the process would consume 25.7 million moles of ZnO and carbon (308 tons carbon) plus 5.4 GWh of heat (4.65*1012 cal); it would produce 25.7 million moles of metallic zinc and 25.7 million moles of carbon monoxide.  Byproduct electricity from the thermal output comes to 204 MWh.  Where it goes from there depends on the process options chosen:

Table 2:  Process outputs per day
  Process option     Electric output     Chemical output     Vehicle miles powered  
  All electric   3570 MWh  n/an/a
  MeOH motor fuel   716 MWh   275,000 gallons MeOH 4.54 million 
  Zn fuel cell vehicle   1230 MWh   1680 tons zinc 9.38 million 

Of the three options, the last is by far the most impressive.  At an average daily consumption of 24 kWh, the electric output of such a plant could power 51,000 homes; the zinc output would be sufficient to drive approximately 188,000 vehicles 50 miles a day.  A second such plant devoted to electricity would power an additional 149,000 homes.  Total carbon consumption would be 616 metric tons per day, or about 7.2 pounds per household per day.  (Much of this carbon could probably be obtained from the organic and plastic content in the residential trash, and the rest from biomass.)  That is a very big win.  A car getting 30 MPG driven 50 miles per day would consume 8.7 pounds of carbon in its gasoline alone; producing 24 kWh from carbon at 40% efficiency would release another 14.5 pounds.

A bedroom suburb with .25 acres per house (including streets and parks) would have 2560 homes per square mile, or 988 homes per square kilometer.  Two square kilometers of solar-zinc plants could power 190 square kilometers of such suburb (188,000 homes), with one vehicle each; this is about 1% of the total suburban land area devoted to power production.  This is clearly something people would accept.

Zinc cars?  Getting more than three times as much useful energy out of a ton of coal, and cutting carbon emissions accordingly?  Where do I sign up?

UPDATE 2005-Jul-1:  Two little bits of fallout from this come to mind.  Okay, three:
  1. 25.7 million moles of zinc per day could yield 25.7 million moles (51.4 tons) of hydrogen.  This hydrogen could fix about 240 tons of nitrogen to make about 291 tons of ammonia.  Every day.  At 86 kg/ha/year nitrogen requirement for crops, one day's operation of the plant in nitrogen-fixing mode would yield sufficient nitrate to fertilize 2790 hectares (almost 28 square kilometers) of farmland for a full year.  If you can't make the green algae trick work, here's a backup that only requires a carbon supply like rice straw or corn cobs to drive the process.
  2. There is no requirement that the off-gas be dumped to the atmosphere.  If the carbon monoxide was burned in e.g. a solid-oxide fuel cell, the product CO2 could be captured and compressed to liquid with relative ease; it could be fully sequestered at low cost.  If the input carbon came from the atmosphere, such as biomass or municipal solid waste (which is largely cellulose), the system could become carbon negative.
  3. Solar heat is good, but this process could be driven by anything which supplies heat at a sufficiently high temperature.  If an HTGR could be operated at perhaps 1300°C (maybe during off-peak hours, cranking the power output down and allowing the tempeature to climb), nuclear heat could keep such a process running 24/7 and during the winter in northern climes.  This would permit carbon-negative waste disposal regardless of night or clouds.
It looks like it's going to be harder and harder to keep technological civilization down, oil or no oil.

Edit 2005-Jul-01:  Corrected entry in Table 2; erroneous figure 204 MWh changed to 716 MWh.

Related items:  Fertilize this!, Going negative

Change log

This post will be updated from time to time as other posts are modified.  Modification dates and post links will be added below this notice, and the date in the sidebar link to this post will be altered accordingly.

UPDATE 2005-Sep-08:  Updated Ethanol Mirage II given good data from a commenter.
UPDATE 2005-Aug-29:  Replaced A bite-sized cogeneration example after required revisions.
UPDATE 2005-Aug-19:  Updated Stupid Blogspot tricks.
UPDATE 2005-Aug-15:  Updated Bad writing, bad thinking.
UPDATE 2005-Jul-1:  Corrected error in Zinc:  Miracle metal?
UPDATE 2005-Jul-1:  Updated Zinc:  Miracle metal?; added related link from Fertilize this! 
Saturday, June 25, 2005

Do hybrids require subsidies?

Over at Chicago Boyz, Jonathan Gewirtz says this about hybrids:
Yes, these vehicles are so good that they won't sell without subsidies.
Aside from being wrong so far as I can tell (the Prius was selling nicely from its introduction in 2000, and I can't find anything about a subsidy from earlier than 2004), Gewirtz implies that hybrids make no economic sense and would not sell on their own merits.

That's a strong assertion.  Does it have any basis?  Time to haul out an old envelope and that pencil stub....

Let's assume a gas-optional hybrid designed to be built in volume for cheap, and go 20 miles before it switches from electric propulsion to burning fuel.  It uses lead-acid batteries of the absorbed glass mat (AGM) type; there is no free liquid electrolyte to leak, and they are sealed in heat-welded plastic cases.  They have a calendar life of about 3 years.  At one cycle per day, they'd need to go about 1100 cycles to last 3 years.  The weight of the motor and its electronics are made up by reducing the weight of the engine versus a conventional car.

The battery life graph I cited in "Is the tide turning?" shows that such batteries would last 1100 cycles if they were discharged to approximately 50% before recharging.  If the car uses 250 watt-hours per mile, a 20-mile range would require 5 kWh and the battery would need an ultimate capacity of 10 kWh.

Some years ago, I re-powered an old UPS.  I removed its failed internal gel-cells and replaced them with a hefty deep-discharge storage battery.  This battery is rated at 105 amp-hours @ 12 volts (1.26 kWh nominal), weighs 65 pounds and cost about $70 at retail.  Scaled up to 10 kWh, this battery would weigh 516 pounds and cost $556.

Extra weight in a vehicle requires extra power to accelerate it and increases rolling resistance.  The battery itself can store (and regenerate) the energy to accelerate itself, but the rolling resistance has to be made up elsewhere.  If the vehicle tires have a rolling coefficient of friction of 0.008, the car would need an additional 8.2 watt-hours per mile to pull the battery.  This can probably be ignored.

The motor and electronics are more difficult to specify.  DC motors offering 28 peak horsepower are going for around $500 retail, with controllers running about the same (about $36/peak horsepower overall); however, these are low-volume items and do not reflect economies of scale.  AC Propulsion estimates a per-unit cost of $3500/unit for their AC-150 drivetrain in volume production (private communication), or $17.50/horsepower overall.  If that same price can be maintained for an 80 HP drivetrain that is highly cost-engineered, it would sell for $1400.  The overall cost of the vehicle would increase by $1956, with a $556 battery replacement every 3 years.

Savings:  If the vehicle runs 20 all-electric miles every day, it would go 7300 miles per year on no fuel whatsoever.  Economy beyond this might run 38 MPG vs. 30 MPG for a conventional vehicle; if the car ran 15,000 total miles per year it would consume 203 gallons of fuel vs. 500 for the non-hybrid.  The savings in fuel would run to $669/year at a price of $2.25/gallon, more at higher prices.  This would be offset by the cost of electricity; at a charger/battery efficiency of 65%, the hybrid would consume 2808 kWh.  At off-peak rates of $0.08/kWh, this would cost $225 for a net savings of $444/year.  Battery amortization costs $185/year, for a total savings of $259/year.

If the money to buy the car is borrowed at 11%/year for 4 years, the additional interest cost of the hybrid drivetrain is $215/year in the first year; the net benefit is small, but positive.  If the car is used for 12 years, the overall costs amount to $4485 ($1956 cost + $861 interest + $1668 replacement batteries) while savings at $2.25/gallon total $5328; net savings are $843.  If gasoline rises to $3.00/gallon, net savings rise to $2667.

Do plug-in hybrids make sense without subsidies?  Even without weighing the benefits of less pollution, greater convenience due to 60% fewer fill-ups, future-proofing and other positive attributes, it appears that they do. 
Wednesday, June 22, 2005

A post-oil vacation

Scenario:  It's the year 2025.  Oil has become effectively unavailable.  Bio-fuels are $8/gallon equivalent, and the product of all thermal depolymerization plants is fully subscribed for lubricants and chemical feedstocks.  But we have wind power at 3¢/kWh and solar PV from micron-thick polymorphous cells at 7¢/kWh (adjusted for inflation).  We have Toshiba-style Li-ion batteries at $100/kWh storage.  They can be recharged in 5 minutes; modern vehicles are full of them.

The high expense of motor fuel has led a resurgence of rail.  Steel has gone back into abandoned rights of way, and the lines which were stripped to single tracks have gone back to doubles and triples.  Yet for all the rail, most of what rides on it is not conventional trains; the Bladerunner dual-mode truck led this as a fuel-saving measure, and it snowballed.  As rail grew beyond the old rights of way into the medians of divided highways, more types of vehicles became rail-capable.  The California Air and Noise Pollution Initiative of 2011 forced most trucks onto the rails, and electrified the rail system with overhead power wires; the program spread to the entire east coast by mandate, and then nationwide as truckers demanded to be able to run on the cheaper electric power.  Diesel roar and clatter has become rare, reserved for high-value oversize loads, the military and routes far from the beaten (or hot-rolled, in this case) path.

Such a high investment in infrastructure needed users to pay for it.  After the freight haulers, private vehicles took to the rails in droves, drawn by the combination of low energy costs, quiet operation and no need to actively drive.  Electric power and automatic cruise control meant a peaceful journey between any two points on the network; this pulled in customers driving vehicles from buses down to pickup trucks.  Among these came thousands of motorhomes:  creatures of summer holiday weekends, streamlined and electrified descendants of Winnebagos and Airstreams, most black-topped with solar panels.  Somewhere along the way, you joined them.

One summer evening you pull out of your driveway in your Ecostream Sunflower.  You and the kids are packed, the fridge is stocked, and its 100 kWh battery [corrected, see comment 3] is fully charged; that's enough for 100 miles of off-network cruising[1], and charging stations are not hard to find.  The drive to the rail terminal 20 miles away doesn't take long.  After a short wait while you confirm your route reservation with the network, you pull onto a rail siding, lift the mast for the overhead brush and engage the bogie jacks; you start drawing power from the overhead as steel wheels lift most of the weight off the road tires.  Electricity flows from the wire overhead through the brush to the rail below, charging the battery; you serve dinner.

After a wait for scheduling and blocking, your motorhome gently starts up and slips into place in a train of vehicles moving nearly nose to tail.  None of them are running engines; there is the click-click of metal wheels, the hum of motors and the buzz of air conditioning fans.  You start a video for the kids as the landscape slides by.  It gets dark; you put the kids to bed.  The train cruises 50 MPH most of the night, slowing gently for termini where some vehicles drop onto their tires and slip out of line like cars going off an exit ramp.  During the night you go through a couple of "exchanges" where your motorhome splits off one line and gets onto another.  The cruise control, auto-steer and network manager handle this; you don't even wake up.

7 AM, and dawn finds you 550 miles from home.  You've had a good night's sleep and not burned a drop of liquid fuel; every kWh you've used has come from wind farms and waste-to-energy plants, and it's cheap because you've been travelling at night during off-peak hours.  Your cost is less than you would have paid for regular no-lead in 2004[2].

At 10 AM you've covered 675 miles and you're nearing your exit.  The train slows over a section where the steel is flush with pavement; you pull up your rail wheels, slide to the right and disengage the cruise control.  The mast for the overhead brush folds itself against the roof.  An hour of driving on back roads puts you at the campground on the lake with a quarter of the battery left, and you're fully rested.  During your week at play, the panels on the roof recharge your batteries; when time comes to go home, you slide out with a soft hum and a crunch of gravel.  In a minute it's as if you were never there.

This is just a mental image with some supporting numbers, but it ought to put the lie to the idea that the end of oil has to mean the end of fun, let alone everything.  Who says we have to choose between living cleaner and living better?  We can have plenty of both... if we decide to do it right.

1.  A motorhome might get 10 MPG at 50 MPH; if the engine is 25% efficient, this is roughly 0.84 kWh/mile at the wheels.  A 100 kWh battery would allow 100 miles of driving plus some extra for accessories and such. [Note:  Original, erroneous numbers were 1.7 kWh/mile.]
2.  0.84 kWh/mile * $0.10/kWh retail = 8.4¢/mile.  A vehicle getting 10 MPG on $2.20/gallon fuel burns $.22/mile.  With the added value of cruise-while-you-sleep and other features, rail operators could probably command a substantial premium in tolls over and above the markup on electricity.  [Note:  Numbers also corrected.]

2010-06-09:  Comments closed to prevent further spam. 
Tuesday, June 21, 2005

The Grand Delusion

I am constantly amazed and disgusted by the pig-headed ignorance of the public at large.  The ignorance allows them to believe the impossible, and pig-headedness leads them to insist that they get it.  This ignorance is promoted at the highest levels of government; the result of this, sooner or later, is going to be disaster.

I can't think of anything in recent history which shows this more clearly than the results of a recent Yale University poll.  Some of the results are encouraging: The answers on several questions are mildly encouraging: With these numbers you'd expect people to be ready to deal with the source of the problem, immediately and personally:  fuel taxes, guzzler taxes, opposition to environmentally-damaging actions, that kind of thing.  Unfortunately, John Q. Public doesn't seem to have a clue as to what it takes to solve the above problems: This is sad and frustrating; when the American people know what they want, they appear to have no clue about what it takes to do it or even what is physically possible.  This conflict of desires vs. knowledge is certain to yield nothing but wasted effort, perhaps with a generous larding of pork for certain special interests charged with finding ways to do the impossible... efforts which are conveniently doomed to failure and thus justify "research" indefinitely.

Who's responsible for this mess?  There are a number of culprits, ranging from the general refusal of the American public to take personal responsibility for e.g. reducing the amount of foreign oil used to special interests protecting their turf.  But there's one group, headed by one person, who have a responsibility to the nation as a whole but have been complicit in this rather than doing something about it.  That person's desk has sported many things over the years, but one slogan stands out:  The Buck Stops Here.

President Bush is personally responsible for many of these misconceptions.  He has directly promoted the idea that we can cajole or drill our way to cheaper gasoline.  He has stated that hydrogen vehicles are a solution, rather than a far-off prospect which may never materialize.  He has signed tax breaks which encouraged people to waste fuel rather than save it.  And, most damning of all, he terminated programs to develop American hybrid vehicles just as the need became obvious and foreign companies readied to take the market.

President Bush is rapidly losing what political capital he had.  I suspect that this is because he is no longer trusted; people have listened to him for five years now, and after many comparisons of words vs. reality and deeds they have finally concluded that he can neither be trusted to say what he knows to be true nor to do what he says he's going to do.  He may already have sunk too far, but some straight talk might raise his stock again.  He would have to begin by telling America what it needs to hear, whether or not it wants to:
  1. World oil supplies and their prices are largely outside of American control.  Neither sweet-talking the Saudis nor drilling in ANWR will have much effect on what Americans pay for gasoline.
  2. American oil production is falling, and nothing will reverse this.
  3. As a consequence, the only way to reduce oil imports is to use less oil.
One can agree on goals but differ on means.  But if I were a Presidential advisor, I'd suggest this:
  1. Put the hydrogen initiative on the back burner.  Cut funding to no more than $100 million for research and demonstrations until cost targets are met.
  2. Eliminate the first-year tax writeoff for heavy trucks; put them back on the normal depreciation schedule for vehicles.  But most importantly,
  3. Demand that, by model year 2012, all cars and light-truck passenger vehicles sold in the US have the option of running at least partly on grid electricity rather than liquid fuel.  Give subsidies to purchasers of vehicles which can do it sooner, phasing out in 2011.
We could have had cars running partly on grid electricity in 1990, when the California Air Resources Board wrote its first ZEV mandate.  Lead-acid batteries would have sufficed for ten to twenty miles of gasoline-free driving; Los Angeles could have been cleaner faster.  And the USA could have started a move away from petroleum as the crucial energy supply for our transport network.

It's fifteen years later.  Technology has moved on; batteries are more powerful and lighter, electronics are smaller and more powerful, electric motors pack more horsepower per pound than ever before.  There is nothing we could have done in 1990 that we cannot do better today.  If the President of the United States said it was important, can we have any doubt that it would finally happen?

UPDATE 6/22/05 02:28 EDT:  Winds of Change has a quote that so perfectly reflects my point that I will substitute just one term (outlined in bold) and otherwise let it stand:
As far as many of them are concerned, the best way to fix the energy situation is to neutralize the administration (in the sense of what they see it's ability to do harm) or at least force it to comply with their preferred policies. They tried to do this in the 2004 election and appear to be moving forward with that policy to this day because, simply speaking, they regard the administration as having screwed up energy policy and don't trust it to do a decent job as far as anything else is concerned.
WoC was talking about Iraq, but I think this is spot-on for so many other things it's scary. 
Sunday, June 19, 2005

Post-oil airliners

One of the big issues of the peak-oil crowd is what will happen to air transport.  If there is no oil, they say, jet aircraft won't fly.  This prospect excites the pastoralists (who seem to find glee in the notion of no passenger vehicle moving faster than a stagecoach) and dismays or depresses most everyone else.  But is it realistic?

Despite neglect over the years, laboratories are simmering with activity in a dozen areas from airfoils to catalytic alkanes to quantum dots.  Human ingenuity being what it is, we can expect some form of relatively inexpensive renewable energy to come to market relatively soon.  The prospects for air transport depend on exactly what takes center stage.  If it turns out to be only wind and photovoltaics, it's a good bet that not many things will be flying; batteries are not up to the job of moving big, fast things through the air, and the production of chemical fuels from electricity is an inefficient and expensive process.  Such a development would likely mean a future of high-speed maglev, not soaring so high as the eagle but doing the job so long as the routes are purely terrestrial.

Things will be quite different if a significant part of the market winds up going to chemical fuels, either biochemical or wholly synthetic.  The University of Wisconsin process which turns biomass to alkanes would probably produce something suitable for jet fuel if it can be made cheaply and in sufficient quantity, but the limits of biological productivity of land plants and competition from other users might price it out of the market.  Aircraft look to be considerably better off if one of three possibilities comes to fruition:  algal biodiesel, methane, or photosynthetic or photolytic hydrogen.

Algal biodiesel or its feedstock would be nearly optimal.  If it could be selected for fractions which would not gel at stratospheric temperatures, it would be an almost exact replacement for jet fuel (at a slight weight penalty due to the oxygen).  An alternative would be to use the UWisc process to turn the raw algal oil into pure alkanes, which would be an exact replacement.  But if algal lipids don't come to market at reasonable prices, there are the simple molecules:  methane and hydrogen.  These have the disadvantage that there is no infrastructure for fueling with them, nor aircraft set up to use them.  But will they fly?

Methane is the easier of the two to obtain, handle and use.  We'll have a healthy supply of it for decades after natural gas wells lose their fizz.  It bubbles out of thousands of landfills nationwide, and isn't going to stop unless we stop dumping garbage (which may happen).  It can be liquefied at temperatures (99 K) where air is still a gas, and has a liquid density of 0.424.  Hydrogen is touchier stuff, not turning to liquid until the temperature gets down to twenty... Kelvin, and is extremely light even as a liquid with a specific gravity of about 0.070.  (Strangely, there's about 50% more hydrogen in a liter of liquid methane than there is in a liter of liquid hydrogen.)

Suppose we were going to fuel a 767 with this stuff, and the aircraft requires about the same amount of energy regardless of the specific fuel used.  A 767-200E carries 23,980 gallons (90,770 liters) of Jet-A, which is approximately the composition of kerosene.  The density, energy/weight and energy/volume ratios of kerosene, liquid methane and liquid hydrogen stack up as follows:

 Property / Fuel   Kerosene   Liquid CH4   Liquid H2 
 Density  0.825  0.424  0.070 
 Energy, MJ/kg  45.9  55.5  146.5 
 Energy, MJ/l  37.9  23.5  10.26 
 Fuel required, kg  74,890  61,930  23,460 
 Fuel required, l  90,770  146,400  335,300 

As we can see, liquid methane is a fairly well-behaved fuel, requiring only about 60% more volume than kerosene and weighing about 13 tons less for the same energy.  It might even fit largely inside insulated wing tanks; if the volume penalty for insulation was 15% and the balance of fuel was held in external tanks, they would only require 69,000 liters of volume.  This would fit in two tip tanks of 2 meters diameter and roughly 11 meters long; if they were made of two layers of 1.5mm aluminum with 5 cm of insulation between, the tanks would weigh about 600 kg each, or 1200 kg total.  Liquid methane fuel would allow the aircraft to weigh almost 12 tons less fully fuelled, allowing roughly another 12 tons of cargo to be carried (minus allowances for drag losses on the new tankage).  This is clearly within the realm of engineering feasibility.  An airliner running on liquid methane might be a better aircraft in some ways than one running on kerosene.

Hydrogen is the outlier in all respects.  The energy equivalent of a 757 full of kerosene is a mere 23 and a half metric tons, more than fifty tons lighter than the dinosaur juice.  It's also close to four times the volume.  Insulating wing and fuselage tanks is probably impractical; it's likely that the full load would have to be carried in external tanks, either on the wing tips or on pylons like outboard engines.

Wherever you put them, they'd be monsters.  A pair of 3-meter diameter tanks would have to be 24 meters long each, or half the overall length of the aircraft.  Bulbous fairings below the fuselage wouldn't do it either; even if the lower cross-section was made square with extra volume, it would hold less than a third of the required fuel.  A massive forward delta-shaped wing root strake might hold a fair amount, but I can't even guesstimate how much.  Were the fuel to be divided among four separate 2.5 meter diameter tanks mounted at various points along the wing, each would have to be roughly 17 meters (56 feet) long.  This is a serious design headache, and would probably be best implemented starting from a clean sheet of paper.  The good news is weight.  Were the tanks made of the same 2 layers of 1.5mm aluminum (strength provided by internal pressure, like a blimp), they would weigh perhaps 5 tons total.  This would make the aircraft's fully-fuelled weight some 45 tons less than the conventional model, a large fraction of which could become extra cargo.  Another bit of good news is hydrogen's chemical and thermodynamic properties; a liquid hydrogen engine can pressurize its fuel, use it to recover energy from expanded exhaust and hot turbine blades, and expand the resulting high-pressure gas through a turbine to yield extra energy.

So what's the verdict on air travel in a post-oil world?  It depends, but if technology can make renewable fuel of any kind available at close to today's prices, we can bet that fleets will be scooting around the sky on it. 
Friday, June 17, 2005

Dare we call it treason yet?

There's a sad pattern in the third world.  A dictator rises to power, and proceeds to install his cronies in every public office of significance, slants the nation's laws (such as they are) so that his own enterprises take a cut of every transaction, and loots the public treasury for good measure.  He may start wars against neighbors to rally the public and paint the opposition as unpatriotic.  The nation sinks into poverty and misery as the dictator and his cronies get rich.

Thank goodness this only happens to other people.

Or is it too early to crow?

The USA has a love/hate relationship with petroleum, especially imports.  It makes our cars and trucks go and runs a fair fraction of the rest of our economy, but it also fouls our air, takes more of our income at the pump than we're comfortable with and finances the enemy's side of the War on Fundamentalist Islam Terror.

Ever since the oil price shocks of the 1970's, there has been an on-again, off-again effort to address the issue of petroleum dependence.  In the "DO SOMETHING!" atmosphere of stagflation, Jimmy Carter's "Moral Equivalent Of War" started with a dozen programs trying to attack the problem from different angles, not all of which were direct but all having potential.  Oil shale.  Synfuels from the USA's 250-year supply of coal.  Wind power.  Solar.  That's about the time I first heard of Ocean Thermal Energy Conversion (OTEC); MHD was also on magazine covers, and all kinds of plants doing all kinds of new things that Might Be The Fix had their fifteen minutes of fame.  The National Renewable Energy Lab (NREL) was started in this spurt of mixed optimism and desperation.  The national speed limit went down to 55 MPH.  The changes went right up to the top; the White House itself got solar collectors, and the thermostats in the building were changed to allow greater temperature tolerances to save energy.

Then (to seriously oversimplify matters) two things happened.  Jimmy Carter, whose MEOW instead of properly rattling our sabers toward Iran got him branded as a pussy, lost to Ronald Reagan in 1980; Reagan installed some no-nonsense talent at the Federal Reserve.  And the inflationary bubble caused by the oil-price hikes of the previous decade finished working its way through the system, causing America to breathe a collective sigh of relief and go back to business as usual.

While everyone's attention was on other things, in Washington's back rooms it was politics as usual.  Most of the Carter-era programs were cut back severely, some eliminated.  The progress at NREL slowed drastically.  And America's demand for imported oil, our Achilles' heel that we had pledged to go back to the river Styx to eliminate once and for all, began to creep up again.

For twelve years little was done.  Progress crept along in the labs, but not much got out of them.  Then came Clinton.  His first attempt at a carbon tax, with umpteen different levies for various uses of more or less the same fuel, accompanied Hillarycare to a well-deserved death in Congress.  But he didn't stop after just one attempt.  On a day that he wasn't leaving embarrassing stains in hard-to-explain places, he started the Partnership for a New Generation of Vehicles (PNGV):  a program to have the auto companies deliver a full-size passenger sedan which would go 80 miles on a gallon of fuel.

PNGV paid the Big 3 roughly a billion dollars through 2000.  Compared to California's ZEV mandate, which put a thousand or so electric cars on the roads for a few years, it didn't actually make any product.  But it was a long-term program, not set to make vehicles for sale until model year 2008; by 2000, at least one of the prototypes (Daimler-Chrysler's ESX3) was yielding 72 MPG and had an estimated cost premium of just $3500 over the conventional models of the day.  This was already about 3 times the average economy of the contemporary fleet; such vehicles would have pushed America a large part of the way toward the goal everyone had thought so important twenty-four years earlier.  (Events did not stand still during this time; oil prices went up and down, to impressive lows during the Asian financial crisis of 1997-98; due in part to this and the CAFE and emissions loophole for "light trucks", the the minivan and then the SUV were born.  Meanwhile, the looming menace of global warming became harder and harder to deny, and so was the world's progression toward its collective Hubbert peak.)

And then George W. Bush beat Al Gore in 2000.  The PNGV died shortly after his inauguration, victim of a knife in the back in a dark alley.  The auto companies breathed their own sigh of relief at the demise of this threat to the old and familiar, and looked the other way as the body was quietly disposed of.

In a previous life, G.W. Bush was an oil man.  In not-long-previous lives so were his veep, several of his cabinet picks and a huge number of his friends and associates.  They were a very insular group by historical standards, not given much to listening to voices outside their circle.  But they knew oil, and what was good for oil people.  This they did.  But they couldn't just leave things at that; the PNGV did have its friends and the American people still had a lingering resentment of imported oil.  This called for a payoff.  The blood money arrived in the form of a hydrogen vehicle program with a bunch of useful properties:  it gave the auto companies something to research in their labs, money to pay the researchers, and no demand to change their modus operandi for probably another 20 years.  It made the American people who weren't paying close attention (which was most of them) think that Something Was Being Done.  Last, it made the oil, coal and gas interests snicker, because they knew that the oil business would have no competition for the foreseeable future and the cheapest sources of hydrogen for quite some time were going to be natural gas and coal; nuclear had a chance too.  All of this was Good For Business, or at least those businesses which were in the Bush camp.

11-Sep-2001 came and went, with the huge upheaval in military, security and law-enforcment apparatus.  Two wars were fought as a direct consequence.  9/11 should have caused a reversal of this carefully-laid scheme, as the source of the danger to America became obvious and the folly of waiting another two decades to address it was laid out in excruciating detail.  Yet the administration stayed its previous course, holding steady not just then but for the next 45 months.  Sticking to the charade that the lightest element was the cure for the nation's ills, G.W. himself cut the ribbon on a hydrogen fuelling station in Washington DC in May and on the fifteenth of June he touted this act in a press conference as if it meant something.

He knew otherwise.  Three months earlier, high administration officials were party to a meeting of the Bilderberg group in Germany.  The group is highly secretive, but someone claiming to have infiltrated it has written a report for the magazine Counterpunch.  One exchange is particularly pertinent:
Another Bilderberger asked about hydrogen alternative to the oil supply. The US government official agreed gloomily that hydrogen salvation to the world's eminent [sic] energy crisis is a fantasy.

If the account is accurate, the White House actually did know what most everyone with an interest in the subject and a little knowledge of physics, chemistry and Google already knew.  This revealed what they were up to:  instead of being amazingly blind and stupid, the Bush administration turns out to have been lying to (if not completely deceiving) its own public for the previous four years.

That makes me feel so much better.  Not.

The administration has had ample notice and opportunity.  At this writing, it has been forty-five months and 6 days since Mohammed Atta and his gang turned four airliners into cruise missiles and got 3 of them to their targets.  The toxic ideology which fuelled them has been revealed, and the source of its funding and strength is known.  If the White House had called for a revival of the PNGV, or production of 70 MPG fish-cars, or other measures that they have to know would have addressed the problem, the rush by Congress and the public to make it happen would have looked like a stampede.

What has the president done instead? In short, he's frustrated both our offensive and defensive responses and given aid and comfort to the enemy in a time of war... so that his cronies could profit.

Is it too soon to call it treason?

Hat tip:  Searching For The Truth, for the Bilderberger link and quotes. 
Wednesday, June 15, 2005

June biomass roundup

The news lately has had a couple of new and interesting (to me) schemes for conversion of waste matter to energy.  These appear to have considerable potential.  Unfortunately, they also seem to have built-in losses which seriously limit the efficiency and thus the useful outputs.

First up:  a biomass to biodiesel process from the University of Wisconsin.  This process proceeds in 5 steps:
  1. Convert plant matter to sugars in water (by means unspecified).
  2. Strip hydrogen from the sugar/water solution using a nickel/tin catalyst.  (Removing hydrogen from the mixture would appear to produce CO2 as a byproduct, but this is not specified.)
  3. Treat the non-hydrogen fraction with acids to dry it.
  4. Convert to alkanes using a solid alkali catalyst.
  5. Convert to light carbon chains using the hydrogen from step 2 and another catalyst.
The fuel product is claimed to be equivalent to conventional biodiesel.  It is immiscible with water and separates by gravity, eliminating distillation steps required with alcohol fuels.

The issue I can see here is efficiency.  Plant matter is largely carbohydrates, which have the general chemical formula of (CH2O)n.  Alkanes have the general formula (CH2)nH2, and have no oxygen; the oxygen in the feedstock has to come out either as water or as CO2.  A process which extracts hydrogen will leave carbon and oxygen, so the obvious byproduct is CO2.

How much?  Consider the production of pentadecane, C15H32.  Each CH2O carbohydrate subunit can yield one atom of carbon plus a molecule of water, or one-half atom of carbon, one-half molecule of CO2 and one molecule of H2.  Pentadecane requires 16 molecules of H2 which consumes 16 CH2O subunits and yields 8 atoms of carbon and 8 molecules of CO2; the remaining 7 atoms of carbon requires 7 CH2O subunits and emits 7 molecules of H2O:

23 CH2O   ->   C15H32 + 8 CO2 + 7 H2O

Assuming none of the feedstock is used to provide process energy, the net carbon loss is 8 atoms out of 23, or 35%.  The theoretical dry-carbohydrate-to-fuel efficiency is 212/690, or 30.7%.  Based on the heats of combustion of sugars vs. decane and assuming no mass losses the energy efficiency of the process is roughly 88%, but the first step (conversion of biomass to sugars) is a huge unknown.  Then there are all the different catalysts.  This looks tricky.

Second is conversion of gasified biomass to ethanol by bacteria from a company called BRI.  This process partially burns waste (of most any sort) to a syngas of CO, CO2 and H2; this syngas is fed to Clostridium ljungdahlii bacteria which ferment it to ethanol, which presumably has to be distilled.  The liquid-fuel yield is 75 gallons of ethanol per ton for municipal solid waste (MSW), rising to 150 gallons per ton for used tires or hydrocarbons (I presume that plastics are equivalent to those feedstocks also).  The process equipment would be divided into modules, each consuming 85,000 (presumably dry) tons of MSW per year, producing 7 million gallons of ethanol and 5 megawatts of electricity as a byproduct.

This process has two steps which massively increase entropy, one in the gasifier and the second in the bacteria.  Its biomass-to-fuel efficiency is correspondingly low:  75 gallons of ethanol is a mere 494 pounds, containing the energy of about 310 pounds of hydrocarbons.  This 15.5% effective biomass conversion efficiency (45% energy efficiency) is about half that of the University of Wisconsin process, but it also yields electricity with an efficiency of about 11%.  This 56% overall efficiency, combined with the lack of catalysts and flexible variation between the fuel and electric products, might be a winner due to low capital costs and ability to tune output to market conditions and maximize total value.

This analysis wouldn't be complete without a reference to a previous headliner of biofuels, Changing World Technology's thermal depolymerization process.  CWT claims a 70% conversion of plastic to alkanes, or 44% conversion of tires to alkanes plus 42% carbon and metal solids.  This is about three times the conversion efficiency of the BRI process, but there's an interesting quirk:  the carbon portion of the product of the TDP process could be gasified in the BRI system and used to produce additional fuel and electricity.  The byproduct heat of the BRI gasifier might also be sufficient to run a TDP converter, and the TDP output gas might be suitable to feed the Clostridium cultures directly (certainly after gasification).  Total efficiency could go way up.

If there's any chance of CWT and BRI "swapping spit" and cross-licensing their patents, this could get a lot more interesting.  The sudden absence of landfills in the countryside could be the least of the outcomes. 
Monday, June 13, 2005

SMH:  anti-nuke propaganda organ?

The Sydney Morning Herald publishes a "sustainable energy" activist's claims that nuclear power does not reduce greenhouse emissions.  I am not a big advocate of nuclear power, but propaganda should not be allowed to stand; unless I am very wrong this claim is, to put it mildly, bunk.

Consider the plant itself, beginning with its containment building.  Plucking figures from around the web, suppose that the reactor containment is a cylinder 40 meters tall, 45 meters inside diameter and 1.5 meters thick capped by a hemispherical dome on top and resting on a flat foundation 3 meters thick.  The total volume of the concrete part (including reinforcing steel) is 19,290 cubic meters.  A maximum-strength, minimum-workability mix is used which has a density of 2400 kg/m^3, is 25% cement by dry weight, and has a water:cement ratio of 0.35; this mix has 550 kg of cement per cubic meter, or 10,600 metric tons of cement overall (the remainder being sand, stone, steel and water).

The making of cement requires 750 kcal/kg, or 8.0 trillion calories for the whole building.  This amount of energy is equivalent to 33.4 trillion joules, or 9,280 megawatt-hours; the plant will make this much electricity in nine and a half hours of full-power operation; a coal-fired plant of the same output would use 8 trillion calories of fuel in a bit over 3 hours.  Energy from the plant could make the concrete for the rest of it in perhaps a day.

Production of raw uranium:  The price of uranium is currently around $20/kg; extraction from seawater is thought to cost as much as $200/kg.  Suppose that this $200 is the cost of the crude oil or equivalent required to refine it to yellowcake; at today's prices, this would be about 4 barrels of crude at roughly 310 pounds each, or 1240 pounds of petroleum.  After enrichment from 0.7% U-235 to 3.5%, each kg of raw uranium yields 200 g of fuel; burnup in an LWR at 50,000 megawatt-days per (metric) ton means each 200 grams yields 10 megawatt-days of heat, or 82 million BTU.  The heating value of #2 diesel is about 19,110 BTU/lb, or 2.4 million BTU for the 1240 pounds.  Even at $200/kg of uranium, the heat produced by the uranium is around 35 times as much as its cost in fuel oil, assuming the entire cost goes for fuel oil (which is silly).

Next, consider enrichment.  According to this reference, a year's fuel for a 1000 MWe LWR requires between 100,000 and 120,000 separation work units (SWU) to produce.  One SWU requires about 2500 kWh in a gaseous diffusion plant, but as little as 50 kWh in a gas centrifuge plant.  If the LWR runs at 80% capacity factor, it would produce 7.01 billion KWH per year, while its fuel would require as much as 300 million kWh (120,000 SWU via gaseous diffusion) or as little as 5 million kWh (100,000 SWU via centrifuge).  This overhead runs from 4.3% down to 0.071% of its output.

All told the overhead of uranium mining and enrichment accounts for considerably less than 10% of the energy output of a light-water reactor, and we haven't even considered the possibilities of natural-uranium burners (no enrichment) or plutonium and thorium breeders (ditto after the first fuel load)  The energy of construction is replaced in days at most, perhaps in the first day of full-power operation.

Should the Sydney Morning Herald's editors be ashamed of themselves for publishing baseless nonsense?  Unless I've slipped a few decimals, it sure looks like it. 
Saturday, June 11, 2005

Dropped balls

I dug through some old files recently and found that I've been talking about the merits of plug-in hybrids for thirteen years.[1]


That's a fairly long time.  It's three design cycles in the auto industry, maybe four.  It's I don't know how many rounds at various boards and bureaus.  Six and a half Congresses.  However you measure it, it's plenty of time to get something done.

For at least thirteen years[2] (assuming that these folks hadn't figured it out themselves before that), Federal and state policy makers and auto companies have known - have to have known - about the feasibility of partial grid power for vehicles and the substantial if not complete freedom from petroleum that they would allow.  The auto companies had to know it, because their own engineers were talking about it.  I was one of them.

Yet every time the opportunity came to them, they dropped the ball.

Thirteen years have passed.  Yet nothing was done:  the California Air Resources Board deliberately passed up the opportunity in favor of a ZEV mandate requiring batteries which are still not available (and now that battery technology is just about to get there, fumbled the ball again just two years ago); the Clinton administration promoted 80-MPG passenger sedans but didn't do anything about petroleum independence; and Bush's hydrogen vehicle program has nothing now and may never yield anything.  (Update after concept but before completion:  the administration knew it would not yield anything in time; more on that later.)

Today the bill is coming due.  Oil supplies are tight up against demand, and price spikes seem inevitable.  Yet despite the decade-plus of time we've had to take action, and the nearly four years of notice we've had since 9/11 that something had to be done.... our transportation network still runs almost entirely on petroleum.  Even if there is never an interruption in supply, escalating prices can do untold damage to our economy and livelihoods (not to mention the hazard of financing religious radicals sworn to kill us).

One thing is certain:  if we drop the ball this time, we are not likely to get another chance.

[1]  Wagers on whether I can prove it are welcome.  Money, good liquor, whatever...
[2]  Or maybe 26 years.  The 1979 Mother Earth News article about the Opel conversion arguably counts, but policy makers can probably be forgiven for discounting the source. 
Thursday, June 09, 2005

Walking the walk

This post is 100% off-grid, powered by batteries.

Yup, the power is out.  The UPS is holding up just fine, and this little experiment in tolerance of low quality of electric service appears to be a complete success.  When the grid comes back I'm going to check the SOC of my backup and write a final report.

UPDATE:  Power was down for approximately 2 hours.  I shut down to disconnect the UPS after another hour; battery voltage was 12.74.  Unless it was recharging very quickly, it probably had many hours of backup left in it.  I need to arrange this setup so I can check the battery's state of charge while it's in operation.... some day. 
Wednesday, June 08, 2005

Comment policy

I've closed The Ergosphere to anonymous comments.

I would rather not have, but I expect posters to take some minimal responsibility and credit for their words.  I would have been happy with people using a nom de plume, but my polite request was ignored by all the anonymous posters as if it wasn't there.

Blogger accounts are free.  Get one if you want to post.

Spam is shot on sight.  (As soon as Senate bill 831974278 is signed into law, this policy will be modified.  S.831974278 designates spammers as not alive but "needing to get a life" and thus not persons under the law, and my policy will become "spammers will be shot on sight".)


Friday, June 03, 2005

Fertilize this!

Running around the blogosphere, you'll find all kinds of people dancing to apocalypso music by various artists.  One favorite song among the fans of the Energy Depletion Band is that agriculture is bound to collapse when supplies of fuel used for production of nitrogen fertilizer become tight.  Here's a typical example (including typos):
Modern food production is depends on oil. There is no way to get fertilizer from solar, wind or nuclear.
I'm no agro-scientist, but I know that this claim is both factually and historically false.

History:  Nitrogen depletion in soil was historically dealt with using legume crops or green manures in crop rotation.  Just where do you think a bean plant gets the energy to fix its nitrogen?  It comes from the sun, turned into carbohydrates which go to symbiotic bacteria which perform the actual work of fixation.  (External nitrogen supplies from guano deposits and then Haber-process ammonia later supplanted green manures for most farming.)

Legume crops don't fix nitrogen fast enough for modern intensive techniques, but it proves that it is indeed possible to make nitrogen fertilizer with solar energy.  The big question is, how hard is it?

Suppose for a moment that we keep using the Haber process, but decide to power it with solar inputs.  We get the hydrogen from green algae trick operating reliably at 1% efficiency.  An area getting as much sun as mid-Kansas would receive about 1550 kWh/m2/year, so a square meter of this algal hydrogen factory would yield 15.5 kWh worth of hydrogen; at 70600 cal/mole, that's about 380 grams of hydrogen per square meter per year.  It takes 3 grams of hydrogen to fix 14 grams of nitrogen, so each square meter of algae farm could make the hydrogen to fix roughly 1.75 kg of nitrogen, or 17.5 tons nitrogen/ha/year.

US farmers use roughly 12 million tons of nitrogen fertilizer per year over 140 million ha of cropland, or about 86 kg/ha/year.  At that application rate, a hectare of algae farm could produce the nitrate to fertilize about 20 hectares of crops; in other words, a 1% efficient sunlight-to-hydrogen process can make all agricultural nitrate from the sun with about a 5% land-use penalty.  The penalty goes down to 1% if the efficiency goes up to 5%, and 0.5% if it hits the 10% target that researchers believe is possible.

If 10% efficiency can be achieved, the hydrogen production goes up to 38 tons/ha/year (1.55 MWh/ha/yr) and it can become the basis of a general energy business.  If crop wastes such as corn stover and wheat/rice straw are used as carbon inputs and have a general chemical formula of (CH2O)n, addition of H2 is all that is necessary to produce methanol (CH3OH).  If the process can use the inputs with 100% conversion efficiency, 2 grams of hydrogen plus 30 grams of carbohydrate yields 32 grams methanol; 38 tons of hydrogen becomes 608 tons of methanol (about 203,000 gallons, holding the energy equivalent of 122,000 gallons of gasoline).  At this level of production, inputs of crop waste are probably the limiting factor; long before this level was reached, the fuel production would satisfy all needs for cultivation.

Conclusion:  it is not only possible to generate all required nitrogen fertilizer from solar energy using known processes or slight improvements, at the limit they could lead to large-scale production of biofuels from crop wastes.  All it requires is hydrogen.

UPDATE:  Advances sometimes come too fast to comprehend.  Researchers at UW-Madison have a process to convert plant carbohydrates to alkanes.  This doesn't address the fertilizer issue directly, but turning grain farmers into net producers of motor fuel eliminates that mode of system failure.

Related items:  Zinc:  Miracle metal? 
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 /

Powered by Blogger

RSS feed

Visits since 2006/05/11: