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---- hydrogen fuel cell faggotry.
BORON: A BETTER ENERGY CARRIER THAN HYDROGEN?
Graham Cowan
If far-flung energy users each possess several tens of kilograms of the
somewhat costly, somewhat toxic substance diboron trioxide (also known
as boria), and occasionally send some to a central power station that
can reduce it to its elements, that station can, by returning only the
boron, transmit back one continuous kilowatt of power for each 5.1
kilograms per day of boria received.
That rate of active material shipment is much larger than in the
analogous hydrogen-economy power coupling, even though a water-splitting
power station needs not 5.1 but 6.8 kilograms of water per kilowatt-day
transmitted. The Earth's atmosphere is an enormous water vapour bank the
station can borrow from and the users repay, and therefore the only
shipping task is distributing the hydrogen. Its mass is 0.76 kilograms
per kilowatt-day.
Elemental boron is now produced at very high prices, 23 to 400 times
more for a pound without oxygen than for a pound with, $360 to $6,400
per contained kilowatt-day.
Its use as a potentially mass-market fuel has not been demonstrated. One
promising approach is a gas turbine that would burn it in a large excess
of pure high-pressure oxygen. Problems would include fabricating boron
-- brittle, refractory, very hard -- in a form amenable to service as
fuel, making the combustion chamber and rotor of materials that neither
pressurized oxygen nor boria will attack, providing the oxygen, and
extracting the boria (for the user to send to the power station again).
Poisoning deaths have occurred with boric acid, which forms
spontaneously when boria and water meet at normal environmental
temperatures:
(1/2) B2O3 + (3/2) H2O(l) ---> B(OH)3, DG° = -22.03kJ/mol
Its acute oral LD50 in rats is listed as 3 to 4 grams per kilogram of
body weight (*1). Taking into account the 0.563 mass fraction of boria
in boric acid, and supposing boric acid acts similarly in rats and
humans, the extrapolated acute LD50 by ingestion of boria is 1.7 to 2.2
grams per body kilogram, i.e. 75 grams for someone weighing 100 pounds.
This is twice the acute toxicity of ingested sodium chloride.
Motivation
To enable noncombustion primary energies -- nuclear, direct solar,
hydraulic, wind -- to take over the jobs petroleum and natural gas now
do, without adopting their safety standards.
After these hydrocarbons have been taken out of the ground, where they
were not in contact with air, it is best to keep them still shut away
from it for as long as they are in processing, distribution, or storage.
Every week this is attempted on a worldwide scale of roughly 100 million
tonnes, seldom without at least one disastrous lapse.
Elemental hydrogen is produced on a scale four orders of magnitude
smaller, and also kept apart from air with great but occasionally
inadequate care. Lethal failures occur, perhaps even somewhat more often
than once in 10,000 weeks. It is therefore just as incongruous to
imagine nuclear power stations producing it as to imagine them producing
gasoline.
Water's great abundance is sometimes called an advantage of hydrogen
power. But there are other very abundant, very strongly bound oxides.
Let us pick one whose deoxidation yields a safer fuel. Corundum and
quartz fit the bill, and maybe periclase. The oxophilic elements in them
are respectively aluminum, silicon, and magnesium. They do not have to
be kept out of contact with air, yet when they burn they burn very
strongly.
Burning regenerates the oxides as fine particles that would not be as
inoffensive to dump as the original minerals. If they were first
consolidated into gravel, then they might not be too much of a nuisance.
A large urban intersection thronged with cars powered by oxidation of
metal or silicon would see the accumulation of approximately one cubic
metre per day.
Hot-pressing equipment to make that gravel on board cars would be
expensive. Perhaps some kind of glue could be used, or bags. In any
case, these energy carriers would either accumulate after use as large
heaps of oxide, or go back to the power station to be deoxidized again.
But if they go back then conceivably they can be used many times, and
more expensive, lighter varieties of atom can work. Two elements are
lighter than magnesium and, when uncombined, share aluminum's and
silicon's trait of burning strongly but not readily: beryllium and boron.
The pursuit of safety has thus with apparent perversity led to toxic
elements. In boron's case there are reasons to think that appearance is
false, and the prospect that its use will give much safer combustion
power than hydrogen or hydrocarbons can is real.
One of these reasons stems from the fact that unlike beryllia or
magnesia or alumina or silica, boria does not emerge from a hot flame as
suspended solid particles. It emerges as mist. This promises to let it
be gathered more easily and effectively than those other oxides could
be. Bags may still have a role to play, but hot pressing and glue don't.
Above 500°C boria is its own glue.
Boria's Unusual Nature Seems Tailored for Extraction from Combustors
Boria can be liquid above 2,000°C and still flow at 400°C. There is some
discord in published values of its normal boiling point -- 4,600 Rankine
(*2), 1,860°C (*3), 2,316°C (extrapolated) (*4), 2,065°C (*5).
However, when boron burns in a 25-fold excess of oxygen, the products
cannot, after mixing, be much hotter than 1,200°C. At such a temperature
virtually all of the boria must be incorporated in droplets. In the
middle of the 20th century air-breathing turbines fuelled partly with
boron were tested in the apparent hope that these droplets would blow by
the turbine airfoils and not stick.
It now seems more reasonable to hope that they will; or at least, it
does if turbines can be constructed on a somewhat different plan, with
blades poking inward from a hoop rather than hanging out from a hub. If
such a turbine airfoil revolves in mist, coats itself with liquid, and
doesn't reach all the way in to spin centre, the liquid will feel a
centrifugal force field of nonzero strength no matter where it is on the
airfoil. It will be conducted radially outward in a flowing film.
Based on assuming laminar flow and constant viscosity, the film depths
necessary for as much to flow away as is arriving are expected to be small:
Film depth = (3 * Power * Viscosity /
(Specific energy * Width * Density^2 * Centripetal acceleration)) ^ (1/3)
The 'Width' here is the stream width, about twice the distance from
airfoil leading edge to trailing edge (because the stream is on both
sides). Suppose the airfoil catches the same fraction of the mist as it
converts of the thermal power, and all the catching occurs at the
innermost point.. Then the amount of boria flowing past any point
farther out is the (Power / Specific energy) part of the above. Specific
energy is the ratio of heat produced to boria produced by the
boron-oxygen reaction upstream of the turbine: 18.0 megajoules per
kilogram.
Suppose an airfoil is 20 millimetres from leading to trailing edge at
radius 30 millimetres, i.e. stream width is 40mm, and its share of the
thermal power is 1 kilowatt. Let it revolve 250 times per second, so
that the film on it at 30 millimetres radius has 74.0 kilometres per
second per second of centripetal acceleration. Let the temperature be
600°C. This fixes liquid boria's density near 1,600kg/m^3 and its
viscosity near 480 pascal-seconds (*6). That is 480,000 times the
viscosity of water at 20°C. Boria at this temperature is thick, syrupy
molten glass.
The film depth works out as 0.22 millimetres, probably small enough
compared to the airfoil's 20mm chord that it won't cease to be an
airfoil. If the temperature were reduced to 400°C the viscosity would
rise to 160,000 pascal-seconds. This huge increase may reflect the fact
that 400° is below the 450°C melting point of (very seldom seen) boria
crystals. Because of the one-third power in the film depth formula the
predicted increase in depth is only 6.6-fold, to 1.5 millimetres.
Diboron trioxide flowing radially outward in a centrifugal force field
is an instance of liquid flowing downhill, a situation sometimes
conjecturally linked to the arrival of liquid at the bottom. If that
happens here, the bottom will be the turbine airfoil root, where it
transmits force and power to the support hoop's inner surface. It seems
possible for drain passages to descend further from that surface through
the support ring to a ledge where the liquid can, by moving along the
axis of rotation, spill over. A stationary scraping blade will take it
before it can fly off on a tangent.
Now flowing down the scraper in a much thicker film than on the turbine
blade because local gravity is so much weaker, it can make its way to
molds. This process will resemble the action of bottle-blowing
machinery, except the glass aliquots can be cooler when they arrive --
boria's work point is roughly 560°C, while that of soda-lime glass is
1,000 to 1,100°C -- and probably won't be blown hollow, just allowed to
freeze as massive transparent vitreous lumps.
Virtuous Boria
The toxicological risk of handling boria in this fashion is limited by
the low surface-to-volume ratio of the lumps and their hardness (Mohs 5,
similar to fluorite or tooth enamel). They are, however, able to
dissolve slowly in water, through the boric acid-forming reaction noted
previously followed by dissolving of the acid.
In recent years studies of aqueous B(III) toxicity to animals have
broadened to include consideration of its possible animal essentiality,
without very definite results yet, but it is known to have a biological
half-life of a day or two. If it isn't a micronutrient, at least it has
little potential for cumulative toxicity. So it seemed not unduly risky
to measure how quickly boria glass dissolves in a continually refreshed
37°C aqueous medium by sucking on a 6mm by 8mm by 1.4mm piece, estimated
mass near one-eighth of a gram. It lost all its thickness in 31 minutes,
0.4 microns per second per side. This suggests a lump too big to swallow
would have to be sucked on non-stop for about a day to deliver the LD50.
Water vapour contacting a boria glass surface forms boric acid. In the
absence of liquid water the resulting tarnish builds up to much less
than a millimetre thick, makes the glass look milky, and then prevents
further reaction. It is a solid lubricant, so pieces of boria aged in
humid air are slippery.
Boria Is Easier to Transport than Hydrogen
For many practical energy-transmission purposes this is true, even
though, as previously mentioned, the same energy can be taken up in
dissociating the boron and oxygen in 5.1 kilograms of boria as is
already in a 6.7 times smaller mass of elemental hydrogen: one
kilowatt-day.
The boria could be considered a carrier of energy demand. It is relevant
to compare its haulage with that of fuel hydrogen because each is the
heaviest cargo, as such, in its system. Hydrogen ash rides the wind and
finds its own way to the power station. Elemental boron can't get quite
as free a ride as that, but as 31 mass percent of boria, it does have
the capability of getting to its destination as a 31 percent load in a
vessel that must go there anyway to pick up a full load of boria for the
next run.
Boria is easier because it won't burn, won't evaporate, and despite
being much heavier than the hydrogen, it takes up much less space. It is
25.6 times denser at room temperature than liquid hydrogen is at its
normal boiling point. Loosely packed spheres would be only 0.65*25.6,
i.e. 16.6 times denser. A dewar flask that could keep 0.76 kilograms of
liquid hydrogen cool would be more than big enough to accommodate 5.1kg
of boria ingots, not necessarily spherical, in its bottom half.
Moreover, those same ingots could also go in a sturdy plastic bag that
would mass less than a tenth of a kilogram. It is not yet certain what
shape the 1.6 kilograms of boron in them will be given when the power
station extracts it, but if it is any sort of pellet, the pellets could
certainly ride back in the bottom of same bag. Boron is a little denser
than boria, insoluble, involatile, infusible, apparently physiologically
inert, and unable to burn in air.
Only very large consignments of low-pressure liquid hydrogen, many
terajoules' worth, could be accommodated in a container less massive
than the contents in the way that plastic bag is. For gigajoules or
less, the container is typically ten or more times more massive. Boria
plus a bag is lighter.
It has been proposed to use stable hydrides such as that of magnesium as
involatile solid forms of hydrogen. As an atomic-scale room temperature
hydrogen container, a magnesium atom does nicely shrink hydrogen, down
to only 64 percent of the specific volume of liquid hydrogen at
-252.87°C, but it follows the ten-times-mass-of-contents rule fairly
closely -- actually 12 times. As a source of fuel hydrogen, magnesium
hydride masses 11.85 kilograms per kilowatt-day.
Magnesium hydride isn't fireproof and neither is the highly expanded,
high surface area magnesium metal left behind when the hydrogen is
thermally driven off. Interestingly, the fire hazards in this scheme can
be much reduced, and the haulage reduced by more than half, if the
magnesium is burned along with the hydrogen.
The heaviest load then is the incombustible magnesium oxide travelling
to the power station, 4.6 kilograms per kilowatt-day, a little lighter
than boria. The hydride leaving the power station is still readily
ignitable, but its quantity is reduced to only 3.0 kilograms per
kilowatt-day, less than a third as much as in the hydrogen-only case.
Magnesia won't ooze out of a combustor and then solidify in void-free
masses the way boria can, though.
Boron Pipelines?
Elemental boron itself does not seem very well suited to being piped.
But much hydrogen now travels short distances through pipelines, as
pressurized gas, and it's interesting to consider whether the analogy
between it and boria might extend to transportability in pipes. If it
does then pipelines can do 76 percent -- one over 1.31 -- of the boron
system's tonne-kilometres of active material transfer, and the
freighters that do the rest can load all the way up on boron, not just
31 percent.
Boria pipelines would have to be tributary ones bringing the substance
from many sources to a few power stations, the opposite to the job
hydrogen pipelines would do. The threat to their steel's integrity would
be boric acid corrosion, not hydrogen embrittlement. Leaks would be less
hazardous, and the pressure behind them might be lower, since boria
doesn't need pressure to be dense.
The observed 400 nanometre per second speed at which 37°C water corrodes
vitreous boria, and the rule of thumb that 10 kelvins less means
reaction twice slower, suggest golf ball-sized boria ingots in a
cold-water slurry would lose 4mm of radius per day of travel. But this
incorrectly treats the water travelling with them as staying fresh.
Actually the sparing solubility of boric acid in cold water means a
slurry with equal masses of water and boria would reach saturation with
most of the boria still solid, even if the boria pieces were smaller
than golf *****.
The lubricity of the lumps' boric acid coats might protect the pipe
walls from abrasion. One might think this could work for boron too, but
at normal environmental temperatures boron is so inert that it is not
subject to superficial oxidation. It would scratch like crazy.
If the nearest place to put boria into a pipeline were a few miles away,
this would be less inconvenient than the corresponding case with
hydrogen, for as noted, it's easier to carry a bag containing 5.1
kilograms of boria than the containment system for 0.76kg of hydrogen.
Large pipelines that now carry natural gas at high pressure might
someday have a less demanding task: carrying boria to the
boron-deoxidizing nuclear power stations built on the sites where the
gas wells once ran.
Fuel Boron Should Hold Still While Flowing Oxygen Devours It
Probably the simplest way one can envision feeding boron to a combustor
at a controllable rate is as filament, through a small hole in the
combustion chamber wall. Inside the chamber the filament tip will
encounter a continuously burning fire that will consume it as fast as it
comes.
Very lean combustion has been mentioned, with much of the oxygen present
not to react with boron but to take up the heat from the small fraction
that does, and be heat engine working fluid. Even at pressure on the
order of 10 megapascals this means a very much larger volume of oxygen
must flow through or past the fire than of boron.
25 O2 + (4/3) B ---> (2/3) B2O3 + 24 O2
Supposing the oxygen behaves as ideal gas and starts at 10MPa and 500K,
the left side includes about 10 litres per mole of it, and 6 millilitres
per mole of boron. So the volume ratio is near 1,700. This means a thin
filament will be at the middle of a roughly 40 times thicker cylinder of
oxygen flow if they both come to the fire at the same speed.
But it makes better sense for the boron to come in slowly and the oxygen
around it to come in faster, in a stream narrower than 40 filament
diameters. Then drag from oxygen helps pull the filament in, and the
fire consuming its tip is an instance of lancing combustion: turbulently
flowing oxygen runs over the burning boron surface, quickly removing
boron oxide vapour -- for the flame temperature can be over 4,000°C, far
above even the highest reported boria boiling point -- and scouring
boron atoms and droplets off the surface.
Lancing combustion has recently been recognized as a harmful phenomenon
that can happen when high-pressure pure oxygen passes through aluminum
regulator valves (*7). But when overcoming the ignition resistance of an
ignition-resistant substance is what is desired, lancing combustion is
good. It allows a lot of chemical power to be converted to thermal power
in a small space.
It is not necessary for all the oxygen to flow past the flame in a
single stream. A small excess might do that, and then the rest could be
blown in in converging jets downstream of the flame, quickly diluting
it. Before dilution the boron-oxygen flame can broadcast a considerable
fraction of its power as visible and near infrared light. Putting the
mixing jets' impingement point not far downstream of the flame would
reduce this fraction.
Continuous filament supports lancing combustion because the part in the
chamber is connected to, and held back against the wind by, all the rest
still coiled outside, in an environment where it cannot burn. However,
today's commercial boron filament is impossibly expensive, and has a
tungsten core.
Boron developed for fuel use might be small unconnected chain links
sintered from pure boron powder. These would behave simply as pellets
during distribution and storage. They would resist breakage better than
filament and could be easily apportioned, and transferred with a scoop
or by hand. But when the fuel feed mechanism linked them together, they
would have the same ability as filament to pull back while inside the
chamber oxygen pulled them forward. It would be important for the
terminal link not to drop pieces of itself, but rather remain linked and
in one piece at all stages of consumption.
Providing Pure Oxygen and Handling It at High Pressure and Temperature
These are major difficulties. Combustion chambers and turbine rotors
can't be made of anything but noble metals, fluorides, and oxides.
Moreover, the oxides must not dissolve excessively in hot liquid boria.
Air oxygen purifiers with sufficiently low energy consumption per
kilogram of oxygen have been demonstrated, but they aren't small or light.
The use of oxygen in large excess might seem to exacerbate this
difficulty, however, the high extractability of liquid boria and the
absence of any gaseous combustion products means it will be possible to
recycle leftover oxygen. (Note that this was never a possibility with
boron-containing fuels that also contained hydrogen or carbon.)
This recycling saves not just the oxygen but also any boria molecules or
droplets that fail to fall out immediately after their birth in the
flame. They can come around and take their next chance, or the one after.
Boron combustors won't be entirely free of gaseous emissions because
their oxygen supply won't be entirely pure. Air-derived oxygen's
principal impurity will be nitrogen, which, diluted in high-pressure
oxygen and occasionally passing through a very hot flame, will tend to
be in the form of nitrogen dioxide.
If a small fraction of the gas flow passes through a polishing circuit
the nitrogen dioxide can be captured by a small amount of alkali there,
as can carbon dioxide and oxides of sulfur. Oxygen, unreacted nitrogen,
and truly inert gases emerging from this polisher can be dumped.
But these are all air gases. Therefore, boron combustors, if they work
at all, will be truly zero-emission devices.
Summary
Although they have a much taller first step, boron power systems promise
to provide emission-free energy from smaller reservoirs than hydrogen
can, using fireproof substances. Boria's high specific binding energy
and the undemanding nature as cargoes of both it and elemental boron
means they will convey energy lightly and compactly, even in small
shipments.
If successfully demonstrated, boron-powered vehicles would show the
ability to run on public roads without depending on special fuelling
stations, since their ash could be sent away and boron could return by
any ordinary freight carrier, even by mail. Operators could blast boron
pellets with propane torch flames and show that they don't burn,
demonstrating that fuel-fed fires during accidents were not possible.
The demonstration vehicles could have fuel/ash reservoirs two or more
times larger than would be safe on a hydrocarbon-burning vehicle, and
since equal energy would require no more than 1.7 times the size,
greater speed and range should be possible.
Despite the initially high cost of fuel boron, there seems to be no
reason why a small demonstration fleet wouldn't form the nucleus of a
quickly growing group of voluntary early adopters, on whose behalf plans
for cheaper, larger-scale boron production would quickly be drawn up.
References
1. Robert B. McBroom, "Boron Oxides, Boric Acid, and Borates",
Kirk-Othmer Encyclopedia of Chemistry and Chemical Technology, 3rd Edition.
2. Leonard K. Tower, "Thermal Relations for Two-Phase Expansion with
Phase Equilibrium and Example for Combustion Products of
Boron-Containing Fuel", Lewis Flight Propulsion Laboratory 1957, p. 35,
available at
http://naca.larc.nasa.gov/reports/19...-rm-e57c11.pdf
on 14 June 2001.
3. Editor Robert C. Weast, "Physical Constants of Inorganic Compounds",
p. B-62, CRC Handbook of Chemistry and Physics, 60th edition, CRC Press
1980.
4. McBroom, table 4: "Physical Properties of Vitreous Boric Oxide".
5. Mark Winter, "The WebElements Periodic Table of the Elements",
available 14 June 2001 at
http://www.webelements.com/webelements/index.html.
6. McBroom.
7. NIOSH, "Fire Fighter Fatality Investigation Report 98F-24", available
14 June 2001 at http://www.cdc.gov/niosh/face9824.html.
A different version of "Boron: A Better Energy Carrier than Hydrogen?",
with boron and boria photos, is currently available at
http://www.eagle.ca/~gcowan/boron_blast.html.
Graham Cowan
If far-flung energy users each possess several tens of kilograms of the
somewhat costly, somewhat toxic substance diboron trioxide (also known
as boria), and occasionally send some to a central power station that
can reduce it to its elements, that station can, by returning only the
boron, transmit back one continuous kilowatt of power for each 5.1
kilograms per day of boria received.
That rate of active material shipment is much larger than in the
analogous hydrogen-economy power coupling, even though a water-splitting
power station needs not 5.1 but 6.8 kilograms of water per kilowatt-day
transmitted. The Earth's atmosphere is an enormous water vapour bank the
station can borrow from and the users repay, and therefore the only
shipping task is distributing the hydrogen. Its mass is 0.76 kilograms
per kilowatt-day.
Elemental boron is now produced at very high prices, 23 to 400 times
more for a pound without oxygen than for a pound with, $360 to $6,400
per contained kilowatt-day.
Its use as a potentially mass-market fuel has not been demonstrated. One
promising approach is a gas turbine that would burn it in a large excess
of pure high-pressure oxygen. Problems would include fabricating boron
-- brittle, refractory, very hard -- in a form amenable to service as
fuel, making the combustion chamber and rotor of materials that neither
pressurized oxygen nor boria will attack, providing the oxygen, and
extracting the boria (for the user to send to the power station again).
Poisoning deaths have occurred with boric acid, which forms
spontaneously when boria and water meet at normal environmental
temperatures:
(1/2) B2O3 + (3/2) H2O(l) ---> B(OH)3, DG° = -22.03kJ/mol
Its acute oral LD50 in rats is listed as 3 to 4 grams per kilogram of
body weight (*1). Taking into account the 0.563 mass fraction of boria
in boric acid, and supposing boric acid acts similarly in rats and
humans, the extrapolated acute LD50 by ingestion of boria is 1.7 to 2.2
grams per body kilogram, i.e. 75 grams for someone weighing 100 pounds.
This is twice the acute toxicity of ingested sodium chloride.
Motivation
To enable noncombustion primary energies -- nuclear, direct solar,
hydraulic, wind -- to take over the jobs petroleum and natural gas now
do, without adopting their safety standards.
After these hydrocarbons have been taken out of the ground, where they
were not in contact with air, it is best to keep them still shut away
from it for as long as they are in processing, distribution, or storage.
Every week this is attempted on a worldwide scale of roughly 100 million
tonnes, seldom without at least one disastrous lapse.
Elemental hydrogen is produced on a scale four orders of magnitude
smaller, and also kept apart from air with great but occasionally
inadequate care. Lethal failures occur, perhaps even somewhat more often
than once in 10,000 weeks. It is therefore just as incongruous to
imagine nuclear power stations producing it as to imagine them producing
gasoline.
Water's great abundance is sometimes called an advantage of hydrogen
power. But there are other very abundant, very strongly bound oxides.
Let us pick one whose deoxidation yields a safer fuel. Corundum and
quartz fit the bill, and maybe periclase. The oxophilic elements in them
are respectively aluminum, silicon, and magnesium. They do not have to
be kept out of contact with air, yet when they burn they burn very
strongly.
Burning regenerates the oxides as fine particles that would not be as
inoffensive to dump as the original minerals. If they were first
consolidated into gravel, then they might not be too much of a nuisance.
A large urban intersection thronged with cars powered by oxidation of
metal or silicon would see the accumulation of approximately one cubic
metre per day.
Hot-pressing equipment to make that gravel on board cars would be
expensive. Perhaps some kind of glue could be used, or bags. In any
case, these energy carriers would either accumulate after use as large
heaps of oxide, or go back to the power station to be deoxidized again.
But if they go back then conceivably they can be used many times, and
more expensive, lighter varieties of atom can work. Two elements are
lighter than magnesium and, when uncombined, share aluminum's and
silicon's trait of burning strongly but not readily: beryllium and boron.
The pursuit of safety has thus with apparent perversity led to toxic
elements. In boron's case there are reasons to think that appearance is
false, and the prospect that its use will give much safer combustion
power than hydrogen or hydrocarbons can is real.
One of these reasons stems from the fact that unlike beryllia or
magnesia or alumina or silica, boria does not emerge from a hot flame as
suspended solid particles. It emerges as mist. This promises to let it
be gathered more easily and effectively than those other oxides could
be. Bags may still have a role to play, but hot pressing and glue don't.
Above 500°C boria is its own glue.
Boria's Unusual Nature Seems Tailored for Extraction from Combustors
Boria can be liquid above 2,000°C and still flow at 400°C. There is some
discord in published values of its normal boiling point -- 4,600 Rankine
(*2), 1,860°C (*3), 2,316°C (extrapolated) (*4), 2,065°C (*5).
However, when boron burns in a 25-fold excess of oxygen, the products
cannot, after mixing, be much hotter than 1,200°C. At such a temperature
virtually all of the boria must be incorporated in droplets. In the
middle of the 20th century air-breathing turbines fuelled partly with
boron were tested in the apparent hope that these droplets would blow by
the turbine airfoils and not stick.
It now seems more reasonable to hope that they will; or at least, it
does if turbines can be constructed on a somewhat different plan, with
blades poking inward from a hoop rather than hanging out from a hub. If
such a turbine airfoil revolves in mist, coats itself with liquid, and
doesn't reach all the way in to spin centre, the liquid will feel a
centrifugal force field of nonzero strength no matter where it is on the
airfoil. It will be conducted radially outward in a flowing film.
Based on assuming laminar flow and constant viscosity, the film depths
necessary for as much to flow away as is arriving are expected to be small:
Film depth = (3 * Power * Viscosity /
(Specific energy * Width * Density^2 * Centripetal acceleration)) ^ (1/3)
The 'Width' here is the stream width, about twice the distance from
airfoil leading edge to trailing edge (because the stream is on both
sides). Suppose the airfoil catches the same fraction of the mist as it
converts of the thermal power, and all the catching occurs at the
innermost point.. Then the amount of boria flowing past any point
farther out is the (Power / Specific energy) part of the above. Specific
energy is the ratio of heat produced to boria produced by the
boron-oxygen reaction upstream of the turbine: 18.0 megajoules per
kilogram.
Suppose an airfoil is 20 millimetres from leading to trailing edge at
radius 30 millimetres, i.e. stream width is 40mm, and its share of the
thermal power is 1 kilowatt. Let it revolve 250 times per second, so
that the film on it at 30 millimetres radius has 74.0 kilometres per
second per second of centripetal acceleration. Let the temperature be
600°C. This fixes liquid boria's density near 1,600kg/m^3 and its
viscosity near 480 pascal-seconds (*6). That is 480,000 times the
viscosity of water at 20°C. Boria at this temperature is thick, syrupy
molten glass.
The film depth works out as 0.22 millimetres, probably small enough
compared to the airfoil's 20mm chord that it won't cease to be an
airfoil. If the temperature were reduced to 400°C the viscosity would
rise to 160,000 pascal-seconds. This huge increase may reflect the fact
that 400° is below the 450°C melting point of (very seldom seen) boria
crystals. Because of the one-third power in the film depth formula the
predicted increase in depth is only 6.6-fold, to 1.5 millimetres.
Diboron trioxide flowing radially outward in a centrifugal force field
is an instance of liquid flowing downhill, a situation sometimes
conjecturally linked to the arrival of liquid at the bottom. If that
happens here, the bottom will be the turbine airfoil root, where it
transmits force and power to the support hoop's inner surface. It seems
possible for drain passages to descend further from that surface through
the support ring to a ledge where the liquid can, by moving along the
axis of rotation, spill over. A stationary scraping blade will take it
before it can fly off on a tangent.
Now flowing down the scraper in a much thicker film than on the turbine
blade because local gravity is so much weaker, it can make its way to
molds. This process will resemble the action of bottle-blowing
machinery, except the glass aliquots can be cooler when they arrive --
boria's work point is roughly 560°C, while that of soda-lime glass is
1,000 to 1,100°C -- and probably won't be blown hollow, just allowed to
freeze as massive transparent vitreous lumps.
Virtuous Boria
The toxicological risk of handling boria in this fashion is limited by
the low surface-to-volume ratio of the lumps and their hardness (Mohs 5,
similar to fluorite or tooth enamel). They are, however, able to
dissolve slowly in water, through the boric acid-forming reaction noted
previously followed by dissolving of the acid.
In recent years studies of aqueous B(III) toxicity to animals have
broadened to include consideration of its possible animal essentiality,
without very definite results yet, but it is known to have a biological
half-life of a day or two. If it isn't a micronutrient, at least it has
little potential for cumulative toxicity. So it seemed not unduly risky
to measure how quickly boria glass dissolves in a continually refreshed
37°C aqueous medium by sucking on a 6mm by 8mm by 1.4mm piece, estimated
mass near one-eighth of a gram. It lost all its thickness in 31 minutes,
0.4 microns per second per side. This suggests a lump too big to swallow
would have to be sucked on non-stop for about a day to deliver the LD50.
Water vapour contacting a boria glass surface forms boric acid. In the
absence of liquid water the resulting tarnish builds up to much less
than a millimetre thick, makes the glass look milky, and then prevents
further reaction. It is a solid lubricant, so pieces of boria aged in
humid air are slippery.
Boria Is Easier to Transport than Hydrogen
For many practical energy-transmission purposes this is true, even
though, as previously mentioned, the same energy can be taken up in
dissociating the boron and oxygen in 5.1 kilograms of boria as is
already in a 6.7 times smaller mass of elemental hydrogen: one
kilowatt-day.
The boria could be considered a carrier of energy demand. It is relevant
to compare its haulage with that of fuel hydrogen because each is the
heaviest cargo, as such, in its system. Hydrogen ash rides the wind and
finds its own way to the power station. Elemental boron can't get quite
as free a ride as that, but as 31 mass percent of boria, it does have
the capability of getting to its destination as a 31 percent load in a
vessel that must go there anyway to pick up a full load of boria for the
next run.
Boria is easier because it won't burn, won't evaporate, and despite
being much heavier than the hydrogen, it takes up much less space. It is
25.6 times denser at room temperature than liquid hydrogen is at its
normal boiling point. Loosely packed spheres would be only 0.65*25.6,
i.e. 16.6 times denser. A dewar flask that could keep 0.76 kilograms of
liquid hydrogen cool would be more than big enough to accommodate 5.1kg
of boria ingots, not necessarily spherical, in its bottom half.
Moreover, those same ingots could also go in a sturdy plastic bag that
would mass less than a tenth of a kilogram. It is not yet certain what
shape the 1.6 kilograms of boron in them will be given when the power
station extracts it, but if it is any sort of pellet, the pellets could
certainly ride back in the bottom of same bag. Boron is a little denser
than boria, insoluble, involatile, infusible, apparently physiologically
inert, and unable to burn in air.
Only very large consignments of low-pressure liquid hydrogen, many
terajoules' worth, could be accommodated in a container less massive
than the contents in the way that plastic bag is. For gigajoules or
less, the container is typically ten or more times more massive. Boria
plus a bag is lighter.
It has been proposed to use stable hydrides such as that of magnesium as
involatile solid forms of hydrogen. As an atomic-scale room temperature
hydrogen container, a magnesium atom does nicely shrink hydrogen, down
to only 64 percent of the specific volume of liquid hydrogen at
-252.87°C, but it follows the ten-times-mass-of-contents rule fairly
closely -- actually 12 times. As a source of fuel hydrogen, magnesium
hydride masses 11.85 kilograms per kilowatt-day.
Magnesium hydride isn't fireproof and neither is the highly expanded,
high surface area magnesium metal left behind when the hydrogen is
thermally driven off. Interestingly, the fire hazards in this scheme can
be much reduced, and the haulage reduced by more than half, if the
magnesium is burned along with the hydrogen.
The heaviest load then is the incombustible magnesium oxide travelling
to the power station, 4.6 kilograms per kilowatt-day, a little lighter
than boria. The hydride leaving the power station is still readily
ignitable, but its quantity is reduced to only 3.0 kilograms per
kilowatt-day, less than a third as much as in the hydrogen-only case.
Magnesia won't ooze out of a combustor and then solidify in void-free
masses the way boria can, though.
Boron Pipelines?
Elemental boron itself does not seem very well suited to being piped.
But much hydrogen now travels short distances through pipelines, as
pressurized gas, and it's interesting to consider whether the analogy
between it and boria might extend to transportability in pipes. If it
does then pipelines can do 76 percent -- one over 1.31 -- of the boron
system's tonne-kilometres of active material transfer, and the
freighters that do the rest can load all the way up on boron, not just
31 percent.
Boria pipelines would have to be tributary ones bringing the substance
from many sources to a few power stations, the opposite to the job
hydrogen pipelines would do. The threat to their steel's integrity would
be boric acid corrosion, not hydrogen embrittlement. Leaks would be less
hazardous, and the pressure behind them might be lower, since boria
doesn't need pressure to be dense.
The observed 400 nanometre per second speed at which 37°C water corrodes
vitreous boria, and the rule of thumb that 10 kelvins less means
reaction twice slower, suggest golf ball-sized boria ingots in a
cold-water slurry would lose 4mm of radius per day of travel. But this
incorrectly treats the water travelling with them as staying fresh.
Actually the sparing solubility of boric acid in cold water means a
slurry with equal masses of water and boria would reach saturation with
most of the boria still solid, even if the boria pieces were smaller
than golf *****.
The lubricity of the lumps' boric acid coats might protect the pipe
walls from abrasion. One might think this could work for boron too, but
at normal environmental temperatures boron is so inert that it is not
subject to superficial oxidation. It would scratch like crazy.
If the nearest place to put boria into a pipeline were a few miles away,
this would be less inconvenient than the corresponding case with
hydrogen, for as noted, it's easier to carry a bag containing 5.1
kilograms of boria than the containment system for 0.76kg of hydrogen.
Large pipelines that now carry natural gas at high pressure might
someday have a less demanding task: carrying boria to the
boron-deoxidizing nuclear power stations built on the sites where the
gas wells once ran.
Fuel Boron Should Hold Still While Flowing Oxygen Devours It
Probably the simplest way one can envision feeding boron to a combustor
at a controllable rate is as filament, through a small hole in the
combustion chamber wall. Inside the chamber the filament tip will
encounter a continuously burning fire that will consume it as fast as it
comes.
Very lean combustion has been mentioned, with much of the oxygen present
not to react with boron but to take up the heat from the small fraction
that does, and be heat engine working fluid. Even at pressure on the
order of 10 megapascals this means a very much larger volume of oxygen
must flow through or past the fire than of boron.
25 O2 + (4/3) B ---> (2/3) B2O3 + 24 O2
Supposing the oxygen behaves as ideal gas and starts at 10MPa and 500K,
the left side includes about 10 litres per mole of it, and 6 millilitres
per mole of boron. So the volume ratio is near 1,700. This means a thin
filament will be at the middle of a roughly 40 times thicker cylinder of
oxygen flow if they both come to the fire at the same speed.
But it makes better sense for the boron to come in slowly and the oxygen
around it to come in faster, in a stream narrower than 40 filament
diameters. Then drag from oxygen helps pull the filament in, and the
fire consuming its tip is an instance of lancing combustion: turbulently
flowing oxygen runs over the burning boron surface, quickly removing
boron oxide vapour -- for the flame temperature can be over 4,000°C, far
above even the highest reported boria boiling point -- and scouring
boron atoms and droplets off the surface.
Lancing combustion has recently been recognized as a harmful phenomenon
that can happen when high-pressure pure oxygen passes through aluminum
regulator valves (*7). But when overcoming the ignition resistance of an
ignition-resistant substance is what is desired, lancing combustion is
good. It allows a lot of chemical power to be converted to thermal power
in a small space.
It is not necessary for all the oxygen to flow past the flame in a
single stream. A small excess might do that, and then the rest could be
blown in in converging jets downstream of the flame, quickly diluting
it. Before dilution the boron-oxygen flame can broadcast a considerable
fraction of its power as visible and near infrared light. Putting the
mixing jets' impingement point not far downstream of the flame would
reduce this fraction.
Continuous filament supports lancing combustion because the part in the
chamber is connected to, and held back against the wind by, all the rest
still coiled outside, in an environment where it cannot burn. However,
today's commercial boron filament is impossibly expensive, and has a
tungsten core.
Boron developed for fuel use might be small unconnected chain links
sintered from pure boron powder. These would behave simply as pellets
during distribution and storage. They would resist breakage better than
filament and could be easily apportioned, and transferred with a scoop
or by hand. But when the fuel feed mechanism linked them together, they
would have the same ability as filament to pull back while inside the
chamber oxygen pulled them forward. It would be important for the
terminal link not to drop pieces of itself, but rather remain linked and
in one piece at all stages of consumption.
Providing Pure Oxygen and Handling It at High Pressure and Temperature
These are major difficulties. Combustion chambers and turbine rotors
can't be made of anything but noble metals, fluorides, and oxides.
Moreover, the oxides must not dissolve excessively in hot liquid boria.
Air oxygen purifiers with sufficiently low energy consumption per
kilogram of oxygen have been demonstrated, but they aren't small or light.
The use of oxygen in large excess might seem to exacerbate this
difficulty, however, the high extractability of liquid boria and the
absence of any gaseous combustion products means it will be possible to
recycle leftover oxygen. (Note that this was never a possibility with
boron-containing fuels that also contained hydrogen or carbon.)
This recycling saves not just the oxygen but also any boria molecules or
droplets that fail to fall out immediately after their birth in the
flame. They can come around and take their next chance, or the one after.
Boron combustors won't be entirely free of gaseous emissions because
their oxygen supply won't be entirely pure. Air-derived oxygen's
principal impurity will be nitrogen, which, diluted in high-pressure
oxygen and occasionally passing through a very hot flame, will tend to
be in the form of nitrogen dioxide.
If a small fraction of the gas flow passes through a polishing circuit
the nitrogen dioxide can be captured by a small amount of alkali there,
as can carbon dioxide and oxides of sulfur. Oxygen, unreacted nitrogen,
and truly inert gases emerging from this polisher can be dumped.
But these are all air gases. Therefore, boron combustors, if they work
at all, will be truly zero-emission devices.
Summary
Although they have a much taller first step, boron power systems promise
to provide emission-free energy from smaller reservoirs than hydrogen
can, using fireproof substances. Boria's high specific binding energy
and the undemanding nature as cargoes of both it and elemental boron
means they will convey energy lightly and compactly, even in small
shipments.
If successfully demonstrated, boron-powered vehicles would show the
ability to run on public roads without depending on special fuelling
stations, since their ash could be sent away and boron could return by
any ordinary freight carrier, even by mail. Operators could blast boron
pellets with propane torch flames and show that they don't burn,
demonstrating that fuel-fed fires during accidents were not possible.
The demonstration vehicles could have fuel/ash reservoirs two or more
times larger than would be safe on a hydrocarbon-burning vehicle, and
since equal energy would require no more than 1.7 times the size,
greater speed and range should be possible.
Despite the initially high cost of fuel boron, there seems to be no
reason why a small demonstration fleet wouldn't form the nucleus of a
quickly growing group of voluntary early adopters, on whose behalf plans
for cheaper, larger-scale boron production would quickly be drawn up.
References
1. Robert B. McBroom, "Boron Oxides, Boric Acid, and Borates",
Kirk-Othmer Encyclopedia of Chemistry and Chemical Technology, 3rd Edition.
2. Leonard K. Tower, "Thermal Relations for Two-Phase Expansion with
Phase Equilibrium and Example for Combustion Products of
Boron-Containing Fuel", Lewis Flight Propulsion Laboratory 1957, p. 35,
available at
http://naca.larc.nasa.gov/reports/19...-rm-e57c11.pdf
on 14 June 2001.
3. Editor Robert C. Weast, "Physical Constants of Inorganic Compounds",
p. B-62, CRC Handbook of Chemistry and Physics, 60th edition, CRC Press
1980.
4. McBroom, table 4: "Physical Properties of Vitreous Boric Oxide".
5. Mark Winter, "The WebElements Periodic Table of the Elements",
available 14 June 2001 at
http://www.webelements.com/webelements/index.html.
6. McBroom.
7. NIOSH, "Fire Fighter Fatality Investigation Report 98F-24", available
14 June 2001 at http://www.cdc.gov/niosh/face9824.html.
A different version of "Boron: A Better Energy Carrier than Hydrogen?",
with boron and boria photos, is currently available at
http://www.eagle.ca/~gcowan/boron_blast.html.
07-30-2006, 01:41 AM
#6
3.0 BAR
Join Date: Oct 2005
Posts: 9,282
Re: ---- hydrogen fuel cell faggotry.
cliffnotes
advantages boron has over hydrogen
can be bought and shipped to ur door.. i.e. no special fueling stations
in the event of an accident. or fire. boron will not combust or explode...
boron running car uses alot less space then hydrogen running car
boron once oxidized can be colleected sent off to be deoxidized and then sent back to the customer to be reused agian?
alot more efficient i cant spell tonight lol too tired
anyways
thanks for the read
and whoever wrote this article is a retard, seems to me it wasnt exactly worded in an easy to understand format.. its like some little trying to tell u a story with and then he went to the and then ummm and then yea and then ummm ummmmm ummmmm ya and then he got that thing from the other thing and mixed it with this other thing to get this thing and this thing is alot better than that thing but not so muh as good as this thing but the best thing is that thing over there next to this thing which just so happpend to be the best thing of all..
advantages boron has over hydrogen
can be bought and shipped to ur door.. i.e. no special fueling stations
in the event of an accident. or fire. boron will not combust or explode...
boron running car uses alot less space then hydrogen running car
boron once oxidized can be colleected sent off to be deoxidized and then sent back to the customer to be reused agian?
alot more efficient i cant spell tonight lol too tired
anyways
thanks for the read
and whoever wrote this article is a retard, seems to me it wasnt exactly worded in an easy to understand format.. its like some little trying to tell u a story with and then he went to the and then ummm and then yea and then ummm ummmmm ummmmm ya and then he got that thing from the other thing and mixed it with this other thing to get this thing and this thing is alot better than that thing but not so muh as good as this thing but the best thing is that thing over there next to this thing which just so happpend to be the best thing of all..
07-30-2006, 10:42 AM
#8
0.0 BAR
Thread Starter
Join Date: Feb 2003
Posts: 0
Re: ---- hydrogen fuel cell faggotry.
Originally Posted by Minor Threat
whoever wrote this article is a retard, seems to me it wasnt exactly worded in an easy to understand format..
Originally Posted by kamilk69
so how is the energy relesed, by oxidation.
