Posted by dlzc on April 6, 2010, 2:07 pm
Your choices are to have a thermal neutron source and wait for them to
decay into hydrogen, or chemically strip the hydrogen from some other
molecule. Currently, hydrogen is removed form fossil fuels.
Could just pressurize water, and use the pressurized fluid stream to
act as the "energy carrier".
David A. Smith
Posted by PolicySpy on April 6, 2010, 6:27 pm
It appears that hydrogen for fuel cells must be made by electrolysis
The idea is to export hydrogen from locations where solar mirror
powerplants are effective.
Hydrogen can be pumped to ports, liquefied, and loaded onto tankers.
Finally, there is a high-temperature electrolysis that seems to be a
good fit with solar mirror powerplants.
I suppose the bottom line is how long it takes to pay for the plant.
Posted by dlzc on April 7, 2010, 4:06 pm
Let me add a calculation...
Lets say you wanted to deliver a terawatt, and lets say you pumped the
pressure on the water to in excess of 60,000 psi (so that biogrowth
was not possible)
60,000 psi = 4,137 bar
1,000,000 kW * 600 / 4,137 = 145,000 liters/min
This is a large force main (55 mgd), and some big thick-walled pipe to
go 250 miles, and you'd want probably at least three pipes, and some
sequencing of which was under max pressure (to keep all pipes
sterilized in turn).
But energy delivery could be on the order of 90-95%, rather than
20-30% by making hydrogen first.
David A. Smith
Posted by daestrom on April 7, 2010, 9:45 pm
To keep fluid friction losses down and control erosion inside piping,
you typically have to keep the velocity under 10 ft/s (3 m/s). So to
get your 145,000 liters/min you need a pipe diameter of just about 1 m.
To contain those kinds of pressures, you're talking a pipe wall on the
order of 15 inches thick of high grade steel (39-inch pipe @ 60,000 psi
=>2.4e6 lbf retained by two pipe walls of 100ksi steel plus safety
margin). What is 250 miles of such pipe going to cost you?
I don't have my Crane book with me, but if I remember tomorrow at work
I'll run an estimate of the losses in 250 miles of extremely smooth pipe
39 inch diameter with 10 ft/s water flow. I can tell you this much, it
won't be pretty.
And how much are the losses in pressurizing this water? Even if the
pipe itself is perfectly leak-tight, the pumps to reach those sorts of
pressures are not 'off-the-shelf'. Positive displacement pumps have
seal-losses and at high head situations a phenomenon where the small
compressibility of the water itself causes another form of loss pump.
If hydrogen is a non-starter, this is worse from a practical engineering
(posted from alt.solar.thermal)
Posted by dlzc on April 8, 2010, 2:45 am
Let's assume 0.1 ft/s, since we have to go so far, and want to
minimize losses. Also, water hammer won't be such a problem, which
will allow for a smaller factor of safety.
Figure 300 of them then. 100 outbound, and 200 inbound.
You'd only have to buy it once. This is not too different from the
drill pipe the ocean platforms use. And figure expansion joints
Pressure losses will consume all power delivered, or more, at that
... by the way, you leak check this pipe the same way you check for
high pressure steam leaks... where the bristles of a broom fall off by
being severed by the inaudible jet, is where the leak is.
They are, but not at these displacements.
Engineering can fix it, if it were financially desirable. Engineering
cannot fix hydrogen.
You don't need to put any more effort into this. The OP does not seem
at all concerned with this notion.
David A. Smith