Energy From Thorium Discussion Forum

It is currently Jun 17, 2018 6:52 pm

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 56 posts ]  Go to page Previous  1, 2, 3, 4
Author Message
PostPosted: Dec 10, 2009 6:53 pm 
Offline
User avatar

Joined: Dec 08, 2009 6:07 pm
Posts: 168
Location: Albuquerque NM USA
The Book

I have read the entire book and think that sending a copy to all the members of Congress is a good idea. However, it would be impossible to write a book with which I would have no reservations, and I do have reservations about Prescription….

The book considerably increased my knowledge about atomic energy, and no doubt it would do the same for many readers. Readers who are uneasy about atomic energy but who are open-minded would have their fears allayed. But, there are problems.

Unfortunately, the likelihood that something will be read often bears an inverse relationship to its length. I just cannot see most members of Congress taking the time to read a book of almost 400 pages. Assuming that the principal purpose of the book is to allay the fears of those who oppose nuclear energy, it would be more effective to have a book which would cover only enough material to do that, i.e., a book that would exclude new methods of powering vehicles, recycling garbage, etc. etc. That isn’t to say that those are not important subjects, but I think that it would be better to have them covered in a separate volume. Prescription… could be in two volumes, the first of which would have as almost its sole purpose the allaying of the fears of those who oppose nuclear energy, thereby increasing the likelihood that it would be read.

I cannot recall that the book says anything about thorium. Although having only one or two designs for nuclear power plants has obvious advantages, it would be a mistake to freeze the designs forever thereby making it impossible to take advantage of advancing technology, but the multiplicity of designs which currently exist also presents problems. For some problems there is no perfect solution.

The GREAT concept was interesting and certainly provides food for thought and discussion. However, it would force nuclear plant operators to live a life which is incompatible with family living, so it could be difficult to get plant operators. A possible solution could be to pay them EXTREMELY well and require a commitment of only a few years; that seems to work to get U.S. citizens to work in Saudi Arabia. Unless the residential compounds were hardened so that living in them would be almost like living in a prison, and unless people living in them were prohibited from leaving, there could be a risk of kidnapping operators and holding them for ransom, at least in some unsettled parts of the world.


Top
 Profile  
 
PostPosted: Oct 09, 2011 11:01 am 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5060
I'm wondering about boron production. It has to be efficient to be attractive.

High purity boron is currently produced for the nuclear and semiconductor industry for use in enrichment, via electrolysis using B4C as a consumable anode.

Interestingly the current efficiency of this process is about 98%, ie very good.

I wonder if this is a method to use boron as an energy carrier for ships and such.

Basically carry boron and carbon as fuel and react them at high temperature to run an external combustion heat engine. B+4C=B4C.

Then take the B4C ash off in port and send to the electrorefiner as consumable anode to make new boron.

For the carbon source an initial load could be high purity petroleum coke. Since this is a closed system, no boron or carbon are used up.

Would this work?


Top
 Profile  
 
PostPosted: Oct 10, 2011 10:11 am 
Offline

Joined: Jul 28, 2008 5:01 am
Posts: 462
Location: Teesside, UK
Cyril R wrote:
......Basically carry boron and carbon as fuel and react them at high temperature to run an external combustion heat engine. B+4C=B4C......

I don't understand why this is particularly attractive. Thermochemistry data on B4C (NIST) says the reaction enthalpy is only 62.7 kJ/mol, or 1.13 kJ/g, about 1/40th of diesel. Comparable to lithium batteries, but you need a heat engine.

Boron oxide B2O3 has formation enthalpy -1273kJ/mol or 18.3 kJ/g for the ash, or 59 kJ/g for boron alone. I'm not convinced about pure oxygen/boron internal combustion for cars, but at ship scale it might be easier.


Top
 Profile  
 
PostPosted: Oct 10, 2011 11:10 am 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5060
Luke wrote:
Cyril R wrote:
......Basically carry boron and carbon as fuel and react them at high temperature to run an external combustion heat engine. B+4C=B4C......

I don't understand why this is particularly attractive. Thermochemistry data on B4C (NIST) says the reaction enthalpy is only 62.7 kJ/mol, or 1.13 kJ/g, about 1/40th of diesel. Comparable to lithium batteries, but you need a heat engine.

Boron oxide B2O3 has formation enthalpy -1273kJ/mol or 18.3 kJ/g for the ash, or 59 kJ/g for boron alone. I'm not convinced about pure oxygen/boron internal combustion for cars, but at ship scale it might be easier.


Thanks Luke. 59 kJ/g is pretty good, twice as much heat as the best quality coal.

But how are we going to electrolyse B2O3 and how efficient will it be? There are 1.5 oxygen atoms for every boron molecule, that does not sound like a good match for efficiency. We need to match 1 gas molecule for every 1 fuel molecule for maximum efficiency.

Boron nitride looks fairly stable, so that means oxygen separation units (ASU's) might be required to combust the boron. That's going to cost money and energy. Then again with such good power density less oxygen is required. I seem to recall that at least 10% of the electricity that an oxyfuel anthracite coal combustion power plant makes, is required to run the ASU. If the anthracite is 30 kJ/g then 30/(44/12)= 8.18 kJ/g CO2 or 18.3/8.18 = 2.24x less oxygen will be required, about 4% of the electricity will be needed to run the ASU. Doesn't hurt too much.


Top
 Profile  
 
PostPosted: Oct 10, 2011 12:40 pm 
Offline

Joined: Jul 28, 2008 5:01 am
Posts: 462
Location: Teesside, UK
GRL Cowan, who sometimes posts here, worked out the details of boron use that Tom put in the book. Pure oxygen combustion is required. He thought 20% loss to air separation might be needed for a portable ASU in a car, but this has rather conservative assumptions. A ship has more space to spend on doing the job efficiently, so 5-10% loss seems reasonable.

GRL Cowan proposed a thermochemical cycle to get the boric oxide reduced without going via electrolysis but as far as I know it has not been demonstrated. The very high combustion enthalpy of boron - about 50% higher per oxygen than hydrogen - makes the reverse step very hard to do by purely chemical means. There is no established electrolytic process either.


Top
 Profile  
 
PostPosted: Oct 10, 2011 1:30 pm 
Offline

Joined: Dec 26, 2007 11:45 am
Posts: 191
The combustion product boron oxide has a fairly low melting point (450C) and is a glassy substance. I have melted some in a pot with a torch and witnessed what a sticky mess it makes. I'm extremely skeptical about the feasibility of ever constructing an engine capable of burning this stuff. It makes a fuel with a highly abrasive combustion product like aluminum seem friendly and manageable by comparison...

This residue was one of the things that led to the demise of the "zip fuels" tested by the air force in the 50s.


Top
 Profile  
 
PostPosted: Oct 10, 2011 1:40 pm 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5060
I asked Graham about the efficiency before but got a rather poetic answer. He does that.

Perhaps an analogue to the Hall-Héroult process is applicable.

NaF-NaBF4 electrolyte dissolving B2O3? The operating temperature would be much lower than a Hall cell, though boron doesn't melt like aluminium does.


Top
 Profile  
 
PostPosted: Oct 10, 2011 1:49 pm 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5060
Owen T wrote:
The combustion product boron oxide has a fairly low melting point (450C) and is a glassy substance. I have melted some in a pot with a torch and witnessed what a sticky mess it makes. I'm extremely skeptical about the feasibility of ever constructing an engine capable of burning this stuff. It makes a fuel with a highly abrasive combustion product like aluminum seem friendly and manageable by comparison...

This residue was one of the things that led to the demise of the "zip fuels" tested by the air force in the 50s.


It would have to be external combustion, for sure. Stirling for small applications and steam/gas turbines for big ones like a ship.

I've seen oxygen ASUs myself and can't imagine to put these things in a car.

Carbon is nice in the sense that its ash is a gas that is easily removed. Uh, a bit too easily...

Carbon also burns with a good match of oxygen: one fuel molecule for one oxygen molecule.

These properties make direct carbon fuel cells attractive. But I don't know how to make carbon from CO2, so it's a GhG problem - not closed loop.


Top
 Profile  
 
PostPosted: Oct 10, 2011 4:15 pm 
Offline

Joined: Dec 26, 2007 11:45 am
Posts: 191
Cyril R wrote:
Owen T wrote:
The combustion product boron oxide has a fairly low melting point (450C) and is a glassy substance. I have melted some in a pot with a torch and witnessed what a sticky mess it makes. I'm extremely skeptical about the feasibility of ever constructing an engine capable of burning this stuff. It makes a fuel with a highly abrasive combustion product like aluminum seem friendly and manageable by comparison...

This residue was one of the things that led to the demise of the "zip fuels" tested by the air force in the 50s.


It would have to be external combustion, for sure. Stirling for small applications and steam/gas turbines for big ones like a ship.

I've seen oxygen ASUs myself and can't imagine to put these things in a car.

Carbon is nice in the sense that its ash is a gas that is easily removed. Uh, a bit too easily...

Carbon also burns with a good match of oxygen: one fuel molecule for one oxygen molecule.

These properties make direct carbon fuel cells attractive. But I don't know how to make carbon from CO2, so it's a GhG problem - not closed loop.


External combustion will last a bit longer. Instead of your pistons or turbine blades becoming a sticky mess it's just the heat exchanger becoming a sticky mess.


Top
 Profile  
 
PostPosted: Oct 11, 2011 3:09 am 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5060
Owen T wrote:
Cyril R wrote:
Owen T wrote:
The combustion product boron oxide has a fairly low melting point (450C) and is a glassy substance. I have melted some in a pot with a torch and witnessed what a sticky mess it makes. I'm extremely skeptical about the feasibility of ever constructing an engine capable of burning this stuff. It makes a fuel with a highly abrasive combustion product like aluminum seem friendly and manageable by comparison...

This residue was one of the things that led to the demise of the "zip fuels" tested by the air force in the 50s.


It would have to be external combustion, for sure. Stirling for small applications and steam/gas turbines for big ones like a ship.

I've seen oxygen ASUs myself and can't imagine to put these things in a car.

Carbon is nice in the sense that its ash is a gas that is easily removed. Uh, a bit too easily...

Carbon also burns with a good match of oxygen: one fuel molecule for one oxygen molecule.

These properties make direct carbon fuel cells attractive. But I don't know how to make carbon from CO2, so it's a GhG problem - not closed loop.


External combustion will last a bit longer. Instead of your pistons or turbine blades becoming a sticky mess it's just the heat exchanger becoming a sticky mess.


If you keep the temp in the HX/boiler/combustion chamber high enough, and make it smooth, like a big reaction chamber, maybe you can let the boria vitrify in a bottom ash tray system?


Top
 Profile  
 
PostPosted: Oct 11, 2011 11:39 am 
Offline

Joined: Feb 21, 2007 7:06 pm
Posts: 97
As someone said above, it is easy to heat B2O3 to an unhappy medium temperature where it is neither rock nor liquid. During the zip fuel project, the avoidance of this misstep was discussed in Preliminary Investigation of Combustion of Diborane in a Turbojet Combustor, W. B. Kaufman, J. B. Gibbs, and J. R. Branstetter:

Quote:
... Reference 1 also reports spatial flame speeds for
diborane-air mixtures as high as 169.5 feet per second,
which is roughly 50 times the flame speed
of paraffinic hydrocarbons. Because of its high flame speed,
diborane would be expected to burn efficiently
under conditions where ordinary hydrocarbon fuels
are inadequate...

... After operation at condition B with an average outlet
temperature below the melting point of B2O3, the thermocouple
rakes at station C-C were covered with heavy crystalline deposits
as shown in figure 10(a). After operation at condition C
with an average outlet temperature above the melting point of B2O3,
the outlet thermocouples showed no appreciable deposits
(fig. 10(b)) .

The tubes installed at station D-D to evaluate various techniques
for alleviating turbine deposits are shown in figure 11.
The tube on the left in figure 11 is the tube designed to operate
at gas-stream temperature. The deposits on this tube were similar
to those on the outlet thermocouples; heavy crystalline deposits
were formed at condition B (fig. 11(a)), and
no appreciable deposits were formed at condition C (fig. 11(b)).

The tube second from the left is the water-cooled tube which was
free of deposits after operation at condition B (fig. 11(a)). Deposits
probably formed on this tube and then spalled. Figure 11(b) shows
an oxide layer just beginning to break away at the conclusion
of operation at condition C. As a layer of low-conductivity oxide
formed on this water-cooled tube, the inside surface
of the oxide layer approached the water temperature
and the outside surface approached the exhaust-gas temperature
until the thermal gradient across the oxide layer became sufficient
to cause spalling. If the solid particles resulting from this spalling
are not so large as to damage the rotor blades, then
extreme turbine cooling may be a feasible method
for eliminating oxide deposits.

The third tube from the left in figure 11 was electrically heated
to 1180° F [910 K] during operation at condition B, and was covered
with a thin glassy deposit (fig. 11(a)) which appears to be
far less harmful than the deposits found on the unheated tube.
This tube was heated to 1750° F [1230 K] during operation at condition C,
and no appreciable deposits formed on the tube (fig. 11(b)).

The tube on the extreme right in figure 11 was formed of porous
wire cloth through which 80°F [300 K] air was passed. After operation
at condition B the air-filmed portion of the tube was free of
deposits (fig. 11(a)). At one end a heavy deposit was formed,
but the tube was not porous near this end due to sealing
of the pores during fabrication.

During operation at condition C, however, this tube was covered
with a heavy deposit (fig. 11(b); the air flow through the pores
was not adequate at this condition.

These data indicate three promising techniques for eliminating
severe oxide deposits on turbine blades and other metal parts.
The three methods are: (1) extreme cooling; (2) heating;
and (3) filming the surfaces with air...

Emphasis mine.

It was eventually decided that nuclear retaliation after nuclear attack could be more cheaply guaranteed with rockets, so as far as I know, the promising solutions were not tried.

The borane fuel part was crazy. People died horribly after getting a little pentaborane on them. To make this possible, much money was spent on pilot plants -- one of which blew up -- and then, childlike, the government of the day lost interest without pursuing the more sensible option of burning elemental boron. As far as I know, slurries in hydrocarbon were as close as they came:

Quote:
The practical problems involved in handling, flowing,
and metering the material as a dry solid
or in the form of powder are great enough to warrant
investigating the possibilities of using the fuel
in the form of a slurry with a hydrocarbon fuel,
even though the heating value, density, and, hence,
fuel performance capabilities are lower
than those for the solid fuel alone.


(From http://naca.larc.nasa.gov/reports/1954/naca-rm-e54d07/naca-rm-e54d07.)

The thermal B2O3 splitting method Luke mentions is at Central Station Deoxidation.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 56 posts ]  Go to page Previous  1, 2, 3, 4

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
cron
Powered by phpBB® Forum Software © phpBB Group