Energy From Thorium Discussion Forum

It is currently Dec 10, 2018 7:38 am

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 42 posts ]  Go to page 1, 2, 3  Next
Author Message
PostPosted: Jan 22, 2011 4:24 pm 
Offline
User avatar

Joined: Jan 10, 2007 5:09 pm
Posts: 501
Location: Los Altos, California
DME has a low energy density, mostly because of that oxygen in it. It also requires a lot of carbon per energy stored.

Can anyone predict anything about C(NH2)4 ?

Molar mass is bigger, liquid density should be more like 700 g/liter.
No oxygen, so energy content should be way better per mol and per liter and per kg.
Half as much C per mol, and better energy than DME, should make for way less carbon for fuel produced.

But... is it stable, or does it just spontaneously decompose to CH4 + N2 + NH3 ?

-Iain


Top
 Profile  
 
PostPosted: Jan 22, 2011 4:42 pm 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5039
We can do better than DME by making methanol and then converting that to higher alkanes with decent efficiency. Shell has a nice zeolite catalyst in use to do this already.


Top
 Profile  
 
PostPosted: Jan 22, 2011 7:59 pm 
Offline

Joined: Nov 23, 2010 6:51 pm
Posts: 123
I'd suspect that an amine fuel would have unacceptably high levels of NOx production when burned, not to mention that they smell terrible. I'm assuming you're talking about using nuclear heat and/or electricity to generate liquid fuels from non-fossil sources, so why not just take the most direct approach - Use the nuclear energy to make hydrogen from water, add some CO2 to make "syngas", then either make methanol for spark ignition engines or use Fischer-Tropsch chemistry to make synthetic diesel fuel. It doesn't matter how much carbon is in the final product if it all came out of the atmosphere and not the ground.


Top
 Profile  
 
PostPosted: Jan 22, 2011 9:16 pm 
Offline
User avatar

Joined: Jan 10, 2007 5:09 pm
Posts: 501
Location: Los Altos, California
Right, I'm writing up the nuclear fueller idea for the Navy.

I made my own estimate for C(NH2)4, and it's not encouraging. I observe that methylamine (H3C-NH2) is CH4 with a H replaced with a NH2. The heat of combustion, all products returned to 25 C, goes from 890.8 to 1085.6 kJ/mol, an increase of 194.8 kJ/mol.

Taking a wild leap, I note that if I do that substitution 3 more times, I get C(NH2)4, and 1670 kJ/mol.

But the basic problem is that nitrogen just sucks for power density compared to carbon. 194.8 kJ/mol added for an increase of 15 g/mol is about 13 MJ/kg. Compare the equivalent substitution of H for CH3: 669.9 kJ/mol added for an increase of 14 g/mol, or 47.8 kJ/kg.

The Navy burns quite a bit more JP-5 than fuel oil. The gain of not having a fuel logistics tail is probably worth cutting the energy density in the ship's fuel store by a factor of 2. But I doubt it's worth cutting the plane's energy density by 2.

So, the problem is getting carbon. Getting it from the atmosphere involves gigantic air handling equipment. If my fueller has 1 GW(e) of reactor onboard, and attempts to make 400 MW of fuel, and that fuel is something like 50 MJ/kgC, then it needs 8 kg/sec of carbon. 385 ppmV of CO2 in the atmosphere is 160 mg/m^3. So, if we can get 90% of that CO2, we'd need to process air at 55,000 m^3/sec. That's a terrible problem.

A Supply-class fast combat support ship is 230 meters long, 33 meters wide, and has a draft of 12 meters. Imagine a similarly-sized nuclear fueller with nearly the entire superstructure consisting of a forced-draft cooling tower. The tower has intakes on each side of the ship, 15 meters tall and 250 meters long. Air flows through this tower at 7.4 meters per second (16 miles per hour). All of this sits on top of a chemical factory and PWR reactor set and blasts through the water at practically any speed it wants, because preposterous amounts of electrical power are available for the screws.

It would be really great to find a different way to get carbon.


Top
 Profile  
 
PostPosted: Jan 22, 2011 10:04 pm 
Offline
User avatar

Joined: Aug 21, 2008 12:57 pm
Posts: 1055
iain wrote:
Right, I'm writing up the nuclear fueller idea for the Navy.

I made my own estimate for C(NH2)4, and it's not encouraging. I observe that methylamine (H3C-NH2) is CH4 with a H replaced with a NH2. The heat of combustion, all products returned to 25 C, goes from 890.8 to 1085.6 kJ/mol, an increase of 194.8 kJ/mol.

Taking a wild leap, I note that if I do that substitution 3 more times, I get C(NH2)4, and 1670 kJ/mol.

But the basic problem is that nitrogen just sucks for power density compared to carbon. 194.8 kJ/mol added for an increase of 15 g/mol is about 13 MJ/kg. Compare the equivalent substitution of H for CH3: 669.9 kJ/mol added for an increase of 14 g/mol, or 47.8 kJ/kg.

The Navy burns quite a bit more JP-5 than fuel oil. The gain of not having a fuel logistics tail is probably worth cutting the energy density in the ship's fuel store by a factor of 2. But I doubt it's worth cutting the plane's energy density by 2.

So, the problem is getting carbon. Getting it from the atmosphere involves gigantic air handling equipment. If my fueller has 1 GW(e) of reactor onboard, and attempts to make 400 MW of fuel, and that fuel is something like 50 MJ/kgC, then it needs 8 kg/sec of carbon. 385 ppmV of CO2 in the atmosphere is 160 mg/m^3. So, if we can get 90% of that CO2, we'd need to process air at 55,000 m^3/sec. That's a terrible problem.

A Supply-class fast combat support ship is 230 meters long, 33 meters wide, and has a draft of 12 meters. Imagine a similarly-sized nuclear fueller with nearly the entire superstructure consisting of a forced-draft cooling tower. The tower has intakes on each side of the ship, 15 meters tall and 250 meters long. Air flows through this tower at 7.4 meters per second (16 miles per hour). All of this sits on top of a chemical factory and PWR reactor set and blasts through the water at practically any speed it wants, because preposterous amounts of electrical power are available for the screws.

It would be really great to find a different way to get carbon.


Tow a net to capture microscopic calcified marine life, sea weed and the like detritus … and floating garbage mostly plastic of which there are giga-tones floating in the upper layers of water.

Your ship floats in a garage pile of almost unlimited scope and dimensions. You might as well utilize it.

The drag performance of this catchment net could be optimized by integrating into a water jet propulsion system… think jet sky.

A sortie of such a ship will do wonders for the purity of the oceans.

_________________
The old Zenith slogan: The quality goes in before the name goes on.


Top
 Profile  
 
PostPosted: Jan 22, 2011 10:46 pm 
Offline

Joined: Dec 14, 2006 1:01 pm
Posts: 379
I think the trick is flexibility. Just bite the bullet and have a pyrolyzer that can take biomass or coal and make synthesis gas. In heavy combat operations, powdered coal bins can make a lot of fuel, fast, so the performance can be optimized. This option alone stretches the fleet's logistical tonnage by the weight of the hydrogen.

The fleet's garbage and sewage can feed the pyrolizer, too, so this tender would be the fleets' honeywagon. This would be economical for light use: The system woudl try to save the coal for heavy combat.

Have small CO2 extraction systems as a back-up, and run them in the exhausts of all the turbine ships. Pick up the carbon on the honeywagon trips.

In logistical emergencies, the pyrolysis system could convert biomass, in addition to stack gasses, garbage, sewage and coal, and the honey-wagon's aerial CO2 extractor gives some make-up capability.

In peacetime, the normal case, coal, sewage and garbage are cheap: Most ports will sell them (you want what!?). When the system stands down, another normal case, the honeywagon's on-board CO2 system can idle at full, slowly building fuel reserves from the air.


Top
 Profile  
 
PostPosted: Jan 22, 2011 10:58 pm 
Offline

Joined: Jul 28, 2008 10:44 pm
Posts: 3060
Iain,
Perhaps the problem is you are trying to make too much fuel.
Does the navy need 400 MW continuous worth of a fueler per ship?
I did not see how much fuel the navy actually consumes.
I could only find partial information suggesting 54 million gallons per year of JP5 consumed for the jet fighter.
How much fuel will your 400 MW continuous generate in a year?


Top
 Profile  
 
PostPosted: Jan 22, 2011 11:55 pm 
Offline
User avatar

Joined: Jan 10, 2007 5:09 pm
Posts: 501
Location: Los Altos, California
Total US Navy fuel burn in 2010 was 8.62 million barrels, or 1,145 thousand metric tons. I think this is just the ships. JP-5 is about 1.5x that. I think there is a major discrepancy (5x) between the numbers the Navy claims to burn, and the numbers the Defense Energy Support Center buys for them. When I attempted to figure out how much it they burn moving the oil to the fleet, it should be around 10% of the oil transported. That's not it.

A 1 GW(e) ship producing 400 MW(fuel) continuously makes 280 thousand metric tons of hydrocarbon. I think 10 of these could supply the fleet with JP-5 and marine diesel. But as I said, the carbon capture system would dominate the ship design in the same way that the flight deck dominates an aircraft carrier. The ships might end up something like the size of an aircraft carrier, if substantially lighter.

-Iain


Top
 Profile  
 
PostPosted: Jan 22, 2011 11:58 pm 
Offline

Joined: Jul 28, 2008 10:44 pm
Posts: 3060
Perhaps it would be better to make 100 such ships than 10. That might make the ship size more manageable and the impact of losing one less critical.


Top
 Profile  
 
PostPosted: Jan 23, 2011 12:43 am 
Offline
User avatar

Joined: Jan 10, 2007 5:09 pm
Posts: 501
Location: Los Altos, California
100 ships would certainly help with getting lots of surface area for the tower.

If you are going to make 100 new ships with nuclear reactors on board, you've now got a supply ship for every few combatants, and I suspect the ships are just too small to be cost-effective. Since big and small ships have quite similar lengths (Arleigh Burke is 70% of the length of a carrier), just knocking the power per fueller down by a factor of 3 might make things more reasonable.

I think it's very interesting that much of the Navy seems to have selected the LM2500 turbine, and usually 4 of these to a ship. It appears to me that a 45 MW(e) reactor combined with a 2,000 metric ton ZEBRA battery (or sodium/sulfur, or whatever) would be a very good fit for a surface combatant. I'm actually confused why the subs don't have big batteries, but then again they've got to store 30 years of fuel so maybe peak power isn't a major problem, or maybe the nice batteries are just too new, or maybe the idea of a quarter of the ship's mass being vacuum-jacketed molten metal seems bad. I used to think the idea of an electric boat seemed like unnecessary complexity, but now I'm starting to think it makes a lot of sense, especially if you have a nuke. And, I think there is a real possibility of a 45 MW(e) modular marine reactor that would be built by the hundreds, at which point it might be used as a civil reactor as well.


Top
 Profile  
 
PostPosted: Jan 23, 2011 2:10 am 
Offline

Joined: Dec 26, 2007 11:45 am
Posts: 191
iain wrote:
...

A Supply-class fast combat support ship is 230 meters long, 33 meters wide, and has a draft of 12 meters. Imagine a similarly-sized nuclear fueller with nearly the entire superstructure consisting of a forced-draft cooling tower. The tower has intakes on each side of the ship, 15 meters tall and 250 meters long. Air flows through this tower at 7.4 meters per second (16 miles per hour). All of this sits on top of a chemical factory and PWR reactor set and blasts through the water at practically any speed it wants, because preposterous amounts of electrical power are available for the screws.

It would be really great to find a different way to get carbon.

If you heat and/or depressurize seawater the dissolved gasses released have a much higher fraction of CO2 than air straight out of the atmosphere because the solubility of CO2 is much higher than other atmospheric gasses. I don't know how practical this will be but you might want to take a look at it.


Top
 Profile  
 
PostPosted: Jan 23, 2011 4:33 am 
Offline

Joined: Dec 07, 2008 2:53 pm
Posts: 50
Location: Santa Cruz, CA
Axil wrote:
So, the problem is getting carbon. Getting it from the atmosphere involves gigantic air handling equipment. If my fueller has 1 GW(e) of reactor onboard, and attempts to make 400 MW of fuel, and that fuel is something like 50 MJ/kgC, then it needs 8 kg/sec of carbon. 385 ppmV of CO2 in the atmosphere is 160 mg/m^3. So, if we can get 90% of that CO2, we'd need to process air at 55,000 m^3/sec. That's a terrible problem.
Sea water contains about 2.8 mg of carbon per liter ,(http://en.wikipedia.org/wiki/Sea_water). If you need 8 kg/s of carbon, and we can remove half of the carbon from the sea water passing through a shipboard processing system you would need 8 x 10^1 / 1.4 x 10^-3 or about 5,700 l/s. This is not a large volume when you are talking about ships. This would take an input pipe of about 2 meters diameter.
As far as processing methods vacuum degassing would be a lot less energy intensive than trying to heat this volume, but there may be other ways to remove the carbon from the stream.

_________________
Mike Swift
Although environmental groups say we must reduce CO2 to prevent global warming they can never mention the “N” word as part of the solution.


Top
 Profile  
 
PostPosted: Jan 23, 2011 7:38 am 
Offline

Joined: Jul 14, 2008 3:12 pm
Posts: 5039
Seawater is very dirty. Air is relatively clean. Well if you're not in Chinese industrial area.


Top
 Profile  
 
PostPosted: Jan 24, 2011 6:03 am 
Offline
User avatar

Joined: Jan 10, 2007 5:09 pm
Posts: 501
Location: Los Altos, California
Tom,

Getting the carbon from seawater is an interesting idea. I get different numbers than you.

http://www.seafriends.org.nz/oceano/seawater.htm says there is 90 mg(CO2)/kg(seawater). So, 8 kg/s carbon is 29.3 kg/s CO2 is 326,000 kg/s of seawater, or 326 m^3/second.

That's like the flow through the prop! If we had a 6-meter diameter pipe, the fluid velocity would be 11.5 m/s and the flow kinetic power would be 21 megawatts, which is about what one of these ships puts out at cruise speed.

If we sucked all that water through a pipe 8 meters tall, so that the pressure at the top was perhaps 20 kPa absolute, we might boil out 80% of that CO2. What we'd actually get would be 194 kg/s of gas with about 15% CO2. At 20 kPa, this gas would be bulky, around 1000 m^3/s. So we'd have to seperate the gas and water, and then the gas would have to be recompressed to atmospheric pressure. I think this would take about 700 kilowatts. The water then gets exhausted out the back as a jet which pushes the ship forward. The gas goes through the rest of the Green Freedom process, now much smaller because just 200 m^3/s is being processed rather than 55,000 m^3/s. The difference in those two numbers is due to the way water dissolves CO2 more than O2 or N2, because most of the CO2 forms carbonic acid. We're using the surface area of the ocean to do our first stage air handling.

I like it.

-Iain

I like it!


Top
 Profile  
 
PostPosted: Jan 24, 2011 8:59 am 
Offline

Joined: Apr 19, 2008 1:06 am
Posts: 2249
Producing DME or other fuel on land for naval fuel is a good idea. A floating synthetic fuel factory facing problems of carbon feed is not. Best way to use a nuclear plant on board is that followed by nuclear submarines or Russian floating power plants/icebreakers. The French are also considering submerged nuclear plants. Sea or a big river is an economical cooling option.
However if you can recover spillages like the recent Deepwater horizon, by all means have floating facilities.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 42 posts ]  Go to page 1, 2, 3  Next

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:  
Powered by phpBB® Forum Software © phpBB Group