Separation Processes to Deal With Reactor Products

Discuss the technical details of an "open source" community-driven design of a polywell reactor.

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Brent
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Separation Processes to Deal With Reactor Products

Post by Brent »

I figured that understanding ways to deal with the reactor products will be useful eventually when the reactor becomes continuous. Hopefully I am not too far off topic. The following is a brief description of what I have found. If anyone finds this interesting, please comment.

I’m investigating ways to deal with the reactor products, such that they can be recycled back in to reactor. I’m considering both a phase separation process and a membrane separation process (possibly a combination of the two).
I expect to separate a tertiary mixture of helium-4, hydrogen, and boron-11 from the pB11 reaction. I predict a phase separation process may easily separate boron-11 from hydrogen and helium-4. It could be as easy as condensing out the boron-11, and then using a phase or membrane separation process to separate hydrogen from helium-4.
I’ve found that a common process for cryogenic separation is the Linde process. A membrane process for gas separation is termed gas permeation. My gut feeling is that the latter would be better suited for small-scale application.

For phase separation, it seems that a fundamental issue is to understand the phase behavior, and extract information about pressure, temperature, and composition.
For those interested in detail, I’m investigating group contribution theory to predict the boron phase behavior. I expect this to be difficult however, since I have found little reliable information about the actual phase behavior of boron, only its normal boiling point and critical temperature. Hence, I really have little to compare my predictions to. For hydrogen and helium-4, I’m employing the virial equation of state, treating each as quantum gases. The quantum gas treatment was at the suggestion of "Molecular Thermodynamics of Fluid-Phase Equilibria", a book by Prausnitz. I should note that deuterium and tritium are also considered quantum gases.

For the membrane, mass transfer issues such as diffusivity will need to be considered. I've found at least one polymer that seems to have a suitable difference in diffusivity for hydrogen verses helium to ensure a separation.

I'm sure engineers with industrial experience could do a better job at this. My goal is to develop something that can take whatever the reactor outputs at some temperature, pressure, and composition.

Brent
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Post by Brent »

Note: Group contribution theory may be a pretty lame thing to use. However, not knowing much about it, may prove useful. I may discover later that it does work. I truth, I chose it because literature was limited to me.

MSimon
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Post by MSimon »

Here is the easiest way to do separation:

1. Condense the Boron
2. Burn the deuterium
3. Collect the helium
4. Electrolyze the D2O
Engineering is the art of making what you want from what you can get at a profit.

cuddihy
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What's the output of a vacuum turbo pump?

Post by cuddihy »

MSimon wrote:Here is the easiest way to do separation:

1. Condense the Boron
2. Burn the deuterium
3. Collect the helium
4. Electrolyze the D2O
What i'm asking is, the vacuum is maintained by vacuum turbo pumps. They are continuously sucking out reactants and products in a mix. But what does that exhaust look like? Is it in a form easy for condensation of Boron? Is there a concern that boron will condense on the outlet & reduce pump effectiveness? :twisted:

Also, why bother burning off the deuterium or separating out the helium? neither are radioactive or useful in the minute quantities p-B fusion will produce them in. What's more of concern would be any trace elements that become radioactive while passing through the reactor.
Tom.Cuddihy

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MSimon
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Re: What's the output of a vacuum turbo pump?

Post by MSimon »

cuddihy wrote:
MSimon wrote:Here is the easiest way to do separation:

1. Condense the Boron
2. Burn the deuterium
3. Collect the helium
4. Electrolyze the D2O
What i'm asking is, the vacuum is maintained by vacuum turbo pumps. They are continuously sucking out reactants and products in a mix. But what does that exhaust look like? Is it in a form easy for condensation of Boron? Is there a concern that boron will condense on the outlet & reduce pump effectiveness? :twisted:

Also, why bother burning off the deuterium or separating out the helium? neither are radioactive or useful in the minute quantities p-B fusion will produce them in. What's more of concern would be any trace elements that become radioactive while passing through the reactor.
Condensation in the turbo pumps may be a problem.

A 100 MWth reactor produces about 1 Kg a day of He. Useful stuff He.

Continuous flow of reactants means it is probably worthwhile to collect the Hydrogen/Deuterium coming out of the reactor. After all you paid to purify it. Why not recycle it?
Engineering is the art of making what you want from what you can get at a profit.

djolds1
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Re: What's the output of a vacuum turbo pump?

Post by djolds1 »

MSimon wrote:A 100 MWth reactor produces about 1 Kg a day of He. Useful stuff He.

Continuous flow of reactants means it is probably worthwhile to collect the Hydrogen/Deuterium coming out of the reactor. After all you paid to purify it. Why not recycle it?
Burn both pB11 and the fraction of recycled DHe3 at the same time? IIRC they require virtually the same conditions to burn, at least in the thermalized systems.

Duane
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MSimon
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Re: What's the output of a vacuum turbo pump?

Post by MSimon »

djolds1 wrote:
MSimon wrote:A 100 MWth reactor produces about 1 Kg a day of He. Useful stuff He.

Continuous flow of reactants means it is probably worthwhile to collect the Hydrogen/Deuterium coming out of the reactor. After all you paid to purify it. Why not recycle it?
Burn both pB11 and the fraction of recycled DHe3 at the same time? IIRC they require virtually the same conditions to burn, at least in the thermalized systems.

Duane
With no reactant flow the pressure in the reactor is 1E-9 torr aprox. To keep it steady (with pumps operating) requires flow. Most of that flow is not going to be reacted. So you collect the output of the pumps and recycle it.
Engineering is the art of making what you want from what you can get at a profit.

djolds1
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Re: What's the output of a vacuum turbo pump?

Post by djolds1 »

djolds1 wrote:
MSimon wrote:A 100 MWth reactor produces about 1 Kg a day of He. Useful stuff He.

Continuous flow of reactants means it is probably worthwhile to collect the Hydrogen/Deuterium coming out of the reactor. After all you paid to purify it. Why not recycle it?
Burn both pB11 and the fraction of recycled DHe3 at the same time? IIRC they require virtually the same conditions to burn, at least in the thermalized systems.

Oops DD and DHe3 that have similar conditions. Still, anything that can use pB11 should be able to burn DHe3.

Duane
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djolds1
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Re: What's the output of a vacuum turbo pump?

Post by djolds1 »

MSimon wrote:With no reactant flow the pressure in the reactor is 1E-9 torr aprox. To keep it steady (with pumps operating) requires flow. Most of that flow is not going to be reacted. So you collect the output of the pumps and recycle it.
So start with the pB11 fuel cycle and introduce small bits of the DHe3 cycle later on as an efficiency measure? Obviously you recycle the pB11 fuel stream.

Duane
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MSimon
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Re: What's the output of a vacuum turbo pump?

Post by MSimon »

djolds1 wrote:
MSimon wrote:With no reactant flow the pressure in the reactor is 1E-9 torr aprox. To keep it steady (with pumps operating) requires flow. Most of that flow is not going to be reacted. So you collect the output of the pumps and recycle it.
So start with the pB11 fuel cycle and introduce small bits of the DHe3 cycle later on as an efficiency measure? Obviously you recycle the pB11 fuel stream.

Duane
Neutron flux is going to be higher with DHe3 than with pB11 because of the D-D side reaction.

And there is the little problem of He3 availability.

Working with gases is advantageous because it avoids the condensation problem.
Engineering is the art of making what you want from what you can get at a profit.

djolds1
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Re: What's the output of a vacuum turbo pump?

Post by djolds1 »

MSimon wrote:Neutron flux is going to be higher with DHe3 than with pB11 because of the D-D side reaction.
Irrelevant if its a minor enhancement to the primary fuel cycle. DHe3 is still largely aneutronic, even if not as much as pB11.
MSimon wrote:And there is the little problem of He3 availability.
Yeah. Brain fart. I forgot that the pB11 reaction only produces He4, w/o a minor He3 side product. I was (erroneously) thinking that recycling of the presumed He3 fraction into the fuel cycle could be advantageous.
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cuddihy
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Re: What's the output of a vacuum turbo pump?

Post by cuddihy »

MSimon wrote:
djolds1 wrote:
MSimon wrote:With no reactant flow the pressure in the reactor is 1E-9 torr aprox. To keep it steady (with pumps operating) requires flow. Most of that flow is not going to be reacted. So you collect the output of the pumps and recycle it.
So start with the pB11 fuel cycle and introduce small bits of the DHe3 cycle later on as an efficiency measure? Obviously you recycle the pB11 fuel stream.

Duane
Neutron flux is going to be higher with DHe3 than with pB11 because of the D-D side reaction.
Not just higher but radically higher, even if the D-D is introduced into the reactor as a very small percentage of the fuel. Look at the D-D cross section for fusion where the p-B rx becomes feasible...in other words, recycling D will take your (nearly) radiation-free p-B fusion machine and turn it into a CRUD magnet within hours. Might as well do a D-D only machine at that point.

Not to mention what all those neutrons do to the coil coolant...pretty soon you get Co-59 involved, and then you're really screwed....

bad, bad juju.

And there is the little problem of He3 availability.

Working with gases is advantageous because it avoids the condensation problem.
Last edited by cuddihy on Wed Mar 26, 2008 2:40 am, edited 1 time in total.
Tom.Cuddihy

~~~~~~~~~~~~~~~~~~~~~
Faith is the foundation of reason.

cuddihy
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Joined: Sat Jun 30, 2007 5:11 pm

Re: What's the output of a vacuum turbo pump?

Post by cuddihy »

djolds1 wrote:
MSimon wrote:With no reactant flow the pressure in the reactor is 1E-9 torr aprox. To keep it steady (with pumps operating) requires flow. Most of that flow is not going to be reacted. So you collect the output of the pumps and recycle it.
So start with the pB11 fuel cycle and introduce small bits of the DHe3 cycle later on as an efficiency measure? Obviously you recycle the pB11 fuel stream.

Duane
Still puzzling over how to keep the vaccuum ports from plugging rapidly with a metal vapor...wouldn't it be better somehow to just suck out the gases and dump everything? That way you don't risk contaminating your reactor with deuterium, and you can control the hydrogen you inject to keep deuterium out. (as in keep it to its natural abundance or lower). You could just coat the chamber walls and coils with B as some have suggested for sputtering protection, and just use that as the primary source of B in the fuel, and then somehow cause the B in the plasma to plate out before entering a restrictive region of the turbopump inlets.

or how about a boron-coated "fuel control rod" or other shape that provides B into the plasma by stray sputtering or other particle interaction?
Tom.Cuddihy

~~~~~~~~~~~~~~~~~~~~~
Faith is the foundation of reason.

MSimon
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Re: What's the output of a vacuum turbo pump?

Post by MSimon »

cuddihy wrote:
djolds1 wrote:
MSimon wrote:With no reactant flow the pressure in the reactor is 1E-9 torr aprox. To keep it steady (with pumps operating) requires flow. Most of that flow is not going to be reacted. So you collect the output of the pumps and recycle it.
So start with the pB11 fuel cycle and introduce small bits of the DHe3 cycle later on as an efficiency measure? Obviously you recycle the pB11 fuel stream.

Duane
Still puzzling over how to keep the vaccuum ports from plugging rapidly with a metal vapor...wouldn't it be better somehow to just suck out the gases and dump everything? That way you don't risk contaminating your reactor with deuterium, and you can control the hydrogen you inject to keep deuterium out. (as in keep it to its natural abundance or lower). You could just coat the chamber walls and coils with B as some have suggested for sputtering protection, and just use that as the primary source of B in the fuel, and then somehow cause the B in the plasma to plate out before entering a restrictive region of the turbopump inlets.

or how about a boron-coated "fuel control rod" or other shape that provides B into the plasma by stray sputtering or other particle interaction?
Working that out may take some time. Maybe a lot of time.

We do have the advantage that Boron plasma is used in the semiconductor industry for doping silicon. So it may already have been worked out in a general way and all we have to do is adapt the solutions to our design.

I have some contact with a guy familiar with semiconductor reactors so I'll give him a shout and see what he thinks.
Engineering is the art of making what you want from what you can get at a profit.

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