Since it is an element and a noble gas that is produced by a very slow process - decay of uranium, thorium and their daughter products - helium could be the bottleneck that would slow development and deployment of Adams EnginesTM. I can point to a lot of esoteric science papers that supported the decision to go in a completely different direction than the conventional gas cooled reactor wisdom as practiced by companies like PBMR and General Atomics, but this video does a much more entertaining job of sharing the reasons for my concern.
Sunday, February 28, 2010
One Reason for Choosing Nitrogen (N2) for Adams Engines is the Growing Scarcity of Helium
One of the reasons that I decided to use N2 gas as the coolant for Adams EnginesTM is the fact that helium supplies are limited enough so that a new large demand would drive up the price of the gas. I fully expect that someday, direct cycle gas turbines using nuclear heat sources will have the potential for rapid market expansion; I determined a long time ago that I did not want to limit the potential for that expansion based on a limit to the amount of available helium.
Since it is an element and a noble gas that is produced by a very slow process - decay of uranium, thorium and their daughter products - helium could be the bottleneck that would slow development and deployment of Adams EnginesTM. I can point to a lot of esoteric science papers that supported the decision to go in a completely different direction than the conventional gas cooled reactor wisdom as practiced by companies like PBMR and General Atomics, but this video does a much more entertaining job of sharing the reasons for my concern.
Since it is an element and a noble gas that is produced by a very slow process - decay of uranium, thorium and their daughter products - helium could be the bottleneck that would slow development and deployment of Adams EnginesTM. I can point to a lot of esoteric science papers that supported the decision to go in a completely different direction than the conventional gas cooled reactor wisdom as practiced by companies like PBMR and General Atomics, but this video does a much more entertaining job of sharing the reasons for my concern.
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How about Supercritical CO2 as a Brayton Cycle Turbine Working Gas?
ReplyDeleteI will be the first to admit that I am not a Brayton cycle turbine expert but some of the guys at INEEL National Lab apparently are. INEEL has been studing Brayton Cycle alternatives including different choices of working gas. The following INEEL report includes suggestions that supercritical CO2 may have (small) advantages over Nitrogen and He.
INEEL/EXT-04-02437
Development of a Supercritical Carbon Dioxide Brayton Cycle: Improving PBR Efficiency and Testing Material Compatibility
Chang Oh, Thomas Lillo. William Windes, Terry Totemeier, Richard Moore
(October 2004)
http://www.inl.gov/technicalpublications/Documents/2906955.pdf
The following two short quotes may be useful:
"Working fluids of helium for both direct and indirect cycle, nitrogen for indirect cycle, and
CO2 for indirect cycle were investigated. The difference between the helium direct cycle
and the indirect cycle was 50.9% vs. 48.7% respectively. Nitrogen gave a cycle
efficiency of 45.5% while CO2 gave a cycle efficiency of 50.7%. Total area ratio (total
heat transfer area of working fluid / total heat transfer area of helium indirect cycle)
gives, 0.65 for helium direct cycle, unity for helium indirect cycle, 1.32 for nitrogen
indirect cycle, and 1.18 for CO2 indirect cycle at 20 MPa. Conclusions from the
investigation are (1) among the three working fluids studied, CO2 has the highest cycle
efficiency due to less compression. CO2 cycle also results in the smallest
turbomachinary, and (2) helium direct cycle eliminates the IHX and consequently
requires the smallest heat transfer area due to the higher heat capacity and thermal
conductivity than those of the other fluids considered."
and,
"Among three working fluids studied for the indirect power conversion study (PCS),
supercritical CO2 has the highest cycle efficiency due to less compression work as a
result of the higher densities of supercritical CO2 than other fluids used for the
indirect cycle. Supercritical CO2 also results in the smallest turbomachinary
components."
Since CO2 is widely considered as a threat to the climate it would seem interestingto propose that gas cooled high temperature reactors might use CO2 as a working gas. Taking CO2 out of the atmosphere and segregating it in the fully enclosed final cooling loop and turbine of VHTRs removes CO2 from the environment.
The elemental abundance of Helium on the sun is about 23%. The video was both fun and informative. Thanks!
ReplyDeleteHelium is rare but Argon is as inert as Helium, 1% of air and quite close to air and Nitrogen in molecular mass (40 against 28).The absorption cross-section is less than that of Nitrogen. Still it is avoided like poison for reasons I cannot understand.
ReplyDelete@Rod - I know you have literally spent years looking at issues relating to closed Brayton cycle turbines and power generation. It is easy for relative newcommers to pop up with suggestions "But what about . . .".
ReplyDeleteI understand that you have tended to favor N2 as the working fluid. N2 has the HUGE benefit of being the main constituent of air. Hence a N2 cycle can build on the enormous industrial experience accumulated with jet engines and aeroderivative fixed turbines for the past 70 years, at least for the rotary side of the machinery. That being said, it still leaves exchangers, recuperators and so on as fairly uncharted territory.
It is a huge the effort is to bring a new type of cycle - or for that matter, any type of industrial process or new product - from the lab to industrial reality. While S-CO2 is interesting to me and I hope designers will give it consideration in the future it would be a huge technical undertaking to develop it.
friend2all - Even when it comes to heat exchangers and recuperators, there is a significant body of design and operating experience with using atmospheric air as the working fluid. That experience can also be transferred to N2 - systems that work well with air will work well with N2 since it has such similar heat capacity.
ReplyDeleteRod - on a podcast I was listening to where you were interviewed about your engines you quoted a price competitiveness of any area where Electric is less than 6 cents a kwh or about a 1 a watt (1 million a megawatt). Do you still think these are achievable prices?
ReplyDeleteI totally agree with your decision. While I like cool new things, combining existing technology in new ways is the way you can have a true change in our energy infrastructure. It seems to me that your greatest challenge is the fuel not the turbines. Your fuel is "new" and not quite off the shelf.
David - the specific numbers for any cost estimation always have to be understood to be valid for the time that they are given. There is generally a need to update estimates to take into account the specific types of inflation that might have occurred during the time between the estimate and the present time.
ReplyDeleteJust using average inflation rates does not work, since labor cost, interest rates, and various materials inputs change at different rates and in different countries.
With all of that waffling taken into account, I remain convinced that simple cycle, low pressure, N2 cooled machines using high temperature gas reactors can be extremely competitively prices once in production. There are significant first of a kind costs since the fuel required is still not readily available in the world market. There is nothing really "new" or exotic about the fuel, it has been manufactured before and is currently being manufactured at a reasonable scale in China and in pilot scale in the US and South Africa.