Environment & Energy

It would be extremely difficult, and no doubt extremely expensive to build, but perhaps not to run once built.

Of course, we do not live in a wise world, so there's that. And of course, our bourgeois airheads here and elsewhere, are cheapskates, completely willing to dump the cost of their ignorance on future generations to save a dime. They prance around insipidly all the time issuing delusional statements that so called "renewable energy" - affection for which is accelerating the extreme global heating we now experience - is "cheap." (They seem not to notice that a large number of European countries want to cut off that coal burning "renewable energy" "nirvana" Germany for driving European electricity prices to unprecedented heights during episodes of Dunkelflaute, the new German word that has become an international term of disgust with antinuke stupidity.)

The basis for my perhaps over optimistic belief that a closed carbon cycle is feasible contains an admittedly dubious "appeal to authority" argument, reference to a paper by the late Nobel Laureate George Olah, who, at least was an expert in carbon chemistry, meaning that the "authority" is somewhat more real than some fossil fuel greenwashing airhead announcing that because Energy Secretary Jennifer Granholm thinks a hydrogen economy is viable, it therefore is. (Secretary Granholm is an outstanding woman, but she is a politician, not a scientist.)

The paper in question is this one: Anthropogenic Chemical Carbon Cycle for a Sustainable Future George A. Olah, G. K. Surya Prakash, and Alain Goeppert Journal of the American Chemical Society 2011 133 (33), 12881-12898

I reference this paper often.

To see a possible route achieving this goal, one should consider the exergy recovery of nuclear reactors which is, to my way of thinking, unacceptably low, as they are designed to be (largely) Rankine type steam cycle devices designed to dissipate, rather than use, waste heat.

According to the World Nuclear Association, in 2023, the world produced 9% of the world's electricity, which amounted to 2,601,617 GWh of electricity, or 9.37 Exajoules (EJ). In the OP, by reference to the IEA data, the primary energy associated with nuclear power was 30 EJ, meaning, to carry one insignificant figure, that the thermal efficiency of nuclear power plants on the planet was 31.₂%. This also means that 20.₆EJ of heat was rejected to the environment, only a small trivial quantity of which was utilized for space heating in urban networks.

It would be energetically expensive to recover this heat for existing reactors with heat pumps, further reducing the thermal efficiency (for the purpose of generating electricity) but suppose instead we built reactors that were designed to not dissipate heat but to let it flow in concentrated form through a series of heat exchangers designed to extract exergy from that heat, that is process intensification. The laws of thermodynamics limit how much of that heat might be captured, but crude calculations on my part, suggest that it might be possible to approach 80% thermal efficiency, rather than 31% efficiency.

An air driven Brayton cycle would necessarily give an avenue to process air, to pressurize it. In this process, CO₂ capture might be achieved as a side product of the process, albeit at an energy penalty for the overall efficiency of the system, but utilizing energy that is currently rejected to the environment.

Suppose we generated 500 EJ of primary energy each year from nuclear energy, requiring 6,000 tons of plutonium per year, roughly, and instead of 31% efficiency, achieved, let's say 70% efficiency, with not all of the exergy coming as electricity, but perhaps in the form of chemical energy (as Olah's paper suggests, DME or Methanol). This would provide about 200 EJ of recovered energy that would be put to use, not rejected. Under these conditions, air capture borders on feasible. I note that it is less energetically intensive to recover CO₂ from seawater than from air, but that's another story.

These things lead me to suspect feasibility, which is nowhere near the same as saying "likely." At the end of my life, I'm sure the embrace of stupidity is far more likely than the embrace of wisdom.

Thanks for your comment.