Sometimes the devil is in the detail and sometimes it isn’t. Direct air capture is just a silly idea.

Aweh dearly beloved fellow Ruminants & Groupies in day 549 of Re-Modified Lock Down Level 2 and with alcohol.

Period as a semi-retired pensioner: 170 days

This week’s blog is on the topic of detail and complexity and when it is important and when it is not. Today’s blog is unfortunately a techno-nerds blog and I apologise for that. Perhaps next week I will talk about the Kardashians. This week has also been a hectically busy one for me, so I have not had the usual amount of time to ruminate as extensively as I usually do.

Often it is necessary to get into the detail and understand the details of a complex subject to a high degree of fidelity. This is of course very difficult and time-consuming and requires a high degree of expertise and requires subject matter experts. When you need to have your detached retina reattached it is best that you use an expert who has spent years if not decades learning and perfecting their knowledge. In the energy and petrochemical industry, you also go to the experts if you want to build a power station, refinery, or chemical plant. The devil truly is in the detail.

However, sometimes it is not necessary to get sucked into the expertise rabbit hole. I would propose that at the one end of the pendulum one can quickly conclude that you need to rely on the experts. Retinal surgery is my chosen example, but there are many. At the other end of the pendulum, there are also many areas where you can short circuit the whole process and just dismiss the experts based on fundamental scientific or logical principles. The theory of astrology (star signs) is extremely complex and there are experts who devote their whole lives to studying the theory. There is, however, no scientific evidence or rationale that your personality is determined by which month of the year you are born. I am a Gemini, and they are inquisitive, intelligent, and great thinkers. Perhaps there is something to this after all. But I digress, astrology is bullshit. I don’t need to study the complex theory. The theory doesn’t help. Humans also devoted a great deal of thought and effort into alchemy which aimed to turn lead or copper into silver or gold. Don’t bother with the theory.

Most patent attorneys will not engage with anyone trying to patent a perpetual motion machine. Thermodynamics tells us this is not possible, but this does not mean that many people have not put enormous effort into trying to prove thermodynamics wrong and they will keep trying.

I have described two ends of a pendulum with the left end being the domain of experts. At the right end of the pendulum, there is bullshit and here you don’t need to bother with the experts. Slightly to the left of the extreme right of the pendulum is a category that I wish to introduce called near-bullshit.  

The example I have chosen for near-bullshit is the concept of direct air capture. Direct air capture (DAC) is a technology to capture CO₂ directly from atmospheric air. It is technically and scientifically possible to do this. If that is the case, why would I call it near-bullshit? Here we need to go back to our old foe thermodynamics. In round numbers, the atmospheric CO2 concentration is 400 parts per million (ppm) on a mass basis. This means that to recover 1 ton of CO₂ you need to process 2500 tons of air. Purifying anything from a very dilute stream is difficult. Humans have been purifying gold from dilute ores for centuries and a reasonable ore grade is 4 g/ton or 4 ppm. That means you need to process a lot of rock to recover the gold. That means it is expensive, very expensive. The only reason it makes sense is that gold is very valuable. One gram of gold is worth $56 which converts to $56 million per ton. Is there a technology magic bullet breakthrough that will make this cheap? Won’t the march of technology make this cheap one day? Gold recovery technology has been improving over the last 100 years and it is significantly better than it was, but the improvements are incremental, and it remains expensive. The problem is fundamentally difficult from a thermodynamic perspective and there is no cheap technology on the horizon nor will there ever be.

Unlike gold CO₂ is not a valuable product and cannot bear the very high costs of purification. It will take a lot of energy to get CO₂ out of atmospheric air. The energy needed to run direct air capture machines in 2100 is up to 300 exajoules (EJ) each year. This is more than half of the overall global demand today. https://www.carbonbrief.org/direct-co2-capture-machines-could-use-quarter-global-energy-in-2100. Anyone with a basic grasp of thermodynamics knows that it will take a lot of energy to get CO₂ out of atmospheric air. It doesn’t matter whether the energy requirement is 100 EJ/yr or 600 EJ/yr it will be an enormous number. The reagent requirements for DAC are enormous. To lift out just one: For DAC1, one of the processes proposed, 5.1–8.7 Gt/yr of NaOH is required, and the production will need 2.15–3.67 TWe-yr (electrical energy for electrolysis = 13.3 GJe/ tNaOH). This will account for about 12–20% of the total global energy supply (TGES; 18.55 TW-yr for 2017, but likely greater than the global electricity generation capacity of 2.92 TWe-yr). https://www.nature.com/articles/s41467-020-17203-7.pdf?origin=ppub.

Direct air capture is near-bullshit and one can analyse it based on a basic undergraduate understanding of thermodynamics and economics. You don’t need to be an expert to smell the bullshit. The notion that “technology improvements” will make DAC cheap is a pernicious lie.

Yet DAC is a thing, and many billions of dollars will be spent and wasted on developing it further, but thermodynamics will win in the end. No amount of detail will change that. The devil isn’t in the detail.

Thank you for your comments and suggestions please keep them coming.

Regards

Bruce