The principles involved in the. railcar-based method of Direct Air Capture (DAC) as explained in the July 20, 2022 Vol 6,Issue 7 of the. scientific. magazine Joule and now being developed. by Texas based 'CO2 Rail' show-
- the use of 'slipstream' from moving transport being used to duplicate the fans currently used in schemes such as Climeworks to produce sufficient airflow over the adsorption material thus saving considerable electrical energy and
- the conversion and storage of waste heat from 'regenerative braking' in diesel /electric rail in batteries to power the DAC process thus largely eliminating the cost (in association with rail car solar panels) of the heat energy currently required in extraction.
As envisaged, the method represents a considerable advance on current DAC methods in that it saves energy currently wasted and utilises existing transport infrastructure thus raising the possibility of DAC being economic and reaching gigaton levels. The .pdf in the longer Joule articles, while giving detailed workings does not mention the weight of the plant to be placed on railcars though a considerable advantage of miniaturisation seems to have been achieved.
Would it be possible (weight considerations allowing) to adapt such a method to commercial airliners to enable them to harvest significant quantities of CO2 inflight?
- Turbofan engines generate significant quantities of waste heat which conceivably could be captured for a similar DAC purpose.(As all answers to-date(26/01/23) have made this point it seemed best to address them in an Edit rather than in individual replies) Question partly relates to recovering waste heat from turbofan engines In High bypass Turbofans approximately 80% of the thrust is supplied by cold slow-moving air and only about 20% by residual ( hot exhaust). Answers so far have portrayed hot turbofan exhaust as sole provider of thrust and heat capture as virtually eliminating it with fundamental changes to flight characteristics. There would appear to be nothing new about suggesting the possibility of such heat recovery or describing it as 'waste heat' Examples of such heat recovery research-and such description- for turbofan exhaust can be found by an internet search and .pdf's obtained by author can be posted on request. Perhaps the 4 providers of answers might care to revisit their answers in the light of the above?
- The study of airflows over aircraft surfaces. -being an integral and essential element of aircraft design and aerodynamics-should make it feasible to incorporate some form of 'slipstream capture' through cowlings or otherwise without interfering with overall aerodynamic performance. ................