Thanks, Andrew. To answer your questions:1) This is not an energy generation scheme, it is an energy consumption scheme (as is most CDR), but where some useful things are done when powered by non-fossil energy: CO2 consumed, H2 generated, ocean alkalinity is increased. You can then do some useful things with the H2: hydrocarbons, electricity, water. Furthermore, given the abundance of the required ingredients, this can scale. The central issue (as in most CDR) is economics: this isn't free, but is also is not going to cost $1000/tonne CO2 as in the case of DAC analyses (House et al; Socolow et al.), primarily because I am not making concentrated (and risky) molecular CO2. I think the cost is more like $100/tonne CO2, especially depending on the local market value of the ingredients needed and the by-products/services produced (e.g., what is the $ value of freshwater in a desert? what is the $ value of neutralizing/offsetting ocean acidity - how much do we value coral reefs?) 2) Certainly we can let nature take it's course and let natural mineral weathering consume all of the CO2 we care to emit, ultimately generating ocean alkalinity and neutralizing ocean acidity. But this will take on the order of 100kyrs to achieve, and that's after we stop emitting CO2. Waiting around for this to happen could be catastrophic. So might there be economically and societally acceptable ways to accelerate this inevitable, effective, but otherwise very slow mitigation?-Greg
--- On Fri, 3/9/12, Andrew Lockley <[email protected]> wrote: From: Andrew Lockley <[email protected]> Subject: Re: [geo] Rapid ocean acidification militates rapid CO2 removal (CDR) To: [email protected] Date: Friday, March 9, 2012, 12:10 AM Why would you electrolyse sea water to make h2 to generate electricity? Isn't that a bit circular? Why would you use electro chemistry to accelerate weathering when you can just let it progress naturally? A reply to list might be helpful. A On Mar 9, 2012 5:40 AM, "RAU greg" <[email protected]> wrote: John, Not sure what solar powered process you are talking out, but re CDR and OA, it is possible to generate carbon-negative H2 electrochemically using base minerals (limestone or silicates), seawater, and photovoltaic Vdc *. The neutralization of the acid normally produced at the anode of a seawater electrolysis cell (neutralization by the presence of base minerals) forces excess OH- to accumulate in the seawater, which rapidly reacts with air or ocean CO2 to form alkaline bicarbonates. Thus CDR is effected in seawater, and ocean acid is neutralize and/or the added alkalinity helps offset the effects of ocean acidification (by elevating carbonate saturation state). As for fuel, it would be most efficient (carbon- and thermodynamics-wise) to directly use the H2 that is produced at the cathode, but if you insist on clinging to hydrocarbons, yes there are schemes for making these from H2 and CO2. The hydrocarbon utilization route of course just keeps more C circulating in the atmosphere. Keep in mind that using fuel cells, H2 can be readily converted to electricity and pure H2O, the value of which would not be lost on your present (and wanabe) coastal desert dwellers. Given the global abundance of seawater, base minerals, photons, and silica (for photocells; or one could go the solar thermal - electricity route), the preceding should scale quite readily, with relatively small land footprint(esp small if one considered using offshore solar or wind). One little problem is the avoidance of Cl2 generation at the anode, but there have been demonstrations of O2-selective anodes and other schemes that could be relevant. Let me know when you are ready to save the world or at least terraform some coastal deserts ;-) Regards, Greg *http://www.goldschmidt2011.org/abstracts/finalPDFs/1698.pdf http://pubs.acs.org/doi/pdf/10.1021/es800366q --- On Tue, 3/6/12, John Nissen <[email protected]> wrote: From: John Nissen <[email protected]> Subject: [geo] Rapid ocean acidification militates rapid CO2 removal (CDR) To: "geoengineering" <[email protected]> Cc: "John Nissen" <[email protected]>, "Peter R Carter" <[email protected]>, "Anthony Cook" <[email protected]>, "Ron Larson" <[email protected]>, "Sam Carana" <[email protected]> Date: Tuesday, March 6, 2012, 6:02 AM [Resent with correction] Hi all, Is there an alternative to rapid CDR to reduce the atmospheric CO2 level and hence slow ocean acidification? Acidification is progressing at the fastest rate for 300 million years, faster even than in the PETM [1], and spells catastrophe if not curbed over the next decade or two.I am supporter of biochar for CDR on a large scale. But few people think biochar can be scaled enough to actually start reducing the atmospheric CO2 level in the face of CO2 emissions set to climb for decades. So we need a combination of low to medium cost CDR schemes, capable of scaling to the very large. Yesterday I heard about a scheme for use of solar energy (e.g. in Sahara) to power the scrubbing of CO2 from the atmosphere and the production of hydrogen from H2O. The hydrogen would then be combined with the captured CO2 to create a carbon-neutral hydrocarbon fuel, which could then be cheaply and efficiently piped to countries wanting a green energy source, e.g. for cars and electricity generation. Apparently it's much cheaper and more efficient to pipe liquid fuel than transmit the equivalent electric power over the same distance. Cheers, John P.S. If hydrogen can be produced from H2O, could a hydroxyl byproduct be used for combination with scrubbed methane (CH4) to produce further carbon-neutral fuel? Atmospheric methane levels are rising ominously. [1] http://planetark.org/wen/64838 -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en. -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. 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