The answer to Ken's rhetorical question is a qualified "yes", if you ignore kinetics and assume you are looking only at the CO2 capture, desorption, clean-up and compression as he described then you can do it for pennies a kg of CO2 which is pennies per kWh. It's a yes because posed this way, ignoring kinetics and the capital and energy cost of the absorber this is the core of the standard engineering case for post-combustion CCS that has been analyzed endlessly for 20 years and for which there is lots of relevant commercial hardware. The qualification is around details of this particular material, but there are other solid and liquid systems that do this. For air capture it's harder because one cannot ignore the kinetics of uptake and the capital cost of the absorber structure. There is not much CO2 in the air so the contacting structure (the thing that actually gets CO2 from the air) must be very cheap. Here are some order of magnitude numbers: 1. You can't afford to move the air faster than a few m/s though the device (100 Pa= 6.1 kJ/mol-C= 13 m/s) 2. At that air flow, even if you get all the CO2 you are getting no more than of order 10 tCO2 m-2 yr-1. 3. Assume it is 10 tCO2 m-2 yr-1 and you don't want to pay more than 50 $/tCO2 for the amortized cost of the structure. Then the cost per square meter of inlet area must be less than 3 $k. (At 15% overall capital charge factor $3000 m-2 is $45 m-2 yr-1 which you then divide by the 10 tCO2 and round). This is hard. Large cooling towers are about $2000 m-2. 4. The amount of absorbing surface you need behind each square meter of inlet is depends on the kinetics of uptake, but at a mass transfer coefficient of 1 mm/sec one needs of order 500 m2 of surface area behind each 1 m2 of inlet. 5. For us a Carbon Engineering, using plastic packing it easy to meet this cost criteria as they cost 1$ per m2 of surface area. For our system packing cost is only a small fraction of contactor cost and a very small fraction of overall turn-key plant cost. 6. In order for a solid system to compete it must either have a much faster mass transfer coefficient or by roughly as cheap; and for a solid one must contrive a way to temperature or humidity cycle the whole solid structure cheaply and without significant air leaks. (Or find a way to gather the solids...). You can see some of our views about solid vs liquid systems at answer Q&A #8 at http://www.carbonengineering.com/wp-content/uploads/2011/04/CarbonEngineering-AirCaptureFAQ.pdf. Of course, the disadvantage of a liquid system is regeneration and management of liquid loss. The problems for solids are (a) getting fast uptake kinetics, (b) cycling given that the whole structure must be cycled either humidity swing or thermal swing, and (c) sorbent lifetime given that all the fancy solid must last for order a decade in air that contains contaminants such as particulates, trace gases and larger debris of all types. Bottom line: this looks like a real advance but without data on kinetics and long-term performance one can't judge how useful it is for air capture. In the near term we are reasonably confident that our liquid system will win for many large-scale air capture applications, but over the long run it's much harder to say what will happen.
From: geoengineering@googlegroups.com [mailto:geoengineering@googlegroups.com] On Behalf Of Ken Caldeira Sent: Wednesday, January 11, 2012 1:47 PM To: r...@llnl.gov Cc: zen...@uci.edu; geoengineering Subject: Re: [geo] New CO2 Sucker Could Help Clear the Air Note that there is an error of 10^6 in the article, as it says 1.72 nmol when the underlying article (attached) says mmol. Here is my little order-of-magnitude analysis: At 1.72 mmol per gram of material, to process 1 ton of CO2, we have would need ~13 tons of polyamine. The 1 g of material absorbs at 25 C needs to be heated to 85 C for three hours to give off the CO2, so this is a 60 C swing. Of course, one thing conventional power plants have is a lot of waste heat. Once it gives off the CO2, it gives it off into some gas, so you still need to figure out how to separate the CO2 from this gas. [Or maybe you make a high vacuum, but how cheap is that? If you didn't want to go with a vacuum, what would be the gas that you would have it desorb into, in order to make that separation step easy?] The average CO2 intensity of electricity production is about 615 gCO2/kWh. So you would need about 8 kg of material per kWh of electricity. If the real process were to take 3 hours, then you would need about 25 kg of material per kW of plant capacity (or 25,000 tons per GW). Can you take 8 kg of material (enough for 1 kWh's worth of CO2), have it absorb CO2, heat it up and let it desorb into a vacuum or a gas (and if a gas, then separate the CO2 from whatever the gas it desorbed into), and then compress and bury it underground, for not more than a few pennies per cycle? [images/cleardot.gif] _______________ Ken Caldeira Carnegie Institution Dept of Global Ecology 260 Panama Street, Stanford, CA 94305 USA +1 650 704 7212 kcalde...@carnegie.stanford.edu<mailto:kcalde...@carnegie.stanford.edu> http://dge.stanford.edu/labs/caldeiralab @kencaldeira On Wed, Jan 11, 2012 at 12:25 PM, Rau, Greg <r...@llnl.gov<mailto:r...@llnl.gov>> wrote: It's easy enough to suck CO2 out of the air; just take the cap off a bottle of conc NaOH, and that can be done at mmoles CO2/gram NaOH, not the nanomoles per gram these guys seem to swoon over. Then there's the little problem of what to do once absorbed. Desorbing at 85degC is an improvement over some other methods, but then what? - semi-concetratated CO2 that must be used or stored somewhere. Don't think this is going to save our bacon. The trick (as nature does) is finding a cheap chemical bases that you can react with CO2 and then keep as (bi)carbonates - CO2 desorption not required. Plastic bases are not one of these, hence the high recycling cost plus molecular CO2 as an end product. -Greg On 1/10/12 2:44 PM, "Charlie Zender" <zen...@uci.edu<mailto:zen...@uci.edu>> wrote: >http://news.sciencemag.org/sciencenow/2012/01/new-co2-sucker-could-help-cl >ear-.html?ref=hp > >-- >You received this message because you are subscribed to the Google Groups >"geoengineering" group. >To post to this group, send email to >geoengineering@googlegroups.com<mailto:geoengineering@googlegroups.com>. >To unsubscribe from this group, send email to >geoengineering+unsubscr...@googlegroups.com<mailto:geoengineering%2bunsubscr...@googlegroups.com>. >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 geoengineering@googlegroups.com<mailto:geoengineering@googlegroups.com>. To unsubscribe from this group, send email to geoengineering+unsubscr...@googlegroups.com<mailto:geoengineering%2bunsubscr...@googlegroups.com>. 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 geoengineering@googlegroups.com<mailto:geoengineering@googlegroups.com>. To unsubscribe from this group, send email to geoengineering+unsubscr...@googlegroups.com<mailto:geoengineering+unsubscr...@googlegroups.com>. 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 geoengineering@googlegroups.com. To unsubscribe from this group, send email to geoengineering+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en.
