Lofting/dispersal of any solid or liquid will likely be at least 5x the cost of lofting a gas, simply because it will require time at altitude to slowly disperse (and avoid immediate coagulation) that is presumably not necessary for a gaseous precursor such as SO2; that both increases mission time (and hence increases number of aircraft needed) and greatly increases fuel (given that time to get to altitude is of order 10 minutes, so if you need an hour at altitude, figure on 6x the fuel as a very crude guess), and hence cost, as well as reducing payload fraction in order to carry the extra fuel instead of payload. Many of us are skeptical that the microphysical benefits of lofting H2SO4 are likely to pay off relative to lofting SO2 (or H2S if you want a fuller list of gas options, though if you don’t like SO2 you surely really wouldn’t like H2S!). Curious why you dismiss SO2 (which is what is virtually always assumed as the default) in a sentence without any detail on why you think it is so much harder. Though I do agree that ground-handling constraints are not well explored. From: geoengineering@googlegroups.com <geoengineering@googlegroups.com> On Behalf Of david.sev...@carbon-cycle.co.uk Sent: Thursday, January 12, 2023 10:44 AM To: geoengineering@googlegroups.com Subject: [geo] Particles and SRM
Particles and SRM The post covers some of the issues around various materials that could be used for SRM, handling and equipment challenges, and issues around creating fine particles of the different materials. I am excluding discussion about how each of the materials might react with other chemical species in the environment of the upper atmosphere. Other previous discussions of this forum have covered this. Sulphuric acid This is probably the most widely discussed material for SRM. I have seen little regarding the handling hazards and the quite serious issues of storage and equipment selection. I have worked on production plant design that has had to incorporate concentrated sulphuric acid. Every aspect of storing, handling, pumping, and dosing this product is problematic and expensive. SRM will by definition need to use reasonable amounts of this material and this will trigger all kinds of health and safety issues for aspects of the operation. The problems get exponentially worse and more expensive if you try to go the route of sulphur dioxide or trioxide. Shifting to diluted sulphuric (50% for example) does not always make things easier. I can guarantee that the costs of using sulphuric acid at any scale will be harder and a lot more expensive than people will initially expect. This will mean higher CAPEX and OPEX costs. I can see real issues of pumping sulphuric acid and spraying at high altitude once you undertake a risk failure analysis for if something goes wrong. The problems are not unsolvable but they will limit where you can do this and they will raise costs. Titanium Dioxide Titanium dioxide has the significant advantage that when it is made, it forms small submicron particles that are well suited for SRM. Regretfully there are other confounding issues with titanium dioxide: - It is quite costly and a limited resource. If a new market emerged to start using more of it the price would become even greater. - It takes a lot of refining and will increase the waste production that is associated with its production. Again I have some experience in this area. It is a non-trivial matter. - Powdered titanium dioxide carries a cancer risk if mishandled. I think if you started seriously talking about spraying particles of this material in the upper atmosphere, there would be public pushback for this reason. Calcium Carbonate Previous, I was a one of the people who early on argued for considering this material. Calcium carbonate could have a lot of advantages (easy to handle, plentiful, etc) but I now realise there is a serious issue that I feel needs to be brought to the fore. Creating submicron calcium carbonate is going to be costly in terms of Capex, OPEX, and energy. Again I have experience here because my team was looking at capturing CO2 by reacting gypsum with CO2 and ammonium sulphate to make pigment quality calcium carbonate (white filler). We solved the purification problem which had defeated all who had attempted this before. We could make 10 micron precipitated calcium carbonate fairly easy and the grinding costs to make 3 micron product (this was our target market) are not bad BUT if you want to make a lot of small fine submicron calcium carbonate, there are issues. When you grind calcium carbonate below 10 micron, the grinding energy exponentially climbs the finer you get. This means if you want to make product with an average diameter below 0.1 micron, the energy costs is going to be very substantial. The production plant will need to be quite large. So you will incur high CAPEX and OPEX costs. Potentially, I think this could be enough to prevent calcium carbonate being a material to use for SRM. Salt (NaCl) There has been a lot of discussion about spraying salt water to make fine particles through different ways. I have done work on spraying reactants. Coalescence is a non-trivial issue that tends to rob you of the fine particles that you were initially seeking. There are solutions but all require more energy and equipment complication. I found nozzle clogging issues became more of an issue the finer that we tried to spray and when we tried to increase the volumes. Again, not an unsolvable problem but if your spray nozzle is tens of miles up, it will likely be an issue to give real thought to. It will definitely be a lot harder to deliver salt particles that are fine submicron rather than above 1 micron salt particles. There may be a more direct solution for salt that I have not previously seen. It would be relatively straightforward to create sub-micron salt particles using a spray drier. This is well established technology that equipment exists for small and large applications. I believe it is likely that you could create bulk salt particles below 10 nm. It would be relatively easy to blow a mixture of dry air and fine salt particles up a tube to high altitude where they would be released. An ideal arrangement would be to have a small spray drier creating fine particle salt from a salt solution that is then directly taken and mixed with dry air and blown up a fine tube to the high atmosphere where it is released. The delivery tube is supported by an aluminised nitrogen filled balloon. I have previous written about using nitrogen filled balloons as stable platforms for lifting and how you would do this. Potentially, a nitrogen filled aluminised balloon would be a very stable lifting platform as the nitrogen would take decades to diffuse out of the balloon envelope. 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