This might be a bit of a reach but I’m wondering if anyone here knows enough about concrete production to help me plan the layout of my next photobash. I’d like to do a scene of a solar-thermal concrete factory – there are several supposedly in the works, like Synhelion’s new partnership with Cemex, funded by the US DoE, or the french company Solpart (whose prototype involved a rotary kiln), or Heliogen. Unfortunately I’ve had a lot of trouble finding decent photos of their setups, and even though Synhelion is apparently working on a pilot industrial-scale solar concrete plant, I haven’t found any plans to work from.

I’ve been doing some reading about existing concrete factories, and plan to keep as much as possible the same, while mostly modifying the kiln to include at least one structure similar to a solar falling particle receiver, and adding some onsite algae farms or greenhouses for capturing CO2 released by the burning of the lime, and a trainyard (either electric trains or fireless steam locomotives, given that it’s a solar plant) for moving material into and out of the plant.

I’ll say upfront I know very little about concrete production, and I’m struggling to come up with a kiln design that’ll hit the required temps for long enough, without burning the lime and messing it up.. Originally I’d pictured basically a rotating kiln feeding into a falling particle receiver, linked up so heat from the sunlight hitting the falling concrete could still travel up the tube and eventually up into the cyclones where the mix is dried. But it seems like the concrete needs a longer, slower firing time than whatever heat it gets wafting up from the aperture, and then a blast of light and heat as it goes past. The diagrams I could find seems to just be a rotary kiln with sunlight being blasted into the open lower end, but I’m not sure if that’s just the design they went with because it was a proof of concept prototype.

I also know that temperature changes are bad for lining of rotary kilns, which are normally run pretty constantly IRL, so it seems like they’d need some changes anyways to cope with the day night cycle?

In case you’re reading this and wondering why make concrete this way, the concrete industry is a huge portion of human CO2 production (around 8% total), due both to the release of CO2 from the chemical process of baking the limestone, and from the tremendous amounts of heat necessary for doing that. A more solarpunk society would hopefully use much less concrete overall, especially with changes in building design and priorities that allow for weaker materials like hempcrete and mycocrete, but for some things we’re still going to need modern concrete. Solar furnaces can hit temps well above what a rotary kiln uses, and heliostat systems aren’t far behind, and it’s a pretty direct use of heat from the sun, which would minimize conversion losses. It’s not a great fit for every current concrete plant, but it seems like it could help.