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26 November 2020

Concentrated solar thermal tech to be used for cement production

Global cement producer Cemex has allied with Swiss solar start-up Synhelion to demonstrate the world’s first emissions-free cement production.

Synhelion’s main agenda has been generating jet fuel from concentrated solar power, using temperatures of over 1,000 °C to ‘reverse combustion’, recombining H20 and CO2 into hydrocarbons. This is relevant to emissions-free cement production as well, as the mechanism to remove carbon dioxide from the atmosphere and instead turn it into fuel, rather than capture and storage.

Powering the world’s existing cement production with renewable electricity would only reduce its emissions by a third or so, as most emissions come from limestone calcination in the process itself. Cement is 7% of the world’s total emissions, so this kind of project is a big deal that could address 5% of global emissions – or at least rework them into the airline industry’s emissions. Prior research on cement powered by concentrated solar hasn’t addressed those emissions except through carbon capture.

On Synhelion’s side, its fuel production needs a supply of CO2. A process to get pure CO2 supplied from cement production won’t be hard to establish, whereas coal plants use ordinary air, meaning their output gas is mostly nitrogen – hard to filter out.

Cemex and Synhelion are planning to commission a $10 million, 1 MW pilot project in 2022. That’ll require 185 square meters, so a full-scale cement plant of 150 MW would still require ‘only’ an area of 28,000 square meters – 167 meters a side. Synhelion says it won’t use the same setup it has for making solar fuel, however. The heliostats, central tower, and energy storage would all be present, but there won’t be a thermochemistry solar reactor. Instead, the CO2 will be mixed with water vapor, with some used as heat transfer fluid (HTF) and the rest collected for use at Synhelion’s fuel-production facilities elsewhere – since the water vapor can be removed by a simple condensation process.

Unlike typical solar thermal plants, which have a temperature range of 220 °C to 565 °C using thermal salt, Synhelion’s will range from 800 °C to 1,500 °C, well into the temperature range for industrial processes, due to using carbon dioxide with water vapor as the heat transfer fluid. This is reminiscent of another alternative heat transfer fluid, liquid sodium, which Australia’s Vast Solar is using in its CSP power plants – it has double the temperature range of solar salt.

Synhelion is based in Switzerland, and held its commercial launch in 2016. For its part Cemex has made more effort than most of the cement industry, though perhaps that’s a dubious accolade. It’s sought to reduce emissions with a variety of energy efficiency techniques, has made some progress with renewable energy adoption, and has participated in carbon-capture projects and in EU-funded waste heat recovery initiatives.

Also in the news this week is German Aerospace Centre (DLR)’s ‘ceramic particle technology’, another instance of thousand-degree concentrated solar. It’s building a $16 million concentrated solar heat pilot project in Foggia, Italy, though this is for a pasta factory, for both heat and electricity, rather than a high-intensity industrial purpose.