Solar reactor development
Three solar reactors have been developed and were tested. A rotary kiln and a horizontal cross-flow fluidized bed were tested at the lab-scale (10-20 kWth). The horizontal cross-flow fluidized bed was selected and tested at pilot scale (40-60 kWth),. The test campaign focused on the calcination of cement raw meal, and on the calcination of calcite and phosphate with the rotary kiln and the pilot scale fluidized bed respectively. A 99% conversion was obtained with the solar rotary kiln for a CRM inlet flow rate of 4 kg/h corresponding to a thermochemical efficiency and an overall efficiency of approximately 10 and 20% respectively. At pilot scale, the solar horizontal fluidized bed achieved 95% calcite decomposition for a continuous feedstock flowrate of 20 kg/h. The thermo-chemical efficiency and the overall efficiency reached 17 and 29% respectively. The quality of the solar lime produced at pilot scale corresponded to the highest quality of industrial lime. Successful calcination of Moroccan phosphate was also achieved at pilot scale in the fluidized bed, with a conversion in excess of 99%.
Scaling up and solar process integration
The process scaling up methodology was based on a modular approach than enables to reach multi-megawatt units. For a 300 ton/day lime production a 40 MWth tower can reach the objective with a 81% capacity factor. The nominal power is reduced to 26 MWth for dolomite due to its lower calcination temperature and reduced endothermic heat of reaction. For a 1400 ton/day phosphate processing, the corresponding data are 45 MWth and 77%. The integration of a solar calcination step in an industrial cement plant of 3500 ton/day capacity needs a 270 MWth solar reactor with a 2-day hot particles storage. Solutions for hot particle conveying were also investigated and selected.
Environmental life cycle assessment
The environmental impacts of the solar-driven (SOLPART) calcination process have been compared with the conventional calcination process via life cycle assessment. The results showed that, compared to the conventional process, the SOLPART calcination system has the potential to reduce global warming potential by over 40% and various toxicity-related impacts by 40-50%. This is due to the SOLPART system utilising solar thermal power as a substitute for fossil fuels, which allowed reducing the fossil energy requirements by 57% compared to the conventional cement production process.
Exploitation and dissemination
For each of the project targeted sector (phosphate, cement and limestone, or dolomite), a study has been performed to confirm their exploitation potential. This has confirmed that in addition to limestone and cement, other calcinations (e.g. dolomite, gypsum, phosphate rock, metakaolin, clays, etc.) are of high interest for SOLPART since the thermal treatment of these minerals occurs at a lower calcination temperature and the endothermic heat of these reactions is significantly lower than the required reaction heat of CaCO3. Therefore, they are considered as a strong relevant test case for the future exploitation of the SOLPART concept. Post-project collaborations will be searched in this field as a very credible follow-up, and especially with OCP.
