Skip to main content

High Temperature Solar-Heated Reactors for Industrial Production of Reactive Particulates

Periodic Reporting for period 3 - SOLPART (High Temperature Solar-Heated Reactors for Industrial Production of Reactive Particulates)

Reporting period: 2018-07-01 to 2019-12-31

Overall objective and importance for society

The main objective of the SOLPART project was to develop, at pilot scale, a high temperature (850-900°C) 24h/day solar process suitable for particle treatment in energy intensive industries (e.g. cement and lime industries). The project aimed at supplying totally or partially the thermal energy requirement for CaCO3 calcination by high temperature solar heat thus reducing the life cycle environmental impacts of the process (reduction of CO2 emission by about 40%) and increasing the share of solar heat in process industries. Cement and lime industries are worldwide the second CO2 emitter after combustion (6-7% of the total antropogenic emission).

These objectives have been achieved by the demonstration in lab-scale and pilot scale solar reactors suitable for cement raw meal calcination and calcium carbonate decomposition (CaCO3 = CaO + CO2) respectively at TRL 4-5. A Life Cycle Assessment of the solar-based solution was developed and demonstrated significant advantages in comparison with the traditional production processes. Solutions for integrating the solar process in existing plants were examined in detail. Finally, an economic evaluation was performed for both the solar process integration solution and the construction of a new solar-base calcination plant.

Issues addressed during the project

- The industrial calcination processes address various types of feedstock towards both composition and particle size (typically from 5 to 500 μm) that are difficult to process in a single reactor.
- The design of thermochemical solar reactors combining solar flux density, temperature, mixing and residence time constraints.
- The integration of a solar step in an existing industrial process is a key issue that must be addressed by researchers and engineers. This was specifically examined for the cement industry.
- A solar process should result in the reduction of the environmental impact of existing traditional processes to make it acceptable by the society and sustainable with respect to exhaustible resources.

The main conclusions

Solar calcination reactors were developed and tested successfully for various feedstock within the wide range of particle diameters. High-quality lime grade was obtained. The integration of a solar step in cement processing needed a two-day storage of hot particles to reach an acceptable capacity factor of approximately 75%. Nevertheless, the cost of the solar option and the size of industrial scale cement plants (several thousands of clinker per day) are great obstacles to large-scale development. The situation is strongly more favorable for application of the solar technology to lime, dolomite and phosphate calcination because the daily capacity is one order of magnitude less than for cement and the product discharged from the solar reactor is the final product (contrarily to cement, where a subsequent very high temperature clinkering is required). The environmental life cycle assessment of the solar option results in very positive indicators for most impact categories considered.
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.
The obtained performance of the pilot-scale solar reactor exceeds the state-of-the-art in solar calcination by a factor of three.
The final TRL is TRL 5 with the testing of a large-scale prototype unit including a solar reactor and a high temperature storage system.
The barriers for integrating a solar process in existing cement plants were identified, and solutions were developed and designed. The potential of the novel technology to offer options for CO2 sequestration is high. The tested fluidized bed technology proved to be able to operate at high CO2 concentration (50% and more) applying a complete exhaust gas control, including dust abatement.
Potential impacts are related to reduced CO2 emissions, an increased solar heat share in industry, and additional employment,
- Reduction of CO2 emissions: potential to reduce the global CO2 emissions from cement industry by up to 1.6 billion tonnes of CO2 per year),
- Increase of solar heat share in industry: about 1 MWth/ton CaO of high temperature solar heat.
Testing of a fluidized bed prototype at the CNRS 1 MW solar furnace.
Principle of the solar calcination process.
Testing of the rotary kiln prototype at the DLR 25 kW solar furnace.
A 1m-long, 0.1m-high fluidized bed solar reactor composed of 4 compartments.
DLR rotary kiln can operate at about 1000°C. It is tested on-sun and with a simulator.