Tech Insights

High-Temperature Solar Device Achieves 1000°C and Beyond

June 10, 2024 by Jake Hertz

The quartz-based solar absorber reached 1,050°C, paving the way for decarbonizing steel and cement production.

Steel, cement, and glass are essential for construction, infrastructure, and other industries. However, their production processes are extremely energy-intensive, relying heavily on burning fossil fuels, resulting in significant carbon emissions. Unfortunately, the high temperatures required for manufacturing and the large-scale production make transitioning to sustainable methods complex and costly. 

Engineers from ETH Zurich have created a device that effectively harnesses solar energy to produce temperatures exceeding 1,000°C. This method could address the environmental challenges of fossil fuel-based manufacturing.

 

Steel production

Steel production. Image used courtesy of Wikimedia Commons

 

Production Challenges

In cement manufacturing, the first step is extracting and grinding raw materials such as limestone and clay into a fine powder. The second step is to heat the resultant powder in a cement kiln to temperatures as high as 1,450°C, causing the chemical bonds in the raw materials to break and form new compounds. This forms clinker, which are small, rounded nodules between 1 mm and 25 mm in size. The clinker is again ground into a powder and then mixed with gypsum to produce cement. The final product, cement powder, is mixed with water and aggregates to create concrete, widely used in construction. 

Cement production contributes significantly to carbon dioxide (CO2) emissions, with estimates suggesting the industry contributes to about 7% of global CO2 emissions.

 

Electric arc furnace steelmaking.

Electric arc furnace steelmaking. Image used courtesy of Adobe Stock

 

Steel production involves either blast furnace (BF) or electric arc furnace (EAF) methods. In the BF method, iron oxides are converted to pig iron using coke, iron ore, and limestone, with coke providing essential heat and gases. This method, dating back to the 14th century, still follows the same principles despite modern advancements. Heating coal to approximately 1,000°C without oxygen produces a high-carbon coke essential for the BF process. The EAF method works to melt scrap steel using electrical energy. 

Like cement, steel production significantly contributes to CO2 emissions, with estimates suggesting the industry accounts for approximately 7-9% of global CO2 emissions. The primary source of these emissions in steel production arises from using carbon-intensive fuels, such as coal, during the iron smelting process.

 

Clean Steel, Cement, and Glass

Researchers from ETH Zurich Steinfeld experimentally demonstrated solar thermal trapping at temperatures above 1,000°C, achieving a milestone in solar thermal technology. Specifically, the team focused on the thermal trap effect, where solar radiation is absorbed by a semi-transparent material, such as quartz, enabling higher efficiency in solar receivers.

The experimental setup involved a quartz rod attached to a silicon carbide absorber. When exposed to concentrated solar radiation equivalent to 135 suns, the absorber's temperature reached 1,050°C while the front face of the quartz rod remained significantly cooler at 450°C. This substantial temperature differential illustrates the thermal trap effect, where the bulk temperature exceeds the surface temperature. This phenomenon reduces reradiation losses, thus improving thermal efficiency.

 

The heat-trapping device reached 1,050°C.

The heat-trapping device reached 1,050°C. Image used courtesy of Casati et al.

 

A 3D heat transfer model, validated by experimental data, was developed to predict the performance of solar receivers using thermal trapping. The results indicated these receivers could achieve target temperatures with higher efficiency or require lower solar concentration than traditional unshielded absorbers. For instance, at a solar concentration ratio of 500, the thermal efficiency of a receiver with thermal trapping was approximately 0.7, compared to 0.4 for an unshielded receiver. This efficiency gain could significantly reduce the costs associated with solar field optics and improve the economic feasibility of high-temperature solar processes.

 

Toward a Cleaner Industry

The study's findings have important implications for decarbonizing industrial heat, particularly in cement manufacturing and metallurgical extraction applications. By demonstrating the practical application of thermal trapping at temperatures relevant to industrial processes, the researchers provided a pathway to more efficient and cost-effective solar thermal technologies. Therefore, this advancement could help address the significant challenge of decarbonizing high-temperature industrial heat, which constitutes a substantial portion of global energy consumption.