Development of a Climate-Neutral Heat Supply for Asphalt Mixing Plants

In the “DekarAsphalt” project, Fraunhofer ISE is investigating the decarbonization of process heat supply in asphalt production through electrification. The project analyzes the integration of electric heaters, heat pumps, storage systems (including thermal and battery storage), and hydrogen to replace or reduce the use of fossil fuels and balance out the fluctuating power generation from renewable energy sources. The goal is to significantly reduce CO₂ emissions and energy costs while simultaneously developing a practical roadmap for climate-neutral asphalt mixing plants.

Initial Situation

Asphalt production belongs to the most energy-intensive processes in road construction: large quantities of mineral aggregates and recycled materials are dried using fossil-fuel-fired burners and heated to high temperatures. High moisture content in the raw materials result in high fuel consumption and CO₂ emissions. Rising energy prices and CO₂ costs are increasing economic pressure on operators, while political climate targets demand significant emissions reductions. At the same time, the expansion of renewable energy sources is leading to very low electricity prices at times, opening up new opportunities for flexible, electric heat generation.

Objective

The goal of “DekarAsphalt” is to develop and evaluate technical and economic concepts for the extensive decarbonization of asphalt mixing plants. The focus is on improving efficiency in the drying process and replacing fossil fuels with electricity and hydrogen. Among other things, the project is investigating heat pumps, direct electric heating, high-temperature heat storage, battery storage, hydrogen burners, and process optimizations. Based on this, operators and plant manufacturers will receive practical decision-making tools for the design of hybrid heating systems.

Approach

For an existing reference plant, a detailed process and energy model was first created and validated using measurement data. A pinch analysis identified heat recovery and efficiency potentials, particularly through the reduction of moisture content and air volumes. Subsequently, concepts for direct electric heating as well as concepts for energy storage using solid-state high-temperature storage, lithium iron phosphate battery storage, and hydrogen supply were technically developed. Using the Fraunhofer ISE simulation environment “ColSim”, these components were dynamically techno-economically optimized across multiple hybrid system variants over a one-year period and in long-term scenarios extending to 2045.

Results

The analyses show that the plant’s energy consumption can be reduced by up to 40% by lowering the water content of recycled materials and mineral streams and by using smaller volumes of air. The use of additional drying with heat pumps enables savings of around 50%. Hybrid concepts combining electric heating (Power-to-Heat, P2H), high-temperature thermal storage, and gas or hydrogen backup can reduce CO₂ emissions from heat generation by more than 50% even with relatively small storage systems—at lifecycle costs comparable to today’s gas-based solutions.

A complete switch to hydrogen, on the other hand, nearly doubles the costs. Battery storage is currently not competitive for direct heat supply but is suitable for optimizing the remaining electricity consumption. The hybrid solution combining power-to-heat, thermal energy storage, and a backup boiler is competitive and should be pursued as the preferred solution. Cost-effective measures to reduce the moisture content in the raw materials are recommended, as this can significantly lower energy requirements and thus operating costs.

The “DekarAsphalt” project was funded by Invest BW, a funding program of the Baden-Württemberg Ministry of Economic Affairs, Labor, and Tourism.