The metal industry is known for being highly intensive, both in terms of energy and material consumption, resulting in a large amount of residual energy and solid waste, such as steel slag. This situation poses significant challenges in terms of sustainability and efficiency.

Hence, in response to this problem, several heat recovery and material reuse technologies have been proposed to transform this sector towards a more sustainable and economically viable model.

One of these technologies is proposed by the European project LIFE Heat It Yourself For Sustainability (LIFE HI4S), which uses a digital twin to optimize and scale the technology ad hoc. Thanks to the work done so far, using Eurostat electricity price data (0.2525 €/kWh), we can consider that, thanks to this modeling work and a first approach towards the optimization of the operation of the plant, we have been able to quantify savings of over 200,000 € by processing only 1-2% of the exhaust gases; being, in addition, recovered about 1,000 MWh of thermal energy and producing about 20 MWh of net electricity.

Metal industry

The metal industry contributes significantly to global greenhouse gas emissions. For example, in the year 2020, approximately 7% of emissions and 11% of carbon dioxide (CO₂), 3.6 gigatons (36 followed by 11 zeros), belong to this industry. Moreover, these numbers, far from decreasing, continue to increase year after year, driven by the growing global demand for steel.

It is important to note that the steelmaking process is not efficient in terms of CO₂ and energy emissions per ton of steel produced. In fact, it is estimated that 1.91 t_CO2/t_steel is emitted and 21.31 GJ/t_steel is consumed on average. This energy consumed represents between 20 and 40% of the total price of the steel produced, so improvements in efficiency would have a significant impact on the cost of the final product.

The European LIFE HI4S project

The LIFE HI4S project addresses this situation by developing a technology for the treatment, recovery and reuse of the residual energy from this industrial process. This recovered energy is used in the preheating of the scrap used as raw material, and in the production of electricity by means of an Organic Rankine Cycle (ORC). In addition, these elements are complemented by a thermal energy storage (TES) based on packed bed technology, using treated metallic slag for heat storage, which copes with the intermittency of the energy source, functioning as a buffer and low-cost storage.

CIC energiGUNE is the coordinator of this European project, contributing also in several partial technical objectives. On the one hand, the systems engineering and technology transfer group contributes its extensive experience with thermal storage and heat transfer for the design of the pilot plant to be installed at Arcelor Mittal in Sestao (Vizcaya, Spain). In addition, the team is in charge of the sizing and design of the preheating system and characterization of the TES.

On the other hand, CIC energiGUNE is in charge of the digital modeling of the complete system through the TRNSYS software; a software that allows modeling, in an efficient way, the dynamic behavior of the plant, making possible the dimensioning of the components at industrial scale and optimizing the control.

Benefits of digital modeling

System modeling or digital modeling in engineering is a virtual representation of a physical system or process using specialized software. These models are fed with algorithms and mathematical equations to simulate real system processes, providing an efficient and accurate way to test and analyze different configurations and parameters before implementing them in the real world, saving time and resources.

One of the digital models being implemented in the LIFE HI4S project seeks validation, scalability of components and reproducibility of the technology. In this project, TRNSYS software has been used, which performs simulations of dynamic systems. Thus, the model is fed with temperature data from the flue gas of the Arcelor Mittal steel plant located in Sestao (Spain), where the pilot plant will be installed.

After the modeling work, it is necessary to validate this model with experimental tests, which brings into play the pilot plant of the project. Once the validation is done, the digital model allows testing different logics, operation modes and configurations of the components, varying sizes or configurations. Consequently, it allows the optimization of the process, improvements or implementation of new degrees of freedom in the operation.

The following image shows the design of the digital model (simplified), where it can be seen how the concept is adapted to the software, including subroutines or pre-designed and own Types, previously validated.

This flexibility in the control and sizing of the components that make up the model makes it possible to modify the behavior of the plant and make decisions in real time about when it is more efficient to load or unload the storage, when to preheat the scrap depending on the needs of the steel plant, while maintaining constant electricity production and keeping the plant active.

Digital modeling at CIC energiGUNE

In the Thermal Energy Solutions (TES) area of CIC energiGUNE we are experts in thermal energy storage, management, recovery and conversion, with a team of researchers and engineers from different specialties covering different areas of knowledge. Among these areas there is the digital modeling with different commercial tools such as TRNSYS, Simulink or Ansys Fluent.

Thanks to these tools and the knowledge we generate at CIC energiGUNE, we are able to provide solutions to the steel industry through projects such as LIFE Hi4S, improving the efficiency and sustainability of its processes and thus contributing to reduce the environmental impact of this sector.