Optimization of a decarbonized brick manufacturing process in tunnel kilns by means of numerical simulation

The decarbonization of the process industry presents a critical challenge, particularly in the context of brick manufacturing. This study explores the transition from traditional natural gas burners to electrification using 100% green electricity as a promising solution for sustainable brick drying and firing. The electrification process requires a fundamental shift in brick firing techniques, necessitating solutions to scientific and technical challenges at various scales, including optimizing temperature profiles, enhancing heat transfer, ensuring temperature uniformity, and optimizing internal heat recovery. To address
these challenges, numerical flow and heat transfer simulations are employed as valuable tools to support the decarbonization of the brick manufacturing process. The study begins with a comprehensive literature review of various modeling approaches for brick firing, considering factors such as brick and kiln composition, reaction kinetics, and radiation phenomena. Computational geometries and calculation meshes are then generated for a three dimensional model of a tunnel kiln zone along with hollowed brick. Transient numerical flow simulations, accounting for various kinetics, turbulence, heat transfer and radiation models, are conducted to analyze fluid flow phenomena in hollowed
bricks and tunnel kiln. Cases with convection and forced convection were conducted with the same surface area of heated walls along with same distance between brick and kiln. Results have shown that case with forced convection requires less time for brick to reach uniform temperature of 950°C with firing time of 4.52 h. Furthermore, the study addresses the challenge of continuous mesh motion in the context of discontinuous kiln operation, providing a detailed procedure for copying cell data between different solid brick stack regions. The complexities of mesh generation and the need for a user-defined function are outlined, emphasizing the steps involved in ensuring proper coordination of cell values between different solid regions. This research contributes to the Austrian NEFI project GreenBricks, which aims to decarbonize the brick manufacturing process while ensuring excellent product quality. The brick manufacturing process itself involves intricate steps, from mining and preparing raw materials to forming, drying, firing, and cooling. Clays of different types are blended to ensure consistent quality, and the choice of raw materials significantly influences the final brick properties. Drying and firing, two crucial stages of brick production, are energy-intensive processes currently reliant on natural gas. This reliance contributes to air pollution and CO2 emissions. The transition to electric heating elements offers a path to emission-free kiln operation. Electrically fueled kilns require significant process adjustments, including changes in kiln design, drying methods, and control systems. Moreover, the research delves into the heating power of electric heating elements available on the market, discussing materials capable of withstanding high temperatures, thus enabling efficient electrification of kilns.