The carbon black reactor is a critical piece of equipment in the carbon black production process. The reactor consists of five main components: the combustion chamber, the throat, the reaction section, the quenching section, and the holding section. Damage to the reactor’s furnace lining materials is primarily caused by erosion from high-temperature, high-velocity gas flows; chemical corrosion; high-temperature melting; and thermal shock resulting from temperature fluctuations during furnace startup and shutdown cycles. The refractory materials used for the inner lining are required to possess the following characteristics:
(1) High refractoriness: the ability to remain unsoftened and undeformed even at extremely high temperatures.
(2) Excellent volume stability at high temperatures, as well as stability within a reducing atmosphere.
(3) Strong resistance to erosion by molten ash.
(4) High-temperature strength to withstand the erosive forces of high-velocity gas flows.
(5) Good resistance to thermal shock.
Refractory Materials for Carbon Black Reactors
Current Status and Development Trends of Refractory Materials for Carbon Black Reactors. Currently, refractory materials used for lining carbon black reactors—both domestically and internationally—can be broadly classified into four major categories: Al2O3-SiO2-based, Al2O3-based, Al2O3-Cr2O3-based, and ZrO2-based systems. The Al2O3-SiO2 system encompasses high-alumina, mullite, and mullite-corundum products. The Al2O3 system consists of corundum-based products. The Al2O3-Cr2O3 system comprises chrome-corundum materials with varying Cr2O3 contents. The ZrO2 system includes chrome-corundum products containing zirconia, as well as pure zirconia products. These materials may take the form of shaped products (e.g., fired bricks or chemically bonded bricks) or unshaped products (e.g., castables or ramming mixes). This discussion covers the selection, service life, and performance characteristics of refractory lining materials for carbon black reactors.
Corundum-mullite products are made by using white corundum as granules and co-ground alumina, clay, and other materials as a matrix, and synthesizing mullite in situ during high-temperature firing. These products are utilized as linings for carbon black reactors, capable of withstanding maximum operating temperatures of up to 1700°C and offering a service life exceeding 48 months. However, a drawback of these products is their susceptibility to reduction in reducing atmospheres, where reducing agents such as H2, CO, and C react with and degrade the mullite. At high temperatures, C or H2 can decompose mullite into corundum and SiO. The resulting SiO either escapes with the process gases or undergoes further reduction to form Si, which subsequently creates a glassy phase within the material; this process leads to structural loosening or vitrification of the product. Consequently, under conditions involving intensified chemical processes and elevated thermal decomposition temperatures of hydrocarbon feedstocks within high-velocity gas streams, corundum-mullite products prove inadequate to meet the comprehensive performance requirements demanded of reactor linings.
Corundum Products
When corundum products are employed as lining materials, they demonstrate superior erosion resistance and a longer service life—compared to corundum-mullite linings—when subjected to high temperatures, high-velocity fluid flows, and reducing atmospheres. Under the influence of H2, the trace amounts of β-Al2O3 present in the corundum material transform into α-Al2O3 as the Na2O component is reduced; this process triggers the recrystallization and growth of the corundum crystals, thereby enhancing the product’s hot strength. Since other high-temperature properties remain largely unchanged, high-purity corundum products are well-suited for long-term service in reducing atmospheres at temperatures ranging from 1800°C to 1850°C.
High-purity corundum bricks have been successfully deployed in the throat sections and reaction zones of carbon black reactors at several carbon black manufacturing plants, where they have demonstrated a service life nearly double that of CA334 castable linings.
Al2O3-Cr2O3 series refractory materials represent a class of high-quality, advanced refractories developed in tandem with the advancement of high technology. These materials are ideally suited for use as linings in carbon black reactors—or other ultra-high-temperature thermal processing equipment—operating at temperatures of approximately 2000°C. This material is synthesized at high temperatures using Al2O3 and Cr2O3 as raw materials; it exhibits superior high-temperature mechanical properties and slag corrosion resistance compared to pure corundum products. At high temperatures, Al2O3 and Cr2O3 form a solid solution, and the temperature at which a liquid phase appears increases as the Cr2O3 content rises. Consequently, the addition of Cr2O3 to Al2O3 serves to enhance the high-temperature mechanical properties of pure corundum products without introducing any adverse effects.
Chrome corundum bricks (GGY-5 and GGY-12) have demonstrated excellent performance when utilized in the throat and reaction sections of carbon black reactors operating at temperatures of approximately 2000°C, achieving a furnace lining service life of over 15 months. Chrome corundum castables have achieved a service life exceeding 12 months. Furthermore, when related products within this series were applied in Texaco gasifiers for ammonia synthesis, the furnaces operated smoothly, and the materials achieved a service life of over three years.
ZrO2-based Refractory Products
In recent years, to meet the demands of intensified carbon black production processes, Al2O3-Cr2O3-ZrO2 composites and ZrO2-based refractory products have been researched and developed. ZrO2-based products are advanced refractory materials with a zirconia (ZrO2) matrix; given that the melting point of ZrO2 is 2677°C, these products exhibit a high softening point, exceptional high-temperature strength, and excellent resistance to slag corrosion and high-temperature thermodynamic instability. Consequently, they are frequently utilized in thermal processing equipment operating at temperatures exceeding 2000°C.
Al2O3-Cr2O3-based systems—or Al2O3-Cr2O3 systems doped with a small amount of ZrO2—are employed as linings for carbon black reactors. The addition of a small quantity of ZrO2 to the Al2O3-Cr2O3 matrix serves to enhance the system’s thermal shock resistance and chemical corrosion resistance, thereby extending the service life of the furnace lining materials. Al2O3-Cr2O3-ZrO2 lining materials (encompassing both shaped and unshaped refractories) can achieve a service life of over 18 months when installed in the throat and reaction sections of carbon black reactors.
ZrO2-based products utilized as linings for high-temperature and ultra-high-temperature carbon black reactors represent a new class of materials that have been researched, developed, and introduced into service in recent years. Pure ZrO2 bricks stabilized with CaO or MgO were trialed as linings in the combustion chambers, throat sections, reaction zones, and cooling zones of advanced carbon black reactors. Post-service evaluations, however, revealed certain limitations: specifically, poor thermal shock resistance and susceptibility to erosive degradation caused by the reaction between ZrO2 and carbon (C) to form zirconium carbide (ZrC) under reducing atmospheres at temperatures around 1600°C. To address these issues and further extend service life, bricks were subsequently developed by incorporating appropriate additives into partially stabilized ZrO2, followed by high-temperature firing; this process significantly enhances both the compressive strength and thermal shock resistance of the final product. When deployed within the high-temperature and ultra-high-temperature reducing atmospheres characteristic of carbon black reactors, these improved materials effectively prevent the erosive damage associated with the ZrO2-C reaction that typically occurs around 1600°C. Laboratory comparative testing and analysis—pitting CaO-stabilized zirconia bricks against corundum, chrome-corundum, corundum-mullite, and high-chrome bricks—revealed that the zirconia bricks possess superior resistance to high-temperature airflow erosion, chemical attack by carbon black particles, and corrosion by impurities present in the fluid stream. Field trials conducted within the throat and reaction sections of actual carbon black reactors at a specific carbon black plant also yielded satisfactory results. However, given the high cost of zirconia, its adoption may not be economically viable; consequently, widespread commercialization remains challenging unless specific, stringent requirements dictate its use.
Based on the operational conditions of carbon black reactors—including working temperature, pressure, airflow velocity, atmospheric environment, and quenching dynamics—the most promising refractory materials for use as internal linings are those characterized by high refractoriness, excellent high-temperature mechanical properties, robust resistance to slag corrosion and thermal shock, and high thermodynamic stability at elevated temperatures. Among these, zirconia, Al2O3-Cr2O3, and corundum-based materials are considered the optimal choices, whereas materials based on SiO2, MgO, or CaO are generally unsuitable for such applications.
With the advent of new technologies within the carbon black industry, the refractory materials used for reactor linings have also undergone continuous evolution. The low-to-intermediate grade refractory materials utilized during the nascent stages of the industry’s development have been progressively supplanted by modern, high-quality, and advanced products. For contemporary, advanced carbon black reactors—which operate under conditions of high to ultra-high temperatures and high pressures—the most promising refractory materials for internal linings are those exhibiting superior high-temperature mechanical properties and thermodynamic stability. These include pure Al2O3, Al2O3-Cr2O3, Al2O3-Cr2O3-ZrO2, and zirconia-based materials, available in both shaped and unshaped forms; practical field experience has conclusively demonstrated that these materials deliver the most effective performance.
Rongsheng Carbon Black Reactor Linings
The design of refractory linings for carbon black reactors must be tailored to specific operating conditions, necessitating the selection of different materials for various sections of the lining. Even within a single reactor utilizing a uniform process, appropriate refractory materials should be selected for each distinct zone; by implementing a comprehensive furnace lining strategy, optimal technical and economic results can be achieved. The scientific selection of refractory materials for carbon black reactor linings—specifically by matching refractory bricks of corresponding compositions to different temperature zones—serves to effectively control production costs while simultaneously ensuring the long-term, stable operation of the furnace lining, thereby achieving a harmonious balance between technical performance and economic efficiency.
