Refractory Selection for Carbon Black Reactors

To select the right refractory bricks for a carbon black reactor, we must first understand its structure and operating conditions.

Carbon black production, especially the modern oil furnace process, is essentially a precisely controlled chemical reaction under extreme high temperatures. The core equipment—the cylindrical reactor—is internally divided into four functionally distinct zones: combustion, throttle, reaction, and quench. Each zone places unique and extremely stringent performance requirements on the lining refractory materials. Ensuring stable, efficient, and long-cycle operation requires a deep understanding of the working environment in each zone and matching it with the most suitable refractory material, which is a core technology in the carbon black industry.

Harsh Operating Conditions and Refractory Challenges in Carbon Black Reactors

The interior of a carbon black reactor is a dynamic and complex physicochemical environment. Starting from the combustion zone, the temperature rises sharply, peaking at the throttle ring area accompanied by the highest gas flow velocity; upon entering the reaction zone, the temperature decreases slightly, the flow stabilizes, and carbon black forms here; finally, in the quench zone, the reaction is abruptly terminated by rapid cooling through water spraying.

This process poses three core challenges to the refractory materials:

1. Extreme High Temperatures: Depending on the grade of carbon black being produced, operating temperatures can range from 1550°C up to 2100°C and above, placing extremely high demands on the refractoriness of the materials.
2. Severe Thermal Shock: When changing carbon black grades or adjusting the quench zone position, the temperature inside the reactor can fluctuate violently, this can easily cause the refractory materials to crack and spall due to thermal stress.
3. High-Temperature Scouring and Corrosion: High-speed, high-temperature gas flows cause continuous mechanical erosion and chemical attack on the reactor lining, particularly at areas like the throttle ring.

Therefore, the ideal lining material for a carbon black reactor must combine high refractoriness, excellent thermal shock stability, high density, low porosity, and outstanding resistance to high-temperature corrosion/erosion.

Zoned Refractory Selection Strategy

The lining of a carbon black reactor typically employs a zoned construction scheme. Different grades of refractory materials are selected based on the temperature and conditions of different zones to achieve the best balance between technical performance and economic cost.

Low-Temperature Zones (1550–1750°C): Corundum bricks with an Al₂O₃ content greater than 90%, using mullite as the bonding phase, are generally selected. In the quench zone, high-purity high-alumina bricks with an Al₂O₃ content of 60–70% are sometimes used.
High-Temperature Zones (1750–1925°C): The hot face of the combustion zone usually employs materials with 90% Al₂O₃ – 10% SiO₂. For the throttle ring and the hot face of the reaction zone, where temperatures are highest and scouring is most severe, pure corundum bricks with 99% Al₂O₃, or chrome-corundum bricks with 90% Al₂O₃ – 10% Cr₂O₃ (where Cr₂O₃ is introduced to enhance thermal shock resistance), are required.
Ultra-High-Temperature Zones (>1925°C, even 2000–2100°C): When producing special grades of carbon black (such as those for low rolling resistance tires), traditional materials are no longer adequate. Ultra-high-temperature refractory materials represented by the Cr₂O₃-Al₂O₃ system (e.g., 70% Cr₂O₃) must be used.