Custom Zirconia Refractory Linings for Extended Carbon Black Production

The Challenge: Temperature, Life, and Installation Efficiency

The manufacturer produces carbon black through controlled pyrolysis of hydrocarbon feedstocks at extreme temperatures. Their operations depended on a direct relationship: every 100°C increase in reactor flame temperature offered the potential of 1% yield improvement, along with a roughly 10% reduction in fuel costs. Reaching 2100°C and above would also unlock the capability to produce premium carbon black grades — specialty products that demanded sustained high-temperature conditions their existing refractory system couldn’t provide.

Their alumina-based refractory linings were suitable for flame temperatures up to 1850°C – 1900°C, with an expected 12-month service life. But the economics of higher-temperature operation were compelling enough to pursue, if the engineering challenges could be solved. Increasing flame temperature to 2150°C introduced a cascade of technical problems that needed to be addressed simultaneously rather than sequentially.

First, traditional alumina refractories couldn’t maintain structural integrity above 1900°C. Thermal stress accelerated degradation dramatically, threatening to reduce reactor life to just months rather than the expected 12-month cycle. Second, higher flame temperatures risked elevating reactor skin temperature beyond the 230°C threshold required to maintain thermal efficiency. Third, the existing installation process for the reactor’s cone section required hand-cutting individual bricks on-site, extending downtime during reactor rebuilds.

The manufacturer faced a complex engineering problem:

• Achieve sustained flame temperature above 2100°C operation without sacrificing refractory life
• Maintain reactor skin temperature safely below 230°C despite the temperature increase
• Eliminate field cutting and reduce installation time during reactor rebuilds
• Deliver a solution that justifies the higher material cost through operational improvements

Without solving all of these requirements simultaneously, the efficiency gains from higher temperatures would be offset by increased refractory costs, more frequent rebuilds, and extended downtime.

The Solution: Engineered Zirconia System With Iterative Development

Zircoa began with early technical discussions to understand the reactor’s dimensional constraints and the manufacturer’s operational goals. The initial approach combined engineered zirconia brick in Composition 1651 for the combustion chamber with custom castable pieces in Composition 0872 for the cone section — the reactor’s hottest zone.

This hybrid design delivered several advantages:

• Eliminated field cutting – Custom-engineered castable pieces with ship lap design arrived ready for installation, removing the need to hand-cut individual bricks in the tapered cone section
• Optimized thermal performance – Zirconia’s thermal shock resistance and structural integrity enabled 2150°C operation, while the engineered porosity provided insulation to maintain safe reactor skin temperatures
• Simplified installation – The ship lap design ensured structural integrity in the cone section while reducing installation time during reactor rebuilds
• Enabled temperature stratification – Proper layering with alumina backup material behind the zirconia hot face optimized the thermal gradient through the reactor wall

The first installation was completed in February 2019. The manufacturer evaluated performance across multiple criteria: refractory life at elevated temperatures, reactor skin temperature stability, yield improvements from higher flame temperature operation, and installation efficiency.

But early operation revealed a critical issue: brick failure at the 12 o’clock position with elevated skin temperature. Zircoa’s failure analysis identified eutectic formation between the zirconia and alumina layers; this phenomenon is where materials react at elevated temperatures to form a lower-melting-point compound that compromises structural integrity.

This discovery triggered a collaborative engineering response. Zircoa and their alumina-backup materials supply partner, HarbissonWalker International, worked together to redesign the material stackup, eliminating the conditions that enabled eutectic formation. The refined design was validated in the second installation, completed in August 2023, incorporating the lessons learned from the first reactor’s performance and failure analysis.

As part of an ongoing performance optimization effort, the team has developed a modified brick design to be featured in the next installation. This enhancement will better accommodate thermal expansion and contraction during dynamic heat-up and cool-down cycles, improving the overall structural stability of the refractory system.