Petrochemical fired heaters (or furnaces) are the workhorses of refineries and chemical plants, providing the intense heat required for processes like cracking, reforming, and heating. While the radiant and convection tubes carry the process fluid, it is the refractory lining that contains the high-temperature flame and gases, protects the steel structure, and maximizes thermal efficiency. Selecting the appropriate refractory is a complex balance of temperature resistance, insulation properties, and resistance to chemical and physical abuse.

Primary Functions of Refractory Linings

Containment & Safety: They form a barrier, containing flames and hot gases (often exceeding 1000°C / 1832°F) and protecting the external steel casing from heat damage.

Insulation: They minimize heat loss to the environment, improving fuel efficiency and creating a stable, high-temperature environment for the process.

Heat Reflection: In the radiant section, refractories with high reflectivity (like ceramic fiber) help direct thermal radiation onto the tubes, optimizing heat transfer.

Structural Support: In many designs, they provide the structural surface for burner blocks, support tube hangers, and form the flue gas ducting.

Key Types of Refractories and Their Applications

Refractories in fired heaters are broadly categorized into monolithic (cast, gunned, or sprayed) and brick/mortar systems. The trend has shifted heavily towards monolithic linings for faster installation and better integrity.

Ceramic Fiber Modules/Linings:

Material: Alumina-silica based fibers, often with chromium or zirconia additions for higher temperature grades.

Advantages: Extremely low thermal mass and conductivity, leading to fast start-up/shutdown cycles and superior fuel efficiency. Lightweight and easy to install.

Applications: Widely used in radiant and convection section walls and roofs of modern heaters, especially where thermal shock is a concern. Not suitable for areas of direct flame impingement or high velocity flue gas erosion.

Castable Refractories (Dense and Insulating):

Material: Hydraulic-setting concretes containing aggregates like calcined fireclay, bauxite, or alumina, bonded with calcium aluminate cement.

Advantages: Versatile, can be poured into complex forms. Dense castables offer excellent abrasion and erosion resistance. Insulating castables provide a balance of strength and low conductivity.

Applications: Dense castables are used in burner floors, hearths, throat arches, and anywhere mechanical abuse is expected. Insulating castables are used as backup lining or in moderate-temperature zones.

Plastic Refractories & Ramming Mixes:

Material: Moldable, clay-bonded materials supplied in a ready-to-use form. They are installed by ramming or pneumatic tamping.

Advantages: Good resistance to thermal spalling and mechanical shock. Can be repaired easily in-situ.

Applications: Ideal for complex shapes, filling gaps, and areas requiring a seamless lining, such as around tube penetrations and bullnose sections.

Firebrick and Mortar:

Material: Pre-fired bricks (e.g., high-alumina, fireclay) laid with a matching refractory mortar.

Advantages: High structural strength and excellent erosion resistance at very high temperatures.

Applications: Traditional material, now often used in specific high-wear areas like heater floors, burner quarls, the lower radiant section, and the shock bank of the convection section.

Selection Criteria and Challenges

Choosing the right refractory involves evaluating:

Maximum Operating Temperature: Must have a rating safely above the skin temperature of the steel casing.

Thermal Conductivity: Lower conductivity improves efficiency but may require a dual-layer system (a hot face and an insulating backup).

Chemical Resistance: Must withstand flue gas composition (e.g., sulfur, alkalis, vanadium) and occasional process spills.

Physical Properties: Resistance to abrasion from soot blowers, thermal shock from cycling, and mechanical impact.

Heater Design & Cycling: Frequent cycling heaters benefit from low-thermal-mass ceramic fiber, while base-load units may use heavier castables.

Conclusion

The refractory lining is a vital system that directly impacts a fired heater’s performance, longevity, and safety. Modern practice favors monolithic solutions, particularly ceramic fiber for walls and roofs, complemented by dense, abrasion-resistant castables in high-wear zones. Proper material selection, coupled with meticulous installation and dry-out procedures, is essential to achieve a reliable, energy-efficient, and long-lasting heater refractory system.