Optimized Design of Silica Bricks for the Upper Section Walls of Glass Melting Furnace Regenerators

01 Properties of Silica Bricks
Silica bricks used in glass melting furnaces possess the following characteristics:
1. High-temperature volume stability: The furnace structure remains unchanged despite temperature fluctuations. Due to their high load-softening temperature and low creep rate, silica bricks ensure the furnace structure remains stable and undeformed at operating temperatures of 1600°C.
2. No contamination of the glass melt: Silica bricks are composed primarily of SiO2; should spalling or surface dripping occur during use, the quality of the glass melt remains unaffected.
3. Resistance to chemical corrosion: When silica bricks in the superstructure are exposed to gases containing R2O (alkali oxides) from the glass batch, a smooth altered layer forms on the surface. This layer slows the rate of corrosion, thereby providing a protective effect.
4. Low bulk density: This helps reduce the overall weight of the furnace structure.

02 Improvement of the Upper Checkerwork in the Regenerator
Burnout and clogging of the regenerator checkerwork—necessitating hot or cold repairs—are primary factors limiting furnace service life. Selecting new, highly corrosion-resistant materials for the upper checkerwork zone can effectively mitigate the issue of short service life associated with traditional configurations. Checker bricks at the top are exposed to prolonged attack by alkali vapors and batch carryover in the high-temperature zone (1300–1400°C); consequently, the upper sections of traditional checkerwork—often constructed from high-purity magnesia bricks—are typically the first to fail, particularly in furnaces fired with petroleum coke. The V₂O₅ present in petroleum coke reacts with the CaO in the interstitial phases of the magnesia bricks to form calcium vanadate and calcium-magnesium vanadate. These newly formed, low-melting-point vanadate phases gradually grow within the high-purity magnesia bricks; as the CaO and MgO are progressively consumed by corrosion, the structural integrity of the bricks deteriorates, leading to a shortened service life.
The use of chrome-corundum bricks is recommended for the top three layers of the checkerwork. The corundum phase within these bricks is protected by a chrome-corundum solid solution, providing effective resistance to V₂O₅ corrosion. In the high-temperature zone (1100–1300°C) beneath the chrome-corundum bricks, it is advisable to install four layers of high-temperature magnesia-zirconia bricks before transitioning to conventional magnesia bricks; the forsterite layer formed within the magnesia-zirconia bricks protects the MgO, thereby slowing the rate of corrosion.

03 Improvements to the Upper Wall Structure of the Regenerator Chamber
Regenerator chambers generally employ one of three interconnection configurations: fully separated, fully interconnected, or a combined interconnection style.

01 Outer Wall
The width of the outer wall (constructed with magnesite bricks) is generally 694 mm, comprising 462 mm of dense bricks and 232 mm of insulation bricks. Given that silica bricks have poor resistance to alkali vapors and the outer wall is directly exposed to flue gas erosion, the wall thickness may be increased to 810 mm (consisting of 578 mm of silica bricks and 232 mm of insulation bricks).
Regenerator walls are typically constructed using standard bricks (230 × 114 × 65 mm) laid in a staggered pattern. When silica bricks are used for the upper section of the wall, the mortar joints become weak points vulnerable to erosion; to reduce the number of joints, the brick thickness can be increased from 65 mm to 76 mm. Consequently, the outer wall construction can alternate between thicknesses of 346 + 232 mm and 462 + 116 mm, requiring three brick types: 462 × 114 × 76 mm, 346 × 114 × 76 mm, and 230 × 114 × 76 mm.
Regarding expansion joints in the outer wall, two concentrated joints are provided between two buckstays; a single concentrated expansion joint is placed at buckstays without partition walls, while no expansion joint is placed at buckstays with partition walls—an arrangement that promotes uniform expansion during kiln heat-up. Special expansion joint bricks must be designed for these concentrated joint locations to prevent gas leakage caused by masonry defects.
At buckstays without partition walls, specially shaped anchor bricks must be designed to integrate with anchor rods and anchor beams via movable connections, thereby accommodating wall expansion. The anchor bricks are designed as large units with a total length of 578 mm, with the anchor rod embedded approximately 230 mm into the wall.

02 Partition Walls
Partition walls come in various configurations, as illustrated below: some extend to the top of the checkerwork, leaving the space above fully open; some reach the spring line of the arch, with the space above open; some terminate 100 mm below the arch (Figure a); and others extend completely through the regenerator arch (Figure b). Taking into account safety, ease of sealing after kiln heat-up, and convenience for hot repairs, the partition wall height is designed to reach the midpoint of the arch, supplemented by retaining bricks and capping bricks. After heat-up, silica-based hot-repair material can be applied directly onto the partition wall between the two arches. Compared to designs where the wall extends fully through the arch, this structure is less prone to brick collapse or flame leakage and offers superior sealing; compared to designs where the wall does not reach the arch, it is less likely to tilt and offers greater stability.

For magnesite brick partition walls, expansion joints are located at both ends of the wall; for silica brick sections, three expansion joints are distributed across the middle. Using specially designed expansion joint bricks at these locations helps minimize the risk of flame penetration. While magnesite partition walls are typically 462 mm thick, the silica brick sections can be widened to 578 mm to reduce damage caused by tilting or burning; large bricks (346×114×76 mm and 230×114×76 mm) are used during construction to minimize the number of brick joints. Structural reinforcement is achieved by interspersing two courses of I-shaped bricks every ten courses and interlocking the partition wall with the inner and outer side walls.

03 End Walls and Inner Side Walls
The end walls and inner side walls have a total thickness of 694 mm, comprising 462 mm of silica brick and 232 mm of insulation brick; standard bricks (230 × 114 × 76 mm) may be used for their construction. Specialized anchor bricks must be designed to secure these walls to the regenerator buckstays. Particular attention should be paid to the silica brick section above the port opening; the pressure within the port causes this section to expand differently than adjacent areas, making it prone to localized inward leaning. To mitigate this, an additional row of anchors and a horizontal securing beam can be installed. Zircon bricks and zircon mortar must be used at the interfaces between the silica brick walls and the inspection ports, as well as at the junctions with the port inlets, to prevent eutectic reactions.

04 Upper Gap Bricks
The interface between the side walls (both inner and outer) and the skewback bricks represents a vulnerable area of ​​the regenerator. Regarding the conventional structure of upper gap bricks shown in Figure (a), the straight joint between the arch and the wall is difficult to seal effectively after kiln heat-up; this often leads to flame leakage that damages the steel skewback supports. To protect the steel skewbacks, the skewback bricks and upper gap bricks can be redesigned to interlock with a "knife-handle" (stepped) profile,  Additionally, the upper gap bricks can be designed with an external groove, allowing for the outward extraction of specific bricks should localized heat damage occur. The span of the regenerator arch should be 70 mm narrower than the internal width of the regenerator chamber. A 5 mm expansion joint is typically provided for every three bricks in the upper gap and skewback brick courses, and forced air cooling should be applied to these bricks during operation to protect the steel skewback supports.

5 Wall Insulation
Graded insulation is recommended for the upper walls and the arch of the regenerator chamber to effectively reduce heat loss and improve thermal efficiency. Traditional insulation coatings tend to fail or peel off after a period of use, leading to diminished insulation performance; in contrast, the graded insulation system—secured internally with high-temperature adhesive and externally with angle steel—offers superior durability and insulation effectiveness. With the application of 250 mm of graded insulation, the surface temperature of the regenerator arch drops below 95°C, while the surface temperature of the regenerator walls above the second-floor level drops below 85°C.

04 Furnace Heat-up and Operational Maintenance
During the heat-up of the regenerator, care must be taken to ensure that expansion joints in the sidewalls and partition walls are free of obstructions and that the jack screws on the regenerator crown skewbacks are loosened, allowing the crown to rise along with the walls. A reasonable heating curve must be established; since silica bricks undergo volumetric expansion due to crystalline phase transformations at 200–300°C and 570°C, the heating rate should not be excessive before reaching 600°C. During furnace operation, the regenerator checkerwork requires periodic purging to ensure the channels remain unobstructed. Furthermore, sound process protocols and strict control over batch composition are essential to align the service life of the regenerator with that of the entire furnace.
05 Conclusion
Flame penetration, structural collapse, and checkerwork clogging in the regenerator partition walls and sidewalls are critical factors affecting the regenerator's service life. This paper presents a design optimization for walls where silica bricks replace magnesite bricks in the upper section of the regenerator. Measures such as increasing the thickness of the silica bricks in the target walls, designing specialized anchor bricks, improving the contact interface between the upper gap and skewback bricks, and upgrading the material quality in the upper checkerwork zone aim to maximize the regenerator's service life. During kiln heat-up and actual production, it is also crucial to monitor wall expansion joints for leakage caused by tight expansion and to perform timely repairs, alongside regular clearing of the checkerwork, to achieve optimal performance.