Selection of Refractory Materials for Glass Melting Furnace Regenerators

Temperature and Environmental Conditions of the Regenerator

Once the regenerator structure—specifically the total height *H* of the checkerwork—and the operating parameters—specifically the upper and lower temperatures (*t*1 and *t*0)—have been determined, the flue gas temperature *t*i at any given level can be estimated using the following formula; this estimation serves as one of the key criteria for selecting refractory materials. The environmental characteristics of the regenerator are summarized in Table 1; consequently, the selection of refractory materials for the regenerator must satisfy the following service conditions: (1) cyclic temperature fluctuations; (2) oxidation/reduction effects; (3) erosion by solid carryover; and (4) the impact of volatile carryover and condensates. Furthermore, the refractory materials used for the checkerwork must possess excellent heat exchange properties to ensure the required thermal efficiency of the checkerwork structure.

Rational Selection of Refractory Materials

2.1 In the upper section of the checkerwork within the regenerator chamber, the temperature drop per meter typically ranges from 80°C to 100°C, while the temperature at the very top of the checkerwork reaches a maximum of 1380°C to 1400°C. For the upper layers of the checkerwork—where temperatures exceed 1300°C—it is advisable to select direct-bonded high-purity magnesia bricks. These bricks are manufactured using high-purity electrofused magnesia grain and are fired at high temperatures (1780°C to 1800°C); they feature low contents of CaO, SiO2, and Fe2O3, and exhibit a direct-bonded periclase structure. This structure effectively prevents the ingress of gaseous and liquid phases into the brick body, thereby endowing the bricks with strong resistance to erosion and minimizing the occurrence of "capping"—the phenomenon where fine dust particles adhere to and seal the brick surface. However, SiO2 present in airborne dust particles can gradually infiltrate the micro-cracks within the brick body, altering the CaO/SiO2 ratio in the matrix phase. This leads to the formation of low-melting-point phases—such as diopside (CMS2), akermanite (C2MS2), forsterite (M2S), and wollastonite (C3MS2)—which generate significant volume expansion effects. Furthermore, under the influence of alkaline vapors, the periclase crystals within the brick body may gradually grow in size. These combined effects ultimately result in the cracking, fragmentation, and spalling of the bricks, thereby shortening their service life. The relevant chemical reaction equations and associated volume effects are presented below:

Furthermore, if the concentration of V2O5 in the heavy oil is high, the following reaction will occur with the CaO in the magnesia bricks:

Under a non-weakly reducing atmosphere, calcium aluminate exists in a liquid phase; it infiltrates the brick structure, thereby promoting the growth of periclase crystals and potentially leading to deformation of the brickwork. Currently, the batch mixtures used in domestic float glass melting furnaces often contain a high proportion of ultrafine quartz sand particles—specifically, those smaller than 0.1 mm. Furthermore, many manufacturers do not utilize granular soda ash (dense soda ash), opting instead for finer-grained varieties. Consequently, for the upper layers of the checkerwork in the regenerators—specifically at the positions corresponding to the No. 1 and No. 2 ports near the batch charging end—it is highly advisable to employ sintered zircon-mullite bricks. These bricks offer resistance against corrosion caused by airborne SiO2 particulates and prevent the formation of "nodular accretions" that adhere to and obstruct the checkerwork channels—blockages that are notoriously difficult to remove during maintenance.

2.2 Middle Layer of the Checkerwork: The temperature in the middle layer of the checkerwork ranges from approximately 800°C to 1100°C; suitable refractory materials for this zone include magnesia-chrome, forsterite, and magnesia-alumina types. Magnesia-alumina materials exhibit strong resistance to sulfate corrosion; however, due to their high cost, they have not yet been widely adopted in domestic applications. Conversely, forsterite bricks are not recommended for use at temperatures exceeding 1050°C and are therefore typically applied in the lower-temperature zones of the middle layer. The middle layer of the checkerwork is characterized by the phenomenon of repeated liquefaction and solidification of sulfates. This process is driven by the presence of residual V2O5—a carbon-chain cracking catalyst—in the heavy fuel oil; this V2O5 catalyzes the conversion of SO2 in the flue gas into SO3, which then gradually corrodes the refractory materials of the checkerwork. Furthermore, the expansion associated with the solidification of these sulfates can induce corresponding stress-related embrittlement and structural damage within the refractory bricks. 

At temperatures exceeding 1000°C, sulfates react with MgSO4 to form NaxMg(yS2O2)2; the intensity of this reaction increases as the Na2O/SO3 ratio rises. To enhance the corrosion resistance of magnesia-chrome bricks, their Cr2O3 content should be maximized, and the degree of direct bonding between mineral phases should be increased such that chrome spinel encapsulates the periclase grains; this approach effectively extends the service life of the bricks.

2.3 Lower Section of the Checkerwork and Other Areas: In the lower section of the checkerwork, temperatures remain below 800°C, and chemical erosion is relatively mild. However, the total weight of the checkerwork within a single regenerator chamber amounts to at least 40 to 50 tons, resulting in a unit load on the lower layers of the checkerwork reaching as high as 8 to 10 t/m². Furthermore, there is a need to periodically clean the checkerwork by flame-melting accumulated deposits. Consequently, it is advisable to utilize high-quality clay bricks characterized by low porosity, strong creep resistance, and excellent thermal shock resistance. To prevent contact reactions between basic bricks and clay bricks, a transition layer of high-alumina bricks may be installed between the middle and lower sections of the checkerwork. Other components of the regenerator chamber—including the crown, side walls, and rider arches—are subject to relatively milder erosion of their refractory materials. Typically, the regenerator crown is constructed using high-quality silica bricks. The side walls are generally divided into three sections: the wall section above the checkerwork (in the upper chamber space) is constructed using high-quality silica bricks, though the target wall may alternatively utilize direct-bonded magnesia-chrome bricks; for the section extending from the rider arches up to the top surface of the checkerwork, an optimal approach is to employ refractory materials identical to those used in the corresponding horizontal zone of the checkerwork itself, thereby extending the service life of the wall structure. An alternative approach involves selecting basic bricks (or direct-bonded magnesia-chrome bricks) of a grade one level lower than the adjacent checkerwork materials for the upper wall section; utilizing direct-bonded magnesia-chrome bricks for the middle section; and employing low-porosity clay bricks for the lower section. Below the rider arches, first-grade clay bricks may be selected. The rider arches themselves are typically constructed using low-porosity clay bricks, although fused-cast AZS materials—supplemented by clay-based protective rider arches—may also be utilized.

Structural Forms of Grid Structures

In glass melting furnaces, the checkerwork within the regenerator chambers is typically constructed using straight bricks arranged in either a Siemens or basket-weave pattern. However, the checker flues frequently become clogged; in cases of severe blockage, "hot repairs"—such as replacing individual checker bricks—must be undertaken. These hot repairs are performed under extremely harsh conditions and entail immense physical labor. By replacing the traditional straight bricks with octagonal tubular bricks, the checkerwork forms a chimney-like structure that is far less prone to clogging. Consequently, hot repairs are rendered unnecessary throughout the entire furnace campaign; only periodic inspections are required. Should minor blockages occur, they can be cleared using a flame-melting technique applied from the bottom upward within the lower section of the checkerwork. One of the key energy-saving technologies for large-scale glass melting furnaces is the widespread adoption of tubular checker bricks. Octagonal tubular checker bricks retain the same physicochemical properties as traditional straight bricks while offering ease of installation. With the bricks aligned vertically, the structure features virtually no unsupported overhangs, ensuring exceptional stability. Furthermore, this design maximizes the heat-exchange surface area per unit volume of checkerwork and offers an extended service life, factors that have garnered increasing attention within the industry. The wall thickness of the tubular bricks can be reduced to as little as 40 mm; this not only reduces the overall weight of the checkerwork unit but also enhances its thermal conductivity. In terms of construction costs, tubular checkerwork is approximately 15% more expensive than the basket-weave configuration, yet approximately 15% less expensive than the cross-bond configuration. Regarding energy efficiency, however, the performance of tubular checkerwork is comparable to that of the cross-bond configuration. While the thermal consumption of basket-weave checkerwork typically increases by 1% to 2% annually, that of tubular checkerwork increases by only about 0.5% per year; this significantly slower rate of "aging" results in substantial energy savings. In the structural design of the regenerator chamber, particular attention must be paid to the interface between the tubular checker bricks and the rider arch. A transitional zone—approximately one meter in height—constructed using straight bricks arranged in a Siemens pattern should be established between the tubular checkerwork and the rider arch. This arrangement ensures a smooth, unobstructed flow through the vertical flues and improves the uniformity of gas distribution as it enters the tubular checkerwork, thereby fully leveraging the inherent advantages of the tubular bricks and enhancing the overall thermal efficiency of the glass melting furnace.

Conclusion

Currently, the regenerators in domestic glass melting furnaces in China have gradually transitioned from traditional uptake structures to box-type partitioned or interconnected configurations. Further strengthening research into the rational selection and zonal application of refractory materials for regenerators—along with the development of new material varieties—is essential to meet the requirements for enhancing regenerator efficiency and service life. This endeavor holds significant importance for the domestic production of high-quality glass, as well as for the timely realization of developmental goals characterized by low energy consumption, high thermal efficiency, large-tonnage production scales, and extended furnace lifespans.