Maintenance Measures for the Late-Stage Operation of Float Glass Melting Furnaces

1.1 Furnace Tank Wall Patching
In domestic practice, the primary reason for undertaking a cold repair on a melting furnace is severe refractory wear on the tank walls; consequently, maintaining the integrity of the tank walls is crucial for extending the furnace's service life. Furnace A has a designed service life of eight years; as of May 2019, it had been in operation for seven years and nine months—approaching the end of its designed lifespan. Inspections of the tank walls extending from the charging end to the back wall revealed severe erosion on the walls adjacent to the #3 through #5 burners on both sides, with the thinnest section measuring a mere 34 mm. The tank walls of Furnace A had previously undergone patching twice; a third patching operation is now scheduled. Based on the specifications of the available patching bricks, the planned patching dimensions are a thickness of 75 mm and a height of 700 mm—specifically comprising two vertical courses of 400 mm and 300 mm (upper and lower layers, respectively). This assembly will be supported by 140 mm wide channel steel, a configuration that also leaves sufficient vertical clearance to accommodate a potential fourth layer of patching in the future.

Following the patch repairs to the tank wall bricks—and even after the furnace had reached its designed service life—operations were successfully extended for an additional six months without any signs of tank wall reddening. Based on projections, and assuming enhanced air cooling is implemented, the safe operation of the tank furnace walls can be further ensured by conducting a fourth round of brick patching after an additional year of extended operation.

1.2 Ceramic Welding

As a thermal repair material, ceramics can adhere to damaged areas of refractory linings. The melting process generates an exothermic reaction capable of reaching temperatures of up to 2200°C; consequently, ceramic materials can be utilized to repair refractories composed of silica, alumina, AZS, and magnesia. Since the welding process does not require a furnace shutdown, its impact on production is minimal.

Furnace A periodically engages ceramic welding specialists to diagnose and perform ceramic repairs on severely eroded refractory components—specifically the L-shaped suspended walls, main arches, breast walls, and regenerators. At the six-year mark of its operation, ceramic repairs were performed on the L-shaped suspended wall at the charging end. At seven years and one month, repairs were carried out on the arch crowns and skewbacks of regenerators #1 and #5 on the south side of the melting furnace; the arch and skewback of regenerator #1 on the north side; the first section of the main arch over the melting tank; and the L-shaped suspended wall at the charging end. At eight years and three months, repairs were conducted on the nose section of the L-shaped suspended wall; the arch crown of regenerator #1 on the north side; the skewbacks of regenerators #3 and #4 on the south side (including the partition wall for #4); and the rear flat arch of regenerator #5 on the south side. Following these repairs, the eroded areas were restored, and "rat holes" were successfully patched. Photographs illustrating the condition before and after the ceramic welding are presented in Figures 2 and 3.

1.3 Checkerwork Unclogging

During the latter stages of furnace operation, slag accumulation within the checkerwork pores accelerates rapidly, leading to severe blockages and localized structural collapse. This not only compromises the stability of flame control but also carries the risk—should operational errors occur—of exacerbating the situation and necessitating an early cold repair. To address this, a combined approach utilizing high-temperature melting and manual clearing methods is employed to unclog the checkerwork, thereby ensuring unimpeded airflow within the structure during the furnace's final operational phase. As Furnace A enters its latter stages of operation, it becomes necessary to unclog the severely blocked checkerwork in the regenerators approximately every six months (Figure 4 illustrates the condition of the checkerwork before and after the unclogging process). In addition to intensifying routine inspections to facilitate the timely repair of detected "rat holes" in the arch crowns and areas where slag has burned through the brickwork, it is essential to establish a rational schedule and methodology for regenerator unclogging to ensure the safe and normal operation of the regenerator system.

1.4 Installation of Monitoring Equipment

1.4.1 Real-time Monitoring System

During the later stages of the furnace's operation, nine monitoring cameras were successively installed at specific locations: along three axial lines at the bottom of the melting tank's charging end, at the four corners of the melting tank's main arch, and on the eastern side of the walkway beneath the bridgewall. These cameras were positioned to monitor for safety hazards such as glass leakage through the tank bottom, arch burnout, and material leakage through the tank walls. By monitoring key areas—including the furnace arch, tank bottom, and bridgewall—from the central control room, on-duty personnel are able to detect potential hazards at an early stage.

1.4.2 Thermal Resistance Alarm and Monitoring System

Eighteen thermal resistors were installed on the tank walls across various sections—specifically the six bridgewalls of the melting tank, the refining zone, the throat, and the cooling zone. Temperature alarm thresholds were established, enabling monitoring personnel in the central control room to promptly proceed to the site to verify the operational status of the tank walls whenever temperature fluctuations are detected.

1.4.3 Infrared Thermometers

Eleven infrared thermometers were installed at the bottom of the refining zone (near the No. 1 bridgewall) to facilitate real-time temperature monitoring. By analyzing temperature curves, monitoring personnel can track the progression of refractory brick erosion, thereby enabling the implementation of preventive maintenance measures in advance.

Case Study: When Furnace A had been in operation for 8 years and 4 months, a minor material leak occurred in the tank wall at the corner bricks of the refining zone throat. The thermal resistance monitoring system triggered an immediate alarm; on-duty operators promptly addressed the leakage site, thereby preventing the incident from escalating and gaining valuable time for emergency repairs.

1.5 Addition of a Bubbler Cooling System

Due to the prolonged operation of the bubbler system, the inner walls of the bubbling tubes had suffered severe corrosion. Consequently, the return water temperature in certain tubes exceeded permissible limits. Simply lowering the temperature of the circulating water in the cooling tower could not fundamentally eliminate the inherent risk of a bubbler tube burning through. After Furnace A had been in operation for eight years and six months, Bubbling Tube #3 did indeed burn through. During the process of extracting the tube from below, a small amount of molten glass began to leak out along the bubbler brick; the extraction operation was immediately halted, and the bubbling tube was reinserted into the brick. Analysis indicated that, due to Furnace A's long-term production of ultra-clear glass, the furnace bottom had suffered severe erosion, and the remaining thickness of the bottom bricks could not be accurately assessed prior to the scheduled furnace shutdown. To ensure safety, a bubbler cooling air system was subsequently installed to prevent molten glass leakage and avert potential safety hazards.

Conclusion
Kiln maintenance requires the formulation of specific measures tailored to the type of kiln and the extent of damage to its various components. In the case of the ultra-white float glass kiln discussed in this paper, measures—including the patching of furnace tank wall bricks, ceramic welding repairs, the unclogging of regenerator checkerwork, the installation of safety monitoring equipment, and the addition of a bubbler cooling system—successfully ensured the safe operation of the kiln beyond its designed service life, thereby generating cost savings for the enterprise.