Causes of Damage to Checker Bricks in Horseshoe-Flame Glass Furnaces and Procedures for Hot Repair and Replacement

Cause of damage

There are numerous reasons for the premature deterioration of checker bricks in the regenerator chambers of horseshoe-flame furnaces; an analysis based on actual operating conditions follows:
1. Fuel-related factors
Excessive harmful impurities in the fuel. For instance, high impurity levels in coal-tar/petroleum-blend oils accelerate chemical reactions with the refractory materials. This also leads to a significant increase in suspended particulates in the flue gas, making the exhaust highly visible under clear weather conditions. In one instance, a furnace operating on high-quality fuel showed no signs of flame leakage through the regenerator arch, and the checkerwork remained largely unobstructed throughout the campaign. However, after switching to a coal-tar/petroleum blend, flame leakage occurred at the expansion joints of the silica brick arch crown within just one year. Despite frequent maintenance, the checkerwork suffered from severe clogging, with blockage rates exceeding 70% during the later stages of the furnace's service life. Similar phenomena were observed across multiple furnaces.

2. Design Factors
The checkerwork volume in the regenerator was undersized. For a specific 80 m² horseshoe-flame furnace, the checkerwork volume was designed at only 160 m³, resulting in high energy consumption and rapid clogging. After expanding the regenerator volume to 240 m³ in one of these units, clogging was significantly reduced, and the daily maintenance workload decreased substantially. The structure of the intermediate partition wall was flawed; settlement of the regenerator foundation or leakage of hot gases after a period of operation caused the upper brickwork to collapse.
The design of the pre-melting zone at the single-side charging port and the selection of the charging machine were inappropriate; excessive batch carryover (dust/fines) entered the regenerator on the opposite side, causing clogging.
The selection of refractory materials was mismatched. For instance, the upper checker bricks exhibited poor slag resistance and were prone to burn-out when low-quality fuel was used.
The glass melt level was set too high. During furnace operation, the melt surface was too close to the flame; the strong impact of the flame against the melt surface caused significant batch carryover into the regenerator.
The clearance between the checkerwork and the regenerator wall was insufficient. Following the furnace heat-up process, the checkerwork expanded and pressed tightly against the wall, leading to deformation and eutectic reactions; this made the wall prone to burn-through and caused misalignment of the checker openings, further accelerating checkerwork damage.
Materials with high thermal shock resistance should be selected for the rider arches (grate arches). Since daily maintenance often involves clearing the checkerwork via methods such as poking/rodding, arches with poor thermal shock resistance are prone to damage. Many furnaces now utilize materials such as sillimanite for these arches.

3. Raw Material Issues
Excessive ultra-fine powder in raw materials, improper moisture content or temperature of the batch mixture, contaminated cullet, use of light soda ash, etc.
4. Furnace Maintenance
Water-cooling of checkerwork. Water-cooling must not be used to lower the temperature of checkerwork during regenerator maintenance, particularly when magnesite materials are used.
5. Furnace Operation
Operational practices involving long flames and high furnace pressure. The flame continues to burn after turning into the regenerator, combined with excessive furnace pressure.
6. Furnace Construction
Changing checkerwork materials or selecting low-quality products without approval from the design department. Failure to strictly level the rider arches, wall inclination, or foundation settlement can also lead to misalignment of the checker openings.

Hot Replacement of Checker Bricks
As furnace technology advances, the sections of this horseshoe-flame furnace in contact with the glass still require protection during the later stages of the furnace's service life. However, severe clogging in one of the regenerator chambers made melting difficult and caused furnace pressure to remain persistently high. Conventional measures such as air purging or mechanical clearing were ineffective. Given the high costs and long downtimes associated with cooling the furnace for repairs, a hot-replacement method for the checker bricks was adopted.
The checker bricks could be downgraded in specification, allowing for the use of reclaimed bricks (provided they had regular shapes) or clay-based products. The primary technique involved inserting a 2520 high-temperature resistant stainless steel plate through the port expansion joint to create a partial partition, while utilizing cold combustion air, to facilitate the rapid replacement of the checker bricks.

Hot Repair Procedure
1.  **Opening the regenerator wall:** A diamond chain saw is used to create clean, precise openings efficiently without requiring excessive water cooling on the wall structure. The contractor operates in continuous 24-hour shifts with adequate staffing; the client typically assists in removing and disposing of old brickwork. Openings must also be made on the side opposite the small furnace (port), and temporary combustion-assist fans may need to be installed. Debris removal must be prompt, and care taken to secure upper brickwork to prevent collapse.
2.  **Cooling the checkerwork:** Portable Venturi fans are used for cooling. Small excavators are employed to clear the checkerwork, ensuring high safety and speed, while refractory materials are cleaned up manually.
3.  **Repairing and leveling the rider arches:** The transition layer must be stacked carefully. The upper checker bricks are laid rapidly; construction standards may be relaxed slightly to allow for immediate inspection as work progresses, with final acceptance occurring upon sealing the access opening.
4.  **Stacking checker bricks:** Bricks are stacked up to a level 2 meters below the small furnace hearth. The stacking height is determined primarily by personnel safety considerations and should not be excessive.
5.  **Sealing the repair opening:** The sealing process takes a total of four days. No reversal of airflow occurs during the hot repair. Once construction is complete, airflow reversal and checkerwork preheating begin at the appropriate time.
6.  **Resuming production:** On the fifth day, all forming equipment is activated; on the sixth day, products meet quality standards, and full production resumes.

Related Adjustments
The hot replacement of checker bricks in a horseshoe-flame furnace must be coordinated with other adjustments. First, ensure the throat remains unobstructed; second, maintain the highest possible furnace temperature to extend production time and minimize the time required for production recovery. Make effective use of cullet and mitigate the impact of cold combustion air.
1. Inspect critical areas, such as the throat. Avoid altering the operating conditions of the throat as much as possible. Inspect and document the condition of all steel structures on the day of the hot repair. Do not reduce the volume of cooling air or water.
2. Gradually increase the cullet ratio and appropriately reduce fuel input to prevent the temperature in the regenerator on the opposite side from becoming excessively high.
3. Maintain the proper glass melt level. Ensure adequate heating in the working end and maintain the correct temperature in the forehearth.

Results of the Hot Repair
The hot repair achieved the following results:
1. Flame brightness and rigidity were significantly enhanced; product color stability improved; bubble formation was reduced; and surface finish and brightness were improved.
2. Kiln pressure stabilized, meeting set requirements and reducing burn damage in the kiln's combustion space.
3. Output increased.
4. Energy consumption decreased by 5%.
Hot-state checker brick replacement has been implemented on multiple horseshoe-flame furnaces. The total cost—including all maintenance expenses and losses due to reduced production—was only about one-fifth of the cost of a shutdown overhaul, thereby improving economic efficiency and extending the service life of the furnaces.