Methods for Extending the Service Life of Fused Casting AZS Tank Wall Blocks in Glass Melting Furnaces

Methods to Mitigate Erosion of Pool Wall Tiles

Slowing the corrosion rate of tank wall bricks—or, in other words, enhancing the corrosion resistance of electro-fused bricks—is key to extending their service life. It is well known that lowering the operating temperature of these bricks is a primary measure for prolonging their lifespan. However, given the variations in location, service stage, and operating conditions, different cooling methods must be employed to achieve the desired cooling effect.

1. Rational Forced-Air Cooling Method (System-Wide Cooling)

This method targets the uninsulated outer surface at the uppermost section of the tank wall (specifically, the top 270 mm). In typical horseshoe-flame furnaces, heating occurs at the surface of the molten glass, resulting in significantly higher temperatures in the upper glass layers compared to the lower ones. Furthermore, processes such as silicate formation and glass fining generate substantial gas bubbles, and vigorous thermal convection occurs within the upper glass melt; consequently, the upper section of the tank wall is prone to rapid corrosion. To address this, it is essential to select appropriate cooling fans and design adjustable air ducts capable of delivering the necessary airflow to specific areas. This cooling system should be installed and activated when the furnace temperature reaches 250–300°C, with the airflow volume gradually increased as the temperature rises.

It is necessary to abandon the outdated practice of waiting until the mid-to-late stages of furnace operation—when the tank wall bricks already show a distinct dull red glow and have undergone partial corrosion—to install and activate cooling. Instead, cooling should commence gently and increase gradually to minimize or prevent brick damage caused by thermal stress resulting from temperature gradient fluctuations.

2. Spot-specific, concentrated, forced-air cooling method

Based on the quality of domestically produced fused-cast AZS bricks and operational experience from manufacturers, the typical service life of AZS bricks ranges from three to five years. After two years of operation—marking the mid-to-late stage of the furnace's campaign—glass leakage may occur at specific locations due to inherent brick variations (such as internal voids) or issues arising during masonry and heat-up (such as excessively wide or improperly treated joints). To address this, a spot-specific, concentrated, forced-air cooling method can be employed.

At one facility, a furnace began leaking glass at the expansion joint of a tank wall corner after two years and three months of operation; by the two-and-a-half-year mark, leakage was also observed at a large brick joint in the tank wall. Implementing spot-specific, concentrated, forced-air cooling proved to be a highly convenient solution, effectively increasing the viscosity of the molten glass and lowering the operating temperature of the bricks. Following this treatment, no further issues occurred for the remainder of the furnace's service life.

3. Air-Water Mist Cooling Method

Certain areas of the melting tank—such as the throat—are particularly susceptible to rapid erosion and are difficult to repair. Although design measures like lowering the position or tilting the structure were adopted to improve operating conditions, the cover bricks were previously ruined after only 2.5 years of service due to intense mechanical scouring and gas-driven "drilling" erosion. Even with forced-air cooling applied from the start, the desired results were not achieved. During this cold repair, a semi-insulated configuration was adopted for the throat (replacing the previous setup where AZS bricks were fully exposed): the AZS bricks were encased in high-alumina bricks and secured with a steel structure. Upon restarting operations, an air-water mist cooling method was decisively implemented; a schematic of the specific setup is shown in Figure 2.

This method is simple to construct, offers stable control, and delivers significant cooling efficiency, while avoiding the brick damage often caused by improper direct water cooling. The latter issue is the primary reason why manufacturers typically avoid water cooling; notably, the same throat section remained in service for over four years following this cold repair.

4. Water-Mist Cooling Method

This method is primarily applicable to the upper and middle sections of the tank wall blocks during the later stages of the melting furnace's operation. Since these sections already feature varying degrees of thermal insulation and are reinforced with external steel plates, the rate of glass melt corrosion is relatively slow; consequently, no issues arise—nor are any measures required—during the early stages of the campaign. However, by the third year following a cold repair, glass melt began to seep through the upper and middle sections of the tank wall. A common characteristic of these leak points was that they almost invariably occurred at the top edge of the insulation bricks; clearly, the melt was escaping via a channel formed between the fused-cast refractory blocks and the insulation layer. This phenomenon indicated severe corrosion of the fused-cast blocks in that area. Given the presence of external insulation, forced-air cooling proved ineffective. Removing the reinforcement bricks would have been labor-intensive and hazardous, while direct water cooling was difficult to control. After evaluating the options, the water-mist cooling method was adopted, allowing these sections to operate safely until the end of the campaign.

The water-mist cooling method involves atomizing ambient-temperature tap water using an atomizer and spraying it directly onto the leak site. The specific procedure is as follows:

(1) Modify an atomizing oil gun based on the principles of fuel oil atomizer design. Since water has a much lower viscosity than oil and atomizes easily, the device can be configured as a wide-angle, broad-coverage flat-nozzle sprayer—capable of a 45° spray angle—to meet the specific cooling requirements of the tank wall blocks.

(2) Install the atomizer 200–300 mm away from the tank wall blocks with an upward tilt, ensuring the core of the atomized spray stream targets the leak site for optimal cooling efficiency.

Adjust the atomizer according to specific cooling requirements; the guiding principle is to ensure the spray hits the target area without causing water droplets to drip or splash. Testing determined that maintaining an air pressure 3 to 5 times higher than the water pressure yields the best atomization results.

Compared to the aforementioned air-water mist method, this approach is more streamlined, featuring a simple system, straightforward operation, and easy adjustability. It requires no additional equipment, offers low failure rates, and operates silently. In terms of operational results, water consumption for atomization is low and the cooling effect is excellent; furthermore, it avoids the formation of water runoff—often caused by unstable direct water spraying—where water flows in streams.

5. External Brick Reinforcement

External brick reinforcement is a common and effective method used by many manufacturers to extend the service life of melting furnaces. When a specific furnace reached the end of its service life, external reinforcement was applied to several critical areas—such as the corners of the charging port and the uppermost sections of the sidewall bricks opposite the charging port. When applying this reinforcement, it is crucial to preheat the bricks before installation, particularly in the case of electro-fused AZS bricks.

6. Strengthening Daily Management

(1) Assign dedicated personnel to monitor furnace operations 24 hours a day, ensuring the proper functioning of cooling systems across all sections of the melting tank sidewalls.

(2) Strictly maintain stable furnace pressure and glass melt levels.

(3) Strictly control the stability of cooling airflow and atomized water usage to ensure effective cooling.

(4) Use temperature measuring instruments to record the external surface temperature of sidewall bricks at fixed locations and times daily; conduct periodic comparative analyses to monitor brick erosion rates.

(5) In the event of power outages, fan replacements, or water supply interruptions, avoid drastic fluctuations in cooling air and water flow; upon restarting, gradually restore operations to normal levels through a step-by-step process.

(2) Implementing measures such as air-mixed water mist cooling and shower cooling on the sidewalls of this electric melting furnace yielded excellent results, demonstrating the viability of using atomized water as a cooling medium for the sidewall bricks.

(3) Particular attention must be paid to the following: if water atomization is poor or system control is unstable, excessive water flow can occur, leading to over-cooling of the bricks. In mild cases, this causes micro-cracks; in severe cases—especially with thinner bricks (less than 50 mm)—steep temperature gradients and high thermal stresses can easily cause the bricks to fracture. Furthermore, if the local temperature of the molten glass drops too low, the resulting increase in viscosity creates a stagnant layer; if this material subsequently enters the forming flow, it can cause defects such as streaks or cords in the finished products. Additionally, cooling over a large area results in significant heat loss, which adversely affects thermal efficiency.

(4) Further research is required to improve atomizer performance—specifically by achieving ultra-fine atomization of the water medium and ensuring uniform mixing with the airflow. Developing atomizers with robust control systems that facilitate easy operation and ensure moderate brick cooling remains a task requiring extensive effort.