E-glass (alkali-free fiberglass) production in tank furnaces is a complex, high-temperature melting process. The melting temperature profile is a critical process control point, directly influencing glass quality, melting efficiency, energy consumption, furnace life, and the final fiber performance. This temperature profile is primarily achieved by adjusting flame characteristics and electric boosting.
I. Melting Temperature of E-Glass
1. Melting Temperature Range:
The complete melting, clarification, and homogenization of E-glass typically require extremely high temperatures. The typical melting zone (hot spot) temperature generally ranges from 1500°C to 1600°C.
The specific target temperature depends on:
* Batch Composition: Specific formulations (e.g., presence of fluorine, high/low boron content, presence of titanium) affect melting characteristics.
* Furnace Design:Furnace type, size, insulation effectiveness, and burner arrangement.
* Production Goals: Desired melting rate and glass quality requirements.
* Refractory Materials: The corrosion rate of refractory materials at high temperatures limits the upper temperature.
The fining zone temperature is usually slightly lower than the hot spot temperature (approximately 20-50°C lower) to facilitate bubble removal and glass homogenization.
The working end (forehearth) temperature is significantly lower (typically 1200°C – 1350°C), bringing the glass melt to the appropriate viscosity and stability for drawing.
2. Importance of Temperature Control:
* Melting Efficiency: Sufficiently high temperatures are crucial for ensuring complete reaction of the batch materials (quartz sand, pyrophyllite, boric acid/colemanite, limestone, etc.), full dissolution of sand grains, and thorough gas release. Insufficient temperature can lead to “raw material” residue (unmelted quartz particles), stones, and increased bubbles.
* Glass Quality: High temperatures promote clarification and homogenization of the glass melt, reducing defects such as cords, bubbles, and stones. These defects severely impact fiber strength, breakage rate, and continuity.
* Viscosity: Temperature directly influences the viscosity of the glass melt. Fiber drawing requires the glass melt to be within a specific viscosity range.
* Refractory Material Corrosion: Excessively high temperatures drastically accelerate the corrosion of furnace refractory materials (especially electrofused AZS bricks), shortening furnace life and potentially introducing refractory stones.
* Energy Consumption: Maintaining high temperatures is the primary source of energy consumption in tank furnaces (typically accounting for over 60% of total production energy consumption). Precise temperature control to avoid excessive temperatures is key to energy saving.
II. Flame Regulation
Flame regulation is a core means of controlling the melting temperature distribution, achieving efficient melting, and protecting the furnace structure (especially the crown). Its main goal is to create an ideal temperature field and atmosphere.
1. Key Regulation Parameters:
* Fuel-to-Air Ratio (Stoichiometric Ratio) / Oxygen-to-Fuel Ratio (for oxy-fuel systems):
* Goal: Achieve complete combustion. Incomplete combustion wastes fuel, lowers flame temperature, produces black smoke (soot) that contaminates the glass melt, and clogs regenerators/heat exchangers. Excess air carries away significant heat, reducing thermal efficiency, and can intensify crown oxidation corrosion.
* Adjustment: Precisely control the air-to-fuel ratio based on flue gas analysis (O₂, CO content). E-glass tank furnaces typically maintain flue gas O₂ content at around 1-3% (slightly positive pressure combustion).
* Atmosphere Impact: The air-to-fuel ratio also influences the furnace atmosphere (oxidizing or reducing), which has subtle effects on the behavior of certain batch components (like iron) and glass color. However, for E-glass (requiring colorless transparency), this impact is relatively minor.
* Flame Length and Shape:
* Goal: Form a flame that covers the melt surface, possesses certain rigidity, and has good spreadability.
* Long Flame vs. Short Flame:
* Long Flame: Covers a large area, temperature distribution is relatively uniform, and causes less thermal shock to the crown. However, local temperature peaks might not be high enough, and penetration into the batch “drilling” zone might be insufficient.
* Short Flame: Strong rigidity, high local temperature, strong penetration into the batch layer, conducive to rapid melting of “raw materials.” However, coverage is uneven, easily causing localized overheating (more pronounced hot spots), and significant thermal shock to the crown and breast wall.
* Adjustment: Achieved by adjusting burner gun angle, fuel/air exit velocity (momentum ratio), and swirl intensity. Modern tank furnaces often use multi-stage adjustable burners.
* Flame Direction (Angle):
* Goal: Effectively transfer heat to the batch and glass melt surface, avoiding direct flame impingement on the crown or breast wall.
* Adjustment: Adjust the pitch (vertical) and yaw (horizontal) angles of the burner gun.
* Pitch Angle: Affects the flame’s interaction with the batch pile (“licking the batch”) and coverage of the melt surface. An angle that is too low (flame too downward) might scour the melt surface or batch pile, causing carryover that corrodes the breast wall. An angle that is too high (flame too upward) results in low thermal efficiency and excessive heating of the crown.
* Yaw Angle: Affects flame distribution across the furnace width and the hot spot position.
2. Goals of Flame Regulation:
* Form a Rational Hot Spot: Create the highest temperature zone (hot spot) in the rear part of the melting tank (usually after the doghouse). This is the critical area for glass clarification and homogenization, and acts as the “engine” controlling the glass melt flow (from the hot spot towards the batch charger and working end).
* Uniform Melt Surface Heating: Avoid localized overheating or undercooling, reducing uneven convection and “dead zones” caused by temperature gradients.
* Protect Furnace Structure: Prevent flame impingement on the crown and breast wall, avoiding localized overheating that leads to accelerated refractory corrosion.
* Efficient Heat Transfer: Maximize the efficiency of radiant and convective heat transfer from the flame to the batch and glass melt surface.
* Stable Temperature Field: Reduce fluctuations to ensure stable glass quality.
III. Integrated Control of Melting Temperature and Flame Regulation
1. Temperature is the Goal, Flame is the Means: Flame regulation is the primary method for controlling the temperature distribution within the furnace, especially the hot spot position and temperature.
2. Temperature Measurement and Feedback: Continuous temperature monitoring is conducted using thermocouples, infrared pyrometers, and other instruments positioned at key locations in the furnace (batch charger, melting zone, hot spot, fining zone, forehearth). These measurements serve as the basis for flame adjustment.
3. Automatic Control Systems: Modern large-scale tank furnaces widely employ DCS/PLC systems. These systems automatically control the flame and temperature by adjusting parameters like fuel flow, combustion air flow, burner angle/dampers, based on preset temperature curves and real-time measurements.
4. Process Balance: It’s essential to find an optimal balance between ensuring glass quality (high-temperature melting, good clarification and homogenization) and protecting the furnace (avoiding excessive temperatures, flame impingement) while reducing energy consumption.
Post time: Jul-18-2025
