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Low-Frequency Pulse Foaming Technology Equipment and Application for a Novel Glass Tank Furnace

Foaming technology in glass tank furnaces emerged as a forced melting technique in the 1950s. After more than half a century of development and continuous improvement, it has become an indispensable measure for forced melting in modern glass tank furnaces.

In China, foaming technology was first applied to the melting of brown and green bottle glass in the mid-1970s and has since been widely used in melting various types of glass.

Over the past three decades, China’s foaming technology for glass tank furnaces has undergone several generations of research and improvement, including continuous foaming, pulse foaming, and low-frequency pulse foaming. It has now reached a considerable level of maturity and perfection.

Especially with the introduction of low-frequency pulse foaming technology and equipment, it has been widely praised by users due to its closer adherence to melting process requirements, ensuring high-quality molten glass, convenient operational control, stable and safe operation, and more reasonable equipment compatibility.

This article discusses and evaluates the impact of tank furnace foaming technology on glass melting and molten glass quality, focusing on continuous foaming, pulse foaming, and low-frequency pulse foaming. It serves as a reference for glass production enterprises when choosing foaming technology and equipment.

The Interrelationship between Glass Tank Furnace Foaming Technology and Melting

Foaming technology in tank furnaces is widely recognized for its role in forced melting, increasing furnace melting rates, improving molten glass quality, saving energy, and reducing melting costs. However, analyzing and discussing the most suitable foaming methods for the glass melting process is crucial to fully harness the benefits of foaming technology.

(1) The Role of Foaming Technology in the Glass Melting Process

  • Improving Homogeneity and Product Quality: Glass produced in foaming tank furnaces exhibits higher homogeneity, with a one-grade increase in cross-sectional uniformity, typically reaching B-grade. The density difference in glass is reduced, reaching Δd≤5×10-4. Visible stones in glass are significantly reduced, and bubbles can be completely eliminated.
  • Increasing Furnace Melting Rate and Output: Furnace melting rates can generally be increased by 5–15% when employing foaming technology.
  • Reducing Furnace Fuel Consumption for Energy Savings: Foaming furnaces typically reduce energy consumption (specific energy consumption) by 5–10%.
  • Adjusting Glass Formulation to Reduce Raw Material Costs: Foaming technology increases the oxidizing capacity and gas volume of molten glass, allowing for a reduction in decolorants and clarifying agents in the raw materials. This cost-effective approach enhances the quality of clarifying agents, providing a clear glass quality.
  • Enhancing Glass Recycling: Foaming technology increases the blending ratio of crushed glass, providing favorable conditions for using externally purchased crushed glass to produce high-quality glass.
  • Shortening Furnace Charging Time: Foaming technology significantly reduces the time required to charge the furnace, allowing for the rapid production of required high-quality molten glass, ensuring uniform composition and color.

(2) Why Does Foaming Technology Have a Positive Impact on Quality, Productivity, and Energy Efficiency?

Within a glass tank furnace, the fundamental principle of melting and homogenizing relies on the radiative heat transfer from the flame to the raw materials and molten glass, as well as the flow of molten glass within the melting pool. All measures for forced melting and improving molten glass quality aim to maximize the heat obtained from raw materials, raise the temperature of molten glass, strengthen the flow of molten glass, and make the thermal convection of molten glass more reasonable and stable.

Foaming technology achieves this by introducing a large air bubble from the bottom of the furnace to the molten glass surface, creating a mechanical circulation flow as the bubble ascends. When this mechanical circulation flow coincides with the liquid fountain area of the melting pool, the thermal convection of the molten glass is intensified, contributing to increased absorption of heat by the surface of the molten glass. This, in turn, promotes heat transfer between different layers within the molten glass, raising the overall temperature of the molten glass and ensuring the orderly progression of each stage of the glass melting process.

Foaming is generally combined with a melting tank, and the refractory block near the furnace wall serves to block the reflux of molten glass, maintaining a high-temperature state in the clarifying zone of the melting pool.

(3) Low-Frequency Pulse Foaming Yields the Best Results in Improving Molten Glass Quality and Forced Melting Process

Practice has shown that several types of foaming methods in domestic furnaces can effectively contribute to forced melting and enhance the uniformity of molten glass. However, the degree of effectiveness varies among different foaming methods. To achieve optimal results in improving molten glass quality, increasing melting capacity, and reducing energy consumption, several characteristics and conditions should be considered.

  • Foaming Bubble Formation: The production of foaming bubbles should involve a large bubble rising from the furnace bottom, reaching the molten glass surface before bursting. This contrasts with a multitude of small bubbles continuously aggregating due to the viscosity and surface tension of molten glass. The latter can lead to the entry of small bubbles into the production flow during their ascent, causing defects in the final product due to the inability to discharge.
  • Foaming Point Selection: The foaming point should coincide with the furnace’s hot spot, namely, the liquid fountain area of the molten glass. This ensures the fundamental orderliness of the glass melting process.
  • Foaming Frequency and Diameter Control: The foaming frequency and bubble diameter should be individually adjustable. They should not be affected by the temperature and viscosity of molten glass, being the main factors for the stable operation of the foaming process. Foaming equipment should have a wide adjustment range, high accuracy, strong safety sensitivity, and meet the characteristics of foaming process stability.
    Under normal circumstances, foaming in the furnace should operate stably at a lower frequency and with larger bubble diameters to achieve the best foaming effects.
  • Durability of the Foaming System: The foaming system, especially the foaming device (foaming pipe), should meet furnace life requirements, satisfy daily melting process needs, and ensure long-term safe operation. The most common issue in foaming devices is the clogging of foaming pipes. Clogging can occur due to two reasons: high-temperature molten glass entering the foaming pipe’s nozzle, which is prone to blockage faults when gas is stopped for some reason; impure gases entering the foaming pipe and causing fouling blockages. Fouling blockages result from inadequate gas purification. Current domestically produced purification equipment can provide sufficiently clean gases. While various measures have been proposed over the years to address molten glass clogging, the effects have been minimal. Therefore, in the event of foaming pipe blockage, the only solution is to adopt the heat exchange tube replacement approach.
    To achieve the optimal effect of foaming technology, it is essential to use anti-blocking foaming devices. These devices can protect against blockages even in the event of a foaming system gas interruption, preventing molten glass blockages.
  • Control System for Foaming, the foaming control system should adopt modern microelectronic automatic control, completely eliminating the mismatch problems associated with electrical component combinations in outdated control devices. This ensures the system’s lifespan is thoroughly guaranteed, and precision is further enhanced. The system should possess high configuration, comprehensive functionality, flexible regulation, accurate control, high precision, intuitive monitoring, safe operation, and a long operational lifespan. Notably, it should provide various automatic operation modes that are suitable for different process conditions.
  • Coordination of Furnace Foaming with Kiln Bricks

According to the aforementioned six criteria, low-frequency pulse foaming technology and equipment are the most suitable for meeting the requirements. It is advisable to coordinate furnace foaming with kiln bricks.

Three Types of Foaming Technology in Glass Furnaces in China

China’s foaming technology for glass furnaces has evolved through three types since the 1970s, namely continuous foaming, pulse foaming, and low-frequency pulse foaming, reflecting the development process of foaming technology in glass furnaces.

  1. Continuous Foaming: Introduced in the 1970s and 1980s, it was the initial form developed through collaboration between glass production enterprises and research institutions. It offers advantages such as simplicity, easy maintenance, and low investment. However, it exhibits notable shortcomings and deficiencies in its effectiveness in glass melting, operational control, and fault prevention.
  2. Pulse Foaming: Developed to address the issues of continuous foaming, this type drew on advanced foaming technology experiences from abroad. It achieved significant improvements in control methods and operational precision. Despite these advancements, there were still evident shortcomings in terms of system operational lifespan, operational modes, and safety. This technology was widely used in China’s glass industry starting from the 1990s.
  3. Low-Frequency Pulse Foaming Technology: Successfully developed and widely applied in the early 21st century. Its prominent features include:
    • Utilization of anti-blocking self-protective foaming devices (a key element for achieving true intermittent low-frequency pulse foaming).
    • Adoption of modern microelectronic control technology.

These advancements brought the foaming technology and equipment to a level that meets the comprehensive application requirements of glass production facilities. It has become an ideal supporting device in glass production.

Application of Low-Frequency Pulse Foaming

In the face of increasingly fierce competition, glass production enterprises have raised their requirements for glass quality, furnace melting rate, and energy efficiency. The low-frequency pulse foaming technology and equipment, as a handy technological means with its distinct advantages, have played a significant role in glass furnaces for bottles, flat glass, drawn glass, electronic glass, alkali bubble glass, etc. It has received unanimous recognition from user units and is increasingly adopted by more glass production enterprises.

(1) Characteristics of Low-Frequency Pulse Foaming Technology

  1. Adoption of Anti-Blocking Self-Protective Foaming Device:
    • Achieves true pulsating gas injection and low-frequency operation in furnace foaming technology.
    • The anti-blocking self-protective foaming device (patented technology product) ensures the unobstructed state of the foaming device even without water cooling or protective gas. It can remain open even after power outage or gas interruption. Therefore, bubble frequency can start from zero.
    • Eliminates the formation of small bubbles in series entering the glass liquid through the foaming device. This ensures the excellent quality of the glass liquid by preventing the generation of small bubbles due to improper foaming.
    • Removes the interference of protective gas on the flow of glass liquid, stabilizing bubble frequency and bubble diameter. This guarantees the stable flow of glass liquid in the melting pool, improving the uniformity of the glass liquid and facilitating molding. It enhances product qualification rates.
    • The use of anti-blocking foaming devices significantly reduces the scouring of the foaming brick area by local circulation, ensuring the furnace’s lifespan.
    • Prevents frequent faults such as foaming pipe blockages, and ensures that the foaming pipe’s lifespan matches the furnace’s age, meeting the requirements for the entire kiln period.
  2. Adoption of Advanced Microelectronic Program Automatic Control System:
    • Achieves intelligent automatic control of foaming operation with features such as comprehensive process functions, high accuracy, flexibility, safe and reliable operation, ease of operation, intuitive monitoring, and complete information.
    • The control system can perform “overall control” of the entire system or “individual control” for each foaming device. This maximizes the satisfaction of melting operations, ensuring accurate control of glass melting states.
  3. Strict Purification Treatment of Foaming Gas:
    • Low-frequency pulse foaming ensures rigorous purification of the foaming gas, eliminating foaming pipe scaling blockages caused by impure gas (air cleanliness reaches the national standard level one).
  4. Safe and Stable Operation with Long Lifespan:
    • Low-frequency pulse foaming operates safely and stably with a long lifespan. When the furnace operates normally, and foaming operations are correct, its lifespan fully meets the furnace age requirements.
    • To ensure the safe operation of the foaming furnace, the system provides air cooling for the bottom foaming brick, slowing down the erosion, scouring, and blocking of the foaming brick area by high-temperature glass liquid. It also monitors the temperature to prevent sudden leakage accidents of the glass liquid.

(2) Application of Low-Frequency Pulse Foaming

  1. Application Scope:
    • Can meet the requirements for enhancing the melting of glass of different varieties and colors.
  2. Considerations for Foaming Application:
    • Foundation Work: Conduct proper design work for foaming based on the melting process requirements and the selection of foaming pool bottom structure and materials.
    • Foaming Process: Implement scientific management after production, strictly and earnestly execute the foaming process operation system. Do not let it run naturally; instead, control it consciously.
    • Foaming Technology Integration: Foaming technology is one of the measures for forced melting. After adopting foaming technology, it is necessary to organically integrate the melting process system with foaming operation: observe and test the furnace conditions promptly after foaming is initiated and make reasonable adjustments to ensure that the furnace operates in the optimal state.
    • Operational Management and Maintenance: Must effectively carry out the operation management and maintenance of the foaming system and its devices.

The emergence of the new generation low-frequency pulse foaming technology and equipment has propelled foaming technology to a new level. Practical experience has shown that this upgraded product is an ideal supporting device that meets the overall production and operation needs of modern glass furnaces. It is believed that this mature technological means and equipment will be adopted by an increasing number of glass production manufacturers, yielding significant economic benefits.

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