Design and Practice of an Extra-Large (138 m²) Horseshoe-Flame Glass Melting Furnace Fired by Producer Gas

Melting Furnace Structural Design
1. Length-to-Width Ratio
Based on design specifications, the melting area is determined to be 138 m². Given the large surface area, and considering flame coverage and the flame length associated with producer gas, a length-to-width ratio of 1.3 was selected to ensure effective melting and refining.
2. Depth
The depth design of the melting furnace takes the following factors into account:
1. Producer gas is used as fuel; it has a calorific value of approximately 1,500 kcal/m³ and high flame radiation intensity. Additionally, the furnace bottom features effective thermal insulation and a bubbling system, resulting in higher temperatures for the glass melt at the bottom.
2. The client requires a high melting rate; therefore, the volume of the glass melt within the furnace must be increased to ensure sufficient throughput.
3. The furnace produces brown glass, which has relatively high heat permeability.
4. The furnace is designed for the production of high-quality lightweight bottles.
5. The production line is equipped with high-performance forming machines capable of high operating speeds.
In light of these factors, and to ensure melting quality and output, a greater depth was selected for the melting zone, with the refining zone bottom lowered by 360 mm.

3. Batch Charging Port and Tank Wall
An oscillating charger with an immersion-type mechanism is employed. Based on the charger's capacity and the furnace's output, two charging ports are provided for bilateral feeding. The charging ports feature a design with a 10° flare angle on both sides and a length of 1800 mm. To effectively minimize heat loss and dust emissions, the charging port enclosure is constructed with an inner arch and an outer arch.
The tank wall utilizes monolithic, high-quality, fused-cast AZS blocks (36% ZrO₂ grade, virtually free of shrinkage cavities). Insulation for the tank wall employs a new type of composite insulation brick developed in-house, with vertical expansion joints left between the tank wall blocks. Notably, the corner blocks at the charging ports are not insulated but are cooled directly by forced air.
Cooling airflow for the tank wall blocks is ≥2700 m³/(h·m) with an outlet velocity >35 m/s; for the charging port corner blocks, the airflow is ≥3600 m³/(h·m) with an outlet velocity >35 m/s.
4. Furnace Bottom
To minimize heat loss and conserve energy, the furnace bottom utilizes a multi-layer composite structure consisting of 120 mm paving blocks and a 50 mm layer of AZS ramming mass. To mitigate phenomena such as downward drilling and upward corrosion at the bottom, the chemical and mineralogical composition of the procured AZS ramming mass must closely match that of the paving blocks, ensuring they sinter into a dense, inseparable monolithic unit at 1250°C. During installation, the ramming mass must be thoroughly compacted to minimize gas porosity.

5. Bubbling and Furnace Dam
Both the furnace dam and the furnace-bottom bubbling system serve to intensify the glass melting process. The static nature of the dam complements the dynamic action of the bubbling system; together, they effectively prevent unmelted batch material from flowing into the refining zone, control the flow velocity, raise the temperature at the furnace bottom, and improve the homogeneity of the glass composition.
The furnace dam is constructed using high-quality, void-free, fused-cast AZS blocks (41% ZrO₂ grade) with precision-ground joints. Positioned at three-quarters of the furnace length, the dam features a double-row staggered joint configuration and is located 600–700 mm below the top of the sidewall.
The bubbling block consists of a single high-quality, void-free, fused-cast AZS block (41% ZrO₂ grade) with a thickness of 500–800 mm; the thickness of the surrounding paving blocks is increased to enhance corrosion resistance. Forced external air cooling is applied to the bottom of the bubbling block to extend its service life and prevent glass leakage at the bubbling pipe interface. The spacing between the bubbling system and the furnace dam is 800–1000 mm. A pulsed bubbling method is employed, with the bubble frequency controlled at 6–10 bubbles per minute.
The top steel structure for the sidewall section at the furnace dam must be decoupled from the adjacent sidewall steelwork and controlled independently using jacking screws.
The cooling airflow rate for the bubbling block is ≥300 m³/h per unit.

6. Combustion Space
The width of the combustion space exceeds that of the melting zone by approximately 500 mm; the combustion space volume is 361.4 m³, and the thermal load is 4.2 × 10⁴ kcal/(m³·h).
The breastwall utilizes reclaimed fused-cast blocks (250 mm thick), while all other sections are constructed using new bricks. The main crown is constructed from premium-grade silica bricks with a thickness of 500 mm and a central angle of 60°. The skewbacks of the main crown are reinforced with a dual-rod system, with the lower rod positioned in the lower-middle section of the skewback brick.
During the construction of the main crown, the total joint width must remain consistent from top to bottom; a configuration where joints are narrower at the top and wider at the bottom is strictly prohibited, and the deviation in total joint width between the top and bottom must not exceed 5%. Before leaving the factory, the silica mortar must be tested by bonding two silica bricks together and firing them in a tunnel kiln or similar furnace at temperatures above 1400°C to verify the ambient-temperature bonding strength; if the bricks fail to bond securely, the batch of mortar cannot be released for use.
7. Throat
The throat employs a submerged horizontal structure. To minimize corrosion of the throat by the molten glass, the corner where the throat meets the tank sidewall is left uninsulated and cooled directly by air; the throat sidewalls receive minimal insulation, with vertical expansion joints left open. Each cover block of the throat is individually reinforced and left uninsulated; the cover blocks are water-cooled, with a flow rate of 20 m³/h and a pressure of approximately 0.3 MPa.

8. Port
The structure of the port must ensure that the flame is evenly distributed within the melting furnace, providing extensive coverage over the glass melt, while also possessing sufficient length and structural rigidity. Producer gas is used as the fuel for this project; the following factors were considered during the port design:
1. An optimal ratio and degree of mixing between the producer gas and combustion air facilitate complete combustion;
2. An appropriate pre-combustion chamber length allows for thorough mixing of the gas and air;
3. Optimized injection angles for the air and gas help keep the flame closer to the surface of the glass melt;
4. The width of the port opening determines the flame coverage area; a well-designed width-to-height ratio expands coverage while minimizing erosion of the breastwall;
5. Production of amber glass requires a reducing atmosphere within the melting furnace.
Based on these considerations, the port for this furnace is designed with a width of 3400 mm and a height of 400 mm, achieving a flame coverage rate of 66%.
9. Regenerator
Due to environmental regulations, glass plants across China have installed flue gas dedusting, desulfurization, and denitrification systems. These systems impose specific requirements on flue gas temperatures—typically necessitating a minimum of 320°C. Additionally, considering furnace maintenance requirements and factory layout constraints, a single-pass regenerator structure was selected for this project. A high regenerator-to-melting-area ratio was adopted to enhance the preheating temperatures of the combustion air and producer gas. To mitigate erosion and clogging of the upper checker bricks caused by high temperatures and batch dust, tubular bricks are used for the checkerwork, and high-temperature magnesia-zirconia bricks are employed at the tops of both the air and gas checker chambers.

Kiln Heating and Heat Preservation
The kiln heating and heat preservation process employs a thermal insulation strategy.
1. Pre-heating Preparations
Before the kiln heating process began, personnel were organized to conduct a rigorous and thorough cleaning of the kiln interior, the gaps between hanger bricks, the gaps at the arch springers, and the small furnace bottom plates. The main arch and the regenerator crown arches were also cleaned.
The adjustability of the crown tie-rods was verified.
Expansion gauges were installed at the crown. The lengths of the tie-rods—particularly those for the main arch and the regenerator crown—were recorded and marked.
The gaps between hanger bricks were packed with polycrystalline mullite fiber.
Ceramic fiber blankets were used to cover the crown, expansion joints, uninsulated sections of the upper tank walls, and the throat cover plates.
2. Heating and Batch Charging

The furnace heat-up process spanned a total of 13 days; the heating rate was 3°C/h between 100°C and 300°C, and 5°C/h between 1000°C and 1200°C. Cullet charging into the melting furnace commenced at 1350°C, with a charging rate of 6–10 t/h.
3. Crown Insulation
Once the temperature recorded by the thermocouple at the furnace's main crown exceeded 1250°C, the ceramic fiber blankets covering the crown were removed, and the expansion joints were monitored; particular care was taken to ensure no foreign matter was present in the brick joints. Any stepped gaps appearing between the crown bricks required immediate attention; siliceous refractory mortar was used to dry-fill and seal micro-cracks that emerged during the heat-up process. Expansion joints were filled and compacted in multiple stages using zircon or siliceous ramming mass, with the fill height extending 20–50 mm above the crown surface to prevent flame leakage.
Conclusion
Since commencing operation in May 2018, the melting furnace has performed well. Ultra-large melting furnaces entail significant investment and high risk, placing extremely high demands on design, materials, construction, and production management. When constructing such furnaces, enterprises must ensure scientific coordination across every stage; avoiding the pursuit of quick gains at the expense of long-term success is essential to achieving a high periodic melting rate.