Analysis of the Advantages and Operational Details of Oxy-Fuel Combustion Technology for LCD Glass Furnaces

01 Introduction to Oxy-Fuel Combustion Technology for LCD Glass Furnaces
In an LCD glass production line, the furnace heats the batch materials, melting them into a high-temperature molten glass fluid; this molten glass then flows through an outlet located at the bottom of the furnace to the subsequent processing stage. A screw feeder is utilized at the charging end to convey the batch materials into the furnace through a feed port situated on the rear wall. The upper section of the furnace employs multiple pairs of oxy-fuel burners, arranged for targeted combustion, to provide the necessary volumetric heat; natural gas is typically used as the fuel source. The lower section utilizes electric boosting to provide further heating to the molten glass. The oxy-fuel burners are distributed in pairs along the breastwalls on both sides of the furnace, while the flue gases generated by the combustion are discharged through exhaust ports located on the rear wall.

02 Advantages of Oxy-fuel Combustion in LCD Glass Furnaces
Compared to air-supported combustion, the adoption of oxy-fuel combustion in LCD glass furnaces offers the following distinct advantages:
(1) Energy Conservation and Consumption Reduction
Natural Gas Combustion:
Air-supported combustion: CH₄ + 2O₂ + 7.5N₂ → CO₂ + 2H₂O + 7.5N₂
Oxy-fuel combustion: CH₄ + 2O₂ → CO₂ + 2H₂O
In air-supported combustion, air serves as the oxidant; since oxygen constitutes approximately 21% of air while nitrogen accounts for about 79%—meaning the nitrogen content is far higher than the oxygen content—the large volume of nitrogen present in the air participates in the combustion process. This nitrogen is heated to high temperatures without contributing to the combustion reaction itself; subsequently, it is expelled from the furnace along with the high-temperature flue gas, thereby carrying away a significant amount of thermal energy. This process reduces the thermal efficiency of air-supported combustion and increases overall energy consumption. In contrast, with oxy-fuel combustion, the oxidant used is pure oxygen, which contains virtually no nitrogen. Consequently, the entire volume of the oxidant participates directly in the combustion reaction, and no nitrogen is wastefully heated to subsequently carry away thermal energy. As a result, oxy-fuel combustion achieves higher thermal efficiency and lower energy consumption, thereby facilitating effective energy conservation and consumption reduction.

(2) Reducing Atmospheric Pollution
One of the key measures for controlling NO gas emissions in the glass industry is the adoption of oxy-fuel combustion technology, which utilizes pure oxygen as the combustion oxidant. Oxy-fuel combustion not only conserves energy and reduces consumption but also mitigates environmental pollution. By employing oxy-fuel combustion, the volume of nitrogen entering the furnace is drastically reduced; consequently, the NOx content in the flue gas discharged from the furnace is significantly lowered, thereby effectively preventing atmospheric pollution.
(3) Increasing Melting Rate
When oxy-fuel combustion is employed, fuel combustion is complete and flame temperatures are elevated. The primary combustion products—CO2 and H2O—exhibit greater emissivity (or "blackness") and stronger radiative power compared to air-supported combustion. This results in an increase of approximately 100°C in the flame's radiative temperature, which accelerates the melting rate of the batch materials and can boost the overall melting rate by more than 10%.

03 Adjustment of Gas Distribution Ratios for Oxy-Fuel Fired LCD Glass Furnaces
LCD glass furnaces are typically equipped with multiple pairs of oxy-fuel burners. The gas distribution ratio assigned to each pair of burners directly determines the natural gas flow rate for that specific pair, thereby playing a decisive role in the spatial energy distribution within the furnace chamber. The natural gas flow rate for a specific pair of burners is calculated as follows: Flow Rate = Total Natural Gas Flow Setpoint × Gas Distribution Ratio for that specific pair.

Under normal operating conditions, the natural gas distribution ratios for the burners are typically allocated evenly. However, observations revealed significant issues in the furnace's forehearth zone, specifically severe clumping and caking of the batch material. This resulted in irregular material flow, an unstable batch pile, and frequent fluctuations in the electrical resistivity of the forehearth zone, ultimately leading to substantial temperature variations at the furnace bottom. By reducing the gas distribution ratio in the forehearth zone—thereby lowering the local temperature—it is hypothesized that the clumping and caking of the batch material could be alleviated, leading to a more stable batch pile and, consequently, a more stable furnace bottom temperature. To validate this hypothesis, the gas distribution ratio in the forehearth zone was appropriately reduced to conduct a comparative trial against the standard "even distribution" method.

Minitab software was utilized to analyze the control capability and fluctuation levels of key process parameters within the furnace during the comparative trial period. For each parameter under investigation, 30 days' worth of data were collected during the trial period, yielding two distinct data samples: one representing the "even gas distribution" scenario and the other representing the "reduced gas distribution in the forehearth zone" scenario. Data points were sampled on an hourly basis; thus, each sample comprised 30 × 24 = 720 individual data points, resulting in a total sample size of 720. Within each sample, every 24 consecutive data points were grouped together to form a single subgroup, establishing a subgroup size of 24.

04 Pre-commissioning Testing of Oxy-fuel Burners for LCD Glass Furnaces
Once the oxy-fuel burners have been fully installed on the LCD glass furnace, but prior to being put into operation, they must undergo testing on a dedicated burner test rig. This testing serves to verify whether the burner's combustion status—including parameters such as flame length and temperature—meets the specified process requirements.
1. Testing Method
After setting the oxygen-to-fuel ratio (defined as oxygen flow rate / fuel flow rate) and the natural gas flow rate, a pair of oxy-fuel burners is ignited using a torch. By observing, measuring, and recording the combustion status—specifically flame length, temperature, and other relevant data—and comparing these results against the process requirements for the LCD glass furnace, a determination is made as to whether the oxy-fuel burner satisfies the necessary operational criteria.
2. Testing Procedure
(1) Move the burner test rig to an appropriate position directly in front of the burner; place a ceramic fiber insulation blanket on the upper section of the support stand.
(2) Position the burner horizontally at a suitable location on the main support stand; connect the natural gas and oxygen supply lines, and open the ball valves located immediately upstream of the burner on both the natural gas and oxygen lines.
(3) Prepare a torch; ignite it and position it directly at the nozzle of the burner.
(4) Once the process personnel in the central control room have configured the oxygen-to-fuel ratio and natural gas flow rate, they initiate the ignition sequence via the combustion system's control interface panel. Subsequently, the pneumatic valves on the natural gas and oxygen supply lines open, delivering a specific flow of gas and oxygen into the burner, where combustion is initiated upon contact with the torch flame at the nozzle.
(5) Once the flame has stabilized, observe its color, brightness, and shape; measure the flame length and temperature, and record all relevant data.
(6) As dictated by production requirements, the process personnel in the central control room shall configure different oxygen-to-fuel ratios (e.g., 2.1 and 2.7) and natural gas flow rates (e.g., 6 Nm³/h and 12 Nm³/h), and then repeat Step (5) to conduct additional trials.
(7) Upon completion of the testing, close the ball valves located immediately upstream of the burner on both the natural gas and oxygen lines, as well as the relevant valves on the main and sub-control panels of the combustion system. Allow the burner to cool down to room temperature before removing it from the test rig.