Application of oxygen-enriched combustion technology in horse-shoe flame glass furnaces

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I would like to share the information on oxygen-enriched combustion that I have found. This is an excellent resource that is very useful for reference. Application of Oxygen-Enriched Combustion Technology in Horse-Shoe Flame Glass Furnaces I. Principle of Membrane-Based Oxygen Enrichment: Membrane-based oxygen enrichment technology makes use of certain inherent properties of polymer materials, such as their ability to selectively permeate different gas molecules, as well as the special processing capabilities of these polymers. Scientists have developed specific polymer materials into gas separation membranes and membrane components that have industrial application value. 　　By using polymer materials and processing them through special techniques to create composite membranes and membrane elements, it is possible to increase the oxygen concentration in air from 21% to 30%. These membranes boast an extremely high gas permeability; compared to glassy polymer membranes, they can produce 4 Nm3/m2·h·bar of oxygen at 30% concentration per unit area, per unit time, and per unit pressure. Compared to oxygen production methods such as cryogenic separation and pressure swing adsorption (when converted to the same concentration), the membrane-based method results in the lowest production costs. 　　II. Principle of oxygen-enriched combustion: The purpose of oxygen-enriched combustion is to ensure complete combustion of the fuel and to make effective use of the amount generated as a result of combustion. The combustion process is crucially related to furnace efficiency. Combustion occurs as a result of high-energy collisions between combustible molecules in the fuel and oxygen molecules; therefore, the availability of oxygen determines whether the combustion process proceeds fully. In conventional combustion systems that use air as an oxidizing agent, this high-energy collision is hindered by nitrogen molecules, which make up nearly four-fifths of the air composition and do not contribute to oxidation; as a result, the chances of collisions between oxygen molecules and the combustible molecules in the fuel are reduced, which directly affects the improvement of combustion efficiency. Moreover, nitrogen absorbs a large amount of heat in the furnace and releases it in the exhaust gases, leading to heat loss and energy waste. Using air with a higher oxygen content than normal air to assist combustion is known as oxygen-enriched combustion; it has the advantages of increasing flame temperature, accelerating the combustion rate, lowering the ignition temperature of the fuel, and improving heat utilization efficiency. 　　III. Description of the horseshoe-flame glass furnace: The horseshoe-flame glass furnace uses inexpensive producer gas (oil or natural gas) as fuel, which not only improves the quality of melting but also **reduces fuel costs**. This furnace type features a rational regenerator structure, which improves the utilization rate of thermal energy and operational efficiency. In the design of the regenerator, the flue gas passes directly through the regenerator into the flue; the regenerator is a heating chamber made up of a hollow lattice constructed from refractory materials. When producer gas and air pass through the regenerator, the air and gas are preheated, and then they enter the small furnace together where they mix and pre-ignite. It allows the fuel to release more heat. As the flue gas rises and falls repeatedly within the regenerative chamber, heat is fully absorbed and stored by the grid bricks; some of the heat is carried away by the exhaust gases, while most of it is utilized effectively in the operational process. 　　IV. Application of oxygen-enriched combustion technology in stoke furnace gas horseshoe-flame glass furnaces 　　Local oxygen enrichment for combustion in horseshoe-flame glass furnaces is not only necessary but also feasible. In the flame zone of a typical glass furnace, the lower part of the flame is always the area with the least oxygen, resulting in incomplete combustion and lower temperatures. If an oxygen-enriched nozzle introduces oxygen into the furnace space at a certain angle and speed, impacting the bottom of the flame, this will create an oxygen-enriched layer near the glass surface that contains fewer unburned carbon particles, thereby ensuring complete combustion and a significant increase in temperature. This asymmetric flame, thanks to the reliable vertical temperature gradient, creates a high-temperature zone on the side closest to the glass melt, thereby increasing thermal radiation and convection from the bottom of the flame toward the interior of the glass melt. On the side close to the kiln ridge, the temperature does not rise, thus protecting the top of the kiln from increased erosion as a result. At the same time, as the flame intensity increases and the flame becomes shorter, this helps to control the temperature distribution within the furnace. Furthermore, it prevents combustion within the heat storage chamber. For regenerative melting furnaces, this also helps to improve the lifespan of the grid bricks. 　　Since the horseshoe-flame furnace feeds material from the side and burns with flames from the front, its material layer is relatively short; to enhance melting, the flame length also needs to be short, and short-flame combustion is generally preferred. Only in this way can the heat from the flame be concentrated in the melting zone of the mixture, thereby enhancing the melting capacity of that area. The length of the flame can also be adjusted by controlling the oxygen flow rate. When the oxygen flow rate is increased to 100 m3/h, the flame length will decrease significantly. 　　Within the flame zone of the horse-shoe flame kiln, oxygen enrichment for combustion can also lead to uneven flame radiation, causing the heat flow to move downward away from the roof of the kiln, resulting in a significant drop in temperature in the area near the kiln roof. As a result, the cold air layer near the liquid surface in the clarified zone was essentially eliminated, the thermal uniformity within the glass melt improved, and ultimately the quality of the formed products was enhanced. 　　(1) Design of the oxygen-enriched combustion assistance system for glass furnaces using gas generated from combustion furnaces: In order to enable a gradient combustion pattern within the furnace, so that the flame temperature near the glass surface is higher than that in the upper areas, if maintenance is required while the furnace is in operation, the oxygen-enriching nozzles can be installed directly on the bricks at the bottom of the furnace. This not only determines the optimal location for using oxygen enrichment but also completely eliminates the problem of having to replace the oxygen-enriching nozzles midway. Oxygen-enriched air is injected parallel to the lower part of the flame and mixes with that region inside the melting pool, thereby creating a high-temperature bottom layer of flame near the feed area of the melting pool. This accelerates material melting, increases the melting rate, prevents the accumulation of material, and ensures that the backflow of the flame does not carry powder into the regenerative chamber, which helps to extend the lifespan of the grid bricks. 　　When using oxygen-enriched combustion, work is generally carried out without shutting down the production process. Taking advantage of the switching time, oxygen-enriched nozzles are drilled and inserted on the outside of the premixing chambers of the two small furnaces, placed close to the bottom surface of these furnaces, with the nozzle angle adjusted according to the direction of the gas flow. The oxygen-enriched air from the two nozzles is ejected parallel to the lower part of the flame, which likewise allows the oxygen-enriched air to mix with the lower portion of the flame within the chamber, thereby creating an effect of oxygen enrichment to aid combustion. 　　(II) Oxygen-enriched combustion design for glass furnaces fueled by fuel oil (or natural gas): Since the melting furnaces use heavy oil as a fuel, and heavy oil has high viscosity and a high ignition point, methods such as heating and atomization are required to ensure its complete combustion during the burning process. Local oxygenation technology primarily increases the oxygen concentration in the air, reduces the amount of air needed for combustion, and decreases the generation of smoke (thereby reducing the heat carried away by the smoke), which in turn lowers the production of NO2 pollutants and improves the environment ； Local oxygen enrichment in the furnace can correspondingly increase the flame temperature and the combustion rate, as well as enhance radiation and convection heat transfer of the glass melt, thereby improving the melting rate ； Local oxygen enrichment facilitates combustion, ensuring complete burning of the fuel in the flame zone; this reduces the temperature of the large structure, decreases the heat dissipation from it, and lowers the energy consumption per unit of molten glass. When designing for oxygen-enriched combustion, it differs from glass furnaces that use burner gas with a swirling flame in that the oxygen-enriching nozzles are placed below each oil gun. 　　The complete set of oxygen-enriched combustion equipment, which was independently developed, designed, and manufactured by our company, was put into use in May 2008 in the No. 1 horse-shoe flame glass furnace at Qingdao Rongtai Glass Products Co., Ltd. It achieved significant energy-saving results; it was then applied to the No. 2 furnace as well, with even better energy-saving effects. A two-month evaluation of the energy consumption of both furnaces was conducted, and the results were as follows:

No. 1 furnace: 99 m2. Before oxygen enrichment, the production volume was 190 T/day, with 45 T/day of coal used. After oxygen enrichment, the production volume increased to 198 T/day, while the coal usage dropped to 40 T/day (with a specific consumption of 202 kg).

No. 2 furnace: 104 m2. Before oxygen enrichment, the production volume was 200 T/day, requiring 46 T/day of coal. After oxygen enrichment, the production volume rose to 218 T/day, with coal usage decreasing to 41 T/day (with a specific consumption of 188 kg).

These two sets of equipment represent a comprehensive solution provided by our company, covering everything from the production of oxygen-enriching membranes and components to the manufacturing, design, and installation of the oxygen-enriched combustion equipment. Overall, this oxygen-enriched combustion technology and equipment not only achieve significant energy savings and a reduced air excess factor, but also alter the operating conditions of the furnace. During operation, it was observed that with the introduction of oxygen, the flame length decreased significantly, the bottom of the flame became brighter, the temperature on the front wall dropped, and the temperature at the top of the furnace fell as well; meanwhile, the amounts of gas and secondary air used were reduced, resulting in energy savings of over 10% compared to traditional methods. Both yield and quality have increased by about 5%. 　　V. Features such as energy saving and environmental protection: 1. Increased flame temperature: With the inclusion of oxygen-enriched air, the nitrogen content decreases, thereby reducing the heat absorbed by the exhaust gases. According to available information, the flame temperature increases significantly as the oxygen content in the air rises. When using a conventional air furnace with a heating temperature of 1300°C, only 42% of the heat can be utilized; however, by using oxygen-enriched air at an optimal economic concentration of 28% to assist combustion, up to 56% of the heat can be utilized, resulting in a 33% increase in heat efficiency. Introducing oxygen-enriched air locally into the furnace is intended to increase the percentage of oxygen in the air within that combustion zone, thereby raising the flame temperature in the furnace and improving heat utilization efficiency. 　　The flame temperature rises rapidly as the oxygen content in the combustion air increases; as can be seen from Figure 1, the flame temperature increases with higher levels of oxygen in the air ； As the concentration of oxygen-enriched air gradually increases, the rate of increase in flame temperature gradually decreases. Therefore, in order to make effective use of oxygen-enriched air, its concentration should not be set too high. When organizing the fuel with an excess coefficient of a=1.1–1.5, an oxygen-enriched concentration of 25–27 is appropriate, and the best results are achieved when the air content is between 21–25. 　　2. Increase in combustion speed: The reason why fuel burns more rapidly in oxygen-rich air is that the increased oxygen content raises the flame temperature; for example, the combustion speed of natural gas in oxygen is 10 times higher than that in normal air. The increased combustion rate leads to the rapid and complete combustion of the fuel within the furnace. 2 　Table of maximum combustion rates in cm/s 　Fuel Air (21% O2) range Maximum possible value Oxygen (100%) range Maximum possible value 　Hydrogen 250-360 280 890-1175 　Natural gas 33-44 37 325-480 395 　Propane 40-47 42 360-400 375 　Butane 37-46 41 335-390 355 　Ethane 110-180 160 950-1280 1130 　3. Reducing the ignition temperature of the fuel 　The ignition temperature is significantly influenced by the reaction rate and heat loss. Oxygen-enriched air helps reduce the \"ignition temperature\" compared to ordinary air, and increases the heat release per unit volume of the flame. The effect is more pronounced with low-quality fuel. 　　The ignition temperature of fuel is not constant under certain conditions. For example, the temperature is 609°C for CO in air, but only 388°C in pure oxygen. Oxygen-enriched combustion takes advantage of this phenomenon by supplying a small amount of oxygen-enriched air directly to the area where the fuel has just been atomized (or where solid fuel has just been vaporized) and ignited. This increases the oxygen concentration in that area sharply, thereby reducing the temperature required for ignition, allowing for earlier ignition, prolonging the time during which the fuel burns in the furnace, and increasing the amount of heat released by the fuel. 　　4. Reducing the volume of exhaust gases after combustion: By using oxygen-enriched air with an oxygen content of 23–24% in the combustion process, compared to burning with normal air, when the excess air coefficient a is set at 1, the volume of exhaust gases is reduced by 10–20%. The heat loss due to exhaust gases is also reduced by 10–20%, thereby improving thermal efficiency and saving energy. 　　The combustion rate of fuel varies significantly when burning in normal air compared to pure oxygen; for example, the combustion rate of natural gas is up to 10.7 times higher in pure oxygen than in air. Therefore, using oxygen-enriched air not only increases the intensity of combustion but also speeds up its rate, which facilitates a more complete combustion reaction. This improves the quality of exhaust gases and reduces environmental pollution caused by unburned substances. 　　When using conventional air with an oxygen concentration of 21%, and assuming an exhaust volume of 1 based on the theoretical air volume for combustion, the exhaust volume tends to decrease as the oxygen content increases. Compared with combustion using air with an oxygen content of 21%, combustion using oxygen-enriched air with an oxygen content of 27% results in a 21% reduction in the volume of exhaust gases when the excess coefficient a=1; the heat loss due to flue gas is also reduced accordingly, leading to energy savings. 　　5. Increase heat utilization rate When the heating temperature is 1300°C, ordinary air is used for combustion. Its thermal efficiency is 42%, while burning with oxygen-enriched air containing 24% oxygen increases this efficiency to over 30%; the energy-saving effect becomes more significant as the heating temperature rises. 　　6. Reducing the air excess factor 　　Oxygen-enriched combustion can effectively reduce the air excess factor, thereby significantly minimizing the heat loss in the exhaust gases and improving the thermal efficiency of the furnace, thus saving energy. When the value of a is 1.1, the fuel usage increases by only 4%; when a is 1.4, it increases by 16%. In high-temperature furnaces, the higher the heating temperature, the greater the increase in the value of a, and thus the greater the heat loss. 　　Complete combustion in the furnace reduces the air excess factor. According to available information, the Japan Energy Conservation Center focuses its research on energy-saving measures for industrial furnaces on reducing the air excess coefficient. Through multiple experiments conducted on a heat treatment furnace, they managed to reduce this coefficient from 1.7 to 1.2, achieving a 29.4% reduction; the average energy savings resulting from this were 13.3%. The actual test results from our furnace show that the excess air coefficient at the chimney exhaust area has generally decreased by around 12–14%. 　　VI. Design and installation of oxygen-enriched combustion support systems: Taking membrane systems as an example, to cope with harsh operating conditions characterized by high dust levels, the membrane modules are equipped with built-in filtration systems; moreover, the membrane stacks can be installed in relatively enclosed indoor spaces. Air enters these spaces after being preliminarily filtered by pre-installed filters. The relatively clean fresh air is then guided by the exhaust fans built into the membrane modules into the membrane separators for oxygen-nitrogen separation. The oxygen-enriched air is pumped to the areas where it is needed using vacuum pump units, while the waste gas is discharged outside through dedicated exhaust fans ； 　　To maintain the stability and reliability of the system, the power equipment—vacuum pump—is the only potential point of failure; a backup unit can be designed to ensure the system’s reliability ； 　　To minimize investment and energy consumption, multiple vacuum pump units can be used in parallel; the standby units should be equipped with variable frequency drives, and these variable frequency units should be used for starting, stopping, switching, and reducing load to ensure an effective fault handling strategy. It is recommended to design the system using a single vacuum pump to meet the requirements. 　　The vacuum pump unit is installed separately in the pump room, with sound insulation and noise reduction measures in place ； 　　The system design is aimed at meeting the extreme conditions of the user’s operating environment, taking into account considerations for high temperatures, low temperatures, and altitude conditions, to ensure that the performance parameters and operational stability of the system at its final installation site are met ； 　　Control level: Centralized control/automatic control, unattended operation, intelligent alarm system, remote transmission interface. VII. Main technical performance features of the system (membrane system) 1. Simple process: A negative pressure flow roll-type membrane oxygen generation process, which uses vacuum power to directly draw oxygen-rich air from the membrane stack ； 　　2. Easy installation: The membrane stack features a modular design, making installation simple and connections convenient ； 　　3. Intensive use of utility resources: small footprint and low requirements for factory buildings ； 　　a) System stability and reliability: All power equipment has a certain failure rate; using backup units in combination with an automatic control system to switch to these backups in the event of a failure is the safest solution. This system allows for the use of one backup unit per multi-stage pump set, and variable frequency technology is employed, taking into full account the system’s failure prevention strategies as well as the need to minimize investment and energy consumption ； 　　b) Easy to operate: start and stop with a single button; simple and convenient to use ； Process control based on frequency conversion technology is fully automated ； 　　c) Easy maintenance: It is possible to carry out repairs on the rotary vane vacuum pump units that have developed faults without shutting down the system.
d) Scalability: The membrane stack and vacuum pump units can be easily used to facilitate straightforward expansion of production capacity