Concurrent Processes: A Complex Challenge in Glass Manufacturing 

These intricate scenarios present significant challenges not only in traditional troubleshooting methods but also pose serious challenges for AI-powered software. These issues require careful consideration and strategic solutions.

Primary Processes: Primary processes such as batching, melting, refining,
homogenizing, forming, annealing, cutting, stacking, and storing in warehouses are fundamental to glass production. Each of these processes can be subdivided into subprocesses, which facilitate the identification and control of basic process parameters. Improper execution of these processes can lead to various defects, including inhomogeneity in the batch, inclusions and stria  in melt, distortion and deformities in the forming process, high residual stress in glass products, and various types of edge defects.

Secondary Processes:  Secondary processes run concurrently with the main process in glass manufacturing. Although generally less critical, they can still be the root cause of significant defects and incidents. Key secondary processes include Segregation, Carryover, lumping of raw materials, Diversion and Inversion of Convection Currents, Devitrification, Reboil in Glass Melt, Phase Separation, Condensation, Dolomite and Limestone Disintegration, and Evaporation. Each of these mechanisms can have a direct or indirect impact on glass quality, process deviation, and the functionality of production equipment. Let’s briefly review some of these secondary processes:

• Segregation: This important secondary process can occur during the handling, storing, and conveying of raw materials and batch, adversely impacting the glass manufacturing process. It can lead to the direct or indirect formation of defects in the final product. Grain size segregation is a phenomenon that occurs in various granular materials, such as silica, feldspar, dolomite, limestone, soda ash, salt cake, or glass batches. It refers to the tendency of particles within the material to separate or segregate based on their size when subjected to mechanical or physical processes, including vibration, shaking, and flowing. The primary factors contributing to grain size segregation are differences in particle size and the way the material experiences external forces or motion. In practical applications, grain size segregation can have significant implications, particularly in material handling, as it can result in the inhomogeneity of glass melt. For instance, the segregation of silica powder during the handling, filling, or discharging from a silo can influence the distribution of grain sizes. This variation intermittently leads to higher concentrations of coarse grains and fine grains. Specifically, a higher concentration of coarse grains may result in the formation of silica stones in the product, whereas a higher concentration of fine grains can lead to seeds in the glass. Additionally, an increase in fine grains can exacerbate the carryover to checkers.
• Carryover: This subprocess primarily occurs during the early stages of melting within the furnace. When the raw materials  dust (fine-grains less than 100 micron) exceeds certain limits, it can be entrained over the furnace chamber and readily carried by the combustion products from the melting chamber through the refractory checkers towards the chimney. During its journey through the checkers, the fine-grain settles inside the openings and channels of the refractory checkers, gradually accumulating and causing blockages  in checkers’ openings. This phenomena contributes to several corrosion mechanisms that affect the refractory materials in the breast walls and checkers. Specific issues include rundown on breast walls and damage to checker bricks, regenerator walls, and crowns.
• Diversion and Inversion of Convection Currents: These phenomena are directly caused by changes in the temperature profiles of the furnace and tin bath. They may also occur due to alterations in glass composition or changes in glass level. These changes adversely affect the quality of the glass and contribute to the corrosion of refractory materials. Maintaining process stability and ensuring that furnace and tin bath temperature profile  stay within their operational and standard limits is crucial to prevent these subprocesses from negatively impacting the glass manufacturing process.
• Refractory Materials Corrosion: Corrosion of refractory materials occurs through various mechanisms, each varying depending on the specific part of the furnace and tin bath. Notable mechanisms include upward drilling in side blocks, downward drilling in the furnace bottom, exudation and phase transformations in side blocks, alkaline diffusion in crown silica bricks, and rat holes in skew backs. These processes can gradually diminish the operational efficiency of the furnace and tin bath, adversely impacting the quality of the glass produced.
• Devitrification: Devitrification typically occurs due to changes in the SiO2 content within the glass, often caused by the volatilization of alkali oxides from the glass’s surface. This volatilization leads to the formation of a silica-rich surface layer, which can remain stagnant for extended periods in the refiner, working end corners, or at the waist pipe. When the glass remains stagnant at the liquidus temperature (the temperature above which a material is completely liquid) or in the “devitrification zone” for a sufficient amount of time, and/or is cooled too slowly, crystal structures can form within the glass. Devitrification can also be triggered by changes in the ratio of stabilizing agents to fluxing agents, making the melt more susceptible to crystallization. Alterations in glass composition, whether general or localized, increase the risk of devitrification. Factors such as poor mixing quality, weighing errors, moisture, and refractory corrosion can alter the chemistry of the batch, affecting the stabilizer to flux agent ratio. Furthermore, the conversion of old melting scum that has accumulated at the waist pipe over time can also lead to devitrification. Devitrified stones are solid-state crystalline materials that form when molten glass undergoes the devitrification process. The most commonly encountered devitrification stones are cristobalite, tridymite, and wollastonite (calcium silicate CaSiO3). Devitrified stones that form from fresh silica-rich glass are primarily cristobalite, while those originating from aged or old silica-rich glass are tridymite. Dough scales are small devitrification pieces on the glass surface caused by devitrification of glass in the colder areas of the furnace. Beta-wollastonite (calcium  silicate CaSiO3) is a common type of devitrification stone that may form due to a change in the ratio of stabilizing agents to fluxing agents. This change not only makes the melt susceptible to devitrification but also to conversion into other crystalline forms such as diopside and aegirine. Devitrification can significantly degrade the quality of glass. Changes in glass pull or load, fluctuations in furnace temperature, variations in glass level, or any other disturbances that disrupt furnace convection currents can cause devitrified materials to dislodge from stagnant areas. These materials then enter the normal currents of the glass, manifesting as inclusions, bubbles, and seeds within the glass. Effective prevention of devitrification involves a combination of strategic actions to ensure optimal conditions. These include designing the furnace and tin bath to eliminate stagnant areas or devitrification zones, regulating the glass composition to reduce its susceptibility to devitrification, maintaining a proper temperature profile in the furnace and tin bath, ensuring an appropriate glass pull rate from the furnace to achieve the right residence time for molten glass, and regularly cleaning any areas where devitrification has occurred. Implementing these combined measures can effectively prevent devitrification issues.
• Reboil in Glass Melt: Glass melt can dissolve various gases through chemical or physical mechanisms. The solubility of some gases is directly proportional to temperature, whereas for others, it decreases with temperature. Additionally, certain gases are more soluble under reducing conditions, while others prefer oxidizing conditions. Dissolution can range from partial to saturated. Reboil occurs when the solubility of a gas changes during the flow of glass within the furnace, often due to fluctuations in temperature or redox conditions, particularly in the furnace’s colder sections. As a result, the glass exceeds its saturation point and enters an over-saturation state, prompting the release of excess dissolved gas in the form of bubbles. The formation of reboil bubbles in molten glass can be influenced by several factors, including residual sulphate at the contact area between different glass currents, internal reactions between different currents of glass that have varying dissolution ratios of sulphide and sulphate, localized heating in downstream sections of the furnace during color changes, and specific instances such as reboils that occur at the back of the tweel where H2 gas has leaked, resulting in bubbles that primarily consist of H2 gas.
• Evaporation: Alkaline evaporation from the surface of molten glass not only creates micro-striae in molten glass but also poses a significant threat to the furnace’s superstructure. This occurs through a diffusion mechanism in which alkaline vapours penetrate silica bricks, accelerating their corrosion. Such phenomena can degrade the quality of the produced glass and lead to defects characterized knots in the glass. Additionally, these vapors can damage checker bricks and the body of the regenerator, compromising their functionality and integrity.
• Disintegration: Disintegration is a phenomenon related to dolomite and limestone that occurs when these materials explosively break down into very fine powders, dispersing as fine dust within the furnace atmosphere. This fine dust adheres to the refractory material of the superstructure, causing the corrosion of these materials through the formation of eutectic liquids. These liquids can then flow over the refractory bricks and into the glass melts, potentially appearing as knots or devitrified stones in the glass. To contain and prevent these problems, it is crucial to carefully inspect, regulate, and standardize the grain size and mineralogy of the raw materials.
• Tertiary Processes: Tertiary processes arise as consequences of deviations in primary processes and the damaging effects of secondary processes. The cascading outcomes from primary and secondary processes frequently initiate new tertiary processes that impact the entire system, including the original processes, machinery, and products. For example, an increase in the percentage of grains smaller than 106 microns in silica powder can be considered a change in the primary process parameter. This change may lead to high silica dust in batches, causing silica carryover as a secondary process. If this non-conformity in the primary process persists over an extended period or occurs intermittently but frequently, the carryover phenomenon will continue. This can lead to the accumulation of silica dust within the checkers network, combined with alkaline dust and vapours. Over time, this accumulation can block the checkers’ openings, deform and damage the checker bricks, and drastically reduce the thermal efficiency of the regenerators. This, in turn, triggers tertiary processes such as increased fuel consumption, elevated furnace pressure, adjustments in stack damper openings, shifts in the furnace atmosphere’s redox state, and ultimately, significant process implications. Excessive carryover can significantly affect the glass product, resulting in various defects such as seeds, stones, and optical distortions.