A comprehensive study of melt foaming in E-glass batch-to-melt conversion process: Effects of sulfate content and chemistry of raw materials

Control of sulfate-induced melt fining without excessive foaming is one of the critical steps in maintaining the stability of E-glass fiber manufacturing processes. Besides, the efficiency of combustion or energy utilization is directly affected by the extent of the melt-foaming. A fundamental understanding of key factors affecting melt foaming under the simulated oxy-fuel combustion environment will enable commercial E-glass fiber production to optimize both batch chemistry and operation conditions to achieve adequate furnace control. In this study, six types of E-glass batches with the same target glass composition were prepared by using four different CaO sources; calcined limes with different SO₃ contents, limestone, limestone with sodium sulfate, and a mixture of limestone and calcined lime. All batch samples were examined by HTMOS-EGA system (high temperature melting observation system with evolved gas analysis). HTMOS enables monitoring batch-to-melt conversation steps by using a high-resolution camera and EGA detects the evolved reaction gaseous, such as CO, CO₂, and SO₂ via an Fourier transform infrared (FTIR) gas analyzer. Gases of water vapor, N₂, and O₂ were introduced accordingly into the fused quartz crucible to simulate similar oxy-fuel atmosphere of the furnace operation. This study aimed to investigate the effects of different SO₃ contents in batches and different raw material chemistries on the foam formation in E-glass melts under the oxy-fuel atmosphere. Different raw materials were characterized by mineralogical analysis, chemical analysis, particle size distribution, chemical oxygen demanding (COD) level, and Brunauer–Emmett–Teller (BET) analysis. Although some of the batches contained the same SO₃ content, different foam formations resulted from the effect of the batch chemistry. Our detailed HTMOS-EGA investigations show that not only SO₃ content in the batch affects foam formation in E-glass melts, but also raw material chemistry and particle size have strong effects on the melt foaming in E-glass batch melting, especially for those of ingredients having hydroxide phases and/or finer particles with higher specific areas.