Effects of raw materials on melt foaming generation in e-glass batch-to-melt conversion process

Abstract

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. The foaming mechanism of E-Glass batch samples in the batch-to-melt conversion process was investigated from three distinct perspectives in this thesis. The first part examines the impact of various raw materials on E-Glass melting foam, including calcined lime(s), limestone, mixtures of limestone and calcined lime, and sodium sulfate. The second part examines the impact of varying concentrations of anthracites on the foam formation, which was divided into three categories. The first set examined the impact of anthracite addition in E-Glass batches containing 100 wt.% calcined lime. The second set investigated the influence of anthracite amounts on the foam formation in E-Glass batches containing a mixture of calcined lime and limestone. The last set investigated the impact of anthracite particle size on E-Glass melting foam. Finally, the third part of this thesis further investigated the foaming mechanism by using batches composed of various high-quartz kaolins with and without sand or a mixture of low-quartz kaolin and sand. In total, eighteen distinct E-Glass batches with the same target glass composition were tested in a laboratory to gain insight of the sulfate-induced melt foaming process and the related mechanism(s). In this research, all batch samples were carefully studied in situ by using 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 gases, such as CO, CO2, and SO2 via an FTIR (Fourier transform infrared) 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. Specifically, the first part examined the impact of various raw materials on E-Glass melting foam, including calcined limes, limestone, mixtures of limestone and calcined lime, and sodium sulfate. Six types of E-Glass batches with the same target glass composition were prepared by using four different CaO sources: three calcined limes with different SO3 contents, limestone, limestone with sodium sulfate, and a mixture of limestone and calcined lime. This study investigated the effects of different SO3 contents in batches and different raw material chemistries on the foam formation in E-Glass melts under the simulated oxy-fuel atmosphere. Different raw materials were characterized by using mineralogical analysis, chemical analysis, particle size distribution, COD (chemical oxygen demanding) level, and BET (Brunauer-Emmett-Teller) 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 showed that not only SO3 content in the batch affected foam formation in E-Glass melts, but also raw material chemistry and their particle size ranges had 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. The second part examined the impact of anthracite concentrations on the melt foam formation.