NCER Assistance Agreement Annual Project Summary

Date of Report: 1/1/08

EPA Agreement Number: X-83254101-1

Center: Center for Environmental and Energy Research (CEER)

Project Title: The Fining Behavior of Selectively Batched Commercial Glasses

Investigator(s): William Carty

Institution(s) of PI(s): Alfred University

Research Category: Congressionally Mandated Center

Project Period: September 2006- February 2008

Objective of Research:

The fining behavior of a selectively batched generic float glass is being investigated. In previous studies selective batching techniques utilizing two granules of different chemical composition have shown up to an 80% reduction in batch free times for SLS and E-glass melts. Our goal is to develop a fast fining process that utilizes selective batching technologies. Shortened batch free times lead to the reduction of CO₂, while a fast fining process could help reduce dependence on saltcake. For each ton of flat or float glass produced in the United States, 1.5 Kg of SO_x is emitted into the earth’s atmosphere. The use of selective batching technologies also inherently reduces NO_x emissions through reduced fuel use. It was originally proposed that by tailoring the size of void spaces between granules, large gas bubbles could be generated and used to sweep smaller intra-granular bubbles to the surface.

Progress Summary/Accomplishments:

Many methods of granulation are known to exist and have been investigated for the selective batching of common commercial glasses, these include; spray drying, pan pelletizing, pin mixing and finally high intensity mixing. Erich high intensity mixers were found to yield the desired size and density granules while conserving energy over the other most desirable method- spray drying. Granule #1’s chemistry is 73.17 SiO₂·26.45·Na₂O·0.26 K₂O·0.12 Al₂O₃ and is mixed from fine ground silica, dense soda ash, potash and EPK. Granule #2’s chemistry is 70.50 SiO₂·20.93 CaO·8.57 MgO and is mixed from fine ground silica, calcium carbonate and dolomitic limestone.

The granulation process uses high and low speed settings on the rotor of an Eirich R-07 mixer. The process for producing dense, narrowly distributed granules involves an initial low speed, dry mix for homogeneity followed by high speed liquid addition mixing. A high speed granulation step followed by low speed growth and dusting steps completes the process. The size of the final granule produced is a delicate balance between water content and the duration of granulation/growth mixing steps. A variety of granule sets were prepared including one variety of generic E-glass two varieties of generic SLS glass and finally the float glass composition melted in this study. The granules were characterized using optical microscopy and granule size/distribution weight measurements. Intra-granular densities and tap densities were measured to gain insight to overall gas bubble to glass volume ratio information.

The study’s main mode of investigation has been melting intermediate (2 Kg) sized batches and cutting cross sections into the melts to count and compare bubble populations. These populations are expressed as a function of vertical position in the crucible. A total of 32 crucibles will have been investigated this way, leading to plots of bubble diameter as a function of height in the crucible.

Glass chemistry and density as a function of melt time have been verified using ICP chemical analysis and helium pycnometry, respectively. Using the Vogel-Fulcher-Tammann equation, viscosity estimates were made from the chemical analysis results of each final glass. The viscosity of each melt at the 5 hour mark was also measured using a hot stage microscope. Viscosity data support batch segregation theory within the conventionally batched melts while suggesting a more uniform, homogenous melt evolves in selectively batched trials.

Within the many steps of any fining operation one of the first steps is the growth and rise of the largest bubbles in the melt. Selective batching allows for the initiation and completion of this step faster than conventional melting by avoiding the inherent high viscosity pockets associated with a melt undergoing batch segregation, while simultaneously achieving lower batch free times.

Publications/Presentations: None

Future Activities:

A re-melt at higher temperatures is underway to try and resolve a greater difference in fining behaviors between conventional and selective batching methods. Concentric granulation combines the two-granule system into a single-granule system with a core and crust of different chemistries and is the next step in developing selective batching technologies.

Supplemental Key Words:

Selective Batching, NO_X, SO_X, CO₂, Granulation, Batch Free Time, Fining, Green House Gas, Hot Stage Microscope, Vogel-Fulcher-Tammann

Relevant Web Sites: http://ceer.alfred.edu