Materials Research

Emissions Reduction of Commercial Glassmaking Using Selective Batching

EPA Grant Number: X83254101-1

Center: CEER at Alfred University

Investigator: Carty, William M.

Institution: Alfred University

Project Period: September 1, 2006 to February 28, 2008

Research Category: Congressionally Mandated Center

Description:  

Commercial glass melting is an energy-intensive process that emits criteria air pollutants NOx and SOx as well as the potential greenhouse gas CO₂.  The current commercial methods of glass making are relatively inefficient, requiring approximately 5.5 to 8.6 million Btu/ton of glass for melting and refining for a process that theoretically requires only 2.2 million Btu/ton of glass.  The technology of selective batching, which is the introduction of raw materials into a glass tank in a manner that controls reaction paths, has resulted in an 80-90% reduction in melting times on a laboratory scale with granules prepared via spray drying.  These preliminary observations also suggested, qualitatively, that bubble formation is also reduced, but this aspect has not been evaluated.  It is proposed to evaluate the fining of glass prepared via selective batching and compare the effect of granule size, temperature, and composition to that prepared via conventional batching. 

Objectives/Hypotheses: 

Under the proper preparation conditions, coupled primarily to granule size, it is proposed that selective batching will result in a reduction in fining time consistent with the tailoring of bubble size in the glass melt and the overall reduction in bubbles formed during the melt reactions.  If this is correct, it will allow the elimination of salt cake (Na₂SO₄) which is added to conventional glass batches to aid in the fining operation. 

Approach: 

Two granule compositions, consistent with the selective batching concepts, will be prepared using a pilot-plant pan pelletizer in the size range of 250µm, 500µm, and 1.0 mm diameter.  These granules will be blended to obtain the desired glass composition and melted in two-kilogram melts in silica crucibles.  The crucibles will be heated to dwell temperatures of 1400°C, 1450°C, and 1500°C, held for a range of times (from 0.5 to 8 hours), quenched, annealed, then sectioned so the bubble populations can be characterized.  An parallel study will be conducted with a commercial composition (with and without salt cake, and using the conventional batching approach instead of selective batching) to evaluate the potential benefits of selective batching on fining operations. 

Expected Results: 

The goal is to decrease emissions through reduced use of salt cake, reduced temperature, and reduced residence time of the glass in the melter. The use of salt cake in commercial glass production is the source of virtually all SOx emissions (assuming natural gas fuel).  About 1.5 kg of SOx are emitted per ton of glass, in addition to the 7 and 4 kg of NOx emitted during production of flat and container glass, respectively.  In the U.S. about 15 million tons of tons of flat and container glass are produced annually, meaning that there is significant potential to reduce SOx, NOx, and CO₂ through the improved performance shown by selective batching.

Supplemental Keywords: 

glass batching, glass melting, fining, green house gas reduction, selective batching, granulation, industrial glass production.

CEER is funded in large part by the United States Environmental Protection Agency.

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