However, there may be another way to reduce energy use without investing large amounts of capital in equipment and systems. According to Charles Merivale, senior vice president of Amalgamet Canada (a Division of Premetalco Inc.), adjusting the batch with additions of certain raw materials, such as lithium, can have a significant impact on the industry’s energy requirements. “There are documented cases of glass and ceramic companies adding lithium to their batch and lowering melting/firing times and furnace temperatures, thereby conserving fuel,” Merivale said. These cases suggest that as much as 5-10% of energy use can be saved through this simple measure. When this strategy is combined with other energy-saving tools, such as modified or new equipment, the savings can be significantly higher. The added raw materials can also provide other benefits, such as increased production speeds and improved product quality.
As the U.S. glass and ceramic manufacturing industries struggle to remain competitive in the face of increasing global competition, such simple solutions may have a significant impact in terms of overall energy and cost savings.
When used in glass, lithium oxide (Li2O), as well as lithium-bearing ores such as spodumene, decreases the melting point, viscosity and thermal expansion of the glass, leading to increased melting efficiencies and/or larger effective furnace capacities. Because Li2O can lower the required processing temperature by as much as 50C, it provides a 5-10% reduction in energy use and can also decrease NOx emissions. Additional benefits include improved glass quality and an increased melt-to-pack ratio as a result of fewer checks and tears, as well as a potential increase in refractory life due to lower operating temperatures.
When used in ceramics, Li2O can increase productivity by reducing the required soak time and/or can reduce energy consumption by lowering the vitrification temperatures by up to 20C. It can also lower rejects and losses in production due to reduced deformation while providing higher green strength, staining resistance and increased mechanical strength. Li2O is also used in frits and glazes, where it reduces the viscosity and increases the fluidity of the coatings, thereby reducing maturing times and lowering firing temperatures.
In other parts of the world, glass manufacturers were also starting to realize the benefits of lithium. In the late 1980s and early 1990s, trials at container glass manufacturing plants in Asia, the UK, Germany, Switzerland, Italy and France all showed that lithium additions between 0.03 and 0.20% by weight provided energy savings in the range of 4-10%, as well as increased production speed and reduced defects. In 1990, Kirin Brewery in Japan reported a 7.5% increase in pull without increased energy consumption using 0.2 wt% glass-grade spodumene.3 In 1994, trials at a container glass manufacturing plant in Central America showed that production was increased 11% with a 3% reduction in energy and equivalent quality compared to the glass without the lithium addition, while trials at a North American container glass manufacturing plant showed increased quality (decreased checks) along with a 5% savings in energy consumption at the same production levels used prior to the lithium addition.4 More recent trials at glass container and tableware manufacturing plants have further substantiated the idea that lithium can provide energy savings, increased product quality, higher throughput and other benefits in glass manufacturing. Many glass plants have been using lithium for several years.
Over the past few years, spodumene has also found its way into sanitaryware applications in Europe and Asia, where firing temperatures have been reduced by as much as 30C with a 4% spodumene addition,5 and unglazed (porcelain) floor tiles, where spodumene has been shown to reduce firing temperatures, decrease flux, zircon and stain additions, and improve freeze-thaw characteristics with a 3-4% spodumene addition.6
Part of the problem is the cost—and perceived cost—of lithium. When many of the early trials were conducted, lithium was considered too costly to implement on a regular basis. However, according to Jim Angelo, industry sales manager at Chemetall Foote Corp., Kings Mountain, N.C., the price of lithium carbonate has dropped considerably over the past several years. Other lithium-bearing ores have also become more affordable. Additionally, data from a number of plant trials have indicated that the energy savings and other benefits that can be achieved with the lithium additions often more than make up for the added material cost.
As global competition continues to place pressure on U.S. manufacturers, companies will be forced to look for more ways to reduce costs without compromising productivity and product quality. While a number of advances will continue to be made in terms of equipment, manufacturers shouldn’t overlook raw materials as a potential part of the overall solution.
“For our industry to remain competitive, it is going to have to consider these other approaches,” Merivale said.
For more information about using borates in glass and ceramics, contact Borax at 26877 Tourney Rd., Valencia, CA 91355; (661) 287-5400; fax (661) 287-5455; or visit http://www.borax.com.
1. “The 2002 Materials Handbook,” Ceramic Industry, January 2002, p. 45.
2. “Bodywork,” Borax Pioneer, November 1999 (www.borax.com/pioneer43.html).
* Borates incorporating soluble metal cations, such as zinc, sodium or calcium, can cause the slurry to thicken, leading to processing difficulties. The borate used in this test, Optibor™ TG supplied by Borax, did not contain soluble metal cations.2