Saving Energy with Raw Materials
Whenever energy conservation measures are considered in the glass and ceramic industry, it is often in terms of equipment and tools designed to increase a plant’s operating efficiency. Even the U.S. Department of Energy’s (DOE) Office of Industrial Technologies (OIT), which is dedicated to partnering with other organizations to research, develop and deliver advanced energy efficiency, renewable energy and pollution prevention technologies to industry, has primarily focused on equipment-related technologies—such as high-efficiency furnaces, burners, sensors and modeling tools—as methods for energy reduction.
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.
How Does It Work?
Lithium is the lightest, smallest and most reactive of all of the alkali metals. It also possesses the smallest ionic radius (the average distance from the center to the outermost electron) and the highest ionic potential (the energy required to cause any atom to lose an electron and thus become a cation). According to Derek McCracken, director of minerals marketing at American Minerals, Inc., King of Prussia, Pa., “All of these factors combine to produce an extremely powerful flux that can be used to benefit both glass and ceramics.”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.
What Evidence Exists?
Using lithium to reduce energy requirements in glass manufacturing is not a new concept. In 1968, Thatcher Glass Manufacturing Co. performed production tests using spodumene, a lithium-bearing ore, as a batch additive. The company concluded that lithium increased the melting rate and lowered melting temperature and fuel usage.1 However, little or no additional production-scale research was reported on lithium’s effect in a glass batch until the early 1980s, when Glass Containers Corp. decided to run two tests, one in Jackson, Miss., and the other in Hayward, Calif., with the assistance of Lithium Corp. of America in Gastonia, N.C. (now FMC Corp., Lithium Division). The results were similar to what had been achieved in Thatcher Glass over a decade earlier—adding lithium carbonate to the glass batch resulted in a 40-50F reduction in furnace temperature, a 12% increase in pull rates, increased machine speeds averaging one to two bottles per minute, and a slight increase in pack, as well as an increased surface brilliancy and sheen of the final product.2In 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
Why Isn’t Everyone on Board?
Despite the success stories from manufacturing facilities around the world, U.S. glass and ceramic manufacturers have been reluctant to consider the use of lithium as an energy-saving solution. Many of the glass manufacturers that ran lithium trials early on have gone out of business or been acquired by other companies, and today’s glass and ceramic manufacturers don’t appear to be too eager to change their product formulations. “[The U.S. industry] seems fixated on the ‘hardware’ of glass and ceramic manufacturing and so far has shown no inclination to consider energy reduction improvements through batch adjustments,” said Merivale.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.
Editor's Note
This article was compiled with the assistance of Jim Angelo, Chemetall Foote Corp., (704) 739-2501, jim.angelo@chemetall.com; Derek McCracken, American Minerals, Inc., (724) 695-7820, DMccrac814@aol.com (on behalf of Anand Sheth, technical mktg. mgr., Sons of Gwalia Ltd., West Perth, Australia); and Charles Merivale, Amalgamet Canada, (416) 366-3954, ext. 224, charles@amalgamet.com (on behalf of Tantalum Mining Corp. [TANCO], Manitoba, Canada).SIDEBAR: The Benefits of Borates
Lithium isn’t the only energy-saving raw material—borates have also exhibited the potential to reduce energy consumption in glass and ceramic applications. Additions of 0.6-1.5% boric oxide (B2O3) can facilitate glass melting and refining, enabling production increases of 20-50% or decreased melting temperatures.1 Boric oxide has also been shown to increase the brilliance, strength, durability and thermal shock resistance of the glass. In tests with porcelanic floor tiles, a specially formulated B2O3* enabled firing temperatures to be lowered by 20 to 30C while also imparting improved strength and decreased porosity to the ceramic body. Other tests have shown that borates can also improve quality and lower firing temperatures in white-body and red-body tiles.2For 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.
Sidebar References
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