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Whenever energy conservation measures are considered in the glass industry, it is often in terms of equipment and tools designed to increase a plant's operating efficiency. 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 lithium can have a significant impact on the industry's energy requirements.
"There are documented cases of glass 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, including increased production speeds and improved product quality.
As glass manufacturers struggle to remain competitive in the face of increasing global competition, such simple solutions can 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 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 25°C (77°F), 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.
With growing competition from plastic and aluminum packaging materials, glass container producers are seeking to develop lighter weight containers by reducing the glass thickness. Lithium can help glass producers achieve this goal by enhancing the mechanical strength of the glass, as well as its hydrolytic and chemical resistance. It also increases the working range of glass, thereby improving the thickness uniformity (from top to bottom) of glass bottles.
According to Anand Sheth, technical marketing manager for Sons of Gwalia Ltd., West Perth, Australia, only a small amount of lithium is needed to reap the benefits. The normal addition rate in glass containers is only 0.1 to 0.17 wt% Li2O or 3 wt% spodumene concentrate (glass grade).
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 40-50°F 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.2
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.
Over the last several years, a number of glass container and cosmetic glass manufacturers in Asia have begun using spodumene in production and have increased their furnace capacities by 20 to 25%, reduced their rejection rates and eliminated the problem of weathering in glass. These manufacturers have also achieved enhanced glass brightness and a lower seed count, which has enabled them to increase sales.
According to Sheth, 0.1 wt% Li2O can provide approximately the same melting effect as a 10% cullet addition to the glass. With the unavailability of high-quality cullet in some countries, lithium is gradually becoming accepted as a better choice since it also provides other benefits that are not achieved with cullet.
"The increased batch costs are typically recovered through a higher glass yield; thus the unit cost of bottles remains largely unchanged or lower, depending on the location and the costs of other raw materials and fuel," Sheth said.
Why Isn't Everyone on Board?Despite the success stories from manufacturing facilities around the world, many glass manufacturers have been reluctant to consider the use of lithium as an energy-saving solution. A number of the manufacturers that ran lithium trials early on have gone out of business or been acquired by other companies, and today's companies don't appear to be 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, suppliers have noted that the price of lithium carbonate has dropped considerably over the past several years, and 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 any added material cost.
Another concern for many glass producers is the effect of lithium additions on the refractories inside the furnace. However, a European glass research lab has shown that small additions of lithium-up to 0.3 wt% Li2O-in glass does not corrode refractories at same furnace load or temperature used previously, and in fact can enhance refractory life when it is used to replace soda or potash in the glass batch. Additionally, lithium does not volatilize and therefore poses no threat to the furnace crown.
As global competition continues to place pressure on 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 such as lithium 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 is an updated version of a previous article published in Ceramic Industry (July 2002), which was compiled with the assistance of Jim Angelo, Chemetall Foote Corp.(contact Gary Otwell, (704) 739-2501, firstname.lastname@example.org ); Derek McCracken, American Minerals, Inc., (724) 695-7820, DMccrac814@aol.com ; Anand Sheth, Sons of Gwalia Ltd., (61) 8-9263-5555, email@example.com ; and Charles Merivale, Amalgamet Canada, (416) 366-3954, ext. 224, firstname.lastname@example.org (on behalf of Tantalum Mining Corp. [TANCO], Manitoba, Canada).