GLASS FORMING & PROCESSING: Saving Energy with Lithium
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,