Energy Guzzler: Manufacturers struggle to improve an inefficient melting process
Architects tout green buildings and sustainable design; fabricators trumpet low-emissivity and insulating glass products, all in the spirit of creating energy-efficient buildings. What about energy-saving manufacturing and production, though?
Each year, the U.S. glass industry uses more than 250 trillion British Thermal Units to produce 21 million tons of glass, according to the U.S. Department of Energy, making it one of the top industrial culprits of energy consumption.
“Second only to [the aluminum industry], the glass industry is the most energy intensive, meaning we have the second highest amount of energy needed to make a pound of product,” says Michael Greenman, executive director of the Glass Manufacturing Industry Council in Westerville, Ohio. Designers and contractors who work in commercial and residential construction are “all being pushed to be more environmentally responsible. The results, however, are new glass products that don’t necessarily involve green manufacturing.”
Throughout the last several decades, float-glass manufacturers have worked to combat energy problems caused much in part by an extremely high-energy melting process. The melting and refining stages require about 8.60 million of the 12.98 million Btu per ton used in U.S. flat-glass production, according to the DOE. Glassmakers have come up with a variety of partial solutions, including more insulation, improved refractory and furnace designs, and more efficient burners. Some have tried changing the fuel source by using oxygen instead of air in furnaces. Other producers used electric boosting to hasten melt times and improve their processes. Most of those improvements, however, produce only small energy savings, sometimes just 1-to-2 percent.
“The glass-making process is ripe for drastic change,” concludes a detailed GMIC assessment in 2004 under a contract of the DOE. In the report, researchers looked closely at the processes of about 75 glass manufacturers in all sectors of the industry, including flat, container, fiber, and pressed or blown. The researchers saw companies exude considerable effort to improve the energy efficiency of the 53-year-old float-glass process by just a couple percent.
Revolutionary and extensive overhauls of the process, as recommended in the report, are greatly limited by the high costs of research and development and changes to the manufacturing process, Greenman says.
Manufacturers report the cost of new float lines using current technology totals about $160 million, while rebuilds reach about $25 million or more if design changes are required.
While the glass industry’s reign as one of the top energy users combined with skyrocketing fuel prices have made the need for change more imminent, small-gain solutions may be all that company executives say they can afford to invest in for the time being.
Following is a sample of some more prevalent small-gain or evolutionary changes to the traditional float glass melting process that some manufacturers in the flat-glass industry have applied or tested in their furnaces, and two revolutionary furnace designs from the GMIC.
The oxy answer
Oxygen-fuel firing has infiltrated about 25 percent of U.S. glass manufacturers in all four sectors of the industry including flat, fiber, container, and pressed or blown glass facilities, according to the GMIC assessment. However, only a handful of U.S. float-glass plant operators use the method, which came into use in its very early forms in the mid-1980s.
Oxy-fuel firing more efficiently melts raw materials than traditional air-fuel firing, reducing emissions and the amount of natural gas necessary, says Philip Ross, president of Glass Industry Consulting in Laguna Niguel, Calif.
“You save a lot without the hundreds of tons of nitrogen [from air fuel] pumped into the furnaces daily that has to be heated,” Ross says. “It’s about a 10-to-12 percent improvement.”
Operators of three U.S. float-glass plants utilize oxy fuel: PPG Industries’ Fresno, Calif., and Meadville, Pa., plants and Pilkington’s Rossford, Ohio, plant. “PPG [officials have] been public by saying oxy fuel produces a more stable glass quality,” Ross says. “In their minds, on a net overall basis, oxy is the way to go.”
However, oxy fuel comes with one notable downside: oxygen, unlike air, isn’t free. Oxy-fired plants require an attached cryogenic facility and quite a bit of electricity to create the pure oxygen for fuel.
“When air is used for combustion, you just take it, no additional energy is required,” says Richard Alonzo, vice president of engineering for Guardian Industries Corp. of Auburn Hills, Mich. “Separating oxygen from air requires a lot of electricity. Oxygen-fired furnaces aren’t going to be more energy efficient than the traditional air-fuel furnace when you take into consideration the additional energy required to obtain the oxygen.”
Company officials still likely see a financial gain from oxy fuel, particularly considering recent spikes in natural gas costs. The energy use, however, will be higher with the added processes involved in the cryogenic facility.
Officials from Cardinal Glass Industries of Eden Prairie, Minn., decided against using oxygen fuel in their new float-glass plant, based on similar reasoning. The Winlock, Wash. facility is set to open in summer 2006.
“We did consider [oxy-fuel] technology,” says Tom Kaiser, vice president for Cardinal. “At the end, the fact that it is still new combined with the costs associated with generating and producing the oxygen led us to stick with a more traditional furnace design.”
The company will improve the plant’s efficiency instead through top-quality furnaces, Kaiser says.
“Note that furnace design and efficiencies have improved since their development,” he says. “Cardinal will install the best, state-of-the-art system to deal with this aspect of glass production, and this system exceeds the [emissions] requirements for the state of Washington.”
Some manufacturers also worry that oxy-fuel will limit the lives of their furnaces. “The products of combustion in an oxygen-fired furnace are far more concentrated than in a traditional air-fuel furnace,” Alonzo explains. “In a traditional furnace, the combustion products are diluted by all the nitrogen in the air. It is well-known in the industry that the higher moisture content found in a oxygen-fired furnace is very corrosive on the furnace refractories, particularly the crown and exhaust ducts.”
Current and future improvements to oxy-firing could lead to dual savings in terms of overall energy and cost, Ross says.
The BOC Group in Murray Hill, N.J., designed Convective Glass Melting technology. By installing oxygen burners in the roof to fire down on a batch, CGM increases pull and improves thermal energy, says Andrew Richardson, CGM inventor and technology manager for BOC.
“One customer described CGM in the following manner; ‘If you are holding a cutting torch, you can place your hand to the side of the flame with no problem, but don’t put it in front of the flame,’ ” Richardson says. “The maximum energy is delivered by applying the end of a flame to a cold object. CGM applies the tip of an oxy-fuel flame to the cold batch entering the furnace, maximizing heat transfer, hence melting glass faster.”
About 30 furnaces worldwide use CGM; six produce flat glass, including Pilkington’s Laurinburg, N.C., plant. So far, CGM has only been used temporarily in flat-glass plants to increase yield and lifespan of an old air-fuel melter, only to be removed upon furnace repair, Richardson says. However, one undisclosed manufacturer will install CGM in one of its flat-glass plants this fall as a permanent fix to increase production capacity throughout the entire furnace life, he says.
“The challenge is to use [CGM] to increase production while maintaining the same mass emissions,” Richardson says. “If we increase the pull rate, we must decrease the emissions on a per-ton basis.”
Another method still in its early stages involves using waste heat from the furnace to get the oxygen, rather than using electricity, Ross explains. The introduction of a working example of this in a furnace could still be a number of years down the road.
“This has been done on smaller scales, but whether it makes its way into flat glass depends on whether the research, participation and funding is there,” Ross says. “Without government funding, it might be more difficult, but the oxygen companies are interested in promoting these types of projects.”
The DOE’s Energy Efficiency and Renewable Energy 2006 budget request for the Industries of the Future program—the source of money for glass-manufacturing research—totaled about $22.0 million, down from $38.2 million approved in fiscal 2005. The glass industry would receive $1.8 million of that.
Other evolutionary solutions
Beyond fuel and furnace improvements, manufacturers and researchers have conceived other methods to improve energy efficiency. Methods such as synthetic silicates and electric boosting build on traditional melting processes, have been tested and are in the commercial market.
Synthetic silicates change the raw materials going into the melter, using a synthetic calcium magnesium silicate called Synsil as a replacement for dolomite, limestone and some quartz, all ingredients for glass. Synsil melts and transforms into glass faster, allowing for decreased temperatures and energy use, and increased yield, says John Hockman, technical manager of Synsil Products in Easton, Pa. The company began producing Synsil in 1997.
Changing raw materials proves easier and less expensive than altering the actual furnace. However, as with oxy fuel, creating synthetic silicates consumes energy, too, Hockman says.
“All raw-material solutions spend the energy somewhere even if it is not at the glassmaker’s facility,” Hockman says. “Even though the global net energy will be increased due to heating materials twice, the opportunity to use different fuel sources does still give some needed flexibility to a global economy. For instance, the glass industry needs to use natural gas to heat its raw materials. The energy source for making the energy-saving glass raw material, i.e., Synsil, does not need to be natural gas.”
Synthetic silicates also increase raw material costs, says George Pecoraro, a former staff engineer at PPG. “Sand sells for $4 a ton,” he says. “If you start messing with that, the price of the batch goes up quickly.”
For silicates to prove an economical solution, manufacturers have to find the “sweet spot,” Hockman says. “Since silicates increase raw material cost while decreasing the fixed cost contribution, the overall production margin gain requires some modeling to find the sweet spot,” he says. “In each [trial], silicates have more than paid for themselves while decreasing energy consumption.” Hockman says float-glass manufacturers have worked with Synsil, but he cannot release company names due to confidentiality agreements.
Electric boosting, on the other hand, heats ingredients faster by sending an electric current through the glass melt, acting as a conductor. Primary users of the process are manufacturers making privacy glass that requires higher iron levels, Ross says.
“From an energy-per-ton point of view, electric boosting is saving some energy, but again, electricity comes from power plants,” Ross says.
Start the revolution
While many manufacturers look to these evolutionary alterations to improve the float process, GMIC officials work to change the way people melt glass, making it more energy efficient and environmentally friendly. More revolutionary approaches, such as GMIC’s high-intensity plasma melter and next-generation submerged combustion melter, could be 10 years down the road until completion and even further off until they achieve acceptance by industry players, Ross says.
With the energy-efficient next-generation melter, GMIC researchers want to create a furnace that can produce the same amount of glass as current furnaces, but in a smaller area with lower emissions and capital costs, says John Brown, GMIC technical director. The melter utilizes a submerged combustion design fueled by oxygen, with the oxy fuel added directly to the molten glass. The oxy-gas bubbles through the melt, causing rapid heat transfer and mixing.
“There is much less energy consumed per ton [in the next-generation melter], because you’re putting more glass through in less time,” Brown says. “This process is transferring heat more easily and doing a tremendous job of mixing.”
Plasmelt technology attempts to overcome the same issue as the next-generation melter by also speeding melt times. It uses high-voltage electricity through a duel-torch plasma arc melting system. The dual-torch system includes an anode torch and a cathode torch that release enormous amounts of energy from above a rotating melt chamber, rapidly increasing melt times.
“This technology generates a column of energy at temperatures higher than the surface of the sun,” Brown says. “Atoms are driven into higher energy shells, and when they drop to standard levels, release the stored energy. Many elements can be boosted to the higher energy state to create plasma, but Argon is best known for this purpose. That’s plasma. …
“You put your raw material into a rotating ceramic line, and the plasma comes into the pool at about 15 thousand degrees Centigrade,” Brown says.
While Plasmelt and next-generation melters could be of use to the entire industry in the future, current designs would best serve fiber and specialty glass that require less refining, Brown says.
The sink-or-swim pressure to change
Glass manufacturers must address rising fuel costs while meeting environmental standards and answering to an increasingly environmentally aware society, explains Cheryl Richards, former GMIC board president and market development manager for member company PPG Industries Inc. of Pittsburgh. The increasing number of overseas competitors further pressures U.S. companies to lower their costs. With cheaper labor and energy, many nations such as China threaten to woo customers with their lower prices. Researchers at U.S. industries will have to discover other methods to decrease their costs to compete, she says.
“The pressures we face include more than just energy. The world has become more aware of what [industries] do to the environment, so we need to meet those environmental standards and turn a profit in the meantime.
“We have to make money, try to meet certain profit points and meet U.S. Environmental Protection Agency restrictions,” Richards says. “It’s not that [U.S. companies] are apprehensive, but we can’t go spending money as freely [on our production processes]. It’s difficult to spend more money on fundamental needs such as fuel while investing in our processes to meet productivity goals and environmental standards when products are coming in from another country that are cheaper.”
Based on that reasoning, Brown says, many industry participants have been fairly willing to becoming involved in the GMIC initiatives.
“No individual company has the money or guts to take on one of these projects on their own, because there is enormous financial risk to make any change in a melting operation,” Brown says. “We allow glass companies to go after pre-competitive problems, and we’re doing it under government supervision.”
Company executives can join forces to combat the industry’s looming energy crisis, or combat the problem on their own. Either way, according to the GMIC report, the need for a change to the float-glass manufacturing process remains imminent, and company managers will either sink or swim. Those waiting idly for others to find solutions could either be washed up or drowned by cheaper overseas competitors.
David Rue, Gas Technology Institute, 1700 S. Mount Prospect Road, Des Plaines, Ill. 60018, 847/768-0500, david.rue@ gastechnology.org, www.gastechnology.org