The U.S. Department of Energy is reducing various risks through its Office of Industrial Technologies (OIT), which shares the cost of developing and implementing technologies that promise to save energy, reduce emissions, and increase productivity of the US steel industry. The OIT signed a compact with the American Iron and Steel Institute and the Steel Manufacturers' Association in May 1995 to collaborate with the U.S. steel industry on three critical research and development areas: process efficiency, recycling, and environmental engineering. Researchers at Oak Ridge National Laboratory in Tennessee developed the nickel aluminide alloy for the rollers, which were centrifugally cast by Sandusky International in Sandusky, OH. This material has superior temperature resistance, which gives it longer service life in the annealing furnace than conventional stainless steel. A phosphor-based sensing technology being tested at Burns Harbor will enable steelmakers to accurately measure the temperature of highly reflective steel strips whose emissivity can skew the readings of optical pyrometers.
New processing technologies are essential for American steelmakers to maintain their competitive edge against offshore competition, but implementing these techniques in actual industrial environments for the first time carries risks. The U.S. Department of Energy is reducing these risks through its Office of Industrial Technologies (OIT), which shares the cost of developing and implementing technologies that promise to save energy, reduce emissions, and increase productivity of the U.S. steel industry.
“The OIT signed a compact with the American Iron and Steel Institute and the Steel Manufacturers’ Association in May 1995 to collaborate with the U.S. steel industry on three critical research and development areas: process efficiency, recycling, and environmental engineering,” explained Scott Richlen, a mechanical engineer and Steel Team Leader at OIT. This government/ private sector alliance is well illustrated through four technologies—nickel aluminide rollers, an oscillating fuel valve, a low NOx oxy-fuel burner, and phosphor sensors—that are being demonstrated at Bethlehem Steel’s plant in Burns Harbor, Ind.
These technologies are the latest fruits of Bethlehem Steel’s long-standing relationship with the OIT, according to Tony Martocci, a chemical engineer, metallurgical engineer, and program manager for corporate energy affairs at Bethlehem Steel. Martocci himself has spent time on OIT committees concerned with energy consumption, costs, and' conservation efforts by the steel industry.
“Everyone wants to talk about how successful new technologies are, but no one wants to talk about the learning curve and expense they entail. Partnering with OIT takes some of the risk out of using a technology for the first time,” said Martocci.
Burns Harbor is a fitting showcase for these new technologies as the flagship operation of Bethlehem Steel, the nation’s second largest steel company.
Bethlehem Steel constructed the 3 1/2-mile-long plant in 1962, establishing its principal operation on the shores of Lake Michigan in northwest Indiana, about 40 miles southeast of Chicago, to ensure its proximity to the steel-consuming manufacturers in the midwestern states. These companies make up the largest single regional market for steel sheet and plate products in the United States.
Burns Harbor’s 6,000 employees produce up to 5.2 million tons of hot-rolled sheet, cold- rolled sheet, and corrosion-resistant coated sheet steel, as well as steel plates. The plant is a major supplier of sheet and plate products to the automotive, service center, construction, machinery, and appliance markets.
Bethlehem Steel has been using cutting-edge technology at Burns Harbor for years. Indeed, since 1983, the company has invested $1.5 billion in state-of-the-art facilities and equipment, including a 72-inch hot-dip coating line, coal-injection unit, vacuum degasser (see April, page 54), second continuous caster, and advanced computer-control improvements throughout the rolling mills. That hefty price tag is a bargain compared to the $6 billion it would take to replace the plant.
It is no coincidence that the four technologies were all placed at the Indiana plant. “We already had the nickel aluminide rolls in place at Burns Harbor, and had agreed to install the low NOx oxy-fuel burner. The good working relationship we built up with Burns Harbor simplified bringing in the other two technologies,” said Richlen.
Longer-Lasting Transfer Rollers
A dozen nickel aluminide rollers installed at Burns Harbor, with another eight to come, were developed under OIT’s Advanced Industrial Materials Program. The rollers are used to transport large steel slabs through an annealing furnace, where they are heated to varying temperatures to make the steel more ductile.
The rollers in an annealing furnace are typically made of cast stainless steel. They become worn from the high temperatures, affecting the surface characteristics of the steel slabs, which sometimes requires the steel to be reworked. Replacing the worn rollers improves energy efficiency and productivity by reducing reworking of material and maintenance downtime.
Researchers at Oak Ridge National Laboratory in Tennessee developed the nickel aluminide alloy for the rollers, which were centrifugally cast by Sandusky International in Sandusky, Ohio. This material has superior temperature resistance, which gives it longer service life in the annealing furnace than conventional stainless steel. The nickel aluminide rollers would thus improve the surface quality of the steel being annealed, reduce the energy costs associated with reworking, and improve productivity by minimizing replacement downtime.
The nickel aluminide rollers at Burns Harbor are 14.5 feet long, 14 inches in diameter, and have a one-inch wall thickness. Sandusky International sought to reduce the cost of the rollers by making trunnions of stainless steel instead of nickel aluminide. “This reduced the cost by more than 25 percent, but presented the challenge of joining two different materials with different characteristics, including coefficients of thermal expansion and strength. We solved this problem by using finite-element analysis to calculate the peak stresses at the joint, as well as the load distribution on the roll body,” explained Vinod Sikka, a metallurgical engineer and Group Leader for Materials Processing at Oak Ridge National Laboratory. Based on this data, Sandusky International pinned the trunnions to the rollers mechanically, a simpler and more durable alternative to welding.
More Accurate Galvanneal Temperature Measurement
A valuable piece of information for steelmakers is knowing the precise temperature of the galvanneal surface during processing. This enables them to achieve the required quality, which hinges on heating a batch of steel to a specific temperature, and saves energy that would be wasted overheating the steel.
Because of steelmaking’s high temperatures, fabricators often use noncontact optical pyrometers to measure temperature. These instruments convert the natural radiation emitted by a heated object into a corresponding temperature. However, when the surface is highly reflective, such as in the galvanneal process, the constantly changing emissivity and strip motion compromises the accuracy of the competing technologies.
For this reason, the American Iron and Steel Institute (AISI) in Washington, with joint funding from the DOE, oversaw the development of a sensing technology using phosphor thermography, which operates independently of emissivity under the auspices of the OIT’s Advanced Process Control program.
As part of the A1SI/DOE program, engineers at Oak Ridge developed a phosphor-based temperature measurement system, which was first tested at National Steel’s Midwest plant in Portage, Ind., in 1997. A second system was installed in March at Burns Harbor on the chromatic coating line.
The galvanneal temperature measurement system uses phosphor powders calibrated for temperature ranges of interest. The powder is contained in a hopper and deposited by air blast onto the surface of the galvanneal steel strip.
“The phosphor powder is excited by a laser beam. Then, light detectors measure the fluorescence of the phosphor, which indicates the temperature of the surface,” explained Joe Vehec, director of the Advanced Process Control program at AISI in Pittsburgh.
The Burns Harbor installation has demonstrated that the phosphor system is accurate to within 5°F on actual production runs. The system is being marketed by Bailey Engineers Inc. of Canonsburg, Pa., and a number of steelmakers have expressed interest in using this temperature measurement technique.
Oscillating Combustion Reduces NOX Emissions
Nitrogen oxides, or NOx, are an industrial pollutant whose emission is being continuously restricted. The Institute of Gas Technology in Des Plaines, Ill., and Air Liquide in Countryside, Ill., developed the oscillating combustion technology to reduce NOx emissions by 50 to 90 percent without the need and expense of replacing standard gas burners with special staging burners. “Staging burners typically use excess fuel or air in the first combustion stage in order to minimize NOx formation. By adjusting the delivery of fuel to a standard burner by simply using a pulsing valve, the same NOx reduction effect would be achieved,” explained Hamid Abbasi, a chemical engineer and managing director of combustion technologies at IGT. An added benefit of this technology to steelmakers is that it can improve heat transfer up to 10 percent, increasing productivity by shortening the furnace-to-product heat-up times.
CeramPhysics Inc. of Westerville, Ohio, manufactured the oscillating fuel valve and controls, which were installed in a 10-burner stack annealing furnace at Burns Harbor under the auspices of the OIT. The unit consists of a valve body containing a temperature-resistant elastomeric membrane that is pulsed by a magnetic switch controlled to increase or decrease the flow of gas to the burner. The controller is directed by the plant s existing computer control system and follows the three primary parameters that will determine the effectiveness of the valve. These are the frequency of oscillation; its amplitude, which determines how much of a fuel-rich or fuel-lean zone is created; and the duty cycle, or the percentage of cycle time the valve is open.
“We will use the Burns Harbor installation to determine how well the hardware performs, and whether the technique is acceptable to operators,” said Abbasi, who noted that other steel mill operators have expressed an interest in the oscillating combustion technique. Indeed, Air Liquide, as part of an agreement with IGT, is leading efforts in developing applications that will burn a combination of oxygen and fuel, rather than air and fuel, as in the Burns Harbor test.
In addition to field tests at Burns Harbor, IGT is developing a marketable retrofit package that includes all the necessary valves, controllers, and instrumentation. The IGT is also building a database based on laboratory testing on a. variety of burners common to the steel industry.
From Glass to Steel
Praxair Inc. of Danbury, Conn., has designed low NOx oxygen burners used by the glass industry to reduce nitrogen oxide emissions by 60 percent. Under the auspices of the OIT’s NICE3 program (the National Incentive for Competitiveness in Energy, Environment, and Economics), Praxair engineers adapted previous-generation burners to design a low NOx oxy-fuel burner for the steel industry that will cut nitrogen oxide emissions by 90 percent and reduce fuel consumption by 50 percent, by providing more uniform heating than conventional burners. NICE3 is a strategic partnership among state energy, economic development, and environmental departments, industry, and the DOE to demonstrate technologies and process innovations that will save energy, improve efficiency, and minimize waste.
“Because the burner uses only oxygen, it eliminates nitrogen from the oxidant. We also design the burners to recirculate maximum amounts of furnace gases' before fuel is combusted with the oxidant, reducing flame temperature and thus the formation of thermal NOx,” explained Ron Selines, a metallurgical engineer and corporate fellow at Praxair. Selines said that the efficacy of the burner hinges on the exit velocities of oxidant and fuel, the separation of fuel and oxygen, and the burner’s orientation.
The new low NOx oxy-fuel burner was installed in July in the batch reheat furnace at Burns Harbor to verify the burner’s low NOx capability and fuel savings. Bethlehem Steel installed the burner on an inherently less efficient batch furnace, where air enters through door leaks and during recharging, to prove conclusively whether the burner can reduce NOx to 10 percent of conventional burners. In addition, Bethlehem Steel will also test the burner’s efficacy when burning coke oven gas, a byproduct of the plant. The latter would help make the burner more economical by reducing the cost of purchasing oxygen fuel.
Praxair is already engaged in testing a second-generation low NOx oxy-fuel burner for the steel industry. They installed burners in a continuous reheat furnace in Auburn Steel’s plant in Auburn, N.Y., under the auspices of a DOE OIT program. “The primary driver in the Auburn application is to significantly increase productivity while cutting NOx by 90 percent,” said Selines, who noted that because continuous reheat furnaces are more efficient than batch furnaces, a projected 30 percent fuel savings is anticipated. According to estimates by Praxair, these reheat burners could save the steel industry 70 trillion BTU/year.
Abbasi lauded OIT sponsorship “for supporting the contractor of a new technology through testing as at Burns Harbor, which provides firsthand knowledge of the technology’s performance in an industrial setting.”
Indeed, Sikka of Oak Ridge stated that OIT encouraged steel companies to take advantage of the DOE’s resources. “Bethlehem Steel is being proactive in working with OIT and the national labs,” he said. “However, in this age of globalization, OIT is one of the best resources, through the national labs, to help manufacturers and materials processors improve the energy efficiency of their processes and competitiveness.”