An aluminum mill slashes chlorine and hydrogen

Transcription

1 Alcan Rolled Products Company s aluminum rolling mill in Oswego, New York, recently An aluminum mill slashes chlorine and hydrogen Alcan Company Profile The parent company of Alcan Rolled Products, Alcan achieved an important mile- chloride emisions Aluminium Ltd., is headquar- stone in a pollution prevention program aimed at minimizing emissions of hazardous air pollutants (HAPs). As a result of the program, air emissions of chlorine and hydrogen chloride have been reduced by 95 percent from 1986 levels. Alcan is also saving $440,000 per year in raw material costs. Moreover, the company has won the First Annual New York State Governor s Award for Pollution Prevention, and EPA has approved Alcan s application for the Early Reductions Program under Section 112 of the Clean Air Act. The goal of Alcan s pollution prevention program at the Oswego plant was to minimize emissions of HAPs generated by molten aluminum cleaning processes in the facility s aluminum scrap recycling operations. The cornerstone of the program is the use of in-line fluxing technology, which dramatically increases the efficiency of chlorine utilization in the metal cleaning process-thereby greatly reducing chlorine consumption and associated HAP emissions. tered in Montreal, Quebec. Alcan Aluminium Ltd. encompasses a worldwide group of companies involved in all stages of the aluminum industry. Alcan operates in 20 countries around the world and employs over 35,000 people. A vital component of Alcan s business is its series of aluminum rolling operations in North America. These rolling facilities produce aluminum sheet and foil for beverage containers, building products, and the printing and transportation industries, as well as products for household and commercial packaging applications. Alcan is, in fact, the world s largest producer of rolled aluminum products. Processes at the Oswego Facility The pollution prevention initiative described in this case study was undertaken at Alcan s aluminum rolling facility located in Oswego, New David J. Lagoe CCC John Wiley & Sons, Inc. a Pollution Prevention Review / Winter / 51

2 employs approximately 800 people. The production process at the Oswego facility begins in the aluminum melting and casting area, where scrap aluminum is recycled by being melted, alloyed, refined, and cast into ingot. This process is a major component of the operations at the Oswego plant. The aluminum scrap used for recycling comes from a variety of sources, the principal source being in-plant process scrap from various cutting and trimming operations at the Oswego facility itself and Aluminum recycling other Alcan plants. Additional clearly benefits the sources of scrap inputs are used environment since it beverage containers, customer allows scrap materials to plant process scrap, and alumibe processed for reuse num scrap purchased on the rather than simply open market from commercial disposed of in landfills. metal recycling operations. After casting, the ingot produced by the melting and casting area is preheated and rolled into coils of aluminum sheet in the hot mill manufacturing area. The final steps in the manufacturing process at Oswego take place in the cold rolling mill, where the aluminum coil from the hot mill is further reduced in thickness and then cut or trimmed to the required dimensions and packaged for shipment. Principal customers for the plant s annual production of over one billion pounds of aluminum sheet are can manufacturers throughout the United States. The plant also supplies beverage container stock to the export market, mainly for use in Japan. One exciting new application for Alcan s products is in the manufacture of body panels and structural components for automobiles. This market has enormous potential for the late 1990s and beyond. The Aluminum Recycling Process Alcan s pollution prevention program at the Oswego facility focused on emissions from the aluminum recycling stage of plant operations, dur- minum ingot. Melting of scrap is performed in reverberatory furnaces fired by oil or natural gas. After the aluminum scrap charge is melted, alloying elements are added as necessary to adjust the chemical composition of the alloy being produced. The molten metal is then transferred to a second, holding furnace for further processing prior to casting. The principal processing operation that takes place in this second furnace is metal cleaning, or fluxing. This operation traditionally used graphite tubes to bubble mixtures of chlorine and nitrogen gas through a bath containing 80,000 to 240,000 pounds of molten aluminum. Following fluxing, the dross or slag is skimmed from the surface of the molten aluminum, and the metal is poured from the holding furnace. The molten aluminum then typically flows through a filtering apparatus to remove oxide particles and finally is poured into water-cooled molds. The entire process, from charging scrap into the melting furnace to completion of ingot casting, takes approximately three hours. Aluminum recycling clearly benefits the environment since it allows scrap materials, such as used beverage containers, to be processed for reuse rather than simply disposed of in landfills. And because recycling aluminum consumes only 5 percent as much energy as producing aluminum from ore (bauxite), recycling dramatically reduces the energy requirements of the manufacturing process. The P2 Challenge: Reducing HAP Emissions While aluminum recycling provides obvious environmental benefits, the recycling process itself can also create environmental problems. This was the case at the Oswego facility during the 1980s, when large quantities of hazardous air pollutants were being produced during the fluxing stage of the recycling process, when the molten metal was cleaned. 52 / Winter / Pollution Prevention Review 1 David J. Lagoe

3 wego plant. Between 1980 and 1986, the quantity of aluminum ingot produced from recycling scrap increased by over 50 percent. There was, however, an undesirable side effect from this growth: a sub. stantial increase in chlorine usage for furnace fluxing operations. By 1986, annual chlorine consumption had increased to over two million pounds from a level of only 1.2 million pounds in This dramatic increase in chlorine usage was not attributable solely to higher production levels. The concentration of chlorine used in fluxing gas mixtures was also increased during this time period in an effort to achieve the improved levels of metal cleanliness needed to meet increasing demands for higher quality products in the beverage container market. The chlorine gas used in the fluxing process reacts with the aluminum and the alloying elements (such as magnesium) to form metallic chlorides, including magnesium chloride and aluminum chloride. At the molten aluminum processing temperature of approximately 700C, aluminum chloride forms very fine solid particles that are emitted as a white fume from the fluxing process. These particles readily hydrolyze to form hydrogen chloride gas and aluminum oxide according to the following equation: 2(A1C13) t 3(H,O) H- AI,O, t 6(HC1) Emission factors were developed from stack emissions testing to relate releases of hydrogen chloride and unreacted chlorine gas to the amount of chlorine used for fluxing. These factors indicated that approximately 55 percent of the chlorine used for fluxing was being emitted as hydrogen chloride, while approximately 5 percent of the chlorine passed through the molten aluminum unreacted andwas emitted to the atmosphere as chlorine gas. Asof 1985, Alcan soswegofacilitywasincompliance with all its air permit limitations. The emis- dispersion modeling and ambient monitoring, which showed that ground-level concentrations of hydrogen chloride and chlorine gas were within acceptable limits. However, the rapid increase in chlorine usage raised concerns about whether the plant could continue to meet regulatory emissions limitations. Additionally, undesirable side effects began to appear as annual chlorine usage topped the twomillion-pound level. Corrosion of metal equipment and building components increased noticeably on the roof of the melting and casting area. Some trees on plant grounds near the melting and casting building also began to exhibit signs of exposure to acid gases, such as spotting on foliage and early loss of leaves in the autumn. Alcan conducted a vegetation monitoring program that involved testing maple leaves from several sampling locations around the facility. As shown in Exhibit 1, the monitoring indicated significantly higher chloride Exhibit 1. Annual Vegetation Survey Results: Chlorlde Content of Maple leaves _ ( Upwind (average) Year 1 Case Study: Alcan Rolled Products Company 1 Pollution Provention Review / Winter / 53

4 and casting area. The cost of purchasing chlorine had also become a concern to Alcan. By 1985, the annual budget for chlorine used at the Oswego plant was approaching $600,000. Alcan s Oswego Facility Pollution Prevention Program By 1986, the Oswego plant s environmental group was deeply concerned about the sharp increase in chlorine consumption and the adverse effects of hydrogen chloride and chlorine emissions. Early that year, the group launched an allout effort to convince the plant management team that it was time to begin a comprehensive program of reducing chlorine usage and the associated emissions. In-line Fluxing Technology By this point, the melting and casting area s technical group had already been investigating inline fluxing technology, which has been in use since the 1970s. This type of equipment removes dissolved gases, such as hydrogen, from molten aluminum as After several months of it is poured from the melting furtesting and development nace prior to casting. Use of inwork, the performance of line equipment allows operators the in-line fluxing to reduce the amount of fluxing equipment was judged to required in the melting and hold- be superior to furnace fluxing. ing furnaces. Early in-line units typically injected argon into molten aluminum to strip away dissolved hydrogen. Beginning in the mid-l980s, chlorine was mixed with the argon. This improved the capability of the equipment, allowing it to also remove alkali metals (such as calcium and sodium) and oxide particles. Significant design improvements were also made to the in-line equipment and the associated maximize the reaction of the gases with the molten aluminum by injecting thegas mixture through a spinning nozzle or rotor, which creates a dispersion of very small gas bubbles. This dispersion maximizes the surface area-to-volume ratio, thus promoting nearly complete reaction of the gases with the liquid metal. Implementing tbe P2 Program Following discussions and presentations involving all relevant technical and management personnel, a commitment was made to install the first in-line fluxing unit at one of the plant s five melting and casting centers. The first in-line fluxing unit was installed in May After several months of testing and development work, the performance of the in-line fluxing equipment was judged to be superior to furnace fluxing in terms of both reduced chlorine usage and improved metal cleanliness levels. Over the next three years, representatives from the Oswego plant worked with equipment manufacturers to further improve the in-line fluxing units. In 1991, the Oswego plant s transition to in-line fluxing technology was completed when two of the facility s older melting and casting centers were replaced with a new, larger, state-of-the-art unit equipped with the latest in-line fluxing technology. The high efficiency of the in-line fluxing system has made it possible to curtail chlorine use for furnace fluxing by up to 80 percent. This was accomplished by reducing both the furnace fluxing time period and the concentration of chlorine gas utilized in the fluxing gas mixture. Further reductions in chlorine usage were achieved through improvements in furnace management practices and operating procedures for in-line fluxing units. In addition, statistical process control techniques have been implemented. These techniques allow furnace operators to monitor chlorine consumption for the entire melting and casting area C( / Winter / Pollution Prevention Revlsw Q David J. Lagoe

5 Reduction from Descrlptlon 01 Change Date 1986 Emlsslon Levels Installed Aipur in-line fluxing unit on Holding Fumace No. 5 May Reduced Cl, in fluxing gas from 50% to 30% for can body stock alloys December Eliminated fluxing in Melting Furnaces Nos. 1, 2. 3, 4, and 5 Reduced fluxing time on Holding Furnace No. 5 from 30 to 10 minutes per cycle installed Union Carbide R-180 in-line fluxing unit on Holding Furnace No. 4 Reduced CI, in fluxing gas from 30% to 20% on Holding Furnaces Nos. 4 and 5 Reduced fluxing time on Holding Furnace No. 4 from 30 to 10 minutes per cyde Commissioned Melting and Holding Furnace No. 6 and removed Melting and Holding Furnaces Nos. 1 and 2 from sewice Reduced CI, in fluxing gas from 30% to 20% on Holding Fumace No. 3 Reduced CI, flow rate from 1.2 to 0.9 Iblminute on Holding Furnace No. 6 implemented furnace operator monitoring of chlorine usage Computerized chlorine consumption monitoring on Melting and Casting Centers Nos. 4,5, and 6 June 1988 March 1989 July 1990 July 1990 July 1991 September 1991 August 1992 October 1992 January October on both an individual cast basis and a daily basis. This level of monitoring has minimized both overand under-utilization of chlorine, thus reducing emissions while ensuring that product quality requirements are consistently attained. Although furnace fluxing has not yet been entirely eliminated, the use of chlorine for this purpose has been drastically reduced. Exhibit 2 summarizes the changes that were made as part of Alcan s Oswego plant pollution prevention program as well as the percentage of chlorine reduction associated with each change. Benefits of the P2 Program The benefits gained from the successful implementation of the pollution prevention program at the Oswego facility were far-reaching, as noted below. Substantial Reduction in Chlorine Usage and Emissions By 1994, chlorine usage had declined by 95 percent compared to 1986 levels, resulting in a corresponding decrease in air emissions of chlorine and hydrogen chloride (Exhibits 3 and 4). This reduction in chlorine usage is currently producing an annual savings of $440,000 in raw material costs since the facility now purchases far less chlorine. Increased Productivity and HiQher Product Oualify The magnitude of the decrease in chlorine usage is made even more impressive by the fact that production from the Oswego plant s melting and casting area increased by 27 percent during implementation of the pollution prevention program. Much of the increased output was directly attributable to changes instituted as part of the program. As in-line fluxing decreased the need for furnace fluxing, the melting and casting process cycle was shortened. A 10- to 20-minute melting furnace fluxing operation was eliminated, and the holding furnace fluxing period was reduced from 30 to 10 minutes. These changes shortened the entire cycle by nearly 20 percent, resulting in a substantial increase in productivity. Moreover, laboratory testing of metal cleanliness levels and customer feedback have confirmed that product quality has also improved as a result of the changes in fluxing procedures. Case Study: Alcan Rolled Products Company

6 Alcan's successful pollution prevention program at the Oswego plant has also significantly I Exhibit 3. Annual Chlorlne Usage Lbslton produced n Exhibit 4. Hazardous Emissions z E 200 a Q 2 150? n " Year ride Year 4 r E 33 n h Workers are in particular danger of being exposed to chlorine when they connect or disconnect chlorine cylinders, since this is the time when leaks are most likely to develop. Because only 63 one-ton chlorine cylinders needed to be connected and disconnected from the delivery system in 1994-compared to 1,160 in 1986-the potential for employee exposure to chlorine gas has been dramatically reduced. The attendant reduction in requirements for loading and unloading one-ton containers of chlorine have further minimized the potential for both employee exposure and physical injury. In 1986,89 truck shipments were required to deliver chlorine to the Oswego plant. By contrast, in 1994, onlyfive shipments were needed. Other initiatives to improve the safety of employees have included installation of an improved chlorine neutralization system for both system maintenance and emergencies, and ongoing employee training in the procedures necessary for safe storage, handling, use, and disposal of various hazardous chemicals, including chlorine. The surrounding community's potential for exposure to chlorine also has been significantly reduced by the 675-ton decrease in HAP emissions achieved by the pollution prevention program. As Exhibit 1 indicates, the plant's annual maple leaf vegetation survey reveals that the chloride content of maple leaves downwind of the melting and casting operations had decreased to essentially ambient levels by The reduction in chlorine truck shipments has also significantly reduced the potential for traffic accidents that could result in releases. 66 / Winter / Poiiutlon Provention RGVIOW David J. Lagoe

7 The successful pollution prevention program could also allow the Oswego facility to avoid having to make substantial investments in pollution control equipment. On January 9, 1995, EPA approved Alcan s application under the Clean Air Act Early Reductions Program. Pursuant to this program, companies are granted a six-year extension for complying with maximum achievable control technology (MACT) standards if they reduce HAP emissions by 90 percent (or particulate HAPS by 95 percent) prior to proposal of a national emission standard for hazardous air pollutants (NESHAP) for their industrial category. Thus, in the unlikely event that Alcan s in-line fluxing technology does not meet the requirements of the MACT definition for the secondary aluminum industry category, the additional time provided by the six-year compliance extension could allow Alcan to develop and implement additional source reduction measures to further reduce emissions in lieu of installing costly-and perhaps less environmentally friendly-end-of-the-pipe pollution control equipment. P2 Award Finally, the achievement that perhaps best facility was named the winner of the First Annual New York State Governor s Award for Pollution Prevention. The purpose of the award is to recognize the outstanding commitment of New York industries to reducing pollutants they generate and discharge to the environment. Formal presentation of the award was made at the Seventh Annual Pollution Prevention Conference in Albany, New York, on June 1, looking Toward the Future The Alcan team is now looking at ways to totally eliminate the need for chlorine gas in furnace fluxing. Considerable research hasbeen completed, and numerous plant trials are under way, in an effort to develop a process that utilizes less hazardous solid phase materials to replace present furnace fluxing procedures. This new process could reduce HAP emissions further-while almost completely eliminating the potential for employee exposure to chlorine gas. David J. Lagos is Environmental Leader for Aican Rolled Products Company in Oswego, New York. Case Study: Alcan Rolled Products Company Pollullon PrsvenllonRevlew / Winter / 57