Burns Harbor
Waste Management
Recycling and minimizing waste have been a way of life in Bethlehem's steel plants for many years. We have recycled, as much as possible, iron-bearing mill scales and dusts to our sintering plants for use in making iron and steel. We've sold slags for use in road construction. We've sold co-products produced during coke-making. And we've burned coke oven and blast furnace gases as in-plant fuel, which conserves the world's reserves of other fuels. We've also been getting better and better at capturing dusts and sludges (wet materials) as we continually improve our abilities and technologies to reduce emissions. We've also been developing techniques and technology for managing these wastes for more than 30 years.
But getting better and better at reducing emissions causes its own problems. In the 1970s and 1980s, as new air, water and waste regulations required more stringent pollution controls, we found ourselves with more waste materials than ever. The better we got at controlling air and water pollution, the more waste we found ourselves sending to solid waste landfills. Although the dusts and sludges we captured contained materials of value, their physical and chemical properties made them unsuitable and uneconomical for recycling and reclaiming.
For years the sintering process has been an integral part of Bethlehem's operations. Sintering is a process which agglomerates fine iron ores, limestone, coke breeze, mill scales and other materials by heating them at high temperature into a product called “sinter,” which can then be used to feed the ironmaking process of a blast furnace. However, many of the fine dusts and sludges collected by our pollution control equipment contain undesirable contaminants, such as excessive amounts of water, oils and residual metals (e.g., zinc), which make them unusable in the sintering process. These contaminants must be removed before recycling because they interfere with the efficiency of the sintering operation and manufacture of high-quality iron and steel products.
Our solution to unusable materials has been to develop and integrate several recycling technologies: thickening and filtering basic oxygen furnace (BOF) slurry, hydrocloning blast furnace sludge and burning oily mill sludge (during the sintering process). This combination of technologies forms a now-patented Integrated Waste Management Process� that makes it possible for a modern iron and steel facility to reuse the majority of its pollution control dusts and sludges.
Reducing Zinc Content in Basic Oxygen Furnace Scrubber Sludge
The basic oxygen steelmaking process converts molten pig iron and recycled steel scrap into high-quality steel. During this process, the basic oxygen furnace emits very fine iron oxide particles (fume) that are removed from waste gases by a wet scrubbing process. This fume can contain high levels of zinc depending on the chemistry of the scrap steel used as an ingredient in BOF steelmaking.
When steel scrap contains a high zinc content, the BOF fume will contain a high concentration of zinc. The zinc-laden fume, with its typically high moisture content, limits its use as feedstock in a sinter plant. One way to keep the zinc content of the BOF fume low is to avoid using zinc-bearing scrap as much as possible. The Burns Harbor Division has been using low-zinc scrap, producing a BOF fume with a zinc content low enough to permit recycling of the fume.
Controlling Blast Furnace Scrubber Sludge Zinc
Process gases from the blast furnace that contain zinc and iron oxides, carbon and other materials are removed in a gas-cleaning scrubber that produces sludge solids. Our research and development of this process found that vaporization and condensation of these zinc solids in the blast furnace deposits very fine particles on other particles that have high surface areas. Learning exactly where the zinc was deposited made it easier to design removal processes and then to recycle the sludge solids.
Followup testing showed that pumping these zinc-bearing sludges through small diameter hydrocyclones operating at high pressure can effectively separate zinc from the iron- and carbon- bearing solids. Although other companies have used similar but more complex hydroclone processes, Bethlehem Steel developed a patentable two-stage hydrocloning process. Hydrocloning is a process in which solids are subjected to centrifugal forces that separate the denser metals from less dense solids. The less-dense solids, which contain most of the zinc, leave the hydrocyclone as overflow. The overflow is dewatered by thickening and filtration prior to disposal at a landfill. The dense, separated solids contain the iron and carbon solids, which leave the hydrocyclone as underflow. The underflow solids are dewatered by filtration and recycled to the sinter plant.
Recycling Secondary Wastewater Treatment Sludge
Burns Harbor's secondary wastewater treatment plant treats all of the plant's waste waters and produces a sludge that contains enough oil and grease to make it impractical to recycle this sludge to the sinter plant in a conventional manner. In order to recycle this sludge, Burns Harbor developed and patented an innovative technology for recycling oily sludges directly into the sinter plant without creating air emission problems. The oily sludge is sprayed on top of the hot sinter, which causes the oil in the sludge to burn without creating air pollution.
Reclaiming Stockpiled Sludges
In addition, Burns Harbor is in the process of recycling previously stored blast furnace filter cake. Prior to being reclaimed, this material must be put through a hydrocyclone, which requires reslurrying and removal of unwanted material, such as slag and debris. Screening helps remove unwanted material, and shearing breaks the clumps into very fine particles. After shearing, the reclaimed slurry is combined with the daily production of furnace scrubber sludge and is pumped to hydrocyclones to remove the zinc.
These low-cost physical treatment processes and practices remove the nonrecyclable materials, such as zinc, from the iron-bearing materials so they can be recycled. Therefore, Burns Harbor is able to reuse the large majority of air and water pollution control dusts and sludges. Only low-tonnage, nonhazardous residual materials need to be landfilled.
Pennsylvania Steel Technologies
New Wastewater Treatment Process
Bethlehem Steel produces steel at its Pennsylvania Steel Technologies (PST) facility, Steelton, Pa., for ingots, blooms, billets, special sections, flat bars and premium quality rail products. These products are made by melting and refining in an electric arc furnace (EAF) that recycles scrap. Most of the steel produced in the energy-efficient EAF contains undesirable gases, such as nitrogen and hydrogen, which must be removed before processing the steel into high-quality steel products.
Vacuum degassing uses steam ejectors to create a vacuum that draws off the gases dissolved in the steel. After extraction, the steam is condensed with water sprays. In addition to removing the undesirable gases, vacuum degassing also removes metals, such as lead, zinc and other materials. Most of the water is cooled in a cooling tower for reuse but solids must be removed first to prevent clogging of spray nozzles and the cooling tower. The water is treated to cause solids to settle, which are then separated in a clarifier. Most of the water is recycled but the excess water must be discharged and must meet very stringent water pollution permit limits.
Bethlehem evaluated conventional water treatment systems and found that the systems could not meet the water pollution discharge limits without producing a hazardous waste. So Bethlehem's environ-mental engineers developed an innovative water treatment process that removes the solids, zinc and lead from the vacuum degassing wastewater to levels well below water permit limits. The process eliminates the generation of 96 tons of hazardous waste each year and the associated cost of disposal. Bethlehem has applied for a patent for this new process.
SUPER DETOX�
Bethlehem Steel was recognized as a 1996 winner of a Pennsylvania Governor's Award for Environmental Excellence in the Technology Innovation category at a dinner in Harrisburg, Pa., on October 28.
The award, accepted by Andy Futchko, president of Pennsylvania Steel Technologies, and John Lynn, senior environmental engineer, corporate safety, health, and environment, was given for developing and implementing SUPER DETOX�, which chemically stabilizes metals such as zinc, lead, cadmium and others in electric arc furnace (EAF) dust to render it nontoxic. The Environmental Protection Agency has accepted this technology as a “best available control technology” for dealing with this EPA-listed hazardous waste.
SUPER DETOX� is being used to treat more than 150,000 tons of EAF dust per year, about 18 percent of the total U.S. volume of this material. This dust is the second largest continuously generated hazardous waste stream in the United States. It is estimated that SUPER DETOX� has helped the steel industry reduce the cost of managing EAF dust by more than 20 percent.
SUPER DETOX� is licensed to Envirosource TDS, which owns and operates regional and site-specific treatment facilities in the United States. SUPER DETOX� was developed by John Lynn, Charlie Jablonski, Walt Egan and Tom Weidner, members of the corporate safety, health and environment department.
Sparrows Point
Water Treatment Alternatives
Sparrows Point discharges about 50 million gallons of water each day from its Humphreys Creek Wastewater Treatment Plant (HCWWTP) into the Chesapeake Bay. New federal standards call for more stringent control of suspended solids and oils in this water. Bethlehem's environmental engineers identified two treatment strategies to meet anticipated new limits: (1) build an entirely new wastewater treatment facility to replace the existing HCWWTP, or (2) treat and recycle the two largest wastewater streams that now flow to the wastewater treatment plant. Before a choice could be made between these alternatives, however, we had to study the feasibility of the second alternative, which required testing different treatment technologies for these two wastewater streams.
Electromagnetic Cleaning of Hot Strip Mill Recirculating Water
The 68-inch hot strip mill at Sparrows Point uses about 38,000 gallons per minute (gpm) of water. Approximately 10,000 gpm of that flow ultimately enters the HCWWTP. This waste water carries more than 40,000 pounds per day (lbs/day) of suspended solids (mill scale—pieces of steel) and over 12,000 lbs/day of oil and grease to this treatment plant. To reduce the suspended solids entering the treatment plant, Bethlehem sought to reduce the flow to about 3,000 gpm, which would reduce suspended solids to no more than 1,800 lbs/day and oil and grease to no more than 600 lbs/day. An added advantage of this treatment method is that it would recirculate far cleaner and cooler water to the mill, which could reduce maintenance costs and improve cooling control.
We determined that the use of conventional concentrated fixed-bed wastewater filtration technologies would not be a reasonable solution to this wastewater treatment problem so we needed to investigate some other technology. We decided to test a method that uses electromagnets to capture the oil iron-bearing solids from the waste water. Based on laboratory results from Carnegie-Mellon University and additional tests carried out by Bethlehem Steel, we purchased a 25-gpm pilot electromagnet and tested it extensively at Sparrows Point. The purchased electromagnet used a highly compressed stack of magnetized metal perforated plates to capture the oil, but we found it impossible to remove the suspended solids and oil from the plates at the end of a filtration cycle. To solve this problem, we replaced the electromagnet filter media plates with a canister of noncompressed split ring washers to collect the oily solids. Then, at the end of a filtration cycle, the washers were agitated slowly and “washed” with forced air and water, which effectively removed the collected solids.
Test results from this modified magnetic filter suggest that nine electromagnets would treat the entire 38,000 gpm recirculated water flow at the hot strip mill and produce the desired water quality. Economic studies of all technologies tested are under way to select the most cost-effective process.
Walnut Shell Filtration of Cold Mill and Hot Mill Wastewaters
Sparrows Point's four cold rolling mills generate a combined wastewater flow of about 8,000 gpm. After primary treatment, these waste waters contribute about 14,000 lbs/day of suspended solids and about 19,000 lbs/day of oil and grease to the wastewater treatment plant. The treatment objective is to remove solids and oils from these mill waste waters and recycle the clean water.
To achieve this target, Bethlehem has experimented with an oil industry technology using carefully sized, ground walnut shells as filter media. Walnut shells are useful because they easily collect oil and grease on their surface. Once saturated, the shells can be cleaned by recirculating them through a centrifugal pump, which bumps the shells about and knocks the oil and solids from the shells. The cleaned shells are then recycled for reuse. A 10-gpm pilot walnut shell filter was rented and tested on Sparrows Point's cold mill waste water for six weeks. Test results suggest that this technology can meet the treatment objectives. Also, the technology was tested on hot strip mill waste water and found to be very effective at cleaning these waste waters as well. Economic studies are under way for these walnut shell filters for both applications.
Multi-Media Agreement Reached
In late 1996, Bethlehem Steel, the Environmental Protection Agency and the Maryland Department of Environment reached an agreement on a comprehensive plan to address environmental concerns at the Sparrows Point Division. The agreement calls for recycling various sludges through the division's sinter plant or the iron or steelmaking processes, developing a maintenance dredging plan for the Tin Mill Canal and developing a comprehensive waste minimization program. Sparrows Point has begun a community outreach effort to keep the public informed of business and environmental issues by meeting with community representatives. The Tin Mill Canal carries waste water to the plant's central waste water treatment facility.
Safety, Health and Environment Department
1170 Eighth Avenue, Martin Tower, 12th Floor, Bethlehem, PA 18016-7699.
For further information, send mail to [email protected]
1996 Environmental Report Table of Contents
