ZERO WASTE ELECTRIC ARC FURNACE (EAF) STEELMAKING
CHAPARRAL STEEL COMPANY TARGET
Libor F. Rostik
ChaparraI Steel Company
EPA Region III Waste Minimization/Pollution Prevention Technical Conference
Sponsored by: EPA Region III February 4-7, 1996 Wyndham Franklin Hotel
Libor F. Rostik
Chaparral Steel Company Midlothian, Texas
Chaparral Steel Company is a market mill located approximately 35 miles south of the Dallas/Fort Worth International Airport in Midlothian, Texas. Chaparral’s facilities and operating philosophy reflect the latest worldwide advancements in steelmaking. The company is committed to the incorporation of new technologies intended to provide the best quality products at internationally competitive prices. Chaparral’s current employment is 960 people. Its initial production of 228,000 tons in 1976 has grown to 1.6 million tons in 1994.
Chaparral owns and operates one of the biggest car shredding facilities in the world which is located on its site. More than 80% of Chaparral’s stock is owned by Texas Industries (TXI) which owns and operates a cement plant located adjacent to Chaparral.
Chaparral Steel’s production is 100% scrap based. Chaparral’s automobile shredder supplies approximately 600,000 tons per year. The rest of the scrap is purchased. Scrap is melted by two computer-assisted Ultra High Powered Electric Arc Furnaces (EAF). Molten steel is refined and is continuously cast in different pre-forms which are hot rolled in the finish products.
Chaparral’s product range includes bars, rounds, structural shapes, flats and beams. Chaparral Steel grades are produced for applications ranging from automotive and forging applications to construction and structural ones.
Chaparral Steel considers itself to be an efficient recycling facility: steel is produced using the most stringent environmental controls and Chaparral seeks to be at the leading edge of environmental technology.
Steel is the most recycled material in the world. Steel produced by electric arc furnaces uses recycled material as prime input and the product is totally recyclable. Chaparral is one of the largest EAF mills in the United States and represents a major recycling facility. As shown in Figure 1, the industry does not produce only steel products. The challenge that Chaparral is addressing is to reduce the generation of by-products, co-products and wastes and to find valuable uses for them through the combined application of technology and economics.
IU.S. EAF Steelmaking Industry 1994 (1,2)
Product Raw Steel Slag Scale Dust U. S. Annual Tons 38,500,000 4,466,OOO 1,078,000 616,000 Chaparral 1994
% of Raw Steel Production % of Raw Steel
Tons Tons Tons
100% 1,600,OOO 100%
11.60%2 170,000 10.95%
2.8%2 30,400 1.9%
1.6%2 18,000 1.15%
THE STAR PROJECT
To organize environmental efforts effectively, Chaparral and TXI initiated a project called STAR (acronym for “Systems and Technology for Advanced Recycling”). The mission of the STAR project is to develop synergies between the steel and cement manufacturing processes and the automobile shredding facility to generate new products, conserve energy and improve the environment. The STAR project will result in reduction of process wastes, conservation of natural resources and pollution prevention through the environmentally and economically sound recycling of waste materials generated by the steel and cement manufacturing processes.
The ultimate goal of the project is to achieve zero waste from the complex through better understanding of the process requirements and the application of innovative technology and sound economics.
Hatch Associates Ltd. is a consulting firm to the metallurgical industry worldwide. It has a long standing relationship with Chaparral Steel. It is associated with Chaparral Steel and Texas Industries in this project, providing process expertise and technological know how.
POWER AUTO BODIES OTHER SCRAP
AUTO SHREDDER RESIDUE NON FERROUS PARTICULATE STEEL ALLOYS REFRACTORIES POWER GASES: NATURAL GAS OXYGEN NITROGEN ARGON STEEL PRODUCTS BAGHOUSE DUST SPENT REFRACTORIES PARTICULATE CO RECOVERABLE ENERGY POWER NATURAL GAS REFRACTORIES MILL SCALE SPENT REFRACTORIES PARTICULATE c o NOX SO2 VOC RECOVERABLE ENERGY
TECHNOLOGICAL CHALLENGES AND OPPORTUNITIES
Chaparral and TXI have addressed a number of technological issues to reduce or eliminate the production of hazardous wastes, to upgrade the value of by-products and to reduce consumption of resources.
Baghouse dust is characterized as hazardous waste and disposal costs are currently $25O/ton. During the period 1990-93, Chaparral has reduced considerably the volume of dust going to disposal which no represents 1.15% of steel production compared to an industry average of 1.6% (Figure 4). Changes to the lime delivery system reduced the lime content of the dust from 30% to less than 4%. A portion of the dust is recycled to the furnaces. The remaining enriched dust is shipped for metal recovery at a lower overall cost. There is thus an incentive to seek on-site recovery of the iron, zinc and other metals in the dust with the metal-rich residues sold to downstream processors.
BAGHOUSE DUST GENERATION
per ton of steel production
The refractories used in the steelmaking process are a mix of alumina and magnesitic materials. No comprehensive solution has yet been found to recycle the remaining refractory after use int he process, with one significant exception. Magnesitic refractories are separated, crushed and returned to the melting furnace as a flux component to help maintain the slag properties required by the process. The further development of this technology will not only eliminate the present practice of landfilling of the used refractories but will also minimize the use of virgin materials.
Solvents used in mill cleaning ark generally classified in three groups: non-organic caustic, halogenated organic, and ignitable organic. The first two groups are considered to be hazardous and subject to control. The target at Chaparral has been to eliminate the use of hazardous materials and to minimize the use of the third group. Figure 4 tracks the attainment of this goal over the last seven years. The elimination of hazardous materials and the overall reduction in material use has resulted in a significant reduction of expenditure for this family of products.
- historical annual usage600 500 400 300 200 100 0 1988 1989 1990 1991 1992 1993 1994 EAF Slag
Molten slag is collected in iron slag pots during the melting of raw materials in the electric arc furnace. Slag is cooled by pouring it in the designated area.
Slag contains significant amounts of iron units and, in 1993, Chaparral upgraded the crushing and processing of the slag in order to recover lower grade metallics and recycle them back to the furnace. This also created synergy with the TXI cement plant.
TXI developed and patented a method which allows this EAF slag to be used in the manufacture of high quality cement. Such use of slag conserves resources and reduces energy requirements as compared with typical cement manufacturing.
Mill scale is generated at the continuous casting and rolling process. It represents approximately 1.9% of steel produced. Chaparral follows the common practice of supplying it as feed stock to cement plants which use it for a production of Portland cement. Since mill scale is approximately 70% Fe (by weight), future developments will aim at recovery of the iron units which will result in higher financial rewards.
be assessed in terms of energy efficiency. Other directions for the future lie in reducing or re-using what is now waste heat. Improved furnace design and scrap pre-heating are some of the measures being considered, as well as the opportunity of utilizing the energy of the liquid slag.
Chaparral was designed from the start as a closed loop water system with total recirculation. Make-up water is required to compensate for evaporation losses. By modifying operating procedures, aquifer pumping has been reduced in half from 450 to 229 million gallons per year. This action has resulted in significant savings in energy and maintenance costs as well as conservation of a valuable resource.
The STAB project also involves activities at the cement plant and shredder facility towards the zero waste target.
TXI now landfills kiln dust that is too fine to be captured into cement. That dust contains a large amount of lime which might be used in the EAF for slag making, a recycling operation that would be of benefit to both the cement plant and the steel mill.
Automobile shredding is an integral part of Chaparral operations. Up to 600,000 obsolete cars are shredded every year providing approximately 30% of the raw material input and a significant competitive advantage.
Automobile shredding is a multistage operation. The ferrous metals are separated first. The non-ferrous materials are separated in several steps involving air separation, the Van-Over process and magnetic separation technologies. In this manner, the auto shredding operation minimizes the residue sent to landfill while optimizing the degree of metals recovery.
ECONOMIC BENEFITS TO DATE
Every step that has been taken so far has been designed to be profitable.
The new lime feed system has reduced the use of lime from 89,500 to 59,700 tons per year. As a result, the carry-over of lime fines in the baghouse has also been reduced, resulting in an additional savings.
In 1994, recycling 5,950 tons of EAF dust to the furnace produced a significant savings. The use of slag in lieu of raw material in cement making has raised the value of the product and has also achieved significant energy savings.
The next steps to be taken will maintain the same target of combining technological progress with economic efficiency.
The continued emphasis on recycling and stewardship will inevitably lead to the development of new technologies and further progress for the industry.
Development work is proceeding on a number of fronts, integrating the managerial, technological and economic goals. The recovery of iron from slag, dust and scale would constitute a major advance. The value of iron to the furnace would be of the order of $180/ton and the low iron slag could be of increased benefit to the cement plant. Work on this subject is proceeding from the conceptual to the testing stage. Such a step could lead to combined processing of slag scale and dust together on-site.
In terms of energy efficiency, improved steelmaking processes that could recover iron units from molten slag would mean significant energy improvement as would other means to recover wasted energy (furnace design modifications, scrap pre-heating, new scrap melting technologies).
Though the ultimate target still lies ahead, a number of conclusions can be reached form progress so far.
This initiative combines aggressive business objectives with challenging environmental goals.
Progress towards the target comes in realistic, incremental steps each of which brings added value to the business.
It is no longer possible for steelmakers to be concerned with only the production of steel. They have to accept responsibility for by-products and waste streams. That responsibility becomes an incentive for innovation and progress.
The proximity of the other businesses has provided Chaparral with many opportunities for synergy. Other circumstances may create different synergies.
The conflict between environmental and development is anachronistic. It is no longer a question of choosing between one or the other but of achieving development that is environmentally sustainable by integrating environment and economic factors in decision-making.
Good environmental management and the wise use of resources make good business.
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