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POLLUTION CONTROLL l h e majority of the iron and steel industry in the United States is centered in integrated facilities of large corporate enterprises, which are numbered among the largest industrial corporations in the country. A comparatively small plant in this industry represents a very large industrial complex. Generalizations about steelmaking operations are difficult because exceptions can be found in every mill. Steel mills range from new, modern facilities built within the past several years to older, marginal facilities built early in the century. Production units are quite large and require great quantities of water for both process and cooling purposes. Water use in the industry is the highest of any manufacturing industry, amounting to an average of 40,000 gal/ton of finished steel for all purposes. Manufacturing processes
Iron and steel manufacturing operations may be grouped as coke production, pig iron manufacture, steelmaking processes, rolling mill operations, and finishing operations. A single mill generally does not incorporate all combinations and variations of these operations that are possible. All operations produce waste water effluents, atmospheric emissions, and solid wastes, but the quantities and characteristics from each source vary greatly. Average water uses in the various departments of an integrated steel mill are shown on the next page. A medium-sized mill may discharge 100 million gallons of water per day. Atmospheric emissions and solid waste 1004 Environmental Science & Technology
generation are of similar magnitude; for example, a blast furnace may use air at the rate of more than 100,000 ft3/min and produce slag in excess of 1,000 tons/day. Coke production
Most large steel mills operate byproduct coke plants which produce the metallurgical coke used in pig iron production. Coke oven gas is a by-product and is used as a fuel within the mill. Crude tar, light oil, and ammonia are the other by-products of the coking operation, and these are further processed or sold depending on plant design and the marketability of specific products. Competition from the petrochemical industry has greatly reduced the profit and, hence, the incentive to manufacture by-products other than as necessary. Principal air pollution problems from coke production are sulfur dioxide generation from combustion of coke oven gas, emissions from ovens during charging and pushing and from door and lid leaks, and emissions from waste water quenching of the incandescent coke. State-of-the-art abatement measures include removing hydrogen sulfide from the gas, oven lid and door maintenance, baffling quench towers, using clean water for quenching, and regulating coking times. Other methods under development here or already in use abroad include negative oven pressures during charging, larry car scrubbers, hood arrangements with collection ducts and gas cleaning equipment, and stack gas cleaning of sulfur dioxide.
Principal water pollution potentials in the coke plant operation are in ammonia still wastes and light oil decanter wastes which average about 44 gal/ton of coal carbonized and contain phenols, ammonia, cyanides, chlorides, and sulfur compounds. Using contaminated waste waters for coke quenching effectively prevents water pollution as long as there is no overflow from the quench system. This practice, however, results in air pollution and severe corrosion on nearby steel structures. Abatement measures include biological treatment either on site or by cotreatment with municipal sewage, chemical oxidation, and carbon adsorption. Coupled with water reuse reducing effluent volumes to a minimum, these measures can eliminate potential water pollution. Blast furnace operations
Blast furnaces are operated primarily to produce iron as hot metal for subsequent steelmaking processes but also produce pig iron, silvery pig iron, and ferroalloys. Sinter plants are typically operated as parts of blast furnace departments to agglomerate fine ores, blast furnace flue dust, and mill scale as part of the blast furnace burden. Slag quenching operations produce granulated or expanded slag depending on the methods used. These various operations can produce particulate emissions in blast furnace gas, from handling blast furnace burden materials including furnace charging, from opening blast furnace pressure release valves due to slips, and from materials handling and agglomeration operations at the sinter
Steelmaking operations produce pollution at almost every step, but it can be controlled by proper treatment or by conserving and reusing materials
Steel Industry Henry C. Bramer
Datagraphics, Inc. Pittsburgh, Pennsylvania 15232
plant. Hydrogen sulfide and some sulfur dioxide are generated in slag quenching. Venturi scrubbers or electrostatic precipitators clean blast furnace flue gas to less than 0.01 gr/ft3 so that major emissions are due to venting or to materials handling in the blast furnace operation. Proper hooding, venturi scrubbers, and baghouses can effectively control particulate emissions from sinter plants. Control of slips can greatly reduce blast furnace venting, and combinations of hooding arrangements and chemical additives are the most likely solutions to controlling particulate emissions from materials handling and sulfur compound emissions from slag quenching. So-called dry-quenching or using minimal quantities of water reduces the emission potential from slag operations. Water pollution problems in the blast furnace department result primarily from gas cleaning with wet washers. Blast furnace gas-washer water contains suspended solids, cyanides, phenols, and ammonia. If the gas-washer water is completely recycled and any blowdown disposed of in dry slag quenching or on ore piles, this pollution source can be eliminated. Cyanides, ammonia, and phenols in gas-washer water result primarily from waste water quenching of coke, but some cyanide is synthesized in the blast furnace in any case. The major solid waste problem in these operations is producing more slag than can be sold for road building. Huge slag dumps continue to build up near most steel mills. Solids recovered from blast furnace gas,
either wet or dry, or from the sinter plant are reusable as blast furnace burden; such wastes are only a disposal problem when a mill has no sintering facilities. Steelmaking processes
The major steelmaking processes are the basic oxygen process ( B O P ) , electric furnaces, and open hearth furnaces which are now generally oxygen lanced. The air pollution potential of all of these processes is in the fume which is generated from the furnaces themselves and during molten metal transfer operations. Control facilities
on basic oxygen and open hearth furnaces are generally either venturi scrubbers or electrostatic precipitators while many new electric furnace installations use baghouses. Emissions of carbonaceous material known as kish, generated during molten metal transfer operations, can be controlled by evacuation hoods and gas-cleaning equipment such as baghouses. Hood designs are critically important in furnace installations; proper hood design can greatly reduce air volumes, permitting greater efficiencies and/or smaller equipment. Water pollution problems in steel-
making result from wet gas-cleaning methods and consist primarily of suspended solids. Recirculating such waste waters with cooling towers is the most generally satisfactory solution. Treatment of waste waters from oxygen steelmaking processes requires chemical coagulants or similar methods and can seldom remove all particulate matter. Magnetic agglomeration has proved to be particularly effective in treating BOP waste waters. Recovered materials from basic oxygen process emissions represent one of the industry’s most troublesome solid waste problems. High concentrations of zinc, originating in the scrap metal charge, are generally regarded as making recovered material unusable
for reuse. Leaching with acid may be a method of removing unwanted zinc, but some recent experiments in BOP operation indicate that unsuitability of the material may be more a matter of conjecture than fact. Rolling mill operations
Rolling mill operations start either with ingots molded from steelmaking processes and subsequently reduced to blooms, slabs, or billets or with slab production by continuous casting. An ever-increasing quantity of steel is processed by the latter, newer process. The semifinished steel is prepared for finishing in a number of ways-chipping, grinding, and scarfing-all of which remove surface defects. Scarf-
ing refers to using oxygen torches to remove surface defects and is accomplished by hand on cold steel or mechanically on hot steel as part of the rolling operation. Finishing mills include a wide variety of mills intended to produce specified steel products-plate mills, mills for rolling rails and structural shapes, bar mills, wire mills, tube mills, and continuous strip mills. Most hot-rolled strip is pickled in acid baths, usually in continuous units, to remove surface oxides. Many other products, such as wire, bars, and pipe, are often pickled in batch-type operations. The primary air pollution source in these operations is scarfing, hot scarf-
Major areas of pollution in steelmaking processes
ing in particular. Airborne particles are extremely fine and difficult to remove, and when wet washers are used, a water pollution potential, of course, results. The principal solid waste problem is in sludge resulting from lime neutralization of spent pickle liquor. Lagoons full of this material, which never dries, is a major problem at many mills. Although crop ends and scale amount to large tonnages of solid material, it is all reused within the mill as internal scrap or is sintered for recycle. Major water pollution potentials from rolling mills are suspended particles of waterborne scale, lubricating oils, spent pickle liquor, and pickling rinse water. As previously indicated,
strong pickle liquors are often neutralized with lime, and rinse waters may be treated in the same manner. Other alternatives include contract hauling, deep well disposal, and pickle liquor regeneration, which is more economically attractive and technically proved when hydrochloric acid is used instead of sulfuric. (Using hydrochloric acid is becoming the general practice.) Contract hauling only removes the problem outside the mill’s boundaries, and deep well disposal is coming into disfavor in many states. Pickling rinse water treatment is analogous to acid mine drainage treatment. Most scale and oil produced in rolling mills is recovered in crude settling chambers called scale pits. (These
chambers have always been used to prevent sewer clogging and are similar to the grit chambers in municipal sewage treatment plants.) Recirculation can be practiced to a high degree in rolling mills, and effective effluent treatments include chemical coagulation, magnetic agglomeration, and deep bed filtration. Primary oil-removal equipment, such as belt skimmers, is necessary to effectively treat rolling mill waste waters. Finishing operations
Finishing operations primarily consist of cold. reduction, tin plating, galvanizing, chrome plating, coating, tempering, and polishing. Air pollution problems associated with these
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Cold-drawn
BOP. These furnaces may emit air and wafer Dollutants as well as solid wastes
operations are negligible except for the practice of open-burning recovered oils. Solid waste problems are associated with internally generated scrap and with sludges which may result from tank cleanouts or precipitates from waste water treatments. Scrap is essentially all reused, but can result in additional waste water problems, such as reclaiming tin-plated or galvanized steel. One of the most difficult waste water treatment problems is treating emulsified oil from cold rolling. Proprietary mineral oils have all hut replaced palm oil in cold rolling, and because they are formulated to yield stable emulsions, their treatment is difficult. Since treatment is usually less than satisfactory, the highest possible degree of recirculation and reuse is necessary with these waste waters. Chemical treatment, such as iron salts and lime followed by air flotation, is a common treatment method. Various emulsion-breaking agents are used, and magnetic separators are effective in cleaning emulsions for reuse. Onsite reclamation of these oils by outside cnntractors is a common practice. Tin plating, chrome plating, and galvanizing waste waters present generally the same problems as d o metal finishing wastes in other industries, except that the volumes are usually greater than commonly encountered in other industries. Other finishing operations do not produce significant waste water problems. Conservation a n d reuse Conservation and reuse practices are quite productive waste control methods in the steel industry because of 1008 Environmental Science & Technology
the sheer magnitude of the quantities involved. Insofar as coke oven gas, blast furnace gas, flue dust, slag, soluble oils, mill scale, some coke oven chemicals, and scrap are concerned, the industry has mostly practiced conservation and reuse because of obvious economic incentives. In most steel mills, however, water has neither been conserved nor reused to a significant degree, nor has reclamation been practiced for such cases as pickling acids, plating solutions, basic oxygen process dust, lubricating oils, and many coke oven chemicals such as sulfur. Air pollution control equipment is frequently required to handle excessive volumes of gas or air, particularly when operations are hooded to prevent emissions. Solid wastes, such as neutralized pickle liquor sludge or BOP dust, accumulate despite the availability of alternatives or due to the lack of simple technology development. When the need arises, the steel industry has adopted methods which will result in effective waste control. Where water is plentiful, most mills use water on a once-through basis and in excessive amounts for most purposes. Where water is scarce, or when legal requirements have been imposed, large steel mills have reduced waste water effluents to as little as 1,000 gal/ingot ton, a fraction of the industry average. Pickle liquor recovery processes have been developed and demonstrated, as have methods for recovering all coke plant chemicals. The steel industry has experienced great changes over the past decade as production costs have increased and vigorous competition has appeared
from oversea steel mills and alternative domestic products. Many of the new production facilities, such as the basic oxygen process, larger electric furnaces, and high-speed strip mills, help reduce unit costs by increasing production, but the newer facilities result in increased pollution potentials. Waste control problems in the steel industry are characterized by large sized equipment, high flow rates, and large quantities of materials. Conservation and reuse are particularly effective measures for waste control throughout the industry, resulting in lessened potential pollution loads and in more efficient treatment facility operation. The industry has shown the capability to develop and apply new technology; waste control can he effectively accomplished by vigorous application of this already proved capability. Additional reading Bramer. H. C., “Iron and Steel,” in “Industrial Waste Water Control,” Academic Press, New York. N.Y., 1985. Bramer. H. C., “New Aspects of Water Pollution Control in the Steel Industry,” paper presented a t the Ohio Water Pollution Control Con. ference, Columbus, Ohio, 1966. Brarner, H. C., Gadd. W. A.. “Magnetic Flocculation of Steel Mill Wastes, paper presented at the Purdue In. dustrial Waste Conference, Purdue, Ill., May 1970. Hoak, R. D.. “Water Resources and the Steel Industry,” Iron and Steel Eng., May 1964. Department of Health, Education and Welfare, Public Health Service, Division of Air Pollution, “Air Pollution Asoects of t h e iron and Steel Industry,” 1961. Federal Water Pollution Control Administration, “The Cost of Clean Water.” Vol 111. Industrial Waste Profile No 1 “Blast Furnace and Steel
Henry c.aramer 1s presiaenr o~ datagraphics, Inc. While attending the University of Pittsburgh, he received his BS and MS in chemical engineering and his PhD in economics. Dr. Bramer has specialized in industrial pollution control, especially in the steel and chemical industries.
