PAT REPORT PRACTICAL, AVAILABLE TECHNOLOGY
Steel industrv sludae is beina reused --u- - - -- -- -
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Colerapa Industries takes waste from a mill’s hot strip-rolling operation and recovers virtually all of the iron value for reprocessing All steel mills put steel slabs through a hot strip-rolling process. On a daily basis, valuable iron units are lost in every facility in the world. Typically, 100 Ibs of raw material charged to a steel mill winds up as finished product ( 7 5 % ) and waste ( 2 5 % ) . Of the latter quarter percent, 22% ends up as slags, and there are many companies that are in the business of reprocessing these slags for further use in steel mills. The remaining 3 YO are sludges-mill scale.
The problem Throughout the hot strip-rolling process, the slab, sheet, bloom, billet, or bar is being oxidized, cooled and washed with a high pressure water spray. When the hot steel is exposed to oxygen in the air as well as the wash water, a layer of iron oxides is formed on the entire surface of the steel as it is being rolled. This layer of oxides is called mill scale or simply scale. As the steel is rolled, this layer of scale is broken away and replaced by a new layer. This generation of new scale occurs each and every time the size or shape of the hot steel is changed. As the scale is broken away from the steel, it falls through the roll tables into
a flume or sewer through which high velocity water is flowing. In addition to the scale and water, a large amount of Iubrication greases and oils from the rolling machinery as well as other mill debris find their way into the flume or sewer. The scale, water, grease and oil combine to form a sludge. This sludge poses a serious water pollution problem if it is discharged into a waterway. In order to control this pollution threat, settling pits and basins are used to collect these sludges and thus prepare the water for reuse or discharge. Much has been done during recent years in the design and construction of these collection facilities to increase collection efficiency. In addition, terminal treatment facilities have been constructed and installed in an effort to upgrade the quality of water at the discharge from the conventional pits. These terminal facilities include terminal lagoons and filtration units. However, as with any collection facility, the efficiency remains high only as long as the system is relieved of what it has already collected. Once collected, the sludge presents a double problem; how to relieve the collection facility and what to do with the sludge once it is removed.
Earlier practice Traditionally, scale drags, ejectors, or mobile cranes equipped with a clamshell bucket were used to remove the sludge in the collection facility. In such practice, the larger solids are removed and trucked for reuse in the iron-making operation at the mill, while the smaller and more concentrated particles (which are more difficult to handle) found in the terminal lagoon and filter backwash are disposed of by dumping in land fills. The required installation of air pollution control systems at agglomerating facilities in the iron-making operation has posed new problems involving the hydrocarbon or oil carryover. Thus, more of the total scale is unacceptable for reuse. The basic concept used in the design of settling pits and basins is to create a quiescent body of water that slows the highly turbulent flume or sewer flow, and thus allow the waterborne solids to fall out of suspension, while permitting light oil fractions in the water to rise to the surface. Problems have arisen in the use of the traditional systems in that the quiescent conditions are disturbed during the excavation of the scale and sludge. Clearly, the conventional ap-
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the river b(ittoni concentrating the iron l.~, ..i^nlinn +r. IJym8sIJcy ,rc,'nnn8'c values that werr ^.._^^A the shore uvhiie disposing of the tailings at the real' of the floating processing unit. Three units operated in the Mahoning River cbver a distance of 16 miles 5 1 d E l l \ , S ".ed l,.l 278,000 tons of finished concentrates from the bottom of the river. The average analysis of this material was 69% total iron with 3 % silica. In addition to efficient excavation at the pit, another important benefit of the Duval process is removal of oil contaminants from mill scale in order to prevent
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preach to managing these sludges has not provided a satisfactory solution to the problem. The new process Colerapa Industries, Inc. (Ravenna, Ohio) converts a sludge that represents waste with serious handling and disposal problems and returns 95-98% of it as usable product having an iron content in excess of the best iron concentrate available. Typically, the material recovered from the process contains 72% total iron and negligible silica: today's best iron ore concentrates contain about 62% total iron with 8-12% silica. The recovered material is put back into a sinter plant or agglomerating facility, and hence right back into the iron-making process. The Steel Company of Canada (Stelco) has been using the process at its Hilton Works Plant (Hamilton, Ontario) since September 1968. The processing services are provided by Euramca International Co. (Hamilton, Ontario). Recently, additional sludges Dreviousiv , wasted from other hot-rollirig mill operations have also been truck€!d to the process station for processin!1 and recovery. Stelco superintendent 01 f utilities and environmental matters T. Mair says, _r .is "the solids from the rolling Oneratinns usually 3 % of the 'put through' tonnage at the mill. It is a substantiial volume of material that requires trt?atment. AIthough the particular Euraimca installation is handling only a p(irtion of the total solids being generatedI in the entire mill complex, we estimate +ha++ha iml. ume of sludge handled is 40,000 tons per year and increasing as more of the mill becomes dependent on the sludge processing operation." Mair adds, "Euramca International is under a IO-yr contract to provide similar sludge processing services in our new Nanticoke Plant which is due to start production in September 1977. The use
of this system is in keeping with Stelco's utilization of the best practical technology in its continuing program Of environmental quality control which to date has involved actual or committed expenditures in excess of $104 million." The total capacity of the existing Hamilton Works plant is 6 million tOnS of steel per year. At the new plant in Nanticoke, Ontario, the steel production capacity is projected at 1.2 million in 1977 and goes up to 3.0 million tons by 1980. How it got started Inventor L. A. Duval of A.urora, Ohio, says that he started the Euramca operation with four people in 1968. Earlier, in 1963 under the Hess-von Bulow name, Duval did work for several steel companies in the U.S. including Republic Steel in Warren, Youngstown and Cleveland, Ohio; Sharon Steel in Farrell, Pa.; and U.S. Steel at McDonald, Ohio and Lorain, Ohio. On the Republic Steel project in 1963, Duval tells how, within 90 days, he and associate J. R. Burton Set up a mill sludge-processing plan1t. In this first practical application the prcIject consisted of the excavation of the? entire river bottom of the Mahoning IRiver in the Youngstown and Warren a rea of Ohio. The river bottom contained years of acmimilitinn __..._.I_._.. nf -. industrial wastes from chemical plants, Inunicipal sewage treatment plants, Ieather processing plants, as well as steel plants. The problem of separatiri g other than steel mill wastes had to bt? solved in order to process the steel mill oxides for reuse ~~~~~~~~~
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ed of a new hydraulic dredging operation that lifted the solids and iransported them to a floating mineral h * Q i n n n h f that was attached as an integral part of the dredging unit. The dt.edge and process plant weighed 126 tons, was mobile, and floated on the ri! ier water. The unit excavated and processed
Stelco's IMair and Inventor Duval convertirig sludge to better use poilution control systems at the consuming sinter plant. Air pollution problems at agglomerating facilities such as sinter or pelletizing plants has necessitated scrubbers or fabric filter collectors to alleviate this problem. These air cleaning methods are hampered by hydrocarbons transported as a coating on the particulates from .the settling pits. Oils present with iron particulates cause condensation in the plant's air handling system, creating serious maintenance problems on the fans and ducts. in the past, some steel mill operations have consumed these initial pit solids (the mill scale) in their sinter plant. However, with the required addition of air handling and poilution control facilities, the hydrocarbon carryover has caused maintenance and operation difficulties that dictate the most complete removal of oil from these solids, thereby limiting the use of this material that should be considered prime raw miterial, COInpanies in the slag (the 22%) reprocessing business include Hecken Engini?ering Co. (Butler. Pa.); International Mill Services (Philadelphia, Pa.); and Edward M. Levy Co. (Detroit, Mich.). ~
Volume 9, Number 7. July 1975
625
