The Operation of Pressure Type Sand
Filters for Hot Mill Waste Waters
CARL BROMAN, Superintendent
Fuel and Environmental Control
Indiana Harbor Works
Youngstown Sheet and Tube Company
East Chicago, Indiana
INTRODUCTION
For those of you not familiar with steel mill terminology, a hot mill is a
process where steel slabs, in our case 10 to 12 in. thick, four to five ft wide, and 25
to 30 ft long, weighing about 20 tons, are heated to 2400 F. The steel is then
continuously reduced, in 13 stages, into final coil form, 60 to 70 in. wide, 15 to 20
gauge some 2,000 ft long. During the rolling process an iron oxide forms on the
surface of the strip due to the exposure of the steel, at elevated temperatures, to the
surrounding atmosphere. This oxide or scale is removed by a 3,000 psi water spray
system, this is necessary to prevent surface defects and to prepare the steel for future
plating operations. As a result, the major contaminate in the waste waters from the
hot mill is a fine iron oxide particle, there is also a small quantity of oil, originating
from the various lubricating systems in the mill.
The waste waters leaving the hot mill empty into scale pits where settling
action occurs, however, the effluent leaving the scale pit is not of sufficient quality
to meet existing standards and, therefore, secondary treatment is necessary.
When Youngstown was in the initial stages of designing a new 84-in. hot strip
mill complex for its Indiana Harbor Works at East Chicago, there was concern as to
what type of secondary treatment should be provided to treat the waste water
discharge. Realizing that the total elapsed time, from design to operation could be six
to eight yr, Youngstown desired a system that could meet standards well beyond
those in existence at the time so as to prevent premature obsolescence. Existing
systems in the steel industry in the early 1960's, either filters or clarifiers, were not
satisfactory in our opinion. We learned, however, that deep bed, pressurized, sand
filters had been used in Europe since 1952 without the familiar problems of "mud
balls" and "rat holding." Visits to French and German installations verified the
excellent results in regard to effluent quality and operational reliability. As a result,
42 filter units were purchased for installation at East Chicago.
The individual filters are 16.5 ft in diam and 15 ft high, each vessel containing
seven ft 11 in. of filter media with 23 in. of free board. Of this total depth, four in. is
made up of 1.5-in. gravel, two in. of one-in. gravel, two in. of 0.75-in. gravel, two in.
of 0.375-in. gravel with the remainder made of 2-3 mm sized material.
The total filtering area installed at the 84-in. hot strip water treatment plant is
9,000 sq ft and based on a conservative filtering rate of seven gal/sq ft/min, the plant
can handle a volume of 3,800,000 gal/hr. We use the word conservative based on a
four month test conducted by Youngstown beginning in May of 1967. One filter was
installed using the scale pit effluent from our 54-in. hot strip mill in order to
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