OPTIMIZATION OF
SECONDARY COOLING WATER FILTRATION
IN A CONTINUOUS STAINLESS STEEL CASTING PROCESS
Scott D. Roser, Graduate Student
David A. Long, Associate Professor
Department of Civil Engineering
Pennsylvania State University
University Park, Pennsylvania 16802
Jeffrey A. Vaughn, Staff Engineer
CH2MHill
Denver, Colorado 80222
Carpenter Technology Corporation (Cartech) of Reading, Pennsylvania, operates a stainless steel continuous casting machine which was designed, installed and commissioned by
Concast, Inc. of Montvale, New Jersey. The continuous casting of steel is a metallurgical
process in which molten steel is converted into semifinished shapes which then are reheated
and converted by reduction mills into finished products. The conversion of molten steel
to semifinished shapes involves the controlled cooling of the steel by water sprays. Spray
cooling in the continuous casting process requires that water be applied to the surface of the
steel at precise rates to achieve uniform cooling. This cooling water cascades down over the
machine picking up mill scale, oil, grease and dirt, and is collected in a sump. The sump discharges into a clarifier where a dragout scraper removes the settleable solids. The cooling
water, which contains mostly iron, chromium, nickel and other metal oxides, then is pumped
through two downflow pressure sand filters, operating in parallel, with a third filter for
stand-by use. The two filters currently are operated as constant rate filters at a hydraulic
loading rate of 5 gpm/ft2 (204 1/min-m2). Constant-rate filtration is controlled by orifice
plates. The filtered water either is passed through a cooling tower and stored in a cold well
to be used again as quenching water or it is recirculated into the clarifier. This routing would
depend on the quantity of water in the cold well which in turn is dependent on the amount
of casting which takes place during any period of time. The water system is a closed system
except for additions to make up for evaporation losses.
The filters are backwashed when headloss through the filter reaches 6 psi(41.3 kN/m2).
In addition, the backwashing is sequenced such that after a filter is backwashed it is put
on stand-by. During backwash, filter effluent is passed up through the filter media and out
into a cone-shaped surge tank in which the solids settle out and the supernatant is allowed to
flow back into the clarifier. The resulting sludge later is hauled to a proper disposal site.
Figure 1 shows a schematic of the spray and cooling water system.
Each year Cartech undergoes a plant shutdown in August for overhaul and replacement of
various equipment throughout the plant. For the purposes of the phase 1 portion of the
study, it was of interest to Cartech personnel as to whether they should replace the existing
sand medium in the pressure filters with new sand, keep the old sand medium which had
been in place for about 2 years, or replace the sand with a different medium that would
yield better effluent quality. In view of this concern, the supplier of the pressure filters,
Roberts Filter Manufacturing Company, proposed to install a pilot plant unit to determine
a more optimum combination(s) of hydraulic loading rate and media for this particular application. The conclusions of the phase 1 study would be used by Cartech to determine what
should be done with their existing sand medium during the plant shutdown and also be of
use to Roberts Filter for similar future applications.
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