pa1778data.pdf

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U.S. STEEL DUQUESNE WORKS
HAER No. PA-115
(Page 108)
effected a plugging of system pipes and spray nozzles.
Furthermore, there developed a tendency in the system for
microbiological organisms to accumulate, which in their natural
life cycle reproduced and caused foul and slimy masses to build
up in the system. In an effort to allay the possibility of
blockage, a variety of chemicals were introduced at the
clarifier, hot well, cold well, and the gas cleaning facilities
at blast furnaces number three, four, and six. These included
sulfuric or hydrochloric acid and/or dispersant for mineral
scale, polymers and surfactant for suspended solids, and biocides
for slime. Despite the addition of these chemicals, the
prevalence of mineral scale, suspended solids, and slime due in
part to the evaporation of water at the cooling towers forced
plant managers to blowdown up to 147 0 gpm of wastewater into
either the slag pits at blast furnaces number one and six or the
river. A corresponding amount of make-up water had to be drawn
into the system from the river.
Although the E.P.A. allowed plant operatives to blowdown as
much as 1470 gpm of wastewater upon start-up of the water
treatment system, progressively stricter guidelines required that
blowdown values not exceed 610 gpm. Given the problems regarding
the increasing concentration of system plugging substances due to
the evaporation of water at the cooling tower, it became
increasingly difficult to meet the more stringent blowdown
guidelines. Moreover, as water passing over the cooling tower
evaporated, it emitted levels of carbon monoxide into the
atmosphere which exceeded E.P.A. standards. As a result of both
of these factors, plant officials shut down the evaporative
system after only one year of operation as part of ongoing
negotiations with the E.P.A. The talks culminated in a
settlement whereby the company agreed to retire blast furnaces
numbers one and three and build a new non-evaporative recycle
water treatment system for Dorothy Six. Built in 1980, the non-
evaporative system was designed to treat 4800 gpm of process
water. It was composed of a gas washer hot well, a gas cooler
hot well, a spray well, two shell and tube type heat exchangers,
and associated chemical feed equipment.
The key components of the new system were the spray well and
heat exchangers. Instead of running the process water through
spray nozzles, thus exposing it to the evaporative effect of the
atmosphere, gas washer and gas cooler water was passed from their
respective hot wells through the heat exchanger tubes which were
in turn sprayed by water from the spray well. The process water
was then pumped over to the gas washer and gas cooling tower
directly from the heat exchangers. In this manner, the process
water was cooled from a temperature of 125° F to 90° P. while