pa1778data.pdf
pa1778data.pdf
pa1778data.pdf
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#<br />
U.S. STEEL DUQUESNE WORKS<br />
HAER No. PA-115<br />
(Page 108)<br />
effected a plugging of system pipes and spray nozzles.<br />
Furthermore, there developed a tendency in the system for<br />
microbiological organisms to accumulate, which in their natural<br />
life cycle reproduced and caused foul and slimy masses to build<br />
up in the system. In an effort to allay the possibility of<br />
blockage, a variety of chemicals were introduced at the<br />
clarifier, hot well, cold well, and the gas cleaning facilities<br />
at blast furnaces number three, four, and six. These included<br />
sulfuric or hydrochloric acid and/or dispersant for mineral<br />
scale, polymers and surfactant for suspended solids, and biocides<br />
for slime. Despite the addition of these chemicals, the<br />
prevalence of mineral scale, suspended solids, and slime due in<br />
part to the evaporation of water at the cooling towers forced<br />
plant managers to blowdown up to 147 0 gpm of wastewater into<br />
either the slag pits at blast furnaces number one and six or the<br />
river. A corresponding amount of make-up water had to be drawn<br />
into the system from the river.<br />
Although the E.P.A. allowed plant operatives to blowdown as<br />
much as 1470 gpm of wastewater upon start-up of the water<br />
treatment system, progressively stricter guidelines required that<br />
blowdown values not exceed 610 gpm. Given the problems regarding<br />
the increasing concentration of system plugging substances due to<br />
the evaporation of water at the cooling tower, it became<br />
increasingly difficult to meet the more stringent blowdown<br />
guidelines. Moreover, as water passing over the cooling tower<br />
evaporated, it emitted levels of carbon monoxide into the<br />
atmosphere which exceeded E.P.A. standards. As a result of both<br />
of these factors, plant officials shut down the evaporative<br />
system after only one year of operation as part of ongoing<br />
negotiations with the E.P.A. The talks culminated in a<br />
settlement whereby the company agreed to retire blast furnaces<br />
numbers one and three and build a new non-evaporative recycle<br />
water treatment system for Dorothy Six. Built in 1980, the non-<br />
evaporative system was designed to treat 4800 gpm of process<br />
water. It was composed of a gas washer hot well, a gas cooler<br />
hot well, a spray well, two shell and tube type heat exchangers,<br />
and associated chemical feed equipment.<br />
The key components of the new system were the spray well and<br />
heat exchangers. Instead of running the process water through<br />
spray nozzles, thus exposing it to the evaporative effect of the<br />
atmosphere, gas washer and gas cooler water was passed from their<br />
respective hot wells through the heat exchanger tubes which were<br />
in turn sprayed by water from the spray well. The process water<br />
was then pumped over to the gas washer and gas cooling tower<br />
directly from the heat exchangers. In this manner, the process<br />
water was cooled from a temperature of 125° F to 90° P. while