Three Portable Dredges Pump up to 1800 GPM of Sludge
over 1000 ft Distances
Simple to control depth of sweep
Three small dredges are currently pumping up to 180 gallons of sludge per minute over distances ranging up to 1000 ft to sludge thickening and dewatering facilities at Bethlehem Steel's Sparrows Point plant near Baltimore.
A little over a year ago, Francis H. Ebersole, General Foreman in the Fuel and Steam Department, saw a demonstration film on the portable dredges. Ebersole, who has been in charge of Bethlehem Steel's Humphreys Creek Wastewater Treatment Facility since its inception, had expressed an interest in possible applications of the dredge for cleaning the plant's settling basins. He was sufficiently impressed with its potential to ask to see the dredge in action at the Front Royal, Va., plant of Avtex Fibers, Inc.
As a result of that demonstration, three portable dredges were purchased to replace a dredge already at the plant. The concept called for placing a portable dredge in each of the three 100 ft X 400 ft settling basins. Even with the one-piece-for-three equipment exchange, the capital investment and operating costs of the three portable dredges proved to be considerably less than those of the dredge they replaced.
"We operate five steel finishing operations that use over 100 million gallons of water a day, so our wastewater treatment requirements are very demanding," explained Ebersole.
Wastewater from the five operations flows to the Humphreys Creek Wastewater Treatment Facility where the water is mixed with lime in an aerator/mixer chamber in order to neutralize the acid in the plant's "pickling" processes. The water is then clarified in one of the three basins before it flows into nearby Bear Creek.
The portable dredges are used to collect the settled solids or sludge which accumulates in the settling basins.
The dredges traverse the settling basins by winching themselves along cables attached to steel platforms at both ends of each basin. The specially designed anchoring platforms make it possible for any of the three dredges to be operated by a single employee who pilots his machine and also moves the cables to enable the dredge to cover an entire basin in ten 8-ft wide swaths.
The sludge is pumped ashore by the dredge's 175 HP engine. The solids are carried through 8" aluminum pipe, kept afloat by pipe aluminum flotation pipes. The floating pipe is attached to a discharge pipe permanently mounted on the sidewall of each settling basin.
The dredges normally operate (one at a time) two shifts a day, five days a week, although in peak periods they have operated around the clock, seven days a week.
According to Ebersole, the main advantages of the portable dredge over the dredge previously used are that it travels in a fixed path and that it is simpler to control the depth being dredged. The patented auger arm will dredge to a maximum depth of 15 ft-more than sufficient to handle the 12-ft depth of Bethlehem Steel's settling basins.
"The portable dredges have handled our requirements very well," said Ebersole, a 24 year veteran at Bethlehem Steel. "Even in cold weather the dredge has given us no problems, and it occasionally gets down to 0º F (17°C) in this part of the country." Bethlehem Steel's Wastewater Treatment Facility operates 12 months a year.
Recently, the three machines were removed from their basins and parked on the "berms" that separate the three basins for maintenance. They got a complete steam cleaning, plus routine engine maintenance and a complete mechanical check. "We were pleased to learn that even though this was the first inspection the equipment had undergone in over a year, there weren't any major problems." said Ebersole.
The only major modification that Bethlehem Steel has made on its dredges was required by the prevailing northwest/southwest winds occasionally blowing the discharge pipe under the back end of the unit. The answer to the problem turned out to be steel plate "bumpers" installed at the rear of all three machines, which have been effective in keeping the discharge pipes trailing properly in windy weather instead of getting in the way of the machine's auger.
Reprinted from Chemical Processing
