Application & reason for dredging: The customer provides slag processing, metal recovery, materials handling, scrap management, surface conditioning (“scarfing”) and a wide range of specialty services to the North American steel industry.
Application description: The customer uses its Rotomite-6000 to remove mill scale to maintain capacity in its cooling water lagoon that supplies wash water to the steel processing facility. Solids build-up in the lagoon negatively impacts the lagoon’s capacity to store cooling water, thus creating issues for the steel facility. The customer dredges its mill scale and discharges it to a holding/mixing tank that in turn feeds a dewatering process. From the mixing/holding tank, the dredged material is pumped to a large filter press where it is dewatered to stackable cake. The cake is then dumped into a containment bin; and eventually hauled away by a front-end loader. The dewatered cake is re-used as road fill, landscaping fill, and for various other applications. The process helps the customer maintain the plant’s cooling water capacity at satisfactory levels (the desired end result of the process).
Site description: One lagoon with a berm to separate the lagoon into two cells. The lagoon is unlined and measures approximately 220’ X 250’ with a depth of approximately 8 feet.
Quantity of material dredged: The complete dredging and dewatering process results in 11 tons of solids every 45 minutes.
Description of material dredged: Mill scale is a black, slimy, heavy sludge that contains heavy metal filings, oil, and mill scale. Mill scale is a milling waste generated while rolling metal in metal extrusion industries. For example, when iron ingots are rolled, pressed or otherwise forcibly converted into different profiles, the upper layer of metal leaves scales that cannot be utilized to make steel unless the scale is reprocessed in sinter feeding steel production units. Iron mill scale generally contains more than 70% of Fe (Ferrous Oxide).
The customer’s, plant superintendent paraphrased his dredge application as follows:
“We have had a used machine (Crisafulli Rotomite) since April 1997. As you can see by the photo (below) the amount of material in the lagoon was to the point that we could not even turn the dredge during initial operations. That machine has since removed approximately 65,000 metric tonnes of material.
“(The customer) has a unique dredging application with material containing a high oil and grease content. A surface oil skimmer is in continual operation to maintain the lagoon. We operate the dredge 1 to 2 hours per day, year around. The dredged slurry is run to a tank, and then through a filter press for dewatering. We operate even at 46 degrees below zero Fahrenheit. The lagoon’s water temp maintains about 40 degrees Fahrenheit.
“Our dredged mill scale slurry is about 20% solids by volume. Mill scale is a very abrasive material that weighs 168 lbs. per cubic foot.”
The plant superintendent asserts: “The machines are very dependable, the design excellent, turning is great, and all workmanship is to be commended. If others would like to call I would be happy to talk with them.”
Two views of the new Rotomite-6000 operating in the customer’s lagoon in 2007.
Observe the Rotomite-6000’s clean lines, uncluttered walkways around the dredge, and the excellent visibility from the operator’s cab.