NEW DEWATERING PROCESS CHALLENGES TRADITIONAL APPROACH
New technology for dewatering solids during dredging processes is claimed by product developers Black & Veatch of Kansas City, Missouri, to be of particular benefit for waterway restoration and marina maintenance. The Rapid Dewatering System™ enables any slurry to be rapidly separated into water and solids. System compatible with Ellicott Series 370 cutterhead dredge.
"The traditional 'scoop, scrape and truck-the-muck' method of waterway restoration is costly, time consuming and a strain on the environment," says Joe McGonagle, president of Black & Veatch Special Projects Corporation. "Compared to other traditional and alternative methods, our Rapid Dewatering System™ finishes the job more quickly and cost effectively. The system has a small operating footprint with a minimal disruption to the sounding area and the environment."Development of the patent-pending technology started in 1990. "We were approached by a client who asked if a more efficient system could be developed to separate water from solids in a dredge slurry," he continued. Systems on the market handle only hundreds of gallons of water per minute. The Rapid Dewatering System™ has a design throughput rate of 3,000 continuous gallons per minute.The dewatering equipment is modular in design and allows flexibility in system configuration and operations. This flexibility enables the technology to be used in a wide range of site conditions and materials. In some cases, beneficial reuse of solids is possible for such applications as structural fill, parks and recreation areas, roadway shoulders and rights-of-way.The Rapid Dewatering System™:
- Is a continuous process, not a batch processRemoves particles down to the 7 to 14 Angstrom rangeCan be located away from the site, requiring no pits, ponds or return channelsIs easily mobilized and demobilizedHas a small footprint of no more than 75ft x 100ft in area (exact size depends upon modular configuration)Requires no exposed pond bottoms or heavy construction equipmentIs discrete in operation, emitting little or no noise or odor
- Simultaneously recycles all recovered water back to the source
Process
In its standard configuration, the dewatering process has a throughput rate of 3000 GPM, equivalent to the production rate of an Ellicott Series 370 Mud Cat™ hydraulic dredge. The modular system can be configured for higher or lower throughput depending upon operational needs. In operation, the system immediately separates all free water from sediment and returns the water to the water body. Coarse grain materials are separated and removed, then the fines flocculated. The Black & Veatch process employs polymers to aid in the recovery of the finest particles. Once this is accomplished, the flocculated material passes through either a one or two step dewatering process, depending upon the degree of dewatering desired.
Cutter Module
The heart of the process is the control module, a fully programmable and automated unit that monitors real-time changes in polymer demands, correctly mixing and metering proper polymer dosages. It assures real-time flow rates to create an idea dewatered product. Polymer additives can be the most costly portions of the process but the control module eliminates polymer waste. The amount of polymer dosage is determined by the nature of the material.From the control module, the polymerised dredged material is discharged to a proprietary 'engineered grid'. The angle of repose allows free water to gravity drain, stripping it from the dredged material as it moves across the grids, leaving capillary and intracellular water. A belt filter press module (if a drier consistency is required) will remove the capillary water.Material exiting the belt press is stackable and can be augured either to a pile management area or directly into transportation for off-site management.
In its capacity as a full service provider, Black & Veatch conducts tests to determine if the material within the marina is a candidate for the process. Sediments vary within any natural or man-made water body, so a truly representative sample must be obtained to determine the exact characteristics of the sediments to be dewatered. Armed with the test results, the company then custom designs a system incorporating treatment modules with screened cyclones that will deliver the most effective package. In most instances the machinery can handle anything that a hydraulic dredge can efficiently deliver. However, there are some instances when the pulp density must be reduced in order to achieve efficient polymer consumption and hence minimize costs to the customer.
Source: MARINA WORLD May/June 2001
