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Title: Feasibility study of hydrocyclone systems for dredge operations
Authors: Tiederman, W. G. (William G.)
Reischman, M. M.
Keywords: Separators (Machines)
Dredging spoil
Dredged material
Suspended sediments
Dredged Material Research Program (U.S.)
Publisher: U.S. Army Engineer Waterways Experiment Station
Series/Report no.: Contract Report (Dredged Material Research Program (U.S.)) ; no. Contract Report D-73-1
Abstract: A major difficulty with dredge spoil is that in most dredging operations small suspended solids become well dispersed in the large volumes of water used to hydraulically transport the solids from the bottom of the waterway. Frequently it is not efficient to transport this entire volume of water to a disposal site and yet in many cases it is also undesirable to return the turbid water to the waterway. However, even when the entire volume of spoil is transported to a disposal site, an overflow of turbid water can occur from the disposal site, particularly when the site is small or almost full. Consequently, the development of processes which will clarify the water and concentrate the small suspended solids in dredge spoil would make transport of spoil more efficient, would make the use of smaller disposal sites possible and would decrease the environmental impact of dredge operations. The purpose of this study was to experimentally determine the feasibility of using hydrocyclone separators for the concentration and clarification of dredge spoil. Since hydrocyclones are also well suited for the task of separating solids into fractions, the feasibility of using hydrocyclones for the recovery of sand and gravel while rejecting fine silt was also investigated. The experimental program was conducted with hydrocyclones and hydrocyclone series designed for overflow flow rates of about 10 gallons per minute. Six dredge spoil samples (supplied by the Corps of Engineers), two clay slurries and one sand were used to determine the effect of particle size, viscosity of the fluid, and inlet solids con-centration upon the effectiveness of the hydrocyclones. Attempts were also made to increase performance by chemically flocculating the solids upstream of the separators. While the clarification and concentration performance of the hydrocyclones was good on low solids content clay slurries, the performance ranged from below average to poor on the spoil samples. The poor capability of the separators to clarify and to concentrate these spoils was due to the combination of high solids content, small particle sizes and highly pseudoplastic (high viscosity) behavior of the spoils. Centrifugation and chemical treatment were not effective on the higher solids content (greater than 100 g/ℓ) spoils either. Spoils with solids contents less than 100 g/ℓ could be flocculated but the flocs were too fragile to survive in the hydrocyclones and neither clarification nor concentration was enhanced by the treatment. The high solids content affects clarification more than it does concentration and thus hydrocyclone concentrators were reasonably effective on all but the highest solids content spoils. Meanwhile, the hydrocyclone proved very successful at recovering sand from the full range of spoils. The hydrocyclone system is recommended for this application of classifying the solids in dredge spoil.
Description: Contract Report
Gov't Doc #: Contract Report D-73-1
Rights: Approved for Public Release; Distribution is Unlimited
Appears in Collections:Contract Report

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