Method for continuous desludging of water bodies with separation of selected sediment fractions
Title of the offer
Method for continuous desludging of water bodies with separation of selected sediment fractions
Offer description
The subject matter of this Invitation is the construction technology for a hydromechanical installation for the removal of sediments from the bottom of a water body with simultaneous separation of selected fractions. The installation was tested in a laboratory and under field conditions (in a flow-through water body). The difference in water levels is the sole driving force for sediment suction and mixture conveying. In the research procedure, spherical particles were used to simulate the sediments and materials collected from the water body.
Under laboratory conditions, with the sediments removed being simulated by spherical particles, the efficiency of the separation process was very high (92%). In the case of sediments collected from the upper part of the water body, the separation efficiency rate was up to 55–65%.
In the field research procedure, the mineral fractions (0.25 mm < d < 1.0 mm) were successfully separated from organic sediments. Under natural conditions, it is preferable that the fractions separated from bottom sediments be similar in particle size to the bed load brought by the river to the water body. The sediments can be safely discharged to the river downstream.
As confirmed by research, the ratio between the average water flow velocity and the free-fall velocity of a solid particle (v1/wss) is an important criterion in determining the required hydraulic conditions of an efficient separation process. Hence, a good criterion for setting the dimensions of a slotted separator is the Hazen number (Ha), calculated as the function of the v1/wss ratio and the specific dimensions of the separator’s process chamber.
The separation process will be effective (at an efficiency rate of no less than 70%) if:
- for the smallest fraction sought, the ratio between the average velocity and the free-fall velocity is less than 4.5 (v1/wss < 4.5), which corresponds to a Hazen number below 0.35 (Ha < 0.35);
- smaller and organic (undesired) fractions are efficiently removed (n < 0.10) if the v1/wss velocity ratio is above 45 (v1/wss > 45);
- the separator has at least three slots separated by a distance no smaller than the width of the slot; the width of the slot should not be smaller than the double diameter of the largest grain size of sediments removed.
