TECHNICAL LIBRARY

 

Circular Screen Separators Minimize Solids Build-Up In Settling Pond Cleanup Systems

When a manufacturer decided to incinerate sludge from oil and retention ponds, they asked a team of local engineers to assist with the system design.

To minimize the build-up of solids in a tank, the engineers selected two Kason VIBROSCREEN circular screen separators because of their record of successful performance in similar applications. By minimizing the solids, pumps are protected from abrasion. Two 60 in. diameter VIBROSCREEN units were installed. One unit is used for removing solids from oil ponds, and a second is used for retention ponds. The sludge and floating material is dredged from the ponds and fed to the VIBROSCREENS at about 500 gpm. Separation is accomplished through the use of 2 mesh and 6 mesh screens. The separators usually operate about one day per week. The material in the ponds is basically oil-coated grit, small stones, scale and salts.

The oil ponds contain oily mill water and the oily products of the emulsion breaking process used to treat the oily mill water.

Typically, pond characteristics are:

Oil Pond A
Oil Pond B
Oil and grease content
20%
19%
Total Solid Content
25% including oil and grease
15%
Specific Gravity
0.98
0.98
Ash
5%
1%
Viscosity
170-310 Centistokes @ 40° F
170-310Cs @ 40° F
pH
6-9
6-9

Emulsion
Oil and Grease Content
2%
2%
Total Solids Content
0.7%
0.9%
Specific Gravity
1.0
1.0
Ash
0.3%
0.2%
pH
6-9
6-9

Sludge
Oil and Grease Content
1.3%
4%
Total Solids Content
Varies to 18%
Varies to 18%
Specific Gravity
1.05
1.05
Ash
2%
2%
pH
6-9
6-9



Retention ponds contain sludges deposited in polishing the treated mill waters prior to discharging from the plant site.

Sludge
Retention Pond A
Retention Pond B
Oil and Grease Content
2% by weight
0.8% by weight
Total Solids Content
7% by weight
6% by weight
Specific Gravity
1.05
1.05
Ash
3% by weight
4% by weight
Viscosity
170-130Cs @ 40°F
70-310Cs @ 40°F
pH
6-9
6-9


Solids that do not pass through the 0. 1318 in. openings on the circular screen separator at the oil ponds fall into containers. The water returns to the ponds. Trucks transfer the solids to a hopper from which the solids feed continuously into an operating incinerator. Solids that come off the screen of the circular screen separator at the retention ponds discharge to a dumpster, while the material going through the screens discharges to a thickener.


Separator Operation

The separators and the two screens in each are made of 316 stainless steel. The Vibroscreen units are self-contained, compact machines that make precise mechanical separations according to particle size through efficient use of multiplane, inertial vibration techniques. Both separators use rotary spray bars and center feed distributors to optimize screening efficiency. The units at the oil ponds use a steam sparger.

In the Vibroscreen unit, a motor with a double extension shaft, fitted at each end with variable eccentric weights, is rigidly mounted to the main screening assembly. It is supported on a circular base by rugged springs that allow the screen assembly to vibrate freely while completely preventing vibration transmission to the floor supporting the machine. All parts above the spring level, including the motor, are integrated as a rigid structure. The spring isolation from the support base results in a self-balancing system that requires minimum power and avoids mechanical stress.

In the Kason Vibroscreen design, adjustable top and bottom eccentric weights enable the machine to efficiently handle a variety of slurries. These weights are independently variable for mass and angular relationship, giving a great deal of control of all vibration components. If the mass of the top eccentric weight is increased, the horizontal throw of the screen will increase. Increasing the bottom eccentric weight increases the vertical component of motion. Vertical motion encourages a maximum quantity of undersize material to flow through the screen without blinding.

The relative angular position of the top and bottom eccentric weights controls the flow pattern that oversize material will follow on the screen. Once the optimum settings have been achieved, it is an easy matter to assure uniform performance. A simple vibration amplitude gauge applied to the vibratory circular screen separator provides a self-stick gauge that lets the operator visually check the horizontal and vertical motion. This results in maximum screening efficiency.

The Vibroscreen units are proving effective for helping this manufacturer separate these oily and abrasive waste slurries so they can be better managed.

Screen Tips - Volume 6, Number 1 Winter 1991