Clarifiers clarifier-thickener

Lamella clarifier/thickener, 22 63, 67-69 Lamellar liquid crystals... 

Clarifier-Thickener Clarifiers can serve as thickeners, achieving additional densification in a deep sludge sump adjacent to the center that extends a short distance radially and provides adequate retention time and pulp depth to compact the solids to a high density. Drive mechanisms on this type of clarifier usually must have higher torque capabihty than would be supplied on a standard clarifier. 

Hydroclones were introduced in 1891 to remove sand from water. They function like a gas-solid cyclone, have no moving parts, and rely on centrifugal force for separation, clarification, and dewatering processes. Hydroclones find use in concentrating slurries, in classifying solids in liquid suspensions, and in washing solids. They may be used alone or in conjunction with clarifiers, thickeners, or filters (Besendorfer, 1996). 

Solid-Liquid Separators. Most of the SO2 transferred from the fine gas into the liquid in the scrubber is converted to solid sulfur compounds in the scrubber and in the reaction tanks. The solid sulfur compounds and the fly ash collected in the scrubber have to be separated from the liquid and disposed of in a way that does not cause water pollution. Clarifier-thickeners, vacuum filters, ponds, etc., are being used as the solid-liquid separators. The liquid is returned to the system, and the solids are removed as waste. 

The settling characteristics of the solid sulfur compounds produced in the lime/limestone scrubber systems vary considerably. Although the clarifier-thickeners are being designed by the vendors, C-E is developing a computer program that could be used to design the clarifier-thickeners for lime/limestone wet scrubber systems. 

The solids concentration of the underflow from the clarifier-thickeners is between 20 and 40 wt % and is not concentrated enough for transportation by either trucks or railroad cars to the disposal areas. For this reason vacuum filters are usually used to concentrate the underflow to 60-80 wt % solids. Ponds are also being used to store solids and to accomplish solid-liquid separation. C-E is doing developmental work to determine the leaching characteristics of the sulfur compounds present in the sludge and also to determine the most suitable filtration system for lime/limestone wet scrubber systems. 

Liquid waste streams with a high-suspended solids content can be cleaned up by solids removal in clarifiers, thickeners, and liquid cyclones and by accelerated settling by inclined Chevron settlers or the like [73]. For waste streams with very finely divided solids in suspension (i.e., less than about 100 pm) dissolved air flotation techniques have been shown to be more efficient than methods employing sedimentation. Final dewatering of the sludges obtained may be carried out on a continuous filter or a centrifuge. The clarified water product can be accepted for more potential options of reuse or final disposal options than untreated water, and the separated solids may be burned or discarded to landfill, as appropriate [74]. 

FIGURE 3.4-1 Clarifier/thickener configuration. Connasy of Eimco Process Equipment Co. 

A problem of some practical importance that arises in connection with clarifier-thickener systems, in which continuously sedimented material is continuously withdrawn, is to deduce the behavior of the flux / as a function of p with hindered settling. For example, with reference to Fig. 5.4.4, the concentration change that is shown there as being brought about by upward-propagating waves (characteristics) is only true if the flux-density dependence is such that u = -djldp > 0. 

LEV, O., RUBIN, E. 8c SHEINTUCH, M. 1986. Steady state analysis of a continuous clarifier-thickener system. AIChE J. 32, 1516-1525. 

Based on preliminary EDS results indicating low total suspended solids in ICB effluent, the sludge clarifier/ thickener might be eliminated. Off-site disposal of concentrated brine rather than dried salts would eliminate the need for the crystallizer and solids filtration steps. Off-site brine disposal would also be consistent with current operations at Tooele, Utah, and planned operations at Newport, Indiana. The basis for the currently designated materials of construction for the evaporator and crystallizer is unclear. If on-site crystallization is included in the final process design, a more extensive evaluation of the materials of construction will be necessary, including stressed-materials coupon-exposure tests. The dried solids from the crystallization step might be... 

Figure 1.5 Lamella clarifier/thickener (Svedala, Pumps Process AB, Sala, Sweden)...

As can be seen, the two-stage system with a clarifier thickens and classifies a little better but the two stage with overflow recycle reduces the cut size to a little lower value. 

---