Clarification enhancement

Tn all but the last 10 or 15 years the majority of decanter applications have been limited by their ability to clarify the liquor. Scale up of these centrifuges Would be based on their clariKcation ability. Thus, a lot of the earlier development has been concentrated on enhancing clarification capacity. Bowl speeds have been increased, bowls lengthened and solids discharge areas increased to ensure solids choking does not inhibit clarification volume. Apart from these obvious methods there are some mechanical modifications which can help, 

With a normal helical conveyor tlie clarified liquor must wind its way around the helix of the flight before discharge. The velocity of the centrale is thus much larger than it would be If it could flow axially. Moreover the velocity must be that much extra to overcome the screwing efi ect of the conveyor. 

To allow axial flow on many modern conveyors, holes or windows are cut in the llighis. To maintain a reasonable strength to the flight the open area for flow is about 5()T of the cross-sectional area available to the depth of the windows. Naturally the windows cannot be cut to the periphery of the flight. 

This feature has the same function as the quasi-axial How. In this design, longitudinal radial vanes are welded to the conveyor hub. say 6 to 12 in number, and a ribbon flight is welded on the outer edge of the vanes. The vanes extend from the feed zone to the front hub. 

In this design axial flow of liquor is assured without any circumferential surface slip. The liquor cannot rotate around the helix due to the build-up of cake in front of the flight sealing under the vanes. 

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A scale-up factor for decanters, indicating the clarification ability A means of increasing the clarification capacity of a bowl, using discs or vanes (see clarification enhancement)... 

Coagulation involves neutralizing charged particles to destabilize suspended soflds. In most clarification processes, a flocculation step then follows. Flocculation starts when neutralized or entrapped particles begin to colUde and fuse to form larger particles. This process can occur naturally or can be enhanced by the addition of polymeric flocculant aids. 

Lime is somewhat different from the hydrolyzing coagulants. When added to wastewater it increases pH and reacts with the carbonate alkalinity to precipitate calcium carbonate. If sufficient lime is added to reach a high pH, approximately 10.5, magnesium hydroxide is also precipitated. This latter precipitation enhances clarification due to the flocculant nature of the Mg(OH)2. Excess calcium ions at high pH levels may be precipitated by the addition of soda ash. The preceding reactions are shown as follows ... 

The function of clarification unit operations- How these units work and how chemical treatment enhances their performance. 

Pectin degradation requires fee combined action of various enzymatic activities. However, evaluation of fee contribution of individual pectinases in Suit juice extraction and clarification is rather complicated. Most commercial pectinolytic enzyme preparations are produced by fermentation wife filamentous fungi, mostly strains belonging to fee genus Aspergillus,. plication studies with mixtures of isolat enzymes obtained by fermentation or by means of fractionation of commercial enzyme preparations can be used to assess the importance of fee various individual enzymes. Subsequently, molecular biology and fermentation technology can be used to enhance specific desirable enzymatic activities. 

Granular bed filters are used in ten coil coating plants to remove residual solids from the clarifier effluent, and are considered to be tertiary or advanced wastewater treatment. Chemicals may be added upstream to enhance the solids removal. Pressure filtration is also used in this industry to reduce the solids concentration in clarifier effluent and to remove excess water from the clarifier sludge. Figure 7.4 shows a granular bed filter and Table 7.13 presents the heavy metal removal data of a lime clarification and filtration system. 

Sedimentation and dissolved air flotation are the most common clarification processes for removal of precipitates. Either sedimentation or flotation is often preceded by chemical coagulation or precipitation, which converts dissolved pollutants to a suspended form, and by flocculation, which enhances clarification by flocculating suspended solids into larger, more easily separating particles. Simple sedimentation normally requires a long retention time to adequately reduce the solids content. The detention time of dissolved air flotation, however, is much shorter. When chemicals are used, retention times are reduced and clarification removal efficiency of either sedimentation or flotation is increased. A properly operated clarification system is capable of efficient removal of suspended solids, metal hydroxides, and other wastewater impurities.10-12... 

Though the existence of these enhancement mechanisms is well established, their details are not well understood, and await further clarification. 

However, it remains to be understood how this type of doping process can induce enhancement in the electronic transport of the polymers. Indeed, the clarification of the doping mechanism of conducting polymers and of the associated electronic band evolution is of fundamental importance for the comprehension of the operational behaviour of these compounds as novel electrode materials. 

The mechanisms by which thyroid hormones enhance antidepressant activity are still unknown. It is of interest that thyroid hormone increases net activity of several neurotransmitters that are putatively involved in the pathophysiology of depression in a way that is descriptively similar to that of estrogens. Receptors for the two hormones belong to the same superfamily. As was previously mentioned [Pfaff 1996], these issues are currently being explored, and clarifications are expected shortly. 

Furthermore, as will be apparent from the following sections, all properties of biological products that lead to their industrial utilization are, by definition, functional ones. The expected enhanced reliance on biological "renewable resources" due to the exhaustion of the fossil materials will necessitate increased emphasis on the clarification, evaluation, and modification of their functional properties as a prerequisite to their efficient utilization. 

The reaction mechanisms for conversion of the refractory sulfur species such as 4,6-dimethyldibenzothiophene (4,6-DMDBT) in gas oil and the inhibition of their HDS by coexistent species need clarification. Novel mechanistic routes that enhance the reactivity or reduce the inhibition are necessary for designing more efficient deep HDS catalysts and processes. 

The fact that thromboresistance of HCP is dependent on the method of immobilization of heparin, together with a rather low activity of covalently immobilized heparin, makes the idea of long-term enhancement of thromboresistance of polymers on their heparinization doubtful 54,70,71J. Naturally, the answer can be given only after a detailed analysis of the interaction of HCP with blood and its components and clarification of the mechanism of the effect of the immobilized heparin on the blood clotting system and relying on the results of in vivo tests of these materials are necessary. 

Clarified Juice. Some citrus juices, notably lime and lemon, are in demand as clarified products. Natural clarification, in combination with filtration, is often used to achieve a sparkling clear serum. However, native PE action is slowed by the high acidity of these juices, and may not give satisfactory cloud removal. In this instance, modified pectins can serve to enhance juice quality by removing cloud. 

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