Section 5.10 Thickener

Thickener, conventional with central mechanism, c/s tank, motor, drive, weirs, baffles excluding sludge pump. FOB cost = 460000 for a surface area = 300 m with n = 0.58 for the range 40-800. TM = 3.0. 

Thickener, single compartment, concrete with 3 m walls, overflow weir, launder excluding central rake, excavation, site preparation, piping feed launder, overflow pump. PM cost = 400000 for a surface area = 100 m with n = 0.38 for the range 80-2000. L-i-M = 3.1. L/M = 0.4. Alloy cost factors c/s X 0.7, concrete X 1.0 rubber lined for acid-leach mineral processing X 1.22. 

Thickener mechanism unpainted c/s including drive, motor, access platform, central shaft and bridge but excluding inlet pipe and overflow launders. FOB cost 98 000 at surface area = 100 m with n = 0.62 for the range 60-7000. Factors sandblast and paint, X 1.2. L-i-M = 1.35. 

CCD circuit single thickener stage. FOB unit including c/s thickener tank, mechanism, motors and drive single compartment unit, FOB cost 515 000 at surface area = 300 m with n = 0.50 for the range 8 to 2000. Factors, single compartment, X 1.00 three compartment, X 1.10. L-i-M = 1.8-2.0. 

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The first term on the right is the common inverse cube law, the second is taken to be the empirically more important form for moderate film thickness (and also conforms to the polarization model, Section XVII-7C), and the last term allows for structural perturbation in the adsorbed film relative to bulk liquid adsorbate. In effect, the vapor pressure of a thin multilayer film is taken to be P and to relax toward P as the film thickens. The equation has been useful in relating adsorption isotherms to contact angle behavior (see Section X-7). Roy and Halsey [73] have used a similar equation earlier, Halsey [74] allowed for surface heterogeneity by assuming a distribution of Uq values in Eq. XVII-79. Dubinin s equation (Eq. XVII-75) has been mentioned another variant has been used by Bonnetain and co-workers [7S]. 

A BrasiHan company has reportedly produced ammonium chloride from hydrogen chloride gas (16). Hydrogen chloride is mixed with air and iatroduced iato a saturated ammonium chloride suspension at 80 °C. Excess ammonia is added to a conical section of the saturator to maintain a pH of 8. The ammonium chloride is recovered from the suspension by thickening ia a hydroclone, foUowed by centrifugation and dryiag. Mother Hquor and the water used to scmb waste gases, are returned to the saturator. 

More detailea descriptions of small-scale sedimentation and filtration tests are presented in other parts of this section. Interpretation of the results and their conversion into preliminary estimates of such quantities as thickener size, centrifuge capacity, filter area, sludge density, cake diyness, and wash requirements also are discussed. Both the tests and the data treatment must be in experienced hands if error is to be avoided. 

One of the ways to increase the bearing strength of a joint is to use metal inserts as in the shimmed joint of Figure 7-40. Another way is to thicken a section of the composite laminate as in the reinforced-edge joint in Figure 7-40. 

Determine the cementing operation time and thus the minimum thickening time. Assume a cement mixing rate of 25 sacks/min. Also assume an annular displacement rate no greater than 90 ft/min while the spacer is moving through the open-hole section and a flowrate of 300 gal/min thereafter. A safety factor of 1.0 hr is to be used. 

Whereas a film formed in dry air consists essentially of an anhydrous oxide and may reach a thickness of 3 nm, in the presence of water (ranging from condensed films deposited from humid atmospheres to bulk aqueous phases) further thickening occurs as partial hydration increases the electron tunnelling conductivity. Other components in contaminated atmospheres may become incorporated (e.g. HjS, SO2, CO2, Cl ), as described in Sections 2.2 and3.1. 

In some cases the use of a section that spans the thick and thin regions can be used to act as a built-in runner. This may be across the product or it may be a thickened edge or frame around the product. Still another approach would be to redesign the product for a more uniform wall thickness. The additional wall thickness required can be supplied on a mating part. 

Attempting to flow past thin sections to fill wider sections is difficult or may be impossible, because the flow thickens enroute acts like plaque forming along walls of a human artery. Even if both of these ills are avoided, the final result may still contain areas of high shear stresses invisible to the eye but waiting in ambush to cause failure later under extreme conditions previously thought to be well within the material s specifications. 

When a fluid flowing with a uniform velocity enters a pipe, a boundary layer forms at the walls and gradually thickens with distance from the entry point. Since the fluid in the boundary layer is retarded and the total flow remains constant, the fluid in the central stream is accelerated. At a certain distance from the inlet, the boundary layers, which have formed in contact with the walls, join at the axis of the pipe, and, from that point onwards, occupy the whole cross-section and consequently remain of a constant thickness. Fulty developed flow then exists. If the boundary layers are still streamline when fully developed flow commences, the flow in the pipe remains streamline. On the other hand, if the boundary layers are already turbulent, turbulent flow will persist, as shown in Figure 11.8. 

Thus, as this short section has shown, the fact that polymer solutions are non-ideal in the sense that they do not obey Raoult s law leads to numerous important applications in the world beyond the chemical laboratory. The use of polymers as thickeners, while lacking the apparent glamour of some applications of these materials, is significant commercially and accounts for the consumption of many tonnes of polymer throughout the world each year. 

Figure 7.4 Comparative schematic representation of the Dj ( ) and D (—) dopamine receptor. The figure attempts to highlight the major differences between extra- and intracellular loops, especially the intracellular loops between transmembrane sections 5 and 6 and the much longer C terminal of the Dj compared with the D2 receptor. It is based on the proposed topography of Sibley and Monsma (1992). The thickened length of the D2 receptor represents the amino-acid sequence missing in the short form of the receptor. No attempt has been made to show differences in amino-acid sequencing or transmembrane topography...

Thickeners, thickeners are primarily used for liquid-solid separation (see Section 10.4). When used for classification, the feed rate is such that the overflow rate is greater than the settling rate of the slurry, and the finer particles remain in the overflow stream. 

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