Slurries system design

There are two basic (and interrelated) useful parameters for an open-channel slurry system design the minimum slope (to maintain slurry suspension) of straight lengths of launder, Smin (usually expressed as a percentage), and the velocity head corresponding to the minimum slurry velocity, K (expressed in metres), is often quoted as part of process technology, and may be arrived at directly by practical experience, whereas K is usually derived. The parameters have an approximate theoretical relationship, and the minimum slurry velocity Kmin is essentially the same as the minimum velocity to avoid settlement in full-flow pipes of comparable diameter, in terms of wetted perimeter. 

Figure 2-48. Critical velocity characteristics depend on whether slurry is heterogeneous or homogeneous. By permission, Deramme-laere, R. H. and Wasp, E. J., Fluid Flow, Slurry Systems and Pipelines, Encyclopedia of Chemical Processing and Design, J. McKetta, Ed., M. Dekker, vol. 22,1985 [25].

The use of V-notches in a trough wall for overflow is more sensitive to leveling problems than the other designs, and for the same %- to Me-in. level tolerance produces a more severe non-uniform flow distribution. The quality of distribution from a V-notch is poor compared to the other types of trough distributor, but does have advantages in slurry systems [131]. It should not be used for critical distillation applications, but is good for heat transfer and where solids are in the system. 

Brown, N. P. and Heywood, N. I. (eds) Slurry Handling. Design of Solid-Liquid Systems (Elsevier. Amsterdam, 1991). 

The need for a reliable source of slurry during CMP stimulated the growth of a whole industry of bulk chemical distribution (BCD) systems. An extended discussion of BCD systems is beyond the scope of this work, but a few words are in order. Slurry distribution systems vary in sophistication from the simple laboratory system consisting of little more than a barrel of slurry and a pump to sophisticated delivery systems designed to supply slurry to tens of CMP tools in a high-volume production environment [56]. 

H. Mizuno, Slurry Delivery System Design for Tungsten Chemical Mechanical planarization Manufacturing Site, presented at ISSM, Oct. 10, 1997. 

Cowper, N.T. Case Studies of Some Major Projects in Slurry Handling Design of Solid-Liquid Systems, Brown, N.P. Heywood, N.I. (Eds.), Elsevier London, 1991, pp. 625-652. 

One area for industrial studies is the whole area of slurry pipelines. Coal is by far the most common material in slurry pipelines, but other pipelines, but other pipelines include iron ore and potash. In large volume solid suspension applications, there is a considerable trade-off between volume of a tank, mixer horsepower, shape of a tank, and many other areas of cost consideration that are important in overall design. In addition to the tanks in these sorts of slurry systems, it must be capable of incorporating slurries into water or vice versa to either increase or decrease the solids concentration of a given system. 

Continuing study of the fractionation system for the SRC-II process, both in pilot plant and engineering work, has indicated that some modification to the original fractionation system design is desirable. In the original design the slurry was passed... 

Starch slurry make-down systems are designed to prepare a uniform suspension, using batch or continuous systems. In modem paper mills, automated batch or continuous systems are used. Water content and bulk density will affect the flow of dry starch.90 In the batch slurry system, weighed increments of starch are drawn from the silo and periodically added to a measured quantity of water in the make-up tank. The suspension is screened and automatically pumped to a larger storage tank on demand by a level transmitter. Continuous make-down of starch slurry is accomplished by simultaneously feeding starch and water at controlled rates into the slurry make-down tank. The dry starch is metered with a volumetric screw feeder. The slurry is screened before dispersion by batch or continuous cooking. 

The chemical component of CMP slurry creates porous unstable oxides or soluble surface complexes. The slurries are designed to have additives that initiate the above reactions. The mechanical component of the process removes the above-formed films by abrasion. In most planarization systems the mechanical component is the rate-limiting step. As soon as the formed porous film is removed, a new one is formed and planarization proceeds. Therefore, the removal rate is directly proportional to the applied pressure. To achieve practical copper removal rates, pressures greater than 3 psi are often required. These pressures should not create delamination, material deformation, or cracking on dense or relatively dense dielectrics used in silicon microfabrication on conventional dielectrics. However, the introduction of porous ultra-low-fc (low dielectric constant) materials will require a low downpressure (< 1 psi) polishing to maintain the structural integrity of the device [7-9]. It is expected that dielectrics with k value less than 2.4 will require a planarization process of 1 psi downpressure or less when they are introduced to production. It is expected that this process requirement will become even more important for the 45-nm technology node [10]. 

Experiments in Slurries, In a slurry system, Borgwardt (14,8) studied enhanced oxidation in a pilot-scale scrubbing system (pH 4.5) with a forced oxidation tank. Even with advanced-design gas distributors, he found the overall rate of oxidation was limited by the mass transfer of oxygen to the solution. An air stoichiometry of 2,6 was used in this investigation. Neither gas distributor orifice size nor chloride concentration had an effect on the rate. 

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