Slurry Preparation Tank

Slurry preparation tanks are used for several operations  

An alternative to stainless steel tanks is open cylindrical storage tanks. Plastic tanks or single-use liner can be used as well. Closed single-use bags with a top mounted paddle mixer and a valve closing with the wall can also be taken into consideration. 

Chromatography resins for manufacturing scale are delivered in standard containers of 10, 20, or 251. Transferring sedimented resin from shipping containers (drums or jerry cans) to the mixing tank can be performed with specific equipment like drum rollers. 

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A pump is necessary to pack, unpack, and provide buffer from the slurry preparation tank to the column. The ideal pump provides constant pressure and flow rate at low shear stress. Because of shear stress reasons rotating parts have to be avoided, therefore diaphragm pumps are preferred. To dampen the pulsing characteristic of a diaphragm pump, typically 2 or 3 pistons are used. 

Figure 7-5. Photograph of a scale model of the limestone process FGD plant on Unit 2 of Alabama Electric Cooperative s Tombigbee Station. Components from left to right are inlet ductwork I.D. fans common recycle tank, spray tower absorbers, one behind the other slurry preparation tank limestone silo and limestone ball mill (in enclosure). Courtesy of Peabody Process Systems, tnc.

A commercial design based on semicontinuous operation was developed for manufacture of silicate powders (27). A slurry, prepared containing the feed materials and water, is fed to the reactor tank and heated by circulating a heat-exchange fluid in channels located on the outside vessel wall. A six-bladed stirrer is operated at about 100 rpm in order to keep reagents well mixed. Once the slurry reaches the operating temperature, the vessel heat is maintained until reaction is complete. For most fine-particle products, this time is less than 1 hr. 

B. Process Parameters. Figure 7.46 shows a typical chemical treatment process. Solutions of caustic and carbonate are stored in feed tanks. While direct use of Na2C03 slurry is possible, this diagram is based on solution feed. There may also be a preparation tank in which carbonate solutions are made off line. The caustic solution is received from the process, preferably before evaporation in a membrane-cell plant. A separate supply of a diluted solution (20% or less) is often used, and ion-exchange regenerant solutions are another possible source of treat liquor (Section 7.5.5.2B). 

In the slurry process, the hydrolysis is accompHshed using two stirred-tank reactors in series (266). Solutions of poly(vinyl acetate) and catalyst are continuously added to the first reactor, where 90% of the conversion occur, and then transferred to the second reactor to reach hiU conversion. Alkyl acetate and alcohols are continuously distilled off in order to drive the equiUbrium of the reaction. The resulting poly(vinyl alcohol) particles tend to be very fine, resulting in a dusty product. The process has been modified to yield a less dusty product through process changes (267,268) and the use of additives (269). Partially hydroly2ed products having a narrow hydrolysis distribution cannot be prepared by this method. 

In Step 9 of the GATS process, the dry, size-reduced dunnage materials and nonprocess wastes from Step 2 are slurried with energetics hydrolysate in preparation for feeding to one of the SCWO reactors. Following the removal of precipitated aluminum compounds by filtration in Step 7, the energetics hydrolysate is transferred to one of two hydropulpers. Spent decontamination solution used in various decontamination operations in the plant also goes to the hydropulper tanks. 

Clean water was flushed through the tank for several weeks in order to reduce contaminant concentrations. Water was then pumped from the tank to lower the water table to the 1 -m depth in preparation for excavation of the 14-40 SMZ. The 14-40 SMZ was manually excavated from the barrier cells starting with Cell 1 (farthest away from the tank wall). Two methods of emptying the cells were used. The first method involved using a small trash pump capable of pumping slurries. This method was somewhat effective and could be used successfully in laiger-scale applications where full-size pumps could be employed. The effluent from the trash pump was placed in a super sack, which acted as a filter to remove the SMZ from the water... 

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 Unipol process employs a fluidized bed reactor (see Section 3.1.2) for the preparation of polyethylene and polypropylene. A gas-liquid fluid solid reactor, where both liquid and gas fluidize the solids, is used for Ziegler-Natta catalyzed ethylene polymerization. Hoechst, Mitsui, Montedison, Solvay et Cie, and a number of other producers use a Ziegler-type catalyst for the manufacture of LLDPE by slurry polymerization in hexane solvent (Fig. 6.11). The system consists of a series of continuous stirred tank reactors to achieve the desired residence time. 1-Butene is used a comonomer, and hydrogen is used for controlling molecular weight. The polymer beads are separated from the liquid by centrifugation followed by steam stripping. 

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