Heterogeneous Slurries

Wilson, K. C. and Puoh, F. ]. Can. Ji. Chem. Eng. 66 (1988) 721. Dispersive-force modelling of turbulent suspensions in heterogeneous slurry flow. 

Finally, in the fourth section the fundamentals of the modelling concerning two basic olefin polymerization processes are examined heterogeneous slurry polymerization and gas-phase polymerization. The SPERIPOL process for making High Impact PolyPropylene (HIPP) is then described as an illustrative example for combining fundamentals and elements of product and technology development. 

If shutdown occurs while pumping a heterogeneous slurry, solids will deposit in a stationary bed along the pipe bottom. To resume the operation of the slurry pipeline, it becomes necessary to resuspend these solids to remove them from the pipe. If the fluid flow rate over the settled solids is gradually increased, a response similar to curve A of Figure 1 is obtained. With increasing shear rate, the wall shear stress decreases until a minimum is reached. The fluid velocity that corresponds to this minimum shear stress is the critical resuspension velocity, Vs (7). 

Figure 1. Flow curves for homogeneous and heterogeneous slurries. (Reproduced with permission from reference 7. Copyright 1991.)...

VI. Circulated Hex. Almost all the remarks, including those concerning shielding, made for the heterogeneous slurry pile apply also for a circulated hex pile. However, the absence of slurry particles alleviates the erosion problem. The problem of corrosion, on the other hand, is especially important because a leak between hex and water would be disastrous. Although several metals stand up very well in pure hex, nothing is known about the corrosion effect of hex under the influence of flssion fragments, and Cannon found that free fluorine pits aluminium in the presence of -radiation. The presence of free fluorine can hardly be avoided under pile conditions. 

Most cellulose ethers including HMHEC polymers are produced by heterogeneous slurry processes consisting of separate organic and aqueous/cellulose ether phases. Yokota of Daicel" studied the propoxylation of cellulose using an aqueous toluene//-butyl alcohol diluent, and he reported a diluent phase separation in which essentially all the caustic partitioned into the lower aqueous phase during the heterogeneous reaction. After the addition of aqueous caustic, two phases form (tlvee if one counts the solid cellulose as a... 

Heterogeneous slurries. Concentration gradients exist along the vertical axis of a horizontal pipe even at high flow rates the fluid phase and the solid phase retain their separate identities. These slurries tend to be of lower solids concentration and have larger particle sizes than homogeneous slurries. 

The primary objective in designing a slurry system is to select a practical velocity/diameter combination which carries the solids and results in reasonable pressure losses. A practical design velocity depends not only upon the physical properties of the solid and liquid, but also on the solids concentration in the stream. A velocity in the range of 4 to 7 feet per second is usually practical and economical however velocities above 7 feet per second may be necessary for strongly heterogeneous slurries. Pipe abrasion is a consideration at about 8 to 10 feet per second, and can be serious at higher velocities. 

This book is intended for engineers, and various examples are included in the text. The purpose of such examples is to simplify the use of complex equations. With modern personal computers, which use simple languages such as quick basic, an engineer can efficiently calculate friction losses for a heterogeneous slurry flow. 

FIGURE 4-5 Velocity regimes for heterogeneous slurry flows. 

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