Entrainment impact

Extensive design and optimization studies have been carried out for this sequence (108). The principal optimization variables, ie, the design variables that have the largest impact on the economics of the process, are the redux ratio in the azeo-column the position of the tie-line for the mixture in the decanter, determined by the temperature and overall composition of the mixture in the decanter the position of the decanter composition on the decanter tie-line (see Reference 104 for a discussion of the importance of these variables) and the distillate composition from the entrainer recovery column. 

In distillation towers, entrainment lowers the tray efficiency, and 1 pound of entrainment per 10 pounds of liquid is sometimes taken as the hmit for acceptable performance. However, the impact of entrainment on distiUation efficiency depends on the relative volatility of the component being considered. Entrainment has a minor impact on close separations when the difference between vapor and liquid concentration is smaU, but this factor can be dominant for systems where the liquid concentration is much higher than the vapor in equilibrium with it (i.e., when a component of the liquid has a very lowvolatiUty, as in an absorber). 

Although it is entirely possible for erosion-corrosion to occur in the absence of entrained particulate, it is common to find erosion-corrosion accelerated by a dilute dispersion of fine particulate matter (sand, silt, gas bubbles) entrained in the fluid. The character of the particulate, and even the fluid itself, substantially influences the effect. Eight major characteristics are influential particle shape, particle size, particle density, particle hardness, particle size distribution, angle of impact, impact velocity, and fluid viscosity. 

Ghadiri et al. (1992b, 1994, 1995) developed a more fundamental approach. They consider the particles entrained into the jet and relate the production of attrited fines to the attrition rates obtained from single particle impact tests (cf. Sec. 4.3). According to their model, it should be possible to predict jet attrition rates in fluidized beds on the basis of single particle impact tests combined with a detailed description of the jet hydrodynamics. 

Davis, A., R. L. Olsen and D.R. Walker, 1991, Distribution of metals between water and entrained sediment in streams impacted by acid mine drainage, Clear Creek, Colorado, U.S.A. Applied Geochemistry 6, 333-348. 

After the throat section, the mixture decelerates, and further impacts occur causing the droplets to agglomerate. Once the particles have been captured by the liquid, the wetted PM and excess liquid droplets are separated from the gas stream by an entrainment section, which usually consists of a cyclonic separator or a mist eliminator. 

To discern the stability of the clusters in the fluidized bed, Hays et al. [26] added baffles to their 6 inch (0.15 meter) diameter fluidized bed. The baffles resembled a simple grating commonly used for floor decking, and were positioned at 1.6 and 2.5 feet (0.5 and 0.76 meters) above the distributor plate. The bed height was 2.5 feet (0.76 meters). As shown in Figure 11.10, the presence of baffles resulted in an increase in the entrainment flux at higher gas velocities. One explanation for this behavior is that the clusters formed in the bed impact the baffles at the high gas velocities and are broken up, which results in smaller clusters and higher entraimnent rates. 

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