Packed columns heat effects

D. PCBS. Vos et al. in 1970 were able to identify PCDFs (tetra- and penta-CDFs) in two samples of European PCBs but not in a sample of Aroclor 1260 (k2). The toxic effects of the PCBs were found to parallel the levels of PCDFs present. Bowes et al. examined a series of Aroclors as well as the samples of Aroclor 12 0, Phenoclor DP-6 and Clophen A-60, that had previously been analyzed ( 2). They used packed column GC and mass spectrometry, and found that the most abundant PCDFs had the same retention time as 2,3,7 8-tetra- and 2,3 , 7 8-penta-CDF their results are collected in Table IV 0 3). Using high-resolution GC and MS, Rappe and Buser (unpublished) have analyzed a number of commercial PCBs, and the results are also collected in Table IV. In general the PCBs contained quite a complex mixture of PCDFs, up to UQ different isomers. The highest level of PCDFs was found in a Japanese PCB used for two years in a heat exchange system, which was found to have about 10 yg/g. The dominating isomer was identified as P j tetra-CDF at a level of 1.25 yg/g (UU ]. 

Another feature of the breakthrough method is that the uniform geometry of the packed column permits fairly straightforward analysis of the thermal waves produced due to heats of adsorption, and of their effect on the shape of the sorption fronts. The most obvious advantage of this method, however, is the fact that the results of the breakthrough experiments can be applied rather directly to the design of commercial adsorbers, with relatively little analysis of the data. 

Example 4.6 Entropy production in a packed duct flow Fluid flow and the wall-to-fluid heat transfer in a packed duct are of interest in fixed bed chemical reactors, packed separation columns, heat exchangers, and some heat storage systems. In this analysis, we take into account the wall effect on the velocity profile in the calculation of entropy production in a packed duct with the top wall heated and the bottom wall cooled (Figure 4.7). We assume... 

Assuming dilute solutions, Table 6.21 lists the equations for sizing absorbers and strippers in terms of a key component and Table 6.22 outlines the calculation procedure. In numbering the relationships in Table 6.21, A, S, P, and T means absorption, stripping, packed columns and tray columns, respectively. Processing dilute solutions implies that heat effects will be small, and therefore, the separation is essentially isothermal. If the column is both isothermal and isobaric, the equilibrium value will be constant. Also, dilute solution means that the gas and liquid flow rates will essentially be constant. In absorption, the gas flow rate is fixed and the liquid flow rate must be estimated, whereas in stripping the liquid flow rate is fixed and the gas flow rate must be estimated. 

At the same time, however, the short residence time does not provide a great deal of heat bleaching or effective deodorization. To overcome this, a holding vessel is provided as part of the system, before or after the packed column. 

Heat transfer of packed bed has been the subject of numerous studies. For cylindrical packed columns, a solution for determining temperature distributions was given using Bessel functions. Here, it is important to find out exact effective thermal conductivity of bed because of flowing gas and relatively high temperatures. Radial temperature distributions are more important than that of axial direction because the latter can be measured and controlled during the operation. 

There are three types of deodorization operations. The batch process is the least common, due to its low efficiency and inconsistent product quality. Semi-continuous and continuous deodorizers have improved processing efficiency. There are several configurations of the continuous deodorizer, including singleshell cylindrical vessel type, vertically stacked tray type, and the thin-film packed column type. This last provides excellent fatty acid stripping with minimum use of steam, but it achieves neither desired heat bleaching nor effective deodorization due to the relatively short retention time. A retention vessel has to be used after the column distillation (De Greyt and Kellens 2000). 

Packed bed Packed columns absorption physical distillation heat effects in... 

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