Entrainment losses

For commercial appHcation, catalyst activity is only one of the factors to be considered. Equally important is catalyst life, but Htde has been pubHshed on this aspect. Partly because of entrainment losses and partly through loss of acid as volatile triethyl phosphate, the catalyst loses activity unless compensating steps are taken. This decline in activity can be counteracted by the periodic or continuous addition of phosphoric acid to the catalyst during use, a fact that seems to have been disclosed as early as 1940 (94). A catalyst subjected periodically to acid addition could remain in service indefinitely, according to a report by Shell (91). A later Shell patent (85) states that complete reimpregnation with acid is required every 200 mn-days. 

Entrainment losses by flashing are frequently encountered in an evaporator. If the feed is above the boiling point and is introduced above or only a short distance below the liquid level, entrainment losses may be excessive. This can occur in a snort-tube-type evaporator if the feed is introduced at only one point below the lower tube... 

As a general nile, the direct-heat units are the simplest and most economical in construction and are emploved when direct contact between the solids and flue gases or air can be tolerated. Because the total heat load must be introduced or removed in the gas stream, large gas volumes and high gas velocities are usually required. The latter will be rarely less than 0.5 m/s in an economical design. Therefore, employment of direct rotating equipment with solids containing extremely fine particles is likely to result in excessive entrainment losses in the exit-gas stream. 

The tube proportions in the basket evaporator are about the same as in the standard vertieal. One important feature of the basket-type evaporator is the ease with which a deflector may be added in order to reduce entrainment from spouting. The boiling in the vertical-tube evaporator is quite violent, and this tends to cause entrainment losses. This condition is accentuated if the liquor level in the evaporator is low. A baffle such as shown in Figure 9 largely prevents these losses and is much more easily added to the basket type than to the standard type. Other differences between the standard and the basket type are largely details of construction. 

Elydranlic (liquid seal) flame arresters require attention on a regular basis similar to that for dry-type flame arresters. It is critical to ensnre that the liquid level is at the required height, and level instmmentation with alarms is recommended. Automatic addition of makeup liquid (to replace evaporation and entrainment losses) is desirable. Temperatnre instrumentation is also recommended to monitor the occurrence of sustained burning (a stabilized flame). See Section 5.3.18 for more details. 

Solubility data on the LIX and Kelex extractants indicate that these materials are poorly soluble in aqueous media. Accordingly, in plant operations at about pH 1.5, reported losses are approximately <15 ppm, which includes both soluble and entrainment losses as determined by inventory (detailed later in Table 7.6). The solubility of LIX 63, LIX 64, and LIX 64N in water at pH 4.8 has been reported at 5.8, 4.3, and 6.2 ppm, respectively [20]. 

Labor and maintenance costs can usually be kept to the order of a few cents per pound of metal produced. However, where a circuit has been improperly designed and several manual operations are required, then labor and maintenance costs can be high. Excessive solvent entrainment losses, mentioned earlier, are added to labor costs. Any crud that forms and has to be removed can result in additional costs from labor requirements. For example, if incorrectly designed contacting equipment is chosen, which results in periodic shutdowns necessary for cleaning because of formation of cruds and precipitates, a major maintenance problem could arise. 

Alternatively, the dispersed phase is chosen because, by definition, it will not contain droplets of the continuous phase. In this way the dispersed phase, after settling, will not entrain the continuous phase and entrainment losses from the settler will be reduced. 

In large-scale operation, the volumetrie flow of the phase to be dispersed is so large that it becomes neeessary to disperse that phase into the mixed phases. Otherwise blobs of the dispersed phase will act locally as the continuous phase, and the intended eontinuous phase will be dispersed in the blobs before the shear forees in the mixer break them up. This can lead to excessive entrainment losses. 

Solvent extraction Podbielniak extraction Membrane solvent extraction Coupled transport Minimum emulsification and associated entrainment loss Enhanced selectivity and concentration... 

Approximately 6 kg of Am-Cm were recovered from the stored Am-Cm-A1(N03)3 waste. The process yielded an overall recovery of 75%. Of the losses, 2.5% represented soluble losses and the remainder was entrained losses. Of this 20% lost to the waste supernate stream, about 14% (yl.l kg) is stored for future recovery the remaining 7% was actually lost to the waste tanks. The major contaminants of the purified Am-Cm product are Fe, Al, and Na. 

Improvement of the deodorizer design by the installation of baffles and demisters in the vapor chimneys has significantly reduced entrainment losses to 0.1-0.2% in chemical refining. For steam refining, an additional loss directly proportional to the FFA content has to be taken into account. For most oils (soybean oil, pahn oil, etc.), NOL is exclusively due to mechanical carry-over. However, in lauric oils, part of the NOL is a consequence of effective evaporation of volatile short-chain mono- and diacylglycerols (30). (Table 13). This distillation loss of NOL is inherently due to the deodorization conditions, but is not affected by the deodorizer design. 

However, high gas velocity, may lead to problems in bed operation. It increases the entrainment loss of fluidizing catalyst particles. It also may give rise to excessive reaction in the particle-disengaging space, which sometimes will lead to reactor instability or to decreased selectivity (as discussed in later sections). Attrition or erosion of the reactor is more likely at higher gas velocity. Thus, there is an optimum gas velocity for fluid beds, which for most catalysts is in the range of 20-80 cm/sec, usually 40-60 cm/sec. 

Our aim is to estimate the duration of the processes and the amount of products. A simplified model was applied based on the following assumptions maximal separation, negligible hold-up on the trays and in the decanter, constant molar overflow, the flow rates do not vary with the time, one-phase liquid streams leave the decanter, negligible duration of pumping between the operation steps (BR), no entrainer loss (in the case of the ternary mixture). The total and component material balances for one column and the decanter are analytically solved. For the DCS we assume that both products reach the prescribed purity at the same time, that is, the duration is nrinimal. The process time (x) for both configurations and for the DCS the optimal division (v ) of total vapour flow rate (V) between the two reboilers and that of the charge (Ub /Uch) are shown. 

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