Classifiers countercurrent

Industrial-scale adsorption processes can be classified as batch or continuous (53,54). In a batch process, the adsorbent bed is saturated and regenerated in a cychc operation. In a continuous process, a countercurrent staged contact between the adsorbent and the feed and desorbent is estabhshed by either a tme or a simulated recirculation of the adsorbent. 

Commercial Extractors. Extractors can be classified according to the methods appHed for interdispersing the phases and producing the countercurrent flow pattern. Eigure 11 summarizes the classification of the principal types of commercial extractors Table 3 summarizes the main characteristics. 

Horizontal belt filters are well suited to either fast or slowly draining soHds, especially where washing requirements are critical. Multistage countercurrent washing can be effectively carried out due to the sharp separation of filtrates available. Horizontal belt vacuum filters are classified according to the method employed to support the filter medium. 

In the United States boric acid is produced by United States Borax Chemical Corp. in a 103,000 2 3 ric ton per year plant by reacting cmshed kernite ore with sulfuric acid. Coarse gangue is removed in rake classifiers and fine gangue is removed in thickeners. Boric acid is crystallised from strong hquor, nearly saturated in sodium sulfate, in continuous evaporative crystallizers, and the crystals are washed in a multistage countercurrent wash circuit. 

According to the three-step model, proposed by the authors, a PBCS can be divided into three subsystems, namely a conversion system, combustion system, and boiler system. It is in the conversion system that the thermochemical conversion of the solid fuel takes place. The conversion system can be designed according to several conversion concepts. The conversion concept can be classified with respect to fuel-bed mode (batch and continuous), fuel-bed configuration (countercurrent, cocurrent and crosscurrent), fuel-bed composition (homogeneous and heterogeneous), and fuel-bed movement (fixed, moving and mixed). 

Adsorption Separation and Purification Processes. Adsorption processes can be classified according to the flow system (cyclic batch or continuous countercurrent) and the method by which the adsorbent is regenerated. The Iwo basic flow schemes arc illustrated in Figure 3 The cyclic batch scheme is simpler but less efficient. It is generally used where selectivity is relatively high. Countercurrent or simulated countercurrent schemes arc more expensive in initial cost and arc generally used only for difficult separations in which selectivity is limited or mass-transfer resistance is high. 

Industrial-scale adsorption processes can be classified as batch or continuous. In a batch process, die adsorbent bed is saturated and regenerated in a cyclic, operation. In a continuous process, a countercurrent staged contact between lire adsorbent and die feed and desorbent is established by cidier a true or a simulated recirculation of die adsorbent. The efficiency of an adsorption process is significantly higher in a eoiuinuous mode of operation than in a cyclic batch mode. For difficult separations, batch operation may require 25 times more adsorbent inventory and twice die desorbent circulation rate than does a continuous operation. In addition, in a batch mode, the four functions of adsorption, purification, desorption, and displacement of the desorbent from the adsorbent are inflexibly linked, wtiereas a continuous mode allows mure degrees of freedom with respect to these functions, and thus a better overall operation. 

Other Synthesis Problems. One recent synthesis publication by Nishitani and Kunugita (1979) is difficult to classify under the above headings, it deals with selecting the optimal vapor/ liquid flow patterns to use for a multiple effect evaporator system. The two obvious patterns are cocurrent (the liquid and vapor proceed through the system together) and countercurrent. Other patterns are possible and often significantly improve the economics. 

Figure 1. Slurry reactors classified by the contacting pattern and mechanical devices (a) slurry (bubble) column (b) countercurrent column (c) co-current upflow (d) co-current downflow (e) stirred vessel (C) draft tube reactor (g) tray column (h) rotating disc or multi-agitated column reactor (i) three-phase spray column — liquid flow —> gas flow.

The majority of spray dryers in commercial use employ cocurrent flow of gas and solids. Countercurrent-flow dryers are used primarily for drying soaps and detergents. Their classifying ability is useful in these applications. Air flow is upward, carrying entrained fines from the top of the chamber. The coarse product settles and is removed... 

As a rule in these processes that can be classified as ion replacement or recovery operations, the conditions are selected to assure a highly convex sorption isotherm. With the development of such a sorption isotherm, the lull recovery of the ions of interest does not require sizable multiplication of the separation reached with one theoretical plate. In view of this, the application of countercurrent columns has been initiated to facilitate further the resolution of these relatively simple problems. 

Contactors in which countercurrent motion is used can be classified as follows (1) contactors with continuous motion of an ion-exchanger compact bed (2) contactors with a suspended or fluidized bed of ion-... 

Liquid-liquid partition chromatography systems have been used with or without stationary-phase support. Support-free LLPC has been classified as countercurrent chromatography (CCC). High-speed CCC techniques, based on planetary motion and coaxial orientation of the coiled column, have been developed that achieve both high partition efficiency and excellent retention of the stationary phase, thus circumventing the need for stationary-phase supports [6],... 

The Hildebrandt extractor consists of a U-shaped screw conveyer with a separated helix in each of the downward, horizontal, and upward sections. Solids are fed to one leg and fresh solvent is fed to the other to give countercurrent flow. In a Dorr classifier, soUd is introduced near the bottom of a sloping tank and is gradually moved up by means of a rake. The solvent enters at the top and flows in the opposite direction of the sohd and passes under a baffle before finally being discharged over a weir. A number of these units can be connected in series to give countercurrent flow. 

The operational modes of the three-phase fluidized beds can be classified by the directions of the gas and liquid flows cocurrenf upward, cocurrent downward, countercurrent, or crosscurrent as shown in Fig. 

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