Contactors equipment

A contactor equipped with an impeller is generally considered to be the most flexible and most generally effective gas disperser known. A porous sparger has no advantage except at very low power inputs. 

When the experiments were set up again in 1990 it became necessary to reconstruct the control system for the beam tubes as well. To ensure reliable functioning, contactor equipment was used for the control section and a programmable controller of proven design for the signalling section. 

The effect of increasing column diameter is to increase the tendency for circulation, and hence to increase the axial mixing (62,63). However, extremely few measurements of axial mixing at the industrial scale are available, so large-scale contactor design must still rely quite heavily on empirical experience with the particular type of equipment. 

However, in a countercurrent column contactor as sketched in Figure 8, the holdup of the dispersed phase is considerably less than this, because the dispersed drops travel quite fast through the continuous phase and therefore have a relatively short residence time in the equipment. The holdup is related to the superficial velocities U of each phase, defined as the flow rate per unit cross section of the contactor, and to a sHp velocity U (71,72) ... 

As the throughput in a contactor represented by the superficial velocities and is increased, the holdup / increases in a nonlinear fashion. A flooding point is reached at which the countercurrent flow of the two Hquid phases cannot be maintained. The flow rates at which flooding occurs depend on system properties, in particular density difference and interfacial tension, and on the equipment design and the amount of agitation suppHed (40,65). 

The earliest large-scale continuous industrial extraction equipment consisted of mixer—settlers and open-spray columns. The vertical stacking of a series of mixer—settlers was a feature of a patented column in 1935 (96) in which countercurrent flow occurred because of density difference between the phases, avoiding the necessity for interstage pumping. This was a precursor of the agitated column contactors which have been developed and commercialized since the late 1940s. There are several texts (1,2,6,97—98) and reviews (99—100) available that describe the various types of extractors. 

Shell process. Universal Oil Pro-ducts sulfolane sulfolane selectivity and capacity insensitive to water content caused by steam-stripping during solvent recov-ery heavy paraffinic countersolvent use 120 rotating-disk contactor, up to 4 m in diameter the high selectivity and capacity of sulfolane leads to low solvent-feed ratios, and thus smaller equip-ment... 

Heat Sensitivity. The heat sensitivity or polymerization tendencies of the materials being distilled influence the economics of distillation. Many materials caimot be distilled at their atmospheric boiling points because of high thermal degradation, polymerization, or other unfavorable reaction effects that are functions of temperature. These systems are distilled under vacuum in order to lower operating temperatures. For such systems, the pressure drop per theoretical stage is frequently the controlling factor in contactor selection. An exceUent discussion of equipment requirements and characteristics of vacuum distillation may be found in Reference 90. 

The main objective for calculating the number of theoretical stages (or mass-transfer units) in the design of a hquid-liquid extraction process is to evaluate the compromise between the size of the equipment, or number of contactors required, and the ratio of extraction solvent to feed flow rates required to achieve the desired transfer of mass from one phase to the other. In any mass-transfer process there can be an infinite number of combinations of flow rates, number of stages, and degrees of solute transfer. The optimum is governed by economic considerations. 

Continuous Percolators Coarse sohds are also leached by percolation in moving-bed equipment, including single-deck and nmlti-deck rake classifiers, bucket-elevator contactors, and horizontal-belt conveyors. 

Table 23-14 gives data for common types of L/L contactors. Since the given range of k a is more than 100/1, this information is not of direct value for sizing of equipment. The efficiencies of various kinds of small liquid/liqiiid contactors are summarized in Fig. 23-38. Larger units may have efficiencies of less than half these values. 

FIG. 23"37 Equipment for liquid/liquid reactions, a) Batch stirred sulfonator. (h) Raining bucket (RTL S A, London), (c) Spray tower with Loth phases dispersed. (d) Two-section packed tower with light phase dispersed, (e) Sieve tray tower with light phase dispersed, (f ) Rotating disk contactor (RDC) (Escher B V, Holland). (g) Oldshue-Rushton extractor (Mixing Equipment Co. ). 

The rating of cuiTcnt-carrying equipment (switchgear assemblies, such as for the main bus system), devices (breakers, switches and contactors) and components (connecting links and wiring etc.) is defined by two parameters ... 

Ozonation systems are comprised of four main parts, including a gas-preparation unit, an electrical power unit, an ozone generator, and a contactor which includes an off-gas treatment stage. Ancillary equipment includes instruments and controls, safety equipment and equipment housing, and structural supports. The four major components of the ozonation process are illustrated in Figure 8. 

Provision of protection for the motor itself in the case of faults and for the equipment controlling it (e.g. the contactor). 

The equipment and connections are simple and the starter is robust. The basic equipment will comprise an isolator, high rupturing capacity fuses, a contactor, overload devices and control switches. 

As a general principle, in electrical resistance boilers, the higher the output, the larger and more complex they become, with an increasing number of circuits, fuses, contactors, and other electrical equipment, until a point is reached at which electrode boilers become more practical and cost-effective. (Although in the marketplace there are low voltage electrode boilers available that are designed to directly compete with small, low-cost electrical resistance boilers.)... 

Efficient contact is produced between the phases in agitated gas-liquid contactors and, therefore, this type of equipment can also be useful for those absorption and stripping operations for which conventional plate or packed towers may not be suited. It may also be useful where the operation involves the contact of three phases—say, gas, liquid, and suspended solids. The latter application could be represented by the low-pressure polymerization of ethylene with solid catalysts (F5). 

Gal-Or (G4) has recently reported bubble-size distribution data in air-water dispersions. The equipment used to evaluate the bubble-size distribution is a new type of multistage gas-liquid contactor without pressure drop in each stage, in which the gas is drawn in from the bottom of the vessel. Typical bubble-size—cumulative-volume data are given in Fig. 2.f The data show that for 99% of the bubbles, 0.1 < 1.4 mm. The surface mean radius a32... 

Solvent extraction carried out in conventional contactors like mixer-settlers and columns has certain limitations, including (a) controlling optimum dispersion and coalescence, (b) purifying both phases to ensure that stable emulsions are avoided (c) temperature control within a narrow band (d) high entrained solvent losses and related environmental and process economic effects and (e) large equipment dimensions and energy requirements when the density differential or selectivity is low. 

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