Cross-current contacting

Average SRS simulant was employed for extraction (0 A = 1 3), 50 mM HNO3 for scrubbing (0 A = 5 1), and 1 mM HNO3 for stripping (0 A = 5 1). All contacts were made at 25 °C. Fresh aqueous phase was used for each contact (cross-current contacting). Data from reference [49],... 

The decision whether to adopt counter-, co-, or cross-current contacting (see Fig. 9) is dictated by factors such as equilibrium limitations, flooding,... 

Fig. 29. Co-, counter-, and cross-current contacting for moving-bed gas-solid reactors.

In designing a unit, each side of the exchanger is independently tailored to the duty required, and the exchanger effectiveness (discussed in Section 9.9.4) can range from 2 5 per cent to values in excess of 98 per cent without fundamental design or construction problems arising. Countercurrent, co-current and cross flow contacting can be employed individually or in combination. 

Figure 6 shows a simplified C02 capture process with two major process units absorber and stripper Zhang et al., 2009. A lean amine solvent (low C02 loading) is fed into the top of the absorber and is in counter-current contact with the gas containing C02. The C02 is chemically absorbed by the amine solvent and the treated gas exits the top of the absorber. The rich (high C02 loading) amine leaves the bottom of the absorber and is preheated by a cross heat exchanger before... 

In order to operate the reaction continuously for a long time, both solid and gas must be continuously introduced to the reactor. There are three types of continuous reactor counter-current (c, d), co-current (e, f), and cross-current (g), depending on the flow direction of solid and gas, as shown in Figure 14.14. A fluidized bed is the most sophisticated method of solid gas reaction, in which the temperature is well controlled, and the solid can effectively contact with the gas. However, caution must be paid to maintain continuous fluidization and not to block the flow system. Continuous flow (h) and batch (i) type reactors are illustrated in Figure 14.14. 

The IRVAD process by Black Veatch Pritchard Inc. and Alcoa Industrial Chemicals is claimed to be a low-cost process for low-sulflir gasoline . The process uses an alumina-based selective adsorbent to counter-currently contact liquid hydrocarbon in a multistage adsorber. The adsorbent is regenerated in a continuous cross-flow reactivator using heated reactivation gas. The process operates at lower pressure, and does not consume hydrogen or saturate olefins. The adsorption mechanism is based on the polarity of sulfur compounds. It is not very selective for gasoline sulfur, and no information is available on diesel sulfur. 

It is important to note that Treyhal (1963, p. 290) has obtained such results for what are called cross current (or cocurrent) multiple contacts. However, the results and analysis are equally valid for the configuration of phase contact selected here. 

Fig. 10.7 Types of fluidized bed reactors [43], Reprinted with permission from the authors. The primary fluidized bed reactor types 1 bubbling fluidized bed, 2 turbulent fluidized bed, 3 circulating fluidized bed, 4 riser, 5 drowner, 6 cross-current fluid bed, 7 counter-current fluid, 8 spouted fluidized bed, 9 floating fluidized bed, 10 twin fluidized bed. The key issues leading to re-design of the conventional bubbling fluid bed A higher gas velocity, B counter-current contacting is beneficial, C incompatible differences in desired environment, D dusty environment, E large paiticles/low gas load...

The ac resistance increase due to skin effect given above should be considered as a minimum. When wires are placed next to one another and placed in layers within a transformer, the near field magnetic effects between wires further crowd the current density into even smaller areas within the wire s cross-section. For instance, when wires are wound next to one another, the current is pushed away from the points of contact along the surfaces of the wires to areas orthogonal to the winding plane. When layers are placed on top of one another the inner layers show much greater degradation in apparent resistance than do the outermost layers. 

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