Dense-phase

An essential component of cell membranes are the lipids, lecithins, or phosphatidylcholines (PC). The typical ir-a behavior shown in Fig. XV-6 is similar to that for the simple fatty-acid monolayers (see Fig. IV-16) and has been modeled theoretically [36]. Branched hydrocarbons tails tend to expand the mono-layer [38], but generally the phase behavior is described by a fluid-gel transition at the plateau [39] and a semicrystalline phase at low a. As illustrated in Fig. XV-7, the areas of the dense phase may initially be highly branched, but they anneal to a circular shape on recompression [40]. The theoretical evaluation of these shape transitions is discussed in Section IV-4F. 

The hydrocarbon feed rate to the reactor also affects the burning kinetics in the regenerator. Increasing the reactor feed rate increases the coke production rate, which in turn requires that the air rate to the regenerator increase. Because the regenerator bed level is generally held constant, the air residence time in the dense phase decreases. This decrease increases the O2 content in the dilute phase and increases afterbum (Fig. 5). 

Fig. 5. Effect of gas residence time on afterburning. The temperature change AT is the difference in temperature between flue and dense phase (30).

Through the use of a combustion promoter, CO combustion occurs readily in the dense phase at temperatures well below 700°C, eg, one report was at 650°C in a commercial FCCU operation (34). 

FGG Gatalyst Goolers. Heat-removal systems have been used in commercial FCCUs since the early 1940s. The three basic designs are internal regenerator bed coils, external cods with ddute-phase upflow, and external cods with dense-phase downflow. 

Dense phase systems are at cost disadvantage when multiple feed points are required, or when incremental compressed air for conveying is not available from existing sources. In the latter instance, the entire investment cost of an air compressor and associated auxiUaries must be allocated to the cost of the conveying system. 

Proprietary designs for rotary valve feeders (star valves) capable of continuous feeding of certain pelleted and granular materials into low velocity, dense phase systems, having system pressures up to 200 kPa (2 bars) have been developed. 

For dense phase transport in vertical pipes of small diameter, see... 

Another deep-bed spiral-activated solids-transport device is shown by Fig. ll-60e. The flights cany a heat-transfer medium as well as the jacket. A unique feature of this device which is purported to increase heat-transfer capability in a given equipment space and cost is the dense-phase fluidization of the deep bed that promotes agitation and moisture removal on drying operations. 

An early study involving a gas proeessing plant design for an offshore platform in the North Sea was performed in the early 1970s. This study indieated that the turboexpander option eontained fewer vessels and equipment. The study results are listed in Table 3-6 note that the turboexpander also represented the option with the lowest operating eost. This plant proeessed natural gas from a eondensate reservoir in a dense phase state. 

There are two regions in the regenerator the dense phase and the dilute phase. At the velocities common in the regenerator, 2-4 ft/sec, the bulk of catalyst particles are located in the dense bed immediately above the air distributor. The dilute phase is the region above... 

As the flue gas leaves the dense phase of the regenerator, it entrains eatalyst partieles. The amount of entrainment largely depends on the... 

An AC corona discharge in the throat leads to a cloud of charged droplets whose large momentum allows very long travel distances. Multiple devices for eliminating static discharges in powder silos have been tested [41] but the tests did not address typical flow rates for large capacity, dense phase pneumatic transfer operations. 

Figure 28. Operating stages of a dense-phase fluid bed.

Remediation of groundwater impacted by dense phase chlorinated solvents is more difficult than spills of chemicals such as gasoline or diesel fuel. Gasoline and diesel fuel are less dense than water and tend to float near the surface of the watertable. 

Model IV Regenerator and reactor at approximately equal elevation and pressure. Catalyst circulates through U-bends, controlled by pressure balance and variable dense-phase riser. 

As shown in Fig. 14.2, the material conveying region is bounded by the air-only curve and the stationary-plug curve, where the air merely percolates through or flows above a packed bed of stationary particles. Dense-phase conveying occurs when v, the velocity of air, is below the so-called saltation velocity. 

The dense-phase regime can be further subdivided into three distinct regions,which are shown in Fig. 14.3. In continuous dense-phase flow the material moves by saltation over a stable creeping bed, in discontinuous dense-phase flow particles move as groups, and in the solid dense-phase the solids are extruded through the pipe as a continuous slag. 

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