Pressure vertical flow

A direct liquefaction technique, the SRC process involves mixing dried and finely pulverized coal with a hydrogen donor solvent, such as tetralin, to form a coal-solvent slurry. The slurry is pumped together with hydrogen into a pressurized, vertical flow reactor. The reactor temperature is about 825°F (440°C) and pressures range from 1,450 to 2,000 psi. A residence time in the reactor of about 30 minutes is required for the carbonaceous material to dissolve into solution. From the reactor, the product passes through a vapor/liquid separation system. The slurry solids remaining in the reactor are then removed and filtered. Various filtration techniques have been developed to remove solids from recoverable oil. 

In vertical flow, axial symmetry exists and flow patterns tend to be somewhat more stable. However, with slug flow in particular, oscillations in the flow can occur as a result of sudden changes in pressure as liquid slugs are discharged from the end of the pipe. 

A knowledge of hold-up is particularly important for vertical flow since the hydrostatic pressure gradient, which is frequently the major component of the total pressure gradient, is directly proportional to liquid hold-up. However, in slug flow, the situation is complicated by the fact that any liquid which is in the form of an annular film surrounding the gas slug does not contribute to the hydrostatic pressure 14. ... 

In summary, therefore, it is recommended that the frictional pressure drop for vertical flow be calculated as follows ... 

Considerably more work has been carried out on horizontal as opposed to vertical pneumatic conveying. A useful review of relevant work and of correlations for the calculation of pressure drops has been given by Klinzing et a/.(68). Some consideration will now be given to horizontal conveying, with particular reference to dilute phase flow, and this is followed by a brief analysis of vertical flow. 

Govier, G. W Radford. B. A. and Dunn, J. S. C Canatl. J. Chem. Eng. 55 (1957) 58, The upwards vertical flow of air-water mixtures I. Effect Of air and water rates on flow pattern, hold-up and pressure drop. 

New test-design procedures for the accurate prediction of pipeline pressure drop, including the effects due to horizontal/ vertical flow and bends. 

Fig. 2. Typical pressure drops, flow patterns, and flow regimes in vertical cocurrent air-water flow [after Govier et al. (G6)l.

A similar equation to that of Eq. (43) was proposed by Bankoff (B6) on the basis of a bubble-flow model for vertical flow. His derivations are discussed in the following section (Section V, B). Finally, it should be mentioned that the momentum exchange model of Levy (L4), and the slip-ratio model of Lottes and Flinn (L7) are more readily applied for the determination of void fractions than for pressure drops. In general, these methods seem to give rather poorer accuracy than those already discussed. 

For mass transfer in two-component cocurrent two-phase flow, very little work seems to have been carried on in systems analogous to those for which pressure-drops have been measured, that is, in tubes, pipes, or rectangular channels. Only two publications dealing with vertical flow (V2, V3), and two concerned with horizontal flow (A5, S6), have appeared. 

Fig. 5 SEM images of ordered GaN nanopillars grown at a substrate temperature of 950 °C. a Reactor pressure of 8 bar with N2 as carrier gas (100 seem) using SMP 1 in a horizontal flow reactor and b at a reactor pressure of 4 bar with N2 as carrier gas (100 seem) in a vertical flow reactor. Inset-, side view of nanopillars...

The theoretical foundation for this kind of analysis was, as mentioned, originally laid by Taylor and Aris with their dispersion theory in circular tubes. Recent contributions in this area have transferred their approach to micro-reaction technology. Gobby et al. [94] studied, in 1999, a reaction in a catalytic wall micro-reactor, applying the eigenvalue method for a vertically averaged one-dimensional solution under isothermal and non-isothermal conditions. Dispersion in etched microchannels has been examined [95], and a comparison of electro-osmotic flow to pressure-driven flow in micro-channels given by Locascio et al. in 2001 [96]. 

The most reliable methods for fully developed gas/liquid flows use mechanistic models to predict flow pattern, and use different pressure drop and void fraction estimation procedures for each flow pattern. Such methods are too lengthy to include here, and are well suited to incorporation into computer programs commercial codes for gas/liquid pipeline flows are available. Some key references for mechanistic methods for flow pattern transitions and flow regime-specific pressure drop and void fraction methods include Taitel and Dukler (AIChEJ., 22,47-55 [1976]), Barnea, et al. (Int. J. Multiphase Flow, 6, 217-225 [1980]), Barnea (Int. J. Multiphase Flow, 12, 733-744 [1986]), Taitel, Barnea, and Dukler (AIChE J., 26, 345-354 [1980]), Wallis (One-dimensional Two-phase Flow, McGraw-Hill, New York, 1969), and Dukler and Hubbard (Ind. Eng. Chem. Fun-dam., 14, 337-347 [1975]). For preliminary or approximate calculations, flow pattern maps and flow regime-independent empirical correlations, are simpler and faster to use. Such methods for horizontal and vertical flows are provided in the following. 

Vertical, upward flow, laminar flow reactors which have been used to study stabilized cool-flames and two-stage ignitions are a development of the atmospheric pressure, vertical, laminar flow reactors, pioneered at the Naval Research Laboratories in Washington [71]. These types of systems have been used by other research groups [72-74]. The flow tube that was... 

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