Pipeline flows

Consider first a dilute phase pneumatic transfer system operating at high velocity and relatively low mass flow density. As discussed in 6-3.1 this 

Nonconductive plastic pipe should not be used for transfer of ignitable powder or for any powder transfer through electrically classified areas. Hazards comprise brush discharges, PBDs and external sparks due to induction. Charge accumulation is discussed in 5-3.2.1. 

To avoid ignition via these indirect sparking mechanisms, the resistance to ground of conductive objects that could be encountered by discharges on powder beds should be less than 1 k 2 and preferably less than 100 2, so that the maximum potential attained is less than 1 kV. 

After cleaning dust and deposits from the connections, one end of the strap is bolted to the cage/venturi assembly and the other to the tubesheet. The resistance between the cage and the tubesheet should be 10 or less. 

Plastic venturis should be avoided wherever there is the potential for isolation of the bag cage or other conductive component. Plastic venturi hazards are noted in [33] a recent dust explosion originating in a bag house might have been due to their use. Criteria for selection of antistatic and conductive filter cloths are given in 6-5.2.1. 

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Other Flow Straightening Deviees Other devices designed to produce uniform velocity or reduce swirl, sometimes with reduced pressure drop, are available. These include both commercial devices of proprietaiy design and devices discussed in the hterature. For pipeline flows, see the references under flow inverters and static mixing elements previously discussed in the Tncompressible Flow in Pipes and Channels subsection. For large area changes, as at the... 

Pipeline Flow (Quenching) For the case of pipeline quenching, the flows are cociirrent. How closely the gas temperature approaches the liquid depends on where Ng varies with l/(droplet diameter)". 

Since the predicted droplet diameter at high velocity pipeline flow varies with (LVelocity) ", as shown by Eq. (14-201), the volumetric performance is strongly dependent on velocity ... 

Pipeline Contactors The power dissipation per unit mass for pipeline flow is similar to that for two-fluid nozzles. 

The ] atio of the I rns velocity fluctuation to the avei age velocity in the irnpelle] zone is about 50 pei cent with many open irnpellei s. If the ] rns velocity fluctuation is divided bv the avei age velocity iji the I est of the vessel, howevei the I atio is on the oi dei of 5 pei cent. This is also the level of I rns velocity fluctuation to the mean velocity in pipeline flow, Thei e ai e phenomena in rnici o-scale mixing that can occiu in mixing tanks that do not occiu in pipeline I eactoi s, Whethei this is good or bad depends upon the process requirements,... 

Wilson, K. C. Hydrotransporl 4 (BHRA Fluid Engineering, Banff. Alberta, Canada) (May 1976) ALL A unified physically-based analysis of solid-liquid pipeline flow. 

Laminar Pipeline Flows. The axial dispersion model can be used for laminar flow reactors if the reactor is so long that At/R > 0.125. With this high value for the initial radial position of a molecule becomes unimportant. 

Correlations for E are not widely available. The more accurate model given in Section 9.1 is preferred for nonisothermal reactions in packed-beds. However, as discussed previously, this model degenerates to piston flow for an adiabatic reaction. The nonisothermal axial dispersion model is a conservative design methodology available for adiabatic reactions in packed beds and for nonisothermal reactions in turbulent pipeline flows. The fact that E >D provides some basis for estimating E. Recognize that the axial dispersion model is a correction to what would otherwise be treated as piston flow. Thus, even setting E=D should improve the accuracy of the predictions. 

Example 9.6 Compare the nonisothermal axial dispersion model with piston flow for a first-order reaction in turbulent pipeline flow with Re= 10,000. Pick the reaction parameters so that the reactor is at or near a region of thermal runaway. 

N. E. Almond. Pipeline flow improvers. In Proceedings Volume, pages 307-311. API Pipeline Conf (Dallas, TX, 4/17-4/18), 1989. 

Baker (B3, B4) has discussed design considerations and operating experiences with two-phase pipeline flows. Flanigan (FI) has outlined a procedure for obtaining test data from operating multiphase-flow pipelines. 

Figure 6.4. Shear and pipeline flow data of a thixotropic Pembina crude oil at 44.5°F. (a) Rheograms relating shear stress and rate of shear at several constant durations of shear (Ritter and Govier, Can. J. Chem. Eng. 48, 50S (1970)]. (b) Decay of pressure gradient of the fluid flowing from a condition of rest at 15,000 barrels/day in a 12 in. line [Ritter and Batycky, SPE Journal 7, 369 (1967)].

Concurrent flow of liquid and gas can be simulated by the homogeneous model of Section 6.8.1 and Eqs. 6.109 or 6.112, but several adequate correlations of separated flows in terms of Lockhart-Martinelli parameters of pipeline flow type are available. A number of them is cited by Shah (Gas-Liquid-Solid Reactor Design, McGraw-Hill, New York, 1979, p. 184). The correlation of Sato (1973) is shown on Figure 6.9 and is represented by either... 

The key property is the droplet diameter, of which many studies have been made under a variety of conditions. In agitated vessels, experience shows that the minimum droplet diameters are in the range of 500-5000 pm. In turbulent pipeline flow, Middleman (1974) found that very few droplets were smaller than 500 pm. Accordingly, for separator design a conservative value is 150 pm, which also has been taken as a standard in the API Manual on Disposal of Refinery Wastes (1969). With this diameter,... 

From our current knowledge, it is suggested that intrinsic kinetics typically plays a minor role in hydrate formation in real systems (turbulent pipeline flow), and instead mass and heat transfer may play a larger role in determining the rate of hydrate formation. 

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. 

Metal ore bodies may contain several different minerals that are separated into individual concentrates. These may be slurry-transported in the same pipeline by pumping them in separate batches, each separated by a slug of water to prevent contamination [607]. Such batching also allows pipeline flow to be maintained when the mine or separation site temporarily runs out of ore. 

Although PEPT is likely to remain the more appropriate choice for most industrially oriented positron-imaging work, PET can be useful in some circumstances, particularly for following slow processes such as diffusion and some classes of diffusion/reaction problems, as well as multi-phase pipeline flow. 

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