Pressure drop, pipelines

Example 6.1. Light hydrocarbons are often stored in spheres and are transported by pipeline at moderate to high pressures in pipelines to chemical plants. To minimize pressure drop, pipeline diameter may be higher than that at the plant. Smaller pipe diameters are preferred in plants to minimize the cost of instrumentation and process control equipment such as valves and flow meters. Calculate the pressure drop, in mbar, resulting from a reduction of 6" Sch40 pipe to 4" Sch40 pipe transporting 10000 kg of n-butane at 60 °F and 7 atm. 

Hydrate formation is possible only at temperatures less than 35°C when the pressure is less than 100 bar. Hydrates are a nuisance they are capable of plugging (partially or totally) equipment in transport systems such as pipelines, filters, and valves they can accumulate in heat exchangers and reduce heat transfer as well as increase pressure drop. Finally, if deposited in rotating machinery, they can lead to rotor imbalance generating vibration and causing failure of the machine. 

The measurement of a crude oil s viscosity at different temperatures is particularly important for the calculation of pressure drop in pipelines and refinery piping systems, as well as for the specification of pumps and exchangers. 

From the above plot, it can be seen that the recovery factor for gas reservoirs depends upon how low an abandonment pressure can be achieved. To produce at a specified delivery pressure, the reservoir pressure has to overcome a series of pressure drops the drawdown pressure (refer to Figure 9.2), and the pressure drops in the tubing, processing facility and export pipeline (refer to Figure 9.12). To improve recovery of gas, compression facilities are often provided on surface to boost the pressure to overcome the pressure drops in the export line and meet the delivery pressure specified. 

Acetylene from calcium carbide can be advantageous in that calcium carbide may be shipped to the point of acetylene usage and acetylene generated on the spot. This avoids the necessity for low pressure, low pressure-drop gaseous acetylene pipelines, or high pressure cylinders for shipping acetylene. 

Section 10 of this Handbook describes the use of orifice meters for flow measurement. In addition, orifices are commonly found within pipelines as flow-restric ting devices, in perforated pipe distributing and return manifolds, and in perforated plates. Incompressible flow through an orifice in a pipehne as shown in Fig. 6-18, is commonly described by the following equation for flow rate Q in terms of pressure drop across the orifice Ap, the orifice area A, the pipe cross-sectional area A, and the density p. 

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... 

Frictional Pressure Drop Usually this does not have a significant effect on the reaclor size, except perhaps when the flow is two-phase. Some approximate relations fbe cited that are adequate for pressure-drop calculations of homogeneous flow reactions in pipelines. The pressure drop is given by... 

The expanders also remove energy from the gas, using that energy to drive a centrifugal compressor for pipeline recompression. As gas expands through the expander s inlet nozzle, pressure drops from 90 bar (1,300 psig) to 55 bar (800 psig). Temperature drops as well, below the dewpoint, and the liquids formed can be separated from the main gas stream. 

The gas system did not inelude any storage other than pipeline paek and one relatively small high-pressure pipe-type holder. Therefore, pressures and flows in all areas of the system varied widely on a daily and seasonal basis. Several years of operating data were reviewed and analyzed to seleet a loeation that met the flow and pressure drop requirements for installation of an expander. Site seleetion also gave eonsideration to the requirements for eonneetion to the gas system, eonneetion to the eleetrie system, and sound attenuation measures neeessary to eliminate any impaet on the surrounding area. 

The pressure drop in the pipeline should be measured, and if it gets too low, a trip valve should be closed automatically. A very reliable, duplicated system may be necessary [16]. 

Figure 2-42. Estimating pressure drop in uphiil sections of pipeline for two-phase flow. By permission, O. Flanigan, Oil and Gas Journal, Mar. 10, 1958, p. 132.

Figure 2-50. Representative plot of pressure drop for slurry flow. By permission, Turian, R. M. and Yuan, T. F., Flow of Slurries in Pipelines, AI.Ch.E. Journal, vol. 23, 1977, p. 232-243.

Pressure drop is directly proportional to viscosity. The effect of heat loss from pipelines and consequent increase in viscosity should also be considered. 

Pressure drop under streamline flow conditions is directly proportional to the quantity of oil flowing. The effect of reduced flow rate after take-off points, as compared with full flow rate throughout the full length of the pipeline when there is no take-off, should be taken into account to ensure that variation in pressure is within the specified pump output. Special consideration is necessary with gravity and ring main systems serving several take-off points. 

When it is necessary to estimate the pressure drop in a pipeline where turbulent flow conditions exist, the following formula will give an approximation ... 

Ninety-eight per cent sulphuric acid is pumped at 4.5 tonne/h (1.25 kg/s) through a 25 mm diameter pipe, 30 m long, to a reservoir 12 m higher than the feed point. Calculate the pressure drop in the pipeline. 

As in the case of Newtonian fluids, one of the most important practical problems involving non-Newtonian fluids is the calculation of the pressure drop for flow in pipelines. The flow is much more likely to be streamline, or laminar, because non-Newtonian fluids usually have very much higher apparent viscosities than most simple Newtonian fluids. Furthermore, the difference in behaviour is much greater for laminar flow where viscosity plays such an important role than for turbulent flow. Attention will initially be focused on laminar-flow, with particular reference to the flow of power-law and Bingham-plastic fluids. 

To reduce the pressure drop, and hence the upstream pressure in a pipeline, for a given flowrate of shear-thinning liquid. 

To increase the flowrate of liquid for any given pipeline pressure drop. 

Because concentrated flocculated suspensions generally have high apparent viscosities at the shear rates existing in pipelines, they are frequently transported under laminar flow conditions. Pressure drops are then readily calculated from their rheology, as described in Chapter 3. When the flow is turbulent, the pressure drop is difficult to predict accurately and will generally be somewhat less than that calculated assuming Newtonian behaviour. As the Reynolds number becomes greater, the effects of non-Newtonian behaviour become... 

In a series of experiments on the flow of flocculated kaolin suspensions in laboratory and industrial scale pipelines(26-27-2Sl, measurements of pressure drop were made as a function of flowrate. Results were obtained using a laboratory capillary-tube viscometer, and pipelines of 42 mm and 205 mm diameter arranged in a recirculating loop. The rheology of all of the suspensions was described by the power-law model with a power law index less than unity, that is they were all shear-thinning. The behaviour in the laminar region can be described by the equation ... 

When an industrial pipeline is to be designed, there will be no a priori way of knowing what the in-line concentration of solids or the slip velocity will be. In general, the rate at which solids are to be transported will be specified and it will be necessary to predict the pressure gradient as a function of the properties of the solid particles, the pipe dimensions and the flow velocity. The main considerations will be to select a pipeline diameter, such that the liquid velocity and concentrations of solids in the discharged mixture will give acceptable pressure drops and power requirements and will not lead to conditions where the pipeline is likely to block. 

In a recent study of the transport of coarse solids in a horizontal pipeline of 38 mrrt diameter, pressure drop, as a function not only of mixture velocity (determined by an electromagnetic flowmeter) but also of in-line concentration of solids and liquid velocity. The solids concentration was determined using a y-ray absorption technique, which depends on the difference in the attenuation of y-rays by solid and liquid. The liquid velocity was determined by a sail injection method,1"1 in which a pulse of salt solution was injected into the flowing mixture, and the time taken for the pulse to travel between two electrode pairs a fixed distance apart was measured, It was then possible, using equation 5.17, to calculate the relative velocity of the liquid to the solids. This relative velocity was found to increase with particle size and to be of the same order as the terminal falling velocity of the particles in the liquid. 

The additional pressure drop due to the presence of solids in the pipeline (—APx) could be expressed in terms of the solid velocity, the terminal falling velocity of the particles and the feed rate of solids F (kg/s). The experimental results for a 25 mm pipe are correlated to within 10 per cent by ... 

Equations 5.37, 5.38 and 5.39 for solid velocity and pressure drop ate applicable only in the absence of electrostatic charging of the particles. Many materials, including sand, become charged during transport and cause the deposition of a charged layer on the surface of the pipe. The charge remains on the earthed pipeline for long periods but can... 

The conveying of fine particles in vertical pipes of diameters 25 mm, 50 mm, and 75 mm has been studied by BoOTHROYD(75 . He measured the pressure gradient in the pipeline, and found that the frictional pressure drop was less than that for air alone in the 25 mm pipe, but was greater in the larger pipes. This effect was attributed to the fact that the extent to which the fluid turbulence was affected by the presence of the particles was markedly influenced by pipe size. 

Sand of particle size 1.25 mm and density 2600 kg/m3 is to be transported in air at the rate of I kg/s through it horizontal pipe 200 m long. Estimate the pipe diameter, the pressure drop in the pipeline and the air flow required. 

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