Pressure drop in pipelines

The pressure drop in a pipe, due to friction, is a function of the fluid flow-rate, fluid density and viscosity, pipe diameter, pipe surface roughness and the length of the pipe. It can be calculated using the following equation  

L = pipe length, m, d = pipe inside diameter, m, p = fluid density, kg/m3, u = fluid velocity, m/s. 

More complex methods are needed to determine the pressure drop of non-Newtonian fluids in pipelines. Suitable methods are given in Volume 2, Chapter 4, and in Chabbra and Richardson (1999) see also Darby (2001). 

Any obstruction to flow will generate turbulence and cause a pressure drop. So, pipe fittings, such as bends, elbows, reducing or enlargement sections, and tee junctions, will increase the pressure drop in a pipeline. 

There will also be a pressure drop due to the valves used to isolate equipment and control the fluid flow. The pressure drop due to these miscellaneous losses can be estimated using either of two methods  

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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. 

So far, only the frictional pressure drop in straight lengths of pipe of circular cross-section has been discussed. The pressure drop in pipelines containing valves and fittings can be calculated from equation 2.13 but with fittings represented by the length of plain pipe that causes the same pressure drop. 

TABLE 6.2. Typical Velocities and Pressure Drops in Pipelines Karman s equation... 

Examples of the use of models for the design of large-scale systems include the measurement of pressure drop and heat transfer in model heat exchangers, the mixing and rate of reaction in a bench-top batch reactor and the prediction of pressure drops in pipelines. 

Determine pressure drop in pipeline, inlet pipe flow rate, and pipe length. 

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. 

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.

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. 

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. 

To have a better appreciation of the utility of these representations let us first consider the laws that govern flow rates and pressure drops in a pipeline network. These are the counterparts to KirchofTs laws for electrical circuits, namely, (i) the algebraic sum of flows at each vertex must be zero (ii) the algebraic sum of pressure drops around any cyclic path must be zero. For a connected network with N vertices and P edges there will be (N — 1) independent equations corresponding to the first law (KirchofTs current... 

Now our experiment has been designed We will use plastic pipe with an inside diameter of 1.6 in. and length of 50 ft and pump water through it at a rate of 27.5 gpm. Then we measure the pressure drop through this pipe and use our final equation to scaleup this value to find the field pressure drop. If the measured pressure drop with this system in the lab is, say, 1.2 psi, then the pressure drop in the field pipeline, from Eq. (2-13), would be... 

You would like to determine the pressure drop in a slurry pipeline. To do this, you need to know the rheological properties of the slurry. To evaluate these properties, you test the slurry by pumping it through a 1 in. ID tube that is 10 ft long. You find that it takes a 5 psi pressure drop to produce a flow rate of 100 cm3/s in the tube and that a pressure drop of 10 psi results in a flow rate of 300cm3/s. What can you deduce about the rheological characteristics of the slurry from these data If it is assumed that the slurry can be adequately described by the power law model, what would be the values of the appropriate fluid properties (i.e., the flow index and consistency parameter) for the slurry ... 

A pipeline has been proposed to transport a coal slurry 1200 mi from Wyoming to Texas, at a rate of 50 million tons/yr, through a 36 in. diameter pipeline. The coal slurry has the properties of a Bingham plastic, with a yield stress of 150dyn/cm2, a limiting viscosity of 40 cP, and an SG of 1.5. You must conduct a lab experiment in which the measured pressure gradient can be used to determine the total pressure drop in the pipeline. 

You want to use a venturi meter to measure the flow rate of water, up to 1000 gpm, through an 8 in. sch 40 pipeline. To measure the pressure drop in the venturi, you have a DP cell with a maximum range of 15in.H20 pressure difference. What size venturi (i.e., throat diameter) should you specify ... 

Determine whether any operating limitations exist, such as pressure drop in columns where flooding occurs or limiting heads for pipelines for gravity flow. 

If the pressure drop in a pipeline is less than 40% of Pla then the Darcy-Weisbach incompressible flow calculation may be more accurate than the Weymouth or Panhandles A and B for a short pipe or low flow. In main pipelines, compressible flow calculations are generally used. 

For reviews and more information on the principles and practice of mineral-slurry pipelining see Refs. [90,615-618]. The relationships among suspension rheology, flow rate, and pressure drop in a pipeline are discussed in Section 6.7.1 and oil pipelining is discussed in Section 11.3.4. 

The pressure drop in the pipeline is high for suspended solids in a carrier fluid. For example, Wasp et al. (6) indicate that at 30% concentration of wood and a velocity of 1.4 m/s, a wood chip slurry in a 214-mm-diameter pipeline has a pressure drop that is three times larger than for water alone. 

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