frictional drag reduction in pipelines using high density polymers

Frictional Drag Reduction in Pipelines using High

Density Polymers

Pawan Kumar16 ME62 R07

Typical Petroleum Transportation network

Source-David Wood & DWA Energy Limitedhttp://www.dwasolutions.com/DWA/DWTrainingOptions.htm

India’s Oil Market

Flow Through a Pipe

The length of the hydrodynamic entry region along the pipe is called hydrodynamic entry length. It is a function of Reynolds No. (Re) of the flow.L for Laminar Flow= 0.05 Re X DL for turbulent Flow= 1.359 DX (Re)^0.25

Flow Through a Pipe• Can be classified as either Laminar or Turbulent.• For Reynolds number less than 2300, laminar and

above that turbulent• More energy is wasted in turbulent flow due to

generation of eddies

Drag Generation in a Pipe Flow

• Drag generated in a pipeline is the loss of pressure or “head” that occurs due to the effect of the fluid's viscosity near the surface of the pipe or duct

*For a real fluid pressure at point 2 shall always be less than pressure at point 1

Boundary Layer in a typical pipe flow

Calculation of Frictional Drag generated in a pipe flow

• Loss in pressure due to Friction (Darcy–Weisbach equation)

h-head loss due to friction (mcl)L-Length of pipe sectionv-average flow velocityd-hydraulic diameter of pipe sectiong-acceleration due to gravity f-coefficient of friction

Calculation of Frictional Drag generated in a pipe flow

• Coefficient of friction (f) in the Darcy–Weisbach equation is different for Laminar and Turbulent flows

• For Laminar Flow

Re is the Reynolds number for the flow• For Turbulent Flow, empirical relations are used

for the calculation of coefficient of friction. Most notables are given below

Re64

f

Calculation of friction factor (f) for Turbulent flow inside a pipe

Calculation of friction factor (f) for Turbulent flow inside a pipe

• A more general equation for calculating “f” for turbulent flow in both smooth and rough pipes was given by Colebrook and White.

• The equation being implicit in nature, has to be solved by iteration.

• For most of the purposes, Moody Chart, which is a graphical representation of “f” and “Re” is used

Loss in Pressure due to friction • Pipe size- 22 inches• Viscosity of fluid-25 cst• Density of fluid- 860 kg/m3Flow rate in m3/hr. 500 600 700 800 900 1000 1100 1200 1300 1400 1500Loss in Pressure (Kpa) per km 8.21 11.27 14.73 18.59 22.83 27.45 32.44 37.78 43.48 49.53 55.93

DRA

• Drag reducing agent (DRA) are the class of chemicals that reduces frictional losses during fluid flow in a conduit or pipeline

Why use DRA

• To decrease the operating pressure of a Pipeline, keeping the same flow rate

• To increase the flow rate, keeping the same operating pressure

• To reduce the energy consumed by prime movers (Engine, Electric Motor etc.)

• To meet peak/ seasonal demands with the existing system

Mechanism of DRA

• Drag reduction phenomenon first reported by British chemist Toms in 1948

• Long chain polymers interact with fluid molecules that reduces formation of turbulent eddies

Mechanism of DRA

• Ultra high molecular weight, long chain hydrocarbon polymers suspended in solvent

Polyalpha-olefins (PAO)

Flow in a pipeline without DRA Flow in a pipeline with DRA

Mechanism of DRA

• On contact it forms long chains of polymer.• Long polymer chains acts as elastic conduits avoiding the flow

in radial direction.• Polymers tend to stretch in the flow and absorb the energy in

the streak, which in turn stops the burst that produces the turbulence in the core and results in a reduction in turbulence.

DRA

Reduction in radial velocity component of fluid particles results in less momentum transfer with the pipe wall and hence less pressure and also an increase in the flow rate

Effectiveness of DRA

Drag Reduction (DR)•Effectiveness of DRA is ascertained from Drag Reduction (DR) obtained

• ∆Po is pressure drop of untreated liquid

• ∆Pd is pressure drop of liquid doped with DRA

Effectiveness of DRA

• Based on Experimental data, drag reduction is related to the thermo physical properties of the fluid, dimensions of the conduit and the concentration of the drag reducing chemical as given under

Where, -Absolute roughness of pipe surface in inches• d- Internal diameter of pipe in inches• Re- Reynolds number• ppm- injection rate of DRA chemical in ppm

kakb (ppm)/d)( (L/d) M(Re)=%Dr

Effectiveness of DRA

As can be seen from the above, the percentage reduction in pressure loss due to friction sharply increases with the concentration of Drag Reducing Agent (a surfactant in this case) being injected in the pipeline

Source:- Ali A. Abdul-Hadi and Anees A. Khadom, “Studying the Effect of Some Surfactants on Drag Reduction of Crude Oil Flow,” Chinese Journal of EngineeringVolume 2013

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