What is drag reduction? Drag reduction is defined as the increase in pumpability of a fluid caused by the addition of small amounts of an additive to the flowing stream. The effectiveness of a drag reducer is normally expressed in terms of percent drag reduction (%DR).
Understanding the benefits of DRA starts with explaining how liquids flow in pipelines, beginning with laminar flow.
Laminar Flow: The illustration shown here is the profile of a liquid as it moves relatively slowly through a pipe in laminar flow. The velocity profile of laminar flow is layers or concentric shells, with the fastest in the center and the slowest at the wall. The flow is governed by the viscous forces of the concentric shells moving past each other. Laminar flow is efficient and orderly,but in practice we require fluids to move much faster down a pipe. However, when the flow rate is increased, a turbulent state eventually results.
Turbulent Flow: When the velocity of the fluid is increased, momentum forces enter and eventually dominate, resulting in turbulent flow. Turbulent flow is characterized by disorderly movement of the fluid particles and a non-smooth parabolic profile. For practical reasons, most petroleum pipelines operate in this regime, and although more practical, the higher velocity is accompanied by an increase in the energy required to maintain the flow rate. It is the energy to overcome the increase in “drag” of the liquid. “Drag” results from a breakdown in the orderliness of the movement at the wall fluid interphase. The disorder caused by the momentum forces starts at the pipe wall. The particles moving randomly and chaotically grow into clusters or eddies. As the eddies accumulate energy they burst and accelerate the propagation of the chaos towards the interior of the pipe’s fluid. Since all this movement is not in the direction of the flow, the energy produced by turbulence is wasted.
DRA Reduces Turbulence
Drag reducing agents are long-chain polymers that act as buffers along the pipe wall and interfere with the propagation of turbulence, and in doing so, reduce the amount of energy lost. Studies have shown that when drag reducer is injected it must dissolve in the liquid so that the polymer can extend along the flow of the liquid. Once completely dissolved, the polymers within the drag reducing agent perform their of function interfering with the turbulent bursts, diminishing pipeline turbulence and reducing wasted energy.
Optum provides industry-leading technology designed for broad spectrum applications in crude oil pipelines.
Optum provides superior, cost-effective drag reducer technology and services to the global pipeline industry with enhanced service, consistency and innovation.