Drag-reducing agents (DRA), or drag-reducing polymers (DRP's), are additives in pipelines that reduce

turbulence In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to a laminar flow, which occurs when a fluid flows in parallel layers, with no disruption between ...

in a pipe. Usually used in

petroleum Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crud ...

pipelines, they increase the pipeline capacity by reducing turbulency and increasing

laminar flow In fluid dynamics, laminar flow is characterized by fluid particles following smooth paths in layers, with each layer moving smoothly past the adjacent layers with little or no mixing. At low velocities, the fluid tends to flow without lateral mi ...

Description

Drag reducing agents can be broadly classified under the following four categories –

Polymers A polymer (; Greek '' poly-'', "many" + ''-mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic an ...

, Solid-particle

suspensions In chemistry, a suspension is a heterogeneous mixture of a fluid that contains solid particles sufficiently large for sedimentation. The particles may be visible to the naked eye, usually must be larger than one micrometer, and will eventually ...

, Biological additives, and Surfactants. These agents are made out of high molecular weight

polymers A polymer (; Greek '' poly-'', "many" + ''-mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic an ...

or micellar systems. The

help with drag reduction by decreasing turbulence in the oil lines. This allows for oil to be pumped through at lower pressures, saving energy and money. Although these drag reducing agents are mostly used in oil lines, there is research being done to see how helpful

could be in reducing drag in

veins Veins are blood vessels in humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated b ...

and arteries.

How it works

Using just a few parts per million of the drag reducer helps to reduce the turbulence inside the pipe. Because the oil pushes up against the inside wall of the pipe, the pipe pushes the oil back down causing a swirling of turbulence to occur which creates a

drag force In fluid dynamics, drag (sometimes called air resistance, a type of friction, or fluid resistance, another type of friction or fluid friction) is a force acting opposite to the relative motion of any object moving with respect to a surrounding flu ...

. When the polymer is added, it interacts with the oil and the wall to help reduce the contact of the oil with the wall. Degradation can occur on the polymers during the flow. Because of the pressure and temperature on the polymers, it is easier to break them down. Because of this, the drag reducing agent is re-injected after points like pumps and turns, where the pressure and temperature can be extra high. To safeguard against degradation at high temperature, a different class of drag reducing agents are at times used, namely, surfactants. ''

Surfactant Surfactants are chemical compounds that decrease the surface tension between two liquids, between a gas and a liquid, or interfacial tension between a liquid and a solid. Surfactants may act as detergents, wetting agents, emulsifiers, foaming ...

'' is a very convenient contraction of the term ''Surface-active agent''. It connotes an organic molecule or an unformulated compound having surface-active properties. All three classes of surfactants, namely, anionic, cationic and nonionic surfactants, have been successfully tried as drag-reducing agents. Knowing what will create the ideal drag reducer is key in this process. Ideal molecules have a high

molecular weight A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioch ...

, shear degradation resistance, are quick to dissolve in whatever is in the pipe, and have low degradation in heat, light, chemicals, and biological areas. With drag reduction, there are many factors which play a role in how well the drag is reduced. A main factor in this is

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...

. With a higher temperature, the drag reducing agent is easier to degrade. At a low temperature the drag reducing agent will tend to cluster together. This problem can be solved easier than degradation though, by adding another chemical, such as

aluminum Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It has ...

to help lower the drag reducing agent's inter-molecular attraction. Other factors are the pipe diameter, inside roughness, and pressure. Drag is higher in smaller diameter pipe. The rougher the inside surface of the pipe, the higher the drag, or friction, which is measured by the

Reynold's number In fluid mechanics, the Reynolds number () is a dimensionless quantity that helps predict fluid flow patterns in different situations by measuring the ratio between inertial and viscous forces. At low Reynolds numbers, flows tend to be dom ...

. Increasing the pressure will increase flow and reduce drag, but is limited by the maximum pressure rating of the pipe.

Areas of use

Drag reducing agents have been found useful in reducing turbulence in the shipbuilding industry, for fire-fighting operations, oil-well fracturing processes, in irrigation systems and in central heating devices. Drag reducers can work in a couple of different fields. The most popular are

crude oil Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crude ...

, refined products and non-potable water. Currently there are several studies with ongoing tests in rats looking to see if drag reducers can help with blood flow.

History

The earliest works that recorded a decrease in pressure drop during turbulent flow were undertaken in the thirties and concerned the transportation of paper pulp. This was, however, not explicitly referred to as a drag reduction phenomenon. Toms was the first to recognize the tremendous reduction in wall shear stress caused by the addition of small amount of linear macromolecules to a turbulent flowing fluid. An extensive bibliography of the first 25 years of drag reduction by polymer additives literature identified over 270 references. Drag reducers were introduced into the market in the early 1970s by Conoco Inc. (now known as LiquidPower Specialty Products Inc. (LSPI)
a Berkshire Hathaway Company
. Its use has allowed pipeline systems to greatly increase in traditional capacity and extended the life of existing systems. The higher flow rates possible on long pipelines have also increased the potential for surge on older systems not previously designed for high velocities. Both proprietary (such as Conoco T-83) and non-proprietary (such as poly-isobutylene) drag reduction additives have been evaluated by the U.S. Army Mobility Equipment Research and Development Center for enhancement of military petroleum pipeline systems.

References

{{DEFAULTSORT:Drag Reducing Agent Drag (physics) Piping Petroleum technology