Drag-reducing agents, or drag-reducing polymers, are additives in pipelines
that reduce turbulence in a pipe. Usually used in petroleum pipelines,
they increase the pipeline capacity by reducing turbulency and therefore
allowing the oil to flow more efficiently.
Description Drag reducing agents can be broadly
classified under the following four categories – Polymers, Solid-particle
suspensions, Biological additives, and Surfactants. These agents are made out
of high molecular weight polymers or micellar systems. The polymers 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 polymers could be in reducing drag in veins 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. 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 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, 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. 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 to help lower the drag reducing
agent's attraction to one another. Another factor is the pipe diameter.
With a decreasing pipe diameter, the drag reduction is increased. Going along
with this, the roughness of the inside of the pipe has a factor. The rougher
the inside, the higher the percent drag reduction occurring. Increasing the
pressure in a pipe will help with drag reduction as well, but often that
pressure is greater than what the pipe can withstand.
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, 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. Drag reducers were introduced
into the market in the early 1970s by Conoco Inc.. 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. External links
QFLO Drag Reducing Agent Chemical Supplier and Application Specialists Web
site Flo-Quest Drag Reducer Supplier, Drag
Reduction Explained Phillips 66 LiquidPower Flow Improvers
Web site Phillips 66 ExtremePower Flow Improvers
Web site References