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What are the Effects of Crude Oil Drag Reducing Agent?

Drag reducer is a kind of polymer compound which has the function of reducing resistance. When it is added to the crude oil during crude oil transportation, it can improve the flow rate and reduce energy consumption.

The chemical agent used to reduce the fluid flow resistance is called drag reducing agent (DRA). Drag reducing agent is widely used in pipeline transportation of crude oil and product oil. It is an important means to improve pipeline circulation capacity and reduce energy consumption in specific sections. The friction resistance of the fluid restricts the flow of the fluid in the pipeline, resulting in the reduction of the pipeline throughput and the increase of energy consumption. The polymer drag reduction method is to inject a small amount of polymer into the fluid to reduce the flow resistance in the turbulent state.

From the perspective of its structure, most of the oil phase drag reducers are high molecular polymers with flowing chain or long straight chain and few side chains, such as ZODR-E400H of Zoranoc. And an olefin having a molecular weight of 10 to 10. This high molecular polymer pure agent is a rubbery solid, which is generally dissolved in a solution of hydrocarbons (kerosene) as a commodity. The 10% drag reducer solution is a very viscous viscoelastic, which is difficult to flow and can be drawn into a very long wire. High polymer drag reducer can be dissolved in crude oil or oil, but not in water. When it meets water, it will curl the long chain of molecules. The drag reducer solution has strong Newtonian characteristics, and the viscosity is as high as 3000pa · s under low shear rate. It will not decompose under 120 ℃, and is relatively stable. Drag reduction is a special turbulence phenomenon. Drag reduction is a macroscopic manifestation of drag reduction affecting turbulent flow field, which is a pure physical effect. The drag reducer molecules do not interact with the oil molecules and do not affect the chemical properties of the oil, but are closely related to its flow characteristics. In turbulence, the motion speed of fluid particles changes randomly, forming large and small vortices. Large scale vortices absorb energy from the fluid, deform and break, and transform into small-scale vortices. Small scale vortices, also known as dissipative vortices, are weakened and subsided by viscous forces. Part of the energy it carries is converted into heat energy and dissipated. In the boundary layer near the pipe wall, this transformation is more serious due to the shear stress and viscous force of the pipe wall.

After thedrag reducer is added to the pipeline, the drag reducer is dispersed in the fluid as a continuous phase. By virtue of its unique viscoelasticity, the molecular long chain stretches naturally in a flow shape, and its micro elements directly affect the movement of the fluid micro elements. The radial force from the fluid element acts on the drag reducer element, causing it to twist and rotate. The gravitational force between the drag reducer molecules reacts on the fluid microelements against the above forces, changing the direction and size of the fluid microelements, so that part of the radial force is converted into the axial force in the forward direction, thus reducing the consumption of useless work and reducing the loss of friction resistance in the macro.

In laminar flow, the fluid is affected by viscous force, and there is no vortex dissipation like turbulence. Therefore, it is futile to add drag reducer. As the Reynolds number increases and enters the turbulence, the drag reducer shows its drag reduction effect. The larger the Reynolds number, the more obvious the drag reduction effect. When the Reynolds number is quite large and the shear stress of the fluid is enough to destroy the molecular chain structure of the drag reducer, the drag reducer degrades, and the drag reduction effect decreases, or even completely loses the drag reduction effect. The addition concentration of the drag reducer affects the thickness of the elastic bottom layer formed in the pipeline. The greater the concentration, the thicker the elastic bottom layer, and the better the drag reduction effect. Theoretically, when the elastic bottom layer reaches the pipe axis, the drag reduction reaches the limit, that is, the maximum drag reduction. The drag reduction effect is also related to oil viscosity, pipeline diameter, water content, pigging and other factors.

Using drag reducer as a short-time emergency measure has great advantages. However, for the pipeline that needs long-term increase in transportation, the economic benefit is not obvious due to the need for a large amount of drag reducer, and the drag reducer injection device is added in the oil transportation system, which improves the operation volume and failure rate of the whole system, which is not conducive to daily operation and management. Therefore, the technology of drag reducer should be given priority, and the application should not be blindly followed. It can be predicted that in the near future, as a new transportation technology, the injection of drag reducer technology will surely create greater economic and social benefits for China's pipeline industry.