Crude oil drag reducer is a kind of polymer additive which can reduce the friction of pipeline fluid flow and increase the delivery capacity. Mainly used in oil and gas transportation pipeline.

It is of great significance to increase transportation, save energy and improve economic benefits of the pipeline. In this article, the mechanism, types, advantages and disadvantages, application and development prospect of drag reducer are introduced in detail.

1.General Situation

The concept of drag reduction was put forward as early as 1940s. In 1948, Toms told the first international rheological conference that when a small amount of PMMA is dissolved in chlorobenzene, the friction resistance can be reduced by about 50%. Therefore, polymer drag reduction is also called Toms effect. In the late 1960s, Conoco developed CDR-101 drag reducer. In the early 1980s, the drag reduction test was carried out on the product oil pipeline, which was used for the drag reduction of gasoline, kerosene, diesel oil, NGL and LPG. By 1984, it was formally applied on the product oil pipeline. In 1982, Zhejiang University of China began to develop and test the domestic drag reducer. In 1985, the pilot production of EDR type drag reducer was carried out, and the pilot test was carried out on the domestic crude oil pipeline. The product performance has reached the level of the early 1970s abroad. In 1984, Chengdu University of science and technology also published the research results of PDR type drag reducer. In recent years, the pipeline science and technology research center of China Petroleum Pipeline Corporation has carried out the research work of drag reducer and achieved success. The performance of EP series drag reducer products has reached the level of similar products in the world.

2.The theory of drag reduction mechanism

Elastohydrodynamic viewpoint:

The drag reduction effect of polymer solution is achieved by the interaction between viscoelasticity and turbulent vortex. Part of the kinetic energy of the vortex in the turbulence is converted into the elastic energy of the polymer molecule, and the consumption caused by the conversion of the kinetic energy of the vortex and the heat energy is also reduced, so the drag reduction effect is realized. Turbulence suppression Theory:

Because of its viscoelasticity, drag reducer has a long rheological property in crude oil. The interaction between drag reducer and crude oil molecules finally transforms the radial force of the fluid molecules into the axial force in the flow direction, so as to reduce the energy conversion effect of the fluid and ensure the mechanical energy of the fluid to the maximum extent. In the laminar flow, because of the stable flow state, the efficiency of adding drag reducer is limited, but in the turbulent flow, the larger the Reynolds number is, the better. When the Reynolds number reaches a certain value, the further increase of the Reynolds number will destroy the molecular chain of drag reducer, resulting in the failure of drag reducer.

3.Classification

According to the hydrophilicity, it can be divided into two kinds: water soluble drag reducer and oil soluble drag reducer.

There are many kinds of water-soluble drag reducers, such as water-soluble polyethylene oxide, which can reduce the resistance of water in the pipeline by 75% with only 25 mg/kg, and increase the rate of water outflow several times. It also includes PEO (polyoxyethylene), PAM (polyacrylamide), saponin powder and so on. For the water-soluble polymer drag reducer, it has been effectively applied in the pipeline circulating cooling system and circulating water system abroad, and it has also been studied and applied in papermaking, mineral processing, agriculture and other systems.

Oil soluble drag reducer

Oil soluble drag reducers include many kinds. For example, when the amount of oil soluble polyisobutylene is 60mg/kg, the transportation capacity of crude oil in the pipeline can be greatly improved, which plays the role of increasing transportation and saving energy. It also includes polyisobutylene, olefin copolymer, polymethacrylate, etc. Oil soluble drag reducer has been successfully applied not only in crude oil pipeline transportation, but also in petroleum product transportation.

4. Advantages of drag reducer

The amount of adding is small and the drag reduction rate is high

It has shear resistance, no obvious degradation during storage, transportation and use, no adverse effect on oil processing and oil quality, simple injection equipment, easy injection process, considerable economic and social benefits.

5. Application examples

For the crude oil pipeline across Alaska in the United States, the original 12 pumping stations were reduced to 10 by using the drag reducing agent scheme, and the daily oil delivery volume increased from 22.26 × 10m to 38.16 × 10m.

The original design of a pipeline in the North Sea oil field in the UK has a diameter of 1066mm. After comparison and selection of schemes, the scheme of adding and reducing resistance agent at peak time is adopted, which changes the pipe diameter to 914.4mm and greatly reduces the investment.

6. Precautions

Avoid places with high resistance such as elbows, flanges and valves; do not inject for a long time intermittently; the pipe diameter has a great impact on it, which needs to be added according to the actual parameters and operation conditions of the pipeline; reasonably select the concentration of drag reducer according to the pipeline throughput.

7.New trends and prospects: (microcapsule drag reducers, composite drag reducers)

Microcapsule drag reducer:

The microcapsule drag reducer is made by encapsulating high concentration drag reducing polymer particles in the shell composed of some inert substances. There are many ways to produce the microcapsule drag reducer, among which including the process of static pressure nozzle and microcapsule.

In this device, the polymerization reaction monomer, catalyst and shell material are respectively added from the central hole and the outer ring, and extruded from the lower end of the device at a certain speed to form the micro capsule drag reducing agent particles.

A kind of Microcapsule shell: the reactants of the shell material and the inner core of the microcapsule cannot react with each other or be miscible. If the inner core of the microcapsule is a σ - olefin polymerization system, in order to avoid catalyst failure, there is no oxygen in the microcapsule shell, and the appropriate shell materials are polybutene, wax, stearic acid, etc.

A kind of the performance of the microcapsule shell is stable during transportation and storage, and its broken or dissolved residue has no effect on the physical and chemical properties of crude oil or petroleum products and oil processing.

Because Microcapsule drag reducers are stored and transported in the form of solid particles, thus saving the cost of transporting solvents, slurry or other carriers.

Composite drag reducer:

Because the drag reducer is a high polymer, its shear resistance is weak in places with high local resistance, which makes the molecular chain break, molecular weight decreases and drag reduction decrease. Although the shear resistance is improved by adding rigid groups or forming a large test base, it can’t completely inhibit the shear degree. Therefore, the composite drag reducer is used, and its intermolecular force can combine small molecules into macromolecules, so that even if degradation occurs, the molecules of the interaction force can still combine and recover into macromolecules, and the drag reduction performance is not reduced.

8. Conclusion

Drag reducing agent has the characteristics of simple and effective process, and it can increase the transmission capacity without equipment transformation after the pipeline reaches the maximum transmission capacity, which has significant economic benefits. At present, the drag reducer developed in China has reached the advanced level in foreign countries and has superior drag reduction performance. In view of the disadvantages and application limitations of drag reducer, more new drag reducer products and technologies need to be developed by us!