At present, most of the domestic high-viscosity crude oil pipelines rely on centrifugal pumps, heavy oil pumps, twin-screw pumps, and Gear pumps. However, these pumps often suffer from low efficiency, high energy consumption, and increased operational costs. For instance, the efficiency of centrifugal pumps used for transporting heavy oil is typically around 40%, while the world’s most advanced centrifugal pumps only achieve about 80% efficiency when pumping water. When it comes to high-viscosity oil, their efficiency drops significantly to 40–50%. On the other hand, rotor-based heavy oil pumps, twin-screw pumps, and gear pumps offer higher efficiency but face issues like wear, instability, and high maintenance demands. These challenges make transporting heavy oil with sand a complex task. Therefore, using a single-screw pump to convey high-viscosity sandy crude oil is considered one of the most effective and cost-efficient solutions.
A single-screw pump is a reliable and simple device based on an eccentric rotor mechanism. It consists of a rotor (a screw with a large lead, high teeth, and small internal diameter) and a stator (a flexible rubber bushing with a double helix). The stator has a lead twice that of the rotor, creating a special contact line—known as the seal line—which divides the stator chamber into isolated, 180° phase-locked sections. As the rotor rotates inside the stator, the sealed chambers move axially from the suction end to the discharge end, allowing continuous fluid transfer.
The stator's elastic rubber material allows it to compress when solid particles are trapped in the seal line. This compression enables the particles to pass through, after which the rubber returns to its original shape. This feature makes the single-screw pump suitable for handling media containing solids.
NETZSCH's NEMO® pump features rotors made from both standard and specialized materials with wear and corrosion resistance. The rotor surface is hardened to better handle sandy crude oil. The pump uses universal joint drive shaft designs, such as cylinder pin or toothed types, ensuring high strength, long life, and stable transmission. The stator is available in various rubber formulations tailored to meet different working conditions, including oil resistance, wear resistance, and high-temperature performance.
Key advantages of the NEMO® pump include:
1. It can handle corrosive, gas-laden, sediment-laden, and high-viscosity media. It can manage up to 75% gas content, viscosities up to 50,000 mPa·s, and solid content up to 60%. Solid particle diameters can be as large as 3.5–32 mm, and fiber lengths up to 37–272 mm. With proper pipeline design, it can reduce or eliminate heating, improving economic efficiency.
2. It has strong self-priming capability, with a suction lift of up to 8.5 meters. No need for priming water, making it ideal for conveying oil and sewage from ground pools.
3. The flow remains constant regardless of pressure, with no turbulence, mixing, or pulsation. Low speed, minimal vibration, and low noise ensure stable and reliable operation with long-lasting components.
4. Flow rate is proportional to speed, allowing for precise pressure control and easy automation.
5. High system efficiency, up to 82%, eliminates the need for export control valves, reducing pipe resistance and enhancing economic efficiency.
6. Simple structure, easy maintenance, and reliable operation.
When using a single-screw pump for crude oil delivery, special attention must be given to process design. If the outlet becomes blocked or operated improperly, the pump may overpressure, potentially damaging internal parts. A safety valve or pressure switch should be installed between the discharge and suction lines. Dry running due to lack of liquid or pipeline blockage can cause overheating, leading to stator damage or failure. A pressure switch or temperature control switch should be installed at the inlet or on the stator. To prevent backflow when stopping the pump, a check valve should be placed on the outlet line.
In conclusion, the NEMO® pump’s unique characteristics make it highly suitable for transporting heavy oil mixed with sediments. Field applications have shown that these pumps offer high efficiency, low vibration, minimal noise, stable operation, easy maintenance, and long service life. They effectively address many of the challenges faced by other pump types when handling heavy oil with sand, making them ideal for sand-laden oil transportation and conveying.
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