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 conventional pumps suffer from low efficiency, high energy consumption, and increased operational costs. For instance, the efficiency of centrifugal pumps used for heavy oil is typically around 40%, while the world's most advanced centrifugal pumps only achieve about 80% efficiency when pumping water. When handling high-viscosity crude oil, their efficiency drops to just 40–50%. On the other hand, rotor-type heavy oil pumps, twin-screw pumps, and gear pumps offer higher efficiency in transporting heavy oil, but they often face issues such as wear, reliability problems, and high maintenance requirements. These challenges make the transportation of sand-laden heavy oil a significant problem. Therefore, using a single-screw pump to convey high-viscosity sandy crude oil is considered one of the most effective and cost-efficient solutions.
**Principle of Single-Screw Pump**
A single-screw pump is a reliable and simple positive displacement pump that operates using an eccentric rotor. It consists of a rotor with a specific shape and a stator with a corresponding internal profile. The rotor is a screw with a large lead, high teeth, and a small inner diameter, while the stator is a flexible rubber bushing with a double helical structure. Due to the difference in pitch between the rotor and stator, the rotor engages with the stator to form a unique contact line—known as a sealing line—that divides the stator chamber into separate, non-communicating sections. As the rotor rotates, these sealed chambers move axially from the suction side to the discharge side, allowing continuous fluid transfer.
The stator is made of elastic rubber, which allows it to compress when solid particles are trapped in the sealing line. This elasticity enables the particles to pass through the seal without damaging the pump, making the single-screw pump suitable for handling media containing solids.
**NEMO (R) Pump Features**
NETZSCH’s NEMO (R) pump features rotors made from both standard and specialized materials that provide excellent wear and corrosion resistance. The rotor surface is hardened to better handle oil-bearing sand. The pump uses a universal joint drive shaft design with pin and tooth structures, ensuring high strength, long service life, and stable transmission. The stator is available in various rubber formulations tailored to meet different working conditions, including oil compatibility, wear resistance, and high-temperature performance.
Key advantages include:
1. **Versatile Application**: Suitable for corrosive media, gas-containing fluids, solid-laden liquids, and high-viscosity crude oil. It can handle up to 75% gas content, viscosities up to 50,000 mPa·s, and solid content of up to 60%, with particle sizes ranging from 3.5 to 32 mm and fiber lengths up to 272 mm. With proper pipeline design, oil-gas mixtures can be transported without heating, improving economic efficiency.
2. **Self-Priming Capability**: Capable of drawing liquid from a height of up to 8.5 meters. No need for priming water, making it ideal for pumping oil and sewage from ground-level tanks.
3. **Stable Flow**: The pump delivers a constant flow rate without turbulence, pulsation, or mixing. Low speed results in minimal vibration and noise, ensuring smooth and reliable operation with extended rotor and stator life.
4. **Easy Control**: Flow rate is directly proportional to rotational speed, allowing precise pressure control and easy automation.
5. **High Efficiency**: System efficiency reaches up to 82%, eliminating the need for outlet control valves, reducing pipe resistance, and enhancing overall economic performance.
6. **Simple and Reliable**: Easy to maintain, with a robust and straightforward design.
**Single-Screw Pump Operation and Safety**
As a positive displacement pump, the single-screw pump requires careful process design during crude oil transportation. If the outlet becomes blocked or the system is operated improperly, excessive pressure can damage the pump components. To prevent this, a safety valve should be installed between the discharge and suction lines, or a pressure switch should be placed on the outlet.
Dry running due to lack of fluid or blockage in the inlet piping can cause overheating and damage to the stator, leading to rubber aging or even burning out. Therefore, a pressure switch or temperature sensor should be installed on the stator.
To prevent backflow when the pump is stopped, a check valve should be installed on the discharge line.
**Conclusion**
The NEMO (R) pump’s unique features make it highly effective in transporting heavy oil mixed with sand. Field applications have shown that these pumps operate efficiently, produce minimal vibration and noise, run reliably, are easy to maintain, and have a long service life. They effectively address the limitations of other pump types when dealing with heavy oil containing sediments. Therefore, the NEMO (R) pump is an ideal solution for sand-laden crude oil transportation and conveying.
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