I. Opening: Don’t Just Focus on Flow Rate & Head! 70% of Failures Stem from Misjudging 3 Hidden Parameters
Twin-screw pumps have become essential in the oil & gas, chemical, and food industries for their ability to convey gas-liquid-solid multiphase media. However, a common issue arises: “parameters match on paper, but failures occur in use”:
- A shale gas well selected a pump based on an “average gas content of 20%”. Later, gas content surged to 95%, causing air binding and 3 shutdowns per week;
- A chocolate factory mistakenly selected a pump using room-temperature water parameters. When conveying 1200 mPa·s slurry, the actual flow rate only reached 45% of the designed value.
The core problem: Ignoring 3 hidden parameters—gas content fluctuation, solid particle size, and operating viscosity—these are the real keys to selection.
II. Pitfall Avoidance 1: Gas Content – Focus on Fluctuation & Form, Not Just Value
1. Key Pitfalls
- Using “average value” instead of “extreme value” (e.g., instantaneous switch between 0%–100% gas content; selecting based on 50% guarantees shutdowns);
- Overlooking gas-liquid form: “Gas-wrapped oil” (gas columns ≥50mm) requires a gas discharge structure, otherwise the gas blockage risk reaches 90%.
2. 3-Step Pitfall Avoidance
① Measure: Use a microwave gas content analyzer for 48 hours of continuous testing (72 hours for slug flow). Record “extreme gas content + gas-liquid form”;
② Select: For fluctuations ≤10%, use a basic model; 10%–50%, use a model with a gas discharge valve; >50%, use a double-suction model + forced gas discharge;
③ Verify: Ask the manufacturer to provide a curve showing “flow rate retention ≥85% at peak gas content”.
III. Pitfall Avoidance 2: Solid Particle Size – Don’t Miss Size, Hardness, or Form
1. Key Pitfalls
- Only checking solid content: With the same 5% solid content, 0.1mm talc can be conveyed directly, while 0.5mm granite requires a wear-resistant pump;
- Missing hardness testing: When conveying corundum particles (HV2000), ordinary stainless steel pumps last less than 1 month.
2. 2-Step Pitfall Avoidance
① Test 3 core items:
| Test Item | Method | Key Data |
|---|---|---|
| Maximum Particle Size | 5-layer wet sieving | Diameter through which 95% of particles pass |
| Hardness | Vickers hardness tester | Average of 10 samples |
| Form | Microscope | Proportion of spherical/needle-like particles |
② Match wear-resistant configurations:
- Particle size ≤0.3mm, HV ≤500: 316L screws;
- 0.3–1mm, HV 500–800: Nitrided screws + anti-clog inlet;
- 1mm or HV >800: Tungsten carbide screws + pre-filter.
IV. Pitfall Avoidance 3: Viscosity – Select Based on Operating Temperature, Not Room Temperature
1. Key Pitfalls
- Using room-temperature viscosity instead of operating viscosity (e.g., crude oil viscosity is 500 mPa·s at 20℃, but only 50 mPa·s at 60℃; selecting based on room temperature causes excessive flow);
- Not adjusting speed for high viscosity: Using 1450 rpm for viscosity >5000 mPa·s easily burns out the motor due to overload.
2. 2-Step Pitfall Avoidance
① Measure: Use a rotational viscometer at “operating temperature ±5℃”. Record “viscosity fluctuation + temperature curve”;
② Match speed + seal (simplified table):
| Operating Viscosity (mPa·s) | Recommended Speed (rpm) | Seal Type |
|---|---|---|
| 1–100 | 1450 | Packing Seal |
| 100–5000 | 750–960 | Mechanical Seal |
| >5000 | 450 | Magnetic Seal |
| Inverter motor is a must for real-time speed adjustment |
V. Ultimate Tool: Concise Selection Checklist
1. Must-Measure Medium Parameters (High-Risk Items)
- Gas: Extreme gas content, gas-liquid form;
- Solid: Maximum particle size, hardness;
- Viscosity: Fluctuation range at operating temperature;
- Basic: Designed flow rate (10% redundancy), head.
2. 3 Must-Ask Questions for Manufacturers
- Is volumetric efficiency ≥80% at peak parameters?
- Is the service life of wear parts ≥12 months?
- Are there 3+ successful cases under the same working conditions?
VI. Conclusion: Selection = Drawing a “Simple DNA” of the Medium
No complex calculations are needed. Just focus on “gas fluctuation, solid hardness, and operating viscosity”, and follow the process of “measure parameters → match configurations → ask manufacturers”. This avoids 90% of pitfalls, extends equipment life by 3x, and reduces maintenance costs by 60%. Save this checklist—finish selection in 1 day!
