Engineering Analysis and Application of the Depmau Depamu-pumps.com/Screw-Pump.html target='_blank'>Screw Pump in a Crude Palm Oil (CPO) Loading Dock

1. Introduction

In the vegetable oil processing industry, the logistics of transferring Crude Palm Oil (CPO) from storage facilities to transport tankers, or vice versa, present unique engineering challenges. The loading dock application is particularly demanding due to the combination of high flow rates, long pipeline distances, and the complex non-Newtonian behavior of the fluid.

This article evaluates the application of a Depmau Screw Pump for a specific heavy-duty loading dock scenario.

Project Specifications:

• Medium: Crude Palm Oil (CPO)

• Flow Rate (Q): 450 m³/h (approx. 1,980 GPM)

• Horizontal Distance: 600 meters

• Vertical Lift: 50 meters (to storage tank)

• Temperature: 35°C

• Viscosity at 35°C: Estimated (industry standard for CPO at this temp ranges between 25–35 cP).

2. Why a Screw Pump for CPO?

While centrifugal pumps are common for low-viscosity fluids, CPO at 35°C presents a complex rheological profile. CPO is prone to shear thinning, and maintaining its quality is paramount to prevent degradation.

The Depmau screw pump (a type of rotary positive displacement pump) is preferred for this application due to three critical factors:

1. Gentle Handling: The laminar flow within a screw pump ensures minimal emulsification or degradation of the CPO, preserving free fatty acid (FFA) levels.

2. Viscosity Tolerance: Unlike centrifugal pumps (which suffer from efficiency collapse as viscosity rises), screw pumps increase in volumetric efficiency with viscosity.

3. Suction Capability: Given the friction losses in 600m of horizontal pipe, the screw pump’s ability to handle entrained air and lower NPSHr is essential.

3. Hydraulic Analysis: Overcoming System Resistance

The total dynamic head (TDH) is not merely "600m horizontal + 50m vertical." The frictional losses in the 600-meter horizontal piping are the dominant factor.

Assuming a carbon steel pipe diameter (likely DN 300 or DN 350) to achieve 450 m³/h (approx 1.4 m/s velocity):

• Friction Loss (Horizontal): At 35°C, the kinematic viscosity is low enough to allow turbulent flow, but friction is high. Approximately 1.5 to 2 meters of head loss per 100 meters of pipe is estimated.

  • Calculation: 600m x ~1.7 m/100m = ~102 meters of friction head.

• Static Head (Vertical): 50 meters (static lift).

• Differential Pressure (Tank backpressure): ~10 meters.

Total Required Differential Pressure:
102m (Friction) + 50m (Static) + 10m (Tank) ≈ 162 meters of head.
This equates to roughly 16 Bar (232 PSI).

Why a Centrifugal Pump Fails:
Even a multistage centrifugal pump operating at 450 m³/h would require a massive impeller and high speed (e.g., 1,450 RPM). At this speed, the shear stress would degrade the CPO quality. Furthermore, if the viscosity spikes during a cold start (unheated line), the centrifugal pump would drop to zero flow (vortexing).

Why Depmau Screw Pump Succeeds:
A Depmau three-spindle screw pump designed for this duty would typically operate at 980 RPM (slower speed). The Total Differential Pressure (P2 - P1) of ~16 bar is well within the standard heavy-duty range of screw pumps (typically capable of 30-40 bar intermittent). The pump provides a steady, non-pulsating flow ideal for loading arms.

4. The Viscosity Factor (Viscosity at 35 Deg. Celsius)

Although the user query cut off before the viscosity value, industry data is available for reference.
At 35°C, Crude Palm Oil has a melting point around 35-39°C; it is just above its cloud point.

• Est. Viscosity: 25 - 35 cP (centipoise).

Impact on Operation:

• At 35 cP: The fluid behaves like a light machine oil. The Depmau screw pump will operate with minimal slip, achieving nearly 100% volumetric efficiency.

• Critical Warning: If the temperature drops even 2°C to 33°C, CPO begins to crystallize. Viscosity can spike non-linearly to 100-200 cP or solidify. A screw pump is "shear-sensitive," but its robust construction allows it to break through the initial high torque requirements (provided a VFD is used), whereas a centrifugal pump would be air-bound.

5. System Design Recommendations for Loading Dock

To ensure the Depmau screw pump meets the 450 m³/h demand with 600m piping, the following engineering controls are recommended:

A. Pressure Protection
Given the 16 Bar required pressure, a relief valve is mandatory. Screw pumps are positive displacement; if the tank isolation valve is closed against a 600m column of oil, pressure exceeds 50 Bar instantly. A full-port relief valve bypassing back to the suction side (or tank) is required.

B. Heating Jacket (Optional but Recommended)
While the transfer temperature is 35°C, ambient temperatures may drop. Depmau offers jacketed heads for their screw pumps. This allows steam or hot water to circulate around the pump chamber during standby, preventing the CPO from solidifying in the clearances (which are typically ~0.1mm).

C. Speed Control
A 450 m³/h flow rate correlates to a relatively large pump frame (e.g., Depmau model frame size 220 or 280). A VFD (Variable Frequency Drive) is highly recommended.

• During Start-up: Slow ramp-up clears the 600m line of settled cold oil without over-torque.

• During Loading: Flow can be matched to the tank truck’s vapor recovery rate.

6. Performance Expectations

7. Conclusion

The application of transferring Crude Palm Oil at 450 m³/h over 600 meters to a 50-meter high tank is a heavy-duty hydraulic challenge that typically discards centrifugal pumps due to cavitation and efficiency collapse.

The Depmau Screw Pump is the optimal solution for this loading dock scenario. Its ability to generate high differential pressure (16 Bar+) at moderate speeds (sub-1,000 RPM) without degrading the Crude Palm Oil ensures operational reliability.

Final Engineering Verdict: Select a Depmau three-spindle screw pump (construction material: Nodular Cast Iron / Carbon Steel) with hard-faced screw profiles. Operate at roughly 900-1,000 RPM using a 250-300 kW motor with a VFD. Ensure the relief valve is set to 18-20 Bar. This configuration will handle the 600m friction loss, the 50m static lift, and the variable viscosity of CPO at 35°C efficiently.