Application of Oval Gear Flowmeters in Heavy Oil Loading and Unloading Metering

**I. Why Oval Gear Flowmeters Are Suitable for Heavy Oil Metering**

Heavy oil (such as fuel oil, residual oil, crude oil, etc.) typically features high viscosity, poor fluidity, and a tendency to solidify. As a positive displacement flowmeter, the oval gear flowmeter offers several key advantages:

1: Strong adaptability to viscosity: It measures by the rotation of a pair of meshing oval gears with extremely small clearances. As liquid viscosity increases, the leakage error actually decreases, resulting in higher accuracy. It is particularly suitable for media like heavy oil with viscosity greater than 10 mPa·s.

1.1 High metering accuracy: In custody transfer, standard accuracy can reach Class 0.2 or even Class 0.1, with a turndown ratio up to 10:1.

1.2 Low requirement on flow profile: Its internal structure makes it immune to pipe turbulence and velocity profile distortion. No straight pipe runs are required before or after installation, which is highly advantageous in space-constrained applications such as loading/unloading.

1.3 Direct volumetric measurement: It can directly provide volume under standard conditions, making it intuitive for trade settlement based on volume.

**II. Specific Application Scheme in Heavy Oil Loading and Unloading**

A typical loading/unloading metering system usually consists of the following components:

1. Loading Metering

1.1 Flow: Storage tank → Pump → Filter → Oval gear flowmeter → Electro-hydraulic valve / Digital control valve → Loading arm → Tanker.

1.2 Batch control: The flowmeter sends pulse signals to the batch controller. When the preset quantity is reached, the controller closes the electro-hydraulic valve in two or three stages to prevent water hammer damage to the gears.

**III. Key Points Requiring Special Attention in Application**

1.1: Heat tracing and insulation: Heavy oil with a high pour point will solidify at ambient temperature. The flowmeter and its upstream and downstream piping must be equipped with steam tracing or electric heat tracing to maintain the oil temperature 30–40°C above its pour point. The flowmeter body can have a jacket for steam or hot oil heating.

1.2 Pulsating flow and vibration: During loading/unloading, pump start/stop and rapid valve closure generate pressure pulsations. A check valve and an accumulator (pulsation dampener) should be installed downstream of the flowmeter, or a digital control valve with staged closure should be used, to protect the gear shaft from being twisted off.