Application of Scraper Flow Meters in Crude Oil Handover Measurement Systems

A volumetric flowmeter, also known as a fixed-rotor displacement flowmeter, uses a mechanical measuring element to continuously divide the fluid into a known volume segment. The total volume is then measured by sequentially filling and discharging this volume segment from a measurement chamber. Volumetric rotor flowmeters, differential-pressure vane flowmeters, and float-type vane flowmeters are classified as three major categories of flowmeters, typically employed for total volume measurement of high-value media such as petroleum.

Volume scraper flowmeters can be classified, according to their measuring elements, into oval gear flowmeters, scraper flowmeters, twin-rotor flowmeters, rotary piston flowmeters, reciprocating piston flowmeters, disc flowmeters, liquid-sealed rotary flowmeters, wet-type meters, and diaphragm gas meters, among others. The advantages and disadvantages of volume scraper flowmeters are analyzed below.

In this project, crude oil is collected from production wells and transported to the central processing station, where it undergoes dehydration, degassing, and desalting processes. From there, the oil is sent to downstream users via external transportation, handover procedures, metering systems, skid-mounted units, and other specialized equipment. The process conditions for the handover and metering skid are as follows: design pressure is 9.5 MPa, design temperature is 85°C, design pressure for specific operations is 7.7 MPa, and design pressure for another critical process is 300 kPa—with a tolerance of 0.15%.

The external transfer handover measurement system consists of a scraper flowmeter skid, a volume pipe skid (featuring a spherical bidirectional volume pipe), and a water calibration skid. The flowmeter skid includes equipment such as inlet and outlet valves, exhaust filters, flow rectifiers, the flowmeter itself, temperature transmitters, pressure transmitters, and associated piping components. The volume pipe skid comprises key equipment like inlet and outlet valves, ball receivers/transmitters, four-way valves, temperature and pressure transmitters, and detection switches. The water calibration skid is equipped with a Class II metal measuring instrument, a pneumatic diverter valve, a water pump, a stainless steel water tank, a verification control cabinet, valves, connecting pipes, and other accessories. Upstream of the scraper flowmeter, a density analyzer and manual/automatic sampling devices are installed to enable real-time monitoring of crude oil density along with automated, time-based sampling using representative oil samples. The measurement accuracy chain of the handover measurement system is as follows: Water calibration tank (using a Class II standard metal measuring instrument with an accuracy of 0.025%) → Bidirectional volume pipe (accuracy of 0.05%) → Scraper flowmeter (accuracy of 0.20%).

The scraper flowmeter features two measurement circuits: one dedicated to measuring flow rate, and the other designed specifically for a DN250 scraper flowmeter. The measurement pipeline has a diameter of DN300, capable of handling flows up to 550 m³/h. Downstream of each measurement pipeline, a flow control valve is installed to precisely regulate the measured flow. Additionally, at the outlet of the slide plate assembly in the bidirectional volumetric pipeline, another flow control valve is positioned—this one serves both to adjust and verify the flow, ensuring accurate measurements throughout the entire scraping process. To maintain consistent temperature conditions during measurement and verification, the pipelines are thermally insulated. At the heart of this flowmeter system is the JK-LJB scraper flowmeter, which delivers exceptional accuracy and repeatability: ±0.15% accuracy and ±0.02% repeatability, with a measurement range of 74 m³/h. The flow computer used in this system is the JK Flow Computer. Meanwhile, the PLC-based control system manages seamless process switching, controls the flow valves, and ensures precise execution of system validation as well as continuous monitoring of production flow rates.