Measure for measure
There is a spectrum of flow metering technologies on offer for custom transfer in the petroleum and petrochemical sector to meet demanding industry standards. Some opt for the traditional industry measurement workhorses of turbine or positive displacement (PD) meters, while others favour newer technologies such as Coriolis or ultrasonic meters. The choice depends on what the company is trying to achieve, the preferred performance parameters and budget considerations.
Turbines for traditionalists
The petroleum industry has strong allegiance to the use of turbine meters. Traditional or mechanical flow meters offer simplicity and easy maintenance, with a single moving part: the rotor. They offer the benefit of a primary output signal which is proportional to the movement of the measuring element, reproducing the actual flow rate.
However, tank operators also recognise that turbine meters are susceptible to the vagaries of liquid swirl and changing fluid velocities.
‘Careful installation is necessary in accordance with specified flow conditioning practice and regular verification,’ says Peter Syrnyk, director of liquid measurement at worldwide supplier of process automation services and technologies Emerson Process Management.
Nevertheless, turbine meters provide reliable and repeatable measurement for clean products, and from a price perspective are generally the most economic type of flow meter. ‘You can get 20 years out of a turbine meter, with merely 0.1% drift as long as they are used for the products they were designed for,’ says Syrnyk. There is certainly plenty of choice on the market.
Emerson is a major player with brands including Daniel, Micro Motion and others.
Emerson’s Daniel Control Series 1500 liquid turbine flow meter serves crude oil and refined product loading and offloading and marketing terminal applications for custody transfer measurement.
The Series 1500 has tungsten carbide bearings and delivers +/-0.15% accuracy and +/-0.02% repeatability, with the option of a second universal mounting box (UMB). A 4in Series 1500 meter costs about $5,500 (€3,900).
Emerson has also developed a turbine meter with a Teflon coated rotor for custom transfer of bioethanol or biodiesel blends. Syrnyk notes that tank operators may need two different sizes of turbine meter to cover a flow range, and a pressure drop of 3-4psi depending on the viscosity of the fluid.
‘Users also need to incorporate flow conditioning on the liquid turbine meter, to take out any swirl in the flow which could affect accuracy,’ he explains.
There has been significant consolidation in the metering equipment market over the last few years. Earlier this year, US-based Idex Corporation acquired French company Faure Herman SA, a leading provider of helical turbine and ultrasonic flow meters for custody transfer.
Faure Herman’s products include the Heliflu helical rotor flow meter as well as the FH8500 ultrasonic flowmeter.
