The Esso Petroleum Company refinery at Fawley on Southampton Water is the largest in Europe. The refinery's 330 kb capacity supplies over 15% of all the oil products used in Britain, with 85% of its products delivered by pipeline to Avonmouth, Birmingham, Manchester, West London, Purfleet and Heathrow airports. The Fawley site also incorporates an integrated chemical plant operated by Exxon Mobil Chemical.
Each type of crude oil has its own composition and flexible operations mean that the Fawley refinery can process between 20 and 30 different types of crude oil from all over the world. As part of a crude tank farm optimisation project, Esso has developed a more efficient method of managing its industry. New flowmeters were required as part of this project in an on-line blending process to bring efficiency to their resources and make provision for cutting costs.
Krohne has supplied six 12" and six 20" diameter UFM500 ultrasonic flowmeters. They are arranged in pairs, with the first flowmeter configured to protect the pump against low discharge flow (which could lead to pump cavitation), and the second for regulating the flow via a control valve to enable the correct crude ratios to be blended.
Ultrasonic flowmeters were chosen to meet the 5% accuracy stipulated by the project for the entire range of flows and viscosity's required for the blending process. The offsite piping-network extends over an area of nearly 8 km2, thus line size flowmeters helped to minimise the inherent pressure drop within the overall system.
Foster Wheeler, the main engineering, procurement and construction contractor for the project, purchased the units on behalf of Esso after Esso's engineering team at Fawley provided the exact flowmeter specification.
It was a demanding specification which, according to expert sources within ultrasonic flow technology, could be difficult to meet because of low velocities and high viscosity's, coupled with the overall range of velocities and viscosities taking the flow through the laminar, transitional and turbulent regions. This process requirement together with physical restrictions resulting in multiple out of phase pipe bends upstream of flowmeters has taken the flowmeters outside their normal performance ranges. Velocities in the range of 1,03 to 3,81 m/s were required for the 12" flowmeters, and 0,41 to 1,37 m/s for the 20" flowmeters, with viscosities ranging from 3 to 1800 centistokes.
Field trials have demonstrated that the Krohne flowmeters were able to meet the performance criteria. With pairs of the flowmeters arranged in series, consistent flow outputs have been achieved despite the potential for a distorted flow profile from the upstream pipe bends and cross talk between the flowmeters. The blending systems control software conducts a self-check of the flowmeters against tank movement via the radar ATG's installed in the crude tanks.
Krohne says that its UFM500 features a unique patented double-beam sensor arrangement with sensor mounts welded perpendicular to the tube centreline. The system reduces overall flowmeter length and increases measuring accuracy and repeatability, with an unimpeded tube cross-section, which means no water and no pressure drop. The parameters for flowrate are 1-450 000 m3/h, while the flow velocity is 0,5-18 m/s, however Fawley is now successfully operating down to 0,41 m/s.
Each Atosonic UFM500 also incorporates a microprocessor controlled signal converter for digital signal processing. At Fawley this is linked to the control system enabling remote process operation from the off-site control room over a conventional 4 to 20 mA loop.
Krohne
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