www.bunkerspot.com Volume 6 Number 2 April / May 2009

BUNKERING OPPORTUNITIES:Technology and teamwork

INDEPENDENT INTELLIGENCE FOR THE GLOBAL BUNKER INDUSTRY

AR-001175 Emerson

34 April / May 2009 bunkerspotwww.bunkerspot.com

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Interest in Coriolis direct mass f low measurement is increasing for marine applications, and fuel

bunkering in particular. Coriolis technology provides measurement of mass f low rate, volume f low rate, density, temperature and batch totals – all from a single device. Coriolis meters have no complex moving parts and require no maintenance, nor do they require f low conditioning or straight pipe runs. Flow and density accuracies of +0.1% and +0.5 kilogrammes per cubic metre (kg/m3) result in unmatched performance and measurement certainty, making Coriolis technology an attractive alternative for fuel bunkering.

While Coriolis measurement is well suited for fuel bunkering, there are other considerations and challenges that must be overcome to ensure optimal performance in marine applications. These include: the ability to handle entrained gas; performance in measuring viscous f luids; and the importance of technical application expertise to promote proper installation and operation practices.

Two-phase flowWhether due to tank stripping, turbulence during f il ling or when changing compartments, it is easy to get gas trapped in heavy fuel oil (HFO). When gas is entrained in bunker fuel, it can take considerable time for it to be released, so measurement equipment must be able to deal with the presence of two-phase f low. But before accuracy can be considered, it is necessary to determine what measurements are the right ones when multiple phases are present.

Consider three measurement devices – a mass f low meter, a volumetric f low meter, and a tank gauge – all measuring bunker fuel with 5% entrained gas. Even though all meters are working perfectly, the volumetric meter and tank gauge both give liquid oil batch errors of +5%. The reason for this is that each meter simply measures what is going through it, which in this case is a mixture of gas and bunker fuel. The operator, however, interprets the measurement as a liquid volume. Because gas has such a low density, it takes up a lot of space, and is interpreted by the operator as a large volume of oil.

On the other hand, the mass of a gas is so small that it does not contribute significantly to the total mass of the mixture. Therefore, even though a Coriolis meter measures mixture mass f low rate when a liquid and gas are present, the mixture mass is nearly identical to the liquid mass, which is the quantity needed. So while a volumetric meter over-predicts liquid quantities by about 5% in the presence of 5% gas, a mass f low meter only over-predicts by 0.01% at typical barge pressures. This is because the mass of a gas is negligible compared to the liquid mass.

However, the presence of two-phase f low can cause significant additional noise in the measurement signal of a Coriolis meter and tends to reduce measurement accuracy. Emerson’s Micro Motion Coriolis meters answer this challenge directly – improvements to the sensor stability coupled with state-of-the-art digital signal processing algorithms to handle the additional noise – to deliver accurate, reliable measurement that is f lexible to changing f luid conditions.

The data in Figure 1 illustrates the benefit of Micro Motion Coriolis mass measurement in the presence of entrained gas. In the graph, liquid-only reference meter measurement is indicated by bold lines, and test meter measurement by thin lines. The mass f low rate of the test meter closely tracks with the reference meter when 5% gas is entrained. The test meter also correctly indicates the mixture volume f low rate, although this value is about 5% greater than the liquid volume f low rate given by the reference meter. Both measurements are correct, but an operator needs liquid-only quantities, not mixture quantities, and therefore only the mass f low measurement is acceptable. Only when measuring in mass is the liquid energy content – the quantity of bunker fuel oil paid for – unaffected by entrained gas.

Joel Weinstein considers the challenges that are

being overcome in order to introduce Coriolis

technology to the bunker industry

Joel Weinstein is a research and applications engineer for Micro Motion, a division of Emerson Process Management, which developed and manufactures the Coriolis flow meter.Dr Weinstein has recently completed a five-year joint research project with the University of Colorado focused on improving Coriolis measurement with entrained gas for difficult industrial applications such as fuel bunkering.

Contact:Joel WeinsteinTel: +1 303 530 8415Fax: +1 303 530 8596Email: Joel.Weinstein@Emerson.com

bunkerspot April / May 2009 35www.bunkerspot.com

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An added benef it of Micro Motion Coriolis measurement is shown by the Drive Gain data represented in Figure 1. The Drive Gain output is a powerful diagnostic tool to check for gas or other impurities during bunkering operations. When gas, liquid, or solid particles of differing density than the bulk f luid are entrained, vibration of the f low tube requires more energy and the Drive Gain output immediately rises. Drive Gain is more reliable than density as a diagnostic for entrained gas because density is also affected by changing f luid conditions such as composition and temperature.

Measurement of viscous fluidsHeavy fuel oil or bunker fuel is thick, viscous, and in many cases must be heated to f low. With no moving internal parts to clog or wear down, Coriolis meters offer advantages over other mechanical f low measurement devices. Even more importantly, Coriolis meters are calibrated on water, which directly transfers to measurement of any f luid – from gases to viscous oils. Also, mass of oil is conserved regardless of changing temperature and pressure, making f luid look-up tables unnecessary. The result is an easy-to-use, robust device that is capable of both accurate measurement and lasting performance in the most challenging of conditions.

Emerson regularly pursues independent third party testing of its Micro Motion Coriolis meters to ensure performance on difficult f luids. The data from the Société du Pipeline Sud-Européen (SPSE) laboratory in France (represented in Figure 2) shows excellent performance from the Micro Motion CMFHC3 Coriolis meter on widely varying f luid types, including fuel oil, all from a single water calibration. MID and OIML certificates have been awarded for +0.2% mass accuracy on liquids.

-1.0%

-0.8%

-0.6%

-0.4%

-0.2%

0.0%

0.2%

0.4%

0.6%

0.8%

1.0%

0 500 1000 1500 2000

Mas

s Fl

ow E

rror

Volume Flow Rate (m^3/hr)

NMi certification testing at SPSE in France, May 2008, CMFHC3 .Widely varying viscosities and densities. Meter passes all tests and iscertified for +/- 0.2% mass measurement on products other than water

Fuel oil ARH Oural Naptha

Technical expertiseEven with a Coriolis meter that can handle two-phase f low and offers proven performance measuring highly viscous f luids, the importance of technical application expertise cannot be overstated. In order to maximise the performance of Coriolis measurement in bunkering applications, it is critical to consider installation best practices and be able to rely upon actual, real-world experience.

Of the measurement challenges that exist in marine applications, and bunkering in particular, ensuring proper installation to minimise – and in some cases completely eliminate – entrained gas, is critical. In order to further understand the specific

measurement challenges, Emerson has visited numerous global customers who experience multiphase f low. It is clear that application requirements are extremely diverse, and that specific guidance on installation and operation best practices for bunkering is imperative to ensure operational performance. For example, the meter must be sized so that velocity in the f low tube is relatively high during bunkering, which ensures a homogeneous mixture if gas is present. Careful placement of the meter on board can reduce or eliminate entrained gas, while intelligent valve sequencing allows barge pipelines to properly pack before f luid enters the meter.

Consider the schematics A, B, and C for meter placement in a bunkering application, represented in Figure 3. Which is the most effective installation? The answer, of course, involves a set of performance and

operational trade-offs, but installations B and C have proven to be the most effective for applications involving batching from empty pipes. The reason is that when the batch begins, the long empty pipeline completely packs before f luid enters the meter. Even a slight elevation increase, such as in schematic B, can dramatically reduce gas entrainment during a batch.

Other issues such as drainability, product hold-up, and available deck space are important and should be considered carefully for each application. Many simple and effective measures can be taken to allow for the best possible performance and ease of use in diff icult metering applications.

SummaryThere are many benef its to using Coriolis direct mass f low measurement in bunkering. Inherent advantages, such as multi-variable measurement and no moving parts are shared among all Coriolis meters. However, the challenges for fuel bunker measurement are clear. The ability to maintain ongoing measurement performance and reliability in the presence of entrained gas or two-phase f low is not characteristic of all Coriolis meters. Nor is the ability to deliver accurate measurement in the presence of highly variable process conditions. It is important, therefore, that measurement devices installed can deliver needed technical performance in harsh conditions, and that device installation and operations are backed with proven Coriolis application expertise in fuel bunkering applications.

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