A prominent Western Cape oil refinery uses a 15 km long underground pipeline with DN 300 outside bore to pump 500 ppm diesel as well as various grades of gasoline to two berths in Table Bay harbour. As this line is used for a number of different products, the challenge is to know which one is being pumped at any given time.
Should 500 ppm diesel be followed by unleaded gasoline, there will be a period where the fuels are mixed, and the overrun then has to be returned for re-refining. Previously this condition could not be controlled by measurement, and therefore a predetermined time was set to allow the mixed fuel to be cleared from the pipeline. This resulted in unnecessary waste.
An ultrasonic solution
System integrator, Indecon Instrumentation, a specialist in process control instrumentation products and consulting, and a Siemens Industry Automation Partner, was called in to solve the problem – three Siemens Sitrans FUH 1010 clamp-on ultrasonic flowmeters were used, one at the refinery and the other two at each of the harbour berths. These meters are designed specifically for hydrocarbon applications where dynamic viscosity compensation that goes beyond the capabilities of standard ultrasonic flowmeters is required.
The FUH1010 flowmeter has an interface detection function which measures the Liquident fingerprint of the process stream and allows the identification of each liquid by its sonic signature. This approach uses a combination of sonic velocity, rate of change in sonic velocity, temperature and density, and is much more sensitive than using a densitometer. The Liquident represents the measured liquid’s sonic velocity compensated for operating temperature and pressure. So, for a given liquid product, the measured Liquident output will remain constant over a wide range of pressure or temperature. It can be compared to a human’s unique fingerprint and provides an extremely accurate way to distinguish products that have even very close densities.
Since the 50 ppm diesel, the mixed product and the gasoline all have different Liquident values, they can be differentiated through accurate signals that are sent to the control room. The user can monitor the Liquident value of the product being pumped at any given time, and by setting relevant threshold levels, can decide when the product is pure enough to deliver. This results in greatly reduced waste, and hence, greatly increased profitability.
Widebeam with autozero adjustment
All FUH1010 clamp-on flowmeters employ Siemens patented WideBeam ultrasonic transit time technology. The technology enables increased precision by reducing sensitivity to any change in the medium type or pressure. By utilising the pipe wall as an amplifier, the signal to noise ratio is optimised considerably, resulting in a stronger ultrasonic signal. WideBeam also makes the flowmeter immune to most pressure reducing valve noises and permits continued operation over an exceptional range of viscosity. WideBeam can be used for steel, aluminium, titanium and plastic pipes and through numerous field tests it has proven especially valuable for hydrocarbon as well as gas applications.
A feature that makes commissioning of the FUH1010 flowmeters particularly easy is the automatic zero adjustment. At the end of initial setup, an automatic zero (AutoZero) routine is automatically invoked. The AutoZero routine, which is performed on a full pipe, carries out a one-time analysis of the pipe wall component of the ultrasound signal to quantify any residual mismatch in the hardware. Once AutoZero is complete, the system memorises the zero offset and subtracts this value from the flow reading.
Flexible product offering
There are two types of FUH1010 flowmeters: a viscosity compensated volume meter and a standard volume (mass) meter. The viscosity compensated volume meter dynamically compensates for changes of viscosity as liquid properties change resulting in continuous correction of Reynolds number. It allows analogue output of inferred viscosity values in addition to valuable diagnostic data. In addition to the functionalities of the viscosity compensated meter, the standard volume (mass) meter has additional features. Volume is compensated to a standard temperature, which can be individually defined by the user. This requires dynamic temperature and pressure inputs, if the pressure varies significantly. The meter infers the density for mass calculation and outputs the density and API values and for even more precise density compensation, an analogue input from a densitometer can be utilised.
The clamp-on ultrasonic hydrocarbon meters are available in three different enclosures: standard IP65 (NEMA 4X) for wall-mount installation; explosion proof compact IP65 (NEMA 7); and explosion proof wall mount with an IP66 (NEMA 7) enclosure. Depending on the required measurement accuracy and the flow profile, the FUH1010 meters are available in dual, triple or optional four beam versions.
No production interruptions
According to Indecon’s Bennie de Reuck, one of the challenges during installation and commissioning was that the system had to be commissioned live, with no production interruptions. With the FUH1010 it was not necessary to cut the pipe or shut down operations to install the flowmeter; the transducers were quickly and easily mounted on the outside of the pipe, minimising maintenance expenses and preventing deposits from forming. The clamp-on design also eliminated the need to modify pipes or interrupt the flow. “The non-intrusive clamp-on flowmeters were perfect for this task,” he concludes.
For more information contact Garreth Fransman, Siemens Southern Africa, +27 (0)11 652 2522, [email protected], www.siemens.co.za
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