Product category:
Coriolis mass flowmeters
News Release from: Invensys Foxboro | Subject: Foxboro CFT50
Edited by the Processingtalk Editorial
Team on 08 May 2006
Coriolis resolves tough pipeline flow
challenges
Recent developments in digital Coriolis technology overcome the challenges of measuring two-phase flow to offer a solution for demanding applications that have been traditionally out of reach
Coriolis technology offers unprecedented accuracy and reliability in measuring material flow in the pipeline and gas industry, and is often hailed as being one of the most superior flow measurement technologies But conventional Coriolis meters have had one significant limitation: they haven't performed well in measuring two-phase flow conditions, flow that involves a combination of gas and liquid mass
This article was originally published on Processingtalk on 7 Nov 2003 at 8.00am (UK)
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Two-phase flow can cause process interruptions and measurement inaccuracies that can significantly affect production and profitability.
Recent developments in digital Coriolis technology overcome the challenges of measuring two-phase flow to improve traditional pipeline flow measurement, while offering a solution for demanding applications that have been traditionally out of reach.
How Coriolis measurement works.
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With worldwide revenues presently greater than US$400 million and expected to exceed US$600 million in the near future, Coriolis meters are among the fastest-growing and widely used flow measurement technologies.
These meters measure flow by analysing changes in the Coriolis force of a flowing substance.
Coriolis force is generated in a mass which is moving within a rotating frame of reference.
That rotation produces an angular, outward acceleration, which is factored with linear velocity to define the Coriolis force.
With a fluid mass, the Coriolis force is proportional to the mass flowrate of that fluid.
To use Coriolis force for measurement, a Coriolis meter has two main components: an oscillating flowtube equipped with sensors and drivers, and an electronic transmitter that controls the oscillations, analyses the results, and transmits the information.
Reliable Coriolis measurement depends on consistent, reliable oscillation, which is determined by the following four factors: the density of the liquid, the balance of the tubes, the dampening caused by the flow stream itself, and the physical isolation of the tubes from the environment.
Compromising even one of these factors will degrade Coriolis meter performance.
Yet two-phase flow compromises every one of them.
Thus applications involving negligible amounts of entrained gas - even as little as 2 percent volume - have been poor candidates for Coriolis measurement.
This has been particularly troubling in applications where reliable, highly accurate flow measurement can confer considerable bottom-line advantage, but where two-phase flow is an integral part of the process or it is necessary to begin with an empty or partially filled flowtube.
Making matters worse, entrained air may not emerge as the culprit until after a frazzled process engineer has invested many hours trying to figure out why he can't get the results he needs.
Our own analysis shows that up to 92 percent of all Coriolis measurement problems are due to entrained air or gas, yet in the vast majority of cases two-phase flow is not even recognised as the problem.
Where accurate flow measurement matters, Coriolis technology is highly accurate in single-phase flow, with perhaps a +/- 0.1 percent error level.
Two-phase flow can boost the error rate to 20 percent or higher.
Following are some of the profitability drains that inaccurate flow measurement causes.
* Lost production: In flow-intensive operations thousands of dollars' worth of lost production can pass undetected in minutes.
* Inaccurate pricing: In custody transfer applications, where measured amount transferred defines payment price, faulty measurements raise financial havoc on either end of the transfer.
* Excess downtime: When traditional Coriolis meters encounter entrained air, they render inaccurate measurements - and if the condition persists, will shut down cutting into valuable production time.
To determine the extent of the problem and find a cost-effective solution, Invensys commissioned a survey of process engineers.
This revealed that entrained air was indeed a major problem in the industry, and that what customers really wanted was a cost-effective meter that could provide accurate measurement despite the presence of air.
Invensys partnered with researchers at Oxford University to develop digital technology for accurate measurement of flow, even when air was entrained in the flowtube.
Working closely with the Oxford researchers, engineers at the Invensys Process Systems Foxboro Measurements and Instruments Division developed a transmitter that applied the Oxford measurement principles.
In the resulting patented product, the Foxboro CFT50 digital Coriolis flow transmitter, new signal processing techniques are incorporated to provide useful measurements of both mass flow and density, and the operational aspects of keeping the Coriolis meter running stably in single-phase or two-phase flow conditions.
One of the many patents it has received involves an advanced control and measurement system with high-speed digital signal processing that responds to changing flow conditions many times faster than standard Coriolis flowmeters.
Another patent relates to detecting and compensating for two-phase flow conditions and generating a validated mass flow measurement.
New solutions for traditional problems.
Coriolis meters measure the mass flow of materials, which is independent of other physical parameters, as well as the ambient conditions in which the measurement is made.
Therefore, the measurement is unaffected by changes in temperature, pressure, density, viscosity and flow profile.
With the ability to handle two-phase flow and compensate for physical conditions, the advanced Coriolis flowmeters have greatly expanded fluid metering applications, including traditionally difficult situations such as custody transfer, proving, tank truck and tanker loading and unloading, and applications where two-phase flow is an integral part of the process.
Accurate measurement at custody transfer points is critical as competitive market conditions drive companies to develop more efficient operations.
By minimising wasted materials left on the bottom of transport vessels and improving transfer yields, advanced Coriolis flowmeters provide more accurate material accountability, which is a direct contribution to bottom line performance.
This is a win-win situation for both entities involved in the transaction.
Advanced Coriolis technology is increasingly replacing positive displacement meters for custody transfer to attain the benefits of Coriolis accuracy, while reducing total cost of ownership.
With no moving parts in the fluid stream, Coriolis meters require little-to-no maintenance and are easily installed.
In pipeline flow measurement proving applications, the frequency and duration of calibration can hinder productivity.
Advanced digital Coriolis flowmeters offer a solution by providing a much faster response time, and greater accuracy and repeatable proving with small volume provers.
A proving run may be accomplished in as little as 20 seconds or less.
This is particularly beneficial in multi-product pipeline applications where fluids varying from light liquefied petroleum gases to heavy crude oils pass through a common flowmeter.
For these applications, flowmeters are often proved several times a day, so slashing each proving process to seconds can significantly boost productivity.
Another issue is unloading railcars and tank trucks until they are practically dry.
To empty out the tank completely, invariably introduces air as the level approaches bottom.
This is exacerbated by the fact that in most cases unloading is done at as high a flowrate as possible to speed up the process.
This high flowrate tends to suck air into the flowmeter.
In these conditions a conventional Coriolis meter would shut down, but advanced Coriolis meters continue to provide a useful flow measurement, enabling faster, more complete unloading of tank trucks and railcars.
Even with the flowtube empty, they respond ten times faster than traditional Coriolis transmitters, which reduce start-up time while increasing production throughput and profitability.
Innovative process improvement.
In addition to improving existing flow measurement applications, advanced Coriolis technology is opening new doors for improving process efficiencies where two-phase flow is an integral part of the process.
For instance, using carbon dioxide (CO2) for enhanced oil recovery (EOR) can increase output by as much as 12 percent.
However, accurate measurement of CO2 has been the Achilles heel of the process.
A large midstream energy company found the solution by applying advanced Corioilis metering technology as part of a three stage EOR program.
The first stage was primary oil recovery, based on natural gas driving the oil to wellheads.
Secondary efforts involved waterflood driven production using natural aquifers.
As primary and secondary production methods declined in effectiveness, tertiary oil recovery techniques were examined.
A number of EOR options were studied and CO2 injection into the oil reservoirs was determined to be the most effective method for extracting and moving oil to the wellbore.
While the yields from this EOR were significant from the start, engineers felt that they could do even better if they could more accurately measure the CO2 flows in each well.
The problem is that when CO2 is above the critical point it exists as a gas and is easily measured with standard gas measuring devices such as orifice plates.
However, below the critical point it can coexist in two phases, liquid and gas.
The company transfers CO2 in pipelines to multiple injection wells throughout the field and variations in ambient temperature and pressure outside the pipeline have a dramatic affect.
On a cool morning, they could have primarily liquid CO2 in the pressurised distribution pipelines.
But in the afternoon, with elevated outside temperatures, they could have primarily gas.
Possible options considered were orifice plates with multivariable DP transmitters, vortex meters, and conventional Coriolis flow meters.
While traditional Coriolis technology is highly accurate in single-phase flow, with a 0.1 percent plus or minus error level, two-phase flow can boost the error rate to 20 percent or higher.
None of these options met the company performance standards, so they explored new avenues of flow measurement technology.
The company tested an advanced digital Coriolis flowmeter to successfully measure two-phase CO2 and, based on the results installed the flowmeters at each of the injection wells.
The advanced Coriolis flowmeters improved the accuracy of CO2 measurement by 300 percent.
This provided the immediate benefits of increasing oil output, as well as the long-term advantages of accurate flow measurement data to correlate optimum production efficiency with the volume of CO2 injected, which is critical for developing oil reservoir strategies.
The above cases are but a small sampling of the many ways in which the benefits of Coriolis accuracy can be attained in areas that have been traditionally out of reach.
Every day we are seeing new applications wherein advanced Coriolis flowmeters are being successfully used to solve traditional problems.
So take a look at your flow measurement challenges.
Are you simply writing off lost materials without knowing exactly what is causing them? Are you experiencing downtime that could be better spent producing profit? Are you investing in outdated technology? If you answer yes to any of these questions, or just feel that better flow measurement would improve your process in any way - advanced digital Coriolis technology may be the solution to today's problems and tomorrow's innovations.
This review was provided by Wade M Mattar, Flow Specialist at Invensys Process Systems, part of the Foxboro Measurements and Instruments Division, USA.
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