Coriolis Flow Meters

When I back look my career at Fluor, my first and last projects are the same: East Tank Farm for Suncor. What a coincidence!

The East Tank Farm Hot Bitumen Terminal was part of Voyageur upgrader project, originally engineered by CB&I. Fluor was doing some revamp when I joined in early 2011. In 2013, Suncor cancelled Voyager and altered this tank farm to serve Fort Hills Oil Sands Mine. The tank farm will receive, store and deliver diluent required for start-up and operations of Fort Hills, as well as receive Fort Hills hot bitumen, cool and blend the bitumen with diluent and deliver it to markets. East Tank Farm Development project was then set up to build 8 more tanks and associated facilities.

Among CB&I’s design, I noticed Coriolis flow meters were used on hot bitumen lines. Unlike volumetric flow meters, Coriolis flow meters directly measure mass flow and product density, insensitive to pressure, temperature, viscosity and density. With the ability to measure liquids, slurries and gases, Coriolis flow meters are universal meters. They have high accuracy and wide application. Considering total cost of ownership, Coriolis meters increasingly replace differential-pressure (DP) devices, and their use is also growing in the oil & gas industry.

So it is good to know things about Coriolis mass flow meters, especially installation requirements as a piping designer.

How Coriolis Mass Flow Meters Work

Coriolis flow meters measure flow by taking advantage of the Coriolis effect. When fluid travels through, the inertial effects are directly proportional to the mass flow of the fluid (Figure 1). The mass flow rate can be captured by measuring the time delay between the inlet and the outlet of the sensor.

Figure 1. Coriolis Meter Operational Principle 

The density measurement is derived from the natural frequency of oscillation of the flow tube, which varies with mass. As the fluid becomes denser and heavier, the vibrational frequency of the flow tubes decreases. If the volume of the flow tube is constant, the oscillation frequency is a function of fluid density

There are two basic configurations: (Dual) bent tube and (single) straight tube. The Coriolis meter with two bent tubes has the highest flow sensitivity.

How to install Coriolis Mass Flow Meters 
·    Coriolis flow meters are not affected by swirling fluid or non-uniform velocity profiles resulting from upstream or downstream piping configurations, so straight runs of pipe upstream or downstream are unnecessary. This is extremely beneficial if space is at a premium.

·    Keep the sensor tubes full of process fluid. When measuring liquids, do not install the sensor at the highest point for gas accumulation. When measuring gas, do not install the sensor at the lowest point for condensate accumulation.

·    Coriolis flow meters can be installed both horizontally and vertically. If in vertical, liquids and slurries should flow upward through the sensor. Gases should flow downward.

·    If air entrainment exists, to avoid the meter from malfunctioning, the Coriolis flow meter should be downwards mounted. If solids are present in the flow, the flow meter should be upwards mounted to ensure that solids do not accumulate in the flow tubes and cause misreading.

·    A shutoff valve downstream of the sensor should always be installed to allow flow to be stopped to enable zeroing of the flow meter.

·    If there are control valves, they should be installed downstream from Coriolis meters to increase backpressure on them and to decrease the probability of cavitation or flashing.

·    Coriolis flow meter designs resist normal pipe vibration if the surrounding process piping properly supports the meter. However, deposits and strong vibration can degrade accuracy.

·    Pipe supports should not be attached directly to the sensor and the sensor should never be used to support process piping.

·    The sensor does not require external supports. The flanges will support the sensor in any orientation. Only some sensor models installed in very small, flexible pipeline have optional installation instructions that allow for external supports.