Emerson meter deflates gas-in-fluid problems

London — The problem of identifying and measuring the flow of liquid containing entrained gas continues to represent one of the most serious common issues for users of flow measurement devices.

As well as the large metering errors caused by these two-phase flow systems, considerable time and resources are often required to identify them as the root cause of a process problem in the first place. Moreover, the solution can involve investment in equipment such as air eliminators or flow conditioning devices in order to avoid costly production stoppages and scrap.

Micro Motion Inc., part of Emerson Process Management, has rolled out a system to address the issue of gas entrainment, for example in custody transfer metering and flow measurement of emulsions, beer, soaps, polymers and dairy products.

Entrained gas conditions are “pretty much the No 1 [flow measurement] challenge in the process sector,” Chuck Stack, director of technology at Micro Motion, declared at a 26 June at a presentation in London.

Micro Motion’s solution has been to optimise the processing speed, signal processing, sensor stability and sensor design. The goal, said Stack, was to deliver high accuracy monitoring of the varying characteristics of processes involving flows such as bubble flow, slug flow, and empty-full-empty batch applications.

This development work has led to an improved Micro Motion Coriolis sensor design that provides accurate signals even in the presence of high flow noise during transient flow conditions. The design, in combination with the increased processing speed of the company’s latest MVD (multi-variable digital) technology ensures much higher accuracy when measuring flows with entrained gas, said Stack.

“The faster MVD digital processing enables responsive and correct measurement during rapidly changing process conditions, such as the onset off slug flow,” explained Stack. The capability, he added, enables advanced handling of different signals during entrained gas measurement.

Stack went on to cite an example of how the Micro Motion unit delivered flow rate readings with just 1% variation from the reference base line (35 lb/min) for a fluid with 15% entrained gas. This, he said, compared to 20% variation for a traditional meter.

Target applications for the new technology range from those where air is required in the product such as hair gel and ice cream, to monitoring fluids with 30% (unwanted) void fractions that commonly occur when switching delivery tanks, said Stack.