Guided Wave Radar: Nr.1 Alternative to Mechanical Level Measurement

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The following examples show how GWR has been used in a range of applications.

Gas-oil separator vessels and compressor tanks: For gas-oil production separators and compressor tanks, GWR minimizes common maintenance issues and reduces inaccuracies resulting from fluid density variations. For example, displacer measurements in a gas-oil separator tank (up to 82 bar and 49 ºC) were erroneous due to density variations, but a Rosemount GWR with a high-pressure probe has been operating reliably.

Oil and water separator vessels: GWR can be used in separator vessels to provide accurate measurements of interface level between oil and water, unaffected by oil density changes. For example, separators at a US Midwest refinery received oil from many different sources, so the oil’s properties changed frequently. The displacer responded to the variations in density, leading to regular carry-over of oil into the wastewater treatment stream. A Rosemount GWR probe was installed directly in the displacer chamber, using the same mounting flange and two-wire loop cabling. The refinery engineers were impressed with the easy installation and have achieved a much more reliable interface measurement. Another benefit has been reduced maintenance. The displacer needed frequent adjustment and cleaning to remove sticky deposits clinging to the sides, occasionally obstructing movement. With the GWR probe, which has no moving parts, maintenance has been reduced to occasional steam cleaning.

Distillation columns: GWR is also being used to provide reliable level measurement at all levels in distillation columns. For example, a chemical plant in the Czech Republic needed a reliable level measurement in a column containing methanol, water and ammonia. This is a difficult measurement as there is both foam and a bubbling surface. All the level measurement sensors tried previously had failed. A Rosemount GWR with a coaxial probe, which eliminates disturbances and mechanically avoids the foam, worked successfully and has continued to provide accurate and reliable results for seven years.

Liquefied gases: GWR is a suitable measurement technology for liquefied gases, including refrigerants. These are typically clean fluids which can be quite turbulent and are often stored at high pressures or low temperatures. For example, where liquid propane is used as a refrigerant in hydrocarbon processing and chemical plants, a standard process problem is monitoring the liquid level in the accumulator tanks to control recirculation and ensure an adequate supply of propane. Historically this has been unreliable because of the surface turbulence, the low temperature, and density variations in the low-dielectric-constant liquid. GWR offers more reliable measurement due to its tolerance of liquid density changes and surface turbulence. A coaxial probe concentrates the measurement into a defined area, almost like a stilling well, and so increases the signal-to-noise ratio of the radar signal. Initial tests with Emerson’s Rosemount GWR were carried out at a chemical company in the US, using a probe length of 1.5 m installed through a flange on an existing process connection on the side of the tank. The propane level was detected immediately, and the GWR has now provided accurate measurements for more than three years.

Power and water utility plants: Water level measurements in power plants and industrial utilities, such as in feedwater heaters, steam separators and deaerators, often use mechanical displacers. Although density variations can cause errors, maintenance can be a bigger issue. GWR works well for these applications as it is immune to density changes, offers easy installation, and can handle vacuum, high pressures and high temperatures. For the more challenging conditions, a Rosemount GWR with Emerson’s DVC is recommended.

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GWR - Guided Wave Radar