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Measuring level through the build-up in a harsh, corrosive environment

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Hydrocarbon Engineering,

Tai Piazza, Refining Industry Manager, VEGA Americas, discusses the use of guided wave radar technology in measuring build-up levels in sulphur pits.

The sulphur pit at any refinery is home to one of the most dangerous and foul by-products of the oil refining process. The molten sulphur inside this concrete pit also contains hydrogen sulphide, a colourless, flammable, poisonous, and corrosive gas. Maintaining a safe level here is just as important as it is dangerous. Fortunately, guided wave radar technology offers a reliable method to measure the level.

As oil refineries convert crude oil into usable products for other industries and consumers, a variety of by-products are removed. The sulphur recovery unit removes any sulphur, which can vary depending on the grade of the incoming crude oil. The molten sulphur is then transferred to the sulphur pit. Maintaining proper process control with an accurate and reliable level measurement in this step keeps the unit running efficiently, and it prevents any dangerous overflows and spills. The environment inside these pits, however, is not accommodating to most level measurement technologies.

Sulphur pits are kept at elevated temperatures to prevent the sulphur from solidifying. However, if the temperature within is upset, the sulphur can vaporise and crystallise. This results in excessive build-up throughout the inside of the sulphur pit, including on any level measurement instrumentation. Build-up on most level measurement sensors will result in a level measurement error or a complete failure, leading to reduced efficiency in the sulphur recovery unit and eventual maintenance, repair, or replacement of the level sensor.

Guided wave radars like the VEGAFLEX 81 avoid all of these issues and continue to measure level through excessive build-up because of how the technology works. A low amplitude, high-frequency microwave pulse is sent downward into the sulphur pit along a transmission probe. Once the pulse reaches the surface of the molten sulphur, the signal is reflected back to the sensor electronics, which uses the time of flight to calculate the level.

The VEGAFLEX 81 is easily installed in the sulfur pit with a variety of available process connections.

In situations with build-up, guided wave radars will continue to operate as intended. The VEGAFLEX 81, which uses either a rod or cable probe in sulphur pit applications, will only experience a slight slowdown of the microwave pulses traveling down the probe. The signal continues traveling along the probe, just at a marginally slower speed. This change alters the time of flight, and operators may notice a small measurement discrepancy – one which will be exacerbated at lower levels in the sulphur pit but minimised at higher levels. Fortunately, this inconsistency and the build-up can be accounted for, fixing the measurement.

The VEGAFLEX 81 guided wave radar uses a rod or cable probe to measure continuous level in the sulfur pit.

A guided wave radar installed in the sulphur pit will continue to experience more and more build-up until eventually, some of the build-up becomes too heavy and falls off. What’s left is the amount of build-up that will be on the probe for the life of the instrument. At this point shortly after the initial installation, operators can recalibrate the sensor to get a more accurate level reading throughout the entire measurement span.

VEGA guided wave radars like the VEGAFLEX 81 are ready out of the box and configured at the factory for the probe’s operating span. Users only need to install the sensor and go through the guided setup procedure to begin receiving accurate measurements within 2 mm. More difficult applications prone to excessive build-up only require the additional step of a recalibration once the sensor has been in use long enough to acquire the expected build-up.

The VEGAFLEX 81 continues to properly measure level despite any build-up on the sensor.

The VEGAFLEX 81 guided wave radar delivers a reliable and accurate level measurement in a critical application that poses a danger to any refinery operation if mismanaged. Guided wave radar provides a solution where other technologies struggle and even fail due to the heat, corrosiveness, and excessive build-up of the molten sulphur.

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