Radar level measurement solves problem for BP

An existing displacer transmitter on a vacuum distillation column at the BP Oil Coryton refinery in Essex has been replaced with an HT (High Temperature) Eclipse guided wave radar system

An existing displacer transmitter on a vacuum distillation column at the BP Oil Coryton refinery in Essex has been replaced with an HT (High Temperature) Eclipse guided wave radar system to solve a very expensive problem.

The Eclipse system from Magnetrol International is based upon the technology of TDR (Time Domain Reflectometry) which uses pulses of electromagnetic energy transmitted down a probe.

When the pulse reaches the process surface that has a higher dielectric than the air/vapour through which it is traveling, it is reflected.

An ultra-high speed timing circuit measures the transit time precisely and provides an accurate measure of the level being checked.

The Displacer Transmitter, which has been installed on the Coryton vacuum distillation column to control the overflash residue levels in the base of the vacuum column, was producing several severe problems.

The first instinct of BP Oil engineers was to consider alternative level measurement technology, such as Neuclonics.

However, Eclipse was demonstrated and has been found to solve the problems, with the added benefits of easy installation and much lower unit cost.

In fact by fitting the Eclipse system instead of Neuclonics, BP Oil has achieved cost savings in the region of £50,000, when taking into account the need for alterations to the steelwork for access.

The operating temperature of 345C dictated that the 7MD high-temperature transmitter was needed as well as gas oil flushing purge to keep coke deposits clear.

If the bed level within the column becomes empty and 'cokes-up', it costs at least ?500,000 to rectify.

Following installation and pre-commissioning trials, a further problem was discovered in that the reading obtained during gas oil purge produced a very unsteady output.

A Magnetrol service engineer checked the installation and settings, only to find that all was in order.

In fact, to prove that the Eclipse was operating correctly, the chamber was isolated from the column and then filled with gas oil fully to the top connection.

The Eclipse followed the level up and then down again as the chamber was drained.

Once the chamber was empty, the output again became unsteady but when the gas oil purge was shut off, the signal became steady again, indicating that there was a small level present in the bottom of the chamber.

This was then proved by opening the drain to allow the remaining oil to drain away.

The conclusion was that the gas oil purge was 'flashing' within the chamber, (361degC was indicated in the control room), the level was also rising and dropping away at a rapid rate with the Eclipse trying to follow.

When a true level was introduced, the instrument was able to follow the liquid surface and provide true readings.

It was decided to stop the gas oil purge which had been carried out to keep the bottom connection of the chamber clear as there was enough heat in the chamber to stop any blocking.

The readout was thus stabilised and the commissioning trials commenced.

Eclipse guided wave radar level transmitters are available with probe lengths from 60cm to 610cm, with maximum temperature / pressure ratings of 50 bar at +20C and +200C at 13 bar.

They have CENELEC intrinsically safe approvals with Eex ia IIC T4, explosion proof EEX d (ia) IIC T4.

Eclipse incorporates HART communications as standard which ensures the flexibility of remote calibration on trouble-shooting over the same two wire pair in the 24V DC loop.

The same model suits general purpose and intrinsically safe installations, the difference being that an approved barrier needs to be installed in intrinsically safe operations.

The explosion proof version incorporates an on-board barrier that produces an intrinsically safe probe circuit into the vessel.

Following the success of applications such as the BP Oil Coryton Refinery, Eclipse is becoming established as a preferred technology.

Consequently, further orders for Eclipse are being secured as GWR technology is being applied to other applications.

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