The petrochemical industry is recognised as one of the most dangerous and difficult environments to work in and instrumentation suppliers know full well that the biggest challenges to their expertise and products will be encountered among a maze of pipes and columns containing hard-to-handle and mostly dangerous media at extreme temperatures and pressures.
Of course, most instrumentation suppliers will know that if you prove your product in the petrochemical environment, you are more than halfway down the road of establishing your brand as a leader in its market segment.
The popularity of magnetic level control equipment has grown significantly in recent times, and more engineers and technicians than ever before recognise the potential of this technology to solve level control problems previously thought unsolvable.
To illustrate the superiority of magnetic level control over, say, level control using a differential pressure transmitter, the following specific example would be a good case in point:
During the second half of last year the technicians at SSF in Secunda approached Kübler Africa, a local specialist, to find a solution for level control on a knock-out vessel in their plant. The process conditions in this particular vessel are of such a nature that the only equipment that was anywhere close to being reliable was a DP cell with capillary connections.
The accurate and reliable control of the level in this drum is of paramount importance; if any oil is carried over to the downstream process, serious compressor damage and even failure could occur. The DP cell arrangement, although functional most of the time, was regarded as unreliable and prone to cause stoppages and false trips, especially during winter months due to the inherent problems associated with capillary systems on sub-zero applications.
In addition, the visual verification of the level inside the drum was very difficult due to the icing-up of the sight glass, and the process personnel had to climb 15 m up a steel ladder to periodically check the level equipment.
The data brief given to this supplier showed the low temperature of -95°C at a pressure of 2,5 MPa (25 bar), with the presence of semi-frozen oil with the consistency of cold syrup. But by far the most challenging factor was the operating density of the medium: 400 kg/m3. Most magnetic level indicators cannot function at such a low density, as a magnetic float of reasonable length, say up to 450 mm, will simply not float.
Some suppliers do offer floats for extremely low densities, but these are usually low-tech, low-cost units with inferior magnetic systems that are extremely lightweight. Of the more reputable suppliers possessing high technology magnetic systems, it is believed that only one manufacturer is able to offer a differentially compensated float. The main advantage of these floats is that they can be very short, down to 150 mm, and still float at SGs down to 350 kg/m3.
The test unit, installed in November 2000 with on-site assistance from the supplier, showed positive results just a few days after commissioning. In the weeks and months that followed, various minor modifications to the magnetic unit were made at the request of the technicians and production personnel on site. Three months after installation, the new unit was accepted by the customer and payment was authorised.
The decision to accept the magnetic bypass was based on reliability, the elimination of unit trips and the very stable control signal that was previously thought impossible on this particular application. An added bonus was that the level of the medium was now visible from ground level, made possible by the magnetic bar graph, eliminating the need for process personnel to climb 15 m to view the sight glass.
Subsequent to the first installation, a second, more expensive magnetic bypass has been purchased by the same customer for a similar application. This second unit is the single most extensively customer engineered magnetic bypass ever sold by Kübler in South Africa, and illustrates the confidence in the projected savings calculated by the end-user in spite of the initial purchase price.
Johan Steyn is Managing Director of Kübler Africa. He is also the present Chairman of the South African Institute of Measurement and Control (SAIMC), Johannesburg Branch. He is a factory-trained Kübler product specialist and has been marketing and selling the KSR Kübler range in South Africa for almost eight years.
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