The cost of waiting to upgrade
We’ve all had that car, appliance, or tool we just refuse to toss out. It works just fine. It just requires a little work or a quick fix every so often. At the time, we rationalised our decisions – a new one just wasn’t in the budget and all those quick fixes never took too long. But long ago, those maintenance costs added up to the cost of an upgrade without us even realising it.
The same can be said about displacer technology at many refineries around the world. This is a mechanical technology using a torque tube or spring loaded float to measure liquid level or interface. The internal mechanical parts experience metal fatigue, and they require regular recalibration. Displacers are also prone to failure due to vibration, turbulence, or just getting stuck in many of the more demanding applications found around the refinery. The amount of time spent cleaning, maintaining, and replacing these instruments adds up.
Retrofitting new technology to replace the old
Replacing displacer technology with an electronic sensor alternative would be the ideal solution to stopping the merry go round of maintenance and cleaning. A guided wave radar is typically the best option for replacing these sensors because displacers are installed in a displacer cage resembling a bridle, bypass chamber, or pipe. Unfortunately, not all displacer cages are created equal, and retrofitting these instruments with a guided wave radar isn’t a one size fits all solution.
Displacer cages come in four different configurations: side to side, side to bottom, top to bottom, and top to side. Configurations without a pipe coming from the top – side to side and side to bottom – can easily be retrofitted. It’s simply a matter of removing the displacer electronics and float and installing a new, more reliable guided wave radar and a necessary flange. The other two configurations containing a pipe at the top require a little more creativity and finesse.
Figure 1. Four different displacer configurations.
Installing a standard guided wave radar in a displacer cage with piping coming in from the top – top to bottom or top to side – just isn’t cost-effective. A refinery would need to free up a process connection at the top of the displacer cage by rerouting piping, an expensive and time-consuming endeavour before a new instrument is even installed and operational. Fortunately, there’s a more economical solution that provides reliable results.
Upgrading pays for itself in less maintenance
A large refinery on the US West Coast had a failing displacer with a top to bottom configuration on their naphtha reboiler. This refinery has a total refining capacity of 120 000 bpd and supplies gasoline, jet fuel, and diesel fuel to the local transportation market and manufactures heavy fuel oils, liquefied petroleum gas, and asphalt for export. The constant maintenance and repairs related to this displacer were adding up, chipping away at the productivity and efficiency of the facility. It was time for a permanent fix.
VEGA, a global manufacturer of process measurement technology, was able to provide the creative, long-term solution this refinery needed without reconfiguring the overhead piping. The VEGAFLEX 81 is a guided wave radar, and customers can order this sensor with a 90° bent rod segment. This way, the piping above and below can remain intact, and maintenance crews only need to install the new guided wave radar where the displacer once was.
Refinery maintenance crews were able to install and calibrate the new guided wave radar in a single maintenance shift during a planned shutdown. Since then, the VEGAFLEX 81 has been working reliably and maintenance-free. This has not only saved the refinery time and money, but they’re now getting a more reliable measurement on their naphtha reboiler.
Refineries have a number of displacers they’re using for level measurement. Unfortunately, displacers are mechanical measurements, so even when they’re working properly, it takes a lot of labour and time to keep them reliable and functional. The single displacer at the West Coast refinery mentioned above needed maintenance every six to eight weeks. This additional work was adding up quickly.
Retrofitting displacer technology with guided wave radar sensors requires a fraction of the time and cost of maintaining old displacers. When refineries are willing to pause for a moment to take the long view, they may just find they can get a big return on investing in upgrades today. Newer level measurement technology will allow them to operate more productively, efficiently, and competitively for years to come.
Author: Tai Piazza, Industry Manager - Refining, VEGA Americas
Read the article online at: https://www.hydrocarbonengineering.com/special-reports/13032019/upgrading-measurement-technology-eliminates-costly-maintenance/