By Rich Merritt, Senior Technical Editor
loat gauges continue to be one of the most widely used level technologies, for one simple reason: They work. And, even though the technology is older than the fruitcake you got for Christmas this year, float gauges handle tough applications and severe environments as well as any other level meter on the market.
K-Tek’s KM 26 float level sensor is such a device: it mounts on the outside of a tank or vessel, has a visible glass section with a float, and a magnet that tracks the float. An operator or technician can read the level locally, just by looking at the indicator. Thousands of similar devices are installed on tanks all over the world.
To bring this technology into the modern world, which requires remote level sensors that can talk to DCSes, K-Tek offers the AT200 transmitter, which mounts onto a KM 26 and transmits a 4–20 mADC level signal with a HART interface.
But is this really an improvement? Is it like putting a diamond tiara harness on a plowhorse? Or 20-in. chrome rims on a four-door Cavalier? Or is it more like polishing a jewel? We asked a few end users why they continue to use this technology in the 21st Century.
“Simply, it works,” says Austin Reed, Controls Owner in the Amines Dept. of Procter & Gamble, Kansas City, Kansas. “I have tried most available level technologies, and none have proven as reliable. It seems that, as the technology increases, the instruments become more application-specific. Thru-air radar may work very well in one tank, and not in another containing the same product, even with everything else being the same.”
“If K-Tek's float will float in your media without sticking problems, then you will have a very â€˜forgettable’ level transmitter,” says Tom Jarrett, Instrument Specialist at Degussa/Jayhawk Fine Chemicals, Galena, Kansas. Jarrett uses K-Tek sensors and transmitters on various process storage tank, receiver vessel, and tower sumps, some containing corrosive media. “The external transmitter is mounted on an existing chemically compatible chamber, making that issue a â€˜non-problem,’ ” explains Jarrett.
“We have them all over our refinery,” says David Land, P.E., Refinery Instrument Engineer at ConocoPhillips Ponca City Refinery, Ponca City, Okla. “They are on the crude and vacuum tower bottoms, and on various other towers in all kinds of service from water to hydrocarbons. We also have them in high pressure applications (600+ psig) and even HF acid applications, where we replaced all the old style gauge glass gauges for safety reasons.”
Although it is a simple, straightforward level sensor, a float gage handles tough applications better than some modern sensors, and it has all the accuracy needed for most applications.
“My first experience with the transmitters was with an application on three knock out vessels on a high pressure ethylene compressor,” explains Dave LeMoine, Instrument Inspector at Shell Chemical, Geismar, La. “DP type transmitters were unreliable, due to the physical properties of ethylene at high pressure and the relatively small span of about 14 in. w.c. We noticed the K-Tek gauge already on the vessels tracked the level with no problems so we decided to mount transmitters on the existing gauge and noticed more accurate and repeatable readings ever since.”
“The reason that we use it here is that no other manufacturers could handle the range of environments that this unit is exposed to,” says P&G’s Reed. “The unit can see pressures from 30 psig to 60 mmHg vacuum, and from 150–350° F. These extremes ruled out standard DP level gauges. Ultrasonics could not handle foaming, thru-air radar proved unreliable, and guided-wave radar was not a proven technology at the time of installation. With the current track record of the KM26, why mess with success?”
Land agrees. “We experimented around with them in the â€˜90s, now we know they will work in most cases,” he says. “We have over 241 KM26s in service at this refinery alone. They are also in use all over ConocoPhillips. Basically, we have standardized on using KM26 gauges for most level gauge applications, especially if there are any safety reasons to consider like high pressure or hazardous materials.”
Hazardous materials pose operational and maintenance problems, but the float sensor appears to be up to the task. “The AT200 and the KM26 are used in both severe service and vented tanks depending on the properties of the fluid,” says Reed. “The KM26 is used in applications that require that the system remain sealed. I also have applications that require the system be evacuated for any maintenance so the AT200 is installed in a sealed dip tube with the float being the only piece to actually see the process fluid. This allows maintenance on the transmitter/waveguide while the tank is full.”
“It's a sealed system, no gaskets to leak, no valve packing to leak,” offers Land. “Much safer and much fewer leak paths. The new EPA LDAR [Leak Detection and Repair] rules have forced us to minimize all potential leaks.”
“In my operation, as in so many others, reliability is the driving force,” says Reed. “I need every pound of production that I can get, and that can only be done if the system is operating. For me reliability is key, then accuracy, then ease of use, and finally good technical support. Cost is secondary. If the unit works reliably, is reasonably accurate, and has options regarding installation, then I'm good to go.”
“I'm in the â€˜responsible’ seat when it comes to meeting production's instrumentation needs for a reliable and cost-effective device,” says Jarrett. “If a K-Tek device meets the application specifications, I know we will get a trouble-free best bang for my company's buck. “It is also a plus that our I&E technicians are all familiar with K-Tek setup and installation. If a float will work, I'll put in a K-Tek.”