Gauging volume accuracy

January 1, 2007 By    

Developments in tank gauge technology could make the rubber mallets commonly used to whack recalcitrant rotary gauges back into calibration obsolete.

Fueling Technologies' MMC system installed atop vertical storage tanks provides users a host of mass measurement data via remote readings.
Fueling Technologies’ MMC system installed atop vertical storage tanks provides users a host of mass measurement data via remote readings.

A handful of devices around the globe are creating new thresholds of accuracy, accountability and ease of installation, especially at bulk storage sites. These systems are connected to remote-reading units that transmit data via radio waves, telephone lines or cellular networks.

A desire to produce a commercially viable, highly accurate gauge that doesn’t require tank purging or puncturing drove the Propane Education and Research Council to solicit research proposals in 2005. The response showed the technology is already entering the marketplace in the form of sonic-based systems and a technique that measures the weight of the stored propane. As a result, no funding was issued for the project.

A battery-powered tank send unit transmits mass measurement data from  the tank.
A battery-powered tank send unit transmits mass measurement data from the tank.

Based on preliminary interest in the new technology, the rotary gauge could go the way of the rotary telephone dial as the propane industry strives for greater accuracy.

A non-invasive sensor is advantageous because it is expensive to replace traditional level gauges due to the need to evacuate tanks, according to Greg Kerr, PERC’s director of research.

“The economics of propane distribution are greatly affected by the logistics of moving product between suppliers, a marketer’s wholesale distribution facilities, the marketer’s remote bulk facilities and the end-users of propane. Typically, inventory turnover through bulk storage comprises one of the least-defined and most difficult parts of a propane marketer’s inventory management cycle during high usage periods,” Kerr says.

Study of 2% error of level versus quantity
Study of 2% error of level versus quantity

“The propane industry will benefit financially through the reduction of inventory uncertainty in the installed base of bulk storage tanks through the availability of a low-cost non-invasive tank level sensor that will work with any telemetry system.”

Among the applicants for PERC funding were innovations applying the basic lessons of fluid/gas physics and a variation of the sonar initially developed for submarine warfare.

Two overseas companies – Andronics of Ireland and Switzerland-based Eurosonics AG – applied for PERC funds. Both firms have non-invasive gauge initiatives related to sonic-based technology. Neither responded to interview requests and their status in the American marketplace is unclear.

Xtero Datacom's communicator uncovered to show unit under snow cover in freezing temperatures. The company says the communicator performed well under snow as part of environmental tests at minus-30 degrees Celsius.
Xtero Datacom’s communicator uncovered to show unit under snow cover in freezing temperatures. The company says the communicator performed well under snow as part of environmental tests at minus-30 degrees Celsius.

The patent-pending Xact Tank Monitoring System from Xtero Datacom Inc., based in Vancouver, BC, Canada uses ultrasonic volume sensors, satellite data communications, the Internet and proprietary data management and reporting software to measure a tank’s contents.

A vestige of the submarine sonar technology originated to detect underwater objects such as approaching ships, the propane version “measures ‘time of flight,’ how long it takes the signal to go through the tank and return to the unit,” says David S. Peachey, company’s president.

“We’ve been working on this for approximately five years. We have developed the technology and have gone through the alpha testing and are starting the beta testing with propane marketers in January.”

Five unnamed retailers are reviewing the system in the United States.

An Xtero Datacom worker prepares the ultrasonic sensor for placement on the bottom of a 30,000-gallon propane storage tank. The satellite communicator and controller are at his feet.
An Xtero Datacom worker prepares the ultrasonic sensor for placement on the bottom of a 30,000-gallon propane storage tank. The satellite communicator and controller are at his feet.

“The first units being tested are for bulk tanks and are due to to hit the market by March. We will follow up mid-year with smaller commercial and residential tanks,” Peachey says.

He says the pricing has not yet been set, but notes that not having to empty, purge and flame a tank at a cost of about $3,000 before the first piece of gauging equipment can be installed is a particular plus.

“The tank does not have to be emptied,” he says. “It takes about 15 minutes to install; it’s all external.”

Extinguishing flare-offs

Ease of installation is among the selling points of the recently developed LPG-MMC system from Fueling Technologies Inc. of Woodinville, Wash., outside Seattle.

Product Benefits
Product Benefits

MMC stands for “mass measurement chamber,” which captures the weight of both liquid and vaporized propane to within an accuracy rate of 99.5 percent, according to FTI President Charles “Chuck” Northrop. The device is unaffected by variations in temperature or tank thickness.

The company started its MMC research and development process about two-and-a-half years ago and began selling the systems in May of 2005.

The system, comprised of a tube mounted next to the tank, processes this “mass” data by analyzing elements such as temperature, pressure and specific gravity to provide the level of liquid net gallons, vapor content net gallons, total net gallons, liquid gross gallons, vapor content gross gallons and total gross gallons along with date and time designations.

“One of its most significant values is that it allows you to upgrade your bulk storage sites without the need to wait for the slow season,” explains Northrop.

“With the MMC you no longer have to empty and flare off your tanks to allow for the gauge to be installed. It is simply a piping alteration with isolation valves; you even save the value of the propane that normally would have been flared off and lost.”

The system’s ability to provide precise measurements can benefit a propane marketer’s bottom line on several fronts, says Northrop.

“Whenever there are differences in the books between perceived inventory and accurate inventory, management must spend time accounting for the differences,” he explains, noting that miscalculations can result in volume figures that are either too low or too high in relation to your demand needs.

“When ordering in truck loads to maintain inventory it is not unusual for the marketer to have a number of ‘no fits’ each season. A ‘no-fit’ is where the transport cannot be fully unloaded as there is not enough room in the storage tanks for the load. They then must reroute the truck elsewhere, pay a rerouting charge, and pay for fuel they were unable to accept,” Northrop says.

“What is the value of knowing your true inventory in ‘tight’ markets so you can make the best purchase decisions,” Northrop ponders, citing an LP-Gas Magazine State of the Industry survey reporting that 69 percent of marketers purchase more than 25 percent of their propane on the spot market.

Easing shrinkage rates

Rockingham Cooperative in Harrisonburg, Va. started using FTI’s mass-based system in May of 2006.

“Now we can reconcile propane coming into the facility and propane going out of the facility. In the past that wasn’t possible,” says General Manager Irvin Armentrout.

“We operate a facility that has propane movement 24 hours a day. What prompted us to take the jump was an inventory control issue. We had shrinkage way in excess of what I thought was reasonable and acceptable.”

Rockingham moves 7 million to 8 million gallons a year. Each month, the usage figures were off by 200 to 800 gallons.

Armentrout is still unsure about what caused the discrepancies, but he’s quite pleased that since installing the new system the total variance has been less than 1,000 gallons over the past seven months.

In addition to bulk storage at the main office site, the co-op has remote storage 20 miles away. The FTI system, which includes radio frequency remote-monitoring capability, cost less than $30,000 to install.

“We’ve already gotten a payback on our investment,” Armentrout says.

“For the money, I don’t know any other way of doing it today,” says Armentrout, who has taken a keen interest in researching industry innovations. “I’m not afraid of going out there and looking for new opportunities to run a more efficient operation. We’re willing to adapt to new technology.”

Armentrout said the simplicity of the FTI system made implementation less intimidating.

“Few retailers are accounting for vapor inventory,” he points out. “That can be as much as 3,000 to 4,000 gallons in 90,000 gallons worth of capacity. With the float gauges there’s no way to account for that unless you do the long math, and most propane retailers aren’t doing that.”

He believes propane retailers no longer should accept vapor loss issues.

“If that were gasoline or diesel fuel (and that much was unaccounted for), someone would be wondering if it was getting into the ground water” through a polluting leak.

Viewing the future

Xtero’s Peachey believes that tighter inventory controls are the wave of the industry’s future, particularly when these systems are tied to monitors that allow you to view supply content levels from the office.

“You’re not sending someone out to read tank levels in a remote location – or even in your yard. You can reduce the number of distribution centers in favor of remote terminals,” he says.

One prospective customer in Kentucky concerned about employee safety is intrigued with the possibility of not having to build an array of meter-reading scaffolding, Peachey noted.

His satellite-based reporting system permits a storage site to remain unattended yet connected to headquarters. The tank can be monitored on an hourly, daily, weekly or monthly basis.

“It gives universal coverage worldwide. A lot of propane tanks are in isolated areas not served by a land line or even cell phones,” Peachey notes.

The system enables better monitor inventories, from large commercial users to residential accounts.

“You don’t have the fear of a tank running dry and losing that customer, which can be an expensive proposition,” he says. “You can also avoid filling a tank that’s more than half full.”

If a tank equipped with his system falls below a set level, it will send a voice mail or e-mail message. It also can send an alert when it hits 20 percent.

“The system allows you to have better scheduling of your deliveries, so you can cut down on your delivery costs or even use fewer bobtails,” Peachey says. “Your drivers can install it quickly and easily, and that’s a big cost savings.”

Power for the bulk system is supplied by a small, 7-volt battery that lasts up to two years; the residential units will run for five years before needing a new battery.

“We’ve invested a lot of money and a lot of time,” says Peachey. “The challenge is to bring the product in at the right cost. We believe the market will embrace this and see the value in the service.”

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