Storage terminal solves expensive metering problem

Feb. 23, 2016
Ultrasonic portable flow meter provides solution.

United Riverhead Terminal (URT) is located on the north shore of Long Island, 80 miles east of New York Harbor and was built in 1956.  All products are received and shipped via marine vessels that load and offload at a deep water platform located one mile offshore in the Long Island Sound.

The platform has two berths that can accommodate ships and/or oceangoing barges, including tankers with up to a 62ft draft, making Riverhead the deepest tanker port on the US east coast. The terminal routinely receives Suezmax class tankers and can accommodate very large crude carriers (VLCCs).

The terminal also operates a 60-foot work boat that transports employees, crews, and supplies to the platform. The work boat is also used for first response for emergencies and can deploy 3200' of sea spill boom that is stored on the platform. Both the platform and workboat also have foam firefighting capabilities. Riverhead's offshore platform is linked to the tank farm by two 24-inch submarine pipelines that connect to 20 tanks with combined storage capacity of 5.2 million barrels. The tanks range in size from 12,000 barrels to 580,000 barrels. Approximately half of the tanks are heated by a low pressure steam boiler system for use in storing heavy fuels, blend stocks, gas oils, and crude oil. The remaining tanks store distillate, gasoline, and crudes.

In November of 2012 Phillips 66 sold the Terminal to United Refining Company, and created a subsidiary called United Riverhead Terminal, Inc. Instead of proprietary storage, United Riverhead Terminal was now going to be used as lease storage. And that created some challenges for Kamm.

"When it was proprietary storage, all we needed to do was monitor the product and we used a multiple of tank gauging systems to do so, one being ENRAF (level) gauges, which were good enough when the transfers were internal," said Kamm. "But now we had become an independent middle man and needed accurate flow rates and barrel amounts."

Although United Riverhead Terminal can store an impressive variety of petroleum products, it's the ultra-low sulfur #2 oil and cutter stock oil that has created an expensive problem.

"To clean and segregate the customer products we use an off-spec #2 cutter stock oil that is stored at the facility" said Kamm. "When we transfer clean ultra-low sulfur #2 oil we have to make sure that there is no remaining cutter stock oil in the pipelines. The terminal personnel make sure a clean cut is made before switching into its customers clean ultra-low sulfur #2 oil storage tank.  Any clean ultra-low sulfur #2 oil that was displaced into our cutter stock tank, the terminal has to purchase from the product owner, which can get very expensive" said Kamm.

The problem was using only tank gauging as an indicator for product amounts. The tank gauging system only gave approximate flow rates so operators would need to start taking samples of the product to tell by color and viscosity when the interface was nearing the valve manifold for switching tanks. A much more accurate flow reading was mandatory.

Enter Kamm's neighbor and business associate, John O'Brien, with a great solution.

Kamm told John of his problem, knowing that he was the Vice President of Flexim Americas, a manufacturer of ultrasonic flow meters.

"The flow meters I knew of couldn't accurately identify the difference between two different fluids without cutting into the pipelines, installing expensive meters, and gravitometers (interface detection device)," said  Kamm. "I asked John if ultrasonic meters could distinguish between the different oil products by giving us gravity, flow rate, and temperature without cutting into the pipelines."

How ultrasonic meters work

The technique most ultrasonic flow meters use is called transit-time difference. It exploits the fact that the transmission speed of an ultrasonic signal depends on the flow velocity of the carrier medium, kind of like a swimmer swimming against the current. The signal moves slower against the flow than with it.

When taking a measurement, the meter sends ultrasonic pulses through the medium, one in the flow direction and one against it. The exterior transducers alternate as transmitters and receivers. The transit time of the signal going with the flow is shorter than the one going against. The meter measures the transit-time difference and computes the average flow velocity of the medium. Since ultrasonic signals propagate in solids, the meter can be mounted directly on the pipe and measure flow non-invasively, eliminating any need to cut the pipe.

A meter designed for petroleum products

"Scott's question was timely," said O'Brien. "We had recently brought to market an ultrasonic meter designed specifically to meet the challenges of the hydrocarbon processing industry.  Hence, its name -- Flexim HPI. The key to the success of the design is specialized firmware that acts like a mini flow computer. It takes the temperature and pressure input and it has tables loaded in it for industry standards for hydrocarbons including TP25 -- the industry standard that defines the characteristics of light hydrocarbons such as propane and butane, ASTM 1250 -- the standard that defines the characteristics of refined fuels such as automotive gasoline, diesel, and jet fuel, and D4311 -- the standard that defines the characteristics of heavy products such as asphalt. The meter calculates density and the correction factors for temperature and pressure as defined by these documents and has the algorithms necessary to calculate net volume. Instead of just an actual flow rate for barrels, the HPI meter will provide a net flow rate for volume corrected for temperature and pressure using industry-standard algorithms. That makes the HPI an ideal meter for precisely detecting the interface between ultra-low sulfur #2 oil and the thicker cutter stock oil."

Testing for accuracy

Kamm liked what he heard and wanted to see the meter in action for both interface detection and check metering. He was expecting a delivery of ultra-low sulfur #2 oil from a vessel that Sunday, so O'Brien brought an HPI portable with him to the Terminal and the two of them installed the meter at a precise location in the manifold.

"We quickly installed the dual beam HPI flow and interface meter onto a 22-inch carbon steel line to monitor a vessel off-load of ultra-low sulfur diesel and to evaluate the potential for URT to be able to use the meter for both interface detection to minimize the amount of downgraded #2 oil and provide accurate check metering for total net (STND) volume of product and cutter movements," said O'Brien.

"The portable flow meter data logged all flow rate/total (standard and gross), temperature, API #, and numerous advanced diagnostics at a 15 second interval during the vessel offload of approximately 59,297 standard barrels of ultra-low sulfur diesel.  The meter determined that the API value changed from 22 (cutter stock) to approximately 36 ultra-low-sulfer diesel (ulsd).  This was detected after approximately 4,000.84 barrels of cutter stock was displaced.  URT personnel began to sample at a higher rate at this time to validate the interface had indeed occurred.  The interface did occur and the pumps were shut down, and valves adjusted to allow for the clean #2 oil to be pumped into its appropriate storage tank.

"Next, after the complete discharge from the vessel, the remaining #2 fuel oil in the pipeline between the vessel and storage tank was "pushed" into product storage tank by the cutter stock oil.  Flexim's portable flow meter data logged all vital flow data at 10-second intervals during cutter "push" process.   Approx. 3,846.34 standard bbls of number two oil was "pushed" into the tank by the cutter oil during the approximately 50 minute cutter stock push process."

"The HPI meter was successful in both exactly identifying both of the interfaces," said Kamm. "That information allowed us to significantly minimize the amount of #2 oil that was downgraded. The meter also provided accurate real-time flow rate, total volume (STND BBLS) of product, and temperature. That saved us between 1,500 and 2,000 barrels in interface which translates into huge savings. The meter paid for itself in its first use. Naturally, we purchased the meter. That should translate to an annual savings of about $750,000. And that savings will increase as we begin storing other types of hydrocarbon products and come to full capacity."

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