Non-intrusive ultrasonic flow meter provides solution to expensive metering problem. Contributed by Oliver Foth, head of marketing, Flexim.
The United Riverhead Terminal is an impressive facility located on the North Shore of Long Island, 80 miles east of New York Harbor and was built in 1956. Most 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 terminal is also equipped with a truck loading rack to supply home heating oil to eastern Long Island homes.
The offshore platform has two berths that can accommodate ships and/or ocean going barges, including tankers with up to a 62-foot 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 3,200 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. Instead of proprietary storage, United Riverhead Terminal was now going to be used as lease storage. And that created some challenges according to the Terminal Manager, Scott Kamm:
“When it was proprietary storage, all we needed to do was to monitor the product and we used a multiple of tank gauging systems to do so, which were good enough when the transfers were internal. But now we had become an independent middleman and needed accurate flow rates and barrel amounts.”
Although United Riverhead Terminal can store an impressive variety of petroleum products, it is the ultra-low sulfur #2 oil and cutter stock oil that have created an expensive problem. To clean and segregate the customer products, the terminal uses an off-spec #2 cutter stock oil that is stored at the facility. When it transfers clean ultra-low sulfur #2 oil, the terminal has to make sure that there is no remaining cutter stock oil in the pipelines and a clean cut is made before switching into its customers clean ultra-low sulfur #2 oil storage tank. Otherwise, any clean ultra-low sulfur #2 oil that is displaced into the cutter stock tank, has to be purchased at an expensive price from the product owner.
The problem was that only tank gauges have been used as an indicator for the product amounts. These tank gauges only gave approximate flow rates so that the operators would need to start taking samples of the product to tell by colour and viscosity when the interface was nearing the valve manifold for switching tanks. A much more accurate flow reading and interface detection was mandatory.
Until then, the terminal operator was only aware of intrusive measurement technologies that could accurately identify the difference between two different hydrocarbons. As cutting into the pipelines was not an option due to the necessity of a costly interruption of the process, Riverhead terminal was looking for an alternative.
Flexim, a manufacturer of non-intrusive ultrasonic flow meters and process analysers provided such an alternative. The company’s HPI meter could fulfill all requirements set by the terminal, such as being completely non-intrusive, clearly distinguishing between the different oil products by measuring their specific gravity as well as providing accurate mass flow rate and media temperature data.
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 Identifying Petroleum Products
Besides just measuring the flow rate, the company’s HPI additionally makes use out of the fact, that many liquid media, including hydrocarbons, can clearly be distinguished by their sonic velocity.
By measuring the sonic velocity, taking into account the individual temperature and pressure of the media and aligning this data with industry standard tables loaded into the meter, 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 HPI meter calculates density, mass flow rate and unambiguously identifies the medium flowing inside the pipe.
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
For first testing purposes at the Riverhead Terminal, the company quickly installed a 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 the Terminal to be able to use the meter for both interface detection to minimise the amount of downgraded #2 oil and provide accurate check metering for total net (STND) volume of product and cutter movements.
The 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-sulfur diesel (ulsd).
This was detected after approximately 4,000.84 barrels of cutter stock was displaced. The Terminal 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.
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. The company’s HPI flow meter data logged all vital flow data at 10-second intervals during cutter ‘push’ process. Approximately 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.
According to Mr Kamm: “The HPI meter was successful in exactly identifying both of the interfaces. That information allowed us to significantly minimise 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 US$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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