Flow Measurement at a Storage Terminal
United Riverhead Terminal (URT) is located on the north shore of Long Island, 80 miles east of New York Harbour 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). URT's offshore platform is linked to the tank farm by two 24" 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 are heated by a steam boiler system for use in storing heavy fuels, blend stocks, gasoils, and crude oil. The remaining tanks store distillate, petrol and crudes.
When the terminal was boughth in 2012 by United Riverhead, it changed from a previously proprietary storage to a rental storage and that created some challenges for the terminal manager. When it was proprietary storage, all what was needed to monitor the product were level gauges that gave virtual time lagged flow rates, which were good enough when the transfer was internal. But now, as the terminal had become an independent middle man, it needed an accurate flow rate monitoring.
Although the terminal can store a variety of petroleum products, it is currently only storing two: number two and number six oil. And it is the number six that has created an expensive problem.
When number two oil is transfered, they have to make sure there is no remaining six in the system. To clean the line off, off-spec number two cutter oil that is already contaminated with six is used. It is heated to 49 °C, stored in the pipe and then pushed through the piping when clean number two oil arrives. When the off-spec oil gets to the slop tank, the valve is opended and the cutter oil is directed out of the pipe. When it is all stored, the valve is closed and the pure number two oil is directed to its storage site. When the pure number two oil is mostly stored, the cutting oil is reintroduced to "push" the last of the clean number two into the storage tank, removing the cutting oil to the slop tank in the same way.
The problem was with the existing level gauges. They only gave virtual flow measurement so operators could start taking samples of the product to tell by color and viscosity when the interface was nearing the valve. Now, according to the rental agreement between United Riverhead Terminal and its customers, all of the oil that became contaminated with the cutting oil had to be purchased by United Refining. A more accurate flow reading was mandatory.
A meter designed for petroleum products
FLEXIM non-invasive HPI flow meter - specifically engineered to meet the challenges of the hydrocarbon processing industry - was the answer. The key to the success of the meter design is the internal 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 propaneand butane, ASTM 1250 – the standard that defines the characteristics of refined fuels such as automotive petrol, 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 meter will provide a net flow rate for volume - corrected for temperature and pressure - using industry standard algorithms. That makes the HPI meter an ideal meter for precisely detecting the interface between number two oil and the thicker cutter oil.
At the United Riverhead Terminal, for first testing purposes a dual beam HPI flow and interface meter was installed onto a 22" carbon steel line to monitor a barge off-load of low sulphur number two fuel oil and to evaluate the potential for URT to be able to use the meter for both interface detection to minimize the amount of downgraded number two and provide accurate check metering for total net (STND) volume of product and cutter movements.
The flow meter data logged all flow rate/ total (standard and gross), temperature, API number and numerous advanced diagnostics at a 15 second interval during the barge offload of approximately 59,297 standard barrels of fuel oil. The meter determined that the API value changed from 22 (cutter) to approximately 36 (fuel oil). 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. It had and the pumps were shut down, the cutter oil was stored in its tanks and valves adjusted to allow for the fuel oil to be pumped into its storage tank.
Next, the remaining number two fuel oil in the pipeline between the barge and storage tank was pushed into product storage by cutter oil. FLEXIM's HPI flow meter data logged all vital flow data at 10-second intervals during cutter pushprocess. Approximately 3,846.34 standard barrels of number two oil was 'pushed' into the tank by the cutter oil during the approximately 50 minute cutter push process.
'The HPI meter was successful in both exactly identifying both of the interfaces,' reveals the URT operator. 'That information allowed us to minimize the amount of number two that was downgraded. The meter also provided accurate real-time rate and total volume (STND barrels) of product and cutter movements.
'That saved us between 1,500 and 2,000 barrels in contaminated oil which translates into $30,000 (€22,000) in savings. The meter paid for itself in its first use. Naturally, I bought one and we're using it on every transfer. 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.'