Fluxo Soluções
 / April 2012

Abreu e Lima: Flow/Rosemount will measure tank level

The Ipojuca Consortium, formed by the companies IESA and Queiroz Galvão, chose Fluxo and Rosemount Tank Radar, a division of the Emerson group, to supply the Tank Telemetry System (STT) for the offsite Abreu e Lima Refinery, where the storage tanks for finished products in raw materials. The supply comprises level gauges and associated equipment for 62 pressurized tanks and vessels for the storage of all types of product.

The choice of radar technology for the Abreu e Lima Refinery was a requirement of Petrobras. In fact, this is the fastest growing technology in the world for level measurement in all types of tanks, from onsite to offsite refineries. Represented by Rosemount Tank Radar, Rosemount Tank Gauging is the world leader in the segment of radars for storage, a fact that also occurs in Brazil, where its instruments are adopted in the absolute majority of Petrobras refineries. Two particularities stand out in this project:

The first is the use of a hybrid system. The level of a refinery's tanks varies over time, due to the change in product temperature, which causes expansion or shrinkage of the tank volume. To allow proper control of the tank inventory, it is necessary that the volume be brought to a reference temperature. In the case of petroleum derivatives, this calculation needs to take into account the average density of the product.

The usual way to obtain this density is to analyze a sample of product from the tank in the laboratory. This method is expensive and labor intensive. However, both API and ISO advocate an alternative method to obtain this density, through the so-called hybrid system. This system consists of associating the information from the level gauge with a high-precision pressure sensor, installed on the side wall near the bottom of the tank. With these two pieces of information, it is possible to calculate the average density of the product with an accuracy of about 0.5 Kg/m3, sufficient for API calculations and to derive the mass of product associated with the volume of the inventory. In addition to accuracy, this system has the main advantage of being standardized by ISO 15169 and API Ch 3.6 standards. Additionally, density measurement does not interfere with level measurement.

The second particularity lies in the use of a redundant configuration for both the concentrator units, called FCUs, which collect information from the level gauges, and the user interface program, called TankMaster, which performs inventory calculations, alarm history, trend chart, etc. This arrangement ensures greater reliability to the assembly, even in situations where some of the components fail, however unlikely this may be.

With the Rosemount level system, Abreu e Lima will be prepared for the technological challenges of the present and the future. The refinery is considered by Petrobras to be the most modern built in the country, with the capacity to refine 100% of heavy oil with minimal environmental impact, and to produce diesel with sulfur content below the strictest international standards today.

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