VISCOSITY MEASUREMENT - Automatic Blending
of Fuel Oil and Other Refinery Operations
SUMMARY
Refinery operations that require viscosity control include Marine Fuel Oil (MFO) blending, Lube Oil blending, Diesel and Bunker Fuel blending, and vacuum tower bottoms or residual material measurements for improved tower efficiency. Because heavy fuel and residual materials have large viscosity/temperature co-efficients, temperature controlled sample loops are often preferred to measure product quality near product specification temperature. When refinery operations are equipped with advanced control systems, engineers may take advantage of Nametre VISCOLINER® features to measure precise viscosity at extreme temperature conditions. Then calculations based on process viscosity can be made to confirm that final product meets specification or to model the refinery operation of interest.
INSTALLATION
Pipeline installation of the VISCOLINER® transducer using standard ANSI flange connections and mounting in an elbow ensures good sample exchange. Steam or hot fluid jackets with insulation ensure minimal heat loss and avoid hardened asphalt collection in the sensor area. An RTD, integral with the viscosity sensor, measures temperature in real time and also guides sensor removal on shutdown. Sensor mounting to a flow-through cell with Class 300 ANSI rated flex hose damps any mechanical shock and pipeline vibration. The VISCOLINER® transmitter is located in a control room up to 1000' from the transducer. A static mixer can be used upstream to homogenize material, eliminate temperature gradients, and to prevent solids from wedging between the pipe wall and sensor. Alternately, a sensor guard may be used or baffle plates should be installed upstream and downstream. Isolation valves should be installed upstream and downstream of the sensor to facilitate sensor removal if heat is lost or line is to be shut down.
OPERATION
Continuous purging of the transducer dome with nitrogen or dry instrument air excludes moisture and allows operation at higher temperatures. On shutdown, sensors should be removed and cleaned. Check instrument calibration once a year. Avoid stagnant flow at high temperature to eliminate coking. Heat-soak the local pipe on startup to melt solid plugs. Wedging a slug between the pipe wall and sensor must be avoided.
TEST
Validation to ASTM D 445 capillary methods should follow procedures described by ASTM designation D 3746. Care must be taken to check viscosity index (VI) when crude oil sources change. Inherent precision of VISCOLINER® technology permits more narrow upper-lower control limits compared to other viscosity methods. Reduced use of more expensive cutter stocks and/or more efficient tower operation is the result.
TYPICAL OPERATING CONDITIONS
Temperature: 250°F to 500°F
Pressure: Partial Vacuum to 60 psig
Viscosity: 5 to 5,000 cP x g/cm3
VISCOLINER® SPECIFICATION
Temperature: -40°F to 850°F
Pressure: Vacuum to 5000psig
Viscosity: 0.1 to 1,000,000 cP
Materials of Construction: 316SS
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