VISCOSITY MEASUREMENT IN ASPHALT BLENDING PROCESS

SUMMARY

Instantaneous softening point information results when VISCOLINER® measures viscosity in a vacuum tower or inline asphalt blending process. Oxidation of hot asphalt is required in order to meet specifications for roofing, paving ink and other applications. Process development is under way which relates bottoms viscosity composition and vacuum tower efficiency.

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. 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 of the sensor to prevent hardened slugs of asphalt from striking the probe. 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 sensors on startup to melt solid plugs. Wedging a slug between the pipe wall and sensor must be avoided. Care should be taken to start up transfer pump only after asphalt is fully melted.

TEST

Ring and ball softening point data correlates well to process viscosity. Waiting for laboratory test results is no longer required and continuous adjustment (or closed loop control) ensures product quality. Care must be taken to check viscosity index (VI) when crude oil sources change.

TYPICAL OPERATING CONDITIONS

Temperature: 250°F to 500°F

Pressure: Partial Vacuum to 60 psig

Viscosity:10 to 10,000 cP x g/cm3

SPECIFICATION

Temperature: -40°F to 850°F

Pressure: Vacuum to 5000 psig

Viscosity: 0.1 to 1,000,000 cP

Materials of Construction: 316SS

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