Summary for the RR1 example simulation

Vacuum transfer lines (VTL) route atmospheric column bottoms from the vacuum charge heater to the vacuum column. VTLs are generally very large in diameter, have a low pressure drop, and are constructed of costly materials to withstand severe operating conditions of high temperature, erosion from high velocity, and experience a large thermal expansion load. Hydraulic calculations for VTLs are generally very tedious and involve critical flashing flow. Hence, the use of conventional two-phase flow software is limited due to the continuous change in vapor-liquid ratios and the fluid properties through the length of the line.

SimSci has developed a specialized simulation in AVEVA Process Simulation to simulate a vacuum transfer line to avoid tedious iterative calculation techniques. AVEVA Process Simulation uses its VLE thermodynamics to generate vapor and liquid ratios and fluid properties. It calculates the two-phase pressure drop using the Beggs and Brill two-phase flow pressure drop method with SimSci’s modification for high velocity flow (BBMHV).

The objective of this simulation is to:

• Design a vacuum transfer line from the vacuum charge heater discharge to the vacuum column flash zone that meets process engineering design requirements.

• Generate pressure and velocity profiles by using the AVEVA Process Simulation Excel add-in.

The simulation includes:

• Segmented pipes (TPPipe) that calculate the two-phase pressure drop in each pipe segment. Each pipe segment:

  • Calculates a two-phase friction factor based on the Beggs and Brill Moody High Velocity algorithm (BBMHV), which applies an acceleration pressure drop term.

  • Calculates the two-phase critical velocity by using the method from Hewit and Semeria. If the flow is critical, AVEVA Process Simulation calculates the critical pressure discontinuity in the final pipe segment.

• Pipe enlargers that calculate the pressure recovery due to fluid acceleration.

The following figure illustrates the VTL system as modeled in AVEVA Process Simulation.