Project Synopsis

Computer process simulation and preliminary process design of a Vacuum Distillation Unit for preliminary capital budget use. Simulation Diagram

Project Summary


The client owns and operates a small, independent petroleum refinery.  Recent tightening of customer metals requirements for the refinery gas oil products caused the client to consider installing a vacuum distillation unit (VDU) for decreasing gas oils metals content.  Process Engineering Associates, LLC (PROCESS) was contracted to execute a computer process simulation and preliminary process design for the VDU for the purpose of providing information to the client that could be used to formulate a preliminary capital budget for purchase and installation. 

Project tasks included:

  • Development of a process design basis
  • Preparation of comprehensive process simulations of VDU operation for two separate design cases
  • Execution of hydraulic calculations for determination of VDU approximate dimensions
  • Preparation of a preliminary process design report.

For the preparation of the process design basis, PROCESS instructed the client to obtain boiling point curves for the gas oil feed streams (#4 oil, or heavy gas oil from the bottom of the atmospheric crude tower; and #6 oil, or black oil, from the bottom of the crude unit preflash tower).  Due to the heavy nature of the feed streams, PROCESS recommended that High-Temperature Simulated Distillation (HTSD) be used as necessary to ensure that complete boiling point curves were obtained.  PROCESS used the boiling point curves; feed temperatures, pressures, and gravities; and the light vacuum gas oil (LVGO) product and heavy vacuum gas oil (HVGO) product desired endpoint temperatures as the design basis for the project.  PROCESS regressed the boiling point curve data using licensed commercial process simulation software for the purpose of producing normal boiling point (NBP) pseudo-component characterizations of the #4 oil and #6 oil feed streams.

PROCESS then used the process simulation software to construct comprehensive process simulations for the following VDU operating scenarios:

  • Case 1 – HVGO production from a feed stream of 100% #6 oil
  • Case 2 – LVGO and HVGO production from a feed stream of 31% #4 oil and 69% #6 oil (by volume).

The process simulation cases were used to determine: VDU vapor and liquid flow traffic; product flow rates, compositions, temperatures, and pressures; fired pre-heater duties; product pumparound flow rates, heat exchanger duties, and return temperatures; overhead vacuum/condenser system loadings; stripping steam and stripper section quenching requirements; product heat recovery potential; and tower mass and heat transfer section heights.

Separate calculations were performed to determine overall VDU tower height (based on knowledge of, and experience with similar units) and tower diameter (based on packed tower hydraulic/flooding relationships).

The information resulting from this project, including simulation software generated process flow diagrams, was summarized in a project report submitted to the client.

Industry Type

  • Petroleum Refining

Utilized Skills

  • Front end engineering design (FEED)
  • Vacuum distillation unit design
  • Computer process simulation
  • Petroleum feedstock characterization
  • Fired heater design

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