Process Simulation

In the oil & gas production, midstream transport and processing, refinery processing, petrochemicals, and bulk chemicals industry sectors, process simulation is a widely used software application. It is employed to optimize process designs and to provide a foundation for the design of key process equipment. Today, process simulation is also often deployed to optimize process operations in the face of many challenges, including:

  • Changing feedstock composition and flowrates
  • Analyzing the effects of process upsets
  • Helping to devise control and operating strategies to achieve product specifications
  • Minimizing energy consumption
  • Assisting in tracking emissions to meet regulatory requirements and 
  • Maximizing production profitability

Early History

The first process simulation software programs emerged in the 1960s, developed by large chemical companies such as Monsanto in the US and Imperial Chemical Industries in the UK. These programs were conceived to solve the heat and material balances necessary for designing complex industrial-scale chemical production processes. Many other chemical companies, as well as emerging process licensors, developed similar software.

In the 1970s, Aspen Plus and PRO/II were commercialized as batch-run simulation tools. These program calculations quickly evolved into complex iterative calculations and had to be executed on mainframe computers. Initially used in chemical process design, their application scope soon extended to refinery operations and oil & gas production. Simulation technology began to be used in optimizing the design of highly integrated processes, such as key refinery process synthesis and distillation units, LNG production and air separation. This period marked a progressive shift from in-house simulation tools to globally licensed commercial process simulation software.

Integrated Flowsheeting

The 1980s saw a revolution in computing technology with the emergence of desktop machines. The advent of the IBM PC and its Microsoft DOS operating system enabled more engineering calculations to be performed interactively. Hyprotech’s HISIM process simulator introduced the concept of a graphical user interface for developing process flow diagrams, coupled with the solution of flowsheet heat and material balances. As the Windows operating system replaced DOS, the Hyprotech HYSYS process simulator began to capture a significant market share, especially in the upstream oil & gas sector.

Eventually, all popular commercial process simulators adopted graphical flowsheets integrated with heat and material balance calculations. Fractional distillation modelling became pivotal in designing separation of chemical compounds, while reactor modelling and rate-chemistry simulations were essential for configuring the processes used to synthesize of important chemical products. Over time, additional critical process engineering design and simulation capabilities were incorporated, such as the sizing of pipelines and equipment for key process unit operations.

Current Commercial Simulators

Today the leading commercial process simulators used worldwide include:

  • Aspen HYSYS®
  • AVEVA PRO/II™
  • Honeywell UniSim Design®
  • KBC Petro-SIM®
  • Kongsberg K-Spice®
  • SLB Symmetry®

Calculations and Solvers

Commercial process simulators use two primary types of solver schemes: sequential modular (SM) solvers and equation-oriented (EO) solvers. 

In a sequential modular approach, the process flowsheet is broken down into individual units (modules) that are solved one at a time. The output from one unit becomes the input for the next, making it easy to implement and understand, but it can be less efficient for complex systems with strong interactions between units.  It requires a lot of iterations where recycled streams mean that upstream unit operations have dependency on downstream operations.  One advantage of the SM approach is the ease with which complex, first principle physics-based unit operations models can be incorporated.

On the other hand, the equation-oriented approach solves all unit operation equations simultaneously as a large system of equations. This method is more computationally intensive but is well-suited for dynamic systems, optimization, and highly integrated processes, where interdependencies between units are significant.