Thus any process engineer needs to consider what the effects of a change in a single variable probably high up the production line - say the feed temperature to distillation unit, will have on the output of another process or unit operation down the production chain - say the efficiency of an absorber down stream. This usually requires quite a number of repetitive calculations. Modelling, therefore in process systems engineering was an almost distant and far fetched phenomena. yes plants and factories have been developed before the advent of the technological day but the work involved was usually cumbersome, and yes this was modelling in itself but the new digital age and its capacity could never be under estimated. Process systems engineering is therefore the development of process and production models and simulating them to visualize anticipated output changes resulting from structured input changes basing on the governing engineering laws - chemical , biological, physical, economic or otherwise. Advances in the technology have already paved way to the extension of the simulations beyond the confines of steady state modelling and simulation! Simulation of dynamic models is also possible and practical, rendering process control systems able to model closer to realistic simulations or follow processes online and make adjustments as per need.
The possibilities of process control modelling and simulation and computer aided design expand the already expanse capabilities of the process engineer. Powerful tools (software) are available commercially from the simplex SuperPro, to the popular Chem CAD or Aspen Hysys which is tailored for Oil and gas industries. MatLab also has some modelling functionality to it, although i have not been able to use it quite efficiently (complex and limited GUI! :) ) Appreciation of these modelling and simulation tools is as essential to any process engineer (or aspiring!) if we are to have ground breaking Fritz Haber or Karl Bosch scale ups in this age!