To begin with, let us look at types of problems that can arise in context of modeling and simulation. Consider a typical small chemical plant consisting of a reactor and a distillation column, which is used to separate the product as overhead (see Figure 1). The reactants, which are separated as bottom product of the distillation column, are recycled to the reactor. We can identify following problems

• To Find: Raw material flow rates, reactor volume and operating conditions (temperature, pressure etc.), distillation column configuration (feed locations and product draws), reboiler,condenser sizes and operating conditions (recycle and reflux flows, steam flow rate, operating temperatures and pressure etc.)

• Process Retrofitting: Improvements in the existing set-up or operating conditions Plant may have been designed for certain production capacity and assuming certain raw material quality. We are often required to assess whether
  — Is it possible to operate the plant at a different production rate?
  — What is the effect of changes in raw material quality?
  — Is it possible to make alternate arrangement of flows to reduce energy consumption?

• Dynamic behavior and operability analysis

  Any plant is designed by assuming certain ideal composition of raw material quality, temperature and operating temperatures and pressures of utilities. In practice, however, it is impossible to maintain all the operating conditions exactly at the nominal design conditions. Changes in atmospheric conditions of fluctuations in steam header pressure, cooling water temperature, feed quality fluctuations, fouling of catalysts, scaling of heat transfer surfaces etc. keep perturbing the plant from the ideal operating condition. Thus, it becomes necessary to understand transient behavior of the system in order to

  — reject of effects of disturbances on the key operating variables such as product quality
  — achieve transition from one operating point to an economically profitable operating point.
  — carry out safety and hazard analysis