A process simulator solves material and energy balances by means of a computer code. A description of a typical process simulation code is reported in figure 1 in which all the most important elements of a simulator and their connections are evidenced. Figure 1 shows clearly that a process simulator include cost estimation routines as well as economic evaluation. The importance of the database is shown in the figure as a necessary source of information for different objects in the structure.

Figure 1: General scheme representing a steady state process simulator

The following different approaches are available in the process simulation:

• Steady state simulation which considers a snapshot in time of the process;
• Dynamic simulation which considers the evolution in the time domain of the equations describing the process;
• Integrated steady state - dynamic simulation, which combines the two previously, described approaches.

Today engineers are oriented to a more comprehensive use of process simulation in the entire 'life' of the plant such as the control strategies design, the process parameters optimization, the time evolution of the process for understanding start up and shut down processes and performing risk analysis, the operator training and the definition of procedure to reduce the unsteady state operations.

The main benefits one can gain from such a comprehensive use of the process simulation are the partial or total replacement of Pilot Plant operations (reduction of the number of runs and runs planning), the reduction of time to market for the development of new processes, the fast screening of process alternatives to select the best solution in terms of economic aspects, environmental aspects, energy consumption aspects and flexibility of the proposed process.

Figure 2: process simulation and the life cycle of a process

Due to the high complexity of chemical process, to get those benefits one must critically simplify the process and apply process simulation techniques in the entire life cycle of a process. Figure 2 shows how process simulation methods can help engineers in different periods of the life cycle of a process, from the process synthesis to the control strategies design.

The procedure to be followed in the process simulation may be briefly outlined as follows:

• Identify the problem
• Obtain all the relevant information:
  • get process data: flow rates operative conditions
  • get thermodynamic data from In house data, Data Banks (such as Dechema, …) or literature or through test run on laboratory / pilot plant
  • get kinetic data: directly from pilot plant or from excess Gibbs energy calculations (if possible) or directly from real plant data. At this stage avoid a rigorous definition of kinetic model and use concept of yield and conversion wherever possible and reasonable
• Select the software
• Steady state simulation: AspenPlus, ChemCad III, Design 2000, Hysim, Pro II
• Dynamic simulation: Speedup, Aspen Custom Model, Hysis, gPRON, ABACUSS
• Integrated solution: Aspen Dynamic, Hysis
• Select the Hardware
• Training on the following topics
• Basic course on process simulation
• Thermodynamic model selection
• Specific topics (heat exchangers, batch, heat integration, cost analysis,…)
• Economic factors
• Energy consumption
• Environmental impact
• Operational procedure

Process Simulation plays a role in the Decision Support Systems (DDS) in the development of a industrial settlement. The DDS is based on fast and reliable communication among all the activities in the manufacturing system. Three layers of activities are normnally present in a manufacturing system: management control, process simulation Off-line and On-line and control system. The information distribution is made through interoperability of the software by using component based software (such as Active X or Java components).