engineer can solve significant flow sheeting problems in as little as a day or two and, moreover, do it much more accurately and in much more detail than was previously possible. The process engineer can now concentrate on the process model and the results rather than concocting a scheme to solve the model equations themselves. The simulation program will do that, at least most of the time. However, things do go wrong at times. Either the problem is very difficult for the simulator to solve or a mistake has been made in describing the process to the program. Thu in order to fix what is wrong the engineer does need to know something about how the simula tion program attempts to solve the problem. This is the subject of Sections v, vlll, and IX of these notes. Steady-state simulation programs are described briefly in Section Xll Simple material balance problems involving only a few variables can still be solved manually. However, it is generally more efficient to use a computer program such as a spread sheet. Both approaches are discussed in Section VIl In order to achieve high levels of mass and energy utilization efficiency, most processes involve the use of recycle. As will be seen, this creates recycle loops within the process which complicate the solution of material balances models for the process. A systematic procedure for identifying recycle loops is presented in Section VI An introduction to problems encountered in determining plant performance from plant is given in Sectionⅹ There are two basic process operating modes that are of interest to chemical engineers, dynamic and steady state. All processes are dynamic in that some or all of the process variables change with time. Many processes are deliberately run dynamically; batch processes being the prime example. However, many large-scale processes such as oil refineries and petrochemical plants are run in what is called the continuous or steady state operation. The appropriate model for dynamic processes are differential equations with respect to time. In general, continuous pro- modeling is discussed briefly in Section XI and dynamic process simulators in Section XI ocess cesses operating in the steady state are modeled by algebraic equations. Dynamic pro Many topics in process modeling are not covered in these notes. The most serious omission is the companion to the material balance, namely, the energy balance. Also, little atten- tion is paid to what are known as first-principle or rigorous equipment models. Such modeling is more properly covered in texts and courses on unit operations and chemical reaction engineering However, a few of the simpler and more useful models are given in Appendix e-4- engineer can solve significant flow sheeting problems in as little as a day or two and, moreover, do it much more accurately and in much more detail than was previously possible. The process engineer can now concentrate on the process model and the results rather than concocting a scheme to solve the model equations themselves. The simulation program will do that, at least most of the time. However, things do go wrong at times. Either the problem is very difficult for the simulator to solve or a mistake has been made in describing the process to the program. Thus, in order to fix what is wrong, the engineer does need to know something about how the simula￾tion program attempts to solve the problem. This is the subject of Sections V, VIII, and IX of these notes. Steady-state simulation programs are described briefly in Section XII. Simple material balance problems involving only a few variables can still be solved manually. However, it is generally more efficient to use a computer program such as a spread￾sheet. Both approaches are discussed in Section VII. In order to achieve high levels of mass and energy utilization efficiency, most processes involve the use of recycle. As will be seen, this creates recycle loops within the process which complicate the solution of material balances models for the process. A systematic procedure for identifying recycle loops is presented in Section VI. An introduction to problems encountered in determining plant performance from plant is given in Section X. There are two basic process operating modes that are of interest to chemical engineers, dynamic and steady state. All processes are dynamic in that some or all of the process variables change with time. Many processes are deliberately run dynamically; batch processes being the prime example. However, many large-scale processes such as oil refineries and petrochemical plants are run in what is called the continuous or steady state operation. The appropriate model for dynamic processes are differential equations with respect to time. In general, continuous pro￾cesses operating in the steady state are modeled by algebraic equations. Dynamic process modeling is discussed briefly in Section XI and dynamic process simulators in Section XII. Many topics in process modeling are not covered in these notes. The most serious omission is the companion to the material balance, namely, the energy balance. Also, little atten￾tion is paid to what are known as first-principle or rigorous equipment models. Such modeling is more properly covered in texts and courses on unit operations and chemical reaction engineering. However, a few of the simpler and more useful models are given in Appendix E