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An Overview of Chemical Process Modeling


Task: What is chemical process modeling and simulation? Discuss the applications of chemical process modeling.


Chemical Process Modeling
Chemical process modeling usuallyinvolves the creation of various mathematical models related to process design through computer aided tools, software and simulations (Ryan, J. and C. Heavey. 2006). It evaluates the behavior of the individual systems as well asoptimizes the performance of the integrated systems.In modern era, the designing of complex chemical processes has become quite simple thanks to the technological advancements in the process modeling. The modern simulation tools has equipped the engineers with diverse skills to cope with the highly complex process problems. The use of the modern computer simulation methodsis increasing in chemical industry to analyze the chemical systems in steady state as well as in dynamic mode and to carry out the performance evaluation of various process equipment (Pegden 2010). Chemical process simulations have become key component for industrial applications and are useful in almost every major chemical engineering field from basic chemical principles to advanced process design studies (Pidd 2004). Some of the important tasks that could be carried out using process simulation tools are mentioned below.

1.Time Saving
Designing and optimization of chemical processes usually involve long and complex calculations. Before the introduction of the digital technology, these calculations were carried out manually and required a long period of time to be finished(Birta, L.G. and G. Arbez. 2013). A small error during the phase of process calculations may cause poor results and would require performing the calculations again from the start. The introduction of process simulations has not only reduced the problem of long and time-consuming process calculations but has also increased the efficiency of engineers to easy perform these calculations without committing errors. Presence of errors in the process calculations can now easily be identified and rectified.

2. Process Design
One of the main applications of the process modeling and simulations is in the designing of a chemical plant. Designing of a chemical process usually involves several different steps such as heat and material balances to calculate mass flow rates, compositions, purities, heating and cooling rates, chemical equipment design and sizing, evaluation of performance and costs, development of PFD (Process Flow Diagram) and P&IDs (Piping and Instrument Diagrams). Process design represents series of complex steps which requires to explore a different number of options and to compare the results for different available options to find the best option for the system under study(Robinson et al 2004). With the application of computer aided tools now engineers can carry out these complex steps of process design more confidently and can take quick decisions by analyzing their systems.

2.1 Material and Energy Balances
Material and energy balance may be considered as the first step of the process design. This step usually requires the estimation of physical and chemical properties of pure substances as well as mixtures. In material balance step, the requirement of raw materials and utilities is generally calculated. Utility streams include steam, fuel gas, cooling water etc. With the help of the thermodynamic models that are present in the simulation tools this step has become just a matter of few clicks now.

Let’s take an example of a production of synthesis gas. Synthesis gas is used to produce other products such as Ammonia and Methanol. Through process simulation, one can easily perform mass and heat balance calculations to know the flow rate of steam and air required in primary and secondary reformer to achieve desired composition of synthesis gas and amount of cooling water required to reduce the temperature of the gas leaving the reformer. Further, the produced synthesis gas is then passed through sweeting process using MDEA (ammine solution) to remove CO2 through absorption. This process is used in ammonia as well as oil and gas industries to capture CO2. Through process simulation, one can easily calculate the flow rate of the ammine solvent needed to meet the required CO2 concentrations in the exit gas and the amount of the CO2 absorbed by the solvents can also be determined which would be required in the solvent regeneration step.

2.2 Equipment Design and Sizing
The next step after the application of the material and energy balance could be the designing and sizing of process equipment such as heat exchangers, compressors, pumps, separation columns, reactors. This is the main step of process design as the major capital cost is based on the cost of the equipment(Sokolowski and Banks 2010). With the help of the process simulations, a variety of different designs of the process equipment can be evaluated under a limited time to choose the right design for the process which also reduces the capital cost of the plant.

If we consider the synthesis gas example again, through the use of the simulations, the designing and sizing of the reactors can be performed. Separation is widely used in process industries. So, to make the separation process cost effective, engineers can perform design calculations of the distillation or packed columns used for the gas sweeting processes. The height of column, diameter, number of plates, plate efficiencies, etc. can be evaluated. The design of the heat exchanger, at the outlet of reformer, can be done through process simulations to determine the number of tubes, size of tubes, pressure drop calculation in tubes and shell and the heat transfer area required to achieve the desired temperatures.

2.3 PFD (Process Flow Diagrams)
Simulations can also be used to develop plant process diagrams in order to deliver it to the other departments. Using these simulations, right selection of the plant layout could be made possible. Right selection of the plant lay out is important because it reduces the piping cost as well as the power requirements of pumps and compressors.

3. Research and development
Researchers are continuously involved in evaluation and improvement of chemical processes. These researches usually involved the process modeling tools at some stage. Reactors are considered integral parts of the chemical processes especially if the reaction is carried out in the presence of the catalyst. Process simulations can be used to evaluate the performance of the reactor and to check the process conditions to changed at the right time.

4. Production planning
Once the plant is in operation, the continuous operation of the plant to achieve production targets becomes the main goal of the engineers to maximize the profitability. Profit of the plant can be maximized by production planning and process simulations help to evaluate constraints such as changes in feed conditions, process parameters to guarantee profitability. It also helps the management to take right decisions.

5. Training and education
Simulations are also used in industries for the training and education of operators and engineers. As chemical processes are becoming more and more complex, training and education of the operators and engineers have become rapidly important(Kelton et al 2013). Operator Training Simulator (OTS) is one of the simulated tools widely used in industries for educational purposes. It helps to train the operators for normal and emergency operations of the plants as well as to learn the shutdown and startup procedures of the process plant. In this way, process simulations not only educate the operators but also make impact on the process safety.

1)Birta, L.G. and G. Arbez. 2013. Modelling and Simulation: Exploring Dynamic System Behaviour. 2nd ed., Springer, London, England.

2) Pegden, C.D. 2010. “Advanced Tutorial: Overview of Simulation World Views.” In Proceedings of the 2010 Winter Simulation Conference, edited by B. Johansson et al, 643?651. Piscataway, New Jersey

3) Robinson, S. 2004. Simulation: The Practice of Model Development and Use. John Wiley & Sons.

4) Ryan, J. and C. Heavey. 2006. “Process modeling for simulation”. Computers in Industry 57, 437–450.

5) Sokolowski, J.A. and C.M. Banks (eds.). 2010. Modeling and Simulation Fundamentals. Hoboken, New Jersey: John Wiley & Sons, Inc.


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