Building process simulation

With these estimates, the heat duties on condenser, reboiling, and cooler are established, which provides the basis for the process simulation. 

A column simulation is conducted in a process simulation software based on tray-by-tray equilibrium calculations for mass and heat balances. Given the data for feed and products in terms of flow rates and compositions, and column operating conditions in terms of pressure and temperature as well as reboUing duty, the column simulation can mimic the mass and heat balances for the current operation. Table 13.2 above shows an example of the data required for conducting simulation of a C2 splitter column. 

The first step is feed simulation. If detailed feed analysis is available, which includes composition and conditions, a feed can be readily defined in simulation. Otherwise, the feed can be back-calculated as the summation of all products for which flow rates and compositions are known. 

The second step is to determine feed tray position. Theoretical stages should be used in simulating a column. If tray efficiency is known, the feed tray in terms of theoretical stage can be determined from the actual feed tray and tray efficiency. 

However, tray efficiency is usually unknown. In this case, a sample lab test may be warranted. It is recommended to take a side sample one tray away from the feed tray. The feed point in simulation is one stage away from the theoretical stage, which matches the sample composition the best. Taking the sample from the feed tray would give compositions that are highly influenced by the feed and hence cannot truly represent the internal compositions inside the column. 

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A typical crude assay includes two types of information for an oil sample (1) bulk properties and [2) fractional properties. Table 1.1 gives examples of both properties of a crude assay. For design and modeling purposes, it is always the best practice to have process data obtained in the same period as assay data, since the properties and composition of crude change over time as it is produced from a given well. Kaes [1] suggests that assay data should not be two years older than the process data used to build process simulation. We explain both bulk and fractional properties in the following subsections. 

Kumar P, Mulheron M, Som C (2012) Release of ultrafine particles from three simulated building processes. J Nanopart Res 14, 771, doi 10.1007/s 11051-012-0771-2... 

Process simulation software can also be used to help build simple energy balances in spreadsheet models, for example, by entering stream data to calculate mixture heat capacities, to calculate stream enthalpies, or to estimate heats of reaction. 

How to use commercial process simulation software to build a process heat and material balance model... 

The first step in building a process simulation is usually establishing the chemical basis for the model. This consists of choosing the components that will be included in the mass balance and deciding which models to use for the prediction of physical properties and phase equilibrium. The correlation of physical properties and prediction of phase equilibrium are described in detail in Chapter 8. This section thus focuses on the selection of suitable components. 

The commercial process simulators contain a range of distillation models with different degrees of sophistication. The design engineer must choose a model that is suitable for the purpose, depending on the problem type, the extent of design information available, and the level of detail required in the solution. In some cases, it may make sense to build different versions of the flowsheet, using different levels of detail in the distillation models so that the simpler model can be used to initialize a more detailed model. 

In this problem we will simulate a batch adsorption process that takes place with two adsorbate components. The simulation will allow us to do computational experiments with the aim of learning how the adsorption and desorption parameters affect the behavior of this process. Building the simulation will provide new experience in developing the model equations, utilizing more complex constitutive relationships, finding numerical solutions to these equations, and displaying the results graphically. 

In process simulation, it is fully sufficient that the liquid density always refers to the saturation line, the pressure effect on the density is neglected. The pressure dependence of the density is necessary e.g. for safety considerations like the calculation of the pressure build-up in a closed volume or for the determination of the speed of sound. For the determination of the pressure effect, there are a number of correlations listed in [6]. The Tait equation... 

In the scoping study, the accuracy of cost estimation is on the order of 30. The main deliverables of the study include building a process simulation, evaluating the effects of changes, as well as conducting high-level cost and benefit estimates. 

You may occasionally encounter situations where both reactions and physical separations take place in a single piece of equipment. In most cases, this is undesirable but unavoidable. In such situations, it will be necessary to divide the unit into two imaginary, or phantom, units. The chemical reactions take place in one phantom unit, and the separation in the second phantom unit. These phantom units are never shown on the PFD, but we will see that such units are useful when building a flowsheet for a chemical process simulator (see Chapter 13). 

Computational fluid dynamics (CDF) presents a relatively new method of computer-aided mathematical tools for process simulation. The description of multiphase systems in the CFD is a promising new field. This is so because only recently sufficiently extensive and accurate spatially resolved measurements in multiphase systems to create mathematical models and to validate them became possible. Often, the modeling is not perceived as a part of the CFD, especially when working with commercial programs, in which the equations are already available. Since mathematical models are developed independently of the CFD, they are seen as outside to the CFD to be supplied accessories. The CFD models build on model developments, which are also common in other techniques, but have their own structure. 

Simulation Model. A key feature of our approach is that we make use of semanti-cally-rich, domain-general patterns to build our simulation models. These patterns, which are better characterized as schemas or frames [3], are declarative abstractions that specify common, recurring inter-related roles and/or behaviors. An example of a schema is the SUPPLY schema, which is quite general and can be used to describe processes in many domains. A listing of the SUPPLY schema s roles and their instantiations for a simple flashlight example is shown in Table 1. 

Monte Cario simulation A computer-based iterative statistical method that uses sets of random values from a set of ranges or probability distributions to determine a quantitative outcome in complex process simulations. The outcome of the iterations is to build up a distribution of the possible outcomes of the simulation as a frequency distribution or in... 

The first step in the flow sheet simulation is to define process flow sheet connectivity by placing unit operations (blocks) and their connected streams. To define a process flow sheet block, select a model from the Model Library (Column and then DSTWU) and insert it in the workspace. To define a process stream, select Streams from the Model Library and click to establish each end of the steam connection on the available inlet and outlet locations of the existing blocks. Building process flow sheet using shortcut distillation form the model library, for fluid package, Peng Robinson EOS is used. Date needed for simulation. 

The first step in building a simulation model is always the collection of information about the process. Engineers rely on draft versions of process descriptions, flow diagrams, and batch sheets from past runs, which contain information on material inputs, operating conditions, etc. Reasonable assumptions and approximations are then made for missing data. The following information is required for modeling a batch process ... 

The hrst attempts to provide a modular-based dynamic process simulator were DYFLO and DYNSYS [28]. These two early modular simulators differed in their approach. DYFLO provided the simulator with a suite of FORTRAN routines that were linked via a program written by the user. Hence, it was to some extent cumbersome, but useable. DYNSYS [28], on the other hand, provided a key word stmcture much like the steady-state simulators of the era allowing the user to build a dynamic simulation. Both simulators found limited use owing to the difficulty of producing a simulation, and the actual run times on the computer hardware of the time were often greater than real time. 

The process used for this workshop is shown in Figure W3.1. Build a simulation of this system using the Wilson activity model as the fluid package. The feed is a 50/50 mixture of water and methanol (100 kmol at 30°C and 200 kPa) which is heated in a steam heater to about 70°C. The hot mixture is then stored in a surge tank for future use. Note that you do not need to enter any further information about vessel volumes, etc. Simply use the default values for hold-ups for dynamic runs. 

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