Simulation

(Steady State Process)Simulation means creating (or modifying) a process to transform a feed into desired products by setting a plan which includes:
Understanding and utilizing the system thermodynamics(1), (or rules of nature, formulized and quantified by thermodynamics), which leads to:
Proper selection of the equipment/modules(2) in the path
Proper definition of streams flow traffic to/from the equipment and modules
Steering and directing the changes on equipment design factors, stream flow rates, T/P conditions, and other process variables to establish a consciously defined platform through which the desired goal would be (qualitatively)achievable
, and
Letting the simulator software to do the hard labour of flash calculations, iterations, repetitive mathematical operations- in order to- deploy your strategic thoughts (defined above)and let you know how to make the next move, and how good (or bad) you have done so far.
Utilizing the outcome of previous runs to fine tune (or make a major change), and move towards the ultimate goal.

The software quantifies your predictions, and goes wrong if you failed to understand or missed – may be-just one little rule of nature. Gives you a hint to re-configure your thoughts, it is still up to you to make the proper decision, and solve the puzzle. That’s why the more complicated the model, the harder the trouble shooting is. You must be really good at knowing the rules of nature, what you do is to re-generate what actually happens in a plant, and you have all these tools : thermodynamic behaviour prediction, mass/energy balance , complicated mathematical operation capabilities– all built in the simulation software to help you compete with the nature, and build a model which behaves very “NATURAL”.
If the model is working really hard to converge, there is something wrong, may be a mass imbalance problem, or ..., but it also shows that there would be problems in real operation to achieve the state you are aiming for. Try to untangle the mess, and once it runs smoothly and on the right track, you can feel good.
------------------------------------------------------------------------------------------------- 1. In fact phase equilibria, is a major aspect in simulation. It’s (mostly) all about it, and that’s a very important part of nature which thermodynamic is trying to formulate/predict, using all those complicated methods.
2. Modules, such as valves, controllers, pipes, or mathematical tools.
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(However, we may get some bad news from our output, because of some mathematical difficulty (and not a real impossibility issue), which by the way that also means: we are at the edge of instability. That state is a hard one to achieve.
And remember always: you should run the model and the model shouldn’t run you (But it can for sure drive you crazy).
There are still many other considerations to be afraid of:
Even a naturally well modeled system, may not be an acceptable design. Think of the corrosions which happen at some points in the plant. Those are completely “Natural”, and you may also very “naturally” and successfully model the system which eventually gets corroded. Well, there are of course guidelines to avoid these situations, and we need a broader knowledge of physical chemistry to handle these situations. Or, we may need to avoid hydrate formation, we must be aware of these issues. In fact a “Simulation Hazop” in the conceptual design case seems a necessary idea to me, so we can utilize the operation experience to avoid conceptual mistakes in the past designs.
So, it was an introduction to the very delightful world of simulation. But it’s not all.
I also need to explain what is “NOT” simulation (or should not be credited as simulation):
To me, some people “abuse” the simulation. Running a bunch of heat exchanger (often on the simple mode, whit out having a clue about heat transfer or phase equilibria) really hurts me. It hurts more, when the results are used for further steps (and referred to as simulation results). In this case, the capability of the simulation software to predict the physical properties is “abused”, and compromises the logical way through which a heat exchanger should be designed.
It’s not at all, knowing the alphabet of simulation, and creating some streams and modules. It’s like letting a child who had recently learned to count from 0 to 100 to be your investment advisor.
Even knowing to work with 2-3 (or 4) simulation packages is not necessarily a plus! Some one may be able to very well play many instruments, piano, guitar, violin, but he may not be a composer yet. And, someone may not be able to play either (which is nowadays impossible!), but be a very talented composer- as were our very smart pioneers in chemical engineering, who developed this field of knowledge, and built the very first refineries (honestly, how did they do that? all those calculations and stuff without having the simulation packages?!).
To make the story short, not everybody should do the simulation. I hate to say this: If your math marks in highschool were not A+, forget it. Sounds silly, but I think it’s a measure of your capacity in advanced thinking skills.