Well, It was the summer of 2017 when I was in the sixth semester of engineering and I saw a pamphlet of DWSIM flowsheet development challenge from FOSSE IIT Bombay. I was not interested initially but every day it uses to come to me whenever I used to pass by the notice board. So, I finally decided to explore this and started looking at the completed flowsheets forum in FOSSE Forum. Frankly, speaking I didn’t know anything what was happening around and how these are developed. Then I started exploring the tutorials given by the Forum and learned the basics. It is very important to learn the basics in this case or else you will end up doing a great chaos, Since there are a lot of controls and this case if you do trial and error method of learning I would suggest spending your time learning the basics than guessing numbers. Another important tip, work on theoretically developing the models of the individual system to be included in the system. For example, I simulated a batch reactor for the first time on DWSIM panel and I had to do a material balance, component balance, and energy balance. It gives you an idea of understanding the flow of material in the system .Done with this, start developing models for all the systems and then go for flowsheet development.

Flowsheet development is an easy task. I remember, the first time I saw a flowsheet development was on my friend’s laptop for the preparation of Cumene. I hope he remembered the same. Then I learned about material streams and energy stream, connecting those are easy but the conditions are difficult to make, It is very important to give initial conditions very precisely because the entire process depends on the initial conditions of the feed. Then, comes the conditions of the individual components such as the distillation column, a catalytic reactor etc. A gentle advice, don’t put vague values and try to see whether the system is getting simulated or not mostly in case of individual components, well it will give you happiness first and trouble later, maybe you get negative flowrates out of the system or errors later saying convergence is not proper or system is not able to converge the process .So, in order to avoid this calculate the exact flowrates, tolerances, pressures, and temperatures theoretically of the components and make sure the units are same as calculated theoretically that you need to see before starting the flowsheet.

Now, I will describe a small process for development of flowsheet for production of ammonia through Haber’s process and the problems faced for the same. I started with learning the same process in Dryden’s technology systems and some other literature and got a raw data for calculations of the same from UK Chemguide, but it was a plant scale process, so I had a thought of doing it the in a bench scale and started working on it. I worked on the initial calculations it was pretty difficult understanding everything at that since I didn’t know many things, So I took help from my teachers and somehow managed the calculations and worked on the modeling of the reactor. To start with the flowsheet, connecting components were very easy you know but the challenges started appearing when reactor came into the picture and its conditions and the selection of base component and the heat of reaction aspects. Base components, are those for which the entire reaction depends on and it is important to choose it wisely or there will be changes in heat of reaction, sometimes it points to infinity as well, so be careful. Following that ammonia, formation takes place with along with some nitrogen and hydrogen. This had to be separated from the mixture of Ammonia, so there are two options either you can use component separators or distillation column or any other separation process suitable for separation. Truly speaking, component separators are hypothetical and have no existence, so better using a distillation column or a flash separator, but take care of the inlet pressures and the pressure of the flash separator.

Now, comes the most challenging task, instead of letting off the hydrogen and nitrogen, recycle is preferred and for that a recycle stream is to be used. The temperature, pressure, and mass tolerances are the most important ones to take care of and I prefer calculating them instead of playing trial and error, and yes if required you can introduce processes such as heating, cooling etc to equalize the temperatures of the streams. Include master property tables for the streams and all the components and arrange the components sequentially to make it look simpler and the last tip never ignores the warnings, maybe they convey an important message so, consider it as a warning as an error and work on it. Most important, review and run it any number of times observe the simulation time is the same for each and every run. Put a good line for the flowsheet and make sure you copy each and every data in a sheet. These are small things we can take care during the development of a flowsheet and run it peacefully. So, that’s all for this blog, hope you guys like it, please comment below how you like it so that I can improve it in my upcoming blogs.