Last week Mobatec was presenting Mobatec Modeller at the ECCE 2013 (9th European Congress of Chemical Engineering) in The Hague (in The Netherlands). It was a great experience to be at this congress for several days and we met a lot of interesting people.
Obviously, the goal of being there was to promote our modelling methodology and tool, since “it is Mobatecs goal to bring this easy to grasp modelling methodology to the world and to teach engineers that modelling can actually be quite easy and very valuable.”
A question I had to answer quite often during our days at the congress was: “I know about this other tool (e.g. Aspen, Hysys, gProms, Matlab, ChemCad, ProSim, etc.). How is your tool different from what I already know?”
I noticed that people (before speaking to us) really did not realise there even could be an alternative approach to modelling and they all were genuinely interested in learning what this new modelling approach could offer. Therefore, I decided to devote a blog to this topic.
As I mentioned in a previous blog post on maintainability of process models there are typically 2 ways of constructing process models nowadays:
The first and most used approach, the “Unit oriented” or “flow sheeting” approach, I would not refer to as modelling myself, since you are only connecting (sub)models, which were completely defined by other people. You are merely “simulating” in this case and hoping that the persons who developed the models did such a good job that you get the results you require for your specific setup, with your required accuracy and your specific goal. In the rare case that you can actually see all the equations (so not only a few ones in some, mostly incomplete documentation file) that are used to get to the simulation results, they are either inaccessible or the listing is very long and very difficult/complex. Don’t get me wrong here, by the way, these tools can be very powerful and useful. I am just referring to the lack of flexibility of these programs to be able to adapt (or even just understand) the actual equations of the used models.
In the other approach, The “Equation oriented” approach, the user has the “freedom” to program everything himself. This is very flexible, but typically also a very tedious job. Much (programming) experience and a lot of patience is required to get a model up and running. The listings usually get very long (and hard to maintain), which paradoxically actually makes the end result quite inflexible.
At the congress I showed people how both approaches can be visualised with Mobatec Modeller (see picture below). On the left side you see a “flowsheet” with columns, pumps, indicators, transmitters, etc. And on the right you see a small part of the (very long) listing of the equations that constitute the entire model.
In the next screenshot you can see how you can “look inside” any part of a model with Mobatec Modeller and “zoom in” to the details of, for example, a column. This specific column was defined as a column with a fixed 3 stages. Zooming in further to the bottom stage, you notice that it consists of a liquid phase system, a vapour phase system and a “metal” system. Also several mass (green) and heat (red) streams to and from these systems are defined. A little bit of theory is needed at this point: The modelling methodology behind Mobatec Modeller assumes that any process can be broken down into systems and connections. Systems represent a capacity, able to store mass and energy. Connections represent the transfer of mass and energy between the defined systems.
Simply “drawing” all the systems and their interconnecting connections is enough for Mobatec Modeller to automatically setup the mass and energy balances. This is a very big advantage for the user, since he cannot make any mistakes in this important part of any model definition. It’s very easy to add, reconnect, remove or copy connections (or any larger part of the model). This only affects the automatically generated part of the model.
Another big advantage of the used approach is that the debugging of the involved equations of any (part of a) model needs to be done only on “object level”, so on the level of each system and connection. Typically, the number of equations that are associated with one system or connection is not more than 10. Above all, the tool will help you with the correct equation setup and sorting, and will notify about any object that has not yet been properly setup, such that you will be assured to have a structurally solvable model.
I presented only a few differences between other tools and Mobatec Modeller for now. In the next blog post(s) I will list several more distinguishing features of Mobatec Modeller and I will elaborate on each one, such you can understand the benefit of each of them.
Mobatec strives to make process modelling easier and more accessible to a larger group of people. If you agree or disagree with our mission and/or methodology, please post your comments, insights and/or suggestions in the comment box below, such that we can all learn something from it.
To your success!
Mathieu.
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“A hazard and operability study (HAZOP) is a structured and systematic examination of a planned or existing process or operation in order to identify and evaluate problems that may represent risks to personnel or equipment, or prevent efficient operation. The HAZOP technique was initially developed to analyze chemical process systems, but has later been extended to other types of systems and also to complex operations such as nuclear power plant operation and to use software to record the deviation and consequence. A HAZOP is a qualitative technique based on guide-words and is carried out by a multi-disciplinary team (HAZOP team) during a set of meetings.” (source: Wikipedia)
As you can read from the definition on Wikipedia, the HAZOP study is traditionally a qualitative study. To give it a more quantitative character, several papers have been written in the last decade that suggest to use steady-state analysis and dynamic simulation to complement the HAZOP study. By definition, a (dynamic) simulation is the imitation of the operation of a real-world process or system over time, which means that in principle it should be the most realistic way of representing an actual process. Combining HAZOP with dynamic simulation could provide the means for investigating (and demonstrating) the consequences of deviations from normal operating conditions. Above all, dynamic simulation could enable a HAZOP team to quickly investigate and test the effectiveness of various suggested strategies dealing with emergency situations.
In the article “Combining HAZOP with dynamic simulation—Applications for safety education” the authors claim to have developed a “Quantitative HAZOP” approach which is more adequate for educational application than the qualitative HAZOP procedure. They elaborate extensively on a relatively simple example (by including all equations and variable and parameter values that describe the model) to demonstrate the proposed procedure.
I agree with the authors that using such an integrated approach can help quite a bit in the process safety education, especially when a good graphical user interface (GUI) is provided. It looks, though, that a considerable effort is needed to construct (and test) both the model and the user interface, before it is useful as a helpful tool to aid in HAZOP studies.
The question that arises is: “Can such an integrated approach be extended and also be helpful for ‘real’ industrial HAZOP studies?”. In these cases typically larger parts of large processes are being evaluated and setting up a model in the way the authors did for the educational example could take several weeks to months (maybe even more). That would, in most cases, not be acceptable.
If setting up a dynamic process model with reasonable accuracy could be done in the order of magnitude of a few days or weeks (depending on the size of the process), this would certainly change the attitude towards using dynamic simulations to aid with HAZOP studies.
As a challenge, we decided to build a simulation model (including a user interface), based on the semi-batch reactor (oxidation of 2-octanol) of the quoted article, within (max) one day of work. A bit against our modelling methodology we chose to use the equations as presented in the article, just to see if it is possible to rebuild such a model in a short period. We had to change some equations quite a bit, though, since with our methodology mass and energy balances are generated automatically and constitutive relations are normally never time dependent, but only state dependent. The result is, of course, not perfect (and could be easily improved), but it does give an impression of what is possible nowadays. (Side note: Most of our time was spent trying to interpret the original model equations, since they gave rise to a lot of questions and I had quite some doubts on the validity of several of the equations) Click here to download the model file that we build. It can be loaded, compiled and run in the demonstration version of Mobatec Modeller.
By having a simulation of the process as a support tool, a deeper, easier and more complete study could be carried out. That would provide a systematic screening of process deviation associated with possible hazardous events, determining the threshold values that may lead to such events and enabling the examination of a particular design for the adequate safe range of operation.
As the article rightfully concludes, dynamic simulation should be seen as a tool that complements the traditional HAZOP procedure, it does not replace it. There are still many processes that cannot be modeled accurate enough due to a lack of enough quantitative information, particularly in emergency situations.
I am curious what your thoughts on this subject are. Under which conditions would a dynamic simulation tool be interesting for doing HAZOP studies?
Please post your ideas in the comment box below, such that we can go one step closer to enhancing the HAZOP methodology by adding a flexible dynamic simulation of (part of) the process!
To your success!
Mathieu.
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In our previous blog we discussed about the integration of modelling and simulation software in the curriculum of High Schools and Universities.
Another very interesting point covered in the paper of the professors from Rowan University is the fact that many (small) companies use self-made macros or programs to solve problems that are readily solved with commercial simulators, simply because they cannot afford the software. This does not mean, of course, that process simulation software is “a tool that graduating chemical engineers should not be familiar with.”
The problem with this self-made or programmed models is that they are normally very difficult to maintain, since they are programs which have been written by individuals. Therefore, it is not uncommon that companies do not allow their engineers to write software. Actually, computer programming (in languages such as FORTRAN, C, or PASCAL) is not a vital skill for chemical engineers in industry anymore.
The chemical engineering community thus may have a use for teaching tools and techniques that challenge students to think logically and develop algorithms without necessarily taking the time to learn a full programming language.
A closely related problem is that, even with commercial simulators there always seems to be an issue with maintainability of models (also in big companies). Especially when models become large and/or highly “custom made”.
Let me sketch a typical scenario (that I have seen several times). A company “hires” a graduate student to make a model for them, because they have no time, no money and/or not enough expertise to do it themselves. The student works on the model for months and does a lot of custom programming. After the student finishes his work, the model typically goes “in the closet” for a few months/years, because nobody has time to do something with it. After a long period, the model could actually be useful, but no one at the company knows how to work with it and no one seems to even get it running. So, they wisely decide to hire another student, who does not completely understand what the previous student has done and therefore decides to start from scratch and redo the entire job….
Not very efficient of course, but, unfortunately quite commonplace.
In my opinion the root of the problem is caused by the fact that there are basically two ways of making models nowadays:

• The “Unit oriented” or “flow sheeting” approach. Hardly any programming is required. The user just drags some predefined units on a flow sheet, connects them and configures some parameters. Quite convenient for most users, but very inflexible (sometimes nearly impossible) when deviations from standard equipment are needed. And, as discussed in our previous blog, users sometimes simply don’t know what they are actually doing.
• The “Equation oriented” approach. Nearly everything needs to be programmed out. This is very flexible, but typically also a very tedious job. Much (programming) experience and a lot of patience is required to get a model up and running

I think a large part of the maintainability issues can be resolved by introducing a “new” approach: The “Equation and system based” approach, which typically is a combination of the best of the two previously mentioned approaches. Without going into details I would state that such a methodology offers a lot of flexibility, but also provides insight in the process that is being investigated. Although this methodology has a learning curve, I have noticed that students/engineers who have mastered it are able to solve problems quicker. Also the generated models tend to be a lot easier to transfer to others, without the need for extra documentation.
What tips do you have to improve maintainability of process models?
I invite to post your experiences, insights and/or suggestions in the comment box below, such that we can all learn something from it.
To your success! Mathieu. ———————————————–

Nowadays, process simulators are an essential tools for some of the courses being taught within the Chemical Engineering degree in most of the Universities and High Schools all over the world. A high percentage of the projects, especially those with a design approach, are normally conducted with the aid of a commercial or academic simulator. It is even becoming more and more common to find assignments in textbooks specifically prepared for a certain process simulation tool.
However, it seems like the “traditional” and “old-school” approach in some parts of the Chemical Engineering education is somehow unchangeable, when it comes to innovation and being updated by using computer-aided tools.
 

 
The professors Kevin D. Dahm, Robert P. Hesketh and Mariano J. Savelski at Rowan University (Glassboro, New Jersey) analyze how effective it is to include computing (particularly process simulation) in the chemical engineering curriculum in their paper “Is process simulation used effectively in ChE course?”.
Currently, some courses in chemical engineering, such as Process Dynamics and Control and Process Optimization, are computer intensive and can benefit from dynamic process simulators and other software packages.
One of the most interesting topics discussed in the paper is the real pedagogical value of these tools from different perspectives: student skills development, industry needs or future technology trends.
Perhaps the most remarkable advantages of integrating simulation tools into a course is that it enables the professor to present in an inductive manner, such that the lectures can become more intuitive and time-efficient.
However, some people, especially teachers, argue that a potential drawback of using simulators is that it is possible for students to successfully construct and use models without really understanding the physical phenomena within each unit operation. So therefore, those tools could be suitable as a pedagogical aid in lower-level course where a high understanding of the process is not required.
We fully agree with the idea of enhancing some courses by including tools that can provide an added-value to the learning process, but of course that should not mean enabling the students to solve problems with only a surface of understanding of the processes they are modelling.
In my years of teaching I have seen too many times that students just “click together” a flow sheet, fill in some parameters and press “solve”. When the program converges to a solution, the students eagerly agree with the solutions, without checking the validity of the answer (At one point in time a student confidently presented me his reactor design with a cross sectional area of 26 million square meters!… ”It was the outcome of the simulation, so it must be right”, was his defence to my serious doubts).
In my opinion there is quite a difference between simulation (by connection a set of models that were developed by someone else) and modelling (in which you think about the involved equations yourself). Students should at least have some knowledge about modelling, before they can use simulation tools efficiently.
We would be more than interested in your view on this, so please leave a comment below.
In the next blog we will cover another interesting point made by the professors from Rowan University.
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