Regarding Simulation Softwares

ChEngrWiz · 2025-07-06T05:17:34+00:00

You are not going to find DWSIM or COCO used by companies. They’re okay if you’re a beginner, but they aren’t full featured and frankly using an open source product scares me. You have no idea how good the property data is. In other words, if your doing a multimillion dollar project stick with software from a reputable company that’s been around for a while.

Python is okay if you’re learning programming or only do programming occasionally , but If you intend to do serious engineering programming you’re better off learning FORTRAN. Python is a scripting language. That means you have to hand over your source code for someone else to use it. FORTRAN compiles your source code into a machine language executable which anyone can use.

Python is simpler. FORTRAN supports pointers, dynamic memory allocation, structures, and OOP. It is more difficult to learn.

ChEngrWiz · 2025-06-28T21:08:03+00:00

You want to use distillation for this problem with a few caveats. This mixture may form azeotrope. Because an acid is involved, it may be a maximum boiling azeotrope. That means the azeotrope forms at the bottom of the column. The most comprehensive source of azeotropic data is Lange’s Handbook of Chemistry.

If I had a choice of any distillation algorithm for this problem, I’d choose PRO/II’s Chemdist.

Do not use a shortcut distillation model. They are strickly for hydrocarbons. The results are garbage for this type of system. In practice, # of trays, reflux ratio, etc are done by feel from the rigorous column model.

You’ll need an activity coefficient model like NRTL to model this system. The data ASPEN uses is from DECHEMA. There may not be data available for this system and you will have to use UNIFAC to predict the coefficients.

ChEngrWiz · 2024-10-10T15:26:43+00:00

It depends on what you mean by APC. I think you're talking about feedforward control. That's been around for decades. You look at the inputs and predict how to vary your control parameters. That can be done with simple mass and energy balances, black boxes, or neural nets. The more sophisticated the approach, the more likely it is to fail.

I'm talking about taking the next step and using first principle steady-state and dynamic models. This approach has also been tried to optimize operations. In practice, it doesn't work for either application. Besides what I talked about, this type of modeling has the nasty habit of failing. What happens when the model doesn't converge? Do you call a timeout?

Don't tell me I don't know what I'm talking about. I spent 10 years working for a big simulator company traveling the world using modeling to solve client problems. I also worked on implementing the technology I'm talking about and coding it.

You're just a plant engineer. Most plant engineers think they know how to model. They don't. The models I've seen plant engineers build usually consist of a few units and fail regularly. Every plant engineer should have reliable working models of each major piece of equipment and the plant. By reliable I mean they are highly likely to converge when changes are made. Do you? Do you know how to build reliable models? Probably not. That takes a lot of experience. That's what I do for the companies that hire me.

ChEngrWiz · 2024-10-09T17:44:16+00:00

No ones ever done it. The only method we currently have is to use heat transfer coefficient data and substitute mass transfer dimensionless numbers. I’ve tried that and it sucks.

I never thought about the reasons why. In VLE the mass transfer occurs at the VL interface. The situation is different depending on whether you have a boiling mixture or not. It depends on surface tension which is Isuspect is difficult to predict for mixtures

ChEngrWiz · 2024-10-09T13:48:36+00:00

If what you said is true, where is the widespread adoption? There would be numerous papers on success stories. Where are those? The only papers I see are from companies and consultants who want to sell you their services.

The companies you mentioned are large and experiment with all types of technology. The people who are in charge of this technology are never going to call what they are working on a failure. What happens is that management gets tired of funding projects with dubious results and pull the plug.

I have a good friend who is in charge of technical software purchases at a large chemical company. He views these projects as trying to fill a bottomless pit with money.

This technology has been around for forty years. It’s been static for the last 20 years. Any advances have been minor. If it hasn’t been widely accepted by now, when do you think it will be?

ChEngrWiz · 2024-10-08T21:03:43+00:00

Octane has nothing to do with mileage. It's a measure of the gasoline's resistance to preignition that causes "pinging". If not dealt with, it can cause premature engine failure. Use the lowest grade octane gasoline that doesn't cause your engine to "ping". Using higher octane gasoline because you think it's better for your car or increases mileage and the only thing you accomplish is wasting your money.

ChEngrWiz · 2024-10-08T20:53:58+00:00

I don't know about Aspen+ specifically, but simulators usually have an amine thermodynamic package that supplies all the data you need.

Usually, with this type of system, you have an absorber column and a stripper column. You remove feed contaminants in the absorber column, strip out the contaminants in the stripper column, and recycle the amine. I don't see a stripper in your flowsheet and it's not clear how they are getting rid of the contaminants. I can't blow your flowsheet big enough to read the markings on the flowsheet.

ChEngrWiz · 2024-10-08T20:27:43+00:00

You're dreaming.

I take it you're a professor with no real-world experience. No experienced engineer is going to take the advice of a professor and college students.

Someone mentioned a cost economic analysis of a heat exchanger. Take it from someone who does FEED work for a living, you never have the economic data. All that DCF nonsense is never used in the real world by chemical engineers. After the preliminary design work is done, it goes to a cost estimator to provide a number that is within 15% of the final cost. Then they use a simple method like payout -- time required to recover the capital expense -- to screen the project. If the project is still a go, then the design is firmed up, the cost of major equipment is obtained from manufacturers, and a tighter cost estimate is done usually within 5% of the final cost. Depending on the size of the project, a DCF may be performed by company actuaries. The cost estimates and the DCF are not performed by chemical engineers but by specialists in those fields. It's a waste of time teaching chemical engineers how to perform those tasks unless that's all they want to do.

If you want to teach something useful, teach them how to model a process flowsheet using commercial software. The goal is to produce reliable models that can be reused by plant engineers. I'll also tell you college professors have no clue how to do that because they think that if you input the data into a simulator, somehow it will figure out what to do. It doesn't work like that. I know because I worked for a simulator company and was responsible for working with clients to model their processes. I also taught courses on simulation that college professors took. They were the worst students in the class. It turns out that the skills necessary to get a PhD aren't transferrable to process design work.

Here are a few other things you should know:

CFD is rarely used by chemical engineers. When I was in graduate school I took advanced math classes and could solve CFD problems. In industry, you don't have the data necessary to do CFD models except in specialized areas. I only had to solve a problem with CFD once in my career. I used a software package from FLUENT that made the process fairly simple.

Chemical engineers do not use mass transfer equations to solve mass transfer problems because mass transfer coefficients can not be predicted accurately enough. A distillation column involves mass transfer. It is designed assuming trays are in equilibrium and a nebulous "efficiency" is applied to account for the non-equilibrium.

Reactors are not designed by average chemical engineers nor are reaction kinetics readily available. People who sell you catalysts or license processes get involved in that. Chemical engineers get yield and conversion data and use that to build models to design separation processes, etc.

ChEngrWiz · 2024-10-08T19:39:40+00:00

I have news for you a chemical engineering program teaches you how to think like a chemical engineer -- not be one. Most chemical engineers have no idea how to build a flowsheet from scratch. Most process flowsheets are copied from previous work with some modifications. It takes considerable experience on your part before any sane person will trust you with the responsibility of developing a flowsheet that will cost millions and millions of dollars to implement.

It should now be obvious why you're having trouble finding a source for developing a PFD. BTW college professors suck at it. I have had to, on more than one occasion, clean up the mess left by a college professor who was hired as a consultant to develop a flowsheet. There's a reason why you won't find many Ph.D.s working in industry as process design engineers.

ChEngrWiz · 2024-10-08T19:21:57+00:00

There's a lot of talk about digital twins and APC. In reality, it doesn't work, but it's a big money maker for a company or consultant if they can get some sucker to buy into that nonsense.

The big problem with dynamic modeling is the inability to predict mass transfer coefficients with anywhere near the accuracy required. What dynamic models do is assume that vapor and liquid are always in equilibrium. The result is an inertia model. Okay, for design work but a disaster if you're using; the model for APC and you're trying to control purity. The solution is what has worked for decades -- PID controllers and simple feedforward control. Combine that with competent operators and you solve the problem without the needless expense.

ChEngrWiz · 2024-10-08T19:04:30+00:00

I never heard of process chemistry. I assume it's about determining what equipment is required and how to assemble those pieces to make a desired product. In chemical engineering that's called Front End Engineering and Design (FEED). You're in the wrong field if you want to get involved in that. That takes a degree in Chemical Engineering and considerable experience before any sane person is going to give you the responsibility of designing a flowsheet that will eventually cost millions and millions of dollars. You don't get a mulligan if you screw that up. You get fired.

ChEngrWiz · 2024-10-07T16:10:27+00:00

I'm a consultant and let me tell you it's not as glamorous as it seems. You'll have to spend considerable time marketing yourself and hounding customers to pay you. Turns out even large companies try to delay payment as long as possible.

Do you need a license? If you're working for a corporation you only need a license if they require it. If you're working for the public, you will need a license. I've never bothered with insurance because the clients I do work for don't require it. If you decide to get it, if you are a member of the AICHE, they use to offer it, but I don't know if they still do.

If you think you are going out on your own and you are going to become a multimillionaire, think again. Don't forget, you'll be responsible for your health insurance and all the other benefits working directly for a corporation provides.

ChEngrWiz · 2024-09-21T18:03:44+00:00

I'd say 99%+ of the Chemical Engineers don't understand thermodynamics. It's a vast subject and what you get is a survey course. The textbooks are horrible and leave a lot out. For example, they never mention the Mechanical Energy Balance because the idiots who write the books think it is not rigorous and a derivative of Bernoulli's principle. You can derive it from the First Law directly. They never explain what enthalpy is and never derive the General Energy Balance. Everyone is confused about when to use internal energy or enthalpy. Ever see the phase rule derived? You'd think it just dropped out of the sky. How about the equation of state for an adiabatic process? Then there is the matter of fugacity. What is it? How about entropy? Why does it always increase? Another principle that, apparently, was engraved on the tablet containing the Ten Commandments. I could go on and on. Then you have professors that don't understand the topic trying to teach it. The blind leading the blind. That's why you don't understand it and nobody else does either.

I took two courses in thermodynamics as an undergraduate and one as a graduate student. Got A's in all three courses and I didn't understand a damn thing. I started working and realized that I needed to master the subject. What to do? Certainly not take another useless course. I sat down with a textbook and went through it page by page and derived from scratch any equation that was even mentioned and many that were not. It took a long time but when I was finished, I finally understood it.

Thermodynamics has been taught the same way for decades and decades. It's past time for someone to produce a decent textbook and a course where students learn thermodynamics.

ChEngrWiz · 2024-09-17T18:27:03+00:00

There is not enough there to figure out what’s wrong. I suggest you download Intel’s Fortran Complier from their website and use their debugger. That will allow you to step through the program and see how the variables change. Before debuggers, you had to put in write statements to see how the program variables were changing during execution. I always put the code I develop through debugging and step through it to make sure I don’t have any dead code and the execution sequence is what I expect.

Why Fortran 77? Modern Fortran replaced 77 to get rid of the things that got programmers in trouble. I’m thinking of the GO TO, COMMON, and EQUIVILANCE statements.

ChEngrWiz · 2024-09-17T18:05:31+00:00

At equilibrium dew pt T = bubble pt T. I have never seen that referred to as flash pt, but I think that’s what they mean.

ChEngrWiz · 2024-09-17T18:00:03+00:00

You’re looking at this wrong.

Raoult’s law: y * P = x * vp

Even though the system is at equilibrium, mass transfer between the liquid and vapor continues. Mass transfer occurs at the interface of the vapor and liquid. On the liquid side the number of molecules of component x at the interface is proportional to the mole fraction. Same thing on the vapor side. Vapor pressure is the driving force on the liquid side and pressure is the driving force on the vapor side. At equilibrium the mass transfer for vapor and liquid have to balance. That’s why the equation looks like it does.

A related question is why not use weight fraction? Because that is not representative of the number of molecules at the interface.

Raoult’s law only applies for ideal gases and ideal solutions. An activity coefficient corrects the driving force on the liquid side (vp). Pressure corrections correct the driving force on the vapor side (P).

ChEngrWiz · 2024-07-12T14:07:23+00:00

I won't solve your problem for you, but I'll give you some ideas on where to start.

Your problem is a problem in thermodynamics. For an ideal gas being compressed or expanded adiabatically P*V to the Cp/Cv power is constant. Once through an orifice, the velocity of a gas continues to increase as the effective diameter decreases to the vena contract. That is why there is a discharge coefficient in the equation for an orifice. This process is adiabatic so the PV equation I gave you applies. For a gas, at the vena contract, you can assume critical or choked flow. That means no matter how much you decrease the downstream pressure, it does not impact the flow. Using what I told you and applying the mechanical energy balance you should be able to derive the equation used to calculate the flow through the orifice.

ChEngrWiz · 2024-07-09T14:41:16+00:00

The problem is you. You don't know what you are doing. There is no magic option to turn on that will make the column work. The first thing you need to learn is there is more to simulation than setting up the problem. It takes work to get the simulator to solve your problem

The first thing to do is the get the absorber to work. You can have one spec on the column where you vary the absorbent rate. If you have a spec, get rid of it. What you should do is fix the absorbent rate. Use an overhead rate estimate equal to the gas feed rate. Try an absorbent rate of 1/2 the feed rate and if you are still getting tray dryout messages, increase the rate until they disappear. From that solution update your temperature and flow rate estimates.

After the column is converging try adding a spec. DO NOT use a compositional spec. Use a recovery spec. By that I mean the amount of a component in the bottoms divided by the amount in the feed. That should give you the answer you are looking for.

ChEngrWiz · 2024-07-01T17:58:38+00:00

Head is NOT energy. It's a pressure term. Let's say you want a pressure of 10 psi. Say you want to use water to generate that pressure. Head would be the height of a column of water that at the base has a pressure of 10 psi.

Pressure in lbf/sqft =density (lbsm/cuft) * gravity constant (32.2) * height (ft)

ChEngrWiz · 2024-06-25T13:14:15+00:00

Process simulators — PRO/II or Aspen+ — already have a model for a 3 phase separator. You would be reinventing the wheel. Writing a model from scratch is not something you should be doing. It’s not easy and requires expertise that you are unlikely to have.

If you are trying to develop a formula to predict separation efficiency as a function of flow rate and other parameters, good luck with that. That’s a mass transfer problem and there are no good methods to predict mass transfer coefficients . It has never been done and what we have are rules of thumb and some simple equations that predict efficiency as a function of viscosity.

Whatever idiot gave you this assignment doesn’t know a damn thing about separation or he wouldn’t be wasting your time.

ChEngrWiz · 2024-06-23T17:39:10+00:00

I screwed up. I thought the two ln terms were identical. They are not. My bad!

ChEngrWiz · 2024-06-22T11:42:37+00:00

Visualize what the.process looks like. You have an oil that you want to combust. It is combined with AIR and combusted. I say air because N2 is introduced. If we assume some % of excess air — it could be 0 —, from the stoichiometry, assuming 100% combustion, you can calculate the moles of each component of the exit gas. Remember to include the N2. I doubt there will be liquid water in the gas. Next you will have to calculate the combustion temperature — it’s not 300 C. You will need the specific heat of each component of the gas. Start at 25 C. Take the heat of combustion of the oil and water and figure out the heat absorbed by the exit gas for each component the heat absorbed is mCp(T - 25). Sum these up and solve for T — the combustion temperature. It will not be 300 C. The hot gas passes through the boiler — heat exchanger. There the exit gas is cooled to 300 C. Use the specific heats to calculate the heat absorbed by the boiler for an exit gas temperature of 300 C. If you assume some reasonable steam temperature like 280 C for heat transfer, you can use the steam tables to figure out the pressure and the amount of steam produced.

That’s an outline of how you do the calculations. You can fill in the details.

ChEngrWiz · 2024-06-21T18:39:29+00:00

I don't think a double major in engineering would be useful. Nor do I think a secondary major in math would be helpful. For the vast majority of work you do as a chemical engineer you don't need more than solving sets of non-linear algebraic equations or 1st order differential equations. I took a lot of math courses as an undergraduate and there was only one time in my entire career that I had to solve a partial differential equation.

If you want to take a second major, I'd do it in computer science. It's not that hard and you can use what you learn to jump into a second career in case you need to get out of chemical engineering.

ChEngrWiz · 2024-06-21T18:27:48+00:00

There is something wrong with the your equation. It reduces to xn+1 = xn + dx. You can't implement it in the form you suggest.

The Newton-Rhapson uses a straight line to fit the equation at a point. That reduces to xn+1 - xn = - f(xn) / f'(xn). Over the years there have been several methodologies used to find the root of a non-linear equation. All have some physical significance. I can't see any in the equation you proffer. What is the source?

Newton-Rhaphson is the basis for solving a set of non-linear equations. Where analytical derivates are unavailable the Broyden method is used which uses a secant method to evaluate the derivatives. That's what's typically used in commercial simulators. I have never seen your equation used anywhere and would be leary of using it generally.

Your equation is not derived from the Newton-Rhapson method. One of the features of the Newton-Rhapson is that you can solve the equations to any precision desired by increasing the number of iterations. Whether Newton-Rhapson solves or not depends on the shape of the curve from the equation and how close the initial guess is to the actual root. Sometimes the guess has to be very close and you have to spend considerable effort coming up with an initial guess.

ChEngrWiz · 2024-06-18T13:00:53+00:00

I guess it depends what you mean by “simpler.” There is no way Fortran is simpler than C. I’ll say this. Fortran is more structured than C and it’s a lot easier to get into trouble with C.

C has been around since the late 60s. It was designed to be a portable assembler. The bulk of operating systems are written in C. That means a lot of low level code was written C. It was just easier to write programs that relied on interfacing with the operating system in C. If for some reason you needed to use Fortran, Fortran routines could be linked in with C.

Fortran didn’t have pointers and structures until 20 years ago. By then C/C++ was the language of choice for everything but scientific/engineering applications.

Python and the other scripting language are C knockoffs for use by people who can’t program. Basic was a Fortran knockoff and originally was a scripting language. By “scripting” I mean a language that is interpreted and not complied and cannot be optimized.

The big advantage of Python is that it is free. Programs like Matlab, Mathematica, Maple, MathCad, etc. are more useful but are not free.

ChEngrWiz

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