“The successful start up and operation of a commercial size unit whose design and operating procedures are in part based upon experimentation and demonstration at a smaller scale of operation.” This whole process is called “scale-up.” (Bentolila, Alshanski, Novoa, & Gilon, 2018). Chemical engineering is all about the conversion of raw products into beneficial ones and this chemical production takes place in two: a chemical reaction followed by purification steps. Typically, a batch or semi-batch configuration is used for chemical production (Bentolila et al., 2018).

In chemical engineering, scale-down and scale-up process are used to optimize production. The scale-down process is involved in the provision of data regarding hydrodynamic and chemical features. This understanding of the data can result in better knowledge about the system.

When a process is fully understood and all its features are recognized, then simulation can be used to convert the scale-up step into the pilot step, especially in chemical factories (Bentolila et al., 2018). The simulation method is time-efficient and allows maintaining control of numerous hydrodynamic parameters that impact the optimization of the process (Basu, Mack, & Vinson, 1999).

Following bench-scale experiments and adjustable calculations, the designed plant can be scaled up into the pilot plant, and hybrid model experimentation can be done. In the end, fine-tuning and designing on a large scale can be done (Bentolila et al., 2018). Hence, when a stand down–stand up strategy is used, identification of crucial elements leads to a more effective simulation and then this simulation can be used in different processes regarding chemical industries (Bentolila et al., 2018).

  References

Basu, P. K., Mack, R. A., & Vinson, J. M. (1999). Consider a new approach to pharmaceutical process development. Chemical engineering progress, 95(8), 82-90.

Bentolila, M., Alshanski, I., Novoa, R., & Gilon, C. (2018). Optimization of Chemical Processes by the Hydrodynamic Simulation Method (HSM). ChemEngineering, 2(2), 21. 

Scale Up Chemical Engineering

As we have explained many times during different opportunities, scale up chemical engineering mainly refers to the main activities of chemical engineering that are in charge to be sure that we are transferring our process adequately from lab to production scale or from one side to the other side. In many companies, the name of these activities is “technological transfer process.” And these activities are very critical for a company because they are involved in a critical step where investing more material is required. We’re performing a very sophisticated and complicated step, that is, transferring our chemistry to a bigger scale.

The main change that happens when we are transferring to a big scale is in the interaction between the materials we are generating when we are controlling our mixing activities. Other parameters like process, raw material, affinity between the materials, fraction, crystallization, the chemical affinity between materials for activities, solubilities, etc., are defined by the materials and the process. So, this aspect of the knowledge won’t be changed. This is the foundation for proceeding to the next step, because we succeeded in the lab or with the older equipment. When we go to the next step, the only thing that can change is the capability of the materials to interact in a way that will generate good results in quality and operation. So, we must control the activities well—and the only way to control them well is to know what environment we’re providing for our materials to interact in. If we are able to use VisiMix well to calculate the mixing, flow dynamics, and other aspects, and to know what environment we are providing to our materials to generate these interactions and progress according to our expectations, we will succeed. But if we know and are controlling our mixing parameters, the most important point is that we will know if the parameters provide our material processes the conditions for the next step, and if we have succeeded or not. If it is not possible to provide these conditions, of course, we will raise a red flag, advising the company to take a different approach and generate the data that will support our next step. But if we are not controlling it—if we are not aware of these many important steps—what will happen is normally what happens in many of companies: deviations occur in the next step. Many of them are big enough deviations that poor performance is generated in the next step. From a business point of view, it isn’t good to progress at this point, because we will lose market material and, mainly, money. So, these points summarize main scale up chemical engineering activities.

And the source of these activities is not some art. They’re not impossible to know; the reality is the opposite. They are very well known and comprise a part of the control by interaction that we provide our materials for progression to the next step. The activities are completely a field within the technological field and are possible to calculate, to connect with the process and knowledge of company we know in order to generate relevant conclusions.

Meso Mixing

Mixing is a unit operation that is a multi-dimensional phenomenon. If we describe in simple words what mixing is, the simple definition in our head is that we are doing these activities to generate homogeneity in our system. But the point is that for the industry, high homogeneity in the tank is not always required in order to generate good results. It really is not an “equal” equation. Good mixing is not equal to a good process. Good mixing is a condition we need to provide the process to generate good results in the industry in quality, purity, and operation. If we are not able to understand the mixing, we will not be able to understand which kind of mixing is good through our process. We will not always have high homogeneity, high shear rate, and high velocity. But the main point of this final definition is that we need to understand what mixing is. Mixing is a sophisticated unit operation that serves the process; it is not the goal of the process. It is really providing service to the process to generate good quality in productivity and operation.

So, the intention of mixing is to generate homogeneity. If we describe what happens in the mixing, we’re talking about multi-dimensional phenomena. We’re talking about the phenomena where, because we are moving our impeller into a tank and generating some flow, this flow will generate some fluid elements that move in the tank and interact in a different way around to the impeller: very far from the impeller, from the wall, and close to the wall. And because we have at least three main different phenomena, we can divide the phenomena into three main ranges of work. The first range of work is the macro mixing. This is the time required to generate 99% of homogeneity in the tank but in the macro. Let’s break down the meaning of this. Let’s say we have balls that are blue, black, and white. If we start to move our impedance, it will take a frame of time in order to generate enough modernity, 99% homogeneity, or, in the intuitive point of view, to put balls in a normal, very good arrangement of black and white, black and white, black and white, large chest, and black ball. The second phenomenon is the interaction between the materials. They will interact in different ways, but what happens is we’re generating fluid elements. The size and time of existence of these fluid elements, turbulence operation, or laminar generation are a function of the local mixing that we are generating. We’re talking about a micro scale step that is the defining the Eddy size and the time that this site is existing, or what we call the Kolmogorov size, Eddy size, and then micro mixing time—the time that these Eddies are existing. Inside these Eddies, the main capability to transfer materials is by molecular diffusivity. And outside this Eddy size, we are talking about the normal inertial mass transfer that we calculate by mass transfer coefficients.

In between them, there is some investigation that is very common in Western parts of the world when we talk about meso mix. The meso mix is a stage between them, not the macro mixing and not the micro mixing.

In this middle step, we can talk about the grading that we have for a zone in the tank that is near where we feed our material into the tank if we are not doing extended circulation time, high velocity of circulation time, lower meso mixing time, or main period of circulation. What will happen is that we will have some gradient between the place that we fit and the zone where we feed the material, and the concentration of material that is very far from this zone. And the meso mixing time will be important. In VisiMix, we don’t consider meso mixing time because this model comes from the Eastern part of the world. To describe this kind of phenomena that can avoid problems like this, we talk about main period of circulation. This refers to how long it takes to do one round in the tank; we can think of our impeller as a pump that is generating some circulation flow. So, if we take the volume by the average circulation flow that we have into the tank, we have some idea about what the meso mixing time is or, in our case, the main period of circulation.

These three main numbers determine how the interaction between the materials in the dynamics will be—not in the position but in the dynamics. And this dynamic is important for reactions, crystallization, and for our capability to purify the crystallization materials or generate a reaction according to what we expected from the main and secondary reaction.