Example 1. Developing a technical solution to improve paint quality
The paint produced at a paint manufacturing plant in Slovenia, in a 1.6 cub m mixing tank with a propeller agitator, did not meet quality requirements. Changes in the paint formula proved to be inefficient. The plant engineers used the VisiMix program to simulate the mixing process in the tank.
The VisiMix simulation showed that the impeller did not ensure a complete suspension and uniform distribution of the solid pigment in the tank. The simulation also made it possible to find an acceptable technical solution that ensured a satisfactory degree of uniformity using the same drive, by replacing the propeller with a correspondingly designed Pitch paddle impeller.
Example 2. Scaling-up: Heterogeneous liquid-liquid chemical reaction
In a chemical laboratory in Ohio, US, an organic synthesis process was developed based on a heterogeneous liquid-liquid chemical reaction. The process was studied experimentally using a 2.5 liter laboratory reactor. The company used VisiMix to reproduce the synthesis on a larger scale. As a first step, As the first step, they defined values of the mixing parameters that are recommended in VisiMix as the key mixing parameters affecting the heterogeneous chemical reaction: specific mass transfer area, micro-mixing time for the disperse phase, etc. Next, they used these values as baseline parameter values for scaling-up VisiMix was used to select the correct mixing conditions (liquid volume, impeller speed, etc.) for reactors of a larger scale (25 liters in the US and 950 liters in Switzerland), in order to obtain the same parameters as those in the laboratory reactor. The synthesis was then reproduced in the larger reactors without any additional testing.
Example 3. Reducing the duration of a heterogeneous reaction by changing the baffle design
A Dutch company developed a process that included a three-phase chemical reaction. In a laboratory vessel, the reaction took 30 minutes. But in a glass-lined 6.3 cub m reactor, the same process was found to take about 4 hours. The VisiMix simulation made it possible to find the cause of the process deceleration and to reduce the reaction time.
The VisiMix simulation of liquid-liquid mixing showed that mixing in the production 6.3 cub m reactor was not good enough to ensure complete emulsification of the liquid reactant. VisiMix also showed how the separation of phases can be avoided by increasing the baffles, and helped develop a special, technically acceptable baffle design. After replacement of the baffles according to these recommendations, the duration of the process decreased dramatically.
Example 4. Changing impeller position to prevent plugging up the discharge tube
An Israeli pharmaceutical company used a 12 cub m reactor in which the discharge tube was constantly getting plugged. The problem was not observed in other reactors, which used other mixer types. The engineers assumed that the problem was caused by bad mixing, and contacted the manufacturer of the equipment, who recommended replacing the mixing device with a new one.
But the company had just purchased VisiMix, and the engineers decided to use the software to analyze the mixing process in the problematic reactor. The calculations performed with VisiMix showed that the mixing conditions of the suspension in the reactor were quite good – at least not worse than in the other reactors, which did not experience plugging. This meant that the problem was caused by something other than mixing, and there was in fact no need to replace the mixer. VisiMix analysis also showed that the volume of suspension below the impeller was relatively large, and that the quantity of solid phase in this volume was large enough to plug up the outlet opening during the final stage of suspension discharge. To reduce this volume, the engineers decided to place the impeller closer to the bottom of the reactor. Mixing conditions and shaft reliability for this modified design were again checked with VisiMix, and the impeller was lowered accordingly. In the modified system, the outlet no longer became plugged.
Example 5. Eliminating shaft vibrations
In a chemical plant in the UK, it was not possible to begin synthesis of some product because of vibrations of the impeller shaft. To meet process requirements, the impeller speed in the reactor had to be at least 600 rpm. At this speed, however, violent vibrations were observed. Plant engineers used VisiMix to study the possibility of avoiding vibrations at increased impeller speeds. Analysis showed that this range of impeller speeds was close to the critical (resonance) frequency of the shaft. Using in parallel the mixing simulation and mechanical calculations functions of the VisiMix program, plant engineers designed a special 2-stage mixing device that provided the necessary process parameters and had a significantly higher critical frequency.