Reactor stirring
Thread Content
Our company used to use 5,000-meter reactors for production without too many problems. Now we use 20,000-meter reactors, but there are a lot of unqualified ones. From the impurities, it seems that there are many problems that are caused by uneven mixing. How to solve the problem of uniform mixing? Does it mean that the mixing is uneven if the volume is large? I would like to ask you for advice.
The volume should not be a problem, because this factor was taken into consideration when designing the reactor. I personally think that the mixer does not match or has low power, or the design effect is not achieved due to the equipment itself during use.
The greater possibility is uneven heat exchange. It mainly depends on your specific reaction process.
Conduct detailed analysis on operating procedures and equipment parameters. Generally, as the container increases, the operating time and various conditions will increase accordingly (not linearly). You can slowly experiment to find the shortest operating time and parameters.
This is a project amplification problem. The product specifications of a 20,000-meter reactor should be the same as those of a 5,000-meter reactor, and should even be the same as the pilot test. If they are different, it means your reactor (including the stirring system) is not designed well. Can you send your process conditions and existing reaction drawings to my email, and I will take a look at it for you. I think I should help you solve it. Mail: shgyhp@21cn.com
I personally think there is a problem with the mixing selection, resulting in insufficient back-mixing.
I think the main problem is stirring. With so much put in the reactor, the stirring may not work very well, and there is no way to better achieve a homogeneous effect. If the material in your reactor has a high viscosity, it will be even more difficult to use. The expansion of the reactor is actually a difficult thing to deal with. This situation also happens in my unit.
Then your mixing time has not changed? I need to do an experiment to determine the mixing time.
If the reactor is large, the stirring will definitely not be as good as that of a small reactor. You can use double-layer stirring and add baffles. This can achieve a good mixing effect. The choice of stirring motor power does not expand linearly. You can give the relevant information to the reactor manufacturer and they will help you provide it.
Although I have no practical experience in this area, I can still learn knowledge from experts. I think the selection of the mixer, mixing power and mixing time are all related. You might as well check these aspects one by one.
1. Stirring problem. With so much put in the reactor, the stirring may not work well. The 5000 is a double-layer or single-layer stirrer. Is the 20000 now a double-layer or multi-layer stirrer? Is its power sufficient? 2. Are the rotation speed of the stirring paddle, heating temperature and heating speed selected appropriately? 3. Whether the viscosity of the materials in the kettle is the same, and whether the stirring paddle is of frame type or blade type. 4. The reaction process does not work just by amplifying it. It does not change linearly. Some successful processes in laboratories do not work well when applied to actual production. You need to experiment many times and carefully consider temperature control, rotation speed, number of blade layers and shape.
Typical industrial equipment amplification issues. Theoretically, it should be a three-pass problem, and the main problem is fluid mechanics, but in fact it is impossible to expect such analysis on the spot. The possible solution now is to modify the mixing. It may be difficult to change the kettle, but it is still possible to add some internal parts of the kettle. In terms of dynamics, the reactor should be a fully mixed flow model, so the medium concentration is required to be the same. In response to the original poster's question, the main focus should be on stirring and adding some internal parts to the cauldron. Several people above also said that we should look for the reason from the number of mixing paddles, power, and number of layers. ； It is still a baffle design, and some work should be done on the guide tube. ； There is also the stirring time (essentially the concept of residence time in dynamics). If you don’t necessarily have any insights at once, you should start by restating the design information, look at the design problems first, and then improve them one by one. I still have to learn something.
Use fluent to simulate and find problems
It may be related to stirring, but it is also related to operating conditions such as reaction temperature, pressure, residence time, etc.
Personally, I feel that the possibility of such a problem has little to do with temperature and pressure, but has more to do with the form of stirring, speed, and residence time.
It is recommended to consider analyzing the impact of amplification factors
If it is a problem with reaction mixing, the rotation speed or stirring paddle structure should be increased.； In addition, external tank circulation can also be carried out and a static mixer can be added.
according to what you said: Many products with unqualified content seem to have a lot of impurities due to uneven mixing. I think this is mainly due to the effect of stirring. It is necessary to 1. speed up the stirring speed, 2. improve the stirring structure, 3. appropriately add baffles to the reaction kettle, etc.
Is it possible to introduce gas from the bottom? :)