The high-shear rotor/stator mixer (HSM), once relegated to a relatively narrow niche of mixing applications, has develop into a mainstay in quite a few applications in the chemical method industries (CPI). The potential to apply intense shear and shorten mixing cycles offers these mixers broad appeal for applications that call for immiscible fluids to be formulated into emulsions, or agglomerated powders to be dispersed into a liquid medium. Especially through the final decade, the emergence of new variations on the original rotor/stator mixer notion has extended the HSM’s usefulness to extra diverse applications. For instance, traditional HSMs in each top rated-getting into batch configurations and inline versions, are broadly used currently for higher-intensity mixing, dispersion, disintegration, emulsification and homogenization.
Applications range from dispersions involving gums, pigments, fumed silica, calcium carbonate and active drugs, to emulsions such as cosmetic creams, lotions, and flavors. Having said that, in spite of the expanding reputation of HSMs in many industries, they are nevertheless widely misunderstood. Business-based and university researchers have focused mostly on operating out the dynamics of conventional low-shear mixing technologies, such as axialand radial-flow turbines. With only a few notable exceptions, high-shear mixing has been largely overlooked in terms of fundamental analysis to unlock its mysteries and support customers to far better predict mixing outcomes, especially during scale-up.
Given that the physique of literature obtainable for predictive engineering related to rotor/stator mixing is really thin, the application of HSMs is generally approached empirically – with heavy emphasis on application-particular testing and development by individual suppliers in the process industries. A handful of users have invested heavily and accomplished impressive good results with HSMs in narrowly defined applications such as ones involving emulsion polymers and pigment dispersions. Others have been much less effective on their own. Most potential customers of HSMs rely on the recommendation of mixer producers, who often retain their proprietary application recommendations a closely guarded secret. The outcome of this lack of available knowledge about high-shear mixing is that misconceptions regarding the appropriate application and use of HSMs have proliferated. There are a lot of frequently held misconceptions and typically created application errors. Readers who are able to stay clear of these errors will save time and income in their search for the ideal rotor/stator mixer, and decrease their risk of choosing a mixing system configuration that looks fine in the laboratory but fails to execute adequately on the plant floor.
Scaling up
In practically any application, scale up is a crucial approach that impacts your business in a multitude of ways, from proper planning of plant floor design and gear configuration, to operating procedures, to the net operating and capital-cost influence on the bottom line. In laboratory-scale trials, misjudging the time needed to obtain mixing equilibrium by just a few seconds can ultimately cost your business millions of dollars, not to mention wasted time and effort and elevated wear-and-tear on the equipment, through industrial-scale production.
The laboratory tabletop HSM typically represents the initial step in exploring the certain benefits of rotor/stator technology for a given application. This familiar laboratory tool is usually equipped with a range of interchangeable attachments that permit it to operate in a selection of mixing modes – as a traditional HSM, as a propeller mixer, and as a higher speed “saw tooth” disperser. Such versatility is essential in bench-scale improvement, because it makes it possible for the investigation-and-development particular person to quickly test many diverse processing approaches.
Having said that, as valuable as the lab scale mixer may be, it is also the source of a single of the most common and expensive blunders in the scale up from laboratory- scale HSM to pilotscale and production machines. Unless バッチミキサー is carried out systematically and with excellent care and accuracy, subtle errors in more than-processing on the benchtop can produce huge errors in scale up projections. Such errors are specifically common, for the reason that many engineers underestimate the lab-scale mixer’s extraordinarily high throughput- to-product-volume ratio.
Before we move additional, let’s explore one far more concept: equilibrium mixing outcomes. For sensible purposes, this is the point at which the mixed item has acquired a target characteristic – such as a certain droplet or particle-size distribution – that will not transform substantially, no matter how long you continue to process the product. When we perform with dispersions, this is the point at which we reach the equilibrium particle size. For emulsions, it’s the equilibrium droplet size.
Regardless of whether we are operating with emulsions or dispersions, this significantly is specific: we will attain equilibrium significantly more quickly with a labscale mixers than with a scaled-up pilot or production unit.
Based upon the application and the rotor/stator design we use, we may possibly reach this mark in one particular tank turnover or in quite a few hundred-tank turnovers.
Now, think about this typical real-globe scenario involving a test with a lab scale mixer. Take a two-liter beaker and add the following components to prepare an emulsion: Water phase
– Oil phase
– Water- or oil-miscible surfactant
Now, reduce the batch-variety lab HSM into the liquid. But just before you push the start button and head down the hall for another cup of coffee, contemplate this: That little 1-3/eight-in. rotor/stator generator on your mixer may perhaps operate with a throughput of 100 liters per minute or extra. With a 2-liter batch in the beaker, that translates to one comprehensive batch turnover each and every 1.two seconds. Presuming that in this application 10 tank-turnovers generate the preferred emulsion (a plausible number for numerous simple emulsions), this implies that you may well reach mixing equilibrium in just 12. seconds!
In the actual planet, this is where human nature takes more than. As you go for coffee, you keep the tabletop batch going for five minutes, and when you check the final results you come across that the droplet size distribution of your emulsion is appropriate exactly where you want it to be. A good results! But what definitely occurred? You processed the batch for 5 minutes, turned the batch over 250 instances, and reached the appropriate endpoint. But your solution did not change once it had reached its mixing equilibrium in just 12 seconds – so the remaining 4 minutes and 48 seconds created no appreciable transform in the mixed solution. That is the margin by which you really overshot your mixing equilibrium. In a lab-scale example, over processing by four minutes and 48 seconds may not look like a significant deal – but consider the implications in terms of productivity, energy charges, labor, and wear and tear when such an error is propagated for the duration of scale up to a bigger pilot- or production-scale unit.
Now, rapidly-forward to your scale up needs applying the above example. Look at that you will need to create this product in 500-gallon batches. If you assume that you will have to have 250 tank turnovers to achieve your process goals (as an alternative of 10, which is seriously all you need to have), then you will pick a top rated-getting into, batch HSM that will approach 125,000 gallons by means of its rotor/stator generator in an acceptable period of time. Drawing from knowledge, we assume that a 30-hp unit with a 7-in.-dia. rotor will pump roughly 500 gal/ min. As a result, our 250 tank turnovers (125,000 gallons) will require 250 minutes (four hours, 10 minutes). This projects to a capacity of roughly two batches per eight-hour shift, or ten per single-shift week. If, at the lab scale, we had better understood that the process aim was reached in just 12 seconds (ten turnovers), we could have projected that the similar production unit would full the activity in about 10 minutes. This projects to roughly 240 batches per week – an improve of 230 batches per week.