For many years the SMX static mixer has been the preferred solution for mixing viscous liquids. As the outcome of its continuing pursuit of optimisation, driven by the most advanced simulation techniques and complex test series, Sulzer is now pleased to present a new mixer generation. The SMX plus mixer excels with extremely efficient homogenisation and about 50 % of the usual pressure drop.
Static mixers represent an attractive alternative to dynamic stirred tanks for mixing fluids. Especially in continuous processes, this mixer type offers a number of interesting advantages such as a low energy requirement, short residence time, small mixer volume and very low shear stress. In a static mixer, the fluids to be mixed are pumped in the desired ratio through a pipe with special internals to produce the mixing effect. With turbulent, low-viscosity fluids, this effect is created by turbulences. In case of laminar flowing, high-viscosity liquids, mixing is achieved by the formation and relocation of layers. In short, many relatively simple mixer geometries can be used to mix turbulent flowing fluids. By contrast, mixing laminar flowing liquids is challenging and only a limited number of mixer geometries are suitable. The SMX static mixer has been the preferred solution for such advanced applications for many years. This model is designed to mix high to very high-viscosity liquids. Low-viscosity additives can be mixed into high-viscosity fluids and non-soluble liquids evenly dispersed, and the mixer is also ideally suited for reactions with a narrow residence time distribution.
The optimum mixer for this kind of application typically has a compact design, a short installation length and a pressure drop that is as small as possible. With advanced applications, such as admixing tiny amounts of a low-viscosity additive to a very high-viscosity fluid, it cannot be taken for granted that the mixer will be able to perform properly.
Optimised mixing geometry
The standard SMX mixer has been the ideal, indeed almost the only, solution for advanced mixing applications in the laminar field for many years. It was therefore uncertain whether there would be any potential for further improvements. The influence of several factors relevant to mixing performance, such as the number of bars, bar thickness, angle between the bars etc., were analysed and optimised using advanced CFD (Computational Fluid Dynamics) techniques. The result came as something of a surprise. It turned out that gaps between the bars resulted in a significantly smaller pressure drop without any negative impact on mixing performance. Several further tests using different methods like LIF (Laser Induced Fluorescence) confirmed these findings. The SMX plus mixer also showed the same excellent performance already achieved with the current SMX design for dispersion and for mixing high / low-viscosity fluids.
The new mixer geometry, for which various patents are pending, will be sold under the brand name SMX plus. The SMX plus mixer provides important advantages compared to the standard SMX models and even more when it comes to other mixer geometries such as helical mixers. The length and volume of an SMX plus mixer will be only 40 % of those for a helical mixer for a given mixing task and a given maximum allowable pressure drop. If there are unequal viscosities and volume flow ratios, the difference in size will even be more dramatic up to the point where a helical mixer is unable to fulfil the mixing task correctly.
Compared to a standard SMX mixer, the SMX plus will have a 20 % smaller diameter, offering substantial cost saving potential. Depending on the application, not just the mixer but the whole plant can be designed on a smaller scale.
For a given mixer size, the pressure drop in an SMX plus mixer is only about half that of its standard SMX counterpart. As a result, energy consumption is reduced and a smaller pump can be installed, depending on the situation. The greatly reduced pres-sure drop additionally has a positive effect on the shear rate. Shear-sensitive products such as polymers can thus be mixed very gently.
The length and diameter of the SMX plus mixer will be designed on a case-to-case basis, depending on the application and the mixing task. The mixer will be supplied with a housing as well as with an integrated dosing system if required. A version with a double jacket for cooling or heating is likewise possible.
The SMX plus mixer will set a new stand-ard and benchmark for mixing and dispersing laminar flowing fluids. It is predicted to further push the steadily growing static mixer market and turn the gentle and more efficient static mixing technology into a viable substitute for dynamic mixers in the near future.
Sulzer Chemtech Ltd.
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