Advanced Mixing Technologies Enhance Process Efficiency

New mixing solutions lead to higher yields, while minimizing energy consumption and material waste

Usually engineered for a specific application in the chemical process industries (CPI), mixing solutions have the potential to enhance the efficiency of any process, leading to higher yields, lower energy consumption and reduced waste. To ensure that chemical processors are getting the most effective mixing technologies, equipment suppliers are improving their designs and applying them in new ways to provide greater efficiencies in existing and emerging applications.

“Mixing equipment can greatly contribute to process efficiency,” says Erin Dillon, media and marketing coordinator with Charles Ross & Son Co. (ROSS; Hauppauge, N.Y.; mixers.com). “The right mixer can shorten processing times, improve product yield and reduce material waste. A well-built mixer is one of the most effective ways to improve efficiency as it will deliver consistent results and withstand the demands of chemical processing.”

Shawn McManus, regional sales manager, chemical market, with Admix (Londonderry, N.H.; admix.com), agrees that equipment that is properly designed for the application is essential to achieving process efficiency in mixing operations: “Mixing equipment can be a primary contributor to process efficiency because it takes a given amount of energy to achieve a goal and the way that the mixer is engineered, designed and sized can determine whether that energy is being used in the most efficient way.”

He adds, “One of the greatest challenges processors experience with mixing operations is selecting the right piece of equipment for the application.”

Steve Knauth, marketing and technical manager with Munson Machinery Co., Inc. (Utica, N.Y.; munsonmachinery.com), explains that several mixer/blender types can often satisfy any given requirement, making it critical to evaluate all applicable machines early in the selection process.

“For example, of the eight mixer/blender types offered by Munson, three machines can overlap in capability: ribbon/paddle/plow blenders; rotary batch mixers; and V-cone blenders,” says Knauth. “While agitated ribbon/paddle/plow blenders are the obvious choice to break down soft agglomerates and blend pastes or slurries, they are often less efficient at blending dry bulk materials than rotary batch mixers and V-cone blenders when gentle blending, short cycle times, total evacuation, rapid sanitizing or energy efficiency are prioritized.”

For this reason, he says, any mixer that is under consideration should be evaluated thoroughly in a test laboratory using the processor’s actual materials.

Innovation removes roadblocks

In addition to assisting processors with selecting the best mixing technology for the job, equipment providers are developing new technologies or tweaking existing designs to help overcome roadblocks to mixing efficiency.

“We are constantly working to find new and better ways to make mixing, dispersion and emulsification more efficient,” says McManus. “Our Rotosolver in-tank, high-shear technology is a prime example. Traditionally, in-tank, high-shear mixing devices would feature a sawtooth-style dispersion blade, but the Rotosolver differs from that technology in its ability to pump with five times more efficiency than conventional sawtooth blades” (Figure 1).

He says sawtooth blades generate laminar flow patterns that can be detrimental to the overall process because they centrifuge large agglomerates and particles toward the outside of the tank, taking them longer to get through the shear zone. “The Rotosolver develops a turbulent pattern by pumping up from the bottom and down from the top of the tank simultaneously. Material collides and is accelerated out through a network of slots that provide a near rotor-stator level of shear without the stator, so it can achieve emulsions where sawtooth blades cannot, providing the same results as a sawtooth blade, but with 25% less energy input and a significantly reduced amount of time.”

Another challenge for chemical processors is the varying properties of ingredients and final products, says Fabian Müller, head of R&D with Gericke (Regensdorf, Switzerland; gerickegroup.com). “This requires the need for both high- and low-shear mixing. Our GMS mixer can handle gentle mixing, but can also be equipped for high-shear mixing, offering versatility for different ingredient properties. And, for highly potent ingredients added at concentrations below 0.01%, the GMS achieves maximum homogeneity and preserves high-radial and axial transfer rates” (Figure 2).

He adds that Gericke’s continuous GCM mixer offers optimal radial and axial mixing to ensure high homogeneity and can prevent de-mixing due to its system design.

When properly dimensioned and designed, these mixers can enhance process efficiency and performance and help reduce overdosing, especially for expensive minor ingredients where a minimum threshold is needed. “A quality mixer ensures homogeneity, reducing extra concentrations and lowering operational costs. The GMS provides ideal mix quality quickly, even for micro ingredients, while the GCM guarantees maximum homogeneity with low active pharmaceutical ingredient (API) concentrations,” says Müller.

Peter von Hoffman, general manager of the compounding machines, engineering plastics and special applications business unit with Coperion GmbH (Stuttgart, Germany; coperion.com), says that achieving repeatable high quality is mandatory in most mixing applications. “Extrusion is a continuous process and within the self-wiping process section of the ZSK twin-screw extruder, the raw materials are intensively mixed and homogenized and leave the extruder as a melt with a consistently very high product quality,” he says. “And, extrusion with the ZSK is a reproducible process, so a specific product quality can be produced again and again with the same process parameters” (Figure 3).

The company continues to develop features for the ZSK twin-screw extruder to achieve higher levels of mixing efficiency. “For example, our Feed Enhancement Technology (FET) equips the extruders with a porous, gas-permeable wall section to which a vacuum is applied externally. This solution helps to feed fine powders into the process section at high rates. This considerably increases throughput rates and cost effectiveness, while the ZS-EG side degassing unit ensures a stable devolatilization of the melt to get rid of solvents or moisture and achieves consistent high product quality,” explains von Hoffman.

New gas-mixing developments

The mixing of gases into liquids can present many challenges when designing agitation equipment, but new technologies are being designed to provide greater efficiency in these operations. “Careful consideration must be taken regarding the mass transfer rate, bubble size control, holdup and distribution of the gas,” explains Irfan Rehman, vice president of the mixing division, with GMM Pfaudler (Mumbai, India; gmmpfaudler.com).

“In applications such as fermentation, where there could be gas, liquid and solid phases, the conversion of gas is fairly low. At times, the gas may be toxic or expensive and venting such gases poses challenges,” notes Rehman. “A self-aspirating impeller system therefore becomes very attractive and can be used to recirculate the unreacted gas from the vapor space back into the bulk mass.”

As such, Pfaudler developed the High Efficiency Gas Induction Impeller (HEGI; Figure 4), which was designed to help induced gas become well dispersed into the reaction bulk, enhancing gas-liquid mass transfer rates. HEGI offers a threefold gas holdup and a better volumetric mass-transfer coefficient compared to traditional induction impellers.

“The amount of gas we can induce with the HEGI is greater than competing technologies, such as pipe and impeller and stator-type impellers. This is due to the unique design of the HEGI impeller,” says Rehman. “The impeller is also able to distribute the catalyst uniformly in the tank.”

ProSep (Houston, Texas; prosep.com) has developed its Annular Injection Mixer (AIM; Figure 5) to achieve efficient mixing of injected fluids with multiphase, gaseous or liquid dominant flows with a low pressure drop over the operating range, says John Sabey, chief technology officer with the company. “In this technology, momentum transfer creates injected fluid dispersion with high mass-transfer properties, while the annular injection ring along the pipe wall creates a homogeneous downstream process fluid.”

The technology is currently being used in applications such as LNG conditioning, LPG quenching and natural gas processing.

Additionally, the company has conducted joint testing on post-combustion carbon capture, which has evolved into a design for compact contactor tower trays for mixing solvent with the flue gas to capture contaminants with a higher efficiency (fewer trays), lower pressure drop per tray and higher throughput velocities, resulting in reduced diameter and height, says Sabey. “The efficiency gains are derived from the higher solvent surface area and more intimate contact between the gas and solvent.

“These developments are still ongoing with the intention of establishing a spin-off company focused explicitly on post-combustion carbon-capture applications,” Sabey continues. “And, it stands to reason, this innovation applies to conventional gas processing for acid gas removal and dehydration, allowing for higher throughput capacity or greenfield applications to reduce the initial system capital investment.”

Process intensification

Due to increased material and energy costs, many chemical processors want to optimize existing processes for greater levels of throughput and efficiency, and this can be done using advanced static mixers, says Didier Schons, head of sales, static mixers for Europe, Caspian and Africa, with Sulzer Chemtech GmbH (Essen, Germany, sulzer.com). “Sulzer Mixer Reactors open up new opportunities for process intensification in terms of high conversion, high throughput and accurate control of heat transfer (for example, by the Sulzer SMR heat exchanger),” explains Schons.

The SMR (Figure 6) is a heat exchanger that allows high-efficiency cooling or heating of viscous media and is applied when effective mixing and controlled heat transfer are requirements. “The unique tube layout in each section is similar to that of a static mixer geometry and induces a radial flow on the shell side that suppresses the formation of laminar layers in viscous streams,” says Schons. “This effect enhances the heat transfer and combines well with the high surface area per unit volume, making the SMR one of the highest performing reactors/heat exchangers.”

It offers well-defined mixing and small reaction volume due to high driving forces for the reaction, low shear for gentle product treatment, as well as fast product transition and fast change of process conditions.

Reducing processing time

Many chemical processors are interested in reducing process time, so modern mixing equipment is more often being designed to combine steps and include monitoring and automation to enhance reliability of equipment and process.

For instance, the ROSS Multi-Shaft Mixers and Planetary Dispersers combine multiple agitation methods in a single vessel, eliminating extra processing steps and improving efficiency, says Dillon. “Vacuum mixing is another game changer because it simplifies the degassing procedure, which used to be a separate downstream operation, while improving product quality in sensitive formulations,” she says. “Ongoing innovations in mixing technology also focus on automation and process optimization. Advanced control systems allow real-time monitoring for machine and process status, predictive maintenance and calibration, automatic data logging and secure batch traceability.”

She continues to say that modern controls (Figure 7) enable tighter process monitoring, allowing for real-time adjustments that improve product yield, shorten cycle times and streamline cleaning and changeovers. “From recipe-driven batch control to fully automated cleaning-in-place (CIP) systems, advancements in monitoring and control combined with the elimination of processing steps help chemical processors improve consistency, reduce operator intervention, minimize waste and enhance overall process efficiency and reliability.”

Also helping to make operators’ tasks easier to perform and increasing overall efficiency are features found on Munson’s Rotary Batch Mixer (Figure 8), which gently mixes batches of free-flowing ingredients with or without liquid additions in one to three minutes, evacuates 100% of the batch and lacks internal seals or bearings, allowing rapid sanitizing with no tools.

The mixer’s proprietary mixing flights create a four-way tumble-turn-cut-fold mixing action that imparts minimal energy to the batch and directs it toward and through a stationary discharge gate as the vessel rotates, preventing segregation, regardless of disparities in the bulk density and particle size or shape of ingredients. Side doors and a retractable inlet provide access to all material contact surfaces for rapid cleaning and visual inspection.

And for small batches, such as laboratory or pilot-production-scale batches, INDCO (New Albany, Ind.; indco.com) offers a mixer that is capable of high-speed dispersion, as well as low-shear gentle mixing with high torque, says Mark Hennis, INDCO president.

The company’s HSM-03V (Figure 9) is a versatile, benchtop lift-style mixer and disperser for containers up to five gallons. Initially designed in collaboration with the printing ink industry and suitable for a range of liquid products, the mixer offers the speed and torque characteristics to handle challenging mixing and dispersion applications normally requiring more than one mixer.

Emerging applications

When it comes to applications in the energy transition and sustainability spaces, available mixing technologies are being applied in novel ways, says Sulzer’s Schons. “For example, we supply static mixers for sustainable aviation fuels (SAF) and hydrotreated vegetable oil (HVO) production,” he explains. “While the static mixers used in these applications are not new patents, the operating conditions of treating the used cooking oil include specific temperatures and viscosities that are different from traditional applications and have mandated the use of new materials and designs adapted for these conditions.

“In these applications, our static mixers are used in pretreatment of the used cooking oils, as well as in hydrotreatment processes to convert the oils into sustainable fuels,” explains Schons.

Another emerging application for static mixers can be found in the production of hydrogen, continues Schons. “The upstream water preparation and the efficient admixing of chemicals and the dispersion of gases in the electrolyte solution are important tasks, where static mixers make the difference,” he explains. “Even more important is the complete homogenization of hydrogen in natural gas to ensure a constant caloric value for gas stoves or to prevent overheated zones in reactors.”

Pfaudler’s Rehman says that there is an opportunity for mixing technology to support emerging applications. “There are so many applications for mixers in the energy transition, carbon capture and plastic recycling sectors,” he says. “We already have the tools and a variety of impellers, so in these applications, it comes down to understanding what the customer is trying to achieve and performing test work, computational fluid dynamics (CFD), validating data and trying to scale up the processes with efficiency. In this way, we can support novel applications and be more innovative with our technologies.”

Joy LePree