The wet and the dry
The venturi system for mixing powders into liquids

Adding powders to liquids is a common requirement in the pharmaceutical and other process industries, yet many companies are still using outdated mixing technologies. Advice from a specialist mixing company can improve process performance.

Most recipes in the chemical, pharmaceutical, cosmetic and food industries require powders to be added to liquids and mixed—whether the product is paint, suppositories, creams or yoghurt. As with many other everyday process operations, there are plenty of methods, both new and old, for mixing powders into liquids. None of these methods is optimal, however, and many industries are still using obsolete equipment for this purpose. The engineers at JetSolutions, in contrast, are continually developing new technical solutions in mixing, and they have applied a specific technology to optimize the introduction of powders into liquids.

Stringent standards
The most important standards relevant to powder/liquid mixing are Atex and GMP/FDA. Atex (EU Directive 94/9/CE) applies to equipment designed for use in potentially explosive atmospheres. It has been in force since June 2003, and by the end of 2006 it will apply to all existing installations as well as new ones. Atex imposes new regulations covering safety in powder handling. For instance, it specifies that powders are no longer allowed to simply fall under gravity into a reactor or hopper. Instead, they must be transferred in such a way as to reduce the risk of static generation, which in turn can lead to an explosion.
The venerable GMP and FDA standards impose on the pharmaceutical, cosmetic and food industries requirements for hygiene, cleanability and the use of sterilizable parts. The GMP/FDA standards, which must be validated, impose stringent requirements on the design, materials and construction of equipment items such as mixers.
As well as Atex and GMP/FDA, operator protection is an important issue for both companies and regulators. With today’s high-potency pharmaceutical active ingredients, reducing operator exposure by controlling dust is a key objective.
The JetSolutions answer to the problem of mixing powders and liquids is to use a venturi, a simple yet effective and versatile concept that can handle a wide range of ingredients and physical properties. The design was patented more than ten years ago, at a time when most manufacturers were more interested in producing lump-free dispersions than in controlling hazards from powder handling.
The venturi concept
The venturi is a reduced-area section of the liquid feed pipe that has the effect of increasing the fluid velocity. The velocity increase creates a region of reduced pressure in the injection chamber, causing powder to be sucked in from the hopper. Additional inlet orifices allow small quantities of other liquids, gels or pasty materials to be added to the mix. The JetSolutions patent is based on the fact that a flat liquid jet maximizes the surface area of liquid available to wet the powder. The powder is sucked in at a uniform rate, and is wetted particle by particle (the “sand-paper effect”). The system can be designed for throughputs of from 10 kg to 10 t per hour.
The venturi system has several advantages for powder mixing. It works with a wide range of fluid viscosities, from water to thick paint; any fluid that can be pumped can also be mixed. More than
100 percent of powder can be incorporated. The mixer can be mounted in-line, or on a vessel for either batch or recirculation mixing.
No moving parts
Unlike a rotor-stator mixer, there are no moving parts inside the venturi mixer. This improves reliability and reduces maintenance requirements. It also helps to make the mixer easy to clean—the process is no harder than cleaning a pipe, and JetSolutions can supply automated systems for cleaning the whole powder-handling zone. The ability of the venturi mixer to work with gravity powder feeding eliminates powder handling operations such as conveyors, pneumatic transport systems and manual discharge from hoppers, so process design is simplified and powder containment is improved.
The absence of rotating parts also makes the mixing process more efficient. This saves energy and reduces undesirable heating of the substances being mixed. To obtain the same mixing performance as a venturi mixer fitted with a
3 kW pump, for instance, a rotor-stator mixer requires a motor rated at 15 kW, or even more for viscous fluids.
Because a venturi mixer operates at lower shear than a rotor-stator mixer, it causes less mechanical damage to the particles. This is especially important for products with long molecular chains, such as Aerosil. Less damage to the particles means that more of the powder remains effective, and the amount of powder in the recipe can often be reduced.
The venturi technology provides clear and strict separation between liquid and powder, which simplifies Atex certification. The simplicity of the design minimizes the number of parts that have to be certified, with a consequent saving in cost of up to 50 percent.
Venturi mixers can be added to many forms of powder storage unit so as to create a closed system. As the injector itself is very small, it can often be located beneath the discharge station for containers, big bags or silos, or under a glove box, for example.
Many applications
The venturi mixer combines high performance on powder/liquid blending tasks with great versatility. Applications include mobile systems, mixers fitted with gloveboxes for maximum containment, discharge systems for containers, silos and IBCs—with automation, dosing and inerting systems as required, and barrel discharge systems. For small quantities, it is also possible to use the vacuum generated by the injector to suck up powder directly from sacks.
The experienced team at JetSolutions helps customers choose the best equipment for their powder/liquid mixing jobs and operate it to best advantage.