Are there vertical mixers with integrated liquid dosing and spray nozzles for binder addition during granulation?
Yes. There are vertical mixers that have integrated liquid dosing systems and spray nozzles for the defined addition of binder in build-up and wet granulation processes. Such systems are used in the pharmaceutical, chemical, ceramics, food and fertiliser industries.
System structure and operating principle
The liquid is usually added via a combined dosing and spraying system. This comprises an external dosing station with a dosing pump as well as a spray lance or nozzle in the mixing chamber. Depending on the application, single-fluid or two-fluid nozzles are used. They produce a defined droplet spectrum and ensure uniform wetting of the product bed.
The nozzles can be arranged in the lid, laterally in the vessel shell or on a lance. The spray liquid is thereby introduced specifically into the active mixing zone. With viscous binder systems, or those that have to be processed warm, heated lines and nozzles are also possible. The spray quantity, the spray pressure and the timing of the addition are usually controlled via a PLC and documented.
The transition from dry mixing to granulation can take place in the same unit. A single-pot process is thereby possible.
Role of the mixing tool
While the spray nozzles introduce the binder, the mixing tool provides the circulation and mechanical fluidisation of the product. The particles are moved intensively and wetted uniformly. Agglomerates that grow in a controlled manner arise in this way. Local over-wetting and the formation of coarse lumps are avoided.
Many vertical mixers additionally have choppers. These break up agglomerates that are too large and support a narrow particle size distribution.
Advantages of integrated spray technology
Integrated liquid dosing offers several advantages. The binder is distributed more uniformly than with manual addition. The grain structure can be influenced in a targeted manner. The granule properties become more reproducible. Process times are also shortened, because mixing, moistening and granulating take place in the same apparatus.
Closed operation reduces dust emissions and improves occupational safety. For applications subject to validation, CIP- or WIP-capable designs are customary. The lines, nozzles and spray lances are then designed so that they can be cleaned well and form no dead spaces.
Typical designs
Typical designs are conical vertical vessels with a central screw as well as vertically arranged ploughshare or paddle mixers. Depending on the construction, the spray nozzles can be mounted in the lid, laterally in the vessel or on an adjustable lance.
Important design parameters
For stable granulation, the binder properties, the spray system, the nozzle geometry and the process parameters must be matched to one another. This includes viscosity, flow rate, droplet spectrum, nozzle seat, mixer speed, fill level and spray timing. It is also decisive that spray lances and lines are of cleaning-friendly design with few dead spaces.
How amixon® implements binder addition and granulation in the batch mixer
Integrated liquid dosing as a feature
amixon® machines such as VM, HM, AM, SH, AMK, KS and GM can be equipped with liquid addition lances on request. The binder liquid is thereby introduced directly into the moving mix. Two-fluid nozzles are used as an alternative or in addition. They produce a particularly fine atomisation and ensure uniform wetting.
The addition takes place within the active zone of the cutting rotor. Local over-wetting is thereby avoided. The main cause of uncontrolled lump formation is markedly reduced in this way. Even viscous binders can be introduced reliably. A temperature-controlled storage vessel keeps temperature-sensitive liquid binders low in viscosity.
Division of labour in the mixing chamber: macro and micro mixing
The SinConvex® mixing tool circulates the entire volume three-dimensionally. It also contributes to the self-cleaning of the mixer. At the same time it continuously feeds fresh powder into the wetting zone. The cutting rotor distributes the liquid microfinely and breaks up coarse agglomerates as they form.
The same amixon® mixer can be used for moistening with low energy input, for gentle build-up agglomeration, for de-agglomerating or for granulating. The process intensity can thereby be adapted to the particular task.
The torque and temperature curves are monitored via the PLC. This supports end-point determination. Dosing profiles with intermediate mixing phases can be stored as a formulation and called up reproducibly.
From batch to continuous granulation
For continuous tasks, the ring-layer mixer-granulator RMG completes the range. It produces round, low-dust granules with a narrow particle size distribution. amixon® examines in the pilot plant, with the original product, which solution makes sense technically and economically.
Verification in the amixon® pilot plant
Evidence comes before the investment. In the amixon® pilot plant at the headquarters in Paderborn, 35 test units of various sizes are available. They are complemented by pilot plant locations in Japan, India, Thailand, China, South Korea and the USA.
The trials are carried out with the original product, at real fill levels and batch sizes and within the intended temperature and pressure range. Mixing quality, product protection, energy input, cleanability and reproducibility in later series operation are assessed. The results are evaluated and documented together with amixon® experts. This creates a robust basis for the later design. Technical and economic risks are reduced.