Are there vertical twin-shaft mixers (HM) with an integrated liquid spray unit for granulation?
Yes, vertical twin-shaft mixers can be equipped with integrated liquid spray units for wet granulation. Such systems enable simultaneous mixing, wetting and granulating in one unit and are used, depending on the design, in construction chemistry, fertiliser production, ceramics, powder metallurgy as well as in chemical and pharmaceutical process engineering.
Technical design of the spray unit:
- Nozzle systems: depending on the process requirement, single- or two-fluid nozzles are used. Two-fluid nozzles with air and liquid flow generate a finer atomisation and support an even distribution of the binder liquid.
- Positioning: the spray lances or nozzles are typically arranged so that the liquid is introduced directly into the moving bed of mix. Wetting and granule formation can thereby be controlled purposefully.
- Dosing: the liquid feed takes place via suitable dosing and pumping systems, frequently with regulated flow monitoring, in order to set the spray rate and product moisture precisely.
- Process monitoring: for reproducible results, torque, product temperature and moisture are frequently recorded in order to determine the granulation end point reliably.
Process engineering advantages:
- Homogeneous wetting: the combination of intensive turnover of the mix and targeted liquid injection encourages an even distribution of the binder.
- Short process times: mixing and granulating can take place in one step, which makes the process more efficient.
- Reproducible granule properties: through precise control of spray rate, nozzle pattern and mixing intensity, grain size distribution, density, porosity and strength can be influenced purposefully.
- Process integration: depending on the plant, pre-mixing, moistening, granulating and in part also subsequent drying can be carried out in one batch.
- Low residual quantities: the vertical design can support good dischargeability and reduced product deposits.
Important design parameters:
- Chemical resistance of the spray lances, nozzles and seals to binders such as aqueous solutions, resins, oils or molasses
- Tendency to clog with highly viscous or solids-containing liquids
- Cleanability and, where applicable, CIP suitability during product changes
- Temperature control of the mixing chamber where thermally activated binders are used
- Special designs for abrasive media, hygroscopic products or ATEX requirements
Vertical twin-shaft mixers with an integrated liquid spray unit are therefore an established solution where controlled granulation with good process management and high reproducibility is required.
Yes – this is how amixon® implements liquid injection and granulation in the vertical twin-shaft mixer HM
Integrated liquid addition as a feature
On request, the amixon® HM can be equipped with liquid feed lances which introduce the binder liquid directly into the moving bed of mix. Alternatively or in addition, addition via two-fluid nozzles is also possible: air and liquid flow thereby generate a particularly fine atomisation and support even wetting. amixon® also uses this principle with the conical mixer AM.
Liquid addition and agglomeration in the vertical twin-shaft mixer HM
The amixon® vertical twin-shaft mixer HM can be executed with integrated liquid addition. The liquid is introduced purposefully into the mixing chamber via feed lances, either below or above the level of the mix, depending on the product, viscosity and desired wetting characteristic. Various spray nozzle geometries are available, for example single-, two- and multi-fluid nozzles. The more evenly the solid surfaces are wetted, the more efficiently agglomeration proceeds and the more stable the later instant behaviour becomes.
The cutting rotor performs a dual function here: it distributes the injected liquid finely within the powder and at the same time breaks up unwanted coarse lumps. In parallel, the SinConvex® mixing tool provides a three-dimensional total flow of the mix. Adding the liquid within the effective range of the cutting rotor helps to avoid local over-wetting and supports the homogeneous formation of liquid bridges throughout the product cross-section.
Adjustable processing modes in the same apparatus
The aim is to manage with as little liquid as possible and nevertheless to agglomerate all relevant dust fractions reliably. In the amixon® HM the mixing and processing intensity can be set infinitely, from gentle moistening with low energy introduction through to intensive moistening with higher energy introduction, compaction, impact loading and targeted deagglomeration.
Instantisation represents the supreme discipline of agglomeration: the powder should subsequently wet easily, disperse well and dissolve quickly. The physical basis is the defined formation of liquid bridges between the particles. With controlled wetting and moderate compaction, mechanically stable agglomerates with even porosity arise which wet well and dissolve again rapidly.
Process environment and hygienic design
For hygienic control of the process, the HM is equipped with hygienic design features, including programmable target-jet washing lances for wet cleaning, generous inspection doors following the Clever-Cut® principle and an OmgaSeal® door seal. The mixing chamber is welded free of joints, and the mixing tool is supported and driven at the top only. On request, the design can be adapted to EHEDG, FDA and 3-A Sanitary requirements; the mixing chamber can moreover be designed ATEX-compliant for Zone 20.
Batch-wise or continuous – the appropriate solution in the pilot plant
Where granulation is to take place continuously, the flow-through mixer and ring-layer mixing granulator RMG complements the portfolio. It serves continuous build-up granulation and produces round granules of similar size from disperse materials.
Which variant is the right one in the specific case, batch-wise granulation in the HM or continuous granulation in the RMG, is clarified by amixon® together with the operator in granulation trials with original products in the company's own pilot plants. Both HM trial units and RMG pilot apparatus are available there in order to verify process parameters, agglomerate structure and product behaviour under real conditions.