Can mixing plants be modularly extended, e.g. with liquid dosing or additional measurement points?
Yes. Industrial mixing plants can frequently be extended with additional dosing, measurement, automation and peripheral modules. Whether a retrofit is technically sensible and economically feasible, however, depends on the existing mechanical design, load-bearing capacity, available installation space, energy and utility supply, safety requirements and the existing control architecture. The earlier extension options are taken into account during planning, the easier later adaptations can be implemented.
A common extension is the integration of liquid dosing. It is used to introduce water, oils, binders, flavourings, additives, active-ingredient solutions or other liquid components into the mixing process in a controlled manner. The choice of dosing system depends on viscosity, temperature, dosing quantity, dosing accuracy, cleaning requirements, chemical compatibility and possible explosion protection. For continuous or reproducible dosing tasks, volumetric pump systems are suitable, for example gear, eccentric-screw, diaphragm or hose pumps. Where a particularly accurate mass balance is required, gravimetric systems with load cells or flow measurement can be used. Coriolis mass flow meters can capture mass and density, while electromagnetic flow meters are suitable for sufficiently electrically conductive liquids.
The injection point and the method of introduction must be matched to the respective mixing process. An unfavourably positioned liquid lance can cause local over-wetting, agglomerates, build-up or uneven distribution. The liquid should therefore be introduced into a sufficiently agitated product zone wherever possible. For fine, dusty or hygroscopic powders, droplet size, spray direction, liquid temperature, dosing speed and, where applicable, atomisation can also be decisive for the result. Before a retrofit, trials with the actual product are therefore advisable, in particular where the liquid addition changes the particle structure, flowability, homogeneity or cleanability.
Additional measurement points can also be retrofitted where suitable installation locations exist or can be created. Temperature probes such as Pt100 or Pt1000 sensors can be used to monitor product temperature, cooling, heating or possible reaction processes. For moisture determination, microwave-based, capacitive or near-infrared measurement methods can be suitable, depending on the product and measurement task. Pressure and vacuum sensors are particularly relevant for closed mixing processes, vacuum drying, inerting or overpressure operation. For liquid or pasty media, pH or conductivity measurements can additionally be useful. Torque, current draw or power of the mixing drive can provide indications of fill level, product consistency, friction, mixing progress or possible build-up, but are not universal quality indicators that are sufficiently reliable on their own.
The mechanical integration of additional sensors should be carried out in a way that preserves cleanability, product safety and leak-tightness. In hygienically sensitive applications, suitable mounting nozzles, flush sensor connections and low-dead-space designs are particularly important. Tri-clamp connections or flanged connections can enable standardised integration; their suitability, however, depends on pressure rating, vacuum operation, cleaning procedure, materials and hygiene concept. Reserve connections, blind flanges and free installation positions already provided for in the basic planning considerably reduce the effort of a later retrofit.
Solids dosing modules can also be added to extend recipe diversity. These include, for example, silos, bag or big-bag discharge stations, screw conveyors, vibratory chutes, loss-in-weight feeders, micro-dosing units or manual charging stations. They enable the automated or semi-automated feeding of main and minor components. Planning must take flow behaviour, bridging, segregation risks, dust generation, cross-contamination risks, cleanability and the precise weighing of the individual raw-material batches into account. Especially for minor components, dosing accuracy can have a considerable influence on product quality.
Mixing plants can also be supplemented with further process modules. Depending on the product and process objective, these can include, for example, screening machines, magnetic separators, lump breakers, homogenisers, cooling or heating systems, vacuum equipment, dedusting systems, filter units, conveying technology or filling systems. However, an extension frequently changes not only the material flow but also the requirements for control, the safety concept, the cleaning strategy and maintenance. Before implementation, it should therefore be checked whether the new component actually increases the capacity of the mixing plant or merely shifts a previously invisible bottleneck to another process stage.
In addition to the mechanics, control-system integration is a central part of every retrofit. Additional pumps, valves, weighing systems and sensors require free inputs and outputs, sufficiently dimensioned control-cabinet capacity, suitable fieldbus nodes, power supply and, where applicable, compressed air, cooling water, steam, vacuum or cleaning media. Common automation interfaces include, for example, PROFINET, EtherCAT, Profibus (Process Field Bus) and IO-Link. For vertical data integration with higher-level systems such as SCADA (Supervisory Control and Data Acquisition), MES (Manufacturing Execution System), ERP (Enterprise Resource Planning) or analytics platforms, OPC UA (Open Platform Communications Unified Architecture) can be used. The suitable interface depends on the existing control landscape, real-time requirements, security requirements and the desired data model.
A modular software structure helps to integrate extensions in a controlled way. Process modules such as dosing skids can be implemented as self-contained functional modules with clearly defined interfaces, operating states, messages and services. The Module Type Package, MTP for short, supports a vendor-neutral description of the functions and interfaces of such process modules. An MTP can be imported into the engineering of a process control system and thereby facilitate the integration of standardised modules. The approach is described in the VDI/VDE/NAMUR 2658 guideline; MTP is also being advanced by NAMUR and ZVEI as a building block of modular process automation.
For batch-oriented production processes, it makes sense to align the control and recipe structure with ISA-88. The standard provides models and terminology for batch control and describes, among other things, recipes, procedures, process phases and equipment modules. This facilitates the clean assignment of new dosing or measurement modules to recipes, batches and process steps. Extensions therefore do not necessarily have to trigger a complete reprogramming of the plant; however, they always require a technical specification, a clear interface design and qualified tests of the changed functions.
For an economical retrofit, reserves should be provided not only in mechanical connections but also in control, power supply, control cabinet, network, compressed air and utility lines. Equally important are up-to-date plant and electrical documentation, a clearly structured software architecture, current P&ID diagrams, valid safety assessments, and clear documentation of the existing sensor technology and interfaces. New measured values must be integrated into visualisation, alarm management, recipe management, data storage and, where applicable, quality evaluation. If critical process parameters are added or changed, measuring range, accuracy, calibration, maintenance, data quality and the interpretation of the measured values must be defined before productive use.
In regulated sectors, extensions must be carried out via a documented change-control procedure. The change should be assessed with regard to product safety, process capability, cleaning, containment, data integrity, qualification and validation status. Depending on the impact, adjustments to the risk analysis, SOPs, technical documentation, control software and cleaning procedures, as well as partial or full requalification, may be required. The FDA points out that changes to specifications, methods, processes or procedures must be verified and, where appropriate, validated before implementation; in the event of changes or process deviations, the process must be evaluated and, where necessary, revalidated.
Modularity and retrofittability at amixon®
amixon® mixing plants can be designed for varying batch sizes, recipes and process requirements. With suitable product and process design, the same mixer can process different fill levels without any mechanical conversion being required. This, however, is not a modular extension but the expression of a sufficiently wide operating range that has been validated through trials. The mixing quality achievable always depends on the properties of the powders used, the fill level, the recipe, the dosing sequence and the selected process parameters.
Depending on the apparatus design, mixing intensity can be adjusted via mixing time, speed, tool configuration and additional process elements. Mixing, dosing and temperature profiles can be stored in PLC-based recipes and executed reproducibly on a batch-by-batch basis. In certain applications, cutting rotors or high-shear tools can be used for deagglomeration or for improved incorporation of liquids. Whether more intensive processing makes sense must be checked against the product, since sensitive particles or granules can be altered by increased shear forces.
A modular extension concerns additional functional modules on or within the existing mixing plant. These include, for example, liquid dosing with addition lances or two-substance nozzles, additional sensor technology and measurement points, temperature-control jackets, vacuum connections, cutting rotors, wash lances, WIP or CIP functions, and discharge and dosing elements such as DosiFlap®. Such extensions can be implemented particularly efficiently if they were already taken into account in the original design. Reserve connections, free installation positions, prepared nozzles, adequately dimensioned utility lines, space reserves, additional I/O capacity and a scalable control architecture considerably reduce the later mechanical and automation effort.
Where these preparations are not in place, retrofits can nevertheless be technically feasible. The effort then increases because, for example, new connection points have to be created, the mixing vessel has to be structurally adapted, piping has to be added, control and safety functions have to be extended, or explosion-protection and cleanability measures have to be reassessed. In regulated sectors, change control, adjustments to the risk analysis, updates to the documentation, and partial or full requalification may additionally be required. amixon® can support operators with retrofits, process-engineering adaptations and the modernisation of existing plants.
The retrofitting of a liquid dosing system must be designed to suit the product and process. The location of the addition point, droplet size, dosing speed, spray characteristics, liquid temperature and the existing product flows influence whether the liquid is distributed evenly or whether local over-wetting, agglomerates and build-up occur. Additional measurement points should be integrated in a way that preserves leak-tightness, cleanability and, where applicable, containment. They can capture, for example, temperature, moisture, pressure, vacuum, fill level, torque or other process variables. Before implementation, it should be clearly defined what process or quality benefit the additional measurement is intended to deliver and how the data is incorporated into control, documentation and evaluation.
Replacement with a larger or smaller mixing plant is not a modular extension but a capacity adjustment. The transfer of recipes or process parameters to a different size must be checked from a process-engineering perspective. Even where the same mixing principle is used, flow conditions, fill level, peripheral speed, heat transfer, dosing behaviour, mixing time and discharge can change. For greater capacities, additional Mixtainer® units can be an alternative with a container mixer, in order to organisationally decouple weighing-in, mixing, transport and filling. The actual capacity gain, however, depends on container logistics, cleaning duration, release processes and the downstream process steps.
The effectiveness of a planned extension should be verified with the original product. At the amixon® pilot-plant locations, mixing quality, liquid distribution, product stress, particle structure, flow behaviour, energy input, discharge and cleanability, among other things, can be assessed under realistic conditions. The documented results support the technical design of the retrofit and reduce risks before implementation. They do not, however, replace the acceptance testing of the converted plant and, where required, qualification or validation in the later production operation.
For reproducibility and traceability, mixing programs with mixing times, speeds, dosing sequences and temperature profiles can be stored in the PLC. A project-specific connection to ERP, MES or other higher-level systems can be provided. Barcode-based material and batch identification can link recipe, batch and process parameters together. For this data to be usable for batch traceability, OEE evaluation or quality assessments, interfaces, data model, time stamps, user rights, data integrity and the handling of transmission errors must be clearly defined.
In regulated environments, amixon® can provide technical documentation for qualification and support operators with DQ, IQ and OQ. The plant can be designed taking project-specific requirements into account, such as GMP-compliant hygienic design, ATEX, EHEDG, FDA requirements, 3-A Sanitary Standards or ASME. Responsibility for the regulatory assessment, process and cleaning validation, and the validation of computerised systems and, where applicable, 21 CFR Part 11, remains with the operator.
According to its own statements, amixon® supports plants with maintenance, modernisation, retrofitting and long-term spare-parts supply. A sustainable extension strategy always requires up-to-date technical documentation, controlled software versions, traceable component lists, and early coordination on critical spare parts, utility connections and interfaces.