What options are there for modular extensions (e.g. additional dosing points, sensors, valves) in mixing plants?
Modular extensions concern additional functional modules on an existing mixing plant, such as dosing points, sensor technology, valves, cleaning or automation technology. They are particularly economical where mechanical connections, space, utility supply, control-system reserves and the safety concept were already provided for in the original design. Where these prerequisites are missing, retrofits often remain possible, but cause additional design, assembly, software, testing and, where applicable, qualification effort.
A frequent area for extension is dosing. Solids can be introduced via additional screw feeders, differential dosing scales, rotary valves or micro-dosing systems. For liquids, depending on viscosity, dosing quantity, temperature, chemical resistance and accuracy requirement, diaphragm, hose, gear or eccentric-screw pumps, for example, may be suitable. Liquid lances, injection nozzles or ring pipes can enable addition into the mixing chamber. What matters is not only dosing accuracy and mass balance, but also the correct point of introduction, droplet size, dosing speed and mixing intensity. Otherwise, local over-wetting, agglomerates, build-up or uneven product distribution can result.
Additional sensor technology can improve process control, quality assurance and maintenance. Only measuring points with a clear purpose make sense. Temperature, pressure, vacuum, level, flow and weighing sensors frequently supply directly usable process information. Torque, motor current, vibration and bearing temperature can provide indications of product behaviour, build-up or mechanical changes. However, without a product- and plant-related assessment they are not direct proof of mixing quality or product quality.
More extensive inline analytics can be relevant depending on the process. This includes, for example, near-infrared spectroscopy for examining certain product characteristics, Coriolis mass flow measurement for balancing liquids, moisture measurement or conductivity measurement in suitable media. Process analytical technology, usually abbreviated PAT, can reduce laboratory samples and make deviations detectable earlier. However, it requires suitable measuring points, calibration, maintenance, robust data interpretation and, where applicable, validation. pH value, redox potential, turbidity or refractometry are useful primarily with liquid or pasty systems; for dry powder mixtures they are generally not suitable.
Valves and fittings are likewise typical extension modules. Pneumatically or electrically actuated shut-off and control valves can control liquid, gas, vacuum or cleaning media. Multi-way valves and valve blocks can switch media flows between several vessels, dosing points or cleaning routes. In hygienically demanding applications, diaphragm, seat or double-seat valves may be suitable depending on the medium and cleaning strategy. Safety valves and bursting discs can protect against impermissible over- or under-pressure. Their design, however, is not a routine after-the-fact measure but must be based on pressure calculation, design scenarios, medium, temperature, standards and the existing plant.
Bypass modules can incorporate filters, heat exchangers, homogenisers or external circuits. They only make sense where the process actually permits recirculation or external treatment. In many dry-working powder mixers, a liquid-like product circuit is technically not present or not economical. Correspondingly, pig-able pipework is also relevant primarily for viscous liquids, pastes and product-carrying pipe systems; for dry powders, other measures such as residual discharge, suitable conveying technology and cleaning-friendly geometries are generally more important.
Mechanical extensions can include additional mixing or de-agglomeration tools, temperature-control jackets, vacuum connections, filters, discharge devices or cleaning modules. A high-shear tool, that is, a tool with high shear stress, can break up agglomerates or incorporate liquids more intensively. However, it can also damage particles, increase energy input or change the particle size distribution. Temperature-control jackets can be helpful with exothermic or endothermic processes, but require suitable heating or cooling media, appropriate control, and an assessment of heat transfer. Vacuum can support degassing or drying, but places higher demands on pressure resistance, tightness, filter technology and the safety concept.
Cleaning systems such as cleaning in place, abbreviated CIP, or sterilization in place, abbreviated SIP, can likewise be retrofitted. CIP refers to cleaning in the installed state without extensive dismantling; SIP refers to sterilisation in the installed state. A retrofit involves not only washing nozzles, but also utility supply, valve technology, return flow, conductivity, temperature and flow monitoring, and an effective emptying and drying concept. The actual cleaning or sterilisation effectiveness must be demonstrated for the product, soiling and method; an automated cleaning cycle is not automatically validated.
Every functional extension requires suitable automation integration. This includes free inputs and outputs, network capacity, cabinet reserves, control logic, alarm and interlock concepts, visualisation and safe operating states. Decentralised input and output modules, often referred to as I/O modules, can connect valves, sensors and drives close to the plant. Interfaces such as IO-Link, PROFINET, EtherCAT or other standardised communication and fieldbus standards can support communication. Their selection depends on the real-time requirement, existing automation, cybersecurity, data model and maintainability.
For batch-oriented mixing processes, the extension should also be incorporated into recipe and batch logic. The standard ISA-88 offers models and terminology for recipes, process steps, plant modules and batch documentation for this purpose. New dosing points or measuring points must not only be connected electrically, but also integrated into the control system as controlled process phases with setpoints, limit values, fault messages, releases and logging.
Vendor-neutral module descriptions can make the software-side integration of suitable, largely autonomous process modules easier. Such description standards define a module's functions and automation interfaces in a structured, vendor-neutral way and are particularly suitable for delineated process modules such as dosing or temperature-control skids. However, they replace neither the mechanical integration nor the review of product, hygiene, safety and process compatibility.
A prerequisite for economical retrofits is up-to-date P&IDs, design drawings, connection lists, circuit diagrams, software versions, risk analyses and a clear interface matrix. This must establish where mechanical, electrical, utility, control-system and safety responsibilities lie. For regulated plants, changes must be assessed via change control. Depending on the risk, updates to operating instructions, risk analyses, cleaning procedures, control-system software, qualification documentation and validations are required.
Modularity and retrofittability at amixon®
A mixing plant is not automatically modular simply because it can process different recipes or is offered in several sizes. Genuine modularity concerns retrofittable functional modules and clearly prepared interfaces. This includes mechanical connections, sufficient installation space, utility supply, control-system reserves, safety technology and documented handover points. Where these prerequisites are already taken into account in the user requirement specification, abbreviated URS, later extensions can be planned in a considerably more controlled and economical way. The URS is the operator's documented requirement specification.
At amixon®, machines can be designed on a project-specific basis using the URS. Where it is foreseeable that liquids will later be dosed, additional process data recorded, temperatures controlled or cleaning functions extended, spare connections, free nozzles, installation positions, space reserves, additional inputs and outputs, and capacity for energy, compressed air, vacuum and cleaning media can be provided for. Without this preparation, retrofits are not ruled out, but they can require significant intervention in the vessel, pipework, supporting structure, control system, safety concept and hygienic design.
The ability to process different batch sizes or recipes with the same machine is not, in principle, a modular extension. With some amixon® mixers, varying fill levels can be processed depending on product and design. Whether high mixing quality is actually achieved across a range of approximately 10 to 100 percent fill level, however, must be investigated for the specific recipe. Powders differ in bulk density, particle size distribution, moisture, cohesion, flow behaviour, abrasiveness and tendency to segregate. Dosing sequence, liquid content, tool configuration and mixing time also significantly influence the result. A varying fill level is therefore not a blanket proof of process flexibility.
Mixing intensity can be influenced by mixing time, speed, tool design and, where applicable, a cutting rotor or a high-shear tool. High shear means high shear stress. Such tools can, in certain applications, break up agglomerates or improve the incorporation of liquids. However, they can equally change the particle size distribution, introduce heat, damage sensitive particles, generate abrasion or worsen flowability. A higher mixing intensity is therefore not generally better. It must be derived from a clear, product- and quality-related objective.
Depending on the starting situation, modules that can actually be retrofitted include, for example, liquid dosing, addition lances, two-fluid nozzles, additional sensor technology, temperature-control jackets, vacuum connections, washing lances, cleaning-in-place or wet-in-place systems, discharge devices and dosing functions. Cleaning in place, abbreviated CIP, means cleaning in the installed state without extensive dismantling. Wet in place, abbreviated WIP, refers to wet cleaning of the installed plant, whose degree of automation can vary depending on the concept.
Retrofitting a liquid dosing system is more than installing a pump and a lance. Dosing quantity, dosing accuracy, viscosity, temperature, chemical compatibility, the position of the injection point, droplet size, spray pattern, dosing speed and product flow determine whether the liquid is distributed evenly. An unfavourable design can lead to local over-wetting, agglomeration, build-up, worsened flowability or extended cleaning times. The function should therefore be trialled with the original product rather than designed on the basis of geometric assumptions alone.
Additional sensors can only create benefit where the measured variable is clearly linked to a decision or an assessment. Temperature, pressure, vacuum, level and flow measurements can monitor important process parameters. Torque, current draw or vibration can provide indications of fill level, build-up, product behaviour or mechanical changes. However, they are not direct proof of mixing quality, homogeneity or product quality. When sensors are retrofitted, the installation location, measuring range, accuracy, calibration, cleanability, tightness, data transmission, alarm limits and the response to measurement errors must be established.
Temperature-control jackets or external heating and cooling systems can be useful for heat-sensitive, exothermic or endothermic processes. However, they require adequately sized utility connections, suitable control, an assessment of pressure and temperature stress, and a check of the heat transfer actually achievable. A temperature-control jacket can limit temperature deviations, but does not guarantee an even product temperature in every powder or every batch size.
Vacuum functions can be useful for degassing, drying or certain reaction steps. They place higher demands on vessel strength, tightness, filter technology, discharge devices, safety assessment and, where applicable, explosion protection. A later retrofit can therefore be more extensive than the after-the-fact installation of a connection nozzle might suggest.
Washing lances as well as CIP or WIP functions can support cleaning. A washing lance alone, however, is proof neither of complete wetting nor of effective cleaning. For a robust design, the spray pattern, nozzle arrangement, flow, pressure, cleaning chemistry, temperature, contact time, drainage situation and the geometry of all product-contact surfaces must be assessed. In regulated areas, cleaning effectiveness must be demonstrated with reference to the product and soiling. Automatic wet cleaning is not automatically validated cleaning.
Discharge devices such as DosiFlap® can be integrated into the plant on a project-specific basis. They can support controlled product delivery, the tightness of the mixing chamber and, where applicable, better discharge. Whether they actually fulfil a precise dosing function depends on flow behaviour, bulk density, dosing quantity, tolerance, weighing concept, pressure conditions and downstream container or conveying technology. For gravimetrically accurate filling, matched weighing technology is generally required. The choice of a discharge device must also take into account cleanability, containment, pressure and vacuum operation, and the interface to the downstream plant.
Switching to a larger or smaller mixer size is not a modular extension but a capacity adjustment. Even where the mixing principle remains the same, recipes and parameters cannot be transferred across the board. Flow conditions, fill level, circumferential speed, energy input, heat transfer, mixing time, discharge and product stress can change. According to the company, amixon® offers certain series in sizes ranging in steps from 100 litres to 50 cubic metres, and the Gyraton® mixer up to 100 cubic metres. This selection allows a suitable plant to be chosen, but does not replace scale-up trials for the specific product.
With the container mixer type COM, additional Mixtainer® units can make the overall system more flexible by decoupling weighing-in, mixing, cleaning, intermediate storage, transport and filling from one another. This is not a modular extension of the mixer, but it can improve the capacity of the overall system. The benefit depends on the number of containers, logistics, cleaning, mixing times, releases and the throughput of downstream process steps. Without a capacity analysis, investing in further containers may merely shift the bottleneck elsewhere.
amixon® can support technical retrofits, modernisation and pilot-plant trials. According to amixon®, more than 30 test machines are available in Paderborn; further test centres are operated in the USA and several Asian countries. With the original product, liquid distribution, mixing quality, de-agglomeration, temperature profile, energy input, discharge, build-up and cleanability, among other things, can be assessed. Such trials are particularly valuable for a retrofit because they verify assumptions about product behaviour. However, they only form a basis for the design and do not replace the acceptance test, safety assessment and, where applicable, requalification of the converted plant at the actual production site.
Mixing programmes can be managed in a programmable logic controller, abbreviated PLC, and run for each batch. A PLC is an industrial computer for controlling machines and processes. Project-specific connection to an enterprise resource planning system, abbreviated ERP system, or a manufacturing execution system, abbreviated MES, can link recipe, batch and process parameters with one another. An ERP system supports the management of orders, materials and corporate resources. An MES supports operational production, data acquisition and batch documentation. Barcode scanners can support material identification. For such a solution to function reliably, the data model, time stamps, recipe version, user permissions, data integrity, audit trails and the behaviour in the event of communication failures must be established.
For regulated applications, amixon® can provide documentation for qualification and support with Design Qualification, abbreviated DQ, Installation Qualification, abbreviated IQ, and Operational Qualification, abbreviated OQ. DQ documents that the plant design meets the defined requirements. IQ confirms proper installation. OQ demonstrates that the plant functions within the defined operating range. The technical design can be aligned with project-specific requirements such as Good Manufacturing Practice, abbreviated GMP, ATEX, EHEDG, FDA requirements, 3-A Sanitary Standards or ASME. Regulatory responsibility, the assessment of changes, cleaning and process validation, and the validation of electronic systems remain with the operator.
Summary
amixon® plants can be prepared for later functional modules such as liquid dosing, sensor technology, temperature control, vacuum, cleaning and discharge technology. However, the benefit and effort of a retrofit depend decisively on whether connections, installation space, utilities, control, safety and cleanability were already considered in the original design. Changing fill levels, new recipes or a different size are not modular extensions and must be process-engineering assessed for the actual product and the specific target plant.