How can energy efficiency, sustainability and durability be assessed when selecting a mixing plant?
When selecting a mixing plant, energy efficiency, sustainability and longevity should not be assessed separately, but as interrelated decision criteria. An energy-efficient plant is not automatically sustainable if it causes high product losses, requires a lot of cleaning medium, or can only be operated with high maintenance effort. Conversely, a robust, long-lasting plant can be economically and ecologically advantageous despite higher acquisition costs, if it works reliably over many years, is readily modernisable and causes low downtime and spare-parts costs. The basis for the assessment should therefore be technical performance data, realistic operating assumptions, environmental metrics and life-cycle costs.
Energy efficiency should be related to the mixing task actually required. A central metric is the specific energy consumption, for example in kWh per tonne of saleable product or per batch, at demonstrated mixing quality. What is decisive is not the mixer's connected load alone. Mixing time, fill level, tool geometry, rotational speed, product behaviour, recipe and the required homogeneity also influence energy demand. A high installed drive power is not automatically inefficient if it is required for start-up torque, high viscosities, load peaks or particular process phases. Conversely, an oversized drive unit can cause unnecessary investment and part-load losses. The drive design should therefore reflect the real load case and provide sufficient reserves for product- or process-related deviations.
Highly efficient motors, low-loss gearboxes and frequency-controlled drives can improve energy efficiency if they suit the application. Frequency inverters enable rotational speed and torque to be adapted to the product, fill level and mixing phase. They can reduce idle times, improve product protection and support demand-appropriate operation. Regenerative energy feedback during braking, however, is only of limited relevance with many classic mixing processes and should only be assessed as an advantage if dynamic braking operations actually occur frequently and the electrical infrastructure allows feedback. The entire drive train should therefore be assessed not solely by its efficiency class, but by its real load profile, the annual operating hours and the specific energy consumption.
The process-engineering design also influences energy efficiency. Flow-favourable mixing tools, a suitable vessel geometry and an appropriate fill level can reduce the mixing time required for a defined mixing quality. A short mixing time, however, is not always the primary goal. With sensitive products or large-volume batches, a longer, slowly conducted homogenisation can be worthwhile if it enables product protection, mixing quality and a lower connected load. The choice of mixer should therefore be based on product trials and clearly defined quality criteria. A suitable comparison considers not only the time to homogeneity, but also energy consumption, product temperature, segregation tendency, abrasion, product losses and cleaning effort.
Besides the mixing drive, all relevant auxiliary equipment also belongs in the energy balance. These include, for example, dosing elements, conveying technology, vacuum and compressed-air systems, extraction, control technology, and systems for heating or cooling. With temperature-controlled mixing, drying or reaction processes, heat and cooling demand should be recorded separately, for example in kWh or MJ per batch or per tonne of product. Good thermal insulation of double-jacket vessels can limit heat losses. Heat recovery is particularly relevant where usable energy actually arises from exhaust air, cooling circuits or process heat. With non-temperature-controlled powder-mixing processes, on the other hand, its potential is often low.
Beyond energy consumption, sustainability encompasses the efficient use of raw materials, water, cleaning chemicals and wear parts. Good residual discharge can reduce product losses and waste, and lower cleaning effort with product changes. Mixing chambers with minimal dead space, good accessibility and cleaning-friendly design can help to limit water and chemical demand. Whether a CIP, WIP or manual cleaning concept is the most sustainable solution depends on product build-up, change frequency, hygiene requirements, available infrastructure and cleaning-validation requirements. The environmental impact should not be measured by water consumption alone, but also by energy use, cleaning-agent demand, wastewater volume and, where applicable, relevant wastewater loads.
In material selection, wear, corrosion, hygiene, repairability and recyclability must be assessed together. Stainless steels are, in many applications, durable, readily cleanable and well recoverable at the end of the use phase. With abrasive products, hardened materials, wear-resistant linings, hard-material coatings or technical ceramics can increase the service life of certain components. However, they should only be used if they are compatible with the product, temperature, cleaning, impact stress and regulatory requirements. For corrosive media, depending on the chemical load, austenitic or duplex steels and suitable special alloys can, for example, be used. A suitable surface quality can reduce product build-up and improve cleanability. In hygienic applications, a roughness value of Ra 0.8 µm or better is often used as a guideline for metallic product-contact surfaces. The actually required surface quality, however, also depends on geometry, weld-seam execution, cleaning method and hygiene risk.
The longevity of a mixing plant is determined by the appropriate sizing of shafts, bearings, gearboxes, couplings, seals and mixing tools. These components should be matched to the actual load spectrum, possible imbalances, changing fill levels, start-up events, product abrasion and the expected operating hours. Rigid target values such as a minimum bearing life of 40,000 hours are not sensible for every application. The required nominal bearing life to ISO 281 depends on criticality, load, rotational speed, maintenance concept, replaceability and the consequences of a failure. With continuous processes critically dependent on availability, higher requirements can be sensible; with easily replaceable or intermittently operated components, other target values can be more economical.
Maintenance-friendliness is a significant factor for technical and economic sustainability. Readily accessible seals, bearings, mixing tools and discharge elements shorten inspection and repair times. Replaceable wear parts, modular assemblies and, wherever possible, standardised components facilitate spare-parts holding and maintenance. Long-term spare-parts availability should be secured contractually or through a traceable service and retrofit strategy, rather than assuming a blanket availability of 15 or 20 years. Sensors for vibration, temperature, torque, current draw or run times can support condition-based maintenance. They help to detect conspicuous trends early and shift maintenance interventions into planned downtime windows. What remains decisive, however, is suitable data quality, expert assessment and a functioning maintenance organisation.
For assessing availability, metrics such as mean time between failures, mean time to repair and overall equipment effectiveness are helpful. MTBF describes the time between failure-related interruptions, MTTR the average time to restore function. OEE combines availability, performance and quality rate. These metrics should not be considered in isolation, since a high OEE could, for example, be achieved at the cost of high scrap quantities or excessive energy use. The analysis only becomes meaningful once energy consumption, product losses, cleaning effort, scrap, maintenance costs and reasons for downtime are evaluated together.
A robust ecological assessment can be carried out with a life-cycle assessment. ISO 14040 describes the principles and framework of a life-cycle assessment, while ISO 14044 sets out requirements and guidelines for the goal and scope, inventory analysis, impact assessment, interpretation, reporting and, where applicable, critical review. For the selection of a mixing plant, this means: system boundaries, functional unit, life stages considered, data quality, assumptions and relevant environmental impacts must be defined in advance. It is not universally true that operating energy dominates the CO₂ footprint in every case. With high utilisation and long run times it can be decisive; with low utilisation, energy-intensive materials, frequent spare parts or particularly emission-intensive raw materials, other life-cycle stages can carry more weight.
Besides the life-cycle assessment, the decision should include a total-cost-of-ownership or life-cycle-cost analysis. Acquisition, installation, energy, auxiliary media, cleaning, maintenance, spare parts, personnel, quality losses, scrap, unplanned downtime, modernisation and decommissioning should be taken into account. The period under consideration should not be set as a blanket ten to twenty years, but should match the expected service life, depreciation logic, technology development and process planning. A weighted-scoring analysis can supplement these economic aspects with non-monetary criteria such as product protection, mixing quality, hygienic suitability, cleanability, flexibility, scalability, CO₂ intensity, availability and serviceability.
The selection of a sustainable mixing plant should therefore be based on robust product trials, measured or traceably calculated energy and utility consumption, a realistic maintenance strategy, and a transparent life-cycle-cost and environmental assessment. ISO 50001 can provide the framework for systematically improving energy performance: the standard supports companies in data acquisition, target-setting, measurement and continuous improvement of energy efficiency, energy use and energy consumption. ISO 14001 can support an environmental management system; ISO 14040 and ISO 14044 are relevant for the methodical execution of a life-cycle assessment.
How amixon® solves this task
At amixon®, sustainability means assessing energy use, raw-material yield, cleaning effort, maintenance and economic service life as a connected system. When selecting a mixing plant, it is not sufficient to compare the installed drive power or the acquisition price alone. What is decisive is the actual mixing task, product behaviour, batch size, fill level, required mixing quality, cleaning requirements and expected mode of operation. amixon® can assess these factors through pilot-plant trials with the original product and through application-related process data.
Energy efficiency is significantly influenced by the mixing principle, tool geometry, rotational speed, fill level and mixing time. In many applications, amixon® mixers operate with low circumferential speeds of the mixing tools. This can enable gentle product turnover and limit the mechanical energy input. The required drive power, however, is always designed on the basis of the product, recipe, mixing task, batch size and desired homogeneity. A low connected load alone is not a sufficient efficiency criterion; what matters is the specific energy consumption at reproducibly achieved mixing quality, for example in kWh per batch or per tonne of saleable product.
Short mixing times can reduce energy consumption per batch, provided the required homogeneity is reliably achieved. With the KoneSlid® mixer KS, amixon® states, under suitable conditions, an optimal mixing quality after around 20 to 30 tool revolutions. This figure is product-specific and cannot be transferred as a blanket rule to other products, fill levels or mixer types. With the twin-shaft mixer HM, superimposed mixing currents can support fast and intensive homogenisation. The actual mixing time, energy demand and mixing quality, however, should always be checked with the original product.
A short mixing time is not the primary goal in every application. Where product protection, homogeneity and a low electrical connected load are the focus, a longer, slowly conducted homogenisation can be economically worthwhile. The Gyraton® mixer GM follows this principle. It is designed for large batches and can circulate the bulk material gently at low rotational speed. This allows the required drive power to remain low in relation to the large batch quantity. Gyraton® mixers are available for batch sizes of up to 100 m³ and, depending on the design, are suitable for dry, moist or wet bulk materials. The specific motor power, mixing time and achievable mixing quality are determined on a project-specific basis according to the product, batch size, fill level and quality requirement.
Besides energy consumption, raw-material yield is a significant sustainability factor. The most complete possible discharge of the mixer can reduce product losses, scrap and cleaning effort. Depending on the product, mixer type and design, amixon® mixers can achieve high discharge rates. For certain designs, amixon® states discharge rates of up to 99.98 percent. With ComDisc® technology, discharge rates of up to 99.997 percent and higher are possible under suitable conditions. The residual quantity actually achievable, however, depends on the flow behaviour, moisture, particle size, bulk density and adhesion tendency of the specific product and should be checked in a trial.
Mixing chambers with minimal dead space and good accessibility can facilitate cleaning. With a suitable process and plant concept, this can reduce the demand for water, cleaning agents, energy and manual intervention. With liquid mixing-in, finely distributed dosing matched to the recipe can help to limit local build-up. Whether this actually results in shorter cleaning times or lower media consumption depends, among other things, on the product, hygiene standard, change frequency and cleaning method. With temperature-sensitive powders, a gentle mixing principle can also help to limit unwanted temperature input. Whether this saves cooling energy should be measured for the specific application.
Longevity is a further sustainability factor. A robust construction, suitable materials, wear-appropriate components, good maintenance accessibility and the possibility of modernisation can extend the economic service life of a mixing plant. amixon® supports operators with maintenance, spare-parts supply, retrofit and modernisation. Retrofits can, for example, involve drives, control systems, sensors, safety functions, dosing technology, cleaning or process documentation. They make it possible to adapt existing plants to new recipes, changed throughputs, higher traceability requirements or regulatory provisions. This can reduce the need for complete replacement investment and the associated material and energy use.
For an informed selection, energy, resource and availability metrics should be considered together. Particularly useful are the specific energy consumption per batch or tonne of product, power consumption over time, the residual quantity after discharge, the product-loss rate, water and cleaning-agent consumption per cleaning cycle or product change, the demand for wear parts, unplanned downtime, and the expected service life. Depending on the automation concept, this data can be recorded and documented on a project-specific basis and used for energy, CO₂, resource or OEE evaluations.
Before an investment, the specific mixing task can be trialled in the amixon® pilot plant with the original product. More than 30 test units in different sizes are available at the main site in Paderborn. In addition, amixon® operates technical centres in the USA, China, Japan, India, Thailand and South Korea. The trials can be carried out with the intended raw materials, realistic fill levels, batch sizes and the relevant temperature and pressure ranges. Mixing quality, product protection, energy input, dischargeability, cleanability and reproducibility are, among other things, assessed. The documented results provide a robust basis for transparently weighing technical, ecological and economic requirements against each other before an investment.